Gprs

General Packet Radio Service(GPRS)Petteri Lappalainen23.11.1998IP Tech SchoolSeminar PresentationBased on the material by Tuomas Niemel (-97), Hannu H. Kari (-98) and ETSI

Wireless roadmap

Contents1. Introduction to GPRSWhat is GPRS ?GPRS characteristicsApplications2. GPRS architectureNetwork elements3. GPRS OperationsRadio interface resource reservationSecurity operationsConnecting to GPRSData transferMobility managementInterworking with GSM services

4. Special issuesSMSChargingO&MSupplementary servicesQoSPerformance5. GPRS business viewWhat must be investedHow to make money with GPRSUsers' benefits of GPRSBusiness model6. GPRS specifications

1. Introduction to GPRS1.1. What is GPRS ?1.2. GPRS access interfaces and reference points1.3. How is GPRS seen by external networks and GPRS users1.4. Air interface resources1.5. GPRS characteristics1.6. Applications

1.1. What is GPRS ?Part of GSM phase 2+General Packet Radio Service General -> not restricted to GSM usePacket Radio -> enables packet mode communication over air Service, not System -> existing BSS (partially also NSS) infrastructure is used Requires many new network elements into NSSProvides connections to external packet data networks (Internet, X.25)Main benefitsResources are reserved only when needed and charged accordinglyConnection setup times are reducedEnables new service opportunities

1.2. GPRS access interfaces and reference pointsGPRS provides packet switched connections from MS to packet data networks (PDN)Different operators GPRS networks are connected through Gp interface

MS

Gi reference point

R reference point

Um

Gp

TE

MT

PDNs orother networks

GPRS network 2

GPRS network 1

1.3. How is GPRS seen by external networks and GPRS users?

1.4. Air interface resourcesAn example of occupied TCH capacity by CS traffic during busy hour with n% blockingCapacity occupied by CS trafficFreeCapacityGPRS "steals" any TCHcapacity not used by CStraffic

Sheet:

East

West

North

south

Sheet:

Traffic

Traffic

North

south

1.5. GPRS characteristicsGPRS uses packet switched resource allocationresources allocated only when data is to be sent/receivedFlexible channel allocationone to eight time slotsavailable resources shared by active usersup and down link channels reserved separatelyGPRS and circuit switched GSM services can use same time slots alternativelyTraffic characteristics suitable for GPRSIntermittent, bursty data transmissionsFrequent transmissions of small volumes of dataInfrequent transmission of larger volumes of data

1.6. ApplicationsStandard data network protocol basedIP based applicationsWWW, FTP, Telnet, ...Any conventional TCP/IP based applicationsX.25 based applications Packet Assembly/Disassembly (PAD) type approachGPRS specific protocol basedPoint-to-point applicationsToll road systemPoint-to-multipoint applicationsWeather info, road traffic info, newsSMS delivery (GPRS as a bearer for SMS)

2. GPRS architecture2.1. Interfaces, reference points and network elements2.2. Functional view on GPRS2.3. Subscription of GPRS service2.4. New network elements2.4.1. GGSN2.4.2. SGSN2.4.3. Other elements2.4.4. GPRS backbones2.5. GPRS Mobile classes2.6. MS multislot capabilities

2.1. Interfaces, reference points and network elements

Gi

Gn

MAP-F

EIR

Gb

Signalling and Data Transfer Interface

Signalling Interface

Gc

MAP-C

Gp

Um

R

TE

MT

BSS

TE

PDN

GGSN

SGSN

Gr

Other PLMN

GGSN

A

Gs

MAP-D

MAP-H

Gd

HLR

MSC/VLR

SM-SC

SMS-GMSCSMS-IWMSC

2.2. Functional view on GPRS

Assignment of functions to general logical architecture

Function

MS

BSS

SGSN

GGSN

HLR

Network Access Control:

Registration

X

Authentication and Authorisation

X

X

X

Admission Control

X

X

X

Message Screening

X

Packet Terminal Adaptation

X

Charging Data Collection

X

X

Packet Routeing & Transfer:

Relay

X

X

X

X

Routeing

X

X

X

X

Address Translation and Mapping

X

X

X

Encapsulation

X

X

X

Tunnelling

X

X

Compression

X

X

Ciphering

X

X

X

Mobility Management:

X

X

X

X

Logical Link Management:

Logical Link Establishment

X

X

Logical Link Maintenance

X

X

Logical Link Release

X

X

Radio Resource Management:

