EDGE GPRS TBF 2

User Description, GPRS/EGPRS Connection Control and Transfer USER DESCRIPTION E Copyright © Ericsson AB 2004-2005 - All Rights Reserved Disclaimer No part of this document may be reproduced in any form without the written permission of the copyright owner. The contents of this document are subject to revision without notice due to continued progress in methodology, design, and manufacturing. Ericsson shall have no liability for any error or damage of any kind resulting from the use of this document. Trademark List Ericsson is a trademark owned by Telefonaktiebolaget LM Ericsson. All other product or service names mentioned in this User Description are trademarks of their respective companies. 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer Contents 1 Introduction 1 2 Capabilities 3 3 Technical Description 5 3.1 General 5 3.2 Set Up of TBF 6 3.3 Ongoing Uplink TBF 14 3.4 Ongoing Downlink TBF 18 3.5 GPRS/EGPRS Load Optimization 25 3.6 Suspend and Resume 27 3.7 Upgrade of a TBF 28 3.8 Re-reservation of a TBF 29 3.9 Downgrade of a TBF 31 3.10 Change of TBF Mode 32 3.11 Release of a TBF 33 3.12 Related Statistics 38 3.13 Main Changes in Ericsson GSM System R12/BSS R12 38 4 Engineering Guidelines 39 5 Parameters 43 5.1 Main Controlling Parameters 43 5.2 Parameter for Special Adjustments 43 5.3 Value Ranges and Default Values 45 6 Appendix 47 7 Concepts 49 Glossary 55 Reference List 59 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer 1 Introduction This GPRS/EGPRS Connection Control and Transfer User Description (UD) describes the actual control of Temporary Block Flows (TBFs), setup and release of TBFs and transfer of data within TBFs. 206/1553-HSC 103 12/7 Uen B 2005-08-18 1 User Description, GPRS/EGPRS Connection Control and Transfer 2 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer 2 Capabilities The capability of the functionality in this GPRS/EGPRS Connection Control and Transfer UD is to: • set up, maintain, upgrade, downgrade, re-reserve and release TBFs in a way that each end-user will get the best possible data throughput. • provide efficient flow control and scheduling • keep the TCP RTT, which reduces the set up times and increases the data throughput. This is done through Delayed Release of Downlink TBF, Extended Uplink TBF Mode, Early set up of Downlink TBF, Loss Free Preemption and Persistent Uplink Scheduling. 206/1553-HSC 103 12/7 Uen B 2005-08-18 3 User Description, GPRS/EGPRS Connection Control and Transfer 4 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer 3 Technical Description 3.1 General The responsibility for the handling of a TBF is split up in the BSS between the so called connection control part and the transfer part. The connection control part handles: • set up of a TBF • release of a TBF • resource reallocation of an uplink TBF • downgrade of a TBF • upgrade of a TBF • re-reservation of a TBF • TBF keep-alive mechanisms • suspend and resume of a TBF. The transfer part handles: • reception of LLC-PDUs from the SGSN and sending LLC-PDUs to the SGSN • scheduling and reception of RLC/MAC blocks from the GPRS/EGPRS MS and assembly of these into LLC-PDUs • reception of LLC-PDUs from SGSN and disassembly of these into RLC/MAC blocks • scheduling and transmission of RLC/MAC blocks to the GPRS/EGPRS MS and from the GPRS/EGPRS MS • scheduling and transmission/reception of RLC/MAC control blocks containing signalling information • flow control. The goal of this UD is to describe ’the life of a TBF’ meaning that the following chapters do not follow the functional order listed above. 206/1553-HSC 103 12/7 Uen B 2005-08-18 5 User Description, GPRS/EGPRS Connection Control and Transfer 3.2 Set Up of TBF 3.2.1 General Different ways to set up a TBF are used depending on if it is a downlink or uplink connection and if PCCCH, CCCH or PACCH is used for the control signalling. PCCCH is used if MPDCH exists in the cell while CCCH is used if no MPDCH exists in the cell. PACCH is used if an uplink or downlink TBF is already in use, regardless if MPDCH exist in cell or not. Two-phase access method has to be used if an MPDCH/CCCH is allocated on a non-EDGE capable TRU that does not support the EGPRS PACKET CHANNEL REQUEST message. For a Dual Transfer Mode (DTM) connection the first TBF (UL or DL) is setup according to Reference [1]. Any secondary TBF (requested while the first TBF is alive) is setup as described in this document. 3.2.2 Set Up of Uplink TBF Using PCCCH The purpose is to establish an uplink TBF to support the transfer of data in the uplink direction. Since, in this scenario, there is a Master PDCH in the cell, a GPRS/EGPRS MS in Standby state is camping on the PBCCH. The set up of an uplink TBF using PCCCH is always initiated at the reception of one of the following messages, on PRACH, from the GPRS/EGPRS MS: • 44.060 PACKET CHANNEL REQUEST (GPRS MS) • 44.060 EGPRS PACKET CHANNEL REQUEST (EGPRS MS). The set up of uplink TBF using PCCCH will fail and the 44.060 PACKET ACCESS REJECT message is sent to the GPRS/EGPRS MS on PAGCH if: • No resources are available. E.g. no PDCH, TFI, USF and TAI. • The access delay is greater than the maximum timing advance allowed in the cell. The proceeding events described below depend on the access type received in the channel request from the GPRS/EGPRS MS. Access Type is One Phase Access Request The multislot class capability of the GPRS/EGPRS MS is included in the channel request and used by the BSS to calculate the number of PDCHs that will be reserved for the TBF. The 44.060 PACKET UPLINK ASSIGNMENT message, including the assigned PDCHs, is sent to the GPRS/EGPRS MS on PAGCH. The uplink scheduling is started. The TBF is established when the Contention Resolution procedure is completed. If the feature Reduced Packet Latency is available, indicated by the parameter MSRACREQPCCCH, the MS RAC is requested from the EGPRS MS in the IE 6 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer Access Technology Request in the 44.060 PACKET UPLINK ASSIGNMENT message. The MS can respond with a 44.060 PACKET RESOURCE REQUEST message including the MS RAC. Access type is Two Phase Access Request The Two Phase Access is requested by the GPRS/EGPRS MS in the channel request message. The purpose of the first phase is to assign a temporary PDCH to the GPRS/EGPRS MS that is used to send additional information to the BSS. The purpose of the second phase is to assign the PDCHs that are to be used for the actual data transmission. First phase: The first 44.060 PACKET UPLINK ASSIGNMENT message including the temporary reserved PDCH and a request to proceed with the two phase access method, is sent to the GPRS/EGPRS MS on PAGCH. The GPRS/EGPRS MS responds with the 44.060 PACKET RESOURCE REQUEST message, sent on PACCH, in the reserved block period. The Contention Resolution procedure is, by the network, considered as completed at reception of this message. The message contains TLLI, Access Type and the MS RAC. The MS RAC and Access Type are used by the PDCH reservation algorithm to calculate the number of PDCHs that will be reserved for the TBF. Second phase: The second 44.060 PACKET UPLINK ASSIGNMENT message including all reserved PDCHs is then sent to the GPRS/EGPRS MS on PACCH. A TBF is established and the uplink scheduling is started. Access type is Short Access Request, Signalling, Page Response, Cell Update or Mobility Management Procedure For the Short Access Request, the multislot class capability is not included in the channel request which is why only one PDCH is reserved. For the other cases, only one PDCH is needed. The 44.060 PACKET UPLINK ASSIGNMENT message, including one reserved PDCH, is sent to the GPRS/EGPRS MS on PAGCH. The uplink scheduling is started. The TBF is established when the Contention Resolution procedure is completed. 3.2.3 Set Up of Uplink TBF Using CCCH The purpose is to establish an uplink TBF to support the transfer of data in the uplink direction. Since, in this scenario, there is no Master PDCH in the cell, a GPRS/EGPRS MS in Standby state is camping on the BCCH. The GPRS/EGPRS MS sends a 44.018 CHANNEL REQUEST or a 44.060 EGPRS PACKET CHANNEL REQUEST message to the BTS on RACH. The BTS forwards the message in a 48.058 CHANNEL REQUIRED message or an EGPRS CHANNEL REQUIRED message to the BSC. 206/1553-HSC 103 12/7 Uen B 2005-08-18 7 User Description, GPRS/EGPRS Connection Control and Transfer The set up of uplink TBF using CCCH will fail and the message 44.018 IMMEDIATE ASSIGNMENT REJECT is sent to the GPRS/EGPRS MS on AGCH if: • No resources are available. E.g. no PDCH, TFI, USF and TAI. • The access delay is greater than the maximum timing advance allowed in the cell. The proceeding events described below depend on the establishment cause or the access type received in the channel request from the GPRS/EGPRS MS. Access Type is regarded as establishment cause in the following text. Establishment Cause is One Phase Packet Access The GPRS/EGPRS MS may be capable of handling several channels, but only one PDCH can be reserved since the GPRS/EGPRS MS capability is unknown. The message 48.058 IMMEDIATE ASSIGN COMMAND including the message 44.018 IMMEDIATE ASSIGNMENT is sent to the BTS and the BTS forwards the message 44.018 IMMEDIATE ASSIGNMENT to the GPRS/EGPRS MS on AGCH and the message IMMEDIATE ASSIGN SENT is sent from the BTS to the BSC. Uplink scheduling is started. The TBF is established when the Contention Resolution procedure is completed. If the message IMMEDIATE ASSIGN SENT is not received from the BTS, the PDCH is released and the set up of uplink TBF using CCCH is terminated. If the feature Reduced Packet Latency is available, indicated