GPRS Overview. GPRS = General Packet Radio Service. GPRS Network

Transcription

1 GPRS - Overview GPRS Overview GPRS = General Packet Radio Service INTERNET/ INTRANET GPRS Network abcde X.25 Disclaimer: These overview slides are intended for informational purposes only. They have not been reviewed or officially presented, thus there may be some unintentional errors. For detailed information, please refer to the GPRS specifications. 1

2 GPRS - Overview GPRS Overview GPRS is an emerging GSM phase 2+ packet radio standard, similar to NAC CDPD: Provides more efficient usage of the radio interface (mobiles can share the same radio channel). Direct interworking to Internet (TCP/IP), X.25 and ISO CLNS networks for point-to-point services (connection-less/connection oriented) and point-tomultipoint services (broadcast and groupcall). Concurrent operation with existing GSM services for Circuit-switched Speech, Circuit-switched data and SMS. Supports Data rates from 9.6kbps to 100+kbps Best suited for burst forms of traffic. Long term replacement for SS7 based SMS. 2

3 GPRS - Definitions GPRS Overview GSN - GPRS Support Node GGSN - Gateway GSN Provides similar functionality as GMSC, for packet data. Uses Packet Data Protocol (PDP address) which contains IP routing information. Routing information is used to tunnel PDUs to the current point of attachment (i.e. SGSN). Required I/Fs: Gn (to SGSN), Gi (to packet network) Optional I/Fs: Gc (to HLR) (can go via Gn and then Gr) 3

4 GPRS - Definitions GPRS Overview SGSN - Serving GSN performs mobility management, authentication procedures and routes packet data. Like the VLR, stores only a subset of subscriber data available at the HLR. Supports the same MAP I/F to HLR as VLR/HLR I/F. [Note: GPRS spec overall assumes co-located MSC/VLR (i.e. no B interface)]. SMSC may transfer short messages to the MS using the GPRS (via Gd interface). Option to queue messages at the SGSN for a short time (versus going to the SM-SC). Required I/Fs: Gn (to GGSN), Gb (to BSS), Gr (to HLR) Optional I/Fs: Gd (to SMS-GMSC or SMS-IWMSC to enable GPRS capable mobiles to send/receive SMs over GPRS radio chans), Gs (to MSC/VLR) (i.e. for class A mobile support for SMS) 4

5 GPRS - Network Overview GPRS Overview Existing GSM Network Elements New GPRS Network Elements SMS-GMSC SMS-IWMSC SM-SC MAP-E MAP-C MSC/ VLR A MAP-F EIR Gs Gf Gd MAP-D Gr HLR Gc TE MT Um BSS Gb SGSN Gn GGSN Gi Packet Network TE Gp MT = Mobile Terminal TE = Terminal Equipment GGSN Other PLMN Signalling I/F Signalling & Data Transfer I/F 5

6 GPRS - Interfaces GPRS Overview Gb - The equivalent of the A interface for GPRS (frame relay) Gc - Interface between the GGSN and HLR so that the GGSN can get the location details of an MS. To avoid implementing MAP/SS7 in the GGSN, this interface is optional. When not present, the GGSN routes inquires to the HLR via an SGSN. Gd - Interfaces the SGSN to the SMS-GMSC. Allows for delivery of SMS traffic over GPRS. This is a MAP interface. Gf - Interface between the SGSN and EIR, similar to the existing MSC/VLR EIR interface Gi - An external interface between GGSN and another type of packet network Gn - SGSN to GGSN interface, based on IPv4 or IPv6. Gp - Inter PLMN GPRS interface. The Gp interface provides the functionality of the Gn interface along with the security functionality required for inter-plmn communication. The security functionality is based on agreements between operators. Gr - Interface between SGSN and HLR, similar to the MSC-HLR interface. This is a MAP interface. Gs - Interface between the MSC and SGSN. This interface is required for some simultaneous GPRS and CS service operation (for some MSs). This is a BSSMAP interface (optional) 6

