Reference [1] Wireless and Mobile Network Architectures Y-Bing Lin and Imrich Chlamtac Wiley Computer Publishing Chapter 18 2

Transcription

1 General Packet Radio Service (GPRS) Interface 1 GPRS network GPRS air interface Um (BSS MS),, GPRS, Gb (BSS SGSN), Gn (SGSN GGSN), Gp (SGSN GGSN in Other GPRS Network), Gs (SGSN MSC/VLR) Gi (GGSN PDN)

2 Reference [1] Wireless and Mobile Network Architectures Y-Bing Lin and Imrich Chlamtac Wiley Computer Publishing Chapter 18 2

3 Outlines Introduction Um (BSS MS) Gb (BSS SGSN) Gn (SGSN GGSN) Gp (SGSN GGSN in Other GPRS Network) Gs (SGSN MSC/VLR) Gi (GGSN PDN) 3, Um (BSS MS), Gb (BSS SGSN), Gn (SGSN GGSN), Gp (SGSN GGSN in Other GPRS Network), Gs (SGSN MSC/VLR) Gi (GGSN PDN)

4 Introduction 4 GPRS Architecture

5 GPRS Architecture SMS-GMSC SMS-IWMSC SM-SC E C MSC/VLR Gd HLR TE R MT A Um BSS Gs Gb SGSN D Gn Gr GGSN Gc Gi PDN TE Gn Gp Gf FIR SGSN GGSN Other PLMN Signalling Interface Signalling and Data Transfer Interface 5 ( ) interface Um (BSS MS) Gb (BSS SGSN) Gn (SGSN GGSN) Gp (SGSN GGSN in Other GPRS Network) Gs (SGSN MSC/VLR) Gi (GGSN PDN) GPRS GSM, GSM, air interface, SGSN, GGSN, GSM protocol protocol, Gs (SGSN<->MSC/VLR), Gr (SGSN<->HLR) Gc (GGSN<->HLR), GSM MAP interface, GPRS Transmission plane signaling plane

6 GPRS Transmission Plane Application IP/X25 SNDCP LLC RLC MAC GSM RF Relay RLC BSSGP Network MAC Service GSM RF Libis Relay SNDCP GTP LLC UDP/ TCP BSSGP IP Network L2 Service Libis L1 IP/X25 GTP UDP/TCP IP L2 L1 MS 6 TCP X25 IP GPRS IP IP IP GPRS GPRS GPRS IP GPRS IP static IP GPRS dynamic host configuration protocol DHCP IP dynamic IP virtual IP IP GPRS IP GPRS IP OSI layer 1 L1 layer 2 L2

7 GPRS Signaling Plane BSSAP+ : Base Station System Application Part+ GMM : GPRS Mobility Management MAP : Mobility Application Part MTP : Message Transfer part SCCP : Signaling Connection Control Part SM : Session Management TCAP : Transaction Capabilities Application Part Relay Interworking 7 GPRS Signaling Plane MS SGSN, GMM/SM layer GPRS session SGSN GGSN Gn interface Transmission Plane UDP GGSN HLR Gc interface MAP GSM MAP GPRS SGSN MSC/VLR Gs interface extended BSSAP, TCAP

8 Um (BSS MS) 8 GPRS Air Interface, GPRS message flow GPRS network

9 Um Interface (MS BSS) [gsm0364] Um radio Interface radio interface between MS and BTS GPRS radio technology Based on the GSM radio architecture New logical channel structure To control signaling and traffic flow over the Um radio interface 9 Um interface [gsm0364] MS BTS radio interface GPRS radio GSM radio architecture logical channel structure Um radio interface

10 Radio Channel Structure The physical channel dedicated to packet data traffic is called a packet data channel (PDCH) Different logical channels can occur on the same PDCH 10 GPRS physical channel, physical channel, logic channel, logic channel physical channel logic channel, physical layer resource physical channel packet data channel (PDCH) PDCH (Logical Channel)

