section four

©Informa Telecoms

UMTS System Overview

UMTS Core Network

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UMTS Core Network

1. CORE NETWORK ARCHITECTURE AND FUNCTIONS1.1 Review of Core Network Architecture & Elements (R ’99) 11.2 The main functions provided by the core network 31.3 The User Equipment and The Core Network 5

2. THE CORE NETWORK CS DOMAIN2.1 User and Control Information in the CS Domain 72.2 Signalling in the CS Domain – SS7 Overview 92.3 CS Domain Control Plane Protocols:

the SS7 Protocol Stack 112.4 CS Domain User Plane Control Protocols 13

3. THE CORE NETWORK PS DOMAIN3.1 User and Control Information in the PS Domain 153.2 PS Domain Protocols 1:

GSN to Service/Database communications 173.3 PS Domain Protocols 2:

GSN to GSN communications 193.4 Tunnelling 21

4. MOBILE IP4.1 Mobile IP: Basics 254.2 Mobile IPv4 vs. IPv6 27

5. CORE NETWORK TRANSMISSION 29

6. CHARGING 31

7. NETWORK MANAGEMENT 33

8. IN/CAMEL IN UMTS8.1 Intelligent Networks 358.2 CAMEL 37

ANNEX 1 OSI 7 LAYER MODELA.1 Protocols & Stack: Basics 39A.2 The OSI Model 41

UMTS Core Network


1. CORE NETWORK ARCHITECTURE AND FUNCTIONS

1.1 Review of Core Network Architecture & Elements (R ’99)

The Core Network of UMTS, in its first release, is taken directly from the architectureand elements of GSM Phase 2+.

Two domains are defined, circuit switched (CS) and packet-switched (PS). The latteris provided by the implementation of GPRS within the GSM network.

These two transport and signalling domains will both interact with a number ofdatabases, which are sometimes grouped under the Home Server Subsystem (HSS),and with service platforms such as the CAMEL Service Environment (CSE), whichprovide services and support for the Virtual Home Environment.

The two key elements of the Circuit-Switched domain are as follows:

• Serving MSC (MSC), the switching node at which the core network interfaces tothat part of the access network in which the mobile station is located. The ServingMSC interacts with, or includes, a database called the Visitor Location Register (VLR),containing information regarding the mobile stations which it is currently serving.

• Gateway MSC (GMSC), the switching node which connects a UMTS core networkwith an external circuit-switched network, such as ISDN or PSTN.

The two key and equivalent elements in the Packet-Switched domain are:

• Serving GPRS Support Node (SGSN), the packet router at which the core networkinterfaces to the part of the access network in which the mobile station is located.

• Gateway GSN (GGSN), another packet router, connecting the UMTS core networkwith an external packet-switched network, such as the Internet, X.25 or similar.

In many networks, the Serving MSC/VLR and the SGSN will interact in order toensure better integrated management and information updating between PS andCS services.

The HSS includes database such as the Home Location Register (HLR), whichincludes a variety of subscriber related data, enabling users to be offered the servicesto which they are entitled. Also included within the HSS is the database forauthentication.

The interface connecting the core and radio access networks (at the Serving MSCand SGSN) is known as the Iu Interface, and is fully defined in UMTS. This interfaceis subdivided into the IuPS and IuCS, in order to support each domain in the corenetwork, but within this subdivision there remains much commonality.

An important new feature of UMTS is that the core network and radio access networkare kept entirely separate and independent by means of this Iu Interface, allowing anyUMTS core network to be connected to any UMTS radio access network.

UMTS Core Network

©Informa Telecoms1

HSS, OSA,CSE etc…

RADIO ACCESS

NETWORK

luCSluPS

SGSN MSC/VLR

GGSN GMSC

Internet, X.25 etc… ISDN, PSTN

PS Domain CS DomainC

OR

E N

ETW

OR

K

2©Informa Telecoms

Fig. 1 – Core Network Architecture (R ’99)


1.2 The main functions provided by the core network

The core network must facilitate the transport of user data between the Mobilestation and the application with which it is interacting, be that application resident inthe core network itself, or operating on some remote party.

