IP TECH SCHOOL seminar / 23.11.1998 / slide 1 NOKIA TELECOMMUNICATIONS General Packet Radio Service...

IP TECH SCHOOL seminar / 23.11.1998 / slide 1

NOKIA TELECOMMUNICATIONS

General Packet Radio Service(GPRS)

Petteri Lappalainen

23.11.1998

IP Tech School

Seminar PresentationBased on the material by

Tuomas Niemelä (-97), Hannu H. Kari (-98) and ETSI



Wireless roadmap



Contents1. Introduction to GPRS

• What is GPRS ?

• GPRS characteristics

• Applications

2. GPRS architecture

• Network elements

3. GPRS Operations

• Radio interface resource reservation

• Security operations

• Connecting to GPRS

• Data transfer

• Mobility management

• Interworking with GSM services

4. Special issues

• SMS

• Charging

• O&M

• Supplementary services

• QoS

• Performance

5. GPRS business view• What must be invested…• How to make money with

GPRS• Users' benefits of GPRS• Business model

6. GPRS specifications



1. Introduction to GPRS

1.1. What is GPRS ?

1.2. GPRS access interfaces and reference points

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

1.4. Air interface resources

1.5. GPRS characteristics

1.6. Applications



1.1. What is GPRS ?

• Part of GSM phase 2+

• General Packet Radio Service • General -> not restricted to GSM use (DECT ?, 3rd

generation systems ?)

• Packet Radio -> enables packet mode communication over air

• Service, not System -> existing BSS (partially also NSS) infrastructure is used

• Requires many new network elements into NSS

• Provides connections to external packet data networks (Internet, X.25)

• Main benefits• Resources are reserved only when needed and charged

accordingly

• Connection setup times are reduced

• Enables new service opportunities



1.2. GPRS access interfaces and reference points

Gi reference point

GPRS network 1

GPRS network 2

PDNs orother networksTE MT

Gp

UmR reference point

MS

• GPRS provides packet switched connections from MS to packet data networks (PDN)

• Different operator’s GPRS networks are connected through Gp interface



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

L ocal areanetwork

R outerC orpor ate 2

L ocal areanetwork

R outer

C orporate 1P ac ketnetw o rkDatanetwork(Internet)

G P R S S UB NE TW O R K

S UB NE TW O R K155.222.33.XXX

S UB NE T W O R K131.44.15.XXX

S UB NE T W O R K191.200.44.XXX

HO S T191.200.44.21

HO S T131.44.15.3

HO S T155.222.33.55

"R outer"



1.4. Air interface resources

0

2

4

6

8

10

12

14

1:00 PM 1:15 PM 1:30 PM 1:45 PM

TCH

An example of occupied TCH capacity by CS traffic during busy hour with n% blocking

0

2

4

6

8

10

12

14

3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00

TCH

Capacity occupied by CS traffic

FreeCapacityGPRS "steals" any TCH

capacity not used by CStraffic



1.5. GPRS characteristics

GPRS uses packet switched resource allocation

• resources allocated only when data is to be sent/received

Flexible channel allocation

• one to eight time slots• available resources shared by active users• up and down link channels reserved separately• GPRS and circuit switched GSM services can use

same time slots alternatively

Traffic characteristics suitable for GPRS

• Intermittent, bursty data transmissions• Frequent transmissions of small volumes of data• Infrequent transmission of larger volumes of data



1.6. Applications

• Standard data network protocol based• IP based applications

– WWW, FTP, Telnet, ...

– Any conventional TCP/IP based applications

• X.25 based applications

– Packet Assembly/Disassembly (PAD) type approach

• GPRS specific protocol based• Point-to-point applications

– Toll road system, UIC train control system

• Point-to-multipoint applications

– Weather info, road traffic info, news, fleet management

• SMS delivery (GPRS as a bearer for SMS)



2. GPRS architecture

2.1. Interfaces, reference points and network elements

2.2. Functional view on GPRS

2.3. Subscription of GPRS service

2.4. New network elements

2.4.1. GGSN

2.4.2. SGSN

2.4.3. Other elements

2.4.4. GPRS backbones

2.5. GPRS Mobile classes

2.6. MS multislot capabilities



2.1. Interfaces, reference points and network elements

MAP-F

Gi

Gn

Gb

GcMAP-D

MAP-CMAP-H

Gp

Gs

Signalling and Data Transfer Interface

Signalling Interface

MSC/VLR

TE MT BSS TEPDN

R Um

GrA

HLR

Other PLMN

SGSN

GGSN

Gd

SM-SCSMS-GMSC

SMS-IWMSC

GGSN

EIR



2.2. Functional view on GPRS

Local areanetwork

Server

Router

Local areanetwork

Server

Router

Corporate 2

Corporate 1

Intra-PLMNbackbonenetwork(IP based)

