1. Chapter 1
The GPRS Network
Contents:
1.1 GPRS and GSM
1. GPRS and GSM
1.2 Network elements and functions
1. The GSM PLMN
2. GPRS Network Architecture
3. Functions of GGSN
4. Functions of SGSN
5. Additional PS core entities
6. Modifications for GPRS in the BSS
7. GPRS MS
1.3 Services and Network evolution
1. GPRS Network Services
2. Network evolution into GERAN
3. GERAN reference architecture (Rel 5)
1

2. Chapter 1.1
The GPRS Network
1.1 GPRS and GSM
1. GPRS and GSM
2

3. GPRS and GSM
higher flexibility on High Speed Circuit Enhanced Enhanced
radio interface! Switched Data (HSCSD) Data rates Circuit
for GSM Switched
channel bundling Evolution Data
115.2 (EDGE) (ECSD)
up to
higher kbps
efficiency new coding schemes:
up to 14.4 kbps/TS
348
higher new up to
kbps
throughput modulation
and
GSM coding
Phase 2+ General Packet Radio schemes Enhanced
Service (GPRS) General
Packet
channel bundling 171.2
up to Radio
kbps
Service
new coding schemes: (EGPRS)
up to 21.4 kbps/TS
+ capacity on demand
476
+ multiplexing of subscribers up to
kbps
on one phy. channel 3

4. The GSM PLMN
The GSM Public Land Mobile Networks (PLMN) consists out of a Network Switching Subsystem (NSS) and a
Base Station System (BSS).
NSS
A E
BTS TC MSC/VLR GMSC
Ater PSTN
C Ext
BSC
F D
MS BTS Abis
BSS (H)
EIR HLR AuC SCP CSE SMSC
SS7
Main element in the NSS is the Mobile Switching Center (MSC) which contains the Visitor Location Register (VLR).
The MSC represents the edge towards the BSS and on the other side the Gateway MSC (GMSC), the connection
point to all external networks, like the Public Switched Telephone Network or ISDN. GSM is a circuit switched
network, there are physical links to transport control information (signalling) and user data. The signalling links are
SS7 based and circuits (voice channels) are switched through the MSC (or GMSC).
HLR Home Location Register, a main database that contains data for each subscriber like IMSI, MSISDN,
subscribed services, access rights etc.
EIR Equipment Identity Register, if supported, may be integrated in the HLR.
AuC Authentication Center, provides Authentication Triplets for every subscriber to perform authentication
and ciphering (performed by MSC/VLR).
SCP Service Control Point, a database for Intelligent Network services.
CSE CAMEL Service Entity, a database for PLMN specific Intelligent Services, e.g. charging of roaming
subscribers.
SMSC Short Message Service Center, used for transfer of short messages.
5

5. GPRS Network Architecture
GERAN NSS
BSS
E Ext
BTS A MSC/VLR GMSC
Ater TC PSTN
BSC
BTS PCU
Abis
F D C
BTS
Home Subscriber
Gs (H)
EIR HLR AuC Server (HSS)
MS Rel 5
BSS
BTS
TC Gf Gc
Gr
GPRS PS Core Network
BTS
Abis BSC Gb Gn IPvX
PCU SGSN backbone
GGSN ISP
BTS Gi
6

6. Functions of GGSN
GMSC
Gateway GGSN Gateway GPRS Support Node
Mobile services
Switching Centre
• signalling evaluation (SS7) • signalling evaluation (IP header)
• switching (cs traffic) • routing and tunneling of packet data (ps traffic)
• operational tasks incl. • operational tasks incl.
- collection of traffic statistics - collection of traffic statistics
- alarms - alarms
- generation of charging records - generation of charging records
• interrogation of HLR • interrogation of HLR
• often interfacing external networks, such as • interfaces external IP networks
PSTN, ISDN
• Interfaces internal IP network (IP BB)
• Allocates dynamic or static IP addresses to mobiles
either by itself or with the help of a DHCP or a
RADIUS server
Gateway GPRS Support Node is an IP router
that provides access to various PDP networks,
7
e.g. the Internet

7. Functions of SGSN
(V)MSC/VLR SGSN
Visited MSC/ Serving
Visitor Location GPRS Support Node
Register
• signalling evaluation (SS7) • signalling evaluation (IP header)
• switching (cs traffic) • routing (ps traffic)
• operational tasks incl. • operational tasks incl.
- collection of traffic statistics - collection of traffic statistics
- alarms - alarms
- generation of charging records - generation of charging records
• Mobility Management, incl. authentication, • GMM (GPRS Mobility Management), incl.
authorisation, location area updates authentication, authorisation, routing area
updates
• Connection Management,
incl. call control, SMS, supplementary • SM (Session Management),
services incl. PDP (Packet Data Protocol) context
management and SMS
• Paging (CS)
• Paging (PS –and CS as option)
• Protocol conversion between IP backbone and BSS
protocols e.g. data compression for IP-Header and
IP payload (V.42 bis, RFC 1144).
8