by the parameter MSRACREQCCCH, the BSC will retrieve the MS RAC after receiving the 44.060 EGPRS PACKET CHANNEL REQUEST message. The MS RAC is requested from the EGPRS MS in the IE Access Technology Request in the 44.018 IMMEDIATE ASSIGNMENT message. The MS can respond with a 44.060 PACKET RESOURCE REQUEST message including the MS RAC. Establishment Cause is Single Block Packet Access The Single Block Packet Access is actually a type of two-phase access (very similar to the PCCCH case). The Single Block Packet Access is requested by the GPRS/EGPRS MS in the channel request message. The purpose of the first phase is to assign a temporary PDCH to the GPRS/EGPRS MS that is used to send additional information to the BSS. The purpose of the second phase is to assign the PDCHs that are to be used for the actual data transmission. First Phase: The message 48.058 IMMEDIATE ASSIGN COMMAND including the message 44.018 IMMEDIATE ASSIGNMENT is sent to the BTS. The BTS forwards the message 44.018 IMMEDIATE ASSIGNMENT, including the temporary reserved PDCH and a request to proceed with the two phase access method, to the GPRS/EGPRS MS on AGCH. The GPRS/EGPRS MS answers in the reserved block period with the message 44.060 PACKET RESOURCE REQUEST. The Contention Resolution procedure is completed on the network side at reception of this message. The message contains TLLI, Access Type 8 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer and the MS RAC. The MS RAC is used by the PDCH reservation algorithm to calculate the number of PDCHs that will be reserved for the TBF. Second phase: The 44.060 PACKET UPLINK ASSIGNMENT message including all reserved PDCHs is then sent to the GPRS/EGPRS MS on PACCH. TBF is established and uplink scheduling is started. 3.2.4 Set Up of Uplink TBF Using PACCH The purpose is to establish an uplink TBF to support the transfer of data in the uplink direction. A prerequisite, in this scenario, is that the GPRS/EGPRS MS is in Ready state and already assigned to a downlink TBF. The 44.060 PACKET DOWNLINK ACK/NACK message or the 44.060 EGPRS PACKET DOWNLINK ACK/NACK message, sent from the GPRS/EGPRS MS on PACCH, is used to initiate the set up of uplink TBF using PACCH. The GPRS/EGPRS MS includes a Channel Request Description IE in the message and it is sent to the BSS. If the capability of the GPRS/EGPRS MS is available, BSS calculates the number of PDCHs that will be reserved for the TBF. A check is also performed to see that there are sufficient number of free USFs and a TFI. The 44.060 PACKET UPLINK ASSIGNMENT message is then sent to the GPRS/EGPRS MS, on PACCH, and uplink scheduling is started if at least one PDCH could be reserved. The uplink TBF is then established. If no PDCHs can be reserved then the message 44.060 PACKET ACCESS REJECT is sent to the GPRS/EGPRS MS on PACCH and the set up of uplink TBF using PACCH is terminated. 3.2.5 Set Up of Downlink TBF Using PCCCH The purpose is to establish a downlink TBF to support the transfer of data in the downlink direction. Since, in this scenario, there is a Master PDCH in the cell, a GPRS/EGPRS MS is camping on the PBCCH. A GPRS/EGPRS MS in standby state will first be paged according to procedures described in Reference [6]. The GPRS/EGPRS MS then responds to the page, with a set up of an uplink TBF using PCCCH described in Section 3.2.2 on page 6 (Access Type = Page Response), by sending any LLC PDU to the SGSN. The GPRS/EGPRS MS now enters ready state and the SGSN may start sending LLC-PDUs. A GPRS/EGPRS MS in ready state can receive LLC-PDUs from the SGSN at any time. The received LLC-PDUs may contain information about the capability of the GPRS/EGPRS MS. This information is used by the BSS to calculate the number of PDCHs that will be reserved for the TBF. If the LLC-PDU does not contain this information, an attempt is made to obtain this information from a recently released TBF that the same GPRS/EGPRS MS had been using. 206/1553-HSC 103 12/7 Uen B 2005-08-18 9 User Description, GPRS/EGPRS Connection Control and Transfer In non DRX (non sleep) mode, the 44.060 PACKET DOWNLINK ASSIGNMENT message including all reserved PDCHs is sent to the GPRS/EGPRS MS on PAGCH. If the GPRS/EGPRS MS is in DRX (sleep) mode the message is sent in a frame that corresponds to the MS PCCCH paging group. The message 44.060 PACKET POLLING REQUEST is sent to the GPRS/EGPRS MS on PACCH. The purpose with this is twofold, to verify contact with the MS and to acquire the timing advance value for the MS. In response the GPRS/EGPRS MS sends the message 44.060 PACKET CONTROL ACKNOWLEDGEMENT in a reserved block period on PACCH. This message consists of 4 access bursts. The BTS calculates the delay for each access burst and passes the 44.060 PACKET CONTROL ACKNOWLEDGEMENT message further on to the BSC. The BSC calculates a new timing advance value. If no 44.060 PACKET CONTROL ACKNOWLEDGEMENT message is received by the BSC, 44.060 PACKET POLLING REQUEST is sent again. New attempts (maximum 3) to set up a downlink TBF are done if no 44.060 PACKET CONTROL ACKNOWLEDGEMENT is received in the BSS. New attempts to set up a downlink TBF can be done using PCCCH, CCCH or PACCH depending on the traffic situation and the configuration of the BSS. If the timing advance is greater than the maximum timing advance allowed in the cell the SGSN is informed and the set up of downlink TBF using PCCCH is terminated. An attempt to get more channels is made. If no more PDCHs have been received for the GPRS/EGPRS MS the message 44.060 PACKET POWER CONTROL/TIMING ADVANCE including the timing advance is sent to the GPRS/EGPRS MS on PACCH. If more PDCHs have been received for the GPRS/EGPRS MS then the message 44.060 PACKET DOWNLINK ASSIGNMENT is sent to the GPRS/EGPRS MS on PACCH, including all PDCHs reserved for the GPRS/EGPRS MS and the timing advance. Downlink scheduling is started and the downlink TBF is considered established when an acknowledge of the first data has been received. If an acknowledge is not received then another six attempts to send 44.060 PACKET DOWNLINK ASSIGNMENT is made in accordance with the section above. If Loss Free Preemption applies (see Section 3.11.4 on page 37) the buffer that was kept at release is used to continue the transfer. 3.2.6 Set Up of Downlink TBF Using CCCH The purpose is to establish a downlink TBF to support the transfer of data in the downlink direction. Since, in this scenario, there is no Master PDCH in the cell, a GPRS/EGPRS MS is camping on the BCCH. 10 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer A GPRS/EGPRS MS in standby state will first be paged according to procedures described in Reference [6]. The GPRS/EGPRS MS then responds to the page, with a set up of uplink TBF using CCCH described in Section 3.2.3 on page 7 (Access Type = Page Response), by sending any LLC PDU to the SGSN. The GPRS/EGPRS MS now enters ready state and the SGSN may start sending LLC PDUs. A GPRS/EGPRS MS in ready state can receive LLC PDUs from the SGSN at any time. The received LLC-PDU may contain information about the capability of the GPRS/EGPRS MS. This information is used by the BSS to calculate the number of PDCHs that will be reserved for the TBF. If the LLC-PDU does not contain this information, an attempt is made to fetch it from a recently released TBF that the same GPRS/EGPRS MS had been using. The 48.058 IMMEDIATE ASSIGN COMMAND message including the message 44.018 IMMEDIATE ASSIGNMENT is sent to the BTS. The BTS forwards the message 44.018 IMMEDIATE ASSIGNMENT including one PDCH to the GPRS/EGPRS MS. The message is sent on the AGCH. If the GPRS/EGPRS MS is in sleep mode then the message is sent in a frame that corresponds to the GPRS/EGPRS MS CCCH paging group. The message IMMEDIATE ASSIGN SENT is then sent from the BTS to the BSC. The message 44.060 PACKET POLLING REQUEST is sent to the GPRS/EGPRS MS on PACCH. In response the GPRS/EGPRS MS sends the message 44.060 PACKET CONTROL ACKNOWLEDGEMENT in a reserved block period on PACCH. This message consists of 4 access bursts. The BTS calculates the delay for each access burst and passes the 44.060 PACKET CONTROL ACKNOWLEDGEMENT message further on to the BSC. The BSC calculates a new timing advance value. If no 44.060 PACKET CONTROL ACKNOWLEDGEMENT message is received by the BSC, 44.060 PACKET POLLING REQUEST is sent again. New attempts (maximum 3) to set up a downlink TBF are done if no 44.060 PACKET CONTROL ACKNOWLEDGEMENT message is received in the BSC. New attempts to set up a downlink TBF can be done using PCCCH, CCCH or PACCH (normal) depending on the traffic situation and the configuration of the BSS. If the timing advance is greater than the maximum timing advance allowed in the cell the SGSN is informed and the set up of downlink TBF using PCCCH is terminated. An attempt to get more channels is made. If only one PDCH has been reserved for the GPRS/EGPRS MS the message 44.060 PACKET POWER CONTROL/TIMING ADVANCE including the timing advance is sent to the GPRS/EGPRS MS on PACCH. 206/1553-HSC 103 12/7 Uen B 2005-08-18 11 User Description, GPRS/EGPRS Connection Control and Transfer If more than one PDCH are reserved for the GPRS/EGPRS MS then the message 44.060 PACKET DOWNLINK ASSIGNMENT is sent to the GPRS/EGPRS MS on PACCH, including all PDCHs reserved for the GPRS/EGPRS MS and the timing advance. Downlink scheduling is started and the downlink TBF is considered established when an acknowledge of the first data has been received. If an acknowledge is not received then another six attempts to send 44.060 PACKET DOWNLINK ASSIGNMENT is made in accordance with the section above. If Loss Free Preemption applies (see Section 3.11.4 on page 37) the buffer that was kept at release is used to continue the transfer. 