Reference [1] Wireless and Mobile Network Architectures Y-Bing Lin and Imrich Chlamtac Wiley Computer Publishing. Chapter 18 [2] Chapter 9. [3] GPRS D

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1 General Packet Radio Service (GPRS) Overview 1 GPRS.

2 Reference [1] Wireless and Mobile Network Architectures Y-Bing Lin and Imrich Chlamtac Wiley Computer Publishing. Chapter 18 [2] Chapter 9. [3] GPRS Demystified John Hoffman McGraw-Hill 2

3 Introduction GPRS Architecture GPRS Air Interfaces GPRS Core Network Summary Outlines 3 : GPRS, GPRS GPRS air interface. GPRS, mobility management PDP context.

4 Introduction 4 Introduction GPRS, GPRS. GPRS.

5 Introduction (1/2) Based on the existing GSM infrastructure Provide end-to-end packet-switched services GPRS standard Initialized by ETSI/SMG in 1994 The main set of GPRS specifications was approved by SMG#25 in Completed in 1999 GPRS core network is designed for GSM, IS- 136, and 3G. 5 GPRS GSM, packet-switched the European Telecommunications Standards Institute / Special Mobile Group GPRS, GSM, IS-136., GPRS IS-136. GPRS core network 3G.

6 Introduction (2/2) New radio channels are defined. The allocation of these channels is flexible. One ~ eight time slots Several active users can share a single time slot. The uplinks and the downlinks are allocated separately. Various radio channel coding schemes 9 Kbps ~ 150 Kbps GPRS fast reservation 6 GPRS BS,. packet, logic radio channel, packet. GPRS, channel,,. timeslot packet, carrier 8 timeslots MS., timeslot, MS. channel, uplink downlink, Web, file transfer asymmetric flow. Channel coding schemes, CS1, CS2, CS3, CS4, 9kbps 150 kbps. coding,, coding. fast reservation, sec. GPRS GSM. packet data. GPRS SMS Circuit-switched. SMS GPRS channel.

7 GPRS Architecture Simplified 7 GPRS GSM GPRS GPRS

8 GPRS Entities MS, BSS, MSC/VLR, and HLR in the existing GSM network are modified. E.g., HLR: GPRS subscriber information. Two new network nodes are introduced in GPRS. Serving GPRS Support (SGSN) Gateway GPRS Support (GGSN) interworking with external packet-switched networks IP-based GPRS backbone network 8 MS, BSS, MSC/VLR HLR GSM, HLR GPRS subscriber information. GPRS GSM : GPRS serving GPRS support node SGSN SGSN MSC. SGSN GGSN At GPRS attach, the SGSN MS MM context (related to mobility and security for the MS). At PDP context activation, the SGSN session PDP context. GPRS gateway GPRS support node GGSN GPRS packet data network GGSN SGSN GPRS backbone network GPRS IP

9 Tunneling PDU (packet data unit) Encapsulate Decapsulate 9 X.25 IP protocol data unit PDU SGSN encapsulate SGSN capsulate tunneling GGSN GPRS

10 GPRS Example 1 10 GPRS MS 1 SGSN 1 MS 2 SGSN 2 SGSN 1 SGSN 2 MS2

11 GPRS Example 2 11 GPRS MS 1 SGSN 1 GGSN 1 GGSN 1 Internet MS 2 GPRS network 2 GPRS GGSN 2 GGSN 2 MS 2 SGSN 2 GGSN 2 SGSN 2 MS2

12 GPRS Example 3 12 GPRS

13 APN (Access Point Name) Access Point Name is a label according to DNS naming conventions describing the access point to the external packet data network. An APN is the logic way to name a GPRS service. Domain Name Service (DNS) server translates APN to GGSN s IP address. 13 GPRS addressing, operator,, APN GPRS, MS. APN, GPRS service, name, APN Label DNS GPRS APN,. Internet domain name a page on a specific server, APN, GGSN. Internet, DNS domain name IP address, GPRS network DNS server, APN GGSN IP address. HLR MS APN, HLR MS APN. HLR APN* default APN, user APN.

14 Access a GPRS Service with an APN Mobile user activates a service. MS sends request to SGSN. SGSN check whether the service has be authorized for this user. SGSN acquires the IP address of this specific GGSN (for the APN) from DNS server. A tunnel is created between SGSN and GGSN. 14 GPRS service : service, MS request SGSN. SGSN HLR, service user. SGSN local GPRS DNS server APN GGSN IP address. local DNS APN IP address: Case 1: user home network, request. Case 2: user foreign network, SGSN MS home network DNS. GGSN IP address, SGSN GGSN tunnel by GTP.