Serving GPRSSupport Node(SGSN)

Point-To-MultipointServiceCenter (PTM SC)

Gateway GPRSSupport Node(GGSN)

GPRS INFRASTRUCTURE

HLR/AuC

MSC

BSCBTS PacketnetworkPSTN

PacketnetworkSS7Network

Packetnetwork

Datanetwork(Internet)

Packetnetwork

Datanetwork(X.25)

Packetnetwork

Inter-PLMNBackbonenetwork

Border Gateway (BG)

Gb

Gr Gd

Gi.IP

Gi.X.25

Firewall

Firewall

Firewall

UmR/S

SMS-GMSC

Gr Gd

Gs

Gs

Gp

Gn

Gn

EIR

MAP-F



Function MS BSS SGSN GGSN HLR

Network Access Control:Registration XAuthentication and Authorisation X X XAdmission Control X X XMessage Screening XPacket Terminal Adaptation XCharging Data Collection X X

Packet Routeing & Transfer:Relay X X X XRouteing X X X XAddress Translation and Mapping X X XEncapsulation X X XTunnelling X XCompression X XCiphering X X X

Mobility Management: X X X X

Logical Link Management:Logical Link Establishment X XLogical Link Maintenance X XLogical Link Release X X

Radio Resource Management:Um Management X XCell Selection X XUm-Tranx X XPath Management X X

Assignment of functions to general logical architecture



2.3. Subscription of GPRS service (1/2)

Subscription storage: HLR

Supports Multiple Subscriber Profile (MSP)

Mobile identification: IMSI

One or several PDP addresses per user

• Each subscribed configuration contains• PDP type (e.g., IP, X.25)

• PDP address (static, e.g. 128.200.192.64)

• Subscribed QoS (level 1…4)

• Dynamic address allowed

• VPLMN address allowed

• GGSN address

• Screening information (optional)



2.3. Subscription of GPRS service (2/2)

Subscription is copied from HLR to SGSN during GPRS Attach

Part of PDP context is copied to relevant GGSNs when a PDP address is activated

Possible PDP address allocation alternatives

• Static address allocated from HPLMN• Dynamic address allocated from HPLMN• Dynamic address allocated from VPLMN

HPLMN operator specifies which alternatives are possible



2.4.1. Gateway GPRS Support Node

GGSN

• Typically located at one of the MSC sites

• One (or few) per operator

• Main functions

• Interface to external data networks

• Resembles to a data network router

• Forwards end user data to right SGSN

• Routes mobile originated packets to right destination

• Filters end user traffic

• Collects charging information for data network usage

• Data packets are not sent to MS unless the user has activated the PDP address



2.4.2. Serving GPRS Support Node

SGSN

• Functionally connected with BSC, physically can be at MSC or BSC site

• One for few BSCs or one (or few) per every BSC

• One SGSN can support BSCs of several MSC sites

• Main functions

• Authenticates GPRS mobiles

• Handles mobile’s registration in GPRS network

• Handles mobile’s mobility management

• Relays MO and MT data traffic

• TCP/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 operator

• Provides protection against intruders from external networks

DNS (Domain Name Server)

• Translates addresses from ggsn1.oper1.fi -format to 123.45.67.89 format (i.e. as used in Internet)

Charging Gateway

• Collects charging information from SGSNs and GGSNs

PTM-SC (Point to Multipoint -Service Center)

• PTM Multicast (PTM-M): Downlink broadcast; no subscription; no ciphering

• PTM Group call (PTM-G): Closed or open groups; Down/up -link; ciphered

• Geographical area limitation



2.4.4. GPRS backbones

Enables communication between GPRS Support Nodes

Based on private IP network

• IPv6 is the ultimate protocol• IPV4 can be used as an intermediate solution

Intra-PLMN backbone

• Connects GPRS Support Nodes of one operator• Operator decides the network architecture

• LAN, point-to-point links, ATM, ISDN, ...