7 GPRS - Addressing Elements/Identifiers GPRS adds the following addressing elements to GSM: PDP Address - associated with each PDP Context. The PDP address itself is a Network layer ( X.121 or IP) address. The fields associated with a PDP context vary across the HLR, SGSN, GGSN and MS, but include items such as: PDP Type (X.25 or IP) NSAPI Compression parameters negotiated Requested and negotiated QoS parameters State SGSN IP address - HLR is enhanced to include GPRS subscription data and routing information including the SGSN IP address and SS7 addresses. NSAPI - Network Layer Service Access Point Identifier - user for Network Layer routing. In the MS, the NSAPI identifies the PDP-SAP. In the SGSN and GGSN, the NSAPI identifies the PDP context associated with a PDP Address. Between the SGSN and the MS, the TLLI uniquely identifies the logical link. The NSAPI is part of the Tunnel ID (TID). TID - Tunnel ID - consists of an IMSI and NSAPI. This uniquely identifies a single PDP context. TLLI - Temporary Logical Link Identifier. Optional. The relationship between TLLI and IMSI is known only in the MS and SGSN. Unique within a RA. TLLI is derived from a P-TMSI allocated by the SGSN. P-TMSI - Packet Temporary Mobile Subscriber Identity. Allocated to each GPRS attached MS ( 03.03) RAI - Routing Area Identity - identifies one or several cells. RAI is broadcast as system information and is used by the MS to determine (when changing cells), if a RA border was crossed. A Routing Area (RA) is a subset of a GSM Location Area (LA). A RA is served by only on SGSN. RAC (Routing Area Code) is only unique when presented with an LAI. A GSM Cell Identifier (CI) is unique when presented with an LAI or RAI. RAI = MCC+ MNC + LAC + RAC. 7

8 GPRS - Mobility Management GPRS Overview HLR has been enhanced to include GPRS subscription data and routing information: IMSI SGSN IP & SS7 addresses up to fifty PDP (Protocol Data Protocol) specific data sets. Large impact to support Class A and Class B GPRS sets. There are 3 categories of GPRS Mobile Sets: Class A - supports full simultaneous connections. (Requires Combined procedures) Class B - supports simultaneous paging for either service, but NOT activation. GPRS services will be put on hold while a CS call is handled. (Requires Combined procedures) Class C - either GPRS or CS modes. 8

9 GPRS - Mobility Management - Location Registration GPRS uses the concept of a routing area (RA), which is a subset of a GSM Location Area (LA). GPRS has three types of Routing Area Registration: Routing Area Updating - when a mobile enters a new Routing Area (RA) GPRS Attach/Detach Indicates mobile activation/deactivation within a Routing Area Prevents paging of a mobile that is not active (visited VLR rejects calls from the HLR or applies Call Forwarding) Note that the mobile station does not maintain an attach/detach state Periodic Routing Area Update Periodicity is determined by the network Ensures that regular radio contact is maintained by the mobile The Routing Area Update can be Intra- or Inter- SGSN. 9

10 GPRS - Inter-SGSN Routing Area Update - Message Flow MS new SGSN old SGSN GGSN HLR MSC/VLR 1. Routing Area Update Request 2. SGSN Context Request 2. SGSN Context Response 3. Security Functions 4. SGSN Context Acknowledge 5. Forward Packets 6. Update PDP Context Request 6. Update PDP Context Response 7. Update Location 8. Cancel Location 8. Cancel Location Ack 9. Insert Subscriber Data 9. Insert Subscriber Data Ack 10. Update Location Ack 11. Location Updating Request 11. Location Updating Accept 12. Routing Area Update Accept 10

