Gprs 03 System

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0RELOH�6WDWLRQA Mobile Station is the combination of a Terminal Equipment ( TE) and a MobileTerminal (MT). One example is a laptop computer connected to a mobiletelephone, providing wireless attachment to the Internet. The TE and MT partscould also be built into the same piece of equipment.

There are three types of Mobile Stations:

Non-GPRS mobiles (circuit-switched only) GSN/GPRS mobiles (circuit- and packet-switched) - Class A: Simultaneous circuit- and packet-switched service - Class B: Automatic switching between circuit- and packet-switched mode - Class C: Must be set in either circuit- or packet-switched mode GPRS-only mobiles (packet-switched only)

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GPRS system file:///Y|/Vanliga/Ericsson/www/read/system.htm

7KH�7HUPLQDO�(TXLSPHQW��7(� is the computer terminal that the end user workson. This is the component used for the GPRS system to transmit and receive enduser packet data. The TE could be for example a laptop computer. The GPRSsystem provides IP connectivity between the TE and an Internet Service Provider orCorporate LAN connected to the GPRS system. From the TE point of view, youcould compare the MT to a modem, connecting the TE to the GPRS system.

More details on TE.

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7KH�0RELOH�7HUPLQDO��07� communicates with a TE, and over the air with a BTS.The MT must be equipped with software for the GPRS functionality when used withthe GPRS system. The MT is associated with a subscriber in the GSM system. TheMT establishes a link to an SGSN. Channel reselection is provided at the radio linkbetween the MT and the SGSN. The IP connection is static from the TE point ofview. This means that the TE is not aware of being mobile and retains its assignedIP address until the MT detaches.

More details on Mobile Stations.

%66The Base Station System (BSS) consists of a Base Station Controller (BSC) and aBase Transceiver Station (BTS). The BTS separates the Mobile Station circuit calls from packet-datacommunication, before the BSC forwards circuit calls to the MSC/VLR, and packetdata to the SGSN.The protocols towards the BSC are standard GSM protocols, for the desiredcompatibility.

More details on BSS.

%76The Base Transceiver Station (BTS) is the radio equipment which transmits andreceives information over the air. The BTS handles communication between theBSC and Mobile Stations in the BSC’s service area. A group of BTSs is controlledby a BSC. The BTS must contain GPRS-specific software.

%6&The Base Station Controller (BSC) provides all the radio-related functions. TheBSC has the functionality to set up, supervise, and disconnect circuit-switched andpacket-switched calls. It is a high-capacity switch that provides functions including

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handover, cell configuration data, and channel assignment. The BSC must beequipped with GPRS hardware and software when used for GPRS. One or severalBSCs are served by an MSC, and a number of BSCs are served by an SGSN.

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366The Packet-Switching System (PSS) consists of GSN nodes. These are the newGPRS-specific nodes for the handling of packet-switched communication.The GPRS Support Node (GSN) is a general notation for SGSN and GGSN. Thefunctionality of SGSN and GGSN may be combined in the same physical node(network element), or they may reside in different physical nodes. SGSN andGGSN contain GPRS backbone network protocol (IP) routing functionality, and theymay be interconnected with IP routers.SGSN and GGSN can be located in different PLMNs. The two PLMNs will then beconnected via Border Gateways for security and interoperability reasons. TheBorder Gateways are part of the GGSNs.

6*61The Serving GPRS Support Node (SGSN) is a primary node in the GSM network,using GPRS, and is a new node in GSM. The SGSN forwards incoming andoutgoing IP packets addressed to/from a Mobile Station that is attached within theSGSN service area. The SGSN provides:

packet routing and transfer to and from the SGSN service area. It serves allGPRS subscribers that are physically located within the geographical SGSNservice area. A GPRS subscriber may be served by any SGSN in thenetwork, all depending on location. The traffic is routed from the SGSN to theBSC, via the BTS to the mobile station. ciphering and authentication session management mobility management logical link management towards the Mobile Station connection to HLR, MSC, BSC, SMS-GMSC, SMS-IW-MSC, GGSN output of charging data. The SGSN collects charging information for eachMobile Station related to the radio network usage. Both the SGSN and theGGSN collect charging information on usage of the GPRS network resources.