15 IP Address Allocation Fixed Addressing IP address is stored in HLR. It is sent to MS when PDP context is activated. Dynamic Addressing GGSN gets an IP address. SGSN assigns an address to the PDP context when it is opened. 15 MS external network PDP context, MS IP address. GPRS MS IP address : Fixed addressing: MS IP address, IP address HLR. MS PDP context APN, HLR IP address SGSN, MS. MS network IP address. fixed IP address, ID. fixed IP address IP, ICANN. Dynamic addressing: MS PDP context, SGSN IP address MS. PDP context, SGSN IP address. IP address GGSN. IP address: ( ) Via RADIUS form an external RADIUS server Via DHCP From a local address pool on the GGSN From the customer network via an L2TP tunnel from the GGSN

16 Mechanism to Get IP Address From a local address pool on the GGSN Via RADIUS form an external RADIUS server Via DHCP From the customer network via an L2TP tunnel from the GGSN 16 GGSN IP address: From a local address pool on the GGSN PSTN dialup server. GGSN IP address pool, MS IP, GGSN pool IP MS., APN address pool. APN IP address space, private network IP range. operator IP,. Via RADIUS form an external RADIUS server RADIUS server customer network. RADIUS server user terminal, fixed IP address. Via DHCP GGSN DHCP server IP address. DHCP server fixed IP address, MS IP address. From the customer network via an L2TP tunnel from the GGSN L2TP layer 2 tunneling protocol. IP user traffic IP network. PSTN dial-up to a Remote Access Server. GPRS, L2TP GGSN customer network router.

17 GPRS Billing Evernt- or Content-based Time-based CDRs Volume- or CDRs Time-based CDRs 17 GPRS Billing GSM. Charging gateway function (CFG) charging data record (CDR). CDR GPRS Billing Mediation ( ), billing record, Billing system,. GPRS billing : Flat-rate billing Per-packet billing Volume-based billing Value-based billing rate factor : Quality of Service Time of day Content, call type, services used Source or destination

18 GPRS Interface 18 GPRS network interface, transmission plane, signaling plane, protocol stack.

19 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 19 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.

20 GPRS Transmission & Signaling Planes The GPRS Transmission Plane Layered protocol structure For user information transfer and the associated control procedures e.g., flow control, error detection, error correction, and error recovery. The GPRS Signaling Plane Layered protocol structure For control of the transmission plane functions. 20 GPRS, OSI 7-layer, interface layered structure. protocol stack : protocol structure transmission plane.,,. transmission plane protocol structure signaling plane.

21 GPRS Transmission Plane Application IP/X.25 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/X.25 GTP UDP/TCP IP L2 L1 MS 21 / International Organization for Standardization/Open Systems Interconnection OSI/ISO GPRS TCP Transmission Control Protocol X.25 IP GPRS IP IP IP GPRS GPRS GPRS IP GPRS IP static IP GPRS dynamic host configuration protocol DHCP IP dynamic IP IP virtual IP IP GPRS IP GPRS IP OSI layer 1 L1 layer 2 L2

22 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 22 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

23 MS BSS GSM Radio Interface MAC (Medium Access Control) RLC (Radio Link Control) 23 physical layer physical link sublayer PLL physical RF sublayer RFL GSM modulation/demodulation radio link control/medium access control RLC/MAC GPRS MAC Aloha slotted Aloha based reservation protocol MAC MAC RLC selective ARQ

24 BSS SGSN BSS SGSN Frame Relay Network Service BSSGP (BSS GPRS Protocol) Relay BSS SGSN LLC (Logic Link Control) SNDCP (SubNetwork-Dependent Convergence Protocol) in transmission plane GMM (GPRS Mobility Management ) in signaling plane 24 NS (Network service) frame relay BSS SGSN Virtual Connection (NS-VC), NS NS-VC BSSGP BSSGP PDU. GPRS GPRS BSS GPRS protocol BBSGP GPRS QoS BSS, BSSGP Relay function RLC/MAC (MS BSS) BSSGP (BSS SGSN) buffering parameter mapping, SGSN MS packet., BSSGP mobility management ( cell to page MS, MS Routing Area) network management ( BSS SGSN, downlink flow control, QoS link). layer 2 LLC, MS SGSN : Flow control, sequence control, error detection and recovery ciphered data link, QoS delay class, ack/unack mode SGSN subnetwork-dependent convergence protocol SNDCP logic link control LLC

25 GGSN SGSN IP-based network GTP (GPRS Tunnel Protocol) Routing QoS 25 GTP TCP UDP User Datagram Protocol IP GPRS GPRS GPRS GPRS Tunnel Protocol GTP X.25 IP GPRS Quality of Service QoS

26 GPRS Air Interface 26 GPRS network air interface Um (BSS MS),, GPRS.

27 Um Interface (MS BSS) Um describes the radio interface between the MS and the BTS. gsm03.64 GPRS radio technology is based on the GSM radio architecture, which introduce new logical channel structure to control signaling and traffic flow over the Um radio interface. 27 GPRS MAC RLC GPRS packet data logic channel GSM GSM

28 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. 28 packet data (physical channel) PDCH PDCH

29 Logical Channel Map PRACH Logical Channels PCCCH PBCCH PTCCH PPCH PAGCH PNCH PTCH PDTCH PACCH 29 packet common control channel PCCCH GPRS packet paging channel PPCH packet random access channel PRACH 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.