11 GPRS - Inter-SGSN Routing Area Update - Message Flow Details 1. The MS sends the Routing Area Update Request to the new SGSN. 2. The new SGSN then exchanges an SGSN Context Request/Response with the old SGSN. 3. Optionally, the GSM security procedures are performed. 4. Upon receipt of the SGSN Context Response and after optional security has been performed, the new SGSN sends an SGSN Context Acknowledge if the user has at least one PDP context active. 5. Upon receipt of the SGSN Context Acknowledge, the old SGSN forwards any packets from the old SGSN. 6. After sending the SGSN Context Acknowledge, the new SGSN initiates the Update PDP Context with the GGSN. 7. Upon completion of this, the Update Location is sent to the HLR. 8. This results in a Cancel Location to the old SGSN. 9. The subscriber data is then sent to the new SGSN. 10. Upon receipt of the Insert Subscriber Data Acknowledgement, the HLR acknowledges the Update Location. 11. (Note: this procedure can be combined with the GSM Location Update. 12. Upon completion of the Location Updating procedure, the new SGSN sends a Routing Area Update Accept to the MS. 11

12 GPRS - Mobility Management - Security GPRS uses some existing GSM security messaging and optional GPRS specific messaging: Authentication Request/Response/Reject - performed by SGSN as per MSC/ VLR Identity Request/Response - SGSN executed as per MSC/VLR TMSI Reallocation Command/Complete Supported by 3 algorithms: Authentication User Data Encryption (Note: the scope of ciphering for GPRS is between MS and SGSN). Generation of cipher key (TDMA frame number is unknown at the SGSN, therefore LLC frame number may replace TDMA frame number as an input to the algorithm). Uses standard key management procedures for Kc. 12

13 GPRS - Authentication Procedure GPRS Overview MS SGSN HLR 1. Send Authentication Info 1. Send Authentication Info Ack 2. Authentication Request 2. Authentication Response 1. If the SGSN does not have previously stored authentication triplets, a Send Authentication Info (IMSI) is sent to the HLR. The HLR responds with Send Authentication Info Ack (Authentication Triplets). Each Authentication Triplet includes RAND, SRES and Kc. 2. The SGSN sends Authentication Request (RAND, CKSN, Ciphering Algorithm) to the MS. The MS responds with Authentication Response (SRES). 13

14 GPRS - Protocol Stack GPRS Overview Application IP/X.25 SNDCP SNDCP Relay GTP IP/X.25 GTP LLC RLC RLC Relay BSSGP LLC BSSGP UDP/ TCP IP UDP/ TCP IP MAC MAC Network Service Network Service L2 L2 GSM RF GSM RF L1bis L1bis L1 L1 MS Um BSS Gb SGSN Gn GGSN Gi 14

15 GPRS - Transmission Protocol Definitions GTP - GPRS Tunneling Protocol - Tunnels user data and signalling between GPRS support nodes in the GRPS backbone network. All PTP PDP PDUs shall be encapsulated by GTP. GTP shall provide the mechanisms for flow control between GSNs, if required (GSM 09.60) TCP - Transmission Control Protocol - carries GTP PDUs in the GPRS backbone network for ptotocols that need a reliable data link (e.g., X.25). Provides flow control and protection against lost and corrupted GTP PDUs. UDP - User Datagram Protocol - carries GTP PDUs for protocols that do not need a reliable data link (e.g., IP). Provides protection from corrupted PDUs. IP - Internet Protocol - GPRS backbone network protocol used for routing user data and control signalling. Initially based on IP version 4 protocol. Ultimately, IP version 6 protocol. SNDCP - Subnetwork Dependent Convergence Protocol (SNDCP) - maps network-level characteristics onto the characteristics of the underlying network (GSM 4.65) 15

