the tcp traffic shares the bottleneck link bandwidth with ... tcp over atm ... ccr current cell rate...

Fawzi SALIH MSc Project

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Summary

In this contribution, the performance of TCP connections over the ATM Available Bit

Rate (ABR) service in a very simple network was investigated. The network topology

comprises two ATM switches, connected by one link; this was the system bottleneck.

The TCP traffic shares the bottleneck link bandwidth with a higher priority background

traffic load (CBR). The effect of running large unidirectional file transfer applications

on TCP over ABR with an explicit rate algorithm (ERICA+) was investigated for both

LAN and WANS. The project starts by understanding TCP and ATM protocols,

designing and implementing of the algorithms, modifying and running CLASS version

6.20h and examining different scenarios.

The simulation results indicate that a maximum throughput can be achieved with a

bigger buffer size. Both CLR and PRR follow the same trends for both LAN and WAN.

Increasing cell interval reduces efficiency of ERICA+. Mean cell waiting time in the

buffer was higher with TCP packet size 9180 than its counterpart 512 for both WAN

and LAN. Several experimental results are presented in Appendices.

In addition to wired ATM, CLASS-wireless version 5.9 has also been experimented

and tested in order to study Hanover procedures. The brief study (due to the time

limitation) has shown that Handover buffer size increases with the increase of both

Mobile Terminal load and SCR. Average cell delays is inversely proportional to the

Mobile Terminal load. At different MT loads, handover buffer size increases as the

cell loss probability decreases


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Acknowledgement

I would like to extend my sincere thanks to Dr. Karim Djemame for responding to all my requests to share his knowledge and experience. The experience gained from this project would not have achieved without his sincerity, hard work and dedication. I would also like to extend my appreciation to Carla Chiasserini from Texas University and Dr. Maurizio M. Munafo from Dip. Di Elettronica - Politecnico di Torino, Italy and Dr. Sonia Fahmy, Dept of Computer Sciences, Purdue University. I am also thankful to the Italian Public Research Centre in Telecommunications and Networking (Centro Studi E Laboratori Telecomunicazioni, CSELT) for their CLASS 6.20h and CLASS-wireless 5.9 simulators. Last, but not least, I would like to thank all the member of staff in School of Computer studies in their support.


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Summary .......................................................................................................................................1 Acknowledgement..........................................................................................................................2

LIST OF ILLUSTRATIONS AND TABLES.....................................................................................4

1 INTRODUCTION.......................................................................................................................... 10

2 BACKGROUND: ATM AND TCP................................................................................................ 12

2.1 ATM .........................................................................................................................................12 2.1.1 Introduction........................................................................................................................12 Fig. 2.1 Stack of TCP over ATM...................................................................................................13 2.1.2 ATM Architecture................................................................................................................13 2.1.3 ATM Service Classes...........................................................................................................14 2.1.4 ATM Traffic Management ...................................................................................................17 2.1.5 ATM Congestion Control.....................................................................................................18

2.2 WIRELESS ATM .........................................................................................................................18 2.2.1 Introduction........................................................................................................................18 2.2.2 Wireless Technologies.........................................................................................................22 2.2.2 Wireless Architecture..........................................................................................................23 2.2.3 Mobility Management .........................................................................................................24

2.3 TCP...........................................................................................................................................25 2.3.1 Overview.............................................................................................................................25 2.3.2 Congestion Control .............................................................................................................25

2.4 TCP OVER ATM........................................................................................................................28

3. ATM/WATM NETWORKS SIMULATION................................................................................ 30

3.1 CLASS VERSION 6.20H..............................................................................................................30 3.1.1 Overview.............................................................................................................................30 3.1.2 Traffic Generators...............................................................................................................31 3.1.3 CLASS Traffic Shaping........................................................................................................32 3.1.4 Shaping Policies.................................................................................................................33 3.1.5 Weighted Fair Queuing in CLASS (WFQ)............................................................................35 3.1.6 Priority Management in CLASS...........................................................................................36

3.2 CLASS WIRELESS VERSION 5.994..............................................................................................36 3.2.1 Overview.............................................................................................................................36 3.2.2 WATM Architecture............................................................................................................36 3.2.3 Protocol Stack in CLASS Wireless V5.994...........................................................................38 3.2.4 Handover Management in CLASS-Wireless.........................................................................39

4. EXPERIMENTAL DESIGN......................................................................................................... 44

4.1 EXPERIMENTAL OVERVIEW ........................................................................................................44 4.2 Designing Experimental Work................................................................................................44 4.2.1 Topology.............................................................................................................................45 4.2.2 Hierarchy of Experiments....................................................................................................46

4.2 WATM......................................................................................................................................46

5. ANALYSIS OF RESULTS............................................................................................................ 48

5.1 TCP OVER ATM ........................................................................................................................48 5.1.1 Effect of Buffer size.............................................................................................................48 5.1.2 Effect of Number of Sources................................................................................................49 Both Figures 19 and 20 gave comparable average window size with TCP packet size 9180...........52

5.2 TCP OVER WATM.....................................................................................................................52

CONCLUSION AND FINAL REMARKS ....................................................................................... 55

FUTURE WORK ................................................................................................................................55

REFERENCES.................................................................................................................................. 57


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List of illustrations and tables

AAL ATM Adaptation Layer Layer for converting upper layer data to ATM cells AAL ATM Adaptation Layer ABR Available Bit Rate ATM traffic class ACR Allowed Cell Rate Parameter used in ABR flow control ACTS Advanced Communication Technologies and Services European research program AL Application Layer OSI layer 7 AMPS Advanced Mobile Phone System 1st generation mobile phone system AP Access Point Base station of the WAND system API Application Programming Interface ATM Asynchronous Transfer Mode B-ISDN Broadband Integrated Services Digital Network BN Backward Notification Field in the header of a RM cell BRAN Broadband radio Access Networks BS Base station BT Burst Tolerance ATM traffic parameter CAC Connection Admission Control CBR Constant Bit Rate ATM traffic class CCR Current Cell Rate Parameter used in ABR flow control CDMA American 2nd generation mobile phone system using CDMA also know as IS-95 CDMA Code Division Multiple Access Access control method CDV Cell Delay Variation ATM dos parameter CDVT Cell Delay Variation Tolerance ATM traffic parameter


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CEC Commission of European Communities CEPT Conference European Des Posts et Telecommunications CI Congestion Indicator Field in the header of an RM cell CLP Cell Loss Priority Field in the header of an ATM cell CLR Cell Loss Ratio ATM QoS parameter COS Cross-Over Switch CPN Customer Premises Network Network owned and operated by the user CRC Cyclic Redundancy Check Error control method CSMA/CD Carrier Sense Multiple Access with Collision Detection CT-1&2 Cordless Telecommunications 1st generation cordless phone systems D-AMPS mobile system, also known as IS-54 DAB Digital Audio Broadcasting Standard for digital audio program broadcasting DCS Digital Cellular System 2nd generation mobile phone system based on GSM DECT Digital European Cordless Telecommunications 2nd generation cordless phone system DIR Direction of the RM-cell Field in the header of a RM cell ER Explicit Rate Parameter used in ABR flow control ERMES European Telecommunications Standards Institute European standardization body ETSI European Telecommunications Standards Institute European standardization body FBTCU Fixed Broadband Termination Control Unit MBS base station controller FBTU Fixed Broadband Termination Unit MBS base station FDD Frequency Division Duplex FDMA Frequency Division Multiple Access FPLMTS Future Public Land Mobile Telecommunication System 3rd generation mobile phone system, also called IMT-2000 FT Fixed Terminal


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GCRA Generic Cell Rate Algorithm Algorithm used for traffic policing in ATM GFC Generic Flow Control Field in the header of an ATM cell GSM Global System for Mobile Communications 2nd generation mobile phone system HAC Handover Admission Control HEC Header Error Control - Field in the header of an ATM cell HIPERLAN High Performance Radio Local Area Network Broadband wireless LAN IBCN Integrated Broadband Communication Network ID RM Protocol Identity Field in the header of a RM cell IMT-2000 International Mobile Telecommunication System 2000 3rd generation mobile system IN Intelligent Networks ITU International Telecommunications Union ITU-T ITU Telecommunication Standardization Sector World wide standardization body LA Location Area LAN Local Area Network LE Local Exchange LLC Logical Link Control Layer corresponding to the upper part of the OSI 2 layer

MAC Medium Access Control Layer corresponding to the lower part of the OSI 2 layer MBS Mobile Broadband System 3rd generation mobile system, RACE 2067 project

MBS Maximum Burst Size MBT Mobile Broadband Termination MCR Minimum Cell Rate Parameter used in ABR traffic class MES Mobility Enhanced Service MT Mobile Terminal MID Multiplexing Identification Field in an ATM cell carrying data of AAL3/4 MONET Mobile NETworks


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RACE 2066 project, developed UMTS MPEG Motion Picture Experts Group Standards for compressing video MSF Mobility Specific Functions MT Mobile Terminal Terminal of a wireless system NI No Increase Field in the header of a RM cell NL Network Layer OSI layer 3 NMT Nordic Mobile Telephone 1st generation mobile phone system NNI Network-Node Interface NNT Nippon Telephone and Telegraph 1st generation mobile phone system nrt-VBR Variable Bit Rate - Non Real-time ATM traffic class NSAP Network Service Access Point Addressing format OAM Operation and Maintenance OSI Open Systems Interconnection Layered reference model for communication systems P-NNI Private Network-Node Interface PACS Personal Access Communication Services 2nd generation cordless phone system PCM Pulse Code Modulation Coding method used for speech, etc. PCR Peak Cell Rate Highest transmission rate of the terminal PDA Personal Digital Assistant Hand held computer PDU Protocol Data Unit PHS Personal Handyphone System Japanese 2nd generation mobile phone system PL Physical Layer OSI layer 1 PM Physical Medium Sub layer of the ATM physical layer (lower part), similar to the OSI 1 PSTN Public Switched Telephone Network PT Payload Type


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A field in the header of an ATM cell PTI Payload Type Identifier Content of the PT field PVC Permanent Virtual Connection VC that is established using network management PVP Permanent Virtual Path VP that is established using network management QL Queue Length Field in the header of a RM cell QoS Quality of Service RA Request / Acknowledge Field in the header of a RM cell RACE Research and technology development in Advanced Communications technologies in Europe European research program RES Radio Equipment and Systems ETSI technical committee RLAN Radio Local Area Network RM Resource Management ATM cell used for traffic management in ABR rt-VBR Variable Bit Rate RealtimeATM traffic class SAAL Signalling AAL AAL used to carry signalling messages SCR Sustainable Cell Rate ATM traffic parameter SDH Synchronous Digital Hierarchy Physical layer transmission standard SN Sequence Number Field in the header of a RM cell SONET Synchronous Optical NETwork Physical layer transmission standard SVC Switched Virtual Connection VC that can be established using call control signalling TACS Total Access Control System 1st generation mobile phone system TC Transmission Convergence Sub layer of the ATM physical layer (upper part) TDD Time Division Duplex TDMA Time Division Multiple Access Tetra Trans European Trunked Radio System Standard for new trunked radio systems


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UBR Unspecified Bit Rate ATM traffic class UMTS Universal Mobile Telecommunications System 3rd generation mobile system UNI User-Network Interface UPC Usage Parameter Control ATM function policing the traffic VBR Variable Bit Rate ATM traffic class VC Virtual Connection Connections in ATM are called VCs VCI Virtual Channel Identifier Field in the header of ATM cell, used for routing VP Virtual Path Group of virtual connections VPI Virtual Path Identifier Field in the header of ATM cell, used for routing W-EXT Wireless Extension Mobility specific protocol described in this thesis WAND Wireless ATM Network Demonstrator ACTS Project developing a wireless ATM WARC World Administrative Radio Conference Organization controlling the use of radio frequencies WATM Wireless ATM The name of the wireless ATM model presented in this report. WWW World Wide Web Multimedia application used over Internet


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1 Introduction

Transmission Control Protocol (TCP) is the connection-oriented transport layer

protocol designed to operate on top of the datagram network layer Internet Protocol

(IP). TCP is the most widely used transport protocol, employed by many applications,

such as email and Web browsers.