In addition to user data transport, the core network is involved in or controls anumber of important processes which are required in order that services can beoffered. These processes involve signalling and control information transport(described as the “control plane”) within the core network which will generally bedealt with separately from user data transport (“user plane”).

The key functions are:

• Mobility Management (MM), including security functions

• Connection Management (CM)

• Session Management (SM)

• charging

• network management

• interworking with external networks

• service provision (hosting of Open Service Architecture, CAMEL etc.)

MM, CM & SM messages are not interpreted by the radio access network. They aresimply exchanged between the MSC/SGSN and the mobile station, transparent to theUTRAN. Note that Connection Management incorporates Call Control (CC),Supplementary Services (SS) and Short Message Service Point-to-Point (SMS).Unlike CC and SS, the Short Message Service can be provided via Circuit Switchedor Packet Switched domains.

UMTS Core Network

©Informa Telecoms3

Fig. 2 – Main Functions of the Core Network

4©Informa Telecoms

• Transport of User Data – CS and PS

• Mobility Management (MM) – CS and PS

• Connection Management (CM) – CS

• Bearer Management

• Call Control

• Supplementary Services

• Short Message Service

• Session Management (SM) – PS

• Charging – CS and PS

• Network Management – CS and PS

• Interworking with external networks – CS and PS

• Service Provision (hosting of Open Service Architecture, CAMEL etc.) – CS and PS

• Security – CS and PS

CS – Applicable to the CS domain

PS – Applicable to the PS domain


1.3 The User Equipment and The Core Network

The main functions of the core network can be provided only if sufficient controlinformation is passed between the core network and user equipment. Hence MobilityManagement, Connection Management (incorporating Call Control, Short MessageService and Supplementary Services), and Session Management protocols have beenspecified. These protocols were all initially specified within GSM.

UTRAN has been specified to carry both User Data and the necessary controlinformation (MM, CM and SM). An additional protocol called Radio Resources Control(RRC) is used between UTRAN and the User Equipment to set up radio bearers forboth the user data and control information. The control information (MM, CM and SMmessages) are transferred from Core Network to the UTRAN within a further protocolcalled Radio Access Network Application Protocol, and then through the UTRANwithin RRC messages. User data is simply framed and transferred through theUTRAN.

UMTS Core Network

©Informa Telecoms5

CORE NETWORK

Signalling Bearer Provided by UTRAN and Radio Resources

/RANAP Protocols

Connection Management, Session Management

Mobility Management

Note: User Data is transferred on the User Plane

Fig. 3 – CN to UE Control Plane

6©Informa Telecoms


2. THE CORE NETWORK CS DOMAIN

2.1 User and Control Information in the CS Domain

Within the CS Domain of the Core Network, MSCs provide the switching functionalityand control for setting up, tearing down and supervising circuits, as well as somesupport for supplementary services. In addition, the HLR and SCP provide supportfor Mobility and Operator Specific Services respectively. The VLR also providessupport for mobility and is co-located with the MSC. This is illustrated in Fig 4.

User data is transferred between MSCs, and between the GMSC and externalnetwork via traffic circuits, without further protocols being added (although overheadis introduced at the physical level, the amount and format being dependent on thetransmission system being used).

The control information is passed within Signalling System Number 7 protocols, andmakes use of the lower layer signalling network (which would usually share the sametransmission infrastructure as the user data).

UMTS Core Network

©Informa Telecoms7

HLR

SCP

MSC/VLR

MSC

MSC

Circuit ( User Data)

Core Network

User Data

Traffic Channel Set Up, Clear Down and Supervision (includes Supplementary Service Support)

Service Control

Mobility Management

Signalling (Control Information)Circuits (User Data)

GMSC

1

2

3

4

1

2

3

4

Fig. 4 – User and Control Information in the CS Domain

8©Informa Telecoms


2.2 Signalling in the CS Domain – SS7 Overview

In the circuit-switched domain, MSCs are switching centres which hold all theswitching functions needed to support mobiles in their area, routing transmissionpaths for both the actual user data, and the signalling messages needed to controlservices. They may also hold interworking functions required to interwork with othernetworks such as the PSTN.