16 GPRS - Transmission Protocol Definitions (continued) LLC - Logical Link Control - provides a highly reliable ciphered logical link. LLC shall be independent of the underlying radio interface protocols in order to allow introduction of alternative GPRS radio solutions with minimum changes to the NSS. (GSM 4.64) Relay - in the BSS, relays LLC PDUs between the Um and Gb interfaces. In the SGSN, relays PDP PDUs between the Gb and Gn interfaces. BSSGP - Base Station System GPRS Protocol - conveys routing and Qos related information between BSS and SGSN. Does not perform error correction. (GSM 8.18) NS - Network Service - transports BSSGP PDUs. Based on the Frame Relay connection between BSS and SGSN and may be multi-hop and traverse a network of Frame Relay switching nodes. (GSM 8.16) RLC/MAC - Radio Link Control/Medium Access Control - layer controlling 2 functions: RLC provides a radio solution dependent reliable link. The MAC function controls the access signalling (access and grant) for the radio channel, and the mapping of LLC frames onto the GSM physical channel. (GSM 4.60) GSM RF - as defined in GSM 05 series. 16

17 GPRS - GPRS Tunnelling Protocol The GPRS Tunneling Protocol (GTP) defines the protocol between GSN nodes in the GPRS backbone network. Applies to both the Gn and Gp interface. Signalling is used to create, modify and delete tunnels. User Datagram Protocol (UDP) used to transfer signalling messages. Defines the following categories of signalling messages: Path Management Messages Tunnel Management Messages Location Management Messages Mobility Management Messages 17

18 GPRS - GPRS Tunnelling Protocol - Path Management The following path management messages can be sent between any type of GSN pair: Echo Request - sent on a path to another GSN to determine if the other node is alive. Echo Response - sent as a response to an Echo Request 18

19 GPRS - GPRS Tunnelling Protocol - Tunnel Management The following tunnel management messages are used to create, update and delete tunnels used to route T-PDUs between a MS and an external PDN via SGSN and GGSN: Create PDP Context Request Create PDP Context Response Update PDP Context Request Update PDP Context Response Delete PDP Context Request Delete PDP Context Response Create AA PDP Context Request Create AA PDP Context Response Delete AA PDP Context Request Delete AA PDP Context Response Error Indication PDU Notification PDU Reject 19

20 GPRS - GPRS Tunnelling Protocol - Tunnel Management Create PDP Context Request Sent from an SGSN to a GGSN node as part of a GPRS PDP Context Activation procedure or the Network-Requested PDP Context Activation procedure. A valid request initiates the creation of a tunnel. The destination GGSN for this message may be obtained by using DNS to get the IP address for the GGSN name in the current PDP context. Contains the following information elements: Information element Quality of Service SGSN Address for signalling SGSN Address for user traffic Selection Mode Flow Label Data I Flow Label Signalling End User Address Access Point Name Protocol configuration options Private Extension Description QoS negotiated by the MS at PDP context activation Specific address for signalling. Specific address for user traffic. Indicates the source of the Access Point Name (APN) Specifies a downlink (GGSN -> SGSN) flow label for G-PDUs Specifies a downlink (GGSN -> SGSN) flow label for signalling msgs. If PDP addr field is empty, then dynamic otw contains static addr. May be used by GGSN to differentiate accesses to different external networks. APN is either MS provided, a subscribed APN or SGSN selected. Applies to IP protocol only. Contains vendor or operator specific information. 20

21 GPRS - GPRS Tunnelling Protocol - Tunnel Management Create PDP Context Response Sent as a response to a Create PDP Context Request. Contains the following information elements: Information element Cause Quality of Service GGSN Address for signalling GGSN Address for user traffic Reordering Required Flow Label Data I Flow Label Signalling End User Address Protocol configuration options Private Extension Description Used to indicate error conditions (i.e. cannot allocate dynamic IP address, network prefix not supported, etc.) QoS may be negotiated downwards Specific address for signalling. Specific address for user traffic. Indicates if reordering of messages is required. May be negotiated downwards (from Yes to No) by GGSN. Specifies a downlink (GGSN -> SGSN) flow label for G-PDUs Specifies a downlink (GGSN -> SGSN) flow label for signalling msgs. If PDP addr field is empty, then dynamic otw contains static addr. Applies to IP protocol only. Contains vendor or operator specific information. 21