Asynchronous Transfer Mode (ATM) developed as part of the Integrated Services

Digital Network (ISDN) effort and now widely used in non-ISDN applications, and

ATM is a technology developed as part of the Broadband Integrated Services Digital

Network (B-ISDN) effort and now widely used in non- B-ISDN applications. ATM is

standard for connection oriented networks which use cell relay communication,

meaning that information for multiple service types, such as voice, video, or data, is

packed and transmitted in small, fixed-size cells [STA98][AJM94a].

Until recently, all the experience in running TCP and IP has been over networks with

relatively few features for congestion control and quality of service. Increasingly, the

TCP/IP protocol stack is being used over ATM networks. Such networks are capable of

complex quality-of-service functions and have a wide range of complex congestion and

traffic control facilities.

The expansive use of TCP/IP over ATM has sparked a large-scale research on its

performance applications. In essence, the question is how best to manage TCP segment

size, window management, and congestion control policies, and ATM’s quality of

service QoS and traffic control policies.

One of the most comprehensive studies so far of TCP performance over ABR reported

in [FAN97]. The authors investigated 15 parameters associated with ABR algorithm

and examined different switch buffer sizes and networks propagation delays. They then

compared binary mode ABR performance with Unspecified Bit Rate (UBR) for both

throughput and fairness. They concluded that the performance and fairness of ABR are

quite sensitive to some of the ARB parameter settings, and in some cases very poor

performance and very poor fairness are witnessed.

The co-operation between both TCP and ATM technologies are needed. ATM would

support the TCP packet with very low transmission error. TCP, being a connection-

oriented transport layer would benefit from the connection-oriented architecture of


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ATM. On the other hand, ATM would equally benefit from TCP for data transfer

application [KAR97][STA98].

This project has two parts, in the first part; we study the performance of TCP

connections using the ATM ABR capabilities in a very simple network. An ATM

simulator CLASS was used in order to analyse the performance of TCP ATM ABR.

The network topology comprises two ATM switches, connected by one link. This link

is considered as the system bottleneck. Different number of TCP connections was

examined with constant buffer size, and different buffer sizes were examined with

constant TCP connections. The TCP traffic shared the bandwidth with a background

traffic load. Explicit Rate Indication for Congestion Avoidance (ERICA+) was used to

allocate bandwidth fairly with a fast response [AJM95a].

In the second part, we examine the handover protocol in a wireless ATM (W-ATM)

simulator called CLASS-wireless. We study relation between Mobile Terminal Load

( oL ) and buffer size at different Sustainable Cell rate (SCR), and Peak Cell Rate

(PCR).

This report begins with network abbreviations, since they are essential for

understanding today’s network literature. Review basic concepts of ATM, W-ATM,

TCP and TCP over ATM in section two. A brief explanation of CLASS and CLASS-

wireless simulators, their traffic generation, buffer allocation and priority management

mechanisms are reported in section three. Section four, illustrates the experimental

techniques used to run the two simulators. In section five we present a discussion for

the experimental results. In section six the report provide some conclusions and

suggestions foe further work.


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2 Background: ATM and TCP

2.1 ATM

2.1.1 Introduction

Both the ITU-T standardisation body and the ATM Forum have developed

specifications for As ATM. ITU-T is primarily concerned with developing ATM

standards as part of the broadband ISDN standardisation effort, whereas the ATM

Forum is interested in a broad range of ATM applications. The function of ATM is to

transfer data in discrete chunks and allowing multiple logical connections to be

multiplexed over a single physical interface. The information flow on each logical

connection is segmented into fixed-size packets called cells.

Physical layer

ATM layer

ATM adaptation layer (AAL)

Higher layer

Control plane

Management plane

User plane


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Fig. 2.1 Stack of TCP over ATM

2.1.2 ATM Architecture ATM was designed to handle multiple service types, including traditional data streams

and so-called isochronous services such as voice and video. To ensure that different

types of traffic are properly identified in transit, ATM provides four common ATM

Adaptation Layers (AAL) [ITUT, 150, 93].

AAL1 is designed for constant bit rate (CBR) traffic sources, such as video and voice.

The information in the header determines if the cells are lost or the header is corrupted.

Cell delay variation is handled to ensure constant bit rate delivery.

AAL2 is designed for variable bit rate (VBR) services, such as compressed voice and

video with different bandwidth demands [ITU-T93].

AAL3 and AAL4 - designed for connection-oriented and connectionless data streams,

respectively - have been absorbed by the more generalised AAL5 services for all

packetised data.

AAL5 is designed for a low overhead alternative to ALL3/4 for data applications such

as HTTP and email.

The differences between these layers might seem quite clear in theory but it is not the

case as far as physical practice is concerned. Many customers use ATM as a backbone

between LANs and WANs. For this reason, many voice and video streams are

packetised for transmission over different nets before they reach ATM. That means that

ATM edge devices (devices connecting ATM and non-ATM networks) may not be able

to identify between the different traffic types. This would mean that, by default, all

voice, video and data traffic would enter the ATM cloud as AAL5, since all of the

incoming streams are encoded as data packets [AJM95c] [STA98].

ATM uses fixed size 53 byte packets for communication. These fixed size packets

contain a 5-byte header and a 48-byte payload. The ATM provides connection-oriented


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services. This means that a connection must be set up between two ATM hosts prior to

data transmission between the two users.

It also means that, for the duration of such connection, user data will follow the same

path, arriving at the destination in sequence [MCD2000].

ATM uses virtual connections as the mechanism to connect and transport data between

a source and destination. The virtual connection is dedicated to the source and the

destination. One or more virtual connections can operate over a single physical link.

Switches are used to interconnect ATM hosts and networks. Switches contain a routing

table consisting of switch ports and connection identifiers. A new entry is made for

each connection during its connection establishment phase. A cell is transported

through the switch based on the connection identifier in its cell header. This simply

means that an ATM network will provide or reserve resources that guarantee a

specified minimum throughput, a maximum delay and maximum data loss for the

duration of a particular connection. This QoS support on a per connection basis enables

ATM to concurrently support any kind of traffic over a single network [ARM93].

Figure 2.2: Example of a private ATM network and a public ATM network carrying voice, video, and data traffic.

2.1.3 ATM Service Classes The ATM network classifies user traffic into five different classes: Constant Bit Rate

(CBR), Variable Bit Rate - real time (VBR-rt), Variable Bit Rate -non real time (VBR-

Nat), Available Bit Rate (ABR), Unspecified Bit Rate (UBR) and Guarantee Frame


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Rate (GFR). When a connection is established, the user specifies the service class to be

used on the connection. The service classes are useful to differentiate between specific

types of connections. For instance, a connection being used for a video conferencing

session will have very different needs to one being used for data transmission session

via interconnecting LANs.

2.1.3.1 CBR Constant Bit Rate or Continuous Bit Rate (CBR) is used for applications and

connections that require a fixed and consistent bandwidth. The peak cell rate (PCR) is

used to define the bandwidth requirements of a connection. The network guarantees

this bandwidth to the user. A source may send data up to the PCR for any length of

time. As can be seen from the Figure 2.2, the bandwidth reserved for a CBR connection

does not fluctuated as it does for other traffic classes. Examples: telephone traffic,

videoconferencing, and television [ATMF 4.0 96].

2.1.3.2 VBR-rt and VBR-nrt VBR-rt and VBR-nrt are variable bit rate for real time and non-real time traffic

respectively. As can be seen from Figure 2.2, the bandwidth requirement constantly

changes. The bursty nature of this type of traffic makes it difficult to manage in an

ATM network. VBR connections define bandwidth requirements in terms of PCR,

MBS and SCR. Cells can enter the network at the PCR for a period of time (i.e. MBS)

but on average must be transmitted at the SCR for the duration of the connection. The

variation in cell input rate enables multiple VBR sources to be statistically multiplexed

over the same physical connection to maximise network resources. Examples of VBR-

rt are voice with speech activity detection (SAD) and interactive compressed video.

Whereas Multimedia e-mail is an example of VBR-nrt. [GOR 95], [MCD98] [HIL95]

[PRC93].

2.1.3.3 ABR The ABR traffic class has been known to achieve better overall network utilisation by

using the free bandwidth. Two limitations, minimum cell rate (MCR) and PCR

determine the bandwidth requirement of an ABR user. The ATM network informs

sources of ABR traffic at exact rate cells can be transmitted at a given time. This

feedback is sent to the ABR source in resource management (RM) cells. These RM

cells contain information regarding the network conditions. This allowed cell rate

(ACR) varies between the MCR and PCR. Typical examples of services that will use


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the ABR traffic class for the transport of their traffic would be a LAN interconnection

service and data transfer. ABR traffic must not be sensitive to delay or delay variation.

From Figure 2.2, it can be noted that the amount of bandwidth available to ABR

connections varies with the burstiness of the VBR connections. That is, during VBR

bursts, ABR users will have less bandwidth available for their use [AJM94a] [STA98].

The algorithm to be implemented within ATM switches for the control of ABR

connections has not been specified at all by the ATM Forum. This because the network

operators want to choose the approaches and algorithms that best suit their users.

However, the recommended feedback format of RM cells has two techniques:

(1) The node can convey a very simple information using two bits, whose

meaning would be “ increase the rate” , or “ fix the rate” , or “decrease the

rate” .

(2) The node can use a specific field in the RM cell where the exact rate of

transmission is clearly stated.

2.1.3.4 UBR The UBR service class is mainly for applications that require no service guarantees for

their traffic. No traffic or QoS parameters are specified on a UBR connection. It can be

noted that a UBR connection will only get access to bandwidth when the requirements

of all other connections have been satisfied. LAN applications, such as file transfer or

the exchange of electronic mail, are suited to this type of ATM connection.

2.1.3.5 GFR GFR is frame-based service designed for applications that may require minimum

guarantee rate and can benefit from accessing additional bandwidth dynamically

available in the network. GFR services requires minimal interactions between users and

ATM and uses AAL5 which enables frame boundaries to be visible at the ATM layer

[PD97a][BON97][ATMF98].

Figure 2.2 ATM bit rate services


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2.1.4 ATM Traffic Management At connection set-up phase, resources are allocated for the duration of the connection.

ATM defines a set of traffic and QoS parameters, which are used to capture the

characteristics of an ATM connection. The traffic parameters, which have been defined,

consist of the peak cell rate (PCR), the sustainable cell rate (SCR), the maximum burst

size (MBS), and the minimum cell rate (MCR). The QoS parameters consist of a peak

to a peak cell delay variation (CDV), a maximum cell transfer delay (CTD), a cell loss

ratio (CLR) and a cell error ratio [ITU-T94]. The ATM network will support QoS of a

particular connection as long as the user's traffic is determined to be complaint. An

ATM network determines whether or not a cell is compliant using the conformance

definition. A conforming cell is one, which passes the test, while a non-conforming cell

fails the test. Non-conforming cells are either discarded immediately or tagged.

Tagging involves setting the cell loss priority (CLP) bit in the cell header. Tagged cells

are discarded before untagged cells during congestion. The conformance test is an

implementation of the (GCRA) which is often referred to as the leaky bucket algorithm

[AJM94b][ITU-T94].

The ATM Forum has identified the following Quality of Service (QoS) parameters to

be associated with traffic management and negotiation. These parameters are:

2.1.4.1 Cell Loss Rate (CLR) CLR is the percentage of cells not delivered at their destination because they were lost

in the network due to congestion and buffer overflow. dtransmittecellstotal

cellslostCLR =

2.1.4.2 Burst Tolerance (BT) BT determines the maximum burst can be sent at the peak rate. This is the bucket-size

parameter for the enforcement algorithm that used to control the traffic entering the

network.

2.1.4.3 Cell Delay Variation (CDV) CDV is a measure of the variance of the cell transfer delay. High variation implies

larger buffering for delay-sensitive traffic such as voice and video.