More details on GSN.

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**61Like the SGSN, the Gateway GPRS Support Node (GGSN) is a primary node in theGSM network using GPRS, and is a new node. The GGSN provides:

interface towards the external IP packet networks. The GGSN thereforecontains access functionality that interfaces external ISP functions, likerouters and RADIUS servers (Remote Access Dial-In User Service), which

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are used for security purposes. From the external IP network’s point of view,the GGSN acts as a router for the IP addresses of all subscribers served bythe GPRS network. The GGSN thus exchanges routing information with theexternal network. GPRS session management; communication setup towards external network functionality for associating the subscribers to the right SGSN output of charging data. The GGSN collects charging information for eachMobile Station, related to the external data network usage. Both the GGSNand the SGSN collect charging information on usage of the GPRS networkresources.

More details on GSN.

3DFNHW�'DWD�1HWZRUNThe Packet Data Networks that GPRS can attach to is the Internet or any other IPpacket networks.

&66The Circuit-Switching System (CSS) is the traditional GSM system, updated withGPRS support.

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06&�9/5The Mobile Services Switching Centre (MSC) performs the telephony switchingfunctions of the GSM circuit-switched system, like the SGSN switches the GSMpacket-switched traffic. It controls calls to and from other telephony and datasystems, such as the Public Switched Telephone Network (PSTN), IntegratedServices Digital Network (ISDN), Public Land Mobile Network (PLMN), Public DataNetworks, and possibly some private networks.

The SGSN Routing Area (RA) is a subset of the MSC (circuit-switched) LocationArea (LA). The SGSN Routing Area is the part of the network that is covered byone SGSN. An MSC Location Area is a group of BSS cells. The system uses theLocation Area to search for subscribers in the GSM idle state. A Location Area isthe part of the network in which a Mobile Station may move around withoutreporting its location to the network. One MSC/VLR Service Area (SA) is made up of a number of Location Areas. TheService Area is the part of the network that is covered by one MSC.

There can be several MSCs corresponding to one SGSN. One MSC can also beconnected to several SGSNs. The configuration is a matter of dimensioning for theactual traffic.

The Visitor Location Register (VLR) database contains information about all MobileStations currently located in the MSC location area or SGSN routing arearespectively. The SGSN in fact contains the VLR functionality for packet-switchedcommunication. Similarly, the Ericsson MSC contains the circuit-switched VLR asan integrated part.

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The VLR contains temporary subscriber information needed by the MSC or SGSNto provide services for visiting subscribers. The VLR can be seen as a distributedHLR.

When a Mobile Station roams into a new MSC location area or SGSN routing area,the VLR of that MSC or SGSN requests and stores data about the Mobile Stationfrom the HLR. If the Mobile Station makes a call at another time, the VLR will thenalready have the information needed for that call setup.

For mobiles supporting both GPRS (packet-switched) and GSM (circuit-switched),both the SGSN and the MSC will obtain location information from the HLR whenthe Mobile Station is combined-attached, that is, both GPRS- andIMSI/CS-attached. The SGSN can receive and execute circuit-switched systempaging requests from the MSC/VLR.

The GPRS VLR consists of software in a Serving GPRS Support Node (SGSN).The SGSN VLR contains the information that this SGSN is used. This informationmarks the communication using the SGSN. For the GPRS system, the HLR directlyinstead of the (circuit) MSC/VLR is used for the authentication procedure of theMobile Stations. The SGSN thus obtains the authentication triplets from the HLR.

More details on MSC/VLR.

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*06&The Gateway Mobile services Switching Centre (GMSC) switches thecircuit-switched calls between the GSM circuit-switched network and the PublicSwitched Telephone Network (PSTN), that is, the fixed telephony network. TheGMSC is not changed for use by the GPRS system.