11 Logical Channel Map PRACH Logical Channels PCCCH PBCCH PTCCH PPCH PAGCH PNCH PTCH PDTCH PACCH 11 packet common control channel PCCCH GPRS packet random access channel PRACH packet paging channel PPCH packet access grant channel PAGCH packet notification channel PNCH packet broadcast control channel PBCCH GPRS packet timing advance control channel PTCCH uplink downlink Packet timing advance control channel in the uplink direction (PTCCH/U) MS random access burst BSS random access burst time advance (TA) BSS Packet timing advance control channel in the downlink direction (PTCCH/D) TA updates MS packet traffic channel PTCH packet data traffic channel PDTCH packet associated control channel PACCH

12 Packet Traffic Channels (PTCH) Packet Data Traffic Channel (PDTCH) One PDTCH one physical channel Up to eight PDTCHs per MS Packet Associated Control Channel (PACCH) Conveys power control, resource assignment and reassignment information PACCH shares resources via PDTCHs An MS currently involved in packet transfer can be paged for circuit-switched services on PACCH 12 packet traffic channel PTCH Packet Data Traffic Channel (PDTCH) PDTCH PDTCH physical channel (PDCH), 8 PDTCHs Packet Associated Control Channel (PACCH) power control, resource assignment reassignment information MS PDTCH, PACCH MS ( PDTCH), ( call delivery) PACCH

13 Logical Channels (PCCCH) (1/2) Packet Common Control Channel (PCCCH) Convey common control channel Whether PCCCH is allocated or not, CCCH can be used to initiate a packet transfer PCCCH includes PRACH, PPCH, PAGCH, PNCH Packet Random Access Channel (PRACH) (MS BTS) To initiate uplink transfer for data or signaling 13 Packet Common Control Channel (PCCCH) GPRS common control signaling GPRS, PCCCH physical resources logical channel CCCH cell, ( ) PCCCH, PCCCH, GSM CCCH packet transfer PCCCH PRACH, PPCH, PAGCH, PNCH Packet Random Access Channel (PRACH) radio channel, (MS BTS)

14 Logical Channels (PCCCH) (2/2) Packet Paging Channel (PPCH) (BTS MS) Page an MS for both circuit-switched and packet data services Packet Access Grant Channel (PAGCH) (BTS MS) Resource assignment in the packet transfer establishment phase Packet Notification Channel (PNCH) (BTS MS) Used to send a Point-To-Multipoint Multicast (PTM-M) notification for resource assignment 14 PPCH (BTS MS) circuit-switched packet-switched, PPCH MS PAGCH (BTS MS), Packet Notification Channel (PNCH) multicast (PTM-M)

15 PBCCH & PTCCH Packet Broadcast Control Channel (PBCCH) Broadcast system information specific for packet data If PBCCH is not allocated, GSM BCCH can be used for broadcast Packet Timing Advance Control Channel (PTCCH) (BTS MS) Transmit a random access burst BSS estimates timing advance BSS to transmit timing advance information updates to MS 15 Packet Broadcast Control Channel (PBCCH) GPRS PBCCH, GSM BCCH Channel Packet Timing Advance Control Channel (PTCCH) (BTS MS) Packet timing advance control channel in the uplink direction (PTCCH/U) MS random access burst Packet timing advance control channel in the downlink direction (PTCCH/D) BSS random access burst time advance (TA) BSS Packet timing advance control channel in the downlink direction (PTCCH/D) TA updates MS

16 Two Concepts for GPRS Channel Management (1/2) Master-Slave Master: at least one PDCH PCCCH: control signalling for initiating packet transfer Salves: Other PDCHs PDTCH: for user data transfer PACCH: for dedicated signalling 16 GPRS Channel Management : Master-Slave ( ) Capacity on Demand ( ) Master-Slave PDCH master, ( ) PCCCH PDCHs slaves, (PDTCH) (PACCH)