2.1.4.4 Peak-to-Peak Cell Delay Variation Difference between the fixed propagation delay and maximum Cell Transfer Delay

(CTD). In other words it is the difference between the best and worst possible CTD

[BR99].


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2.1.4.5 Peak Cell Rate (PCR) PCR is the maximum cell rate at which the user will transmit. PCR is the inverse of the

minimum cell inter-arrival time.

2.1.4.6 Sustain Cell Rate (SCR) This is the average rate, as measured over a long interval, in the order of the connection

lifetime [ATMF 4.0, 96].

2.1.5 ATM Congestion Control An ATM network consists of ATM switches that are connected to each other using an

interface called the Network-Node Interface (NNI). Terminals are connected to the

network using User-Network Interface (UNI). If there are privately owned switches in

the network, the interface between the public and private part of the network is called

the Public UNI and the connection between two private switches a Private NNI (P-

NNI) [SCH98][AJM95b].

The ATM connection is called a virtual connection (VC). There are two main types of

virtual connections; Permanent Virtual Connections (PVC) and Switched Virtual

Connections (SVC). Figure 3 shows an example of an ATM network, where terminals

A and B have an active switched virtual connection. In a switch, the traffic on a virtual

connection is routed according to two identifiers; the Virtual Path Identifier (VPI) and

the Virtual Channel Identifier (VCI). Besides the VPI/VCI also the identity of the

incoming link is used to identify a VC. A VPI/VCI is allocated for a virtual connection

by the switch when the connection is set up, and it remains unchanged for the entire

lifetime of the connection. It should be noted that the VPI/VCI values of a single

connection are most likely to be different on different links. [STA98][I.371, 93].

2.2 Wireless ATM

2.2.1 Introduction In recent years, dedicated telecommunication networks for voice, data and multimedia

communication evolve rapidly around broadband integrated service digital network (B-

ISDN) based on Asynchronous Transfer Mode (ATM) as the basic multiplexing,

packet-switching and transport technology. The provision of an efficient wired and

wireless access to an ATM backbone network is a challenging technical and

economical issues [ATMF96], [ATMF98], [AYA96], [JAB96].

The last decade of the 20th century has been confronted with a formidable goal of

achieving location independent communications and multimedia. This has been


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illustrated as the concept of personal communication networks (PCN) and personal

communication services (PCS) [RAY94], [ACO 96]. Because of the exponential

increase in multimedia and computer applications in communications, a great deal of

research and development is taking place in the field of wireless broadband multimedia

communication (WBMCS) in Europe, North America and Japan. RACE (research and

development in advanced communication in Europe), ACT (advanced communications

technologies and services), MBS (mobile broadband system) and UMST (universal

mobile telecommunication system) are few projects launched in recent years [AJM98c]

[PAN96], [PAD95][AJM98d].

Although wireless networking and mobile computing are often interrelated, they are not

identical,. As Table (1) shows, portable computers are sometimes wired. When plugged

into a socket in a hotel here, you have mobility without wireless network. On the other

hand, some wireless computers have no room for mobility. An example is a building

with wireless LAN.

wireless Mobile Applications

No No Stationary workstation in offices

No Yes Using a portable in a hotel

Yes No LANs in old unwired building

Yes Yes Portable office; PDA for store inventory

Table (2.1) Combination of wireless networks and mobile computing [TAN96]

Wireless computing refers to computing systems that are connected to their working

environment via wireless links. This term is applied to the computing devices

participating in a wireless LAN, with gateways to wired networks (Kat94). The most

important point is the ability to work within a collection of computing devices and

servers for sharing data and information. This means symmetrical bandwidth between

wireless nodes and the network, and a desire for as a high bandwidth as possible,

approaching Ethernet speeds. Under this definition, wireless email is particularly

primitive form of wireless computing [AJM98b][TAT98].

Wireless ATM (WATM) is an imminent technology, viewed as advanced gateway to

broadband networks in order to provide users with seamless integrated services.

WATM possess all the capabilities required to provide a networking platform for

wireless broadband systems.


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Fully exploitation of WATM service capabilities is demonstrated in medical

consultation in hospital environment. The JVTOS (Joint Video Telecommunication

Operating System) is used with an X-ray viewing system using both video and audio

services over ATM. With WATM, Doctors will be able to retrieve patient medical

records from the network and consult experts all over the world to share the documents

[JOU96].

However, the integration of wireless networks into B-ISDN/ATM networks raised a

number of issues which originated from the inherent mismatch between wireless and

wired links in terms of transmission speed and bit error rate (BER). Dynamic channel

allocation and error control schemes might be able to alleviate some of these challenges

[AJM98a].

One of the major technical and economical issues facing the telecommunication

industry world-wide is the development and commissioning of high capacity, wireless

systems. Third generation wireless systems (3G) are currently being deployed such as

the Universal Mobile Telecommunications Systems (UMTS) in Europe and the future

global wireless access system called International Mobile Telecommunications-2000

[IMT2000].

In addition, wireless local area networks (WLANs) are designed for high-speed data

transmission such as those considered by the IEEE 802.11 and HIPERLAN standards.

A wireless asynchronous transfer mode (WATM) standard is being developed under

the auspices of the ATM Forum and is supposed to extend wired ATM/B-ISDN into

the wireless domain. Particular needs of professional and private users regarding

security, authentication and other issues led to development of Professional/Private

Mobile Radio (PMR) systems such as the Trans-European Trunked Radio (TETRA).

The Packet Data Optimised (PDO) component of the TETRA standard is currently

being considered for migration to provide for data rates up to 155Mbps as part of a

future generation system called Digital Advanced Wireless Services (DAWS).

These future wireless systems are planned to offer telecommunication services carrying

"anything, anywhere, anytime". Applications range from traditional voice services over

real-time video to high rate data and multimedia services. Professional and private

users will do business the same way as they are used to do in a wired environment, e.g.

exchange of electronic documents, money transfers, or tele shopping.


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Some of the techniques related to radio aspects, which will assist the realisation and the

transition from second to third and future generation mobile communication systems,

includes:

• Provision of bandwidth on demand

• Dynamic channel equalisation

• Optimised coding and modulation

• Multi-user detection

• Smart antennas

• Software radio

Delivering hard QoS guarantees in the wireless domain is rather difficult since

assumptions made in providing QoS guarantees in wired ATM networks do not always

hold in their wireless extension due to large-scale mobility requirements, limited radio

channel resources and fluctuating network conditions. Renegotiations of resources

allocated to the connection are often needed. At the same time though, the flow (e.g.,

audio or video) should be transported and presented `seamlessly' to the destination

device with a smooth change of perceptual quality. These conditions impact our ability

to deliver hard QoS guarantees in mobile ATM networks [JAI96] [FON96] [ALA99].

Although researchers have addressed the isolated areas of handoff criteria, connection

re-routing, signalling extension, and QoS provision in mobile ATM networks, a great

deal of research has been directed toward the development of a handoff protocol which

supports the seamless delivery of scalable multimedia flows with controlled QoS,

which is our research aim. The term "controlled QoS" is used to emphasise media

scaling with QoS renegotiations for adaptive multimedia applications in wireless ATM

networks, instead of the "hard" QoS guarantee offered by wireline ATM networks

[JOU96].


22

Fig (2.3) Medical consultation User Trial [MiI96]

2.2.2 Wireless Technologies Currently, Wireless LAN technologies comprises of infrared (IR), UHF radio, spread

spectrum, and microwave radio ranging from frequencies of Ghz to infrared

frequencies. The personal communication network (PCN) may use a shared wideband

code-division multiple access (CDMA). There is a considerable discussion among

experts in this field regarding the relative advantage of CDMA and TDMA for private

communication network (PCN)[RAY94]. The preferred option may vary with the

different PCN scenario to be implemented.

2.2.2.1 Spread Spectrum (CDMA) The term spread spectrum defines a class of digital radio system in which the

bandwidth in use is significantly bigger than the information rate [LEE93]. CDMA is

often refers to the possibility of transmitting several signal in the same portion of

spectrum by using pseudorandom codes for each signal. It was originally initiated for

military purposes, where the difficulties of detecting or jamming this type of signal

made it the best choice to transmit military information.


23

2.2.2.2 Time Division Multiple Access (TDMA) The idea of TDMA is basically simple. Traditional, voice channels have been created

by dividing the radio spectrum into very narrow radio frequency (RF) carriers, with

one conversation occupying one duplex channel. This technique is known as FDMA

(frequency division multiple access). On the other hand, TDMA divides the radio

carriers into an endless repeated sequence of small time slot (channels), and one

conversation occupies only one slot.

2.2.2 Wireless Architecture The Wireless ATM items are divided into two different parts: Mobile ATM (Control

Plane), and Radio Access Layer (Wireless Control), as shown in Figure 2.4. Mobile

ATM deals with the higher-layer control/signalling required to support mobility. These

control/signalling include handover, location management, routing, addressing, and

traffic management. Alternatively, Radio Access Layer is responsible for the radio link

protocol for wireless ATM access . Radio Access Layer consists of PHY (Physical

Layer), MAC (Media Access Layer), DLC (Data Link Layer), and RRC (Radio

Resource Control) [RAH93][SHA97][CON95]. Here is a brief description of WATM

architecture.

User Plane Control Plane

ATM Adaptation Layer

ATM Layer WirelessControl

Data Link Control

Medium Access Control

Radio Access Control

Mobility “M” Specification

Radio Access “R” Specification


24

Figure 2.4 Wireless ATM Protocol Architecture

2.2.2.1 Radio Physical Layer A fixed ATM station transmits data in the range of 25 to 155 Mb/s. These figures are

extremely difficult in a wireless environment. A several GHz spectrum would be

needed to achieve high speed wireless transmission. At the moment, 5 GHz is

considered to be used to transmit 52 Mb/s using advanced modulation and coding

techniques.

2.2.2.2 Medium Access Control (MAC) MAC in WATM is responsible for providing point to point link for the higher protocol

layer. Another design issue of MAC layer is to support multiple Physical Layer

[JAM2000][ATMF96].

2.2.2.3 Data Link Control Data Link Control provides service to ATM layer. Monitoring the effect of radio

channel errors before the cell is sent on the ATM layer.

2.2.2.4 Radio Resource Control (RRC) RRC supports control plane functions related to the radio access layer. It should also

support radio resource control and management functions for physical layer, medium

access control layer and data link control.

2.2.3 Mobility Management 2.2.3.1 Handover Management In WATM networks, a mobile user establish a virtual connection (VC) to communicate

with another mobile user or fixed ATM user. When the mobile user moves from access

point (AP) to another AP, proper handover mechanism is required to reduce the

interruption to cell transmission process, otherwise, an efficient switching of the active

from the current path to a new one will be seriously affected. When handover takes

place, the new data path might not support the current Qos. In this situation a


25

negotiation is needed to specify a new set of QoS. Since users have access to many

APs, they might select the one, which provides the best QoS [FES2000].

During the handover, an old path is realised and a new one is established, and there is a

possibility that some cells will be lost. A buffer is used to guarantee that no cell is lost

and cell sequence is intact. Cell buffering consists of downstream buffering and

upstream buffering. Upstream buffer is needed to store outgoing cells if VC is broken

when the mobile user is transmitting cells to AP, while the counterpart needed to store

downstream cells for any interruptions, congestion, or retransmissions.

2.2.3.1 Location Management Location management is needed to find a mobile ATM end point when a connection is

required with another ATM end point. There are two location management schemes:

the mobile Private Network-Network Interface PNNI scheme and the location register

scheme [ATMF96][LAU2000].

In the mobile PNNI scheme, when a mobile moves, updated cell locations propagates

to the nodes in a limited region. Switches have the correct information about the cell

location. When a switch in this region originates a call, it can use the location

information to establish the connection. Similarly, if a call is originated by a switch

outside this region, a connect is established between this switch and the mobile’s home

agent, which then forwards the cells to the mobile [ATM97][JAM2000].