3671The Public Switched Telephone Network (PSTN) is the fixed telephony network.Other networks reachable with circuit-switched technology are Integrated ServicesDigital Network (ISDN), Public Land Mobile Network (PLMN), Public Data Networks,and possibly some private networks.

+/5The Home Location Register (HLR) is the database that holds subscriptioninformation for every person who has bought a subscription from the GSM/GPRSoperator.

The HLR stores information for circuit- and for packet-data communication. TheHLR contains information about, for example, supplementary services,authentication parameters, and whether or not packet communication is allowed. Inaddition, the HLR includes information about the location of the Mobile Station. ForGPRS, subscriber information is exchanged between HLR and SGSN. Note thatthe authentication triplets for GPRS are fetched directly from the HLR to the SGSN,that is, do not use the MSC/VLR as for circuit GSM.

The information going from HLR to SGSN is what the operator sets up for the

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subscriber. This information transfer is done when the operator changes thesubscriber information, or when a new SGSN needs to have data for a subscriberafter attach or roaming. The old SGSN also gets informed of the roaming. Theinformation going from SGSN to HLR is the routing information that is transferredupon Mobile Station action, for example attach or roaming. For a roaming mobile,the HLR may be in a different PLMN than the SGSN serving the mobile.

More details on HLR.

$8&The Authentication Centre (AUC) is not affected by the GPRS functionality.

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606�,:�06&The Short Message Service Interworking MSC (SMS-IW-MSC) is connected to theSGSN to enable GPRS Mobile Stations to send and receive SMS over GPRS radiochannels. The SMS-IW-MSCs are not changed for GPRS use.

606�*06&The Short Message Service Gateway MSC (SMS-GMSC) is connected to theSGSN to enable GPRS Mobile Stations to send and receive SMS over GPRS radiochannels. The SMS-GMSCs are not changed for GPRS use.

6&The Short Message Service Centre (SC) is connected to the GPRS network via theSMS-GMSC and the SMS-IW-MSC.

6��*356�QRGHVThe nodes specific for the packet core network are:

the Serving GPRS Support Node (SGSN) the Gateway GPRS Support Node (GGSN).

In addition, the Terminal Equipment (TE) is introduced with the GPRS system.

Some other GSM system nodes are used and affected by GPRS functionality:

the Mobile Station the Base Station System (BSS) the Mobile services Switching Centre/Visitor Location Register (MSC/VLR) the Home Location Register (HLR) the Operations Support System (OSS) or corresponding the Ericsson GPRS Terminal (EGT) the Billing Centre or Billing Gateway (BGw)

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Note that some GSM nodes are partly replaced by GSN functionality when it comesto packet-switched communication. See for example the descriptions of MSC/VLR,HLR, and OSS respectively.

*356�6XSSRUW�1RGH��*61�The GSN is a general-purpose, high-performance packet switching platform. Itcombines features usually associated with data communication, such ascompactness and high functionality, with features from telecommunications, suchas robustness and scalability. Designed for non-stop operation, the platformincorporates redundant hardware, and software modularity enabling individualmodules to be upgraded without disturbing the traffic.

The Ericsson-developed GSN platform is based on industry standards, and is easilymanaged via a web-based management system. The GSN is highly robust, withadvanced functions for capturing software faults, isolating hardware faults, andprotecting against overload.

A GSN consists mainly of the PSS Core platform (hardware and software) on whichthe SGSN and/or GGSN application software executes. The PSS Core platformconsists of:

Hardware - backplane switch - interface - processors Software components - operating systems (Solaris and VxWorks) - high-availability support middleware - operation and maintenance support

The SGSN and GGSN applications include GPRS protocols and session andmobility management as well as operation and maintenance.

