Wireless networks - Lecture 18: GPRS: General packet radio service (Part 2). The main topics covered in this chapter include: GPRS protocol architecture; GPRS air interface; data routing and mobility; uplink data transfer; downlink data transfer; QoS in GPRS;...
Wireless Networks Lecture 18 GPRS: General Packet Radio Service (Part II) Dr Ghalib A Shah Outlines GPRS Protocol Architecture ► ► ► ► MS – BSS BSS – SGSN SGSN – GGSN GGSN – PDN GPRS Air Interface Data Routing and Mobility Uplink Data Transfer Downlink Data Transfer QoS in GPRS Last Lecture Introduction to GPRS GPRS Architecture Registration and Session Management Routing Scenario in GPRS Channels Classification Logical Channels Mapped by the MAC to physical channels Control channels for control, synchronization and signaling • Common • Broadcast • Dedicated Packet Traffic channels ► Encoded speech ► Encoded data Control Channels Packet Common Control Channel (PCCCH) ► When allocated in a cell, GPRS related mobiles camp on it ► Divded into • Random Access (PRACH): MS initiate packet transfer or respond to paging messages • Paging (PPCH): to page an MS prior to packet transfer • Access Grant (PAGCH): send resource assignment to MS prior to packet transfer • Packet Notification (PNCH): used to send a PTM-Multicast notification to group of MS Control Channels Packet Dedicated Control Channel (PDCCH) • Slow Associated Control Channel (SACCH) – – Radio measurements, power control and data SMS transfer during calls • Fast Associated Control Channel (FACCH) – – For one Traffic Channel (TCH) Carry Ack • Stand-alone Dedicated Control Channel (SDCCH) – is used in the GSM system to provide a reliable connection for signalling and Short Message Service Control Channels Packet Broadcast Control Channel (PBCCH) ► Frequency correction channels • Allows the MS to synchronize their Local Oscillator (LO) to the Base Station LO, using frequency offset estimation and correction ► Synchronization channel (MS freq vs BS) ► Broadcast control channel for general information on the base station GPRS Architecture Other GPRS PLMN GGSN Gp BSC Gb SGSN Gf Gs BTS MS Gn BTS EIR Gr D Gc GGSN Gi HLR MSC/VLR PDN Protocol Architecture Trans mis s io n Plane ► The protocols provide transmission of user data and its associated signaling S ig naling Plane ► Comprises protocols for the control and support of functions of the transmission plane Transmission Plane GPRS Bac kbo ne :S GS N GGS N ► S ubne two rk de pe nde nt c o nve rg e nc e pro to c o l ► It is used to transfer packets between SGSN and MS Data link laye r ► ► GTP tunnels the user packets and related signaling information between the GPRS support nodes LLC(MS-SGSN) RLC/MAC(MS-BSS) Phys ic al laye r ► ► PLL:channel coding,detection of errors, forward error correction, interleaving, detection of physical link congestion RFL:modulation and demodulation 10 Media Access Control (MAC) Performs contention resolution between channel access attempts Connection oriented Connections are called Temporary Block Flows (TBF) ► Logical unidirectional connection between two MAC entities ► Allocated resources on PDCH(s) ► Temporary Flow Identity (TFI) is unique among concurrent TBFs in the same direction 13 MAC: Channel Access & Resource Allocation Slotted Aloha ► Used in PRACH • MSs send packets in uplink direction at the beginning of a slot • Collision: Back off ->timer (arbitrary) ->re-transmit Time Division Multiple Access (TDMA) ► Predefined slots allocated by BSS ► Contention-free channel access 14 Network Layer (IP or X.25) Relay SNDCP GTP GTP LLC TCP/UDP TCP/UDP BSSGP IP IP MAC Network Service Network Data Link Service Service Data Link Layer PLL RFL Phy Layer Phy Layer Phy Layer Phy layer Relay RLC BSSGP Gm Gb BSS SGSN GGSN RLC :Radio link control BSSGP:BSS GPRS Application protocol PLL :Physical link layer GTP :GPRS tunneling protocol RFL :Physical RF layer TCP :Transmission control protocol MAC:Medium access control UDP :user datagram protocol IP :Internet