Inter-PLMN backbone

• Connects GPRS operators via BGs• Provides international GPRS roaming• Operators decide the backbone in the roaming agreement



2.5. GPRS mobile types

Class A:

• Simultaneous GPRS and conventional GSM operation• Supports simultaneous circuit switched and GPRS data transfer

Class B:

• Can be attached to both GPRS and conventional GSM services simultaneously

• Can listen circuit switched and GPRS pages (via GPRS)• Supports either circuit switched calls or GPRS data transfer but

not simultaneous communication

Class C:

• Alternatively attached in GPRS or conventional GSM• No simultaneous operation• ‘GPRS only’ mobiles also possible (e.g. for telemetric

applications)



2.6. GPRS multislot capabilities

0MS RX

MS TX

Monitor

1 2 3 4 5 6 7 0 1

0 2 3 4 5 65 6 7 1

MS RX

MS TX

Monitor

0 1 2 3 4 5 6 7 0 1

0 2 3 4 5 65 6 7 1

MS RX

MS TX

Monitor

0 1 2 3 4 5 6 7 0 1

0 2 3 4 5 65 6 7 1

3 slots: 4th slot: 5th slot:

1-slot

2-slot

3-8 -slot



3. GPRS operations

3.1 Security: Basic security rules

• Authentication, key management, ciphering

3.2 GPRS attach

3.3 Data transmission

• MO, MT, MO+MT

3.4 Mobility management

3.5 Interworking with GSM services



3.1. Security: Based on GSM phase 2

Authentication

• SGSN uses same principle as MSC/VLR:• Get triplet, send RAND to MS, wait for SRES from MS, use Kc

• MS can’t authenticate the network

Key management in MS

• Kc generated same way from RAND using Ki as in GSM

Ciphering

• Ciphering algorithm is optimized for GPRS traffic (‘GPRS - A5’)• Ciphering is done between MS and SGSN

User confidentiality

• IMSI is only used if a temporary identity is not available• Temporary identity (TLLI) is exchanged over ciphered link



3.2. GPRS Attach

GPRS Attach function is similar to IMSI attach

• Authenticate the mobile• Generate the ciphering key• Enable the ciphering• Allocate temporary identity (TLLI)• Copy subscriber profile from HLR to SGSN

After GPRS attach

• The location of the mobile is tracked• Communication between MS and SGSN is secured• Charging information is collected• SGSN knows what the subscriber is allowed to do• HLR knows the location of the MS in accuracy of SGSN



3.3. Data transfer: Basic rules (1/4)

• SGSN:

• Does not interpret user data, except• SGSN may perform TCP/IP header compression

• Does not interpret source or destination addresses• Sends all packets to specified GGSN that handles

the PDP context

• GGSN:

• Performs optional filtering• Decides 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)

Local areanetwork

Server

Router

SGSN

GGSN

BG

BSCBTS


SGSN

GGSN

BG

BSC BTS


Packetnetwork

Inter-PLMNbackbonenetwork

Packetnetwork


Corporate

HPLMN VPLMN




Mobile terminated (left when MS in HPLMN, right when in VPLMN, with/without filtering/screening)

Local areanetwork

Server

Router

SGSN

GGSN

BG

BSCBTS


SGSN

GGSN

BG

BSC BTS


Packetnetwork


Packetnetwork


Corporate

HPLMN VPLMN




Mobile originated and terminated (left MSs in same PLMN, right MSs in different PLMN)

Local areanetwork

Server

Router

SGSN

GGSN

BG

BSCBTS


SGSN

GGSN

BG

BSC BTS


Packetnetwork


Packetnetwork


Corporate

HPLMN VPLMN

BSCBTS

SGSN



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:

• MS’s location is known in accuracy of Routing Area• MS 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 Area

• MS may initiate MO data transfer at any time




• READY:

• MS’s location is known in accuracy of cell• MS must inform its location after every cell change• MS can initiate MO data transfer at any time• SGSN does not need to page the MS before MT

data transfer• MS listens continuously GPRS PCCCH channel

• DRX in READY state is optional




Mobility management messages:

• Cell update (implicit, with any message)• When MS changes the cell within a Routing Area in

READY state

• Routing Area update• When MS changes the cell between two Routing

Areas in READY or STANDBY state

• Two types of Routing Area Updates (from MS’s point of view only one type)

– Intra-SGSN Routing Area Update

– Inter-SGSN Routing Area Update

• Periodic Routing Area updates are applicable



3.5. Interworking with GSM services (1/3)

• GPRS can interwork with GSM services through Gs-interface

• If no Gs interface exists:

• Type of the location update procedure is indicated by the network in the response message to MS

• Effects on different MS classes if Gs does not exist:

• A-class mobiles must use conventional GSM services via normal GSM channels

• B-class mobiles won’t get simultaneous support from the network. Depending on MS design