22 GPRS - GPRS Tunnelling Protocol - Tunnel Management Update PDP Context Request Sent as part of the GPRS Inter-SGSN Routing Update procedure or PDP Context Modification procedure. Used to change QoS and the path. Contains the following information elements: Information element Description Quality of Service SGSN Address for signalling SGSN Address for user traffic Flow Label Data I Flow Label Signalling Private Extension QoS negotiated by the MS Specific address for signalling. Specific address for user traffic. Specifies a downlink (GGSN -> SGSN) flow label for G-PDUs Specifies a downlink (GGSN -> SGSN) flow label for signalling msgs. Contains vendor or operator specific information. 22

23 GPRS - GPRS Tunnelling Protocol - Tunnel Management Update PDP Context Response Sent as a response to the Update PDP Context Request. Contains the following information elements: Information element Cause Quality of Service GGSN Address for signalling GGSN Address for user traffic Flow Label Data I Flow Label Signalling Private Extension Description Used to indicate error conditions (i.e. cannot allocate dynamic IP address, network prefix not supported, etc.) QoS may be negotiated downwards Specific address for signalling. Specific address for user traffic. Specifies a downlink (GGSN -> SGSN) flow label for G-PDUs Specifies a downlink (GGSN -> SGSN) flow label for signalling msgs. Contains vendor or operator specific information. 23

24 GPRS - GPRS Tunnelling Protocol - Tunnel Management Delete PDP Context Request Sent as part of the GPRS Detach Procedure or the GPRS PDP Context Deactivation procedure to deactivate an activated PDP Context. Contains Private Extension Information Element. Delete PDP Context Response Sent as a response to the Delete PDP Context Request. Contains Cause and Private Extension Information Elements. 24

25 GPRS - GPRS Tunnelling Protocol - Tunnel Management Create AA PDP Context Request Sent as part of the GPRS Anonymous Access PDP Context Activation. Used to create a tunnel between a context in the SGSN and a context in the GGSN. Contains the following information elements: Information element Quality of Service SGSN Address for signalling SGSN Address for user traffic Selection Mode Flow Label Data I Flow Label Signalling End User Address Access Point Name Protocol configuration options Private Extension Description QoS negotiated by the MS at Anonymous Access PDP context activation Specific address for signalling. Specific address for user traffic. Indicates the source of the Access Point Name (APN) Specifies a downlink (GGSN -> SGSN) flow label for G-PDUs Specifies a downlink (GGSN -> SGSN) flow label for signalling msgs. Contains the address of the Anonymous Server. May be used by GGSN to differentiate accesses to different external networks. APN is either MS provided, subscription not verified or Network provided, subscription not verified. Applies to IP protocol only. Contains vendor or operator specific information. 25

26 GPRS - GPRS Tunnelling Protocol - Tunnel Management Create AA PDP Context Response Contains the following information elements: Information element Cause Quality of Service GGSN Address for signalling GGSN Address for user traffic Reordering Required Flow Label Data I Flow Label Signalling End User Address Protocol configuration options Private Extension Description Non-zero value indicates error conditions QoS may be negotiated downwards Specific address for signalling. Specific address for user traffic. Indicates if reordering of messages is required. May be negotiated downwards (from Yes to No) by GGSN. Specifies a downlink (GGSN -> SGSN) flow label for G-PDUs Specifies a downlink (GGSN -> SGSN) flow label for signalling msgs. Contains the requested PDP type with the PDP addr field empty Applies to IP protocol only. Contains vendor or operator specific information. 26