Um Management

X

X

Cell Selection

X

X

Um-Tranx

X

X

Path Management

X

X

2.3. Subscription of GPRS service (1/2)Subscription storage: HLRSupports Multiple Subscriber Profile (MSP)Mobile identification: IMSIOne or several PDP addresses per userEach subscribed configuration containsPDP type (e.g., IP, X.25)PDP address (static, e.g. 128.200.192.64)Subscribed QoS (level 14)Dynamic address allowedVPLMN address allowedGGSN address Screening information (optional)

2.3. Subscription of GPRS service (2/2)Subscription is copied from HLR to SGSN during GPRS AttachPart of PDP context is copied to relevant GGSNs when a PDP address is activatedPossible PDP address allocation alternativesStatic address allocated from HPLMNDynamic address allocated from HPLMNDynamic address allocated from VPLMNHPLMN operator specifies which alternatives are possible

2.4.1. Gateway GPRS Support NodeGGSNTypically located at one of the MSC sitesOne (or few) per operatorMain functionsInterface to external data networksResembles to a data network routerForwards end user data to right SGSNRoutes mobile originated packets to right destinationFilters end user trafficCollects charging information for data network usageData packets are not sent to MS unless the user has activated the PDP address

2.4.2. Serving GPRS Support NodeSGSNFunctionally connected with BSC, physically can be at MSC or BSC siteOne for few BSCs or one (or few) per every BSC One SGSN can support BSCs of several MSC sites Main functionsAuthenticates GPRS mobilesHandles mobiles registration in GPRS networkHandles mobiles mobility management Relays MO and MT data trafficTCP/IP header compression, V.42bis data compression, error control MS- SGSN (ARQ)Collect charging information of air interface usage

2.4.3. Other elementsBG (Border Gateway)(Not defined within GPRS)Routes packets from SGSN/GGSN of one operator to a SGSN/GGSN of an other operatorProvides protection against intruders from external networksDNS (Domain Name Server) Translates addresses from ggsn1.oper1.fi -format to 123.45.67.89 format (i.e. as used in Internet)Charging GatewayCollects charging information from SGSNs and GGSNsPTM-SC (Point to Multipoint -Service Center)PTM Multicast (PTM-M): Downlink broadcast; no subscription; no cipheringPTM Group call (PTM-G): Closed or open groups; Down/up -link; cipheredGeographical area limitation

2.4.4. GPRS backbonesEnables communication between GPRS Support Nodes Based on private IP networkIPv6 is the ultimate protocolIPV4 can be used as an intermediate solutionIntra-PLMN backboneConnects GPRS Support Nodes of one operatorOperator decides the network architectureLAN, point-to-point links, ATM, ISDN, ...Inter-PLMN backboneConnects GPRS operators via BGsProvides international GPRS roamingOperators decide the backbone in the roaming agreement

2.5. GPRS mobile typesClass A:Simultaneous GPRS and conventional GSM operationSupports simultaneous circuit switched and GPRS data transferClass B:Can be attached to both GPRS and conventional GSM services simultaneouslyCan listen circuit switched and GPRS pages (via GPRS)Supports either circuit switched calls or GPRS data transfer but not simultaneous communicationClass C:Alternatively attached in GPRS or conventional GSMNo simultaneous operationGPRS only mobiles also possible (e.g. for telemetric applications)

2.6. GPRS multislot capabilities1-slot2-slot3-8 -slot

3. GPRS operations3.1 Security: Basic security rulesAuthentication, key management, ciphering3.2 GPRS attach3.3 Data transmission MO, MT, MO+MT3.4 Mobility management3.5 Interworking with GSM services

3.1. Security: Based on GSM phase 2AuthenticationSGSN uses same principle as MSC/VLR: Get triplet, send RAND to MS, wait for SRES from MS, use KcMS cant authenticate the networkKey management in MSKc generated same way from RAND using Ki as in GSMCipheringCiphering algorithm is optimized for GPRS traffic (GPRS - A5)Ciphering is done between MS and SGSNUser confidentialityIMSI is only used if a temporary identity is not availableTemporary identity (TLLI) is exchanged over ciphered link

3.2. GPRS AttachGPRS Attach function is similar to IMSI attachAuthenticate the mobileGenerate the ciphering keyEnable the cipheringAllocate temporary identity (TLLI)Copy subscriber profile from HLR to SGSNAfter GPRS attachThe location of the mobile is trackedCommunication between MS and SGSN is securedCharging information is collectedSGSN knows what the subscriber is allowed to doHLR knows the location of the MS in accuracy of SGSN

