GPRS: GSM Packet Radio Service

Transcription

1 GPRS: GSM Packet Radio Service GPRS Internet GPRS-1 Data Services in GSM Data transmission standardized with only 9.6 kbit/s advanced coding allows 14.4 kbit/s not enough for Internet and multimedia applications HSCSD (High-Speed Circuit Switched Data) mainly software update bundling of several time-slots to get higher AIUR (Air Interface User Rate) (e.g., 57.6 kbit/s using 4 slots, 14.4 each) advantage: ready to use, constant quality, simple disadvantage: channels blocked for voice transmission AIUR [kbit/s] TCH/F4.8 TCH/F9.6 TCH/F GPRS-2

2 GPRS: GSM Packet Radio Service Packet-switched data over GSM Interconnects to Internet Strict separation between radio subsystem and network subsystem GPRS does not mandate changes to an installed MSC base GPRS Internet GPRS-3 GPRS Channels 1 to 8 radio interface slots can be allocated per TDMA frame timeslots are shared by the active users uplink and downlink slots are allocated separately radio resources can be shared dynamically between speech and data 4 Coding Schemes CS1, CS2, CS3, CS4 giving user data rates of approx. 6, 9, 10, 14 kbps per slot, raw data rates 9.05, 13.4, 15.6, 21.4 kbps per slot GPRS-4

3 GPRS Raw Data Rates (kbps) Coding scheme 1 slot 2 slots 3 slots 4 slots 5 slots 6 slots 7 slots 8 slots CS CS CS CS GPRS-5 GPRS Traffic Supports various traffic classes, from intermittent and bursty transfers, to occasional transfer of large volumes of data Four different QoS levels Fast reservation to begin transmission of packets, typically 0.5 to 1.0 sec GPRS-6

4 GPRS MSs Three classes of MS Class A MS can operate GPRS and other GSM services simultaneously Class B MS can monitor control channels for GPRS and other GSM services simultaneously, but can operate only one set of services at a time Class C MS can operate GPRS services only GPRS-7 GPRS Architecture (GSM view) VLR BTS BSC MSC PSTN HLR GSM SGSN GTP GGSN Internet GPRS GGSN: Gateway GPRS Support Node SGSN: Service GPRS Support Node GTP: GPRS Tunneling Protocol GPRS-8

5 GPSR Architecture (data view) SGSN G n MS BSS SGSN GGSN PDN U m G b G n G i MSC HLR/ GR VLR EIR GPRS-9 Serving GPRS Support Node (SGSN) at same hierarchical level as MSC delivers packets to MS within its service area queries HLRs for profile data of GPRS subscribers detects new GPRS mobile stations in a given service area processes registration of new MSs and keeps a record of their location GPRS-10

6 Gateway GPRS Support Node (GGSN) used as interface to external packet-switched networks connected to SGSN via an IP-based GPRS backbone network maintains routing information that is necessary to tunnel the Protocol Data Units (PDUs) to the SGSNs that service particular mobile stations one or more GGSNs may support multiple SGSNs GPRS-11 GPRS Network Enhancements Base Station System (BSS): must be enhanced to recognize and send user data to the SGSN that is serving the area Home Location Register (HLR): must be enhanced to register GPRS user profiles and respond to queries originating from SGSNs regarding these profiles MSC/VLR: optionally enhanced to coordinate GPRS and non-gprs e.g. combined location updates, SGSN paging for GSM calls GPRS-12

7 GPRS Network Operations For GPRS user, network is connectionless HOWEVER, a network connection must be established for each transaction, and released once the transaction is completed GPRS-13 Network Access GPRS attach request from MS to begin a transaction GPRS detach request from MS to end a transaction Attach/detach requests are infrequent e.g. daily Location updates much more frequently GPRS-14

8 Network Access... User Registration associates the MS ID with the user address In home area, HLR is enhanced to reference GPRS data Outside home area, dynamically allocated records are references in VLRs Authentication - via GSM mobility management protocols Call Admission Control determines n/w resources for QoS GPRS-15 Routing and Data Transfer Routing is performed by the GSNs on a hop-by-hop basis, using the destination address Routing tables are maintained by the GSNs using the GTP layer Data may be Forwarded Tunneled Compressed Encrypted GPRS-16

9 Mobility Management Mobility Management used to track the MS SGSNs communicate to update the user location Logical link is established between the MS and the SGSN GPRS-17 GPRS Protocol Architecture MS U BSS m G SGSN b G GGSN n G i apps. IP/X.25 IP/X.25 SNDCP LLC SNDCP LLC GTP UDP/TCP GTP UDP/TCP RLC RLC BSSGP BSSGP IP IP MAC MAC FR FR L1/L2 L1/L2 radio radio From GPRS-18

10 GPRS Network Protocols Sub-Network Dependent Convergence Protocol (SNDCP): maps a network-level protocol, such as IP or X.25, to the underlying logical link control. provides compression, segmentation and multiplexing of network-layer messages to a single virtual connection Logical Link Control (LLC): a data link layer protocol for GPRS which functions similar to Link Access Protocol - D (LAPD). This layer assures the reliable transfer of user data across a wireless network. GPRS-19 GPRS Network Protocols... Base Station System GPRS Protocol (BSSGP): BSSGP processes routing and quality of service (QoS) information for the BSS. BSSGP uses the Frame Relay Q.922 core protocol as its transport mechanism. GPRS Tunnel Protocol (GTP): GPRS Tunnel Protocol (GTP): tunnels the protocol data units through the IP backbone by adding routing information. GTP operates on top of TCP/UDP over IP GPRS-20

11 GPRS Network Protocols... GPRS Mobility Management (GMM): handles mobility issues such as roaming, authentication, and selection of encryption algorithms. Network Service: manages the convergence sub-layer that operates between BSSGP and the Frame Relay Q.922 Core by mapping BSSGP's service requests to the appropriate Frame Relay services. GPRS-21 GPRS Network Protocols... BSSAP+: protocol that manages paging for voice and data connections and optimizes paging for mobile subscribers BSSAP+ is also responsible for location and routing updates as well as mobile station alerting GPRS-22

12 EDGE (Enhanced Data rate for GSM Evolution) Uses GSM/GPRS, but with higher-level modulation (8-PSK instead of GMSK) Choice of 9 modulation schemes Allows up to 48 kbps per timeslot, 384 kbps using 8 time slots GPRS-23 References Christian Bettstetter, Hans-Jörg Vögel, and Jörg Eberspächer, GSM Phase 2+ General Packet Radio Service GPRS: Architecture, Protocols and Air Interface, IEEE Communications Surveys Third Quarter 1999, vol. 2 no. 3 A. K. Salkintzis, A survey of Mobile Data Networks, IEEE Communications Surveys Third Quarter 1999, vol. 2 no. 3 Trillium Digital Systems, Generalised Packet Radio Service (GPRS) White Paper, Hannu H. Kari, General Packet Radio Service (GPRS), Hannu H. Kari, GPRS overview and links, GPRS links: EDGE: GPRS-24