27 GPRS - GPRS Tunnelling Protocol - Tunnel Management Delete AA PDP Context Request Sent as part of the GPRS PDP Anonymous Access Context Deactivation procedure to deactivate an activated PDP Context. Contains Cause and Private Extension Information Elements: Delete AA PDP Context Response Sent as a response to the Delete AA PDP Context Request. Contains Cause and Private Extension Information Elements: Error Indication Sent to the GGSN when a tunnel PDU is received for the following conditions: No PDP context exists PDP context is inactive No MM context exists GGSN deletes its PDP context when the message is received. Sent by the new SGSN to the old SGSN if no PDP context exists or is inactive for a received tunnel PDU. The old SGSN deletes its PDP context when message is received. Sent by the GGSN to the SGSN if no PDP context exists for a received tunnel PDU. The SGSN reestablishes the PDP context to the GGSN when the message is received. 27

28 GPRS - GPRS Tunnelling Protocol - Tunnel Management PDU Notification Request When receiving a Tunneled PDU (T-PDU), the GGSN checks if a PDP context is established for the given PDP address. If no PDP context has been established, the GGSN may initiate the Network-requested PDP Context Activation procedure by sending a PDU Notification Request to the SGSN. Message contains End User Address and Private Extension. PDU Notification Response Sent by the SGSN to the GGSN in response to the PDU Notification Request. Message contains Cause and Private Extension. PDU Notification Reject Request Sent when the PDP context requested by the GGSN cannot be established. Message contains a Cause indicating the reason why the Context could not be established, an End User Address and Private Extension. Upon receipt of this message, the GGSN may reject or discard the stored T-PDUs, depending on the PDP type. PDU Notification Reject Response Sent by the GGSN to the SGSN as a response to a PDU Notification Reject Request. Message contains a Cause. 28

29 GPRS - PDP Context Activation Procedure MS SGSN GGSN 1. Activate PDP Context Request 2. Security Functions 3. Create PDP Context Request 4. Create PDP Context Response 5. Activate PDP Context Accept 1. The MS sends an Activate PDP Context Request ( NSAPI, PDP type, PDP Address, Access Point Name, Qos Requested, PDP Configuration Options) message to the SGSN. Access Point Name is either a GGSN IP address or a logical name referring to the GGSN to be used. PDP Configuration Options is send transparently through the SGSN to the GGSN. 2. Security Functions are optionally executed (previously discussed). 29

30 GPRS - PDP Context Activation Procedure (continued) 3. The SGSN receives the Activate PDP Context Request: The SGSN checks that the MS is allowed to activate the PDP address against the subscription data that was stored in the SGSN during GPRS Attach. If allowed, the SGSN creates a Tunnel Identifier (TID) for the requested PDP context by combining the IMSI stored in the MM context with the NSAPI received from the MS. The GGSN used is the GGSN address stored in the PDP context (or if the PDP address in the context indicates that a dynamic address is allowed, the GGSN indicated by the Access Point Name in the Activate PDP Context message is used). The SGSN sends a Create PDP Context Request ( PDP Type, PDP Address, Access Point Name, QoS Negotiated, TID, PDP Configuration Options) to the GGSN. 4. The GGSN receives the Create PDP Context Request: The GGSN creates a new entry in its PDP context table, which allows the GGSN to route PDP PDUs between the SGSN and external PDP Network. The GGSN sends a Create PDP Context Response(PDP Address, BB Protocol, Reordering Required, PDP Configuration Options, Cause) message to the SGSN. The PDP address is included if the GGSN allocated a PDP address. BB protocol indicates whether TCP or UDP shall be used to transport user data on the backbone network between the SGSN and GGSN. Reordering Required indicates whetehr the SGSN shall reorder N-PDUs before delivering to the MS. 5. The SGSN receives the Create PDP Context Response message: The SGSN inserts the NSAPI along with the GGSN address in its PDP context. If the MS requested a dynamic address, the PDP adddress received from the GGSN is inserted in the PDP context. The SGSN sends as Activate PDP Context Accept ( PDP Type, PDP Address, NSAPI, QoS Negotiated, PDP Configuration Options) message to the MS. 30