3.3. Data transfer: Basic rules (1/4)SGSN:Does not interpret user data, exceptSGSN may perform TCP/IP header compression Does not interpret source or destination addressesSends all packets to specified GGSN that handles the PDP contextGGSN: Performs optional filteringDecides where and how to route the packet

3.3. Data transfer (2/4)Mobile originated (left when MS in HPLMN, right when in VPLMN, no filtering/screening)

3.3. Data transfer (3/4)Mobile terminated (left when MS in HPLMN, right when in VPLMN, with/without filtering/screening)

3.3. Data transfer (4/4)Mobile originated and terminated (left MSs in same PLMN, right MSs in different PLMN)

3.4. Mobility management (1/3)Instead of Location Area, GPRS uses Routing Areas to group cells. RA is a subset of LA.

IDLE: MS is not known by the network (SGSN)STANDBY:MSs location is known in accuracy of Routing AreaMS can utilize DRX (to save battery)MS must inform its location after every Routing Area change (no need to inform if MS changes from one cell to another within same Routing Area)Before the network can perform MT data transfer MS must be paged within the Routing AreaMS may initiate MO data transfer at any time

3.4. Mobility management (2/3)READY:MSs location is known in accuracy of cellMS must inform its location after every cell changeMS can initiate MO data transfer at any timeSGSN does not need to page the MS before MT data transferMS listens continuously GPRS PCCCH channelDRX in READY state is optional

3.4. Mobility management (3/3)Mobility management messages:Cell update (implicit, with any message)When MS changes the cell within a Routing Area in READY stateRouting Area updateWhen MS changes the cell between two Routing Areas in READY or STANDBY stateTwo types of Routing Area Updates (from MSs point of view only one type)Intra-SGSN Routing Area UpdateInter-SGSN Routing Area UpdatePeriodic Routing Area updates are applicable

3.5. Interworking with GSM services (1/3)GPRS can interwork with GSM services through Gs-interfaceIf no Gs interface exists:Type of the location update procedure is indicated by the network in the response message to MSEffects on different MS classes if Gs does not exist:A-class mobiles must use conventional GSM services via normal GSM channelsB-class mobiles wont get simultaneous support from the network. Depending on MS design MS can try listen both paging channels simultaneously by themselvesMS does IMSI detach and use only GPRS serviceNo effect on C-class mobiles as simultaneous services are not supported

3.5. Interworking with GSM services (2/3)Combined GPRS and IMSI attachTo save radio resourcesMS indicates its request for combined attachMS sends combined GPRS and IMSI attach to SGSNSGSN may authenticate the MSSGSN informs MSC/VLR about the new MSCombined Location and Routing Area updateTo save radio resourcesMS indicates its request for combined updateThis is done when both Location Area and Routing Area changes at the same timeCombined Location and Routing Area update is not done if MS has CS connection

3.5. Interworking with GSM services (3/3)Paging CS services via GPRS networkMSC/VLR gets MT call or SMS In VLR, presence of SGSN address tells that the MS is in GPRS attached stateMSC/VLR sends the paging request to SGSN address (not to BSC)SGSN checks the location of MS (identified by IMSI)SGSN pages the MS via GPRS channels indicating CS page statusMS replies to the page using normal GSM channels

4. Special issues4.1. SMS4.2. Charging4.3. O&M4.4. Supplementary services4.5. Quality of Service4.6. Performance

4.1 Special issues: SMS supportMO and MT SMSs can be carried via GPRS networkHLR stores and returns two SS7 addresses to GMSC: SGSN address MSC/VLR addressPrimary route:Via SGSN, if availableSecondary route:Via MSC/VLR, if available and primary failed

4.2 Special issues: GPRS charging of PTP (1/2)SGSN gathers charging:usage of radio resources (packets, bits)usage of packet data protocols (time)usage of general GPRS resourcese.g. signaling messages, GPRS backboneGGSN gathers charging :based on destination/source of data packets usage of external data networks (packets, bits)usage of general GPRS resourcesOperator selects what information is used for billing

4.2 Special issues: GPRS charging of PTM (2/2)SGSN gathers usage of:usage of radio resources amount of datageographical areasnumber of repetitionusage of general GPRS resourcesPTM Service Center gathers charging :usage of general GPRS resourceusage of PTM-G groups

4.3 Special issues: Operation and managementGSM related parts can be handled with Q3GPRS backbone network is based on IP network IP network uses Simple Network Management Protocol (SNMP)

4.4 Special issues: Supplementary servicesMost of the conventional GSM supplementary services are not applicable for GPRSE.g., Call forwarding when busy, Calling line identification, Call waitingSome supplementary services may be applicableAdvice of charge (can be difficult to realize)Closed user group (can be implemented as part of external data network)GPRS has its own supplementary servicesBarring of GPRS Interworking Profile(s)

4.5 Quality of ServicePrecedence class (1,2,3)Delay class (1-4)Reliability classPeak throughput class; andMean throughput class.

