Master in progettista di servizi radiomobili Web Based Overview Physical and Logical Channels General Packet Radio System (GPRS) Overview © 2 dicembre 2000 - Gianni Redaelli

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

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

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

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

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, http://www.jochenschiller.de/ MC SS02 4.6

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, http://www.jochenschiller.de/ MC SS02 4.7

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, http://www.jochenschiller.de/ MC SS02 4.8 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller

Supporting Nodes – main functions

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, http://www.jochenschiller.de/ MC SS02 4.10 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller

GSM/GPRS Architecture, simplified

GPRS/GSM Protocols - Overview

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

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

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

Routing in GPRS

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.

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.

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

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)

PDP Context Activation GEA-GPRS Encryption Algorithms

GRPS Detach