bab vi.c. wan technology 3
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Bab VI.c
WAN Technologies 3
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Komputer
Komputer Komputer
Komputer
WANOption
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Komputer
Komputer Komputer
Komputer
WANOption
PSTN
x D
S L
X.25
FRAMERELAYISDN
GPRS
3G
ATM
PPP
MPLS
WIMAX
GPON
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Wan Tech. Option
1. X.25
2. Frame Relay
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Intro to X.25
X.25 is a packet-switching WAN
Developed in 1976 by ITU-T
X.25 is an interface between data terminalequipment (DTE) and Data Circuit-terminating equipment (DCE) for terminaloperation in the packet mode on public
data networks
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Intro to X.25
X.25 define how a packet-mode terminalcan be connected to a packet network for the exchange of data
X.25 describes the procedures necessaryfor establishing, maintaining andterminating connections.
X.25 is what is known as a Subscriber Network Interface (SNI) protocol.
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Intro to X.25
SNI defines how the user’s DTEcommunicates with the network and howpackets are sent over that network using
DCE.It uses a virtual circuit approach to packetswitching (SVC and PVC) and uses
asynchronous connection.
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SVC Basics(Switched Virtual Circuits)
An easy way to imagine this distinctionis to think of your telephone. Every timeyou want to exchange data (i.e., the sound
of your voice), you need to make a call bydialing a number. When someone answersthe phone on the other end of the line, theconnection is established, and you can
talk to each other. When you are finishedtalking, you hang up and break theconnection. This is an SVC connection.
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SVC Basics(Switched Virtual Circuits)
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PVC Basics(Permanent Virtual Circuits)
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Limitations on PVCs and SVCs
PVC connections are less flexible, inthat only one endpoint at a time can beconnected with another on a given LCN.
SVC connections are very flexible in that itis possible for multiple callers to call thesame number.
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X.25 layers
X.25 protocol specifies three layersn Physicaln Framen Packet
These layers define functions at thephysical, data link and network layers of
the OSI model
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X.25 layers
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Physical Layer
At the physical layer, X.25 specifies aprotocol called X.21
X.21 has been specifically defined for X.25
by the ITU-TX.21 is similar enough to other physicallayer such as EIA-232 (Serial)
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Frame Layer
X.25 provides data link control using Link Access Procedure, Balanced (LAPB),which is a subset of HDLC
The flag, address, control and FCS fieldsare exactly the same in HDLC
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Frame Layer
3 categories of Framesn I-Frames
Are used to encapsulate packet from the network
layer n S-Frames
Are for flow and error control in the frame layer
n U-Frame
Are used to set up and disconnect the links betweenDTE and DCE
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Frame layer phases
In the frame layer, communicationbetween a DTE and a DCE involves 3phasesn Link Setupn Transferring datan Link Disconnect
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Frame layer phases
Link Setupn The link between DTE and DCE must be
setup before packets from the packet layer
can be transferred. Either the DCE or the DTEcan set up the link by sending an SABM (Set
Asynchronous Balance Mode) frame, theresponding party sends an ACK frame
( Acknowledgement ) to show the link is ready
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Frame layer phases
Transferring datan After the link has been established, the 2
parties can send and receive network layer
packets using I-frames and S-framesLink Disconnectn When the network layer no longer needs the
link, one of the parties can issue a disconnect
(DISC) frame to request a disconnection
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Packet Layer
The network layer in X.25 is called thePacket Layer Protocol (PLP).
This layer is responsible for establishing
the connection, transferring the data, andterminating the connection
In addition, it is responsible for creating
the virtual circuits and negotiating networkservices between 2 DTEs
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Packet Layer
While the frame layer is responsible for making a connections between a DTE anda DCE, the packet layer is responsible for
making a connection between 2 DTEsNote (important)n X.25 uses flow and error control at two levels
Flow and error control between DCE and DTE are
under jurisdiction of the frame layer Flow and error control between 2 DTEs are under jurisdiction of the packet layer
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Packet Layer
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Virtual Circuits
X.25 protocol is a packet-switched VirtualCircuit network
The Virtual circuit in X.25 are created at
the network layer (not the data link layer)This means that a physical connectionbetween a DTE and DCE can carryseveral virtual circuits at the network layer
with each circuit responsible for carryingeither data or control information.