4.5.1 Reliability ClassData reliability is defined in terms of the residual error rates for the following cases (see GSM02.60):Probability of data lossProbability of data delivered out of sequenceProbability of duplicate data deliveryProbability of corrupted data

4.5.2 Throughput classes

Peak Throughput Class

Peak Throughput in octets per second

1

Up to 1000 (8kbit/s).

2


3


4


5

Up to 16000 (128kbit/s).

6

Up to 32000 (256kbit/s).

7

Up to 64000 (512kbit/s).

8

Up to 128000 (1024kbit/s).

9

Up to 256000 (2048kbit/s).

Mean Throughput Class

Mean Throughput in octets per hour

1

Best effort.

2

100 (~0.22bit/s).

3

200 (~0.44bit/s).

4

500 (~1.11bit/s).

5

1000 (~2.2bit/s).

6

2000 (~4.4bit/s).

7

5000 (~11.1bit/s).

8

10000 (~22bit/s).

9

20000 (~44bit/s).

10

50000 (~111bit/s).

11

100000 (~0.22kbit/s).

12

200000 (~0.44kbit/s).

13

500000 (~1.11kbit/s).

14

1000000 (~2.2kbit/s).

15

2000000 (~4.4kbit/s).

16

5000000 (~11.1kbit/s).

17

10000000 (~22kbit/s).

18

20000000 (~44kbit/s).

19

50000000 (~111kbit/s).

4.6 Performance 1/3SGSN that handles 2 Mbps up and downlink trafficAverage packet size 500 octets (4000 bits)=> Each packet must be processed totally every 1 millisecondsIP stack in backbonepossible UDP (de)fragmentation, IP checksumsGTP header processing, finding the right contextpossible paging of the MScompression in SNDCP level, possible segmentationLLC CRC, LLC acknowledges, LLC timershandle GPRS ciphering/decipheringBSSGP protocolFrame relay protocol

Example

4.6 Performance 2/3Background tasksEnsuring the QoS for every mobileScheduling pending packets to time horizonRescheduling everything after MS has changed the cellHandling charging data collectionPerformance monitoringHandle SGSN operating system, task switching, etc.Handle diagnostics of the network elementIf SGSN handles 65 Mbps, instead of 2 Mbps?=> SGSN has just about 30 micro seconds to do all aboveExample continued

4.6 Performance 3/3Each network element has limited capacity (x packets/second)If operator needs more capacity (e.g. 50x)use 50 parallel boxesfor example,every GGSN boxes are really independent of each othereach SGSN handles its own area (list of cells)Capacity grows linearly but complexity in each box remains the sameReliability? Configuration?

Solution to the example

5. GPRS Business View 5.1. What must be invested to get GPRS up and running?5.2. How to launch GPRS with minimised incremental cost5.3. How to make money with GPRS?5.4. Users' benefits of GPRS5.5. Business model

5.1 What must be invested to get GPRS up and running?Updates on existing network elementsBTS, BSC, MSC/HLR, O&M, billing system, network planningNew network elementsTotally new network for GPRS backbone, based on IPNew packet network nodesA lot of Internet "stuff" (routers, DNS servers, firewalls, )Totally new skills needed"Internet way" of thinkingNew mobiles and new type of usersNew type of business thinking

5.2 How to launch GPRS with minimised incremental costA single SGSN/GGSN combined functional unitBTSs support basic GPRS services with software update only, BSCs need HW upgrade to add connection to SGSNUse existing paging and control channels for GPRSLimit the number of radio channels available for GPRSGs interface can be deleted => no MSC developments

5.3. How to make money with GPRS?

New usersMore subsribersNew servicesNew ways to get money from usersNew intances to pay instead of the users (e.g. advertisers)New applicationsNew ways to get money from usersMore data trafficMore data trafficSmall payments per packet, but huge number of packets