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7HUPLQDO�(TXLSPHQW��7(�The end user needs a TE. This can be for example a standard PC/laptop, aPersonal Assistant, or a SmartPhone. The TE could be integrated with the MobileStation. The TE must be connected to a Mobile Station, and must include theTCP/IP (Transmission Control Protocol/Internet Protocol) and PPP (Point to PointProtocol) stack to gain access to an Internet service Host.

0RELOH�7HUPLQDOThe end user requires a Mobile Terminal (MT) to connect to the GPRS system. TheMT must include GPRS packet-data procedures in compliance with the GSMstandard. The MT must also have a Terminal Equipment (TE) interface. Thisinterface could, for example, support High-level Data Link Control (HDLC) such asframing of PPP messages, depending on what the TE requires. The underlyinglayer between the TE and the MT must be described by the MT vendor.

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%DVH�6WDWLRQ�6\VWHP��%66�The GPRS system communicates over the air with the Mobile Stations, using radiosignals transmitted from and received by a BSS. Only the GPRS-specificfunctionality is described here.

The BSS handles the transmission and reception of radio signals for speech/circuitdata and packet-data communication. The BSS is provided with specificfunctionality (for the Ericsson BSS: software and a BSC hardware unit) adapted tothe packet-data services utilised in the GPRS system. The BSS separatesspeech/circuit data and packet-data TDMA slots from each other. In this way onlythe packet data will reach the SGSN.

The GPRS-specific functionality in the BSC is the following:

GPRS Mobility Management Frame Relay and BSSGP interface to SGSN Allocation of PDCH in cells Distributing paging GPRS information broadcast

The GPRS-specific functionality in the BTS is the following:

Support of PDCH Support for MAC and RLC interfacing via BSC to SGSN Resource administration

GPRS will use the common pool of physical resources for the radio interface inco-existence with standard GSM. This means that it is possible to mix GPRSchannels with circuit-switched channels in a cell. The GPRS resources can bedynamically allocated in-between gaps in the circuit-switched sessions. Thus, thespectrum is used much more efficiently. GPRS communication will also useefficient data coding within the data packets. In addition, GPRS channels areallocated only when data is actually sent or received.

There is more networking information in the section GPRS radio network.

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0RELOH�VHUYLFHV�6ZLWFKLQJ�&HQWUH�9LVLWRU�/RFDWLRQ�5HJLVWHU��06&�9/5�Network operation Mode I allows for two optimizations, saving radio resources andterminal battery consumption:

Combined Location Area /Routing Area update. A Mobile Station will do aLocation Area update to the MSC and a Routing Area update to the SGSNseparately. Through their interfaces, the MSC and SGSN can keep eachother updated about the area of a Mobile Station. This will save signallingover the radio interface. In order to support this interface, the Ericsson GSMMSC/VLR needs a software upgrade.

Circuit-Switched Paging over GPRS: the network sends a circuit-switchedpaging message for a GPRS-attached Mobile Station, either on the samechannel as the GPRS paging channel (that is, the packet paging channel or

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the CCCH paging channel), or on a GPRS traffic channel. This means thatthe Mobile Station needs only to monitor one paging channel, and that itreceives circuit paging messages on the packet-data channel when it hasbeen assigned a packet-data channel.

The MSC/VLR can order the SGSN to inform about the next radio contact with theGPRS Mobile Station. An example for using this mechanism, is to trigger thedelivery of an SMS which was unsuccessful via circuit communication.

The Suspend/Resume functionality for terminals working in class B mode issupported by MSC and SGSN. When a class B terminal is engaged in a datasession and a circuit-switched call is coming in, the MSC will use the circuitinterface to the BSS, and the BSS-SGSN interface, to notify the SGSN. It is theBSC that requests the SGSN to suspend the data session. The SGSN will suspendthe data session, and the user can take the circuit-switched call. When that call isfinished, the data session can be resumed. Without the MSC-SGSN interface thereis no support for class B terminals. It is assumed that initially, most GPRS-readyterminals will be of class B type. Therefore, this interface is essential if the operatorwants to be able to offer an effective service for both types of traffic.