• MS can try listen both paging channels simultaneously by themselves

• MS does IMSI detach and use only GPRS service

• No effect on C-class mobiles as simultaneous services are not supported




Combined GPRS and IMSI attach

• To save radio resources• MS indicates its request for combined attach

• MS sends combined GPRS and IMSI attach to SGSN

• SGSN may authenticate the MS

• SGSN informs MSC/VLR about the new MS

Combined Location and Routing Area update

• To save radio resources• MS indicates its request for combined update• This is done when both Location Area and Routing Area

changes at the same time• Combined Location and Routing Area update is not done if

MS has CS connection




Paging CS services via GPRS network

• MSC/VLR gets MT call or SMS

• In VLR, presence of SGSN address tells that the MS is in GPRS attached state

• MSC/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” status

• MS replies to the page using normal GSM channels



4. Special issues

4.1. SMS

4.2. Charging

4.3. O&M

4.4. Supplementary services

4.5. Quality of Service

4.6. Performance



4.1 Special issues: SMS support

MO and MT SMSs can be carried via GPRS network

HLR stores and returns two SS7 addresses to GMSC:

• SGSN address • MSC/VLR address

Primary route:

• Via SGSN, if available

Secondary 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 resources

• e.g. signaling messages, GPRS backbone

GGSN gathers charging :

• based on destination/source of data packets • usage of external data networks (packets, bits)• usage of general GPRS resources

Operator 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 data

• geographical areas

• number of repetition

• usage of general GPRS resources

PTM Service Center gathers charging :

• usage of general GPRS resource• usage of PTM-G groups



4.3 Special issues: Operation and management

GSM related parts can be handled with Q3

GPRS backbone network is based on IP network

• IP network uses Simple Network Management Protocol (SNMP)

S G S N

G G S N

IP R O UTE R

B S CB TS

G P R Sbackbonenetwork(IP based)

P ac ketnetwork

Inter-operatorbackbonenetwork

P acketnetwork


G P R S /G S M O MC

O perator A's G P R S bac kbone management

Inter-operator's G P R S bac kbone management

Data network management

O perator B 's G P R S bac kbone management



4.4 Special issues: Supplementary services

Most of the conventional GSM supplementary services are not applicable for GPRS

• E.g., Call forwarding when busy, Calling line identification, Call waiting

Some supplementary services may be applicable

• Advice of charge (can be difficult to realize)• Closed user group (can be implemented as part of

external data network)

GPRS has its own supplementary services

• Barring of GPRS Interworking Profile(s)



4.5 Quality of Service

• Precedence class (1,2,3)

• Delay class (1-4)

• Reliability class

• Peak throughput class; and

• Mean throughput class.



4.5.1 Reliability Class

• Data reliability is defined in terms of the residual error rates for the following cases (see GSM 02.60):

• Probability of data loss

• Probability of data delivered out of sequence

• Probability of duplicate data delivery

• Probability of corrupted data



4.5.2 Throughput classesPeak Throughput Class Peak Throughput in octets per second

1 Up to 1 000 (8 kbit/s).2 Up to 2 000 (16 kbit/s).3 Up to 4 000 (32 kbit/s).4 Up to 8 000 (64 kbit/s).5 Up to 16 000 (128 kbit/s).6 Up to 32 000 (256 kbit/s).7 Up to 64 000 (512 kbit/s).8 Up to 128 000 (1 024 kbit/s).9 Up to 256 000 (2 048 kbit/s).

Mean Throughput Class Mean Throughput in octets per hour

1 Best effort.2 100 (~0.22 bit/s).3 200 (~0.44 bit/s).4 500 (~1.11 bit/s).5 1 000 (~2.2 bit/s).6 2 000 (~4.4 bit/s).7 5 000 (~11.1 bit/s).8 10 000 (~22 bit/s).9 20 000 (~44 bit/s).

10 50 000 (~111 bit/s).11 100 000 (~0.22 kbit/s).12 200 000 (~0.44 kbit/s).13 500 000 (~1.11 kbit/s).14 1 000 000 (~2.2 kbit/s).15 2 000 000 (~4.4 kbit/s).16 5 000 000 (~11.1 kbit/s).17 10 000 000 (~22 kbit/s).18 20 000 000 (~44 kbit/s).19 50 000 000 (~111 kbit/s).



4.6 Performance 1/3

• SGSN that handles 2 Mbps up and downlink traffic– Average packet size 500 octets (4000 bits)

– => Each packet must be processed totally every 1 milliseconds

• IP stack in backbone

• possible UDP (de)fragmentation, IP checksums

• GTP header processing, finding the right context

• possible paging of the MS

• compression in SNDCP level, possible segmentation

• LLC CRC, LLC acknowledges, LLC timers

• handle GPRS ciphering/deciphering

• BSSGP protocol

• Frame relay protocol

Example



4.6 Performance 2/3

• Background tasks– Ensuring the QoS for every mobile

• Scheduling pending packets to time horizon

• Rescheduling everything after MS has changed the cell

– Handling charging data collection

– Performance monitoring

– Handle SGSN operating system, task switching, etc.