3.2.7 Normal Setup of Downlink TBF Using PACCH The purpose is to establish a downlink TBF to support the transfer of data in the downlink direction. A prerequisite, in this scenario, is that the GPRS/EGPRS MS is already assigned to an uplink TBF. Normal setup of Downlink TBF using PACCH is initiated in the BSS when a LLC-PDU has been received from the SGSN. The received LLC-PDU may contain information about the capability of the GPRS/EGPRS MS. This information is used by the BSS to calculate the number of PDCHs that will be reserved for the TBF. If the LLC-PDU does not contain this information, an attempt is made to fetch it from a recently released TBF that the same GPRS/EGPRS MS had been using. A 44.060 PACKET DOWNLINK ASSIGNMENT message is sent to the GPRS/EGPRS MS if at least one PDCH can be reserved. The message is sent on one of the PACCHs that the GPRS/EGPRS MS uses, for the uplink TBF. The downlink scheduling is started and the first RLC Data Block is sent to the MS with a request to send a 44.060 PACKET DOWNLINK ACK/NACK message to the BSC. When the 44.060 PACKET DOWNLINK ACK/NACK message is received, the TBF is considered to be established. If no 44.060 PACKET DOWNLINK ACK/NACK message is received then this procedure is repeated maximum six times. If still no 44.060 PACKET DOWNLINK ACK/NACK message is received then the procedure is terminated If a 44.060 PACKET DOWNLINK ACK/NACK message id received then downlink scheduling is started. The downlink TBF is established. If Loss Free Preemption applies (see Section 3.11.4 on page 37) the buffer that was kept at release is used to continue the transfer. 3.2.8 Early Setup of a Downlink TBF Using PACCH The purpose of this Ericsson proprietary function is to let the end of a data flow in the uplink trigger the establishment of a downlink TBF which immediately can 12 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer support a possible future transfer of data in the downlink direction. This, since most packet data sessions begin with an uplink request from the GPRS/EGPRS MS, followed by downlink data in response to the request. It further enables the setup of a new uplink TBF using the PACCH of the downlink TBF. A prerequisite is that the GPRS/EGPRS MS is already assigned to an uplink TBF. The multislot class must also be known and contention resolution must have been completed on the uplink. BSS initially determines if the number of free TFI in downlink direction in the current PSET exceeds the value of the exchange property TFILIMIT. If the value of the TFILIMIT is not exceeded, the Early Setup of a Downlink TBF using PACCH is not performed. Values from the uplink TBF, describing the capability of the GPRS/EGPRS MS, are used to set up the downlink TBF. If up-to-date information exists from a prior downlink TBF for the same GPRS/EGPRS MS, it is used. If no PDCHs can be reserved, the early set up is terminated and the normal release procedure of the uplink TBF is initiated instead. If at least one PDCH can be reserved, the message 44.060 PACKET DOWNLINK ASSIGNMENT is sent to the GPRS/EGPRS MS. The message is sent on one of the PACCHs that the GPRS/EGPRS MS is using for the uplink TBF. The poll bit is set in the message indicating that the GPRS/EGPRS MS shall answer with a 44.060 PACKET CONTROL ACKNOWLEDGEMENT message. If the 44.060 PACKET CONTROL ACKNOWLEDGEMENT message is not received in the BSC, new attempts (maximum 3) to set up a downlink TBF are done. New attempts to set up a downlink TBF can be done using PACCH (normal) depending on the traffic situation and the configuration of the BSS. If the 44.060 PACKET CONTROL ACKNOWLEDGEMENT message is received, downlink scheduling is started and the downlink TBF is established. The TBF is kept alive using dummy LLC-PDUs which are created and sent to the GPRS/EGPRS MS if there is no data to send. Dummy LLC-PDUs are being sent until timer ESDELAY expires after which the TBF is released. If data arrives, before the expiry of timer ESDELAY, data transmission can start immediately without any setup delay. If Loss Free Preemption applies (see Section 3.11.4 on page 37) the buffer that was kept at release is used to continue the transfer. 3.2.9 Set Up of Downlink TBF Using PACCH After Release of a DL TBF The purpose of this function is to be able to set up a Downlink TBF using PACCH shortly after the release of a DL TBF. When a downlink TBF is released, the GPRS/EGPRS MS starts timer T3192 and stays on the PACCH until T3192 expires. In the BSS there is a corresponding timer T3193 that is started when 206/1553-HSC 103 12/7 Uen B 2005-08-18 13 User Description, GPRS/EGPRS Connection Control and Transfer the TBF has been released. The PDCHs that were assigned to the TBF are still reserved for the GPRS/EGPRS MS for the duration of timer T3193. See Reference [8] for more information. If more data arrives from SGSN before T3193 has expired, a new DL TBF is set up and 44.060 PACKET DOWNLINK ASSIGNMENT message is sent to the GPRS/EGPRS MS on the PACCH. The poll bit is set in the message indicating that the GPRS/EGPRS MS shall answer with a 44.060 PACKET CONTROL ACKNOWLEDGEMENT message. If this message is not received by the BSC new attempts (maximum 3) to set up a downlink TBF are done. New attempts to set up a downlink TBF can be done using PCCCH, CCCH, PACCH (normal) or PACCH (after release) depending on the traffic situation and the configuration of the BSS. If this message is received, the downlink scheduling is started and the downlink TBF is established. PDCHs and TBF is finally released if/when BSS timer T3193 expires after which normal set up of downlink using PCCCH, CCCH or PACCH will have to be used to set up a new downlink TBF. If Loss Free Preemption applies (see Section 3.11.4 on page 37) the buffer that was kept at release is used to continue the transfer. 3.3 Ongoing Uplink TBF 3.3.1 Introduction After having set up the uplink TBF according to one of the set up of uplink TBF procedures described in Section 3.2 on page 6, the GPRS/EGPRS MS starts monitoring the downlink transmission on each of the PDCH(s) that has been assigned to it. It is explicitly informed when the GPRS/EGPRS MS has the permission to send an uplink radio block. There are two types of blocks: RLC data blocks and RLC/MAC control blocks. RLC/MAC Control blocks are forwarded to the BSS where the handling of them depends on the message type. RLC Data blocks are forwarded to the BSS where they are assembled into LLC-PDUs which are then transmitted over the Gb Interface to the SGSN. 3.3.2 Scheduling of Uplink Data Blocks and Uplink Control Blocks An GPRS/EGPRS MS can be assigned several PDCHs, and several GPRS/EGPRS MSs can be assigned to each PDCH. See Figure 1 on page 15. The purpose of the scheduling algorithm then is to determine which GPRS/EGPRS MS should be allowed to transmit on each PDCH in each radio block period. If a PDCH is shared by more than one TBF, which TBF to 14 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer schedule is based on the QoS profile of each TBF. See Reference [7] for more information about QoS in general, QoS profiles and QoS Scheduling. PDCH 1 PDCH 2 MS 1 MS 2 Figure 1 MSs. PDCH 3 PDCH 4 MS 3 Example of How PDCHs Can be Shared Among GPRS/EGPRS A GPRS/EGPRS MS is scheduled for uplink transmission of RLC/MAC blocks by inserting the USF of the GPRS/EGPRS MS in any downlink RLC/MAC block on the PDCH that the GPRS/EGPRS MS is assigned to. The USF is used depending on the following: Scheduling Uplink TBFs using the USF At TBF setup, a GPRS/EGPRS MS is assigned a USF value for each PDCH allocated for the packet transfer. The BSS schedules an uplink RLC/MAC block on a particular PDCH by inserting the GPRS/EGPRS MS’s USF in the header of a downlink RLC/MAC block. When the GPRS/EGPRS MS reads its USF, it transmits an RLC/MAC block on that PDCH in the next uplink block period. Reserved USF The Reserved USF is a USF value which is not assigned to any one particular GPRS/EGPRS MS. It is used to prevent more than one GPRS/EGPRS MS from attempting to transmit on the same PDCH in the same block period. The PCU may inform an GPRS/EGPRS MS that one or more future uplink blocks have been reserved for it on a particular PDCH. The GPRS/EGPRS MS may have an uplink or downlink TBF, or no TBF at all. When the reserved radio block period is reached, the network sends the Reserved USF. Only the GPRS/EGPRS MS to which this block has been assigned is allowed to transmit. The Reserved USF is used in the following situations: • During the second phase of a two-phase access. 