This document describes the handling of TBFs -------------------------------------------- Notes: TBF Instance for one temporary block flow. LLC Frame Current frame to be transmitted or received. If tbf->llc_length is not 0, the frame exists, if 0, the frame does not exist. If tbf->llc_index is not 0, parts of the frame have been transmitted or received so far. LLC Queue Queue of next frames to be transmitted. States: GPRS_RLCMAC_ASSIGN After a downlink TBF is created, it resides in this state until the block flow can start. This is required to give the mobile time to listen to connect to downlink PDCH. GPRS_RLCMAC_FLOW, During packet flow, this state indicates downlink and uplink TBF block flow. GPRS_RLCMAC_FINISHED, Uplink TBF: After final block is received AND all other blocks are completely received, the state is entered. The PACKET CONTROL ACK is still not received. (Counter N3103 is counted on each poll request.) Downlink TBF: All blocks including the final block has been transmitted. Not all downlink blocks are acknowledged yet. (Counter N3015 is counted on each poll request.) GPRS_RLCMAC_WAIT_RELEASE, The all blocks on downlink TBF have been acked by mobile. The penalty timer T3192 is running on mobile. GPRS_RLCMAC_RELEASING, Wait for TFI/USF to be re-used. This state is entered when a counter reaches it's maximum and T3169 is running. When downlink LLC PDU is received: If downlink TBF exists for given TLLI, but not in RELEASING state: If downlink TBF is in FLOW or FINISHED state: Enqueue PDU to LLC Queue of TBF. Done. If downlink TBF is in WAIT RELEASE state: Attach PDU to LLC Frame of TBF. Put TBF back into FLOW state. Done. If dowlink TBF does not exists for given TLLI, or in RELEASING state: Create new downlink TBF. Attach PDU to LLC Frame of TBF. If uplink TBF exists for given TLLI, but not in RELEASING state: Assign packet channel PACCH. Done. If uplink TBF does not exists for given TLLI, or in RELEASING state: Assign packet channel AGCH. Done. When channel request for uplink TBF is received: Create new uplink TBF. If channel request was received on RACH Assign packet channel AGCH. Done If channel request was received on PACCH Assign packet channel PACCH. Done Handling of LLC Frame of downlink TBF and LLC Queue of downlink TBF: If a downlink TBF is created, the LLC PDU is attached to LLC Frame of TBF (downlink flow is assigned to MS). If a downlink TBF exists, the LLC PDU is enqueued to LLC Queue of TBF. During transfer of downlink blocks, the LLC Queue is dequeued whenever all segments of LLC Frame were used for generation of downlink blocks. (If a block is partly filled with LLC Frame segment, its remaining space is filled with the next LLC Frame from the Queue.) If the transfer is finished, no more LLC Frames are dequeued from the LLC Queue, in case a new frame has arrived during lifetime of TBF. If the all downlink blocks have been acknowledged, the LLC Queue is dequeued and an existing frame is attached to LLC Frame. If so, the new state is FLOW (downlink flow is assigned to MS), otherwise WAIT RELEASE. If a new LLC PDU is attached to LLC Frame during WAIT RELEASE state, the state is changed to FLOW (downlink flow is assigned to MS). Handling of LLC Frame on uplink TBF: Received uplink blocks are appended to LLC Frame of TBF. If the PDU is complete, it is forwarded to the upper layer. Control TS: On uplink or downlink assignment, it is required to have one timeslot that can be used to receive and transmit. This timeslot is used at uplink TBF to acknowledge and to assign other TBF. This timeslot is used at downlink TBF to poll acknowledgement and to assign other TBF. The first common TS (first_common_ts) is calculated when channels are allocated. After creation of TBF or after assignment to different TS layout, the first common TS is used for control TS. The first common TS (and so control TS) must not need to be allocated to MS as uplink TBF. (E.g. in case of non-available USF for this slot) Polling: In order to poll uplink control block from MS, a special poll state and frame number is stored at TBF. The scheduler reads that value and will not assign uplink resource for other TBFs at that frame number. When there is no uplink transmission received on the block, a timeout is indicated by layer 1 interface. There are two ways of checking timeout: - The received frame is bad (BFI). - The GSM indicates that the block should have been already received. Because polling requires uplink response from MS, the polling must be performed at control TS. Data structures of TBFs and PDCHs: There is a global structure for BTS. The BTS structure has 8 TRX structures. Each TRX structure has 8 PDCH structures, one for each timeslot. There are two linked lists of TBF instances: - uplink TBFs - downlink TBFs Each TBF instance also has: - a direction - a TFI of range 0..31 - an array of 8 PDCH structures, one for each assigned timeslot - in case of uplink TBF: an array of 8 USFs, one for each assigned timeslot Each TRX and all it's PDCH structures also have: - an array of 32 uplink TBFs that are assigned to this PDCH - an array of 32 downlink TBFs that are assigned to this PDCH On creation of a new TBF, it links to all assigned PDCHs. Each PDCH links to that TBF. The TBF is added to the list of TBFs. In case of uplink TBF: The allocated USFs are stored for each timeslot. On release of a TBF, the link to this PDCH is removed from all assigned PDCHs. The TBF is removed from the list of TBFs. The TBF is destroyed.