1 General Packet Radio Service (GPRS) Miao Lu Nancy Samaan SITE, Ottawa University CSI 5171 (95.533) Network Architectures, Services, Protocols and Standards

2 Agenda Introduction  Introduction  Part I GPRS Architecture  Part II  Bearer Services and Supplementary Services  Mobility Management  GPRS Limitations

3Introduction  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

4 Packet-switched technique  Share radio resources: users share a pool of channels Channels are allocated to users only when packets are to be sent or received Users can use several time slots (packet data channels) simultaneously  Volume-charging: charging is based on traffic volume instead of the duration of a session

5Comparison  Packet-switched High bit rates (up to 170kbit/s) Short 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 (maximum 14.4kbit/s) Long access times Unfriendly bill (based on duration) Limited application support Large volumes

6 GPRS Architecture

7 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

8 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.  Participates into routing, as well as mobility management functions.  Detects and registers new GPRS mobile stations located in its service area

9 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.

10 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.

11 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.

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

13 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.

14 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.

15 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.

16 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.

17 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)

18 Packet transfer

19 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.  GPRS packets routing information and handset location information are updated in other GSM components, such as HLR.  SGSN communicates with GGSN.  GGSN sends the packets to PDNs.

20Agenda  Introduction  Part I GPRS Architecture  Part II  Bearer and Supplementary Services  Mobility Management  GPRS Limitations

21 Bearer and Supplementary Services of GPRS bearer services  The bearer services of GPRS offer end-to-end packet switched data transfer.  Two different kinds of bearer services : PTP (Point-to-point) services PTM (Point-to-multipoint) services Supplementary ServicesSupplementary Services : SMS call, call forwarding unconditional (CFU), call forwarding on mobile subscriber not reachable (CFNRc), and closed user group (CUG).

22 GPRS Bearer Services PTP services Two types :  Connection-Oriented Network Service (PTP-CONS) : A logical relation is established between users. supports bursty transactional or interactive APs based on X.25. Multiple packets are sent between a single source and destination. Examples : Credit card validations, Telnet, and Database access.  ConnectionLess Network Service (PTP-CLNS) : A datagram type service based on the connectionless network protocol (ex: IP). Supports bursty non-interactive applications. No logical link required between users. Each packet is sent is independent of other packets. Examples :Electronic mail, Internet ‘ s World Wide Web.

23 GPRS Bearer Services PTM Services enables the transmission of a single message to multiple destinations.  Multicast service (PTM-M): Addressed to all subscribers in a geographical area group identifier indicating whether to all subscribers or to a specific PTM group Example : News, Weather and Traffic reports.  Group call service (PTM-G): Only a predefined group of subscribers controlled by a multicast server will receive the message transmitted. Group members must join the PTM-G call. Real time delivery. Example: Conferencing services.  IP Multicast (IP-M ): Messages are transmitted to a specific group. Group members must join the IP-M call. Real time delivery. Examples : Live multimedia transmissions.

24 Mobility Management Mobility management is the means by which GPRS keeps track of a mobile subscriber location while connected to the Network. Main concepts : GPRS Identifiers. GPRS service areas. GPRS mobility management states GPRS network access. Attachment. Location management Packet Data protocol PDP context Detachment Routing Example

25 Mobility Management Identifiers (IMEI) :  International Mobile station Equipment Identity (IMEI) : Specified for each equipment by the manufacturer (IMSI):  International Mobile Subscriber Identity (IMSI): It is stored in the subscriber identity module (SIM). (TMSI):  Temporary International Mobile Subscriber Identity (TMSI): assigned by the VLR. (P-TMSI):  Packet Temporary Mobile Subscriber Identity (P-TMSI): (during attachment by the SGSN). (TLLI):  Temporary Link Layer Identifier (TLLI): During the attachment phase, a TLLI is randomly generated by mobile.