– Handle diagnostics of the network element

• If SGSN handles 65 Mbps, instead of 2 Mbps?

– => SGSN has just about 30 micro seconds to do all above

Example continued



4.6 Performance 3/3

• Each network element has limited capacity (x packets/second)

• If operator needs more capacity (e.g. 50x)– use 50 parallel boxes

– for example,

• every GGSN boxes are really independent of each other

• each SGSN handles its own area (list of cells)

• Capacity grows linearly but complexity in each box remains the same

• Reliability? 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 cost

5.3. How to make money with GPRS?

5.4. Users' benefits of GPRS

5.5. Business model



5.1 What must be invested to get GPRS up and running?

• Updates on existing network elements– BTS, BSC, MSC/HLR, O&M, billing system, network

planning

• New network elements– Totally new network for GPRS backbone, based on IP

– New packet network nodes

– A lot of Internet "stuff" (routers, DNS servers, firewalls, …)

• Totally new skills needed– "Internet way" of thinking

• New mobiles and new type of users

• New type of business thinking



5.2 How to launch GPRS with minimised incremental cost

• A single SGSN/GGSN combined functional unit

• BTSs support basic GPRS services with software update only, BSCs need HW upgrade to add connection to SGSN

• Use existing paging and control channels for GPRS

• Limit the number of radio channels available for GPRS

• Gs interface can be deleted => no MSC developments



5.3. How to make money with GPRS?

• New users– More subsribers

• New services– New ways to get money from users

– New intances to pay instead of the users (e.g. advertisers)

• New applications– New ways to get money from users

• More data traffic– More data traffic

– Small 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 practice

– Quicker access to Internet• No set up time, Iternet access all the time available

– Lower cost• Flat rate or volume based billing

– Or no cost• via anonymous access (somebody else pays the bill)



5.5. Business model1/2

• If 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 packets

– Somebody else may pay the bill (e.g. anonymous access)

# sub- QoS level Monthly Cost/kB Volume/ Monthly Total annual Total datascribers fee (FIM) FIM day (FIM) cost/subs cost (MFIM) volume (GB)

Business users 100000 High 50 0,02 1000 650 780 36500"Normal" users 1000000 Normal 25 0,01 20 31 372 7300Web surfers 1000000 Best effort 50 0 250 50 600 91250Computers 100000 High 50 0,1 20 110 132 730Total 2200000 1884 135780

Example business model



5.5. Business model 2/2

Average data per day 372 GB/dvolume per hour 15,5 GB/h

per sec 4,3 MB/sper sec 34,3 Mbps

Peak hour data per year 43800 GB/avolume per day 120 GB/d

per hour 30 GB/h all data in 4 busy hoursper sec 8,3 MB/sper sec 66,7 Mbps

Number of time 6667 TSs average 10 kbps/TSslots needed

Carrier 833 Carriers

Volume calculations



6. GPRS Standardization

GPRS Phase 1: Release 97

• Basic set of GPRS functionality• Optional features

GPRS Phase 2: GPRS for UMTS

• Certain issues defined in stage 1 documents are not included in the first release of the GPRS standard

• New requirements have been pointed out for UMTS

Standard was approved March/June 1998



6.1 List of participants

The 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, Vodafone

EU sponsored project team PT8OV to expedite GPRS standardization

Support of PT12



6.2 GPRS SpecificationsGPRS document structure

Doc. Title

01.60 Requirements Specification of GPRS

Stage 102.60 General GPRS Overview10.60 GPRS standarsisation status and overview

Stage 203.60 General System Description and Newtwork Architecture03.64 Radio Architecture Description03.61 Point to Multipoint – Multicast (very draft)03.62 Point to Multipoint – Group Call (non existing)

New Stage 304.60 Radio stage 3: RLC/MAC Radio Protocol04.61 PTM-M Services (not existing yet)04.62 PTM-G Services (not existing yet)04.64 LLC04.65 SNDCP07.60 User Interworking08.18 BSSGP: The Gb Interface08.16 Gb Network Service08.14 Gb Layer 109.16 Gs Layer 209.18 Gs Layer 309.60 GPRS Tunnelling Protocol (GTP): Gn & Gp Interface09.61 External Interworking Networks

IP TECH SCHOOL seminar / 23.11.1998 / slide 1 NOKIA TELECOMMUNICATIONS General Packet Radio Service...

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