These MSCs are connected to each other and to the HLR and other databases usinga variation of the ITU standardised SS7 (signalling system 7). SS7 is a “common-channel” signalling system, and the circuit-switched user data network is actuallyseparated from the packet-switched SS7 signalling network. SS7 operates using aspecified stack of protocols.

SS7 provides call control by exchanging control messaging between the MSCs andfixed network switches. This may be via direct paths or via signalling transfer points(STPs), designed to route packets across this network.

A third entity, the service control point (SCP), is a database which may controlinformation relevant to routing, for example translating a freephone (0800) numberinto a routing address within the network. No longer do individual switches need tobe modified to introduce a new service. Instead, such changes are made to the SCPelements within the signalling network, which controls the user data switchingperformed at the MSCs/Switches. The SCPs and MSCs/Switches communicate viaa standardised interface, and (if it has this functionality), the MSC/Switched is termeda Service Switching Point (SSP).

In the UMTS CS domain, the MSCs correspond to the SS7 SSPs, providing bothbasic switching, plus access points to supplementary and advanced IN services.Location registers, such as the HLR and VLR, and additional service elements suchas the CAMEL Service Environment, are similar in functionality to the SCPs.

Where remote data bases are being accessed, a Signalling Point Relay (SPR) allowsthe SS7 entity’s unique global address to be translated into the simpler format (pointcodes) used in the individual SS7 packet-switched networks (called the MessageTransfer Port), as the signalling message is passed from one network to anotheren-route to its remote destination.

UMTS Core Network

©Informa Telecoms9

Databases(SCP, HLR, CSE)

MSC(SSP)

MSC(SSP)

STP

STP

SS7 NETWORK

Use

r D

ata

Fig. 5 – SS7 within the Core Network CS Domain

10©Informa Telecoms

• Signalling between MSCs may bedirect or via STPs

• SPRs are also available foraccessing remote databases


2.3 CS Domain Control Plane Protocols: the SS7 Protocol Stack

In mobile networks, there is a high proportion of signalling messages which is necessary toensure that the relevant control information is passed between the various network entities.This control information is in addition to the standard call control messages found in basicfixed networks. More protocols are involved due to the complex nature of the SS7 networkwhen extended to such controlling entities. The protocols are described below. Delivery viaMTP levels 1, 2 and 3 is common to both the (database) control information and thestandard call control messages.

Communication between MSCs and between MSCs and location registers within theCS domain utilises the protocol stack shown in Fig •, the functions of which define theSS7 network.

Above the “physical layer”, which defines the actual physical network over which thesignalling information is transmitted, sit three elements which comprise the “networkservices layer” of the standard SS7 protocol stack:

MTP2, “Message Transfer Part Level 2”This is known as the Signalling Link Level and ensures reliable transmission throughflow control, sequence validation, error checking and so on, and is applied to individualSS7 links.

MTP3, “Message Transfer Part Level 3”This is the Signalling Network Level, providing message handling (routing) and signallingnetwork management for the signalling messages themselves.

SCCP These two layers, in combination with the underlying physical infrastructure provide a high-speed, low-delay, connectionless link. The 3rd element of the network services layer liesabove these, and is known as the Signalling Connection Control Protocol (SCCP), providingthe link through which higher level protocols can communicate via SS7.

Transaction Capabilities Above this Network Services Layer is the Transaction Capabilities Application Part, TCAP,again a standard SS7 protocol. TCAP is used above the previous layers to control the noncircuit-related communications between the signalling nodes. These communicationsbetween signalling nodes are the control functions and procedures which for examplequery the various databases, perform mobility management and support the othercomponents to provide specific services (for example communication between the GMSCand HLR).

MAP In GSM networks, the actual GSM information, functions and procedures are containedwithin the Mobile Application Part (MAP) messages. MAP is used to control implementationof functions such as location updating & roaming, SMS delivery, authentication and callrouting, supplementary service support. This is also the case for UMTS.

UMTS Core Network

©Informa Telecoms11

HLR

SCP

MSC/VLR

MSC

MSC


Core Network

MAP – Mobile Application Part (Mobility Management)CAP – CAMEL Application Part (Service Control)

GMSC

CAPTCAPSCCP

MTP3MTP2

Physical Layer

MAPTCAPSCCP

MTP3MTP2

Physical Layer

Fig. 6 – CS Domain Protocols (Non Circuit-Related Signalling)



CAPAn exception to the use of MAP for control messages occurs where CAMEL is present. In this case communication between the CAMEL Service Environment (CSE)and the MSC is carried as CAMEL Application Part (CAP) messages, although signalling between the CSE and HLR and other databases still uses MAP.