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Virtual Circuits
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X.25
n X.25 also checks for errors from source todestination at the network layer
n Two layer operations for error checking and
flow controln Much of the traffic on an X.25 network is
devoted to error checking to ensure reliabilityof the service
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X.25
Only one-fourth of this traffic is message data
Such extensive traffic wan necessary at the timeX.25 was introduced because transmissionmedia were more error prone then, than they aretoday
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Virtual Circuit Identifiers
Each virtual circuit in X.25 should beidentified for use by the packets
The Virtual Circuit Identifiers is used
The VCI in X.25 is called Logical ChannelNumber (LCN)
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X.25 SVC networking allows for multiplesimultaneous connections
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Summary
X.25 is an old and used to be popular packet-switching WAN
The X.25 protocol defines the procedures
for data transmission between a DTE anda DCE
The X.25 protocol specifies three layersn Physical layer n Frame layer n Packet layer
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Summary
LAPB is the protocol used by X.25 at theframe layer for data link control functions
The packet layer handles connection
establishment, data transfer, connectiontermination, virtual circuit creation andnegotiation of network services between
two DTEs
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Summary
There are 3 types of X.25 packetsn I framesn S framesn
U framesThe first is a data packet,The latter two arecontrol packets
There are flow and error control at both the
frame layer and the packet layer The virtual circuit identifier in X.25 is called LCN
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Wan Tech. Option
1. X.252.
Frame Relay
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2. Frame Relay Network
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Frame Relay Intro
Frame Relay is a Virtual-Circuit technologythat provides low-level (physical and datalink layers) service.
Frame relay provides the following servicen Higher data rates at lower costn Bursty data
Frame relay can provide Bandwidth on Demand
n Less overhead
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Differences between X.25 andFrame Relay
The bad things about X.25n X.25 provides extensive error checking and
flow control
n Frames are checked for accuracy at eachstation
n Each station keeps a copy of the originalframe until it receives confirmation from the
next station that the frames has arrivedcorrectly
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Differences between X.25 andFrame Relay
n X.25 also checks for errors from source todestination at the network layer
n Two layer operations for error checking and
flow controln Much of the traffic on an X.25 network is
devoted to error checking to ensure reliabilityof the service
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Differences between X.25 andFrame Relay
Only one-fourth of this traffic is message data
Such extensive traffic wan necessary at the timeX.25 was introduced because transmissionmedia were more error prone then, than they aretoday
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Differences between X.25 andFrame Relay
n Improvements in traditional transmissionmedia and greater use of fiber-optic cable,which is far less susceptible to noise thanmetallic cable, have decreased the probabilityof transmission error to a point where thislevel of caution is not only unnecessary butcounterproductive as well.
n Frame relay does not provide error checkingor require acknowledgment in the data linklayer.
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Differences between X.25 andFrame Relay
n All error checking is left to the protocols at thenetwork and transport layer.
n Many data link layer operations are eliminated
while others are combined
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Differences between X.25 andFrame Relay
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Advantages of Frame Relay
Frame Relay operates at a higher speed(up to 1.544 Mbps and recently 44.376Mbps)
Frame Relay operates in just the physicaland data link layersn Means it easily can be used as a backbone
network to provide services to protocols thatalready have a network layer protocol
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n If TCP/IP wants to use the services of X.25,there is a duplication in the network layer andFrame Relay fucntions, X.25 has its ownnetwork layer and TCP/IP has its own
n There is no duplication in the case of FrameRelay, TCP/IP uses it s own network layer andFrame Relay provides services at the Physicaland the data link layers
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Frame Relay allows bursty data. Users donot have to adhere to a fixed data rate
Frame Relay is less expensive than other
traditional WANs
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Disadvantage of Frame Relay
Not fast enough
Frame Relay uses variable-length framesn This may create a varying delays for different users,
example : Delay of a small frame following a largeframe may be different than the delay of a small framefollowing another small frame
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Frame Relay operation
Frame relay provides Permanent VirtualCircuit and Switched Virtual Circuit
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Frame Relay Virtual Circuit
Frame Relay is a virtual circuit networkLike any other virtual circuit network, ituses a virtual circuit identifier
Virtual Circuit in Frame Relay operates at
the data link layer, in contrast with X.25,they operate at the network layer
Virtual circuit in Frame Relay is identifiedby a number called Data Link ConnectionIdentified (DLCI)----- in X.25 LCN
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When a virtual circuit is established by thenetwork, a DTE is given a DLCI number that it can use to access the remote DTE
The local DTE uses this DLCI to sendframes to the remote DTE
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Frame Relay Layers
Frame Relay has only physical and datalink layers
C i l i F R l
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Comparing layers in Frame Relayand X.25
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Wan Tech. Option
1. X.252. Frame Relay
ATM
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ATM
(Asynchronous Transfer Mode)
ATM adalah interface untuk transfer cell (cell relay) dengan kecepatantinggi.