26 Mobility Management GPRS service Areas[8] SA : Service Area RA: Routing Area

27 Explicit Detach Mobility Management Mobility Management States IDLE READY STANDBY GPRS Attach GPRS Detach Timer expiry/ Force STANDBY/ Abnormal RLC condition PDU Transmission /Reception reachable mobile unreachable mobile

28  IDLE State  GPRS MS is unreachable - MS may receive PTM-M message  READY state  MS can send and receive PDP PDU, and receive PTM-P and PTM-G data. MS informs SGSN when it changes cells.  A timer monitors the ready state and upon its expiry, the MS is put on standby.  STANDBY State  MS is attached to GPRS MM. - MS and SGSN have established MM contexts. MS can receive PTM-M and PTM-G data (i.e. can receive paging message)  MS execute MM procedure to inform SGSN when MS enter a new RA  PTP data reception and transmission, and PTM-G data transmission are not possible  MS does not inform SGSN when a change of cell in the same RA Mobility Management Mobility Management States (cont.)

29 Mobility Management GPRS network access attachAn MS can connect to the GPRS network by requesting a GPRS attach procedure. mobility management context The outcome is the establishment of a logical link between the MS and a single SGSN and the creation of a mobility management context. TLLI The logical link is uniquely defined by the identifier TLLI and is used subsequently in messages exchanged between the MS and SGSN. This identifier is changed when the MS is served by a new SGSN.

30 Mobility Management Attachment Before a mobile station can use GPRS services, it must register with an SGSN of the GPRS network. The network checks if the user is authorized, copies the user profile from the HLR to the SGSN, and assigns a packet temporary mobile subscriber identity (P-TMSI) to the user. Steps : Inform the network for the MS’s request to be active Network checks the Ms’s identity Download MS’s subscription information from HLR to SGSN. Update MSC/HLR

31 Mobility Management Attachment GPRS Attach function : Authenticate the mobile Generate the ciphering key Enable the ciphering Allocate temporary identity (TLLI) Copy subscriber profile from HLR to SGSN After GPRS attach The location of the mobile is tracked Communication between MS and SGSN is secured Charging information is collected SGSN knows what the subscriber is allowed to do HLR knows the location of the MS in accuracy of SGSN

32 Mobility Management - Attachment [5] 1.Attach Request MSBSSNew SGSNOld SGSNGGSNEIR New MSC/VLR HLR old MSC/VLR 2. Identification Request 3. Identification Response 3. Identity Request 3. Identity Response 4. Authentication 5. IMEI check 6a. Update Location 6b. Cancel Location 6c. Cancel Location ACK 6d. Insert Subscriber Data 6d. Insert Subscriber Data ACK 6e. Update Location ACK 8. Attach Accept 9. Attach Complete 10. TMSI Reallocation complete 7c. Cancel Location 7d.ACK 7a. Location Update Request 7b. Update Location 7e. Insert Subscriber data 7h. Location Update Accept 7f. Insert Subscriber data ACK 7b. Update Location ACK

33 Mobility Management – Location management Three types of location management procedures: Cell Update: MS informs the network of its current cell location( in READY state). MS listens periodically to special control channel for cell identity. Intra-SGSN routing update :Intra-SGSN routing update : MS changes RA and remains in the same SGSN(STANDBY &READY states). Inter-SGSN routing update:Inter-SGSN routing update: When the entry of MS to a new RA triggers a change of SGSN service area( STANDBY &READY states).

34 Mobility Management Packet Data Protocol ( PDP) Session An MS can request to activate one or more PDP (Packet Data Protocol) contexts which specify the PDNs (Packet Data Networks) it want to access. A PDP context activation procedure is initiated for each required PDP session. Triggered by the MS or a request from a PDN. Contains the parameters required to transfer packets between the MS and the PDN via a GGSN. An MS can have more than one PDP context.