2.3 TCP

2.3.1 Overview

The most widely used reliable transport layer protocol is the transmission control

protocol (TCP). It is byte stream connection-oriented protocol that combines

congestion control with flow control. It uses sliding window flow control scheme at the

sender and cumulative ACKS from the receiver. Congestion avoidance and control is

implemented by how the sender grows or shirks the congestion window.

2.3.2 Congestion Control TCP is one of the few transport protocols that has its own congestion control

mechanisms. The key TCP congestion mechanism is the so-called “Slow Start” . TCP

connections use an end to end flow control window to limit the number of packets that

the source sends, The sender window is the minimum of the receiver window (Wrcvr)

and a congestion window variable (CWND). When a TCP connection losses a packet,

the source does not receive an acknowledgement and it times out. The source retrieves


26

the congestion window (CWND) value at which it lost packet by setting a threshold

variable SSTHRESH at half the window. More precisely, SSTHRESH is set to max { 2,

min{ CWND/2, Wrcvr} } and CWND is set to one [RAJ96][AJM96e].

The source then retransmits the lost packet and increases its CWND by one every time

a packet is acknowledged. This phase is called “exponential increase phase [KAL96].

The window increases exponentially when plotted as a function of time (figure2.5).

This continues until the window is equal to SSTHRESH. After that the window enters

“ linear increase phase” . Although the congestion window may increase beyond the

advertised receiver window, the source window is limited by that value. When packet

losses occur, the retransmission algorithm may retransmit all the packets starting from

the lost packet. That is, TCP uses a go-back-N retransmission policy[AJM96f]

[FAH96].

The enhancement of TCP’s congestion control algorithms using Explicit Congestion

Notification (ECN) over ATM networks was investigated. The research indicated that

TCP ECN performs better relative to TCP Reno. The research also concluded that in

most of the experiments the throughput achieved was better for TCP Explicit

Congestion Notification (ECN) than TCP Reno [ADE 2000].

A new flow and congestion control algorithm between IP network and ATM network

was investigated [LEE2000]. The research applied the rate-based scheme to the

window-based TCP control called RBCA (Rate-Based Credit Adaptation). The

research found that the proposed algorithm is able to achieve very packet loss rates.

Wrcvr

Window

Exponential

Loss Timeout

SSTHRESH

Linear


27

Figure 2.5 TCP Window Vs Time using Slow Start

The source then retransmits the lost packet and increases its CWND by one every time

a packet is acknowledged. This phase is called “exponential increase phase [KAL96].

The window increases exponentially when plotted as a function of time (figure2.5).

This continues until the window is equal to SSTHRESH. After that the window enters

“ linear increase phase” . Although the congestion window may increase beyond the

advertised receiver window, the source window is limited by that value. When packet

losses occur, the retransmission algorithm may retransmit all the packets starting from

the lost packet. That is, TCP uses a go-back-N retransmission policy[AJM96f]

[FAH96].

The effect of various factors which influence TCP throughput such as TCP timer

granularity, switch buffering, ABR parameters and the cell drop policy at the switches

was studies [KAL96]. The findings indicated that TCP achieves maximum throughput

when there are enough buffers at the switches and when maximum throughput is

achieved, the TCP sources are rate-limited by ABR and not window limited by TCP.

A new packet discard scheme called forgiveness mechanism that can be plugged into

the existing buffer management scheme was investigated [ElA2000]. The research

found that switches with larger buffer size lead to higher TCP efficiency, EPD+

enhanced performance of TCP over ATM-UBR and EPD+ increases efficiency but

does not sacrifice fairness.

The performance of TCP connections exploiting the ATM available bit rate (ABR)

transfer capabilities in a simple network was investigated [AJM96d]. They observed

that the dynamic behaviour of the TCP sources is quite close to good behaviour when

the channel load is low, the TCP sources increase their transmission rate, and when the

channel load increases the TCP sources progressively lower their rate. They also noted


28

that in the case of two TCP connections, the shorter one responds faster to the network

feedback.

An investigation was carried out to study how current TCP implementations fare in a

congested environment competing against TCP with SACK [FLO96]. The research

concluded that using the SACK option would open the way for research on

modifications of the TCP congestion control algorithms, such as wireless or satellite

links.

2.4 TCP Over ATM TCP over ABR traffic operates in two quite different modes: window limited and rate

limited. In window-limited mode, a TCP source is controlled by the TCP flow and

congestion control mechanism. When a TCP connection is established and a VC is

assigned, ABR will typically allocate a relatively high rate to the source, only reducing

the rate if congestion experienced. Therefore, for a time TCP can send as much data as

it can. This rate therefore determined by the congestion window and the TCP slow-start

mechanism. Until this point, TCP is likely to be window limited. Once TCP sends

segments continuously, connection may experience and the connection becomes rate

limited [KAL97][AJM96c].

Figure 2.6 shows the sending process generates a block of data and sends this data to

TCP. TCP might break this block into very small pieces to handle it. For each of those

pieces, TCP appends control information in the TCP header, forming a TCP segment.

The control information is to be used by the peer TCP. TCP hands each segment over

IP, which instruction to transmit it to host B. IP appends a header of control

information to each segment to form datagram. Each IP datagram is presented to the

network access layer for transmission. The network access layer appends its own

header, creating a packet or a frame [STA98][TAN96].

IP header20 bytes

TCP header20 bytes

PAD

TCP segment

IPdatagram


29

Figure 2.6 TCP/IP over ATM stack

Additional considerations are needed when carrying TCP traffic over the ATM ABR

and UBR service categories. TCP/IP is the most common data traffic running over

ATM networks today. During congestion conditions and subsequent loss of cells, the

ATM network device does not notify the sender that re-transmission is needed, instead

higher-layer protocols, like TCP must notice the loss via a timeout and retransmit the

missing packets. Not only does one cell cause the missing packet to be retransmitted,

but all packets after it up to the end of transmission window. Excessive discards within

a TCP window can adversely affect the recovery process and cause host time-outs

causing a great deal of interruptions and delay of several seconds [AJM96c] [ROM95].

Poor performance has been always associated with of TCP over ATM networks. This is

due to the dynamic nature of TCP often worsened when implemented over ATM. A

great deal of studies has been conducted to find a possible solution such as switch

buffer size, number of sources and segment size. One of the key parameter to improve

the performance of TCP over ABR was using a larger buffer. It has been shown that the

maximum throughput can be achieved on the connection. The study has also shown

that smaller buffer sizes have resulted in window-limited sources and a reduction in

throughput [KAL96].

In several researches carried out to study the complex issue of congestion control

algorithm of TCP over ABR have reported that the end-end flow control, the network-

based drop policies and congestion control policies are some of the effective methods

in improving performance. A very recent research on fair buffer management for the

best effort network traffic has also shown that when the sources are window limited, a

larger number of sources each having a small window, could improve the utilisation of


30

the network. This can be explained by the role of multiplexing in many sources

[KAR97][AJM96b].

3. ATM/WATM Networks Simulation

3.1 CLASS Version 6.20h

3.1.1 Overview Class is a simulator for ATM networks developed by the Electronics Department of

Politecnico di Torino in co-operation with CSELT (Centro Studi E Laboratori

Telecomunicazioni- the Italian public research centre in telecommunications and

networking). Various contracts such as the Technical University of Budapest and

Wurzburg University have contributed to the development of CLASS. CLASS stands

for ConnectionLess ATM Services Simulator, and it was designed for the simulation of

the connectionless traffic resulting from the connectionless services offered by B-ISDN

[AJM98]. CLASS stands for ConnectionLess Atm Service Simulator.

The network models simulated by CLASS version 6.20h are made of three basic

entities:


31

1- ATM switches, these switches perform the cell switching services and

implement the traffic management algorithms relative to nodes.

2- Channels, that transfer cells between either adjacent nodes or user-node pairs

3- Users, act as sources and sinks for cell flows, and implement the traffic

management algorithms relative to users.

During this project two versions of CLASS were used. The main CLASS version 6.20f

deals with TCP connection over ABR transfer capabilities. The TCP protocol is based

on a TCP a window mechanism that governs the flow of data units. The throughput

obtained by a TCP connection is automatically adjusted to the resources available on

the networks by either increasing or decreasing the transmission window. The

transmitted data are divided into medium-size units called segments, adding some

redundancy for control purposes. The segments are then divide into cells assuming an

AAL-5, hence assuming 48 bytes available for the data. Since segmentation does not

indispensably contain an integer multiple of 48 bytes, the last cell of each segment may

be chosen at the beginning of the simulation with maximum of 9180 bytes, which is the

approved size for segments in SMDS [AJM94b] [AJM96a].

When a connection is set-up, the receiver determines a maximum window size, the

actual window size at the source is always less or equals the maximum receiver

advertised window, and a threshold is initially set to half the maximum receiver

advertised window size. The maximum window in CLASS simulator is not advertised

by TCP-RECEIVER users, but is a parameter determined by the user for each TCP-

TRANSMITTER user. The actual window size at the source is originally set to one

segment and it is increased in two phases: the slow-start phase, where the window

increases geometrically, and the congestion avoidance phase, where the window

increases linearly. During the slow-start phase, the window size doubles at each

transmission cycle: two data segments are transmitted for every received ACK, but

once every window an ACK causes the transmission of two segments determining the

linear increment. The source node changes from the slow-start phase to the congestion

avoidance phase when the actual window size reaches the current threshold. When the

maximum window size is reached, the transmission continues without further

increasing the window size [AJM94d].

3.1.2 Traffic Generators The CLASS simulator version 6.20f provides 24 different users, corresponding to

different traffic generation schemes along with different policies of traffic shaping.

Twelve of those users simulate connectionless services with three different traffic-


32

shaping policies. Two are assigned to the simulation of the TCP transport protocol, two

assigned for connection-oriented services, while the remaining one is generic receiver

[CLA98]. The difference between connection-oriented and connectionless user lies on

the type of traffic they create and they way this traffic is created. Connection-oriented

users generate a stream of cells that are sent to a given destination, the same for all

cells. Connectionless users create single message, i.e., a bunch of cells, and send them

to destinations that may be different from one message to the other. Messages are

normally fairly short, rarely longer than a few hundred cells [AJM95b][AJM95c].

3.1.3 CLASS Traffic Shaping

A number of shaping policies and algorithms have been reported in literature each of

witch has its own advantages and disadvantages [TUR86], [COO90], [RAT91]

[SID89]. CLASS applies the Virtual Scheduling Algorithms (VSA) described in the

recommendation of I.371 of ITU.

Every time a cell is ready for transmission, VSA determines if the cell is conforming to

the Traffic Contract of connection. The VSA not only provide to control the traffic

characteristics, but also provide a means for the formal definition of traffic

conformance to the traffic Contract. The VSA requires only the definition of two

parameters: the increment between cells T and the time limit τ . The time increment

between cells is clearly the time that should pass between two consecutive cells if the

traffic was generated at constant bit rate. τ is the time jitter and related to cell delay

variation.

The VSA keeps footprints of a Theoretical Arrival Time (TAT), which is “nominal”

arrival time of the next cell assuming that there is equal space between cells when the

source is active. If the true arrival time of a cell is not too early relative to TAT, i.e.,

TAT-τ , then the cell is declared conforming to the Traffic Cortex, otherwise, the cell is

non-conforming.

A Cell arrives attime ta

TAT< ta

TAT> ta+

The cell is non conformits transmission is

delayed until TATTAT = TAT + T

TAT= ta

YES

τ


33

Figure 3.1. Flow Chart of the Virtual Scheduling Algorithm

From Figure 3.1, we can make the following points:

Assume the arrival of the first cell be ta.. In this situation the cell is transmitted

immediately and Theoretical Arrival Time TAT is initialised to the ta(1) + T. For all

subsequent cells one the of the following alternatives is given:

1- The arrival time ta of the cell is greater than or equal to TAT; then the cell is

compliant, it is transmitted immediately and TAT is updated to the value ta + T.

2- The cell could arrive at time ta with TAT-τ ≤ ta < TAT,

The cell is again conforming and the TAT is increased again by the increment T:

TAT= TAT + T.