Protocol Transmission Plane 15 Gi GPRS Air Interface Time Slot Number F1 Uplink F2 F3 Carrier Frequency F4 F F F F 4 Downlink Voice User1 GPRS User1 Voice User2 GPRS User2 GPRS User3 16 GPRS Air Interface Master slave concept • • • One PDCH acts as Master Master holds all PCCCH channels The rest of channels act as Slaves Capacity on demand • PDCH(s) are increased or decreased according to demand • Load supervision is done in MAC Layer 17 Uplink Data Transfer MS PRACH or RACH PAGCH or AGCH PACCH PACCH PDTCH PACCH PDTCH PACCH BSS Packet channel Request Packet Immediate assignment Packet resource Request Packet resource assignment Random Access Transmission Frame Transmission Negative Acknowledgement Retransmission of blocks in error Acknowledgement 18 Downlink Data Transfer MS PPCH or PCH PRACH or RACH PAGCH or AGCH PACCH PACCH or PAGCH PDTCH PACCH PDTCH PACCH BSS Packet paging request Packet channel Request Packet Immediate assignment Packet paging response Packet resource assignment Paging Transmission Frame Transmission Negative Acknowledgement Retransmission of blocks in error Acknowledgement 19 Mobility A mobile station has three states in GPRS system: ► Idle ► Standby ► Active The operation of GPRS is partly independent of the GSM network However, some procedures share the network elements with current GSM functions 20 Data is transmitted between a mobile station and the GPRS network only when the mobile station is in the active state In the active state, the SGSN knows the cell location of the mobile station In the standby state, the location of the station is known only as to which routing area it is in In the idle state, the mobile station does not have a logical GPRS context activated or any Packet-Switched Public Data Network (PSPDZ) addresses allocated, The MS can receive only those multicast messages that can be received by any GPRS mobile station 21 QoS Support Assumes that IP multimedia applications are able to ► Define their requirements ► Negotiate their capabilities ► Identify and select available media components GPRS specifies signaling that enable support for various traffic streams ► Constant/variable bit rate ► Connection oriented/connection less ► Etc 22 QoS Profile for GPRS Bearers parameters: ► Service precedence • classes ► Reliability parameter • classes ► Delay parameters • classes ► Throughput parameter • Maximum and mean bit rates 23 QoS Profile for GPRS Bearers QoS profile is included in Packet Data Protocol (PDP) context Negotiation managed through PDP procedures (activation, modification and deactivation) 24 Conclusions S ame GMS K mo dulatio n as GS M 4 c hanne l c o ding mo de s Pac ke tmo de s uppo rting up to abo ut 144 kbps Fle xible time s lo t allo c atio n (18) Radio re s o urc e s s hare d dynamic ally be twe e n s pe e c h and data s e rvic e s Inde pe nde nt uplink and do wnlink re s o urc e allo c atio n 25 EDGE Airlink Exte nds GPRS pac ke t data with adaptive mo dulatio n/c o ding 2x s pe c tral e ffic ie nc y o f GPRS fo r be s t e ffo rt data 8PS K/GMS K at 271 ks ps in 200 KHz RF c hanne ls s uppo rts 8.2 to 59.2 kbps pe r time s lo t S uppo rts pe ak rate s o ve r 384 kbps 26 Summary GPRS Protocol Architecture ► ► ► ► MS – BSS BSS – SGSN SGSN – GGSN GGSN – PDN GPRS Air Interface Data Routing and Mobility Uplink Data Transfer Downlink Data Transfer QoS in GPRS 27 ... PACCH PACCH or PAGCH PDTCH PACCH PDTCH PACCH BSS Packet? ?paging request Packet? ?channel Request Packet? ?Immediate assignment Packet? ?paging response Packet? ?resource assignment Paging Transmission Frame Transmission... to transfer packets between SGSN and MS Data link laye r ► ► GTP tunnels the user packets and related signaling information between the GPRS support nodes LLC(MS-SGSN) RLC/MAC(MS-BSS) Phys ic... Allocation Slotted Aloha ► Used in PRACH • MSs send packets in uplink direction at the beginning of a slot • Collision: Back off -> timer (arbitrary) -> re-transmit Time Division Multiple Access (TDMA)