RLC/MAC One-phase access [Under
GPRS >> RLC/MAC]
» MS-BSS Interface; RLC/MAC -
04.60 «
»
GPRS radio channels - 5.02 «
»
Conformance tests - 51.010-1, section 41 «
»
GMM procedures - 24.008 «
Let us take GMM attach procedure as an example.
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 | FCH/SCH
Synchronisation with BTS | |
| BCCH
SYS_INFO 1-4 | | | Get information related to channel configuration, GPRS support, location of PBCCH etc. | |
| PBCCH
PACKET SYSTEM INFORMATION 1-8, 13-15 | | | Get information related to GPRS channel configuration etc. | |
| RLC/MAC receives LLC PDU containing GMM Attach message, splits in blocks. MS need to start TBF procedure. | |
| PCCCH
Wait for USF=FREE (7). | | | USF=FREE in DL PCCCH indicates PRACH on next uplink RLC/MAC block. | |
| PRACH
PACKET CHANNEL REQUEST |  | | GMM PDU so one-phase will be requested. This message contain random reference number for later resolution. MS need to listen to PCCCH for resource allocation. | |
| PCCCH
PACKET UPLINK ASSIGNMENT | | | MS gets above message with matching reference number. Message contain dynamic allocation - physical channel information (timeslot), USF, TFI, USF granularity, TA1 etc. | |
| PDTCH
Wait for assigned USF | | | MS should start tranmission of blocks over corresponding uplink once assigned USF appear over downlink RLC/MAC blocks | |
| PDTCH
BLOCK 0 [CV=3, TLLI, assigned TFI] | | | The network need to respond back with PACKET UPLINK ACK/NACK message after contention resolution. The contention resolution is completed on the network side when the network receives an RLC data block that comprises the TLLI value that identifies MS and TFI value associated with that TBF. | |
| PDTCH
BLOCK 1 [CV=2, TLLI, assigned TFI] | |
 | PACCH
PACKET UPLINK ACK | | | Contain TLLI, (optional) Timing Advance. This indicate that at network side, at least one RLC/MAC block has been correctly received and contention resolution in terms of TLLI and TFI is OK on network side. The contention resolution is OK on MS side when TLLI match. | |
| PDTCH
BLOCK 2 [CV=1, TLLI, assigned TFI] | |
| PDTCH
BLOCK 3 [CV=0, TLLI, assigned TFI] | |
| PACCH
PACKET UPLINK ACK | | | Final indicator bit will be 1 to indicate final ack (i.e. all RLC/MAC blocks received and no retransmission needed). Header field, RRBP (Relative Reserve Block Period) now specify uplink PACCH radio block reserved for MS to send PACKET CONTROL ACK. Validity of RRBP is based on S/P (Supplementary/Polling) bit. | |
| PACCH
PACKET CONTROL ACK | | | MS sends this message in uplink radio block mentioned in RRBP field of PACKET CONTROL ACK. This message indicate to network that TBF can be released. | |
| This complete one TBF. Network can reuse this TFI now. For further communication, MS or Network need to initiate TBF procedure again. In current example of GMM attach, MS has sent GMM Attach request, and need to wait for response from Network | |
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1: Note about Timing Advance
GPRS has number of ways to Timing Advance control
One method is to calculate TA based on PACKET CHANNEL REQUEST
burst sent over PRACH and inform MS in PACKET RESOURCE (UL/DL)
ASSIGNMENT. During block flow, packet UL ack/nack can be used for
informing TA. Later Network can update TA by sending PACKET POWER
CONTROL/TIMING ADVANCE message.
GPRS also has a concept of Continuous Timing Advance procedure.
This uses PTCCH (Packet Timing Control CHannel). A MS (group of
MSs) is given a TA index (TAI) and TS number in PTCCH. TA
Information Element sent in PACKET CHANNEL REQUEST and PACKET
RESOURCE (UL/DL) ASSIGNMENT messages contain either TA value or
(TAI and TS). MS then need to send access burst over PTCCH as
allocated and receive timing advance value in downlink channel.
We will continue with GMM attach example.
References: GPRS
in Practice by McGuiggan
| Copyright © Samir Amberkar 2010 | § § §
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