8. Additional PS core entities
Domain Name Server:
DNS used to convert IP names into IP
GPRS PS Core Network addresses or vice versa.
Border Gateways: BGs are to interconnect operators'
GPRS backbone networks via a secure
SGSN IPvX
GGSN BG connection to support roaming
backbone
Charging Gateway:
DNS LIG BG CG GPRS charging data records (CDR) are generated by
SGSNs and GGSNs, and sent to the CG via interface
Billing Ga.
Inter-PLMN
LEA Network Centre The Charging Gateway
•collects all this data together
CG •processes it
•passes it to the Billing System
Lawful Interception Gateway:
•Lawful interception is an action based on the law, which is performed by the GPRS network
•It provides information for a Law Enforcement Agency (LEA) about some pre-defined target subscriber
•Information could include
•data sent and received by the interception target
•location information
LIG •subscriber information
•etc.
9

9. Modifications for GPRS in the BSS
BTS BSC site SGSN site
CCU
Abis Gb
PCU
CCU
Ater
PCU The PCU (Packet Control Unit):
Performs radio specific functions (Radio Resource Management)
• Manages sub-multiplexing of multiple MS on one physical channel
• Decides which radio resources are dynamically allocated to packet switched or circuit switched use
• Is responsible for packet segmentation and re-assembly
• Guarantees reliable link to MS
• Terminates Gb interface
In most vendors implementation the PCU is a part of the BSC, in principle it could be as well a standalone
module or integrated in the BTS.
Channel Codec Unit:
CCU BTS SW upgrade for new Coding Scheme (CS 1-4 or CS 1+2).
10

10. GPRS MS
simultaneous
• attach
Simultaneous
CS and PS
• activation class
• attach class • monitor
• invocation A
• activation
• monitor B • traffic class
of GSM and GPRS pure GPRS or
no simultaneous alternative use of C
traffic GSM and GPRS only
A class A MS may be attached to the CS and PS core simultaneously. While the MS is in packet transfer mode
and there is an incoming call the MS can continue its packet session while making the call and enters the Dual
Transfer Mode (DTM). DTM requires additionally support by networks (BSS).
A class B MS may be attached to the CS and PS core simultaneously. While the MS is in packet transfer mode
and there is an incoming call the MS can take the call, the packet transfer has to be suspended and resumed
after the call is finished.
A class C MS may be attached to the CS or PS core. While the MS is in packet transfer mode there can be no
incoming call. Usually these MSs are PCMCIA cards.
11

11. GPRS Network Services
The objective of this training are the (E)GPRS signalling protocols, and to show, how a user data packet is
transmitted through the GPRS network. The user data transmission can be seen from two points of view:
• end user's point of view:
The subscriber wants to exchange user data packets between the mobile terminal (MT) attached to his MS (or
internal) and an application server, located in a PDN.
Application
Server
user's point of view
GPRS
ISP ISP
GGSN Inter-
MS
net
Router
• operator's point of view: Router
The operator is especially responsible to transmit the user data from one access point of the PLMN to another.
The access points to and from the PLMN are the MS and the GGSN.
The operator is required to offer a certain Quality
of Service (QoS) in order to enable new services.
Services are categorized into (Rel 99)
Interactive class
BSS
NSS ISP Background class
IP Streaming class
PCU SGSN backbone GGSN
13
Conversational class

12. Network evolutions into GERAN
2G Network Support of Interactive and Support of streaming (Rel 4) and
Background PS Services (Rel 99) conversational PS Services (Rel 5)
GERAN (GSM/EDGE Radio Access Network)
HSCSD ECSD
In order to deliver the required
QoS for a certain service the
GSM existing networks are enhanced.
ETSI standardized the GSM radio
EGPRS interface and defined GSM, GPRS,
GPRS
classic EDGE access to PS Core Network
(Rel 97, 98 ,99). Due to aspects of
harmonization and interworking
with 3G the specifications has
been moved to 3GPP. Rel 99 has
TDMA/136 + been adopted by 3GPP. Since then
the GSM access network is
referred to as GERAN. The
evolution of GERAN is done in Rel
TDMA/136HS EGPRS 4, 5, 6,... (along with the evolution
TDMA/136
Outdoor compact of CN entities).
Currently Rel 4, 5 and 6 features
are adopted in order to fullfil the
TDMA/136HS requirements for new services
indoor
14

13. GERAN Reference architecture (Rel 5)
Enhanced -Interactive,
compared to Rel 99 GERAN
-Background,
(Support of Realtime BSS
-Streaming
Packet services)
PS Services
Iur-g
Um A
MS BTS
To 2G CN (A/Gb mode)
BSC Gb required for Rel 4 or older MSs
MS BTS
IuCS
To 3G CN (Iu mode)
Iur-g (cancelled) BSS IuPS
-Interface carries only
control signalling-no user Iur-g -Interactive,
data -Background,
-improved interworking UTRAN IuCS -Streaming
To
GERAN-UTRAN RNC 3G -Conversational
IuPS
-Radio specific CN PS Services
procedures handled
completely inside RAN GSM/UMTS
Core Network
A MS may operate in Gb mode (class A, B or C MS) or Iu mode. For Iu
mode the MS may operate
• CS/PS mode: correspondends to Class A in A/Gb mode
• PS mode: MS can only operate packet switched services
• CS mode: MS can only operate circuit switched services 15