2.4 CS Domain User Plane Control Protocols

Although control plane (signalling) data is transferred across the SS7, packet-switched network made up of the MSCs and intervening STPs, the user data itselfsimply transfers across the circuit-switched network between MSCs.

The lower layers of the SS7 protocols are still applied, MTP2 & MTP3, providingrouting and reliability of the Call Control messages themselves.

TCAP is required only to control the non circuit-related information of MAP or CAPmessages, and so is not relevant to the circuit-switched call. Instead, the ISDN UserPart (ISUP) protocol is used to provide control for these circuit-switched userservices, both between MSCs and between MSCs and switches of other externalnetworks.

Since ISUP includes basic functionality for the establishment and clearing of CS calls,ISUP lies directly above the MTP3 layer, replacing also the functions of SCCP. Aprotocol known as TUP can also be used for communications between MSCs andother networks, and is another standard SS7 protocol, but provides fewer featuresthan ISUP.

UMTS Core Network


HLR

SCP

MSC/VLR

MSC

MSC


Core Network

ISUP – ISDN User Part (Traffic Channel Set Up, Clear Down and Supervision (includes Supplementary Service Support)

GMSC

ISUPMTP3MTP2

Physical Layer

Fig. 7 – CS Domain Protocols (Circuit-Related Signalling)



3. THE CORE NETWORK PS DOMAIN

3.1 User and Control Information in the PS Domain

The Packet-Switched domain uses packets of information to carry both user data andthe control information for the user data between GSNs. This means a common set ofpacket protocols can be defined to allow this exchange of information to take place.The intermediate routers handle the information in the same way, simply routing it onto its “final” destination (the SGSN or GGSN).

For mobility control and provision of operator specific services, the GSNscommunicate with the HLR and SCP respectively using the standard techniquesfound within the Circuit-Switched domain.

UMTS Core Network


HLR

SCP

SGSN GGSN

Signalling (Control Information)Packets of Data(Control and UserInformation)

Router

Router

Packets (U ser & Control Data)

Core Network

User Data

Control Data

Service Control

Mobility Management

1

2

3

4

1 2

4

3

Fig. 8 – User and Control Information in the PS Domain



3.2 PS Domain Protocols 1: GSN to Service/Database communications

Within the PS Domain, packets of actual user data, plus any higher layer controlinformation, pass transparently between the external data network and the mobilestation, using tunnelling and encapsulation. The GGSN and SGSN are simply routers,which send these data packets on to the correct location, based on the PDP Context.

However signalling & control communications may occur not only between the SGSNand GGSN, but also between the SGSN/GGSN and the HLR, SMS-GMSC, SMS-IWMSC and other components which are shared with the CS domain.

For signalling communication between a GSN and one of these common CS/PSdomain elements, the same protocol stack as in the CS domain is used, consistingof MAP or CAP lying above a standard SS7 protocol stack. An interworking functionis required at the GSN to convert between this stack and a different protocol stackwhich is used for communications between the SGSNs and GGSNs.

One exception to this is in the case of signalling between the SGSN and MSC/VLR.In this case, a protocol known as the Base Station Subsystem Application Part +(BSSAP+) is used in place of the TCAP & MAP layers, although this is simply anenhanced version of the standard protocol used between the MSC and BSC in GSM.

UMTS Core Network



Fig. 9 – PS Domain Protocols 1 – Control Signalling Between GSN andService/Mobility Databases

Physical Layer

MTP2

MTP3

SCCP

TCAP

BSSAP+

MAP/CAP

GSNSMS-GMSC etc…

HLR, CSE,SGSN MSC/VLR


3.3 PS Domain Protocols 2: GSN to GSN communications

The protocol stack for communication between two GSNs can be described in fivelayers. Since the purpose of this communication is simply to route PDUs which arriveat the GGSN through to the user via the SGSN, whether the PDU consists of just userdata or user data plus some higher level control information is irrelevant. Each nodejust sees this PDU as a packet of information to be tunnelled.