3- The cell arrives in a time smaller than TAT-τ , then the cell is non-conforming; the

cell transmission time tt is set to actual value of TAT and TAT is updated to the

value TAT + T.

In practice, the TAT of the next cell is always set to the present cell transmission time,

plus the time increment, i.e.,

TAT(k+1) = tt (k) + T

There are several possibilities for implementing CLASS traffic shaping. The easiest

solution is to perform the shaping at the front end on the transmitter, negating the

traffic parameters for all the traffic generated by the user.

3.1.4 Shaping Policies


34

There are two shaping policies avaiable in CLASS 6.20h: VP-based and VC-based

shaping policy. Due to time limitation we will talk briefly about VP-based shaping

policy [CLA98][AJM95d].

Users categorised under this policy perform shaping of the traffic at the interface

between the user buffer and transmission link. Here, users have only a single traffic

shaper that operates upon the whole traffic generated by the user, regardless of the

destination, VCI, or traffic relation. From Figure 3.2, it means that there is only one

group and the output multiplexer is not present, all the VC are grouped together and the

multiplexing among the VCs is done at the message level. This means, all the cells of

the same message are in any case transmitted sequentially one after the other without

flitting with cells of the other messages.

The user negotiates the bandwidth needed for the transmission of the whole traffic with

the node, and sets accordingly the traffic parameters. The T parameter needed by VSA

is computed automatically by CLASS given the average bandwidth needed by the user.

β.wB

CT =

Where wB is the mean bandwidth required by the user, β is the Bandwidth

allocation Factor (BAF) and C is the capacity of the link.

Qs1

Qsn

M

U

X

TXqueue

Qt

MUX

Shape 1

VC1 Group1

MUX

Shape N

Group N

Ca-CcTta-Ttc

Cx-Cz

Ttx-Ttz

segmentation

segmentation

segmentation

segmentation

VCM

Message generation

Message generation


35

Figure 3.2 Architecture for traffic shaping

3.1.5 Weighted Fair Queuing in CLASS (WFQ)

Analytical and simulation investigation by Demers et al (Demers,92) showed that WFQ

can share link bandwidth in a fair manner and protect the well-behaving sources from

ill-behaving ones. Since then a number of WFQ versions have been proposed in the

literature [DEM92], [PAR93], [GOL94]. However, most of the Fair Queuing Schemes

are proved difficult to implement. A new Virtual Spacing Algorithm has been proposed

[ROB94],[AJM95] which is approximately equivalent to PGPS (Packet by Packet

General Processor Sharing and it allows a relatively simple implementation in ATM

switches even in high speed environment. The Virtual Spacing Algorithm has been

independently proposed under the name Self-Clocked Fair Queuing Algorithm

[GOL94].

Choosing the right rate for WFQ is very important for its effective work. The following

are the main traffic sources:

TCP traffic has a special bandwidth allocation for WFQ and it has a special buffer

allocation as well since, not having TCP a predefined bandwidth allocation, it is not

possible to allocate the buffer the standard way. In presence of TCP connections the

buffer allocation is done as follows:

First the same size of a separate buffer is allocated for each TCP connection. The user

defines the size of this parameter. The remaining buffer size is subdivided among the

non-TCP connections proportionally to their allocated cell rate.

��

��

�=

sumww r

Size

TBuff .

1

Where Buffw is the buffer size for non TCP connections, Tw is the inverse of

allocation rate, rsum is the sum of all connections except the TCP and Size is the size of

remaining link buffer after TCP buffer allocation.

For unshaped TCP traffic the user must define a bandwidth for calculating the

inverse of the allocated rate. It is normally done using the following formula:

tcpw B

CT =


36

Where C is the link capacity and tcpB is the predefined TCP bandwidth.

Choosing a low value for tcpB relative to the bandwidth of other connections means

that cell of TCP connections only get significant bandwidth if the other connections are

not transmitting.

3.1.6 Priority Management in CLASS

To support the management traffic flows with different quality of service (QoS)

requirements, the ATM nodes need to identify the different class of service and serve

them in an appropriate manner. CLASS simulator has applied the concept of priority

classes and assigned a certain level of priority to each traffic generated by the user. Up

to four priority classes can be determined in CLASS and buffers are served in a strict

priority manner. Firstly, the priority 0 buffer is visited and, if it not empty, one cell of

this buffer is served. If the priority 0 buffer is empty, the priority 1 buffer is visited and

possibly served. The same procedure happens for each following priority level. In this

way, the cells belonging to priority number of class 1 level are served only if no cells

with higher priority have to be transmitted on the same link.

3.2 CLASS Wireless Version 5.994

3.2.1 Overview The reference model adopted in CLASS for wireless ATM assumes the full integration

of mobile terminals with B-ISDN. This means, the radio interface is packetised and

optimised for ATM cell size. The protocol stack within the mobile terminal comprises a

standard ATM access, up to the ALL (ATM Adaptation Layer), while the base stations

implement the protocol stack only up to the ATM layer [AJM97].

3.2.2 WATM Architecture

The Mobile Broadband System (MBS) is considered as the air interface protocol

[MAX95][UMTS95]. The MBS is a wireless cellular network designed to be fully

integrated into B-ISDN. The MBS air interface allows mobile users to be part of a B-

ISDN system by transmitting information using the ATM cell format. This approach

offers a homogenous network architecture with end–to-end ATM delivery between


37

nodes making use of ATM service. Each cell will be transmitted over the radio channel

connecting the mobile terminal to local exchange (LE), and routed through the ATM

network.

A shown in Figure 3.3, MBS in CLASS comprises Mobile Terminal (MT), Base

Stations (BSs), ATM node and Fixed ATM [AJM97d][AJM97c]. A brief description

of each component is as follows:

3.2.2.1 Mobile Terminals: Mobile terminal is the endpoint of connections whose main characteristic is a radio

access to the network that enables mobile terminal to roam through the service area; the

point where the connection from a MT enters the network is a BS through a Wireless

Access Point (WAP). The MT can have multiple connections with different remote

hosts, as any B-ISDN terminal.

Fixed Network

MT

LE

BS2BS1


38

Figure 3.3 WATM Scenario

ATM switches and BSs are wired together and form the fixed network segment. On the

other hand a MT can only communicate with BSs.

3.2.2.2 Base Stations Base Stations are the interface between the wired and the wireless part of the network.

Depending on the implementation and the network structure, a Base Station can have

switching capabilities. Base Stations behave like an ATM node collecting several

connections from Mobile Terminals and delivering them onto the network. A Base

station quite often has a connection with the fixed network, and can sometimes acts as a

mobile (e.g., ship, aircraft or satellites). If a Base Station acts as a mobile, the

connection changes over time and through a radio channel [AJM97b].

3.2.2.3 ATM nodes ATM nodes are the primary infrastructure of the B-ISDN core. These nodes have the

typical ATM capabilities as well as providing support for mobility services in WATM.

Most ATM nodes must be mobility aware, and provide support for this kind of services

either mobility server or directly embedded within the switch or nodes.

3.2.2.4 Local Exchanges (LE) Local Exchanges are mobility-aware ATM nodes connected to BSs. The Local

Exchange can be regarded as BS if it has switching capabilities. Figure 3.4 illustrates

the protocol stack of the user plane of WATM. As it has been mentioned before, Base

Stations might be furnished with switching capabilities, and they can either connected

to many ATM nodes, or act as ATM nodes. The thick solid line indicates the logical

path followed by the information flow from the application to the remote host to which

the MT is connected, likewise the information follow the reverse direction. As it can be

seen from the diagram, the MTs, ATM nodes and BSs have their own entities that

operate directly at the ATM level to facilitate the handover procedures when the

terminal moves from one base station to another (AJM97b)[AJM97c].

3.2.3 Protocol Stack in CLASS Wireless V5.994

Mobil ity Management

Fixed BaseStation

Mobile ATM Terminal

ATM Node

peer-to-peer communication

Data flow


39

Figure 3.4. Protocol stack in CLASS-Wireless [AJM99]

In Figure 3.4, the thick solid line represents the logical path followed by the

information flow from the MT application to the remote host to which the MT is

connected. It is also the same path followed by the information on the opposite

direction. In CLASS-wireless simulator, all the components of the network , such as

MTs, BSs and ATM nodes have specialised entities, that operate at ATM level and that

are capable of managing handover procedures when the terminal moves from one base

station to another. The peer-to-peer communication between these entities in CLASS-

wireless contains control information relevant to the ATM.

3.2.4 Handover Management in CLASS-Wireless Handover procedures comprise set of operations such as co-ordinating between the

network and the mobile terminal to allow the re-routing of the connections that reach

the mobile terminal while this roams through the network [VEE97]. In practice,

handover procedures provide the means for the mobile terminal to change its access

point to network without interrupting the communication, i.e., to move from one micro-

cell or domain to another without the need of tearing down and setting up connections.

The target handover procedure should be the degree of compatibility with B-ISDN

characteristics, hence it should be seamless and grant very low data loss probabilities

[SCR98][AJM98d].


40

There are two different types of handover: hard handover and soft handover.

This subdivision is mainly referred to the capability of the MT radio interface to

manage more than one radio connection at the same time. If the MT can deal only with

one connection at a time, then the handover is hard, with the assumption that the MT is

connected either to one BS or to the other, but not both at the same time. The soft

handover is exactly the opposite, if the MT can deal with more than one radio

connection, then the handover is soft, i.e., the MT might be connected to both the

source and the destination BSs [AYA98].

The network architecture and service always affect the handover procedures.

TDMA based networks, like GSM, eventually use hard handover procedures with

channel interruption, while CDMA based networks are associated with soft handover

procedures [TOH96], [MIT96][KRI98].

3.2.4.1 Seamless Handover in CLASS-Wireless The main issue of mobile services that can be perceived through CLASS-Wireless

simulator is the management of network handovers, i.e., the type of procedures for re-

routing of ATM connection in the event of mobile terminal movement from one cell to

another.

The mobile terminals in CLASS-Wireless roam through a predefined set of cells, each

one covered by a radio base station, following a mobility pattern defined by the user in

probabilistic terms. In case of failed handover for lack of resources, the corresponding

connection is not dropped instead, the failure is recorded and the handover is re-

scheduled after arbitrary delay [ATI95][RAM98][AJM99].

Figure 3.5 shows the sequence of the main events that reflects the seamless handover

protocol, including action taken by the MT, the ATM crossover switches and

destination BS (BS2 in the above scheme). First, the MT sends a handover request to

the existing base station (BS1) requesting changing the current BS. While waiting for

reply of the ATM network, the MT continues to transmit and receive cells using the

existing connection path. If the network accepts the handover request, an ATM switch

directed to be the crossover switch for the handover and the incremental path between

the crossover switch and BS2 is established [POL96] [AJM97d]. At some point, the

crossover switch begins deflecting the downstream cells over the incremental path and

sends the handover confirmation message to the MT through BS1. During this time, the

upstream cells continue to flow from the original path through BS1. The upstream

connection will be re-routed at the crossover switch only after the last upstream cell

transmitted through BS1 has arrived the switch. By the time the handover confirmation

is received, the MT has received all the downstream cell transmitted through BS1 and


41

stops sending upstream cells to BS1. Immediately after that, the MT disconnects from

BS1 and tries to establish a wireless link with BS2. Until a new wireless link is

established, cells can not be transmitted between MT and BS. During this time t it

would be necessary to

Figure 3.5. Seamless Handover procedure

save upstream traffic at MT and downstream traffic at BS2. Cells are stored at BS2

when they arrive the BS before a new wireless is established, i.e. if T < t, where T is

the difference between the cell propagation delay from the crossover switch to BS2 and

the propagation delay from the crossover switch to BS1. T is a random variable whose

actual value depends on the level of congestion in the network. On the other hand,

upstream cells may arrive at BS2 before upstream connection is re-established, if τ ,

the re-routing time of the upstream connection at the crossover switch is larger than t.

