About GPRS Network

1. Telecommunication Basics
(GPRS Network)
Software Engineering Lab - 김영기 책임

2. Remember Again !!!
1G 2G 3G 3.5G 4G
WiMAX track 802.15e Wave1 802.15e Wave2 802.16e 802.16n
(Mobile WiMAX) (Mobile WiMAX) WiMAX R1.5 WiMAX R2.0
CDMA-1X CDMA-1X CDMA-1X
CDMA track
EV-DO r0 EV-DO rA EV-DO rB UMB
AMPS IS-95 A IS-95 B CDMA-1X
EV-DV
GSM track EDGE
LTE LTE Advanced
NMT GSM GPRS W-CDMA W-CDMA W-CDMA W-CDMA
W-CDMA
R5 R6 R7 HSPA+
R3
(HSCPA) (HSUPA) (HSPA+) Phase2
음성 통화 통화, 문자, 이메일 통화, 문자, 멀티미디어, 무선인터넷 초고속 인터넷 초고속 무선 인터넷
유,무선간 연동

3. What is GPRS ?
 GPRS (General Packet Radio Service)
 General = Not restricted to GSM use
 Packet Radio = Enable Packet mode communication over air
 Service = Not System, Existing BSS (Partially also NSS) infrastructure is used
Part of GSM phase 2+
Required many new network elements into NSS
Provides connections to external packet data networks (Internet, X.25)
 Benefits
Resources are reserved only when needed and charged accordingly
Connection setup times are reduces
Enables new services opportunities

4. GPRS Characteristics
 GPRS uses packet switched resource allocation
Resource 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, busty data transmissions
Frequent transmissions of small volumes of data
Infrequent transmission of larger volumes of data

5. GPRS Architecture
BSC
BTS PSTN
Um
MSC
Gb HLR/AuC SMS-GMSC
Gr
Gr Gd
Serving GPRS
Support Node(SGSN) Gs Gd
SS7 Coperate1
Gn Network Server
Border EIR
Intra-PLMN
Gateway (BG)
Backbone MAP-F
Inter-PLMN Gp Network
Backbone (IP Based) Gateway GPRS
Network Support Node Local area
Router
Gn (GGSN) Gi.IP Data Network
Network
Point-To-Multipoint (Internet)
Service Center
(PTM-SC) Coperate2
Server
Gi.X.25
Data Router
Network
(X.25)
Local area
Network

6. GSM to GPRS

7. Interfaces

8. Radio Interface Protocols
 2 Plane
User plane
Control Plane
 3 Layers
Layer 1 : Physical (PHY)
Layer 2 :
Data Link
Media Access Control (MAC)
Radio Link Control (RLC)
Packet Data Convergence Protocol (PDCP)
Layer 3 :
Radio Resource Control (RRC) for lu mode
Radio Resource (RR) for A/Gb mode

9. Protocol Stack
 GPRS Control Plane Protocol Stack
GMM/SM GMM/SM
LLC
LLC LLC
Relay
RLC RLC BSSGP BSSGP
MAC MAC Network Network
Service Service
GSM RF GSM RF L1bis L1bis
MS BSS (PCU) SGSN
Um Gb
GMM/SM (New in GPRS)
GPRS Mobility Management and Session Management
GPRS Attach/Detach
PDP Context 구성 및 해제
GPRS 단말 위치 갱신 – Routing Area Update/Location Update
인증
Radio Resource Assign

10. Protocol Stack
 GPRS Traffic Protocol Stack
Application
IP/X.25 IP/X.25
E
X.25 N
SNDCP SNDCP GTP GTP IP
D
LLC
LLC LLC UDP/TCP UDP/TCP
N
RLC RLC BSSGP BSSGP IP IP O
MAC MAC Frame Relay Frame Relay L2 L2 D
E
GSM RF GSM RF L1bis L1bis L1 L1
MS BSS (PCU) SGSN GGSN Gi
Um Gb Gn

11. Assignment of functions
Function MS BSS SGSN GGSN HLR
Network Access Control
Registration √
Authentication and Authorization √ √ √
Admission Control √ √ √
Message Screening √
Charging Data Collection √ √
Packet Routing & Transfer
Relay √ √ √ √
Routing √ √ √ √
Addressing Translation and Mapping √ √ √
Encapsulation √ √ √
Tunneling √ √
Compression √
Ciphering √ √ √
Mobility Management √ √ √ √
Logical Link Management
Logical Link Establishment √ √
Logical Link Maintenance √ √
Logical Link Release √ √
Radio Resource Management
Um Management √ √
Cell Selection √ √
Um-T ranx √ √
Path Management √ √