206/1553-HSC 103 12/7 Uen B 2005-08-18 15 User Description, GPRS/EGPRS Connection Control and Transfer • If a downlink RLC/MAC block contains a valid Relative Reserved Block Period (RRBP) field. The receiving GPRS/EGPRS MS uses its reserved block to send a single control message. • If USF Granularity is in use (see below). The GPRS/EGPRS MS uses its three reserved blocks to send RLC data blocks and/or control messages. Free USF The free USF is only available on a Master PDCH. It is used to denote that the next uplink block period is for PRACH only. This channel is utilized during the first phase of a set up procedure. All GPRS/EGPRS MSs are allowed to transmit a 44.060 PACKET CHANNEL REQUEST or 44.060 EGPRS PACKET CHANNEL REQUEST on PRACH. The free USF is used in all downlink blocks if there are no GPRS/EGPRS MSs being scheduled on uplink and according to PRACH allocation. For PRACH allocation see Reference [6]. Multiplexing EGPRS/GPRS mode TBFs using USF Granularity When allocating uplink resources to a GPRS only capable MS, downlink radio blocks must use a GMSK-based coding scheme to allow a GPRS MS to read its USF value. When there is no MPDCH in the cell, the following applies: • If a GPRS only capable MS has an UL TBF on EGPRS channels, USF Granularity is applied. • In all other cases USF Granularity is not applied. When there is a MPDCH in the cell, the following applies: • USF Granularity is not applied. The reason for not applying USF Granularity for the MPDCH case is that USF Granularity would (if used) degrade performance of an EGPRS DL transfer. When USF Granularity is used, a GPRS MS that reads its own USF value, in the header of a downlink RLC/MAC block, may send uplink data in the next four radio block periods on the PDCH. The network then transmits the Reserved USF with the next three downlink RLC/MAC blocks. Hence, with USF Granularity a GMSK radio block need only be sent every fourth downlink block, limiting the negative impacts on the EGPRS downlink throughput (for any EGPRS MSs using the same channels as were USF Granularity is applied). If a GPRS MS has an ongoing uplink or downlink GPRS TBF, it must receive at least one GMSK radio block every 360 ms in order to maintain synchronization. The GMSK radio block actually does not need to be destined for that specific GPRS MS. 16 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer No Reply to a USF A GPRS/EGPRS MS is given a certain limited number of times to transmit an RLC/MAC block in response to its USF. If no RLC/MAC block is received from the GPRS/EGPRS MS, the connection is presumed lost and TBF is released. 3.3.3 Handling of LLC-PDUs and RLC/MAC Blocks Every 20 ms the Physical Link layer in BSS can receive an RLC/MAC block on each PDCH. RLC data blocks contain a TFI to indicate which TBF they belong to. Within each TBF, blocks are numbered sequentially to allow them to be reassembled into LLC-PDUs. LLC-PDUs are assembled using data from one or more RLC data blocks, and are transmitted together with control information to the SGSN over the Gb interface in the order in which they were received. 3.3.4 RLC Mode Two RLC modes exist, acknowledged and unacknowledged mode. The GPRS/EGPRS MS indicates which RLC mode it will use in the uplink TBF set up procedure. This is indicated by the GPRS/EGPRS MS sending either a 44.060 PACKET RESOURCE REQUEST message or a 44.060 PACKET DOWNLINK ACK/NACK message. The RLC mode of the TBF is changed if the message 44.060 PACKET RESOURCE REQUEST contains a request to change the RLC mode. If the GPRS/EGPRS MS performs one-phase access with a 44.060 PACKET CHANNEL REQUEST message or a 44.060 EGPRS PACKET CHANNEL REQUEST message, the RLC mode will be acknowledged. If the EGPRS MS has an EGPRS downlink TBF, the RLC mode for a requested uplink TBF can be received in the Channel Request Description IE in a 44.060 EGPRS PACKET DOWNLINK ACK/NACK. Acknowledged mode A 44.060 PACKET UPLINK ACK/NACK is transmitted to the GPRS/EGPRS MS when a certain number of RLC data blocks have been received. The frequency of this message depends on the transmission quality, the PCU-MS roundtrip delay, the number of PDCHs used for the TBF, and whether a Stall Condition for the RLC protocol has occurred or not. Each 44.060 PACKET UPLINK ACK/NACK contains a positive or negative acknowledgement for a range of RLC data blocks. The GPRS/EGPRS MS retransmits all blocks that are negatively acknowledged. 206/1553-HSC 103 12/7 Uen B 2005-08-18 17 User Description, GPRS/EGPRS Connection Control and Transfer If a Stall Condition arises, the GPRS/EGPRS MS sets the Stall Indicator (SI) in uplink RLC/MAC blocks. The GPRS/EGPRS MS will then retransmit not yet acknowledged blocks continuously. The network transmits a 44.060 PACKET UPLINK ACK/NACK when it receives the SI for the first time. As long as the SI bit is set in uplink blocks, the interval between successive 44.060 PACKET UPLINK ACK/NACK messages is shorter than normal. Unacknowledged mode In unacknowledged mode no retransmissions are made. LLC-PDUs are padded with filler octets in place of missing RLC data blocks. 44.060 PACKET UPLINK ACK/NACK messages are transmitted to the GPRS/EGPRS MS at fixed intervals. The size of this interval is optimized for the radio resources used. In unacknowledged mode the purpose of these messages is to inform the GPRS/EGPRS MS that the network is still receiving data. 3.3.5 Flow Control In an overload situation, the scheduling of USFs for uplink data transfer is gradually restricted for the entire PCU. 3.3.6 Reallocate an Ongoing Uplink TBF The GPRS/EGPRS MS can send the message 44.060 PACKET RESOURCE REQUEST on PACCH to change the quality of service or the RLC mode of the ongoing uplink TBF. The message 44.060 PACKET UPLINK ASSIGNMENT is sent to the GPRS/EGPRS MS on PACCH. If the GPRS/EGPRS MS has not read the last set of PSI2 messages (if PBCCH present in the cell) a 44.060 PACKET ACCESS REJECT message is sent to the GPRS/EGPRS MS on PACCH and the TBF is released. The version of the PSI which is known to the GPRS/EGPRS MS is indicated in the 44.060 PACKET RESOURCE REQUEST message. 3.4 Ongoing Downlink TBF 3.4.1 Introduction After having set up the downlink TBF according to one of the downlink TBF set up procedures described in Section 3.2 on page 6, LLC-PDUs are received and disassembled into RLC data blocks. The RLC data blocks as well as the RLC/MAC control blocks are then scheduled at the right time to the GPRS/EGPRS MS. RLC/MAC blocks are sorted according to the priority order between the RLC/MAC control blocks and RLC data blocks. The next block to be transmitted on a PDCH is selected from the logical channel with highest priority and with 18 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer available blocks. RLC/MAC control blocks have higher priority than RLC data blocks. If two or more TBFs share a PDCH, scheduling is based on their QoS profiles. 3.4.2 Handling of LLC PDUs and RLC/MAC Blocks 48.018 DL-UNITDATA messages are sent from SGSN to BSS over the Gb Interface. Each message contains an LLC-PDU and control information necessary for the transmission of the LLC-PDU across the radio interface. Within a TBF, LLC-PDU containing user signalling data are always queued at a higher priority than LLC-PDUs containing user data. When the QoS feature is activated, data PDUs may be queued at different priorities - see Reference [7]. The LLC-PDUs are disassembled into RLC data blocks. For GPRS an RLC/MAC block is created for each RLC data block which are then being scheduled. For EGPRS a RLC/MAC block may contain one or two RLC data blocks depending on the MCS used. For MCS-1 to MCS-6 there is one RLC data block, whereas for MCS-7 to MCS-9 there are two RLC data blocks. See Reference [2] for more information. 3.4.3 RLC Mode There are two RLC modes, acknowledged and unacknowledged. Each 48.018 DL-UNITDATA message indicates which mode should be used for its transfer. If the RLC mode is changed by the SGSN during a data transfer, all LLC-PDUs with the original RLC mode are transferred first. A new TBF is then established with the new mode. After a certain number of RLC data blocks have been transmitted to a GPRS/EGPRS MS, the S/P Bit is set in the header of the next RLC/MAC block sent. The RRBP header field indicates how many TDMA frames the GPRS/EGPRS MS should wait after receiving the block before returning a reply. The header of the downlink RLC/MAC block in the frame reserved for this reply will contain the Reserved USF (see Section 3.3.2 on page 14). For EGPRS RLC/MAC blocks, the ES/P field is used to indicate the validity of the RRBP field. It also indicates what fields the specified uplink control block shall contain. Note that using the S/P or ES/P field to schedule an uplink control block is referred to as ‘sending a polling request’, or simply ‘polling the GPRS/EGPRS MS’. Acknowledged Mode In acknowledged mode, the GPRS/EGPRS MS returns a 44.060 PACKET DOWNLINK ACK/NACK or a 44.060 EGPRS PACKET DOWNLINK ACK/NACK control message in reply to a polling request. This contains a positive or 206/1553-HSC 103 12/7 Uen B 2005-08-18 19 User Description, GPRS/EGPRS Connection Control and Transfer negative acknowledgement for a range of RLC data blocks. Those that are negatively acknowledged are rescheduled for downlink transmission. If an RLC/MAC block contained two RLC data blocks and only one of these are successfully acknowledged, then only the negatively acknowledged RLC data block is retransmitted. Acknowledgements for blocks that have already been acknowledged or that have not yet been sent are ignored. If an expected control message is not received by the network, the N3105 counter is incremented and the GPRS/EGPRS MS is re-polled. If after a number of consecutive polling requests this counter reaches a value N3105max, then a timer is started. The TBF is released after expiry of the timer. Unacknowledged Mode In unacknowledged mode no retransmissions are made. However, there is one exception: the final RLC/MAC block in a TBF can be retransmitted a certain limited number of times. This is done to ensure that the GPRS/EGPRS MS is aware that the TBF is finished. In an unacknowledged mode GPRS TBF, the reply to a polling request will be a 44.060 PACKET DOWNLINK ACK/NACK unless the RLC/MAC block is the last in a TBF, for which a 44.060 PACKET CONTROL ACKNOWLEDGEMENT is returned. In an unacknowledged EGPRS TBF, the reply to a polling request that is not the last in a TBF is a 44.060 EGPRS PACKET DOWNLINK ACK/NACK control message. Otherwise the handling is that same as for GPRS TBFs. In the case where an expected control message is not received by the network, the N3105 counter is incremented and the mobile is re-polled. When a reply to a polling request is not received by the network, the regularity of the polling requests is increased. If after a number of consecutive polling requests this counter reaches a value N3105max, then a timer is started. The TBF is released after expiry of the timer. 