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+RPH�/RFDWLRQ�5HJLVWHU��+/5�The existing HLR will be reused for GPRS, with software updates. It containsGPRS subscription data and routing information. The HLR information is accessiblefrom the SGSN (downloading subscription information to the VLR function in theSGSN). For roaming mobiles, the HLR may be in a different PLMN than its SGSN.Already installed HLRs need software updating for the support of GPRS serviceslike:

whether the subscriber is allowed to access GPRS, circuit GSM, or both subscription records: PDP type, APN, IP address, Quality of Service (QoS) support of SMS over GPRS

Configuration management of the HLR is done in the same way as for thetraditional GSM system, that is, by MML (man-machine language) commands or viathe Service Order Gateway interface.

The GSM Service Order Gateway needs software upgrading for the support of theGPRS services.

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6*61�LQWHUIDFHV�WR�&66The SGSN has signalling interfaces to the following nodes of CSS:

SGSN to HLR (the Gr interface)(SGSN obtains the authentication triplets from HLR.)

SGSN to MSC/VLR (the Gs interface)(This interface connects the databases in the MSC/VLR and the SGSN.)

SGSN to SMS - GMSC (the Gd interface)(This interface makes it possible to receive and send SMSs via the GPRSradio channels.)

SGSN to SMS - IW - MSC (the Gd interface)(This interface makes it possible to receive and send SMSs via the GPRSradio channels.)

All of these interfaces use SS7, a global telecommunications standard. Using astandard like this is necessary for roaming.

The SGSN will need to communicate with a large number of HLRs, MSC/VLRs, andSMS-GMSCs and SMS-IW-MSCs in the local PLMN as well as in the PLMNs ofvisiting Mobile Stations. The SGSN will therefore be connected to a few signallingtransfer points, which are connected to the global SS7 network.

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The protocol stacks are as follows, for respective interface:

SS7 Interfaces Protocol Stacks

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The SS7 physical layer is MTP1. The following physical layers are supported:

64 kbps PCM time slots on E1 physical connections 56 kbps PCM time slots on T1 physical connections

The data link layer is MTP2. Both the basic and preventative cyclic methods forerror correction are supported. The supported features include:

processor outage handling normal and emergency initial alignment flow control

MTP3 is the SS7 network layer. It provides load sharing between differentredundant links in the same or different set.

SCCP provides the transport layer. Class 0 and 1 in the connectionless mode aresupported. Connection-oriented communication is not supported. The SCCPsupports segmentation and reassembly.

TCAP provides the SS7 session and presentation layers. It provides support forboth structured and unstructured dialogues, node segmentation, and the followingQuality of Service parameters:

in-sequence delivery message return option

BSSAP+ is an adaptation of the BSSAP (Base Station System Application Part)protocol to GPRS. BSSAP contains BSSMAP and DTAP. BSSMAP (BSSManagement Application sub-Part) is a protocol for signalling between MSC andBSC. DTAP (Direct Transfer Application sub-Part) is a protocol for data transferbetween Mobile Stations and MSC.The MAP (Mobile Application Part) protocol handles the exchange of signallinginformation.


6*61�LQWHUIDFH�WR�%66��WKH�*E�LQWHUIDFH�This section describes the signalling plane. The data interface is described in thesection Payload Handling in GSN.

The Suspend and Resume signalling is sent over the interface SGSN - BSS. Theconnection for end user traffic between the SGSN and BSS uses the followingprotocols:

SGSN - BSS Interface Protocols

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Frame Relay is a data communication standard. E1 and T1 are telecommunicationstandards.

The connection for end user traffic between the SGSN and a BSC uses E1 or T1connections. When the BSC is connected directly to the SGSN, onlypacket-switched traffic uses this direct connection. Circuit-switched traffic must usethe interface circuits which are connected to the MSC. However, when the BSC isconnected indirectly via MSC to the SGSN, the sets of time slots on the E1/T1 canbe allocated to circuit, packet, or a combination of circuit and packet traffic. Thismeans that circuit and packet traffic can share the same link, but of course not thesame time slot.