L1 and L2 are equivalent to the Physical Layer and Network Interface Layer of thestandard TCP/IP protocol stack most commonly associated with the Internet.L1 controls the physical network hardware, and L2 describes how to organise thedata for transmission over the physical network.

These layers are not defined in the core network in the first phase of UMTS, althoughthey are defined to support ATM at the interface between the core network andUTRAN (the Iu Interface).

IP is used on the next layer, the “internet layer” of TCP/IP, to specify the format ofpackets, and the mechanisms to forward these packets to the correct nodes. Nodesmust have valid IPv4 addresses in order to achieve this, with IPv6 as an option, andthe likely direction of future evolution.

The next layer, the “transport layer”, uses either UDP, the User Datagram Protocol orTCP.

UDP sends a message from one application to another, without requiring that thedestination application be active. It is therefore connectionless, but does notguarantee delivery or protection against duplicate data. However it does allow veryrapid data transfer, and minimum network resource and requirements.

TCP is used for protocol data units which require a reliable connection, since TCPsupports reliable, point-to-point, connection oriented services. In particular, TCP willensure that transmission is repeated if packets are lost, and that connections don’tshut down until all data has been transferred.

Finally, above UDP/TCP is the GPRS Tunnelling Protocol, GTP. GTP includes bothsignalling (GTP-C) and data transfer (GTP-U) procedures, and allows multi-protocolpackets to be tunnelled through the PS domain core network between the GGSN andSGSN and (after conversion for the Iu interface) onwards through the UTRAN to theend user.

UMTS Core Network


L1

L2

IP

UDP/TCP

GTP-C(Control)

GTP-U(User)

USER INFORMATIONPACKET DATA UNITS – PDU'S

Information tobe "tunnelled"

Fig. 10 – PS Domain Protocols 2 – GSN to GSN Communications



3.4 Tunnelling

3.4.1 Tunnelling in the PS Domain 1: Transmission

The GGSN provides interworking with external packet-data networks, and connectsto the SGSN via an IP-based backbone network. The actual structure of this IPnetwork is not important, since the aim is simply to tunnel data packets through it,using the PDP context information. Tunnelling occurs in both directions.

Packet Data Units (PDUs) arrive at the GGSN or SGSN as either IP datagrams or X25packets. The GTP encapsulates the PDU, by adding a GTP header. For signallingpurposes, GTP can specify a tunnel control protocol which is used to create, modifyand delete tunnels, with the effect of allowing the SGSN to provide network access tothe mobile station.

This packet is then handed down to be encapsulated further as either UDP or TCP,and finally down to the IP layer, where an IP header is added. This IP header containsthe address of the SGSN or GGSN to which the message should be tunnelled.

In cases where the final IP Datagram which results from encapsulation through theselayers is bigger than a defined maximum transfer unit (defined to ensure speed andreliability of connection), the datagram may then need to be fragmented.

Note that the GTP protocol is also used to tunnel packets of data over the IuInterface between the core network and UTRAN.

UMTS Core Network



Fig. 11 – Tunnelling – Transmission

PDU

GTP

UDP/TCP

IP

Prepare for Transmission

Header, Tunneling Info

Header

Header (IPv4 Address)Fragmentation


3.4.2 Tunnelling in the PS Domain 2: Reception

IP datagrams which arrive at the SGSN or GGSN (or RNC for Iu Interface tunnels) arefirst reassembled if they were fragmented, and then the IP header is removed.

This payload is then passed upwards to the UDP/TCP layer, with processes such aschecksum performed as required, and the UDP/TCP header is removed.

Finally the GTP layer strips off the GTP header such that the PDU is now ready fortransport across to the Radio Access Network or into the external network. This latterprocess requires further modification, via an interworking function, in order to formatthe PDU ready for transport across the Iu Interface.

UMTS Core Network


PDU

GTP

UDP/TCP

IP

Received Data

Remove Header

Checksum etc…

Remove HeaderReassemble

Fig. 12 – Tunnelling – Reception



4. MOBILE IP

4.1 Mobile IP: Basics

Mobile IP is an ongoing standardisation project within the IETF (Internet EngineeringTask Force), who are now also a market representation partner within 3GPP.