3.4.4 Scheduling of Downlink Data Blocks Each downlink TBF is assigned to one or more PDCHs. As for uplink TBFs, several TBFs can share a single PDCH, seeFigure 1 on page 15. A short queue of RLC/MAC blocks is maintained for each downlink TBF. Every 20 ms, a synchronization signal from the Physical Link layer is received for each PDCH. A single RLC/MAC block on each PDCH is sent for transmission to the BTS. RLC/MAC control blocks are prioritized ahead of RLC data blocks, see Section 3.4.8 on page 22. After the RLC/MAC blocks have been transmitted on all PDCHs, more data blocks are put in the queue. Blocks that have been negatively acknowledged by the GPRS/EGPRS MS (acknowledged mode TBFs only) are either retransmitted or new blocks are created and filled with LLC data. By delaying segmentation of LLC-PDUs until BSS is ready to transmit the data, the optimal 20 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer coding scheme can be chosen to suit the prevailing radio conditions. See Reference [9] and Reference [2] for more information. Multiplexing EGPRS/GPRS mode TBFs If a GPRS MS has an ongoing uplink or downlink GPRS TBF, it must receive at least one GMSK radio block every 360 ms to stay synchronized. This is done by maintaining a minimum level of the scheduling of GMSK blocks. The GMSK radio block actually does not need to be destined for that specific GPRS MS. 3.4.5 Downlink Flow Control When GPRS support is activated in a cell, a 48.018 FLOW-CONTROL-BVC message is transmitted to the SGSN. This message indicates that the cell is ready to receive downlink LLC data. It includes a buffer size and data flow rate. These are set high enough to accommodate the maximum GPRS traffic volume in the cell. The 48.018 FLOW-CONTROL-BVC message also contains default flow control parameters for any GPRS/EGPRS MS that enters the cell. The SGSN uses these values for a GPRS/EGPRS MS until it receives a 48.018 MS-FLOW-CONTROL message with individual parameters for the GPRS/EGPRS MS. This message is sent at the beginning of a TBF. Buffer size and leak rate depend on the MS multislot capability, and whether the TBF is using GPRS or EGPRS. As buffer occupancy and transmission speed vary during the lifetime of the TBF, additional messages may be sent to alter the flow control parameters. The Current Bucket Level Procedure is supported which involves synchronizing buffer levels in the PCU of the BSC and the SGSN. This procedure makes flow control in the SGSN more responsive to changing conditions in the PCU. 3.4.6 Time Supervision of LLC-PDUs Each 48.018 DL-UNITDATA message includes a PDU lifetime timer specifying how long the enclosed LLC-PDU may be queued in the PCU of the BSC. The PCU checks how long each LLC-PDU has been queued before it is disassembled into RLC data blocks. If PDU lifetime has expired, it is discarded and a 48.018 LLC-DISCARDED message is sent to the SGSN. The SGSN may also specify that an LLC-PDU should be queued indefinitely. In this case, PDU lifetime is never checked. 3.4.7 Flush LL Procedure If a GPRS/EGPRS MS moves to a new cell during a downlink data transfer, BSS may receive a 48.018 FLUSH LL message from the SGSN over the Gb Interfaces. This message will indicate whether all queued LLC-PDUs should 206/1553-HSC 103 12/7 Uen B 2005-08-18 21 User Description, GPRS/EGPRS Connection Control and Transfer be discarded, or whether they should be transferred to the GPRS/EGPRS MS’s new cell. If the PCU is ordered to discard all queued LLC-PDUs, the downlink TBF is released. A 48.018 FLUSH LL ACK is returned to the SGSN indicating how many LLC-PDUs were discarded. If the PCU is ordered to reroute queued LLC-PDUs to the GPRS/EGPRS MS’s new cell, all PDUs whose PDU lifetime has expired are first discarded. All other LLC-PDUs are then rerouted to the new cell, and a 48.018 FLUSH LL ACK is returned to the SGSN indicating how many LLC-PDUs were rerouted or discarded. The old TBF is released and a new TBF is set up in the GPRS/EGPRS MS’s new cell. All LLC-PDUs are discarded at RA change. See Reference [4] for more information about cell reselection. 3.4.8 Scheduling of Downlink Control Blocks The Section 3.4.4 on page 20 explained how downlink data blocks are scheduled. Data blocks sent during a downlink TBFs are always sent on the logical channel PDTCH. However, a number of other logical channels may coexist with PDTCHs on the same physical channels. Each GPRS/EGPRS MS is assigned to one or more PDCHs. There are two types of PDCHs, slave PDCH and Master PDCH. A slave PDCH is a carrier of the logical channels PACCH and PDTCH. Additionally, a Master PDCH also carries one PBCCH, up to 705 PAGCHs and up to 705 PPCHs. RLC/MAC blocks are scheduled for a given GPRS/EGPRS MS on the PDCH(s) that have been assigned to that particular GPRS/EGPRS MS. The Physical Link layer transmits a synchronization message to indicate when it is time to transmit an RLC/MAC block to the BTS. The synchronization message is used to transmit blocks to the Physical Link layer at the right time. All PDCHs belonging to the same PSET are selected for transmission in timeslot number order. After an RLC/MAC block has been transmitted, the next RLC/MAC block is immediately scheduled. That block is selected from the logical channel with highest priority on the particular PDCH. Blocks from logical channels with lower priority are not selected as long as there are blocks from logical channels with higher priority. For a Master PDCH, the priority order from highest to lowest is: 22 • DRX PAGCH • DRX PPCH • ’no DRX‘ PAGCH • ’no DRX‘ PPCH 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer • the circuit switched Paging PACCH • PACCH • PDTCH. There is one exception to the priority order for a Master PDCH: BN 0 is always reserved for the PBCCH, and other BNs may be reserved by operator command. See Reference [6] for more information. For a Slave PDCH, the priority order from highest to lowest is the circuit switched Paging PACCH, the PACCH and the PDTCH. These are shown in Figure 2 on page 23. High Prio. PAGCH drx PPCH drx PAGCH no drx PBCCH Low Prio. Figure 2 PPCH no drx CS Paging on PACCH CS Paging on PACCH PACCH PACCH PDCCH PDTCH Master PDCH Slave PDCH Message Priority on the Master PDCH and the Slave PDCH 206/1553-HSC 103 12/7 Uen B 2005-08-18 23 User Description, GPRS/EGPRS Connection Control and Transfer 3.4.9 Nothing to Schedule on a PDCH Master PDCH If there are no downlink RLC/MAC blocks to schedule on a Master PDCH, then a 44.060 PACKET DOWNLINK DUMMY CONTROL BLOCK is transmitted in order to make uplink scheduling possible. If there is no traffic on uplink either, then a 44.060 PACKET DOWNLINK DUMMY CONTROL BLOCK is transmitted with the free USF according to the PRACH allocation. The PRACH allocation is described in Reference [6]. The free USF allows any GPRS/EGPRS MS to transmit a 44.060 PACKET CHANNEL REQUEST or a 44.060 EGPRS PACKET CHANNEL REQUEST. Slave PDCH If there are no downlink RLC/MAC blocks to schedule on a Slave PDCH and there is traffic on uplink, then a 44.060 PACKET DOWNLINK DUMMY CONTROL BLOCK is transmitted in order to make uplink scheduling possible. If there are no downlink RLC/MAC blocks to schedule and there is no traffic on uplink, then nothing is transmitted on downlink. 3.4.10 Active Queue Management The Active Queue Management (AQM) feature is a queue management feature for the radio link in downlink. With the AQM feature the data buffers are kept in the BSS instead of SGSN. AQM can be used for QoS class Interactive and Background. AQM can not be used for QoS class Streaming and signalling. For applications using TCP as transmission it is important with a rapid feedback of the radio link data rate to the TCP protocol in the server. Feedback of the radio link data rate is reported to TCP sender in the server by discarding IP packets. In this way the TCP sender will faster adjust its send rate according to the radio link capacity and TCP slow-starts are avoided. Whether the AQM feature is activated or not is shown by the BSC Exchange Property AQMSUPPORT. When the AQM feature is activated the Flow Control function is not used for the MSs. If the feature “QoS and Scheduling” in BSS is active, the queue management feature is applied to Interactive class and Background class data. The Active Queue Management feature is applied per Traffic Class for each MS. The queue management feature is not applied to GMM/SM signalling messages, SMS, LLC acknowledged mode data and Streaming class data when QoS is active. For SMS, LLC acknowledged mode data and Streaming class data a maximum buffer is set and when the buffer is overflowed packets are discarded starting from front of the buffer. If the feature “QoS and Scheduling” in BSS is passive, the queue management feature is applied to all payload data, but not to GMM/SM signalling messages and LLC acknowledged mode data. For LLC acknowledged mode data a 24 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer maximum buffer is set and when the buffer is overflowed packets are discarded starting from front of the buffer. The reason for not using the queue management feature for data using the Streaming class is that streaming applications use UDP as transport protocol. UDP has other rate controlling mechanisms than TCP/IP for which discarding of data would be harmful. Discarding of data for Streaming will only be done in case