17 Two Concepts for GPRS Channel Management (2/2) Capacity on Demand The Allocation of capacity for GPRS is based on the needs for actual packet transfers The operator decides the allocation of physical resources (ie PDCHs) for the GPRS traffic PCCCH and PBCCH are not necessary to exist 17 Capacity on Demand GPRS Channel Operator (ie, PDCHs) GPRS PDCH PCCCH PBCCH cell PCCCH, GPRS-attached MSs CCCH cell PBCCH, GPRS-attached MSs BCCH

18 Access and Assignment Phase 18 MS PDCH, network resource MS access request network (access and assignment phase), 2 phase: One-Phase Approach ( instructions) MS PRACH RACH : Packet channel Request PRACH MS, PDCHs, MS RACH packet channel, RACH, MS,, Two-Phase Access Network packet channel radio blocks Network PAGCH AGCH MS Two-Phase Access Approach ( 2 instruction) Network MS, PAGCH two-phase access PAGCH network MS PACCH (message 3), PACCHs (messages 3 and 4), MS network

19 GPRS Uplink Packet Transfer MS Network Access and Assignment PDTCH PDTCH PDTCH PDTCH PACCH PDTCH PDTCH PDTCH PACCH PACCH PDTCH PDTCH PACCH 19 GPRS packets access and assignment phase PDTCH (Packet Data Traffic Channel) Network PACCH (Packet Associated Control Channel) Packet Uplink Ack/Nack Network MS Packet Uplink Assignment PACCH MS MS PACCH Packet Control Acknowledgement Network data, network PACCH Packet Uplink Ack/Nack(final)

20 Um Protocol Layers RF Layer (RFL) Performs modulation/demodulation Physical Link Layer (PLL) Provides services for information transfer over a physical channel Medium Access Control (MAC) MAC is responsible for channel access (scheduling, queuing, contention resolution), PDCH multiplexing, and power control Radio Link Control(RLC) block segmentation and reassembly, buffering, and 20 retransmission with backward error correction RF Layer (RFL) PLL, PLL Physical Link Layer (PLL) ( frame,, ) Radio Link Control/Medium Access Control (RLC/MAC) Backward Error Correction Procedures ( ) RLC,, backward error correction MAC (,, ), PDCH,

21 Four GPRS Coding Schemes Coding Scheme User Data Rate Correction Capability Worst- Link Budget Max Cell Range CS1 905 Kbps Highest 135 db 450 m CS2 134 Kbps 133 db 390 m CS3 156 Kbps 131 db 350 m CS4 214 Kbps None 1285 db 290 m 21 GPRS Coding Scheme (ex, CS4),, user / (ie, ), (Link Budget), Cell

22 Gb (MS BSS SGSN) Application IP/X25 SNDCP LLC RLC MAC GSM RF Relay RLC BSSGP Network MAC Service GSM RF Libis Relay SNDCP GTP LLC UDP/ TCP BSSGP IP Network L2 Service Libis L1 Relay MS 22 BSS SGSN Gb, Gb layer 1, layer 2 BSS SGSN, LLC layer, MS SGSN, BSS relay

23 Gb Interface (MS BSS SGSN) The Gb interface allows many users to be multiplexed over the same physical resource The Gb interface includes Physical Layer Layer 2 NS (Network Service; Frame Relay) BSSGP (Base Station System GPRS Protocol) Relay Function LLC (Logical Link Control) Layer 3 SNDCP (SubNetwork Dependent Convergence Protocol) GMM SM (GPRS Mobility Management Session Management) 23 GSM A interface, GSM, circuit-switched GPRS Gb interface, Gb (multiplex/de-multiplex), BSS, BSS physical resource packet BSS layer 2 (LLC Relay Function)