The aim of Mobile IP is to enable a mobile to communicate using the same IPaddress at all times, regardless of the IP network through which it accesses theInternet. If this were not the case, then active TCP sessions would be broken eachtime the mobile wanted to access through a different network (e.g. UMTS vs. LAN),meaning that guarantees of service quality, and a “seamless view” for the application,would not be possible.

Mobile IP provides a mechanism whereby a mobile station is given a permanent IPhome address, which belongs within its original home network. If accessing throughthis home network, it will therefore just act like any non-mobile station and can bereached through normal IP routing.

However when it accesses through some visited network, it is assigned a “care ofaddress” (COA) which belongs to this visited network, and which identifies the currentlocation of the mobile. Since other stations do not know the location of the mobile,they will send packets to its permanent home address, where the packets arereceived by a router which is assigned the status of the “home agent” (HA).

This HA forwards packets onto the mobile station using tunnelling, having previouslybeen provided with the COA by the mobile. The mobile station can answer directly tothe other station, although using its home address rather than the COA as the sourceaddress for the message. Any time the mobile station moves to attach via a differentIP subnetwork, it will register its new COA with its HA.

UMTS Core Network


HomeAgent

“COA”

COA – “Care of Address”

(Uses Home Address, not COA)

Can Answer Direct

CalledCaller

“Permanent(Home) Address”

Visited Network

Fig. 13 – Mobile IP



4.2 Mobile IPv4 vs. IPv6

In the case of IPv4, a COA address will most likely be a router, called the foreignagent (FA), which will have the functionality to enable it to forward messages onto the mobile station. A single COA may apply to more than one mobile station.Overlaying Mobile IP onto a GPRS/UMTS network means enabling the GGSN to havethis FA functionality, able to set up a PDP context for the mobile station, and tunnelPDUs from the GGSN towards the user.

A key advantage in moving to IPv6 is that the number of IP addresses availablebecomes effectively unlimited. It is possible to assign mobile stations a direct COA,using some form of automatic assignment mechanism. Messages from the homeagent can be tunnelled directly towards the mobile station.

If the mobile station has a direct COA, then the core network tunnelling provided byGTP becomes redundant, since data can be tunnelled directly from source to user.Indeed it will be possible to combine the GGSN and SGSN into a single InternetGPRS Support node (IGSN), which acts as the FA and marks the end of the UMTS-specific network. The IGSN would need to support current SGSN functionality,supporting MAP communication with UMTS location registers, plus of course supportMobile IP and any accounting procedures required by an FA.

In effect, an ultimate scenario is that Mobile IP may handle mobility management andtunnelling within the PS domain core network.

UMTS Core Network


a) IPv4 Plus GPRS/UMTS

HA

“COA”

PDP/GTP

PDP/GTP

Visited Network

GGSN/FA

SGSN

HA

“COA”“COA”

Visited Network

IGSN

b) IPv6 Plus GPRS/UMTS

COA – “Care of Address”HA – Home AgentFA – Foreign AgentIGSN – Internet GPRS

Support Node

Fig. 14 – Mobile IP Evolution



5. CORE NETWORK TRANSPORT

The CS Domain will in most cases be brought forward directly from an operator’sexisting GSM Phase 2+ core network. Such networks commonly use PDH or SDH,although there is no standard specified for this.

Equally in the PS domain, no standard transport is specified – any IP network can liebetween the GGSN and SGSN. ATM is a common choice, since it is designed forrobust support of packet networks.

ATM is already specified for transport within the UTRAN. It seems likely that both corenetwork domains may also migrate to ATM in UMTS networks, particularly whenoperators seek to combine the transport systems of the CS and PS domains, a majorgoal behind the network architectures proposed in Release 4 and beyond.

Such an upgrade will require the addition of an interworking function within the MSCsto support ATM-PSTN interworking, and provide support for the ATM protocol stack.

However currently, the choice of transport layers remains up to the operator, and isnot defined in the standards.