Memungkinkan koneksi lojik ganda di-multiplex-kan pada sebuahinterface fisik tunggal.
ATM bagian dari broadband ATM
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Arsitektur Protokol
1. User plane• Provides for user information transfer
2. Control plane•
Call and connection control3. Management plane
• Plane management• whole system functions
• Layer management• Resources and parameters in protocol entities
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ATM Logical Connections
Virtual channel connections (VCC)Analogous to virtual circuit in X.25Basic unit of switchingBetween two end usersFull duplexFixed size cellsData, user-network exchange (control) and
network-network exchange (networkmanagement and routing)
Virtual path connection (VPC)Bundle of VCC with same end points
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ATM Connection Relationships
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ATM Cells
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ATM Service Categories
Real time1. Constant bit rate (CBR) ; kecepatan konstan terus-menerus.2. Real time variable bit rate (rt-VBR); kecepatan tidak konstan.
Non-real time1. Non-real time variable bit rate (nrt-VBR)2. Available bit rate (ABR)3. Unspecified bit rate (UBR)4. Guaranteed frame rate (GFR)
CBR
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CBR(Constant bit rate)
Fixed data rate continuously available
Tight upper bound on delay
Uncompressed audio and videon Video conferencingn Interactive audion A/V distribution and retrieval
rt VBR
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rt-VBR (Real time variable bit rate)
Time sensitive applicationn Tightly constrained delay and delay variation
rt-VBR applications transmit at a rate that
varies with timee.g. compressed videon Produces varying sized image framesn
Original (uncompressed) frame rate constantn So compressed data rate varies
Can statistically multiplex connections
nrt VBR
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nrt-VBR(Non-real time variable bit rate )
May be able to characterize expectedtraffic flow
Improve QoS in loss and delay
End system specifies:n Peak cell raten Sustainable or average raten
Measure of how bursty traffic ise.g. Airline reservations, bankingtransactions
UBR
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UBR(Unspecified bit rate )
May be additional capacity over andabove that used by CBR and VBR trafficn Not all resources dedicated
n Bursty nature of VBRFor application that can tolerate some cellloss or variable delaysn
e.g. TCP based trafficCells forwarded on FIFO basis
Best efforts service
ABR
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ABR(Available bit rate)
Application specifies peak cell rate (PCR)and minimum cell rate (MCR)
Resources allocated to give at least MCR
Spare capacity shared among all ARBsources
e.g. LAN interconnection
GFR
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GFR(Guaranteed Frame Rate)
Designed to support IP backbone subnetworksBetter service than UBR for frame based trafficn Including IP and Ethernet
Optimize handling of frame based traffic passingfrom LAN through router to ATM backbonen Used by enterprise, carrier and ISP networksn Consolidation and extension of IP over WAN
ABR difficult to implement between routers over
ATM networkGFR better alternative for traffic originating onEthernetn Network aware of frame/packet boundaries
n When congested, all cells from frame discarded
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ATM Bit Rate Services
AAL P t l
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AAL Protocols
Convergence sublayer (CS)n Support for specific applicationsn AAL user attaches at SAP
Segmentation and re-assembly sublayer
(SAR)n Packages and unpacks info received from CS
into cells
Four typesn Type 1n Type 2n Type 3/4n Type 5
AAL Protocols
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AAL Protocols
Segmentation and Reassembly PDU
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Segmentation and Reassembly PDU