24 Network Service (NS) (1/2) Physical layer (BBS SGSN) : frame relay link Each frame relay link supports one or more Network Service Virtual Links (NS-VLs) To construct an end-to-end virtual path between BSS and SGSN The path is Network Service Virtual Connection (NS-VC) NS manages NS-VCs 24 NS physical layer, BSSGP, layer 2 The NS layer delivers SGSN BSS encapsulated packets BSS SGSN : Directly connected by a frame relay link Indirectly through cascading links in a frame relay network physical frame relay link network service virtual links (NS-VL) NS-VL BSS SGSN end-to-end virtual link virtual link NS-VC NS NS-VC

25 Network Service (NS) (2/2) Using NS-VCs, NS transports data from uplayered BSSGP Packet Data Units (PDUs) The NS layer delivers encapsulated packets (SGSN BSS) Load sharing to distribute the packet traffic among the unblocked NS-VCs 25 NS NS-VCs, BSSGP ( BSS SGSN ) PDU NS encapsulated packets NS BSS NS-VC load sharing NS primitive, packet, congestion, NS user (eg: capacity) NS NS-VCs, eg, Resetting (eg, when a new NS-VC is set up) Testing, to check that an end-to-end communication exists (peer NS entities on given NS-VC) Blocking (when a NS-VC is not available) Unblocking (when a NS-VC becomes available again)

26 BSS GPRS Protocol (BSSGP) BSSGP Virtual Connection (BVC) provides communication path between BSSGP entities (ie, BSS, SGSN) BVC is supported by NS-VCs Each BVC transports BSSGP PDUs BSSGP provides the radio-related QoS and Routing Information required to transmit user data (BSS SGSN) Three service models supported by BSSGP: 1 BSSGP/RL service model 2GMM Model 3NM Model 26 GPRS GPRS BSS GPRS protocol BBSGP GPRS QoS BSSGP NS layer 2 sublayer, LLC BSSGP BSSGP Virtual Connection (BVC) BVC NS NS-VC, BSSGP BVC BVC BSS SGSN PDUs Each BVC is used to transport BSSGP PDUs between peer Point- To-Point functional entities, peer Point-To-MultiPoint functional entities, or peer-signaling functional entities BSSGP radio-related QoS BSS SGSN routing information BVC, a QoS profile MS ID SGSN BSS queues contexts BSSGP 3 services, : BSSGP/RL (BSS GPRS Protocol/Relay) service model GMM (GPRS mobility management) model NM (Network management) model

27 BSSGP/RL Service Model (1) BSSGP/RL service model In BSS, Relay function provides buffering and parameter mapping between RLC/MAC and BSSGP In SGSN, BSSGP controls the transfer of LLC frames across the Gb interface PDU contains User information (an LLC packet) RLC/MAC-related information A QoS profile PDU lifetime 27 BSS Relay (RL) service model LLC frames Um RLC Gb BSSCP BSS, Relay function RLC/MAC BSSGP buffering parameter mapping SGSN BSSGP service model LLC frames DL-UNITDATA primitive: A UL-UNITDATA PDU (BSS SGSN) UL-UNITDATA primitive: A DL-UNITDATA PDU (SGSN BSS) The PDU is either acknowledged (using RLC/MAC ARQ functionality) or unacknowledged (using RLC/MAC UNITDATA) functionality BSSGP PDU : User information (a LLC packet) RLC/MAC-related information ( MS radio access capability) QoS profile ( layer 3 signaling PDU data PDU ) PDP lifetime ( PDU BSS (queue), BSS )

28 GPRS Mobility Management (GMM) Service Model (2) GMM Model BSSGP GMM service model performs mobility management functions between SGSN and BSS Examples of GMM service primitives provided by BSSGP are PAGING SUSPEND RESUME 28 mobility management, SGSN BSS BSSGP GMM model, BSS, ( cell MS), MS BSSGP GMM service primitives : PAGING MS PAGING SGSN BSS: For Packet-switched transmission (if initiated by SGSN) For Circuit-switched transmission (if initiated by an MSC/VLR) Procedure, SGSN BSS cell SUSPEND GPRS, MS BSS SUSPEND PDU SGSN SUSPEND procedure RESUME MS GPRS, BSS MS Routing Area BSS RESUME PDU SGSN MS GPRS service