UMTS Core Network


Mobility & Service

Databases

PS DOMAIN

UTRAN

• PDH or SDH

• Any IPNetwork

• Commonly uses ATM

CS DOMAIN

• ATM Based

• Goal is to combine PS & CS Transport Systems (Release 4 Architecture)

Fig. 15 – Transport in the Core Network



6. CHARGING

In the circuit-switched domain, charging continues to be based simply on theduration of the call, as in 2nd Generation Networks today, combined with informationon the location of the mobile.

However in the PS domain, charging can be not only time based, but also datavolume based or QoS based.

In the PS domain, a Charging Gateway function (CGF) collects charging recordswhich are collected at the GSNs as follows:

Charging data recorded at the SGSN:

• usage of the radio interface (amount of data & QoS characterisation)

• length of time for which PDP addresses were used

• usage of PS domain resources

• location of the mobile station

at the GGSN:

• destination and source addresses

• usage of external data network (amount of data)

• length of time for which PDP addresses were used

Another new requirement in UMTS is that such data needs to be available on a real-time basis, to allow real-time and online billing to the user.

UMTS Core Network


Fig. 16 – Charging


CS Domain:

• Time

• Location

• Number of Channels

PS Domain:

• Time

• Location

• QoS

• Data volume


7. NETWORK MANAGEMENT

Network Management refers to a huge range of processes and functions which linktogether the various network elements, operations and systems within a UMTSnetwork. This includes managing information flows which are related tocommunications between network elements, fault tracking & solving, security, billing& accounting, performance measurements, service provisioning & assuranceoperations, and various customer care operations.

In implementing a network management structure, the key aims for the UMTSOperator are as follows:

• minimise the cost & complexity

• maximise the flexibility

• manage equipment supplied by different vendors

• ensure scaleability

• re-use existing standards, and ensure interoperability with other networks

The ITU has developed a model known as TMN (Telecommunications ManagementNetwork Standard), which is used as the basis for UMTS network managementwhenever relevant and possible. TMN provides:

• an architecture of Operational Systems and Network elements with definedinterfaces between them

• tools to refine the management architecture in a given network management area

• common functions which can be applied to various TMN interfaces

A broad overview of the interactions needed within a network management scheme isshown in Fig. •.

The definition of standards for interfaces within an operator’s own operational systemis not required. However interfaces between the UMTS operational system (OS) andthe enterprise systems of that same UMTS organisation, and between the operationalsystems of different UMTS organisations were not defined in R ’99. As a first priority,interfaces between the UMTS OS and the network elements are being defined.

The latter are to be prepared on the basis of protocol-independent informationmodels, since UMTS may involve convergence of elements from varioustechnologies, and because information needs generally change on a much longertimescale than do protocols.

UMTS Core Network


EnterpriseSystems

UMTSOperations

System

NetworkElements

OperationsSystem

TMN

UMTS Organisation A UMTS Organisation B

Fig. 17 – Network Management



8. IN/CAMEL IN UMTS

8.1 Intelligent Networks

Intelligent Networks originally provided advanced features such as freephone, callingcard and so on, by providing intelligence within databases which could translatethese dialled numbers into standard routing numbers within networks. These earlyservices were soon followed up by further advanced services based on thisintelligence, incorporating interaction with the user to further customise services.

Traditionally, switching equipment would need to be upgraded each time a newservice was required. IN separates service intelligence and switching, such that toimplement any defined “Capability Set” of services, upgrades to switches arerequired, but the addition of the actual services within this capability set do notrequire switch upgrades. This means that new services can be quicker and cheaperto install, and that service creation and switching is split into two markets, therebyincreasing vendor competition.

IN can provide such services only when there is an exchange of data betweenthe switch and an application or database which has knowledge about numbertranslation or other features. Most INs, including GSM Phase 2+ networks, use lowerlayer SS7 protocols to enable the Switches (known as Service Switching Points, orSSPs) to communicate with databases known as Service Control Points (or SCPs).

The application or database must reside in the IN, and a standardised protocol layerknown as INAP is used to enable interaction between the SSP and SCP. INAP liesabove the internationally standard protocols which form the SS7 signalling system,incorporating MTP, SCCP and TCAP.