Then, upstream cells should be saved at BS2 until a new upstream connection is

established through the crossover switch [AJM97].

tx handoverrequest

rx handoverconfirm

disconnectfrom BS

connectto BS2

rx handoverrequest

downstreamrerouting

tx handoverconfirm

radio linkinterruption

downstreamcells at BS2

upstreamrerouting

t>T

Noupstreambuffering

at BS2

t <No upstreambuffering

at BS2

downstreambuffering at BS2

upstreambuffering at BS2

no no

yes yes

tT

τ

τ

τ


42

Since the buffer size at the BS is always limited, CLASS-wireless forces the terminal

transmission rate not to exceed the Sustainable Cell Rate (SCR) and permitting the

network to empty the handover buffers at the Peak Cell Rate (PCR). Moreover,

CLASS-wireless allows buffer sharing among multiple handovers towards the same

destination BS to achieve statistical multiplexing. The available handover buffer space

is shared by all connections, but each connection has its own logical queue [AJM98a].

3.2.3.2 Network Hanover Modelling The behaviour of the handover buffers at the destination BS and transmission buffer at

the MT during the network handover network can be characterised by five phases as

can be illustrated in Figure 3.6.

Figure 3.6. Network Handover Modelling

BS BUFFER

BS1MT

RADIO L INK

BS BUFFER

BS1MT

RADIO L INK

BS BUFFER

BS2MT

RADIO L INK

BS BUFFER

BS2MT

RADIO L INK

BS BUFFER

BS2MT

RADIO L INK

BS BUFFER

BS2MT

RADIO L INK

VC

VC

VC

VC

VC

VC

(a)

(b)

(c)

(d)

(e)

(a)

TX BUFFER

TX BUFFER

TX BUFFER

TX BUFFER

TX BUFFER

TX BUFFER


43

In phase (a) upstream cells transmitted by MT are received by the current base station

1BS ( 2BS ) and immediately transmitted to the other end user via the current ATM

connection. Equally, downstream cells received by the current BS are promptly

transmitted to the MT. During this phase cells may store at the MT transmission buffer

due to the bursty nature of the generated data. On the contrary, at the BS cells are

necessarily not to be stored, since they are transmitted over the radio link at the

Sustainable Cell Rate (SCR) and on wired ATM connection at the Peak Cell rate

(PCR), with SCR≤ PCR.

In phase (b) the radio link is not active, illustrating the hard handover case. Here the

MT has disconnected from 1BS and has not yet connected to 2BS . During this phase

newly generated cell stored at the transmission buffer of the MT.

In phase © the radio link between MT and BS is not functioning, but the connection

between 2BS and Cross-Over Switch COShas been established. Cells generated stored

at the transmission buffer of the MT, while downstream cells are stored in downstream

handover buffer.

In phase (d) the radio link between MT and BS2 is functioning, and upstream cells are

transmitted at SCR. However, the connection between 2BS and Cross-Over Switch

COShas not been established yet, hence cells transmitted by the MT stored at the BS

upstream handover buffer.

[TOH96], [MIT96][KRI98],

In phase (e) both the radio link and ATM connection are established and the network

handover is formally terminated. Nevertheless, some cells are still stored in the

handover buffers. In order to cut this transient, cells arrive at the handover buffers at

the SCR and leave the buffer at the rate PCR. Handover cycle is defined as the time

interval when the MT disconnects from BS1 and ends at the moment when the cells are

transmitted and the handover buffers are empty at (a’) [AJM98a]


44

4. Experimental Design

4.1 Experimental Overview The experiments are designed to investigate the performance of the ABR ATM

capabilities when TCP connections were used. TCP has a deep-rooted capability to

modify its transmission rate to match its transmission window, depending on the state

of network congestion. However, the fact that ABR is implemented with procedures at

the ATM layer implies that ATM layer entities cannot have direct control over the TCP

functionality, and in particular over the TCP window size.

Fig. 4.1 Stack of TCP over ATM

4.2 Designing Experimental Work

My study considers a very simple network topology, whereby two ATM switches

connected by one channel. TCP traffic sources are connected to one of the two switches

and TCP traffic sinks to the other one. The distance between the two ATM switches are

TCP Application

TCP

IP

AAL5

ATM (ABR)


45

either 10 km or 100 km long. The data rate on all channels both user-node and node-

node, is 150 Mb/s.

All TCP connections are unidirectional, in a way that TCP transmitters send data

segments, and TCP receivers return only ACK segments. TCP connections share the

bandwidth of the link connecting the two ATM switches with a background traffic load

(CBR). This link becomes the system bottle-neck. The background traffic is made of

cells resulting from the segmentation of user messages generated according to Poisson

process, with truncated geometric message length distribution with mean of 20 cells

and maximum of 200 cells.

Experiments were performed on two different network configurations (LAN and

WAN). For each scenario, the simulation was run for (1) constant number of sources

and varying buffer size, and (2) constant buffer size and varying number of sources.

Small end to end propagation delays of 100 microseconds were used for LANs of size

10 km while delays of 1 millisecond was used for WANs that spanned 100 km. The

effect of packet size was investigated using TCP sources that generated 9180 bytes and

512 bytes segments of data. The 512-byte packet size was selected to demonstrate TCP

application with small packet size. The 9128-byte packet size is chosen to demonstrate

a big packet size. This size is recommended in RFC-1626 (ATK94) and RFC-238,

(AP99)

4.2.1 Topology

21

3

4

1

2

3

4

n

SW0 SW1

CBR

Topology

1 -10 km

Senders Receivers

n1-10 km 10- 100 km (LAN) (WAN)


46

Fig. (4.2) Experiment Topology

4.2.2 Hierarchy of Experiments

Fig. (4.3) Hierarchy of Experiments

As can be seen from Figure 4.3, LAN and WAN Configurations used a TCP packet of

9180 bytes. This is called the maximum Transfer Unit (MTU), since “TCPIPSend” is

set to 9128 + 52= 9180 bytes as recommended in RFC [ATK94][ALL99].

4.2 WATM Due to the time limitation, the analysis of WATM is limited to the upstream handover

buffer. The upstream handover buffer is the memory space that must be reserved at the

Top down design

WANLAN

9180 512 9180 512

ERICA+1

ERICA+ 2

ERICA+1

ERICA+2

ERICA+1

ERICA+2

ERICA+2

ERICA+1

TCP Packet size

ERICA+ terms


47

BS destination to store the cells that are transmitted by the MT before the ATM VP is

re-established.

The simulator was tested under the following parameters:

1- Links connecting BSs to LE have a capacity of 30Mbit/s.

2- Links between ATM switches have a capacity of 150 Mb/s

3- The propagation delay between BSs and LE is 0.25 ms, accounting for 50 km.

4- The number of MT is 10 and they free to move at random from one BS to another.

5- The radio bandwidth allocated to each MT is 2 Mb/s

6- The Message is generated according to Poisson point process and length is

modelled by a truncated geometric random variable, 20 ATM cells to 100 cells

7- The load of MT is variable to study the influence of MT load on system

performance.

8- Mobile Terminal Rate=1.99 Mb/s,

9- Radio Link Rate = 2 Mb/s

10- Link length N-N= 100 km, BS-N = 10 km

11- 0LPCRSCR ≤≤


48

5. Analysis of Results

5.1 TCP over ATM

5.1.1 Effect of Buffer size 5.1.1.1 LAN Configuration ERICA +, 20 sources, TCP –reno Figures 1-4 show the effect of buffer size on throughput, CLR, PRR and switch average

buffer utilisation respectively. As can be seen from these graphs, TCP packet size 9180

has experienced lower throughput than TCP 512. On the other hand, TCP 9180

Fig (6.1) effect of buffer size on throughput (LAN)

2.E+06

2.E+06

2.E+06

2.E+06

2.E+06

0.E+00 1.E+05 2.E+05 3.E+05

Buffer size (bps)

Thr

ough

put

(bps

)

TCP 9180

TCP 512

Fig.(6.2) effect of buffersize on CLRLAN

0.0E+00

2.5E- 03

5.0E- 03

7.5E- 03

1.0E- 02

0.E+00 5.E+04 1.E+05 2.E+05 2.E+05 3.E+05 3.E+05

buffer size (bps)

TCP 5 12

TCP 9 18 0

Fig. (6.3) effect of buffer size on PRRLAN

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0.E+00 5.E+04 1.E+05 2.E+05 2.E+05 3.E+05 3.E+05

Buffer size (bps)

TCP 9180

TCP 512

Fig(6.4) effect of buffer size on buffer utilisation (LAN)

0

20

40

60

80

0.E+00 5.E+04 1.E+05 2.E+05 2.E+05 3.E+05 3.E+05

Buffer size (bps)

TCP 512

TCP 9180


49

displays higher percentages of CLR and PRR than TCP 512 counterpart. As far as

switch utilisation the results show the similar trends.

5.1.1.2 WAN Configuration ERICA +, 20 sources, TCP –reno

Figures 5 to 8 present throughput, CLR, PRR and average buffer utilisation at different

buffer sizes. The graphs reveal that the TCP packet size has a significant influence on

CLR but, negligible effect on PRR and CLR at low buffer size. Generally speaking,

The trends in WAN follow the LAN.

5.1.2 Effect of Number of Sources

5.1.2.1 LAN Configuration ERICA +, buffer size, 3.0E+05, TCP –reno

Fig(6.5) effect of buffer size on throughput (WAN)

0.0E+00

1.0E+07

2.0E+07

3.0E+07

4.0E+07

5.0E+07

6.0E+07

0.E+00 5.E+04 1.E+05 2.E+05 2.E+05 3.E+05 3.E+05

Buffer size (bps)

TCP 512

TCP 918 0

Fig(6.6) effect of buffer size on CLR(%) (WAN)

0

0.0015

0.003

0.0045

0.00E+00

5.00E+04

1.00E+05

1.50E+05

2.00E+05

2.50E+05

3.00E+05

Buffer size (bps)

TCP 512

TCP 9180

Fig. (6.7) effect of TCP packet size on PRR (WAN)

0.0E+00

8.0E- 04

1.6E- 03

2.4E- 03

3.2E- 03

4.0E- 03

0.E+00 5.E+04 1.E+05 2.E+05 2.E+05 3.E+05 3.E+05

Buffer Size (bps)

TCP 9180

TCP 512

Fig.(6.8) effect of buffer size on buffer utilisation (WAN)

0

10

20

30

40

50

60

70

0.E+00 5.E+04 1.E+05 2.E+05 2.E+05 3.E+05 3.E+05

Buffer size (bps)

TCP 512TCP 9180

Fig (6.10) effect of number of sources on CLR (LAN)

0.08

0.1

0.12

0.14

TCP 512

TCP 9180

Fig.(6.9) effect of number of sources on throughput (LAN)

2.4E+07

3.2E+07

4.0E+07

TCP 512

TCP 9180


50

Figures 9 to 12 show the throughput, CLR, PRR and average buffer utilisation,

respectively. The graphs clearly indicate that throughput is slightly affected by the TCP

packet size. As can be seen the throughput increases as the number of source increases .

This due to the fact that these TCP sources are window limited and 20 sources with

small window will deliver more data than two sources with small window. The PRR

curves for both packet sizes are symmetrical. TCP packet size 512 achieved lower cell

loss and packet retransmission. The difference between the two packet size was less

noticeable with buffer utilisation.