30 GPRS Uplink 30 GPRS PRACH packet channel request packet immediate assignment PACCH packet resource request packet resource assignment PDCH PACCH PRACH ( phase 1) ( phase 2 optional) GPRS PDCH PRACH PAGCH MS GSM RACH AGCH

31 GPRS Downlink 31 PPCH packet paging request PRACH packet channel request PAGCH PACCH packet paging response

32 GPRS Core Network 32 GPRS core network MS, MM (mobility management), PDP context QoS profile.

33 GPRS Service Domain The core network consists of two service domains: Circuit-switched service (CS) domain Packet-switched service (PS) domain GPRS Terms Mobility Management (MM) context Packet Data Protocol (PDP) context Quality-of-service (QoS) profile 33 CS domain GSM PS domain packet 3 GPRS : MM context PDP context QoS profile package 3

34 Location Tracking In the CS domain Cells are partitioned into location areas (LAs). The LA of an MS is tracked by the VLR. In the PS domain Cells are partitioned into routing areas (RAs). An RA is typically a subset of an LA. The RA of an MS is tracked by the SGSN. SGSN also tracks the cell of an MS when packets are delivered between the MS and the SGSN. 34 MS CS domain PS domain location mobility management MS CS domain (i.e., GSM MS ) IMSIattached LA MS, VLR MS PS domain, GPRS-attached RA MS MS SGSN MS MS, SGSN cell MS

35 Mobility Management Mobility Management (MM) finite state machine Exercised in both the SGSN and the MS. Three states in the state machine: IDLE: MS is not known to GPRS. STANDBY: MS is attached to GPRS. MS is tracked by the SGSN at the RA level. READY: MS is tracked at the cell level. Packet data units can only be delivered in this state. 35 MM state MS GPRS mobility, states: Idle state: MS GPRS mobility management (not GPRS-attached) Standby state: MS GPRS MM location (GPRS-attached) Ready state: MS GPRS MS cell (GPRS-attached) MS data, GPRS-attached procedure MS SGSN MS Ready state MM context authentication/ciphering GPRS-attached MS SGSN GPRS 2 location tracking (Standby: RAs v.s. Ready: cells) Ready state SGSN MS cell packet MS, paging cost location update cost MS cell location update Standby state, SGSN MS RA packet MS paging cost location update cost MS RA location update

36 Mobility Management (MM) Context (1/2) The MM context consists MM state Other MM-related information Both in MS and SGSN Note that a GPRS MS can be IMSI-attached and GPRS-attached GPRS-attached only IMSI-attached only The IMSI attach is the same as that for a GSM MS. 36 MS SGSN MM Context MM state MM-related information Note: GPRS MS GSM GPRS (IMSI-attached and GPRSattached) (IMSI-attached GPRS-attached)

37 Mobility Management (MM) Context (2/2) In GPRS attach procedure Step 1: Both the MM states in MS and the SGSN are moved to the READY state. Step 2: An MM context is created in each of MS and SGSN. Step 3: Authentication/Ciphering may be performed. Step 4: A logical link is established between MS and SGSN. 37 MS IDLE state MM procedure GPRS-attach IDLE state READY state MM context MS SGSN MM context authentication ciphering MS SGSN logic link, MS GPRS attach (Ready, Standby), GPRS detach ( idle), session

38 Mobility Management State Machine T1 (Idle Ready): MS perform GPRS attach. T2 (Ready Idle): MS is detached from the GPRS. T3 (Idle Ready): MS sends a packet to SGSN. T4 (Idle Ready): a Ready timer is timeout. T5 (Idle Ready): when tracking of MS is lost. T1 Idle T5 Standby T4 T3 Ready T2 38 T1 T5, : T1 MS T2 MS SGSN T3 MS SGSN page MS sends packet T4 MS SGSN MS SGSN Ready timer timeout MS packet Standby state SGSN READY timer Attach Accept Routing Area Update Accept MS timer paper SGSN Ready timer MS cell, Standby T5: SGSN MS SGSN state machine Idle state HLR SGSN Cancel Location (MS SGSN ) Idle state