31 GPRS - Network-Requested PDP Context Activation Procedure MS SGSN HLR GGSN 1. PDP PDU 2. Send Routing Info for GPRS 3. Send Routing Info for GPRS Ack 4. PDU Notification Request 5. PDU Notification Response 6. Request PDP Context Activation 7. PDP Context Activation Procedure 31

32 GPRS - Network-Requested PDP Context Activation Procedure (continued) 1. When a PDP PDU is received, the GGSN determines if the Network-Requested PDP Context Activation Procedure needs to be initiated. (The GGSN may store subsequent PDUs received for the same PDP address). The GGSN may send a Send Routing Information for GPRS(IMSI) message to the HLR. 2. The HLR receives the Send Routing Information for GPRS message: If the HLR determines the request can be served, the HLR includes the IP address of the SGSN that currently serves the MS in the Send Routing Information for GPRS Response (IMSI, SGSN Address, Cause) message. 3. The GGSN receives the Send Routing Information for GPRS Response If the SGSN address is present and Cause is not present or equals No Paging Response, the GGSN sends a PDU Notification Request (IMSI, PDP Type, PDP Address) message to the SGSN indicated by the HLR. Otherwise, the GGSN sets the MNRG (Mobile Station Not Reachable) flag for that MS. 4. The SGSN receives the PDU Notification Request. 5. The SGSN sends a PDU Notification Response (Cause) message to the GGSN to acknowledge that it will request the MS to activate the PDP context indicated by the PDP Address. 6. The SGSN sends a Request PDP Context Activation ( PDP type, PDP Address) message to the MS to activate the indicated PDP context. 7. The PDP context is activated per the PDP Context Activation Procedure described previously. 32

33 GPRS - GPRS Tunnelling Protocol - Location Management The following location management messages are used to obtain subscriber location information from the HLR to support the Network-Requested PDP Context Activation. If the GGSN does not have an SS7 MAP interface the messages are sent via a GTP-MAP protocol converting GSN in the GPRS backbone network: Send Routing Information Request - sent by the GGSN to obtain location information for the MS. Message contains the IMSI of the MS and Private Extension. Send Routing Information Response - sent by the HLR to return the address of the SGSN currently serving the MS. Contains Cause, IMSI, IP address of the SGSN, Map Cause and Private Extension. Failure Report - sent by the GGSN to the HLR when a PDU reject message is received. GGSN sets the Mobile Detached Flag for GPRS (MDFG) and requests the HLR to set the flag and add the GGSN to the list of nodes to report to when activity from the subscriber that owns the PDP address is detected. Message contains the subscriber IMSI and Private Extension. Failure Report Response - sent by the HLR to the GGSN to acknowledge receipt of Failure Report. Contains Cause, MAP Cause and Private Extension. Note MS Present - When the HLR receives a message from a mobile with MDFG set, it clears the MDFG and sends the Note MS Present message to all GGSN s in the subscriber s list. Contains subscriber IMSI, GSN Address and Private Extension. 33

34 GPRS - GPRS Tunnelling Protocol - Mobility Management The following mobility management messages are used for GPRS Attach and Inter-SGSN Routing Update: Identification Request Sent by the new SGSN to the old SGSN to request the IMSI for a MS when a GPRS Attach is done with a P-TMSI and the MS has changed SGSNs since the GPRS Detach was done. Contains the following parameters: Information element Description RAI P-TMSI P-TMSI Signature Private Extension Routeing Area Identity from old SGSN. Packet TMSI from old SGSN. Conditionally provided by the MS to the new SGSN for identification checking purposes per GSM and Contains vendor or operator specific information. 34

35 GPRS - GPRS Tunnelling Protocol - Mobility Management Identification Response Sent in response to the Identification request. Contains the following parameters: Information element Cause IMSI Authentication Triplet Private Extension Description Only value in the message if Cause is anything other than Request Accepted. IMSI of MS, matching the P-TMSI and RAI in the Identification Request. Authentication triplets for MS. Contains vendor or operator specific information. 35