29 The Network Management (NM) Service Model (1/2) (3) NM Model NM service model handles Functions related to Gb interfaces BSS and SGSN Node Management Control BSSGP protocol machine Examples of BSSGP-supported NM service primitives are FLOW-CONTROL-BVC FLOW-CONTROL-MS No flow control is performed in the uplink direction There is a downlink buffer for each BVC 29 NM service model Gb interface ( flow control), BSS/SGSN SGSN BSS, SGSN BSSGP protocol machine, BSS BSSGP protocol machine BSSGP BSS SGSN radio-related QoS routing information BVC, a QoS profile MS ID SGSN BSS queues contexts Examples of BSSGP-supported NM service primitives: FLOW-CONTROL-BVC ( BVC, BSS SGSN MS ) FLOW-CONTROL-MS ( MS, BSS SGSN MS ) Uplink flow control BVC downlink buffer flow control

30 The Network Management (NM) Service Model (2/2) Flow control message FLOW-CONTROL- BVC (FLOW-CONTROL-MS) sent from the BSS to the SGSN To control downlink transmission at the SGSN Parameters: buffer size and the bucket leak rate PDU in the downlink is not transferred to the MS before its lifetime expires PDU is deleted from the BVC downlink buffer This action is reported to SGSN 30 SGSN downlink transmission, BSS flow control SGSN Primitive: FLOW-CONTROL-BVC FLOW-CONTROL_MS Flow control Parameters: buffer size BVC (MS) bucket leak rate BSS buffer PDU MS, PDU BVC downlink buffer SGSN

31 Logical Link Control (1/3) To convey information between Layer 3 entities (ie, MS and SGSN) To provide logical link connections with Flow control Sequence control Detection and recovery of Transmission errors Format errors Operational errors on logical link connection 31 LLC in Layer 2: MS SGSN layer 3, LLC, connection Flow control logic link connection frames Sequence control (detection) (recovery) connection transmission, Format and operational errors

32 Logical Link Control (2/3) LLC maintains a ciphered data link (MS SGSN) Independent of the underlying radio interface protocols The LLC layer supports several QoS delay classes with different transfer delay characters The LLC layer supports transmission with both ack and unack modes 32 LLC : LLC MS SGSN ciphered data link LLC,, BSS MS BS, SGSN, ciphered data link, SGSN, new LLC link QoS delay classes LLC LLC acknowledge unacknowledge

33 Logical Link Control (3/3) In the signaling plane LLC provides service to GPRS Mobility Management (GMM) protocol GMM includes functions : Attach, Authentication, and Transport of Session Management Messages In the transmission plane LLC provides service to SNDCP SNDCP: multiplexing of data coming from the different sources to be sent across LLC 33 signaling plane: LLC GMM SM (GPRS Mobility Management Session Management) LLC GMM, GMM, attach,, session ( ex: for PDP context activation/ deactivation), LLC layer GMM LLC, MS SGSN transmission plan: LLC SNDCP (SubNetwork Dependent Convergence) SNDCP multiplex, data (maybe network layer protocol, IP, X25) LLC SNDCP user data redundant protocol information segmentation, reassembly, compression Compression channel GPRS network layer protocols, network layer protocol GPRS SNDCP, SNDCP network layer protocol, GPRS network SNDCP network layer protocol, GPRS

34 Gn (SGSN GGSN) & Gp (SGSN GGSN in Other GPRS Network) 34 SGSN GGSN SGSN PDN GGSN, Gn interface SGSN GPRS network GGSN GGSN, Gp interface

35 Gn & Gp interfaces (1/3) Both Gn and Gp interfaces utilizes the GPRS Tunneling Protocol (GTP) Gn (SGSN GGSN) Gp (SGSN External GGSN) Gp is the same as Gn except Extra security functionality for internetwork communications over the Gp interface With GTP, An SGSN may communicate with multiple GGSNs A GGSN may connect to many SGSNs 35 Gn Gp GSN, GTP user data GPRS signaling, GTP tunnel Gp Gn Gp operator GPRS network external GGSN, security, security functionality These security functionality is based on mutual agreements between operators GTP, SGSN GGSN, GGSN SGSN MS, BSS, MSC/VLR, and HLR are not aware of the existence of GTP