5.1.2.2 WAN Configuration ERICA +, buffer size, 3.0E+05, TCP –reno

Fig (6.11) effect of number of sources on PRR (LAN)

0.0E+00

2.0E- 04

4.0E- 04

6.0E- 04

8.0E- 04

1.0E- 03

1.2E- 03

0 2 4 6 8 10 12 14 16 18 20 22 24

Number of sources

TCP 512

TCP 9180

Fig. (6.12) effect of buffer size on buffer utlisation (LAN)

0.0E+00

1.0E+01

2.0E+01

3.0E+01

4.0E+01

5.0E+01

6.0E+01

7.0E+01

0 2 4 6 8 10 12 14 16 18 20 22 24

Number of sources

TCP 512

TCP 9180

Fig (6.14) effect of number of sources on CLR (WAN)

0.0E+00

2.0E- 02

4.0E- 02

6.0E- 02

8.0E- 02

1.0E- 01

1.2E- 01

1.4E- 01

0 2 4 6 8 10 12 14 16 18 20 22 24

Number of sources

TCP 512

TCP 9180

Fig (6.13) effect of number of sources on throughput (WAN)

0.0E+00

2.0E+07

4.0E+07

6.0E+07

8.0E+07

1.0E+08

0 2 4 6 8 10 12 14 16 18 20 22 24

Number of sources

TCP 512

TCP 9180


51

The results shown in Figures 13 to 16 indicate that throughput is slightly higher with TCP packet size of 9180. The different behaviour can be seen in terms of CLR and PRR. The results in Figure 16 show there is no a remarkable difference in buffer utilisation. 5.1.3 The effect of TCP Packet Size on Efficiency

Figure 17 and 18 report efficiencies for LAN and WAN respectively. It can be observed that efficiencies of both configurations are quite close and more or less follow the same trends. As can be witnessed, increasing the number of sources from 10 to 20 increases efficiencies of TCP packet size 512 and reduces efficiencies of its counterpart.

Fig (6.15) effect of number of sources on PRR (WAN)

0.0E+00

4.0E- 04

8.0E- 04

1.2E- 03

1.6E- 03

2.0E- 03

0 2 4 6 8 10 12 14 16 18 20 22 24

Number of sources

TCP 512

TCP 9180

Fig. (6.16 effect of number of source on buffer utilisation (WAN)

0.0E+00

1.5E+01

3.0E+01

4.5E+01

6.0E+01

7.5E+01

0 2 4 6 8 10 12 14 16 18 2 0 22

Number of sources

TCP 512

TCP 9180

Fig. (6.17) number of sources vs. efficiency (LAN)

0.94

0.95

0.96

0.97

0.98

0.99

1

0 2 4 6 8 10 12 14 16 18 20 22 24

Number of sources

TCP 9180

TCP 512

Fig.(6.18) number of sources vs. efficiency WAN

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1

0 5 10 15 20 2 5Number of sources

TCP 9180

TCP 512


52

5.1.4 The effect of Packet Size on Average Window size

Both Figures 19 and 20 gave comparable average window size with TCP packet size

9180.

5.1.5 The Effect of Number of Sources on Cell Mean Waiting Time on the Buffer

Figures 21 and 22 exhibit the cell waiting time in the buffer. The difference between

TCP packet size 512 and 9180 are remarkable: even a quick look comparison between

LAN and WAN with TCP packet 9180 shows WAN is higher than LAN.

5.2 TCP over WATM 5.2.1 Effect of Mobile Terminal Load on Buffer Size

Figure 23 and 24 report the size of the upstream handover buffer as a function of

Mobile Terminal (MT) loads (L0) when the cell loss probability Ploss is fixed at 10-6 and

Fig(6.19) number of sources vs average window (segment) (LAN)

0

5

10

15

20

25

0 2 4 6 8 10 12 14 16 18 20 22 24Number of sources

TCP 512

TCP 9180

Fig. (6.20) number of sources vs. Average window (segment) (WAN)

18

18.5

19

19.5

20

20.5

0 2 4 6 8 10 12 14 16 18 20 22 24

Number of sourcesTCP 512

TCP 9180

Fig (6.21) number of sources vs mean cell waiting in the buffer (LAN)

0

1

2

3

4

5

0 5 10 15 20 25

Number of sourcesTCP 512

TCP 9180

Fig (6.22) number of sources vs cell mean waiting time in buffer (WAN)

0

1

2

3

4

0 5 10 15 20 25

number of sourcesTCP 512

TCP 9180

Fig.( 23 ) Handover buffer Size vs Locell loss proability is 10 -̂6

0

50

100

150

200

250

300

0 0.5 1 1.5 2

Mobile Terminal Load (Lo) Mb/s

SCR=1.9

SCR=2.0

Fig.(24) Handover buffer size vs. Locell loss proability is 10^-8

0

50

100

150

200

250

300

350

400

0 0.5 1 1.5 2MT load (Mb/s)

SCR=1.9SCR=2.0


53

10-8 respectively. As can be seen, the buffer size required for two different values of

SCR, 1.9 and 2.0 Mb/s has not significantly altered by the values of SCR.

5.2.2 Effect of Mobile Terminal Load on Average Cell Delay

Figure 25 and 26 present the influence Mobile terminal load on average cell delay for

two values of SCR (1.9 and 2.0 Mb/s). As can be seen, the average cell delay decreases

as the Mobile Terminal load increases.

5.2.1 Effect of Number of Pivots on Handover

Table (2) the effect of number of Pivots on refused handover

Mobile initiated and handover is connected

Number of Pivot Total HO in NW Effective HO HO refused % of refused

HO

1 34 34 0 0

2 4 4 0 0


Mobile initiated and handover is disconnected

Total HO in

NW

Effective HO HO refused % of refused

HO

No. of Pivot 1 37 37 0 0

No. of Pivot 2 34 34 24 70.6

Fig. (25) Average Cell delay vs LoSCR= 1.9 Mb/s

0

3

6

9

12

0 0.5 1 1.5 2

Mobile Terminal Load (Lo) Mb/s

Fig. (26) Average Cell delays vs. LoSCR= 2.0 Mb/s

0

2

4

6

8

10

12

0 0.5 1 1.5 2

MT Load [Lo] (Mb/s)


54


Base station initiated and handover is connected

Total HO in

NW


HO

No. of Pivot 1 34 34 0 0

No. of Pivot 2 38 38 30 78.9


Mobile initiated and handover is connected SCR = 1.9 and Lo 1.5

Number of Pivot Total HO in NW Effective HO HO refused % of refused

HO

1 132 123 9 9%

2 64 64 56 88


Mobile initiated and handover is disconnected, SCR = 1.9 and Lo 1.5

Total HO in

NW


HO

No. of Pivot 1 30 30 0 0

No. of Pivot 2 40 40 30 75

Table (7) the effect of number on refused handover

Base station initiated and handover is connected, SCR = 1.9 and Lo = 1.5 Mb/s

Total HO in

NW


HO

No. of Pivot 1 40 40 0 0

No. of Pivot 2 105 105 81 77


55

Conclusion and Final remarks The project has covered most of our preliminary objectives. Time was the major factor

for studying, designing, implementing and analysing TCP over ATM ABR and

handover management on WATM. Researching these topics will need further work in

the near future.

For the network we studied, with the two CLASS simulators and traffic model we used,

we came to the following conclusions:

1) The maximum throughput can be achieved with bigger buffer sizes.

2) Both CLR and PRR follow the same trends on both LAN and WAN

configurations

3) Average buffer utilisation tends to be identical for both TCP packet sizes

4) Increasing cell interval has reduced efficiency of ERICA+

5) Mean cell waiting time was significantly higher with TCP 9180 for both

configurations

6) A highest window utilisation was observed with TCP 9180.

7) Generally speaking, efficiency was more consistent with TCP 512

8) Handover buffer size increases with the increase of both Mobile Terminal

load and SCR.

9) Average cell delays is inversely proportional to the Mobile Terminal load

10) At different MT loads, handover buffer size increases as the cell loss

probability decreases.

Future Work ATM and WATM are a topic that raises a global interest at the moment. Most of the

activities are carried out within the universities and corporate research laboratories.

Some examples are NTT AWA (advanced Wireless Access system), Olivetti Research

Laboratory and Politecnico Di Torino Dipartimento Di Elettronica.

This project addresses the issue of TCP over ATM and Wireless ATM networks. The

Research in this area is one of the most important topics in the field of distributed

multimedia system. This project provides only some indications about throughput,

CLR, cell delay, mobile terminal load and cell loss probability. Much more time and

resources are needed to implement ABR in wireless ATM by using a basic client-server

architecture and/or CLASS-wireless.


56

In wireless networks, the topology is changing in time, this, as well as other mobility

feature, these elements present a real network management challenge. Research should

focus to maintain the dynamic nature of the network topology.

More research also is needed to study the Virtual Scheduling Algorithm and other

traffic policing mechanisms.


57

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AYA96 E. A Ayanoglu, et al, “ Wireless ATM Limits, Challenges and Proposals” , IEEE Personal Communications 18-34, August 1996. AYA98. E.Ayanoglu, K. Y. Eng and M. J. Karol: Wireless ATM: Limits, Challenges

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Manual, Software Version 6.20f” , © 1993/98 Politecnico Di Torino, Dpiartimento Di

Electtronica, May 1998.

http://www1.tlc.polito.it/class/

COO90 C.A. Cooper, K.I. Park, “ Towards a Broadband Congestion Control

Strategy” , IEEE Network Magazine, May 1990.

DAL97 Daly, F., “Interconnecting Legacy LANs via an ATM Backbone”, MSc thesis, Department of Computer Science and Information Systems, College of Informatics and Electronics, University of Limerick, Ireland, 1997.

DEM92 A. Demers, S. Shender, L.Zhang “ Supporting real-time Application in an

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ELA2000 El-Abd, A. and Mostafa, M., A., “ EPD+ : A New Packet Discard Mechanism to Improve TCP Performance over ATM-UBR”, Proc of the IEEE


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Conference on High performance Switching and Routing, Heidelberg , Germany, June, 2000. FAH96 S. Fahmy, R. Jain, S. Kalyanaraman, R., Goyal, F. Lu, “On Source Rules For ABR Service on ATM Networks with Satellite Links” , Submitted to the First International Workshop on Satellite-based Information Services (WOSBIS), New York, November 1996. FES2000 A. Festag, T. Assimakopoulos, L. Westerhoff, and A. Wolisz, “ Re-Routing

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FLO96 Floyd, S., “ Issues of TCP with SACK”, March 1996. FON96 I. Fong, and W. Wang, “ Design of Architecture for “Soft” Handoff on WATM Network”, Electrical Engineering, Columbia University, December 1996. http://www.comet.columbia.edu/~mobiware/e6950/slides_ifong.html GOR95 Goralski, W. “Introduction to ATM Networking. New York: McGraw-Hill,

1995.

GOL94 S.J. Golestani, “ A Self-Clocked Fair Queuing Scheme for Broadband

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Date of access, 12/06/2000


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Appendix 1

My Personal Experience

The project I have always wanted to do a research in computer network. I was very fortune to do this project. I have gain extensive experience in networking in general, and TCP/IP, ATM and WATM in particular. My supervisor has given me increasingly responsible task, which was the corner stone for working more than recommended 400 hours. The project was challenging and the discussion with Dr. Karim was stimulus and very fruitful. I should emphasise the role of my supervisor, whose organising methods were adapted to suit the complexity of the project. Quite often we used to meet more than twice a week to discuss the detail of the project. My project was not completely defined at the first stage and it structured the current shape after several meeting and academic discussions with my supervisor. This was a golden opportunity to develop my own ideas, confronting these ideas by reading in the literature and coming with solving strategies. I am very pleased to gain such experience in the field of wired and wireless ATM. I am quite confident with WATM skills and I am sure I will use these skills and gain more experience in my future career. One of the most important lessons I have learnt is time managing, and working under enormous pressure. My project required a considerable amount of reading and leaning the script of the simulator I was using, My suggestion would be for student-undertaking project in the field of networking, is to explore different techniques and compare it with the one have used here. This simulator can be further evaluated to find the strength and the weakness of wireless ATM. One final suggestion is to think ahead and perhaps by the end of the first semester what sort of project you would like to pursue, and if you could make preliminary sketch for this project it would help you when you choose your project in Easter.


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School of Computer Studies

MSC PROJECT OBJECTIVES AND DELIVERABLES This form must be completed by the student, with the agreement of the supervisor of each project, and submitted to the MSc project co-ordinator (Mrs A. Roberts) by 7th April 2000. A copy should be given to the supervisor and a copy retained by the student. Amendments to the agreed objectives and deliverables may be made by agreement between the student and the supervisor during the project. Any such revision should be noted on this form. At the end of the project, a copy of this form must be included in the Project Report as an Appendix.