of buffer overflow in the BSS. When the queue management feature is turned off the GPRS Flow Control function will be active. The data flow from the SGSN is then regulated per BVC and per MS. 3.5 GPRS/EGPRS Load Optimization 3.5.1 General GPRS/EGPRS Load Optimization is an optional feature intended to let TBFs sharing the same radio resources adapt the scheduling to the quality of the radio environment. A TBF with low throughput due to a bad radio environment is scheduled more seldom. A TBF in a better radio environment is then scheduled more often and this increases their throughput. The available radio resources are used more by a TBF that has a good radio environment and the number of users with a relatively high throughput in the network increases. In order to put a TBF in Low Scheduling Mode the following conditions must be fulfilled: • QoS classes Interactive and/or Background • The data volume level for the TBF is Medium or Large • MAC mode is Dynamic Allocation (uplink) The feature affects the scheduling for TBFs that have the QoS traffic classes Interactive and Background. It is possible to use the GPRS/EGPRS Load Optimization feature even if the QoS feature is not activated. In this case all users are handled by the GPRS/EGPRS Load Optimization feature. The parameter LOADOPT defines if the feature is activated and for which QoS priority it is activated. The TBF is put in Low Scheduling Mode for 5 seconds. When the time has elapsed the TBF is put in Normal Scheduling Mode again. The radio link bit rate is calculated as follows: 206/1553-HSC 103 12/7 Uen B 2005-08-18 25 User Description, GPRS/EGPRS Connection Control and Transfer Number of Received Bits * Block Transmission Time Radio Link Bit Rate = Number of Sent Radio Blocks Figure 3 3.5.2 Radio Link Bit Rate Downlink TBF A DL TBF is considered to be in a bad radio environment when it has a low throughput. A sliding window is used to store radio link bitrate values for the last 50 RLC/MAC blocks. The radio link bitrate is calculated for every 44.060 (EGPRS) PACKET DOWNLINK ACK/NACK that is received from the MS. When the calculated radio link bitrate is lower than or equal to the threshold LOPTGTHR or LOPTETHR the TBF is put in Low Scheduling Mode. At this point the sliding window is cleared. This is to avoid that old values put the TBF back in Low Scheduling Mode after 5 seconds. The data buffer level for the TBF must be medium or large, see Reference [5], to fulfill the criteria for low scheduling. If the data buffer level and the recommended coding scheme for the DL TBF is lower than or equal to 2 the sampling of the radio link bit rate starts. The radio link bitrate calculation continues at every reception of 44.060 (EGPRS) PACKET DOWNLINK ACK/NACK to evaluate if the DL TBF should be put back in Low Scheduling Mode after 5 seconds. In case of an update of the QoS priority for the TBF, during Low Scheduling Mode, a check is made to see if the TBF still fulfill the QoS priority criterion specified by the parameter LOADOPT. If not, the Low Scheduling Mode is aborted. The Low Scheduling Mode is also aborted if the coding scheme is changed above CS-2 or MCS-5. In case an MS, with a DL TBF in Low Scheduling Mode, is performing a NACC the basic System Information messages needed for NACC is sent to that MS with the same scheduling priority as if the DL TBF was in Normal Scheduling Mode. 3.5.3 Uplink TBF An UL TBF is considered to be in a bad radio environment when it has low throughput. An UL TBF is only put in Low Scheduling Mode if it is in Dynamic Allocation mode. An UL TBF that is in Extended Dynamic Allocation mode is first switched to Dynamic Allocation mode before the evaluation is done. A sliding window is used to store radio link bitrate values for at least 100 RLC/MAC blocks. The radio link bitrate is calculated for every 44.060 (EGPRS) PACKET UPLINK ACK/NACK that is sent to the MS. The radio link bitrate 26 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer is stored together with the number of scheduled USFs since the previous 44.060 (EGPRS) PACKET UPLINK ACK/NACK. When 100 RLC/MAC blocks have been ACK/NACKed, the average radio link bitrate is calculated from the stored values. RLC/MAC blocks, dummy blocks and retransmitted RLC/MAC blocks are included in the radio link bitrate calculation. When the calculated radio link bitrate is lower than or equal to parameter LOPTGTHR or LOPTETHR the UL TBF is put in Low Scheduling Mode. At this point the sliding window is cleared. This is to avoid that old values put the TBF back in Low Scheduling Mode after 5 seconds. The radio link bitrate calculation continues at every reception of 44.060 (EGPRS) PACKET UPLINK ACK/NACK to evaluate if the UL TBF should be put back in Low Scheduling Mode after 5 seconds. 3.6 Suspend and Resume 3.6.1 General A GPRS Attached Class B GPRS/EGPRS MS can indicate to the SGSN that it will temporarily suspend its GPRS/EGPRS service. Suspend is done when a circuit switched connection is about to be established. When the circuit switched connection is completed then the Resume procedure may be initiated by the BSC. A prerequisite for the Resume procedure is that the Suspend procedure was successful. If the resume procedure is not initiated by the BSC or it fails then the GPRS/EGPRS MS is expected to perform a Routing Area Update after the circuit switched connection is released to indicate to the SGSN that it has resumed the suspended GPRS service. 3.6.2 Suspend GPRS Service in Packet Transfer Mode To suspend the GPRS service, the GPRS/EGPRS MS sends the message 44.018 GPRS SUSPENSION REQUEST to the BSS. 48.018 SUSPEND PDU message is sent to the SGSN. Scheduling of the TBF is stopped and the TBF is released. The SGSN answers with a 48.018 SUSPEND-ACK PDU message or a 48.018 SUSPEND-NACK PDU message. The suspend procedure is successfully accomplished if the 48.018 SUSPEND-ACK PDU message is received. If 48.018 SUSPEND-NACK PDU is received, the message is discarded and when the circuit switched connection is released the suspend procedure is considered unsuccessful. If nothing is received from the SGSN within 48.018 T3 timer another 48.018 SUSPEND PDU is sent to the SGSN. This procedure will be repeated according 206/1553-HSC 103 12/7 Uen B 2005-08-18 27 User Description, GPRS/EGPRS Connection Control and Transfer to 48.018 maximum number of suspend retries. Then the suspend procedure is considered unsuccessful when the circuit switched connection is released. 3.6.3 Suspend GPRS Service in Packet Idle Mode A GPRS/EGPRS MS in Packet Idle Mode can send the 44.018 GPRS SUSPENSION REQUEST message to the BSC. A 48.018 SUSPEND PDU message is sent to the SGSN. The SGSN answers with the message 48.018 SUSPEND-ACK PDU or 48.018 SUSPEND-NACK PDU. The suspend procedure is successfully accomplished if the 48.018 SUSPEND-ACK PDU message is received. If 48.018 SUSPEND-NACK PDU is received, the message is discarded and when the circuit switched connection is released the suspend procedure is considered unsuccessful. If nothing is received from the SGSN within 48.018 T3 timer another 48.018 SUSPEND PDU is sent to the SGSN. This procedure can be repeated according to 48.018 maximum number of suspend retries. Then the suspend procedure is considered unsuccessful when the circuit switched connection is released. 3.6.4 Resume The resume procedure can be initiated when the circuit switched connection is completed. A 48.018 RESUME PDU is sent to the SGSN if the Suspend procedure was successfully accomplished and the call was released in the same RA as it was set up in. If the SGSN answers with a 48.018 RESUME-ACK PDU message then the GPRS service is resumed. If the SGSN answers with a 48.018 RESUME-NACK PDU message then the network has failed to resume the GPRS service. If nothing is received from the SGSN within 48.018 T4 timer, no retries will be made meaning that the network has not been able to resume the GPRS service. If the CS call is released in another RA than it was setup in then the network is not able to perform the resume procedure for the MS. The MS will have to send a routing area update. 3.7 Upgrade of a TBF 3.7.1 General The purpose of the TBF upgrade is to add PDCHs to a TBF without moving the TBF from its current PDCHs. The functionality described in the UD GPRS/EGPRS Channel Administration is responsible for the provision of eligible TBF upgrade candidates and for the PDCH Reservation. 28 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer The following PDCH reservation enhancements are enabling the upgrade of a TBF: • Upgrade of PDCH reservation. • Dynamic downlink/uplink PDCH reservation. See Reference [5] for more information about PDCH reservation in general and the enhancements mentioned above. 3.7.2 Upgrade of an Uplink and Downlink TBF When an eligible TBF upgrade candidate (a TBF that is running on less PDCHs than it is capable of) is found, either a 44.060 PACKET DOWNLINK ASSIGNMENT message (to upgrade a DL TBF) or a 44.060 PACKET UPLINK ASSIGNMENT message (to upgrade a UL TBF) is sent to the GPRS/EGPRS MS in order to assign the additional PDCHs. In both cases, the poll bit is set in the message indicating that the GPRS/EGPRS MS shall answer with a 44.060 PACKET CONTROL ACKNOWLEDGEMENT message. The upgrade is successful when the 44.060 PACKET CONTROL ACKNOWLEDGEMENT message is received in the BSS after which the scheduling is modified according to the new PDCH reservation. Note that it might be necessary to release a TBF in Extended Uplink Mode to be able to upgrade the MS’s DL TBF. With simultaneous reconfiguration it is possible to upgrade one TBF at the same time as the other is downgraded or both TBFs can be upgraded. The reconfiguration is only done if both TBFs are in Packet Transfer Mode. If both TBFs are in Packet Transfer Mode and no release is ongoing then the message 44.060 PACKET TIMESLOT RECONFIGURE is sent to the MS. The poll bit is set in the message indicating that the MS shall answer with a 44.060 PACKET CONTROL ACKNOWLEDGEMENT message. If the message is not received then the 44.060 PACKET TIMESLOT RECONFIGURE message is resent. Totally two attempts are performed. 