The interface SGSN-BSC can be connected point-to-point or via a Frame Relaynetwork. For a point-to-point setup, the BSC will act as the user equipment side(Data Terminal Equipment) and the SGSN will act as the network side (DataCommunication Equipment). Otherwise, when connected via a Frame Relaynetwork, a Frame Relay switch connects the SGSN and the BSC. The SGSN isthen considered a TE. The Network Service protocol provides resilience.

Each fractional E1 or T1 physical connection must be a multiple of 64 kbps andhave contiguous time slots. The bigger the physical connection, the more bandwidth the Frame Relay layer will give.The protocol on top of Frame Relay/Network Service is BSSGP. BSSGP (the BSSGPRS protocol) carries out the flow control from the SGSN to the BSS.

It is possible to use the Ericsson MSCs for cross-connecting the interfaces betweenthe BSC and the SGSN. In that way the SGSN lines are routed through the MSCwhere they can be multiplexed together. It should be noted that this solutionrequires Group Switch (GS) and Exchange Terminal Circuit (ETC) capacities in theMSC unit.

6*61�LQWHUIDFH�WR�0RELOH�6WDWLRQV��WKH�*E�LQWHUIDFH�This section describes the signalling plane. The data interface is described insection Payload Handling in GSN.

The connection for end user traffic between the SGSN and a Mobile Station usesthe following protocols:

SGSN - MS Interface Protocols

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The SNDCP protocol implements segmentation and re-assembly of the IP payloadpackets.

The GMM (GPRS Mobility Management) protocol handles procedures like GPRSattach, GPRS detach and holds the related information in the Mobility Managementcontext.

The SMS protocol is the protocol used for handling Short Message Services.

The LLC protocol can run in acknowledged or unacknowledged mode. Simulationscarried out by Ericsson show that unacknowledged mode is more efficient for IPtraffic, and it is therefore recommended. The operator decides which QoS (Qualityof Service) profile including acknowledged/unacknowledged mode the operatoroffers within each subscription type.

,3�LQWHUIDFHV�LQ�366This section describes the signalling plane. The data interface is described in thesection Payload Handling in GSN.

The following interfaces are used in the packet-switched system:

SGSN - GGSN (the Gn interface)(This interface is used for the internal GSN passing of packet data. TheSGSN provides packet routing to and from the geographical SGSN servicearea. The GGSN realizes the interface towards the external IP packetnetworks.)SGSN - GGSNs in other PLMNs (the Gp interface)GGSN - access server in Packet Data Network (the Gi interface)(This is the actual interface towards the PDN, e.g. Internet or X.25)GSN - Management Network (the Gn interface)(This is the GSN interface towards the Management Network)GSN - Service Network (the Gn interface)(This is the GSN interface towards the Service Network)


All of these interfaces support all of the following protocols respectively:

Protocols used for E1/T1-based communication

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Protocols used for SDH/SONET-based communication


Protocols used for Ethernet-based communication

E1 and T1 are Pulse Code Modulation (PCM) connections.

The interfaces can be used in the following configurations:

non-channelized, using the entire interface of 2 Mbps for E1, and 1.5 Mbpsfor T1, as one channel channelized into 64 kbps channels for E1 and T1, and 56 kbps channels forT1 fractional, using multiple 64 kbps channels for E1 and T1, and multiple 56kbps channels for T1, per physical interface. E1 will have 31 channels of each64 kbps, and T1 will have 24 channels of 64 or 56 kbps each depending onthe PCM network. Many fractions per interface are supported, covering up toall time slots.

The 155 Mbps ATM / SDH or SONET interface is a standard ATM Forum UNI TE.ATM PVCs are supported. IP is carried over AAL5.

Ethernet interfaces 10Base-T (10 Mbps) and 100BaseTx (100 Mbps) aresupported. Both interface types are supported on the same physical interface andare runtime configurable, with the interface inactive, to 10/100 Mbps.