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AAL Type 1
CBR source
SAR packs and unpacks bits
Block accompanied by sequence number
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AAL Type 2
VBR
Analog applications
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AAL Type 3/4
Connectionless or connected
Message mode or stream mode
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AAL Type 5
Streamlined transport for connectionoriented higher layer protocols
ATM Adaptation Layer
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ATM Adaptation Layer
CBR rt-VBR Nrt-vbr ABR UBR
AAL1 Voice
AAL2 Voice Video
AAL3/4 Data Service
AAL5 LANEmulation
Voice FR, ATM EmulationLANE
IP
ATM Network
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ATM Network(integrated voice, video, and data services)
ATM St d d
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ATM Standards
ITU-T, ATM Forum, IETFUser-to-Network Interface (UNI) 2.0UNI 3.0, UNI 3.1, UNI 4.0Network-to-Network Interface (NNI)
PNNIn Private NNIn Public-Network Node Interface
RFC 2684 (Multiprotocol encapsulation over ATM)
LAN Emulation (LANE)Multiprotocol over ATM (MPoA)
ATM N t k C t
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ATM Network Components
ATM
Network
ATM?
ATM C ll F t
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ATM Cell Format
Generic Flow Control (GFC) – typically not used.Virtual Path Identifier (VPI) – 8 or 12 bits
Virtual Channel Identifier (VCI) – 16 bits
Payload Type (PT)— 3 bitsn first bit: user data (0) or control data (1)n second bit: 0 = no congestion, 1 = congestion),n third bit: whether the cell is the last cell (1) in a series of AAL5 frame
Cell Loss Priority (CLP)—Indicates whether the cell should bediscarded (1) if it encounters extreme congestion as it movesthrough the network.
Header Error Control (HEC)—checksum on the first 4 bytes of theheader.
Discussion: compare ATM cell with Frame Relay frame
ATM Vi t l C ti
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ATM Virtual Connections
ATM switching is based on VPI/VCIHowever, VPI+VPI is not called ATM address.
VPI/VCI has local significance only.
ATM R f M d l
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ATM Reference Model
ATM Ad t ti L
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ATM Adaptation Layer Function: Add control information and break ProtocolData Unit (PDU) into cells
Segmentation and Reassembly (SAR)
AAL1:n Designed for voice application
n Constant Bit Rate (CBR)n Circuit Emulation Service (CES)
AAL2n Variable Bit Rate (VBR)n VBR-rt (voice)n VBR-nrt (data)
AAL5:n Designed for data applicationn Unspecified Bit Rate (UBR)
Physical
ATM
AAL
AAL5
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AAL5
CPCS-PDU Payload
Padding (0-47)
CPCS-UU (1)
CPI (1)Length (2)
CRC (4)
up to 216 -1
why do we need padding?
CPCS: Common Part Convergence SublayerPDU: Protocol Data UnitUU: User-to-user interface informationCPI: Common Part Indicator
ATM Quality of Service (QoS)
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ATM Quality of Service (QoS)CBR: Constant Bit Raten Guaranteed transmission rate
VBR: Variable Bit Raten rtVBR and nrtVBRn Peak Cell Rate (PCR), Sustained Cell Rate (SCR),
and Max Burst Size (MBR)
UBR: Unspecified Bit Raten No guarantee, best effort
CBR
VBR
UBR
PC
RSCR
Service
BitRate
ATM Q S
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ATM QoS
How does a carrier ensure that QOS can be met?n Connection Admission Control (CAC)
Procedure for determining whether each new SETUPrequest should be granted or denied based on currentnetwork conditions
n Usage Parameter Control (UPC)Procedure for verifying whether customer is conforming totheir contractual Traffic Parameters.
n Resource Management (RM)Procedure for notifying ABR users when they should slowdown
n ABR: Available Bit Raten Selective Cell Discard (SCD)
Procedure for discarding cells (CLP=1)during congestion.
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