36 Gn & Gp interfaces (2/3) In the transmission plane, GTP is supported by the Transmission Control Protocol (TCP) for connection-oriented transmission User Datagram Protocol (UDP) for connectionless transmission GTP transmission uses a tunneling mechanism to carry user data packets Two-way, point-to-point path Tunneling transfers encapsulate data between GSNs GTP implements out-of-band signaling 36 GTP layer 3, user data, IP-UDP/TCP transmission network X25 IP GPRS Quality of Service QoS Tunnel, GTP out-of-band signaling ( signal tunnel )

37 Gn & Gp interfaces (3/3) In the signaling plane, GTP is supported by UDP A GTP tunnel is defined by the associated PDP contexts in two GSN nodes, and is identified with a tunnel ID GTP performs Path Management Tunnel Management Location Management Mobility Management 37 signaling plane, GTP UDP transmission network GSN, path path tunnels GTP tunnel GSN nodes associated PDP contexts, tunnel ID GTP performs Path Management Tunnel Management Location Management Mobility Management

38 Path and Location Managements in GTP Path management To detect failures occurring in the path Echo_Request and Response message pair Location management If GGSN does not support SS7 MAP for communication with an HLR the interaction (GGSN HLR) is done indirectly through a specific GSN that performs GTP-MAP protocol conversation (usually through SGSN) 38 GTP Path management: GSNs Echo_Request Response message GTP path GTP Location management: GGSN HLR SS7 MAP, location management, GGSN HLR GTP-MAP GSN ( SGSN)

39 GTP Tunnel Management Creating Tunnels Updating Tunnels Deleting Tunnels 39 GTP Tunnel Management : Tunnels Tunnels Tunnels

40 GTP Tunnel Management: Creating Tunnel SGSN GGSN SGSN select one GGSN IP address Create_PDP_Context_Request GGSN creates a PDP context entry, a charging ID Create_PDP_Context_Response 40 SGSN GTP Tunnel: Step 1 SGSN DNS, GGSN IP, GGSN IP, Greate_PDP_Context_Request message GGSN Step 2 GGSN, SGSN DNS GGSN IP address ( GGSN IP ) Step 3 GGSN, PDP context entry MS, charging Identification entry, GGSN SGSN PDN,, Step 4 GGSN Create_PDP_Context_Response message SGSN message TCP UDP Note: GSN path, tunnel

41 GTP Tunnel Management: Activate PDP Context SGSN GGSN SGSN requests that the MS activate the indicated PDP context PDU_Notification_Request PDP_Context_Response GGSN asks HLR for serving SGSN 41 MS, GGSN activate a PDP context: Step 0 GGSN HLR MS serving SGSN Step 1 GGSN PDU_Notification_Request message SGSN Step 2 SGSN MS activate PDP context Step 3 SGSN PDU_Notification_Response message GGSN

42 GTP Tunnel Management: Updating Tunnel SGSN GGSN Want to update RA or PDP context Update_PDP_Context_request message (new SGSN address, Tunnel ID, QoS Negotiates) GGSN consider QoS constraint Update_PDP_Context_Response Or negative Update_PDP_Context_Response to reject the request SGSN will deactivate the PDP context 42 GTP Updating Tunnel, SGSN RA information PDP context, SGSN Update_PDP_Context_request GGSN Message : SGSN address Tunnel ID QoS Negotiates GGSN message, SGSN QoS negotiated, update, GGSN PDP context GGSN, QoS negotiated GGSN negative Update_PDP_Context_Response message SGSN, SGSN deactivate PDP context GTP ( Update_PDP_Context_request, negative Update_PDP_Context_Response ) PDP context GGSNs, load balancing