3.8 Re-reservation of a TBF 3.8.1 General The purpose of the re-reservation is to get more resources and more bandwidth. The GPRS/EGPRS Channel Administration feature is responsible for the provision of eligible TBF re-reservation candidates and for the PDCH Reservation. There are two different types of re-reservations: 206/1553-HSC 103 12/7 Uen B 2005-08-18 29 User Description, GPRS/EGPRS Connection Control and Transfer • Re-reservation due to adding resources which is moving an existing TBF from channels that in some way do not fulfil the requirement of the TBF, to channels that better correspond to the requirements, for example when the only way to upgrade a TBF is to move it first. A TBF occupying PDCHs of a PDCH type that it can not fully use is also a candidate for re-reservation. • Re-reservation due to balancing which is also a way of re-reservation. This is not to improve a specific TBF but level out the total TBF load on the PDCHs. An existing TBF is moved from channels with high TBF load to channels with lower load. The imbalance may occur when TBFs sharing the same channels are released. See Reference [5] for more information. The re-reservation of a TBF differs depending on if both the uplink and the downlink TBF are to be moved or if only the downlink TBF is to be moved. 3.8.2 Re-reservation of an Uplink and Downlink TBF The following events will occur when an eligible uplink and downlink TBF re-reservation candidate is found: • remaining DL buffers in the MAC layer are sent to the GPRS/EGPRS MS and the downlink scheduling is suspended • uplink scheduling is suspended • a 44.060 PACKET TIMESLOT RECONFIGURE message is sent to the GPRS/EGPRS MS in order to assign the new PDCHs, new USF and new TFIs. Downlink and uplink scheduling is started on the new PDCHs after three block periods, so that the GPRS/EGPRS will have sufficient time to switch to the new PDCHs. The first data block sent to the GPRS/EGPRS MS contains a request for a 44.060 PACKET DOWNLINK ACK/NACK message. If the 44.060 PACKET DOWNLINK ACK/NACK message is received, the old PDCH reservations are released and transmission continues on the new PDCHs. If the 44.060 PACKET DOWNLINK ACK/NACK message is not received, another two attempts to send the 44.060 PACKET TIMESLOT RECONFIGURE message are performed before the re-reservation is considered unsuccessful. 3.8.3 Re-reservation of a Downlink TBF The following events will occur when an eligible downlink TBF re-reservation candidate is found: 30 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer • remaining DL buffers in the MAC layer are sent to the GPRS/EGPRS MS and the downlink scheduling is suspended • a 44.060 PACKET DOWNLINK ASSIGNMENT message is sent to the GPRS/EGPRS MS in order to assign the new PDCHs and new TFIs. Downlink scheduling is started on the new PDCHs after three block periods, so that the GPRS/EGPRS will have sufficient time to switch to the new PDCHs. The first data block sent to the GPRS/EGPRS MS contains a fixed request for a 44.060 PACKET DOWNLINK ACK/NACK message. If the 44.060 PACKET DOWNLINK ACK/NACK message is received, the old PDCH reservations are released and transmission continues on the new PDCHs. If the 44.060 PACKET DOWNLINK ACK/NACK message is not received, another two attempts to send the 44.060 PACKET DOWNLINK ASSIGNMENT message are performed before the re-reservation is considered unsuccessful. 3.9 Downgrade of a TBF 3.9.1 General An uplink and/or a downlink TBF is downgraded if: • A PDCH, that is not used for sending the continuous TA to the GPRS/EGPRS MS is pre-empted. The 44.060 PACKET PDCH RELEASE message is sent on the PACCH associated with the PDCH that is about to be released. • A PDCH, that is not used for sending the continuous TA to the GPRS/EGPRS MS becomes faulty. A 44.060 PACKET PDCH RELEASE message is sent, on PACCHs associated with other PDCHs in the PSET. A downlink TBF is downgraded if: • 3.9.2 The DL TBF is in Delayed Release Mode and restricts the number of PDCHs that the corresponding UL TBF is reserved for and it is believed that the main direction of the transmission is in the uplink. See Section 3.9.2 on page 31 for more information. Downgrade of a Downlink TBF in Delayed Release Mode The purpose is to downgrade a downlink TBF that has entered the Delayed Release Mode in order to enable an upgrade of an existing uplink TBF running on fewer PDCHs than it is capable of according to the multislot capability of the GPRS/EGPRS MS. This downgrade can be seen as the first step in 206/1553-HSC 103 12/7 Uen B 2005-08-18 31 User Description, GPRS/EGPRS Connection Control and Transfer the ’Dynamic downlink/uplink PDCH reservation’ enhancement described in Section 3.7 on page 28 and in Reference [5]. A downlink TBF with no more real data to send enters the Delayed Release Mode. The downlink scheduling is modified to only include the remaining PDCHs in the downlink TBF, according to the new PDCH reservation. The 44.060 PACKET DOWNLINK ASSIGNMENT message is sent to the GPRS/EGPRS MS. The poll bit is set in the message indicating that the GPRS/EGPRS MS shall answer with a 44.060 PACKET CONTROL ACKNOWLEDGEMENT message. The downgrade is successful when the 44.060 PACKET CONTROL ACKNOWLEDGEMENT message is received in the BSS. 3.10 Change of TBF Mode Change of TBF mode is a feature intended to make it possible to change the TBF mode for an ongoing TBF. This feature is for packet data connections only. MSs having only an UL TBF or TBFs belonging to DTM connections are not handled by this feature. The availability of the feature is defined by TBFMODEACT. Change of TBF mode is triggered by the following cases: • Change of QoS to traffic class Streaming is requested but only possible by changing TBF mode. The procedure to change TBF mode is initiated immediately. • The requested GBR or higher than the negotiated GBR for a streaming TBF is possible to reach by changing TBF mode • Higher bandwidth for TBFs of QoS traffic classes Interactive or Background is possible to reach by changing TBF mode. The message 44.060 PACKET TBF RELEASE with the cause normal is sent to the MS requesting an acknowledgement. This will trigger the MS to do a release of the UL TBF at the nearest end of an LLC-PDU and then send an acknowledgement. If no acknowledgement is received from the MS then the message is sent again. If still no acknowledgement is received from the MS the 44.060 PACKET TBF RELEASE with the cause abnormal is sent to the MS. At the same time as the first 44.060 PACKET TBF RELEASE message is sent the DL TBF is ended. A DL TBF is released by boosting sending of radio blocks up until the end of the nearest LLC-PDU and the send Final Block. The MS then responds with a final acknowledgement. The content of the DL data buffer is kept using the mechanism in Loss Free Pre-emption, see Section 3.11.4 on page 37. 32 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer 3.11 Release of a TBF 3.11.1 General A TBF is released if: • there is no more data to transfer in the downlink or uplink direction and the delayed downlink release timer or the extended uplink TBF timer expires. • the GPRS/EGPRS MS makes a cell reselection to another cell. • an uplink TBF is lost. • the PDCH used for sending the continuous TA to the GPRS/EGPRS MS is preempted or becomes faulty. • the GSL becomes faulty. • the cell is halted. • GPRS/EGPRS support is deactivated in the cell. For a downlink streaming TBF also the timers ’Streaming Start Timer’ and ’Streaming Pending Timer’ must not be running. 3.11.2 Uplink TBF Release Uplink TBFs can be set up in two different modes depending on the GPRS/EGPRS MS capability and if the MS RAC is known or not in the BSS: • ’non extended UL TBF mode’ if the GPRS/EGPRS MS is Release 99 (or earlier) compatible or if the MS RAC is unknown in the BSS. • ’extended UL TBF mode’ if the GPRS/EGPRS MS is Release 4 (or later) compatible and the MS RAC is known in the BSS. Note that a TBF may change mode from ’non extended’ to ’extended’ if BSS receives information that the GPRS/EGPRS MS is Release 4 compatible. The proceeding events described below depend on the Uplink TBF Mode. Non extended UL TBF mode The GPRS/EGPRS MS initiates the release of an uplink TBF by setting the countdown value (CV) to zero in the header of the last RLC/MAC block. No new data will now be sent in this TBF. For an acknowledged mode TBF, all RLC data blocks must be successfully received by the network before the release procedure can begin. For an unacknowledged mode TBF, reception of the block with CV set to zero is sufficient to initiate the uplink TBF release procedure. 