12. Gateway GPRS Support Node
 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
Converts the GPRS packets from SGSN to the PDP format
Routes mobile originated packets to right destination
Converts PDP addresses change to GSM addresses of the destination user
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
Performs authentication
Many-to-many relations among SGSNs & GGSNs

13. Serving GPRS Support Node
 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
Delivers data packets to mobile stations & vice-versa
Authenticates GPRS mobiles / Maintain user profile
Handles mobile’s registration in GPRS network
Handles mobile’s mobility management / Packet Routing, Transfer
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

14. Other Elements
Entity Functionality
 Not defined within GPRS
BG  Routes packets from SGSN/GGSN of one operator to a SGSN/GGSN of an other
(Border Gateway) operator
 Provides protection against intruders from external networks
DNS
 Translates addresses from ggsn1.oper1.fi-format to 123.45.67.98 format
(Domain Name Server)
Charging Gateway  Collects charging information from SGSNs and GGSNs
 PTM Multicast (PTM-M)
- Downlink broadcast, No subscription, No Ciphered
PTM-SC
 PTM Group call (PTM-G)
(Point to Multipoint-Service Center)
- Closed or open groups, Down/Up link, Ciphered
 Geographical area limitation

15. GPRS Backbones
 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
Connect 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

16. Physical Channels
 FDMA + TDMA
Defined by timeslot (0~7) and Radio frequency channel
 Shared Basic Physical Sub Channel
Shared among several users (up to 8)
Uplink Stage Flag (USF) controls multiple access
 Dedicated Basic Physical Sub Channel
One user support
 Packet Data Channel (PDCH)
Dedicated to packet data traffic from logical channels (Refer Next Slide)
Control
User data

17. Logical Channels
Mapped by the MAC to physical channels
Control channels for control, synchronization and signaling
Common/Dedicated/Broadcast
Packet Traffic Channels
Encoded speech/Encoded data
Packet Data Logical Channels
Traffic Channels
Control Channels
PCCCH PBCCH PDCCH PDTCH
PTCCH/U PTCCH/U PTCCH/D PACCH PBCCH PTCCH/U PTCCH/D PACCH PDTCH/H PDTCH/D
[Up] [Down] [Down] [Down] [Down] [Up/Down] [Down] [Up] [Up] [Down]
PCCCH = Packet Common Control Channel PPCH = Packet Paging Channel Up = Uplink Direction
PBCCH = Packet Broadcast Control Channel PAGCH = Packet Access Grant Channel Down = Downlink Direction
PDCCH = Packet Dedicated Control Channel PNCH = Packet Notification Channel
PDTCH = Packet Traffic Channel PACCH = Packet Associated Control Channel
PRACH = Packet Random Access Channel PTCCH = Packet Timing Advance Control
Channel

18. Control Channels
 Packet Common Control Channel (PCCCH)
Paging (PPCH)
Random Access (PRACH)
Grant (PAGCH)
Packet Notification (PNCH)
 Packet Broadcast Control Channel (PBCCH)
Frequency correction channels
Synchronization channel (MS freq. vs. BS)
Broadcast control channel for general information on the base station
Packet broadcast channels
Broadcast parameters that MS needs to access network for packet transmission

19. Packet Traffic Channels
 TCH
Traffic Channels (TCH)
Encoding of speech or user data
Channels are either predetermined multiplexed or multiplexing determined by
MAC
Full rate / Half rate
On both SBPSCH and DBPSCH
Modulation techniques
GMSK (Gaussian Minimum Shift Keying) = MSK + Gaussian filter
8-PSK

20. GPRS Mobile Types
 A/Gb mode
Class Description
 Simultaneous GPRS and conventional GSM operation
Class A
 Supports simultaneous circuit switched and GPRS data transfer
 Can be attached to both GPRS and conventional GSM services simultaneously
 Can listen circuit switched and GPRS pages (via GPRS)
Class B
 Supports either circuit switched calls or GPRS data transfer but not simultaneous communication
 Most common for handsets today
 Alternatively attached in GPRS or conventional GSM
 No simultaneous operation
Class C
 ‘GPRS only’ mobiles also possible (e.g. for telemetric applications)
 E.g. expansion cards for laptops
 lu mode
Mode Description
CS/PS  Same as Class A in A/Gb mode
PS  MS can only operate packet switched services
CS  MS can only operate circuit switched services

21. Service Types
 Point-to-Point
Internet access by user
 Point-to-Multipoint
Delivery of information (e.g. news) to multiple locations or interactive conference
applications
 IP Multimedia Subsystem
Simultaneous access to multiple different types of real-time and non-real-time
traffic
IMS provides synchronization between such components