The intelligent applications which control IN services are defined by the operator, andare not themselves standardised. This means that IN offers a route to operatordifferentiation, but equally that in many cases the same services cannot be offeredoutside the network of that operator.

UMTS Core Network


Switching&

Service Control

Switching

ServiceControl Point

ServiceSwitching Point

Intelligent Applications

SS7 (INAP)

IN:

Pre-IN:

ServiceCreation

Tools

Fig. 18 – Intelligent Networks


• SCP controls user interaction when required


8.2 CAMEL

CAMEL (Customised Application for Mobile network Enhanced Logic) is a featuredesigned to provide support for services of operators which are not standardisedservices (e.g. operator-specific IN services), even when subscribers are roamingoutside the home network. CAMEL is a network feature, not a supplementary service.

In order for CAMEL to function, information exchange is required between the Homeand Visited networks, and subscribers who have access to CAMEL services aremarked within each network.

The concept is basically that of IN, in that it is the MSCs (now termed SSPs within theCAMEL context) which communicate with the SCP. The big difference is that the MSCand SCP may well be in different networks (the SCP will be located in thesubscriber’s home network for home network operator specific service support).

Due to different networks being involved, the CAMEL standard is more tightly definedthan IN capability set 1 (IN CS-1), although it is still seen as an extension of CS-1.It is specified within GSM Phase 2+, but is a core feature of the Virtual HomeEnvironment (VHE) concept of UMTS.

GPRS and Circuit-Switched connections are both supported by CAMEL.

UMTS Core Network


CAMELService

EnvironmentSCP

HOME UMTS

NETWORK

SERVING UMTS

NETWORK

GatewayMSC/GSN

ServingMSC/GSN

(SSP)

Cam

el In

tera

ctio

ns

Traffic

Cha

nnel

Fig. 19 – CAMEL Within UMTS


• User interactions are supervisedby SCP where required

UMTS Systems Overview

UMTS Core Network



ANNEX 1OSI 7 LAYER MODEL


ANNEX

A.1 OSI 7 LAYER MODEL

A.1.1 Protocols & Stack: Basics

A network protocol simply defines a set of rules for communication between elementsin a network, so governing things like format, timing, sequencing and so on, withoutwhich a network element cannot make sense of the bits.

Because there are many processes and complexities involved, communication isbroken down into a series of steps. Each step has its own rules of operation – its own protocol. These steps are executed in a certain order. The hierarchicalarrangement of these protocol steps is known as a stack. A stack as a wholetherefore represents the set of rules for a communication, and is executed in theorder from top to bottom in transmission, and bottom to top in reception, as shown inFig. A1.

Thus applications sit at the highest layers in protocol stacks. Data from an applicationwill pass down through the stack in order to prepare the data for actual transmissionover a physical network. At each stage, signalling information may be added to theoriginal data, and/or its format may be changed, for example by being divided intopackets.

At the receiving end, data is taken off the physical network, and passed up throughthe layers, where reverse operations are performed. So packets may be reassembled,signalling information removed and so on, until the original data arrives once again atthe highest layers, for example another application.

UMTS Core Network



Fig. A1 – Protocol Stack Operation

Data In Data Out Applications

L4

L3

L2

L1

L4

L3

L2

L1

Transmission Reception


A.1.2 The OSI Model

The OSI model provides a reference model for protocol layering, and is often referredto in numbered layers in a protocol stack. However protocol stacks can consist ofany number of layers, and multiple functionalities shown in the OSI reference modelmay be combined within a single protocol, or multiple protocols may be used todefine sublayers within such a reference model.

The OSI layers are as follows:

Layer 7 Type of communication, e.g. e-mail, fileApplication Layer transfer etc.

Layer 6 Encryption, data conversion and so onPresentation Layer

Layer 5 Starts and stops sessions, and maintains Session Layer order

Layer 4 Ensures delivery of entire messages Transport Layer or files

Layer 3 Routes data between and through different networks,Network Layer based on network addresses

Layer 2 Transmits packets from node to node Data Link Layer within networks

Layer 1 Electrical and mechanical interface to the Physical Layer actual network medium (cable, radio)

UMTS Core Network


Application

Presentation

Session

Transport

Network

Data Link

Physical

Fig. A2 – The OSI Model


section four

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