43 GTP Tunnel Management: Deleting Tunnel SGSN To detach MS or deactivate a PDP context GGSN Delete_PDP_Context_Request Delete_PDP_Context_Response 43 GTP Deleting Tunnel : SGSN GGSN Delete_PDP_Context_Request Delete_PDP_Context_Response detach a MS deactivate a PDP context GGSN activate a PDP context: Step 1 GGSN PDU_Notification_Request message HLR SGSN ( MS SGSN) Step 2 SGSN MS activate PDP context Step 3 SGSN PDU_Notification_Response message GGSN

44 GTP Mobility Management (1/2) GTP MM functions: GPRS Attach GPRS Routing Area Update Activation of PDP Contexts 44 GTP Mobility Management (MM) GTP MM : GPRS Attach GPRS RA Update PDP context activation

45 GTP Mobility Management (2/2) New SGSN Old SGSN MS sends P-TMSI Identification_Request (P-TMSI) Identification_Response (IMSI) SGSN_Context_Request (old RA ID, old P-TMSI, new SGSN address) SGSN_Context_Response (MM, PCP contexts, LLC ack) SGSN_Context_Acknowledge Buffered User Data 45 MS new SGSN, GTP layer mobility management Step 1 MS SGSN SGSN, MS P-TMSI SGSN SGSN SGSN Identification_Request Identification_Response message MS IMSI IMSI HLR MS record Step 2 SGSN SGSN_Context_Request message SGSN MS MM context, PDP contexts SGSN_Context_Request RA ID, P-TMSI SGSN address Step 3 SGSN message, SGSN_Context_Response message SGSN, message SGSN_Context_Response MM context, active PDP contexts, LLC acknowledge Step 4 SGSN Reponse message, SGSN_Context_Acknowledge message SGSN, SGSN MS Step 5 SGSN MS data SGSN

46 Gs (SGSN MSC/VLR) 46 SGSN GSM MSC/VLR Gs

47 Gs interface [GSM 0918]: SGSN MSC/VLR signaling plane interface BSSAP+ SS7 (MTP1, MTP2, MTP3) SCCP

48 Gs Interface (2/2) BSSAP+ procedures coordinate the location information of MSs that are both IMSI- and GPRS-attached BSSAP+ are used to convey some GSM procedures via the SGSN Paging Procedure Suspend Procedure Resume Procedure Location Update Procedure 48 BSSAP+ GSM GPRS interworking, Paging Procedure Suspend Procedure Resume Procedure Location Update Procedure MS GPRS network location update, GPRS network location update GSM network

49 Gs Interface: Paging Procedure (1/2) VLR can use GPRS to page MS for MSC/VLR-based service Class A or Class B MS can simultaneously IMSIand GPRS-Attached It is not necessary to page an MS for both GSM and GPRS services Reduce the overall paging load on the radio interface 49 MSC/VLR-based service MS VLR GPRS Class A Class B MS, Class A Class B MS IMSI- Attached GPRS-Attached Class-A mode of operation MS voice (GSM service, CS domain) data (GPRS service, PS domain) MS duplexer Class-B mode of operation MS GPRS GSM, voice data MS, (CS domain),, data GSM GPRS, MS radio interface

50 Gs Interface: Paging Procedure (2/2) Step 1 VLR sends the GPRS_PAGING to the SGSN Step 2 SGSN checks if the MS is GPRSattached and is known by SGSN Yes: SGSN sends the Gb PAGING to the BSS Step 3 SGSN forwards the paging result back to the VLR If the MS does not respond, VLR or BSS retransmits the paging message The SGSN is not responsible for retransmission of the message 50 Step 1 VLR GPRS_PAGING message SGSN paging procedure Step 2 SGSN, MS GPRS-attached SGSN, SGSN Gb PAGING message BSS Step 3 SGSN paging VLR MS, VLR BSS paging message, SGSN message