35 Mobility Management Packet Data Protocol ( PDP) Session An MS specifies its network service access point and the Access Point Name (APN) of the PDN it wants to connect to. The SGSN identifies the corresponding GGSN and make its aware of the MS. A two way point-to-point path (tunnel) is uniquely identified by a tunnel ID (TID ) and is established between the SGSN and the GGSN. At the MS a PDP context is identified by a Network Service Access Point Identifier(NSPAI), used by the MS for data transfers. Ms can be assigned static or dynamic addresses

36 Mobility Management Packet Data Protocol ( PDP) Content A PDP (PACKET Data Protocol) contains: The type of network PDP used (X25, IP...). PDP Addresses of the terminal (x.121, IP). IP Addresses of the SGSN where the subscriber is localized. The access point to the service network used (NSAPI). The quality of service.

37 Mobility Management Packet Data Protocol ( PDP) Session[8] An MS with two PDP contexts Active

38 Mobility Management PDP context Activation [5] MS SGSN GGSN Activate PDP Context Request MS Activate PDP Context Accept Create PDP Context Request Create PDP Context Response PDP type,PDP Address QoS Requested,Access Point,… PDP type,PDP Address, IMSI, QoS Negotiated,Access Point,… PDP type,QoS Negotiated,… PDP type,PDP Address QoS Negotiated,…

39 Mobility Management PDP context Deactivation [5] MS SGSN GGSN MS DEACTIVATE PDP CONTEXT REQUEST(NSAPI) GTP DELETE PDP CONTEXT REQUEST (NSAPI,IMSI) GTP DELETE PDP CONTEXT RESPONSE SM DEACTIVATE PDP CONTEXT ACCEPT(NSAPI)

40 Mobility Management Detachment Two types of Detachments : MS initiated Detachment: Network Initiated Detachment: (Ex : service Termination, Network congestion)

41 Mobility Management MS Initiated Detachment [5]

42 Mobility Management Network Initiated Detachment [5]

43 Routing Example 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 LAN Host SGSN BSC BTS

44 GPRS Limitations Speeds Much Lower in Reality Support of GPRS Mobile Terminate by Terminals is Not Ensured Packet switching means that data packets can traverse different routes and then be reassembled in their final destination leading to potential transit delays affecting the Quality of Service. Operators may decide to charge based on time rather than volume, which may destroy the cost advantage that GPRS provides today. Requires major network modifications: Many network elements to be upgraded and totally new to be introduced Expensive: Not much time for invest to be returned due to upcoming 3rd generation technology

45 References (papers) [1] Dale R. Shelton, “General Packet Radio Service”, Aether Systems, Incorporated, 2001 [2] Agilent Technologies, “Understanding General Packet Radio Service (GPRS)”, Technical report, [3] Christian Bettstetter, Hans-J¨org V¨ogel and J¨org Ebersp¨acher, “GSM Phase 2+ General Packet Radio Service GPRS: Architecture, Protocols, and Air Interface”, IEEE Communication Surveys, vol. 2, n. 3, [4] ETSI, “GSM Digital cellular telecommunications system (Phase2+): General Packet Radio Service, Service Description Stage 1”. [5] ETSI, “GSM Digital cellular telecommunications system (Phase2+); General Packet Radio Service, Service Description Stage 2”, [6] L. Logrippo D. Amyot, N.Hart and P. Forhan, “Formal Specification and Validation using a Scenario-Based Approach: The GPRS Group-Call Example”,ObjecTime Workshop on Research in OO Real-Time Modeling, Ottawa, Canada, pp. 99–118, Jan. 1998

46 References (papers) [7] B. Ghribi L. Andriantsiferana and L. Logrippo, “Prototyping and Formal Requirement Validation of GPRS: A Mobile Data Packet Radio Service for GSM”, Proceedings of 7th Int. Working Confrence on Dependable Computing For Critical Applications (DCCA-7), san Jose, California,USA, pp. 99–118, Jan [8] B. Ghribiand L. Logrippo, “Understanding GPRS: The GSM Packet Radio Service”, Computer Networks, vol. 34, pp. 763–779, [9] Herman Rao Yi-Bing Lin and Imrich Chlamtac, “General Packet Radio Service (GPRS): Architecture, Interfaces, and Deployment”, Journal of Wireless Communiations and Mobile Computing, vol. 1, n. 1, pp. 77–92, 2001.