1 General Packet Radio Service (GPRS) Adapted from a presentation by Miao Lu Nancy Samaan SITE, Ottawa University

2Introduction  GPRS (General Packet Radio Service) Reuse the existing GSM infrastructure Introduce packet-switched routing functionality Better data transfer rates Low cost and connectivity-oriented Migration Path to 3G Networks

3 Packet-switched technique vs. circuit-switched  In circuit-switching, resources (e.g. a channel) are allocated to user for duration of connection Inefficient use of resources User pays for the whole connection High QoS: channel maintains real-time connection  In packet-switching, resources are allocated to user only for the time it takes to send each packet A channel can serve many users User pays by the packet Ideal for bursty data connections

4Comparison  Packet-switched High bit rates (up to 170kbit/s) Shared bandwidth Variable access times Friendly bill (based on volume) Robust application support Frequent transmission of small volumes Infrequent transmission of small or medium volumes  Circuit-switched Low bit rates (14.4kbit/s) Reserved bandwidth Fixed access time Unfriendly bill (based on duration) Limited application support Large volumes

5 GPRS Architecture

6 GPRS Architecture - Components  New components introduced for GPRS services: SGSN (Serving GPRS Support Node) GGSN (Gateway GPRS Support Node) IP-based backbone network  Old components in GSM upgraded for GPRS services: HLR MSC/VLR Mobile Station

7 GPRS Architecture SGSN – Serving GPRS Support Node  At the same hierarchical level as the MSC.  Transfers data packets between mobile stations and GGSNs.  Keeps track of the individual MSs’ location and performs security functions and access control.  Detects and registers new GPRS mobile stations located in its service area  Participates into routing, as well as mobility management functions.

8 GPRS Architecture GGSN – Gateway GPRS Support Node  Provides inter-working between PLMN and external packet-switched networks.  Converts the GPRS packets from SGSN into the appropriate packet data protocol format (e.g., IP or X.25) and sends out on the corresponding packet data network.  Participates into the mobility management.  Maintains the location information of the mobile stations that are using the data protocols provided by that GGSN.  Collects charging information for billing purpose.

9 GPRS Architecture Backbone Network  Tunnels of data and signaling messages between GPRS support nodes.  Protocol architecture based on the Internet Protocol (IP).  GTP (GPRS Tunneling Protocol) used to tunnel user data and signaling between GPRS Support Nodes. All PDP (Packet Data Protocol) PDUs (Protocol Data Units) shall be encapsulated by GTP.

10 GPRS Architecture Backbone Network (cont.)  Two kinds of GPRS backbone Network: Intra-PLMN backbone network: The IP network interconnecting GSNs within the same PLMN. Inter-PLMN backbone network: The IP network interconnecting GSNs and intra-PLMN backbone networks in different PLMNs.  Two intra-PLMN backbone networks are connected via the Gp interface using Border Gateways and an inter-PLMN backbone network.  Border Gateway handles the packet transfer between GPRS PLMNs.

11 GPRS Architecture Backbone Network Inter-PLMN Backbone Packet Data Network Intra-PLMN Backbone GGSNBG SGSN BGGGSN SGSN Gi Gp

12 GPRS Architecture HLR  Enhanced with GPRS subscription data and routing information.  Accessible from the SGSN via the Gr interface and from the GGSN via the Gc interface.

13 GPRS Architecture MSC/VLR  Not needed for routing of GPRS data.  Needed for the co-operation between GPRS and the other GSM services. e.g., Paging for circuit-switched calls that can be performed more efficiently via the SGSN Combining GPRS and non-GPRS location updates  Receives location information from SGSN or sends paging requests to SGSN via the Gs interface.

14 GPRS Architecture Mobile Station  GPRS MS includes two components: MT (Mobile Terminal). Typically a handset used to access the radio interface. TE (Terminal Equipment). Typically a laptop or a Personal Digital Assistant (PDA).  Could be one unit combing the functionalities of a MT and a TE.

15 GPRS Architecture Mobile Station (cont.)  Three types of MS: Class-A: Could be attached to both GPRS and other GSM services, and the MS supports simultaneous operation of GPRS and other GSM services. Class-B: Could be attached to both GPRS and other GSM services, but the MS can only operate one set of services at a time. Class-C: Could be exclusively attached to one service type at a given time.

16 GPRS Architecture Interfaces TEMTBSSSGSNGGSN PDN TE MSC/VLRHLR SGSN CGF EIR Billing System Other PLMN GGSN RUm A Gs D Gr Gc GbGnGi Gn Gp Gf Ga CGF(Charging Gateway)

17 Packet transfer Intra-PLMN backbone PLMN

18 Packet Transfer  A laptop connects with a GPRS-capable handset.  The handset communicates with GSM base station.  Base station sends the GPRS packets to SGSN.  SGSN encapsulates packets  Handset location information is updated in other GSM components, such as HLR.  SGSN sends encaps. packets to GGSN.  GGSN decapsulates and sends to PDNs.

19 Communication betw. GPRS station and IP host PLMN1 PLMN2 MS BTS BSC SGSN Gn Intra-PLMN GPRS Backbone Gn SGSN GGSN Gi Packet Data Network(PDN) Eg.Internet,Intranet Border Gateway Gp Inter-PLMN GPRS Backbone Border Gateway Intra-PLMN GPRS Backbone GGSN Router Host SGSN BSC BTS Brasche and Walke (adapted) Go red Return blue

20 Routing example  MS located in PLMN1 sends IP packet to host (e.g. Web server) SGSN where sender MS is registered encapsulates IP packets Routes them through intra-PLMN backbone to appropriate GGSN GGSN decapsulates packets and sends them to IP network, that forwards to appropriate host  host sends return packet to home PLMN2 of MS PLMN2’s GGSN queries HLR and finds that MS is in PLMN1 Packet is encapsulated and sent to SGSN in PLMN1 SGSN decapsulates packet and delivers to MS Note usefulness of inter-PLMN backbone so GPRS routing does not need to go through PDN No encapsulation-decapsulation needed to traverse backbone