Student: Fawzi SALIH______________________________________

Programme of Study: MSc DMS_______________________________________

Supervisor: Dr. Karim Djemame_______________________________________

Title of project: Available Bit Rate (ABR) in a Wireless ATM___________________________

External Organisation*: _______________________________________

* (if applicable)

AGREED MARKING SCHEME

Understand the Problem

Produce a Solution *

Evaluation Write -Up Appendix A TOTAL

%

20 40 20 15 5 100

* This category includes Professionalism (see handbook)

OVERALL OBJECTIVES (continue overleaf if necessary): Evaluation of ABR Performance in A ATM/WATM

(1) Introduction Research on Wireless Asychronouns Transfer Mode (WATM) is advancing on a daily basis. These landmark research activities are due to the increasing role of multimedia and computer applications in communication and development of wireless broadband multimedia communication systems (WBMCS). WATM has an Objective of providing the user communication ir-respect of his/her location and time. This has been formulated as a personal communications networks (PCN) and personal communication services (PCS). Also, WATM is an emerging technology, viewed as right venue to broadband networks in order to provide users with integrated systems (audio, video, text and graphics). WATM has all the capabilities for wireless broadband services. Future communication systems should take into account the amount of data traffic load,

exponential growth of users, and diversity of services.


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(2) Why WTAM? WATM is needed for mobile computing applications in both business and consumer

applications. The basis of WATM is to provide services for mobile user (1). This

means the network should combine a sufficient degree of mobility support with

capabilities to take different types of user data with different quality of service (QoS)

requirements. WATM also has to provide access to services connected to the fixed

ATM network. This means, the 48-byte ATM cell payload should become the basic

transfer data unit.

The WATM consists of a fixed ATM network infrastructure and a radio access

segment, while in wireless ATM network, the switches which communicate directly

with wireless station or wireless end user devices, are mobility enhanced ATM

switches. These switches set-up connections on behalf of the wireless devices. They

serve as the “entrance” to the infrastructure wired ATM network. The other ATM

switching elements in the wired ATM networks are the same.

The radio access segment can be divided into: (1) Fixed Wireless Components where by the end user devices and switching devices

are fixed.

(2) Mobile End Users where by the end user devices are mobile and communicate

directly with the fixed network switching devices via wired or wireless channels. At

the same time, end user devices should be facilitated with wireless terminal adapter

(3) Mobile Switches with Fixed End Users. Here end user devices are connected to

switches through wired or wireless channels.

(4) Mobile Switches with Mobile End Users. In this case the end user is mobile.

(5) Interworking with PCS. PCS terminals send data to proper PCS base stations

through wireless link, which then establish connections to the fixed network

switching elements through a base station controller.

(3) WATM Design WATM adopts ATM to provide data communications services so the architecture is

based on the ATM protocol stack.

The protocol architecture proposed by ATM Forum is shown in Figure (1).


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Fig. (1) WATM Protocol Architecture ([email protected] )

(4) ABR Service Class Available Bit Rate (ABR) is non real-time services and the ATM forum has specified a

rate-based flow control scheme in the traffic management (TM) specification 4. This

class of ATM provides rate-based flow control and is aimed at data traffic such as file

transfer and email. Although the standard does not require the cell transfer delay and

cell-loss ratio to be guaranteed or minimised, it is preferable for switches to reduce

delay and loss as much as possible. Depending on the congestion situation in the

network, the source is aimed to control its rate. The users are allowed to declare a

minimum cell rate, which is guaranteed to the connection by the network. The feedback

from the switches to the sources is indicated in resource management (RM) cells,

which are generated continuously by the source and send around by destination.

The main issue is how to utilise the available bandwidth if any of virtual paths (VP)

that are not utilised by constant bit rate (CBR) and variable bit rate (VBR) real-time

service classes. This means to inform a source of an ABR connection any availability

of bandwidth.

(5) Research Area In the first part of the project (see research time table) I will study wireless ATM

Protocol Architectures and how the QoS characteristics of the ATM networks can be

maintained for the mobile user implementation. The study will concentrate on

performance evaluation of flow control, location and handover management, routing,

and addressing.


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More technical papers in the field of WATM in general and ABR in particular will be

explored and cited. The research will be equipped with thorough reading from the

library and Internet. Mean while all relevant materials and references will be recorded

in chronological order prior to final report writing. Two simulators will be studied and

a possible scenario(s) will be designed for the experiment.

Hopefully the study will cover handover, location management, routing, addressing,

and traffic management in greater detail.

(6) Literature Review Research involving WATM is advancing rapidly; Deborah et al (1) has carried

out an investigation to study a dynamic packet reservation multiple access scheme

for Wireless ATM. Their primary goal was matching dynamically the traffic

source generation rates with assigned portion of the channel capacity. They

performed the study by a controlled algorithm that devised the actual amount of

channel capacity assigned to users. They observed that the protocol is capable of

providing QoS guaranteed to multiple users and also to multiple traffic types.

Their results concluded that improved performance over a system with a modified

version of the packet reservation multiple access (PRMA) scheme.

Al-agha et al (2) carried out a research programme on multi-agent WATM to provide a

flexible integration technique regarding BS (base stations), MS (mobile stations) and

MSCs (mobile switching centres). They examined two applications, resource allocation

and error correction using simulations. They outlined a new architecture based on

intelligent agent.

Tanenbaum (3) in his book “Computer Network” illustrates the role of WATM in near

future. He explained how the mobile computing and wireless networking are often

related although they are not quite identical. He said that portable computers are

sometimes wired when a user plugged his mobile computer into his room telephone

socket. Also some wireless computers are not portable. Tanenbaum found that wireless

LANs are easy to install but they have some problems such as very low capacity 1-2

Mbps that will make them slower than wired LANs. He also stated that error rates

would be much higher.

Bush et al (4) has proposed a design for virtual network configuration

(VNC). They design an orderwire system of packet radio network which overlays

the mobile wireless ATM network.


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Savanto et al (5) investigated the way of adapting mobile wireless networks to support

some aspects of QoS and traffic classes. They revealed that their mobile network

adapters have solved some limitations. This was due to the protocol architectures. Their

prototype implementation indicated that priority based multiplexing of traffic is useful

for delivering real-time and non-real time data to and from a mobile terminal. Their

solution was also to support both seamless and lossless handover.

Fahmy et al (6) defined ABR multipoint-to-point connections. They examined four

fairness definitions for multipoint connections based on source-based fairness, virtual

channel (VC)/ source-based fairness, flow-based fairness and VC/flow-based fairness.

They concluded that traffic management for multipoint connections may be

implemented differently in VC merge and VP merge implementations. VP merge uses

the VCI field to distinguish among different sources in the same mulipoint VC, while

VC merge does not distinguish sources, and implementation packet-level buffering at

the merge points.

Krieger et al (7) carried out a simulation experiment to study performance evaluation of

ABR flow-control protocol in WATM network. They used object-oriented simulation

model of a basic client-server scenario in WATM network. They examine the role of

error-prone WATM communication channel and mobility management techniques

determined by different handover procedures.

Pandya and Ercon Sen (8) have analysed the ATM potentiality in their joint published

book. They highlighted the significance of ATM technology in the integration of

diversified services such as voice, video, image, and data. They concluded that ATM –

based virtual path (VP) and dense wavelength division multiplexing (DWDM) present

very significant opportunities in the transport market today. As far as bandwidth cost,

they predicted the cost to be continually declining as the bandwidth capacity increases as

a result of using DWDM and expansion of fiber network using quality polarisation mode

dispersion (PMD) free fiber cable.

(7) Project Tools

Throughout this project two sets and yet similar simulations will be examined. These

simulators are currently available to academic institutions for research purposes.

Simulators . ANCLES http://www1.tlc.polito.it/ancles/

. CLASS http://www1.tlc.polito.it/class/


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ANCLES ANCLES (ATM Networks call Level Simulator) is a well known ATM simulator

developed by an Italian research the Telecommunication Networks Group of Politenico

di Torino (Italy) and CSELT (Centro Studi E Laboratori Telecomunicazioni).

By using ANCLES we would hope the performance of different routing algorithms and

call admission control techniques can be compared. We would also be able to choose

any number of nodes within the network, the number of ports connected to each node

and examine congestion situations with a great freedom of choice. ANCLES is written

in ANSI C, and using such common tools as FLEX and YACC for its lexical analyser,

ANCLES is completely machine-independent.

CLASS CLASS is another simulator available for academic parties for research purposes. It

works at the cell level. It takes into account routing and switching functions, the

allocation of the bandwidth to different connections. The special nodes of the network

help management of connectionless traffic and many other functions that may influence

the performance on the network as a whole.

CLASS is written in ANSI C language and works on several platforms such as

OpenVMS (VAX and AXP), Linux, HP-UX, Ultrix and MS-DOS (using DJGPP, the

MS-DOS version of the GNU C compiler). It requires the presence of YACC and

FLEX. No graphical interface has been so far developed.

Some of the CLASS features are:

• Managing Wireless ATM Networks and the analysis of different handover

strategies.

• Implementation of the ATM Forum ABR transfer capability

• Several ABR traffic control schemes such as radio resource control, explicit

control (RRM, ER) are implemented in the nodes

• Integration with ANCLES, the companion Call Level simulator

Computer Platform Both simulators will be running on Linux machine.

(8) Research Time Table Date from-to Activity Outcome 25/05 10/06

Reading and studying WATM architecture

Information building and restructuring literature review

10/06 Studying ANCLES and CLASS Capabilities of simulators


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25/05 simulators and possible development 25/06 25/07

Designing scenarios and running experiments

Preliminary results for evaluation and analysis

26/07 5/08

Running further experiments Final evaluation

6/08 20/08

Outlining the final results and collection of information

Final project report

(9) Project Log

Project log is available at: http://www.csdb.leeds.ac.uk/mscyfs/mydata.html

References (1) Deborah A. Dyson and Z. Hass, “A dynamic Packet Reservation Multiple Access

Scheme for Wireless ATM”, Mobile Networks and Applications, 4 1999, pp. 87-

99.

(2) Kalhdoun Al agha and Houda Laboid, “ MA-WATM a new Approach towards an

Adaptive Wireless ATM Network” , Mobile Networks and Applications, 4 1999,

pp. 101-109.

(3) (3) Andrew S. Tanenbaum, “Computer Networks” , A Simon Schuster Company,

New Jersey, USA, 1996.

(4) S. F. Bush et al, “A Control and Management Network for Wireless ATM System”, Wireless Networks Volume 3 (1997), pp. 268-283. (5) Savanto, J, et al, “ Introducing Quality-of-Service and Traffic Classes into Wireless

Mobile Networks” , ACM Publications, 1998, pp. 21-30.

(6) Fahmy, S., et al “ATM ABR Multipoint-to-point Connections and Fairness Issues” ,

Network Systems Conference, Vpl. 3530, November 1998.

(7) Krieger, R,, and Savoric, M, “ Performance Evaluation of ABR Flow-Control

Protocol in A WATM Network”, ACM publications, 1998, pp. 73-82.

(8) Pandya, A.S., Sen E., “ ATM Technology” , Library of Congress Cataloging-in-

Publication Data, USA

(8) ftp://ftp.netlab.ohio-state.edu/pub/jain/courses/cis788-97/wireless_atm.pdf

(9) http://www.acm.org/pubs/articles/proceedings/comm/288338/p73-krieger/p73-

krieger.pdf

10) http://atm2000.ccrle.nec.de/

(11) http://www.acm.org/pubs/contents/journals/wireless/1999-5/

(12) http://www.cam-orl.co.uk/


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(13) http://cell-relay.indiana.edu/cell-relay/docs/ftp.cisco.com/ATM-

Internetworking.pdf

(14) [email protected]


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Appendix 3

the tcp traffic shares the bottleneck link bandwidth with ... tcp over atm ... ccr current cell rate...

Documents