5.4. Users' benefits of GPRS

GPRS Selling arguments:Higher capacity Internet access Up to 171,2 kbps in theory, 40 kbps in practiceQuicker access to InternetNo set up time, Iternet access all the time availableLower costFlat rate or volume based billingOr no costvia anonymous access (somebody else pays the bill)

5.5. Business model1/2If the users are paying little (or nothing), how does this make profit to the operator?

Not the high cost per time but the large number of packetsSomebody else may pay the bill (e.g. anonymous access)Example business model

Sheet1

# sub-QoS levelMonthlyCost/kBVolume/MonthlyTotal annualTotal data

scribersfee (FIM)FIMday (FIM)cost/subscost (MFIM)volume (GB)

Business users100000High500.02100065078036500

"Normal" users1000000Normal250.0120313727300

Web surfers1000000Best effort5002505060091250

Computers100000High500.120110132730

Total22000001884135780

5.5. Business model 2/2Volume calculations

Sheet1

# sub-QoS levelMonthlyCost/kBVolume/MonthlyTotal annualTotal data

scribersfee (FIM)FIMday (FIM)cost/subscost (MFIM)volume (GB)

Business users100000High500.02100065078036500

"Normal" users1000000Normal250.0120313727300

Web surfers1000000Best effort5002505060091250

Computers100000High500.120110132730

Total22000001884135780

Average dataper day372GB/d

volumeper hour15.5GB/h

per sec4.3MB/s

per sec34.3Mbps

Peak hour dataper year43800GB/a

volumeper day120GB/d

per hour30GB/hall data in 4 busy hours

per sec8.3MB/s

per sec66.7Mbps

Number of time6667TSsaverage 10 kbps/TS

slots needed

Carrier833Carriers

6. GPRS StandardizationGPRS Phase 1: Release 97Basic set of GPRS functionalityOptional featuresGPRS Phase 2: GPRS for UMTSCertain issues defined in stage 1 documents are not included in the first release of the GPRS standardNew requirements have been pointed out for UMTSStandard was approved March/June 1998

6.1 List of participantsThe following companies and organizations have been participating in GPRS work in last 3 years

Some of the manufacturers, operators and others participating GPRS standardization:Alcatel, BT, CNET, CSELT, Detemobil, Eplus, Ericsson, France Telecom, IBM, Inmarsat, Lucent, Mannesmann, Motorola, NEC, Nokia, Nortel/Matra, Omnipoint, OPI, Philips, SFR, Siemens, Telecom Finland, Telia, UIC, VodafoneEU sponsored project team PT8OV to expedite GPRS standardizationSupport of PT12

6.2 GPRS Specifications

GPRS document structure

Doc.Title

01.60Requirements Specification of GPRS

Stage 1

02.60 General GPRS Overview

10.60GPRS standarsisation status and overview

Stage 2

03.60 General System Description and Newtwork Architecture

03.64Radio Architecture Description

03.61 Point to Multipoint Multicast (very draft)

03.62 Point to Multipoint Group Call (non existing)

New Stage 3

04.60Radio stage 3: RLC/MAC Radio Protocol

04.61 PTM-M Services (not existing yet)

04.62 PTM-G Services (not existing yet)

04.64LLC

04.65 SNDCP

07.60 User Interworking

08.18 BSSGP: The Gb Interface

08.16 Gb Network Service

08.14 Gb Layer 1

09.16 Gs Layer 2

09.18Gs Layer 3

09.60 GPRS Tunnelling Protocol (GTP): Gn & Gp Interface

09.61 External Interworking Networks

The packet data protocol (PDP; e.g., IP, X.25, FrameRelay) context is adata structurepresent on both theserving GPRS support node(SGSN) and thegateway GPRS support node(GGSN) which contains the subscriber's session information when the subscriber has an active session. When a mobile wants to use GPRS, it must first attach and thenactivate a PDP context. This allocates a PDP context data structure in the SGSN that the subscriber is currently visiting and the GGSN serving the subscriber's access point. The data recorded includesSubscriber'sIP addressSubscriber'sIMSISubscriber'sTunnel Endpoint ID (TEID) at the GGSNTunnel Endpoint ID (TEID) at the SGSN

Border Gateway (GPRS)A BorderGatewayfunction terminates the Gp interface to aPLMN(Public LandMobile Network). This function is typically an edge router supporting theBGP(BorderGatewayProtocol) and security protocols such asIPSec(IPSecurity).

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