22. Mobility Management (1/2)
 3 different state
Data can only be transmitted in the ACTIVE state
State Description
 No logical PDP context activated
 No network address (IP) registered for the terminal
IDLE
 No routing of external data possible
 Only multicast messages to all GPRS handsets available
 Only routing area is known
- RA is defined by operator  allows individual optimizations
STANDBY
 When downlink data is available, packet paging message is sent to routing area
 Upon reception, MS sends it’s cell locations to the SGSN and enters the ACTIVE state
 SGSN knows the cell of the MS
ACTIVE  PDP contexts can be activated/deactivated
 Can remain in this state even if not data is transmitted (controlled by timer)

23. Mobility Management (2/2)
 Mobility Management Message
Cell update
When MS changes the cell within a Routing Area in READY state
Routing Area update
When MS changes the cell between Routing Area 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

24. PDP Contexts
 Packet Data Protocol (PDP)
Session
Logical tunnel between MS and GGSN
Anchored GGSN for Session
 PDP activities
Activation
GGSN에게 단말의 존재를 알림
GPRS Data 수신/전송을 위해 (Session 이용을 위해), 반드시 IP 할당이 필요하며,
IP 주소 등을 할당하는 과장
Modification
Deactivation

25. PDP Context Procedures
 MS initiated
MS BSS SGSN GGSN
Activate PDP Context Request
Create PDP Context Request
Create PDP Context Response
Activate PDP Context Accept
 GGSN initiated
MS BSS SGSN GGSN
Packet from ext. nw.
PDU Notification Request
PDU Notification Response
Activate PDP Context Activation
Activate PDP Context Request
Create PDP Context Request
Create PDP Context Response
Activate PDP Context Accept

26. GPRS Call Scenario 1
 GPRS Attach
Previous
MS SGSN HLR/AuC SGSN
BSS
Packet Channel Request
Packet Uplink Assignment
RLC Block (attach request)
Attach Request
Send Authentication Info.
Packet Control
Acknowledgment Authentication and Send Authentication Info RR
Ciphering Request
Packet Downlink Assignment
RLC blocks (Authentication
and Ciphering Request)
Packet Downlink Ack
Packet Channel Request
Packet Uplink Assignment
RLC blocks (Authentication
and Ciphering Response)
Packet Uplink Ack Authentication and
Ciphering Response Update GPRS Location
Packet Control Cancel Location
Acknowledgement Cancel Location RR
Insert Subscriber Data
Insert Subscriber Data RR
Update GPRS Location RR
Attach Accept
RLC blocks (Attach accept)
Packet Downlink Ack
Packet Downlink Reponses
Packet Uplink Assignment
RLC blocks (Attach complete)
Packet Uplink Ack Attach Complete
Packet Control Acknowledgement

27. GPRS Call Scenario 2
 GPRS/GSM Attach
Previous Previous
MSC HLR MSC HLR
MS BSS SGSN /VLR /AuC /AuC
/VLR
Attach Request
Send Authentication Info
Send Authentication Info RR
Authentication and Ciphering Request
Authentication and Ciphering Response
Update GPRS Location
Cancel Location
Cancel Location RR
Insert Subscriber Data
Insert Subscriber Data RR
Update GPRS Location RR
Update Location Request
Update Location
Cancel Location
Cancel Location RR
Insert Subscriber Data
Insert Subscriber Data RR
Update Location RR
Update Location Accept
Attach Accept
Attach Complete

28. GPRS Call Scenario 3
 RA update
New Old HLR
MS SGSN SGSN GGSN
BSS
Routing Area Update Request
SGSN Context Request
SGSN Context Response
Authentication and Ciphering Authentication and Ciphering
SGSN Context Acknowledge
Forward Buffered PDUs
Update PDP Context Request
Update PDP Context Response
Update GPRS Location
Cancel Location
Insert Subscriber Data
Insert Subscriber Data RR
Update Subscriber Data RR
Routing Area Update Accept
Routing Area Update Complete

29. [별첨] GSM vs. GPRS
Email via GSM Email via GPRS
Auth. Auth.
Server Server
GSM PSTN Internet GPRS Internet
Email Email
User Modem Modem Server Virtual Authenticated Server
GPRS Path to Email
Data Tunnel Server
Initial Call Process Time (s) Initial Call Process Time (s)
GSM Call 4 GPRS Call 4
Train Model 30 Login and Authenticate 11
Login and Authenticate 11 Download mail 180
Download mail 180 Total 3min 45s
Total 3min 45s Subsequent Call
Subsequent Call Not applicable – Permanent Virtual
0
Repeat Above 3min 45s Circuit