1. Master in progettista di servizi radiomobili Web Based Overview
Physical and Logical Channels
General Packet Radio System (GPRS)
Overview
© 2 dicembre Gianni Redaelli

2. Introduction General Packet Radio Service (GRPS) today
“Packet overlay” network on top of the existing GSM (Digital) circuit switched voice-based network
TCP/IP-based: allows data packets to be conveyed across the mobile network using packet switching
“Always on” / “always connected”
After initial “log-on”, user is permanently connected to IP services
Instant access, no further log-on
Flat rate (about $30/mo in the LA area)
User perceived performance: fluctuates (as GPRS users defer to voice users) to a max of 50Kbps
Network resources only used when information ready to be exchanged – bandwidth on demand …
More efficient utilization of air-time

3. GSM - GPRS Provides high speed packet data access
uses modified GSM hardware (different phones/cards)
Several time slots can be (dynamically) allocated to transmit a block of data

4. GPRS (General Packet Radio Service) packet switching
using free slots only if data packets ready to send (e.g., 50 kbit/s using 4 slots temporarily)
standardization 1998, introduction 2001
advantage: one step towards UMTS, more flexible
disadvantage: more investment needed (new hardware)
GPRS network elements
GSN (GPRS Support Nodes): GGSN and SGSN
GGSN (Gateway GSN)
interworking unit between GPRS and PDN (Packet Data Network)
SGSN (Serving GSN)
supports the MS (location, billing, security)
GR (GPRS Register)
user addresses

5. GPRS quality of service
Universität Karlsruhe
Institut für Telematik
Mobilkommunikation
SS 1998
GPRS quality of service
Prof. Dr.-Ing. Jochen Schiller, MC SS02 4.5
Prof. Dr. Dr. h.c. G. Krüger
E. Dorner / Dr. J. Schiller

6. Examples for GPRS device classes
Receiving slots
Sending slots
Maximum number of slots 1 2 3 5 4 8 10 12
Prof. Dr.-Ing. Jochen Schiller, MC SS02 4.6

7. GPRS user data rates in kbit/s
Coding scheme
1 slot
2 slots
3 slots
4 slots
5 slots
6 slots
7 slots
8 slots
CS-1
9.05
18.2
27.15
36.2
45.25
54.3
63.35
72.4
CS-2
13.4
26.8
40.2
53.6 67
80.4
93.8
107.2
CS-3
15.6
31.2
46.8
62.4 78
93.6
109.2
124.8
CS-4
21.4
42.8
64.2
85.6
107
128.4
149.8
171.2
Prof. Dr.-Ing. Jochen Schiller, MC SS02 4.7

8. GPRS architecture and interfaces
Universität Karlsruhe
Institut für Telematik
Mobilkommunikation
SS 1998
GPRS architecture and interfaces MS
BSS
GGSN
SGSN
MSC Um
EIR
HLR/ GR
VLR
PDN Gb Gn Gi
Prof. Dr.-Ing. Jochen Schiller, MC SS02 4.8
Prof. Dr. Dr. h.c. G. Krüger
E. Dorner / Dr. J. Schiller

9. Supporting Nodes – main functions

10. GPRS protocol architecture
Universität Karlsruhe
Institut für Telematik
Mobilkommunikation
SS 1998
GPRS protocol architecture MS
BSS
SGSN
GGSN Um Gb Gn Gi
apps.
IP/X.25
IP/X.25
SNDCP
SNDCP
GTP
GTP
LLC
LLC
UDP/TCP
UDP/TCP
RLC
RLC
BSSGP
BSSGP IP IP
MAC
MAC FR FR
L1/L2
L1/L2
radio
radio
Prof. Dr.-Ing. Jochen Schiller, MC SS
Prof. Dr. Dr. h.c. G. Krüger
E. Dorner / Dr. J. Schiller

11. GSM/GPRS Architecture, simplified

12. GPRS/GSM Protocols - Overview

13. Uplink/downlink
The uplink channel is shared by a number of mobiles, and its use is allocated by a BSC (Base Station Controller)
The MS (Mobile Station) requests use of the channel in a “packet random access message”.
The BSC allocates an unused channel to the mobile and sends a “packet access grant message” in reply
The downlink is fully controlled by the serving BSC and random access is not needed

14. GPRS Mobility Tunnelling
GSM EDGE Radio Access Network (GERAN): 3rd Generation Partnership Project (3GPP)

15. SNDCP: Sub Network Dependent Convergence Protocol
SNDCP: Sub Network Dependent Convergence Protocol. This is part of layer 3 of a GPRS protocol specification.
SNDCP interfaces to the Internet Protocol at the top, and to the GPRS-specific Logical Link Control (LLC) protocol at the bottom.
Interfaces A, Gs, Gr, GC, and D are used for signalling without involving user data transmission in GPRS.
Note that the A interface is used for both signalling and voice transmission in GSM.
Interfaces Um, Gb, Gn, Gp and Gi are used for both signalling and transmission in GPRS

16. Routing in GPRS

17. Mobile Address Allocation
GGSN Address Pools
Static, dynamic allocation at GPRS packet data activation
HLR
The HLR may keep a static IP address that is fetched by the SGSN at GPRS attach
RADIUS
The GGSN may interact with an external AAA server in order to perform AAA functions as well as dynamic IP address allocation at GPRS packet data activation
DHCP server
The GGSN may interact with an external DHCP server to perform dynamic IP address allocation at GPRS packet data activation
IPv6 auto configuration
AAA server - Authentication, Authorization and Accounting Remote Authentication Dial-In User Service (RADIUS) for user authentication.

18. GPRS initial State
Dialup users of data networks that use the point-point protocol (PPP) make use of a network address identifier (NAI) for user identification. NAI is also being used for roaming and tunneling service in data networks.

19. GPRS Attach
When a MS is turned on, the first function it performs is a GPRS attach
GSM access authentication (towards Home Network, HLR (Authentication Center))
User profile is downloaded from HLR to the serving SGSN
When the GPRS attach is complete, the MS is physically connected to the visited network

20. The Packet Data Protocol (PDP) Context
Once an application wants to access the Internet for the first time, an IP address is requested from the network. This procedure is referred to as "PDP (Packet Data Protocol) context activation".
In order to be able to send and receive data, the mobile must set-up a packet data bearer(carrier/conveyor/bringer)
The PDP conveyer is associated with contexts in each nodes that data are traversing (passing thro’ , navigating)
The bearer is set-up via “PDP context activation” procedures
PDP context describes requirements of the connection to the packet networks: Type, network address, Access Point Name (APN), QoS, etc.
SGSN validates request against subscription information downloaded from HLR during GPRS Attach
Access point name sent to DNS, IP address(s) of suitable GGSNs returned
Logical connection using GPRS tunnels (GTP) between SGSN and GGSN
IP address allocated (GGSN pool, DHCP, RADIUS)

21. PDP Context Activation
GEA-GPRS Encryption Algorithms

22. GRPS Detach