51 Gs Interface: Suspend Procedure To perform circuit-switched activity for a Class B MS (both IMSI- and GPRS-attached) VLR uses the SUSPEND procedure to inform the SGSN to suspend the GPRS activities of the MS MS VLR SGSN Circuit-switched activity request GPRS Signaling Message T6-1 SUSPEND T6-2 SUSPEND FAILURE T6-3 T VLR SUSPEND procedure SGSN MS GPRS, Class B ( IMSI-attached GPRS-attached) MS circuit-switched (ex ) Step 1 MS Circuit-switched activity request VLR Step 2 VLR T6-1 ( Timer T6-1 expires ) SUSPEND message SGSN, SGSN SUSPEND message, MS GPRS Step 3 T6-3, MS GPRS Signaling Message SGSN, SGSN, VLR Step 4, SGSN MS, SGSN SUSPEND FAILURE message VLR SUSPEND T6-2 VLR SUSPEND_FAILURE message, SUSPEND Procedure

52 Gs interface: Resume Procedure VLR sends a RESUME message to the SGSN to resume the GPRS activity of the MS VLR SGSN RESUME RESUME_ACKNOWLEDGE 52 Class B MS circuit-switched activity, VLR RESUME message SGSN MS GPRS activity

53 Gs Interface: Location Update Procedure A MS-initiated GPRS location update Step 1 SGSN sends GPRS_LOCATION_UPDATING_Request to VLR Step 2 The VLR Checks to determine if the IMSI is known If IMSI is unkonw, VLR retrieves the MM context of the MS from the HLR Success: VLR returns a GPRS_LOCATION_UPDATING_Accept to SGSN Fail: SGSN informs the MS that the location update failed SGSN does not hear from the VLR within a period T8-1 VLR replies with a GPRS_LOCATION_UPDATING_Reject to SGSN 53 MS GPRS network location update, GPRS network location update GSM network Step 1 SGSN GPRS_LOCATION_UPDATING_Request message VLR Step 2 VLR MS IMSI, VLR HLR MS MM context Step 3 SGSN T8-1 VLR, VLR GPRS_LOCATION_UPDATING_Reject message, SGSN MS location update location update, VLR GPRS_LOCATION_UPDATING_Accept message SGSN

54 Gi (GGSN PDN) 54 GGSN PDN Gi

55 Gi Interface (1/3) GGSN Interworks with PSDN (Public Switched Data Network) PDN (Packet Data Network) Gi GGSN PSDN/PDN The interworking models to PSDN includes X25 and X75 An MS is assigned an X121 address This address dynamically or permanently assigned The interworking models to PDN includes IP and Point-to-point (PPP) The IP address is statically assigned or dynamically allocated when PDP context activation 55 GGSN GPRS network external data network access point GGSN PSDN/PDN Gi interface GPRS network PSDN interworking model X25 X75 MS X121 address, PSDN (MS) MS X121 PSDN MS PDP context activation X121 GPRS X121 address pool GPRS network PDN interworking model IP PPP GPRS internet intranet, GPRS network IP network, GGSN router GGSN firewall, operator screen, IP, PDP context activation, GGSN DHCP

56 Gi Interface (2/3) GPRS may Transparently access the Internet Non-transparently access the intranet and ISP In transparently access the Internet, IP address from the GPRS operator s addressing space This address is used on GPRS network No authentication request at PDP context activation Domain name services provided by the GPRS 56 GPRS (transparently) Internet, Intranet ISP (transparently) Internet : MS IP GPRS operator IP GGSN GGSN Internet MS MS PDP context activation,, GGSN GPRS Domain name

57 Gi Interface (3/3) In nontransparent access to an intranet or ISP, IP address of an MS from the intranet/isp address space At PDP context activation, the MS must be authenticated by the intranet/isp DNS provided by the intranet/isp 57 Intranet ISP : MS IP intranet ISP, server intranet/isp PDP context activation, MS intranet/isp GPRS operator Domain name intranet/isp