All IP interfaces may also use the optional feature IPSec for security.

More information on the radio network is included in the section GPRS radio

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network.

*356�,QWHUQDO�%DFNERQHThe GPRS Internal Backbone is

the network connecting the routers between GSNs, or connecting the GSNs,when the routers are the ones internal to GSN the Management Network

The following figure shows examples of the GPRS Internal Backbone together withparts of its environment. The Management LAN (Management Network) and theService LAN (Service Network) are described separately. The Border Gateway isused in case the GSNs are in different PLMNs.


The first figure shows two separate Management LANs, both of which are used toconfigure and administrate the SGSNs.


The GSN always contains a router. It is, however, also possible to include aseparate router between GSNs, in the GPRS backbone, together with a switch forData Communication Equipment (DCE) functionality at that network point.

The following figure shows another example backbone, with more example context.The figure shows a huge GPRS network, which uses ATM as protocol for thebackbone. This backbone can be used for traffic or traffic and O&M. On the rightside of the figure you can see a Management LAN, which is connected to oneSGSN. It is possible to use the ATM Network to administrate all SGSNs andGGSNs from the Management LAN.

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Another possible configuration is to have SGSN and GGSN in the same unit.

0DQDJHPHQW�1HWZRUNThe management network is the network for administrative hosts, for example aGSM OSS host. It could also include charging hosts. The hosts connected to themanagement network are only accessible from the GSNs.

6HUYLFH�1HWZRUNThe service network is the network for hosts providing Internet services for the enduser, for example public DNS, e-mail, and WWW services. Hosts connected to theservice network are accessible to any Internet service Host or the mobile network.

3D\ORDG�+DQGOLQJ�LQ�*61A distinct separation is made in the Ericsson GPRS system between the user datatraffic (IP packets) and the signalling (control and mobility management).This allowsfor software changes or restarts in the control part without affecting ongoing traffic,and vice versa.

This separation also gives the possibility to let the user data traffic and thesignalling parts utilise hardware and software, which are optimized to handle eachtype of task.

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Payload traffic is transported across the GPRS network encapsulated in anapplication-specific protocol, the GPRS Tunnelling Protocol (GTP). GTP packetsuse UDP as their transport protocol. Both signalling and payload are carried on thesame ports. The GTP packets contain a message-type field that allows the GTPprotocol to discern signalling from payload. The other protocols used in theTransmission Plane are the same as in the signalling plan, and thus described inthe signalling sections.

If multiple links are used between an SGSN and a GGSN, the network elements willsplit the load over all the available links.

A variety of tariff packages based on the delay of data packets through the SGSNsmay be offered to the home network subscribers. A variety of tariff packages forroaming subscribers are also supported. The subscriber may also be given achoice of QoS classes within a tariff package, in accordance with his/her needs.


3D\ORDG�+DQGOLQJ�LQ�WKH�6*61Mobile Station-originated PDP context activation is supported in the SGSN. Afterthe procedure has been completed, and the admission control function has beenused to negotiate the QoS with the Mobile Station, the Mobile Station will be in theREADY state and data traffic may be sent.

Within a specific time period, all packets of QoS Class 1 are delivered before anypackets of QoS Class 2, and packets from Class 2 before Class 3, etc. Traffic toand from Mobile Stations, with the same QoS delay class, can be subject toqueuing in a first-in-first-out line for that QoS class.

In overload situations, an alarm is raised, and the SGSN discards PDUs in asystematic manner in order to preserve committed QoS levels as far as possible,that is, giving priority to QoS Class 1 over Class 2, etc. The maximum time that aPDU can be buffered within the SGSN before it is discarded can be defined by acommand. The value range is 1 to 63 seconds.

3D\ORDG�+DQGOLQJ�LQ�WKH�**61SGSN-initiated PDP context activation is supported in the GGSN. While a PDPcontext (session) is active, the GGSN delivers packets to the relevant SGSN ordata network.


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Gprs 03 System

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