39 STANDBY States MS is attached. Detect page for GPRS data or signaling No data transmission allowed May initiate GPRS detach procedure to back to Idle. Change to Ready when data or signaling is sent (page response, PDP context activation...) May initiate activation or deactivation of PDP context Not inform the SGSN on a change of cell in the same RA Perform GMM Routing Area update procedure 39 Perform GPRS cell selection and re-selection locally MS GPRS-attached MS STANDBY : STANDBY MS ( READY ) PDP context activation ACTIVE PDP context INACTIVE MS data (PDP context ACTIVE) MS READY GPRS-detach MM Idle MM SGSN MS RA MS RA GMM Routing Area update procedure

40 READY States (1/2) MS is attached or attaching. Perform GPRS cell selection and re-selection locally or controlled by the network Perform cell update, but if RA changed, perform RA update BSSCP header of the data packet include CGI+RAC+LAC May send and receive PDP PDUs. NWK will not initiate GPRS pages for an MS in this state Cs pages may be done via SGSN 40 MS GPRS-attached MS READY : GPRS GPRS cell selection re-selection cell cell update RA RA update BSSCP header CGI (Global Cell Identity) RAC (Routing Area Code) LAC (Location Area Code) PDP PDUs READY state GPRS CS Page: SGSN MSC Calls SMS GPRS Channel GSM Channel

41 READY State (2/2) Other futures: May activate or deactivate PDP contexts Move to Standby when Ready timer expires or force to Standby Move to Idle after detach 41 : PDP context activation ACTIVE PDP context INACTIVE Ready State timer MS Standby

42 PDP (Packet Data Protocol) To create a data transmission path, MS initiate PDP Context Activation procedure. Two PDP states: ACTIVE or INACTIVE. PDP context in ACTIVE state contains mapping and routing information for packet transmission between MS and GGSN. The PDP contexts stored in MS, HLR, SGSN, and GGSN. Active Inactive 42 GGSN MS PDP context session MS HLR SGSN GGSN PDP context MS PDP context activation procedure PDP context deactivation PDP context : ACTIVE INACTIVE PDP context GGSN MS MS

43 PDP Context A PDP context is created for each communication session. An MS in STANDBY or READY MM state may activate a PDP context. MS moves its PDP state from INACTIVE to ACTIVE. T MS is known to the GGSN The ACTIVE PDP context becomes INACTIVE when the PDP context is deactivated. When the MS is detached from GPRS, all PDP contexts are deactivated. 43 MS STANDBY READY MM state PDP context PDP context INACTIVE ACTIVE GGSN MS MS PDP context session MS, PDP context IP address terminal Multiple IP addresses ACTIVE PDP context deactivated ACTIVE INACTIVE state MS GPRS-detached PDP contexts

44 QoS Profile A QoS profile is maintained in the PDP context to indicate radio and network resources required for data transmission. Each PDP context has an associated QoS that negotiated during PDP context activation procedure. QoS attributes includes Precedence class, Delay class, Reliability class, Peak throughput class, Mean throughput 44 QoS profile attributes : Precedence class: 3 congestion Delay class: class 1 delay 0.5 sec, class 2 delay 5 sec, class 3 delay 50 sec class 4 best-effort ( ) Reliability class: data loss out-of-sequence corrupted data error rates 5 Reliability class 1 acknowledgement for GTP mode LLC frame mode RLC block mode LLC data Reliability class 5 acknowledgement LLC data Peak throughput class: (maximum data transmission rate). 9 8Kbps 2,048 Kbps Mean throughput: (average data transmission rate). 19 best-effort 111 Kbps

45 Reliability - QoS Reliabili ty Class GTP Mode LLC Frame Mode LLC Data Protection RLC Block Mode Traffic Type 1 Ack Ack Protected Ack Non real-time traffic, errorsensitive application (cannot cope with data loss) 2 Unack Ack Protected Ack Non real-time traffic, errorsensitive application (cope with infrequent data loss). 3 Unack Unack Protected Ack Non real-time traffic, errorsensitive application that can cope with data loss, GMM/SM, and SMS. 4 Unack Unack Protected Unack Real-time traffic, errorsensitive application that can cope with data loss. 5 Unack Unack Unprotected Unack Real-time traffic, error nonsensitive application that can cope with data loss. 45 reliability classes Ack Acknowledgement, Unack Acknowledgement Protected LLC Data Traffic Type class

46 Relationship between MM Context, PDP Context, and QoS Profile 46 MM Context PDP Context QoS Profile PDP Context maintain PDP Context ACTIVATE GPRS QoS Profile negotiated radio network resources

47 Summary GPRS Architecture GPRS Air Interface GPRS Core Network 47

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