36 GPRS - GPRS Tunnelling Protocol - Mobility Management (continued) SGSN Context Request Sent by the new SGSN to the old SGSN to request the MM and PDP Contexts for the MS. Information element Description RAI TLLI P-TMSI Signature Receive State Variable (V(r)) Flow Label Signalling MM Context PDP Context Private Extension Routeing Area Identity Temporary Logical Link Identifier Conditionally provided by the MS to the new SGSN for identification checking purposes per GSM and From the LLC in the old SGSN. Specifies a flow label chosen by the old SGSN. The new SGSN includes this flow label in the GTP header of all subsequent signalling msgs sent from new SGSN to the old SGSN related to the PDP context(s) requested. Contains the Mobility Management, MS and security parms. Contains the session mgmt parms. Contains vendor or operator specific information. 36

37 GPRS - GPRS Tunnelling Protocol - Mobility Management (continued) SGSN Context Response Sent by the old SGSN to the new SGSN. Contains the following: Information element Cause IMSI Receive State Variable (V(r)) Flow Label Signalling MM Context PDP Context Private Extension Description Non-zero value indicates error conditions IMSI of MS, matching the TLLI and RAI in the SGSN Context Request. From the LLC in the old SGSN. Specifies a flow label chosen by the old SGSN. The new SGSN includes this flow label in the GTP header of all subsequent signalling msgs sent from new SGSN to the old SGSN related t the PDP context(s) requested. Contains the Mobility Management, MS and security parms. Contains the session mgmt parms. Contains vendor or operator specific information. 37

38 GPRS - GPRS Network - Routing in Home PLMN to/from External PDN MS BSS SGSN GGSN External PDN SNDCP PDU (TLLI, NSAPI, PDP PDU) ocontext: TLLI + NSAPI -> GGSN +TID GTP PDU (TID, PDP PDU) ocontext: TID -> PDP Context (PDP Address) PDP PDU PDP PDU ocontext: PDP Address-> TID -> SGSN + TID GTP PDU (TID, PDP PDU) SNDCP PDU (TLLI, NSAPI, PDP PDU) ocontext: TID -> TLLI + NSAPI + RAI + CI 38

39 GPRS - GPRS Network - Backbone Networks Packet Data Network Inter-PLMN Backbone Gi Gp Gp Gi GGSN BG BG GGSN Intra-PLMN Backbone Intra-PLMN Backbone SGSN SGSN SGSN SGSN 39

40 GPRS - GPRS Network - Data Routing for a Roaming MS Visited PLMN Home PLMN MS BSS SGSN GGSN PDN GGSN External PDN SNDCP PDU (TLLI, NSAPI, PDP PDU) ocontext: TLLI + NSAPI -> GGSN +TID GTP PDU (TID, PDP PDU) ocontext: TID -> PDP Context (PDP Address) PDP PDU PDP PDU ocontext: PDP Address-> TID -> SGSN + TID GTP PDU (TID, PDP PDU) SNDCP PDU (TLLI, NSAPI, PDP PDU) ocontext: TID -> TLLI + NSAPI + RAI + CI 40

41 GPRS - References GPRS Overview [1] GPRS (General Packet Radio Service). Overview and Strategy Proposal, Nik Allen and John Candish, , version 1.0.0, May 11, [2] GSM (version 6.1.1) - General Packet Radio Service (GPRS); Service Description; Stage 2. [3] GSM (version 6.1.0) - General Packet Radio Service (GPRS); GPRS Tunnelling Protocol (GTP) across the Gn and Gp Interface. 41

42 GPRS - Channel Types GPRS Overview Packet Data Traffic Channels: Carry user information and signalling information (e.g. Session Management (SM) and Mobility Management (MM)) in packet mode. Allow a plurality of information streams, associated with different users to be multiplexed in a pre-emptive and dynamic fashion. Signalling functions between MS and BSS are carried out over control channels. 42