206/1553-HSC 103 12/7 Uen B 2005-08-18 33 User Description, GPRS/EGPRS Connection Control and Transfer Regardless of the RLC mode used, a higher protocol layer in the network will probably want to send a reply to the GPRS/EGPRS MS. A new downlink TBF would be needed to send this reply. Therefore, a timer is started to delay the uplink TBF release, to allow time for a downlink TBF to be setup on PACCH instead of (P)CCCH. If a downlink TBF is already ongoing, this delay is unnecessary and the release procedure proceeds immediately. To release the TBF, the network sends a 44.060 PACKET UPLINK ACK/NACK with the FAI bit set to ‘1’ and resets a counter, N3103. The GPRS/EGPRS MS replies with a 44.060 PACKET CONTROL ACKNOWLEDGEMENT message. The TBF is released on successful reception of this message. If the 44.060 PACKET CONTROL ACKNOWLEDGEMENT message is not received in the radio block specified by the RRBP field, counter N3103 is incremented and the 44.060 PACKET UPLINK ACK/NACK is resent. If the counter exceeds a maximum value, N3103max, then the TBF is released. Extended UL TBF mode In this mode when the GPRS/EGPRS MS has no more RLC data to send and has indicated that CV=0, the UL TBF is kept alive for a temporary inactivity period which is the duration of a timer ULDELAY, possible to set by the operator. Then if more data are to be sent from GPRS/EGPRS MS before the expiry of the timer, the RLC data transmission continues on the same UL TBF instead of setting up a new TBF. The GPRS/EGPRS MS is also allowed to interrupt the countdown of a UL TBF and send more data on the very same TBF. If no more data are to be sent from GPRS/EGPRS MS after the expiry of the timer, the UL TBF is released using the non extended Uplink TBF release procedure. Before entering the temporary inactive period, a check is first performed to see if there are enough free TFIs and USFs, according to TFILIMIT and USFLIMIT parameter settings. See Section 5.1 on page 43 for more information about the parameters. When in the temporary inactive period, the GPRS/EGPRS MS is sending repeated 44.060 PACKET UPLINK DUMMY CONTROL BLOCK messages according to it’s scheduled USF value. The scheduling frequency of the USFs depend on whether Persistent Uplink Scheduling is used or not. If Persistent Uplink Scheduling is not used the frequency of the USFs are reduced so that the scarce radio resources can be freed up for real data traffic but at the same time ensuring a relatively short delay if the MS shall transmit real data. If Persistent Uplink Scheduling is used the USF scheduling interval is done according to the setting of the PULSCHEDINT parameter. See Section 5.1 on page 43 for more information about the parameter. Persistent Uplink Scheduling is used for an UL TBF if the feature is active and if there is no active UL TBF on the PDCH. In all other cases Persistent Uplink Scheduling is not used. An active UL TBF has not entered the temporary inactive period. 34 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer Furthermore, the scheduling is done taking into account the QoS classes and the probability of having new data in the uplink. The BSS indicates that it supports the “Extended Uplink TBF” procedure with a new parameter, NW_EXT_UTBF, in the GPRS Cell Options IE broadcast in SI13 on the BCCH or in PSI1 on the PBCCH, if a MPDCH is defined. The Release 4 compatible GPRS/EGPRS MSs indicates the support of Extended Uplink TBF Mode in the MS RAC IE sent to BSS, during the two-phase access, in the 44.060 PACKET RESOURCE REQUEST message. The GPRS/EGPRS MS also indicates the support by including the MS RAC in the Attach Request and RA Update Request messages sent to SGSN meaning SGSN knows the MS RAC. The PCU will then obtain the MS RAC from the 48.018 DL-UNITDATA messages sent from SGSN. However, there are some cases when BSS will not know the MS RAC where the ’non extended Uplink TBF mode’ will be applied. 3.11.3 Delayed Release of Downlink TBF It has been observed that a typical user session consists of several uplink and downlink TBFs. Overall transmission speeds can be increased by keeping TBFs alive for a longer time. This reduces the number of TBFs in a user session, and thereby significantly cuts the time spent on TBF setups. The purpose of the delayed release of downlink TBF is to keep a downlink TBF alive during the temporary inactive periods when there are no data to send. When new data arrives from the SGSN, setup of a new TBF is not needed. For an acknowledged mode TBF, the delayed release procedure is initiated when all data have been acknowledged by the GPRS/EGPRS MS. For an unacknowledged mode TBF, it begins when all data has been sent from the PCU. To avoid ending the TBF, the PCU adds dummy LLC-PDUs to the back of its data queue. Dummy LLC data are added at the end of the RLC/MAC block containing the last ’real’ data. This allows all ’real’ data to be transmitted without the FBI bit set to ’1’ which would end the TBF. Typically, the GPRS/EGPRS MS will want to respond to the downlink transfer with an uplink TBF. To allow this TBF to be established on the PACCH, new RLC/MAC blocks containing dummy LLC-PDUs are sent periodically with a polling request. The GPRS/EGPRS MS transmits a 44.060 PACKET DOWNLINK ACK/NACK in response to each poll that it receives. When it is ready to send a response to the downlink TBF, it can include a request for an uplink TBF in one of these messages. The frequency of sending dummy LLC-PDU with a polling request depend on if Persistent Uplink Scheduling is used or not. Persistent Uplink Scheduling is used for a DL TBF if the feature is active and if there is no active DL or UL TBF on the PDCH. In all other cases Persistent Uplink Scheduling is not used. An active UL or DL TBF has not entered the temporary inactive period. If 206/1553-HSC 103 12/7 Uen B 2005-08-18 35 User Description, GPRS/EGPRS Connection Control and Transfer Persistent Uplink Scheduling is used the interval of sending dummy LLC-PDUs with polling requests are done according to the setting of the PULSCHEDINT parameter. See Section 5.1 on page 43 for more information about the parameter. If Persistent Uplink Scheduling is not used the frequency of sending polling requests are reduced (compared to during data transfer) so that the scarce radio resources can be freed up for real data traffic but at the same time ensuring a relatively short delay if the MS shall transmit real data. When more data arrive from the network side in response to the uplink TBF, it can be sent immediately as part of the existing TBF. If no new data arrive within a certain time, a dummy LLC-PDU is sent in a new RLC/MAC block. The FBI bit is set to ’1’ in this block to end the TBF. Parameter DLDELAY specifies how long the Delayed Release Procedure should last before the FBI bit set to ’1’ is sent. Its value should be set to the length of time during which new data are likely to arrive from the SGSN. Note that if the downlink TBF was established using the Early Setup procedure, the duration of the TBF is determined by parameter ESDELAY, and DLDELAY is not used. The delayed release procedure is identical for an EGPRS TBF, except that the GPRS/EGPRS MS returns a 44.060 EGPRS PACKET DOWNLINK ACK/NACK in response to a polling request. Release of Acknowledged Mode Downlink TBF TBF release begins with the network sending the final RLC data block in the TBF together with a polling request. The FBI bit is set to ‘1’ in this block. If it is successfully received in the GPRS/EGPRS MS, a 44.060 PACKET DOWNLINK ACK/NACK message is returned with the FAI set to ‘1’. If this message does not arrive in the network when it is expected, the final RLC/MAC block is retransmitted with a new polling request. The TBF is released when FAI=1 is successfully received. Abnormal release of a downlink TBF can occur if the GPRS/EGPRS MS fails to respond to N3105max successive polling requests. A timer is started in the PCU to allow time for a 48.018 FLUSH LL message to be received from the SGSN. If this message does not arrive, the TBF is released. Release of an EGPRS TBF is identical to the procedure described above, except that the GPRS/EGPRS MS returns a 44.060 EGPRS PACKET DOWNLINK ACK/NACK in response to a polling request. Release of Unacknowledged Mode Downlink TBF To release an unacknowledged mode TBF, the network sets the FBI bit to ‘1’ in the final RLC data block, and accompanies it with a polling request. The GPRS/EGPRS MS responds with a 44.060 PACKET CONTROL ACKNOWLEDGEMENT. If this does not arrive in the network at the expected time, then the final RLC/MAC block is retransmitted with another polling request. 36 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer The TBF is released when the GPRS/EGPRS MS’s reply is successfully received in the BSS. As for an acknowledged mode TBF, abnormal release can occur if the GPRS/EGPRS MS fails to respond to N3105max successive polling requests. If some LLC-PDUs are still queued for the GPRS/EGPRS MS, a timer is started to allow time for a 48.018 FLUSH LL message to be received. Otherwise, the TBF is released immediately. Release of an unacknowledged mode EGPRS TBF is the same as for a GPRS TBF. 3.11.4 Loss Free Preemption Loss Free Preemption is used to reduce negative affects from temporary interrupts in downlink transfers on RLC level. This may be important to, for example, avoid TCP timeouts and re-transmissions on TCP level in certain situations. Temporary interrupts on RLC level (and thus when Loss Free Preemption applies) may come from: • Preemption of essential PDCH • TBF setup failure • Intra cell handover of Dual Transfer Mode (DTM) connection • Mobile switches from DTM to Packet Switched only mode (CS call release) • BSS switches Abis transmission rate when Flexible Abis applies (see Reference [3]) When the DL TBF is released or not setup successfully a check is done to see whether Loss Free Preemption applies or not. If it applies the LLC-PDUs in the downlink buffer in the PCU is kept for a certain time period, and this buffer can then be used to continue the transfer when applicable. All LLC-PDUs where the PDU lifetime has expired are discarded and the SGSN is informed by sending 48.018 LLC-DISCARDED message. If Loss Free Preemption does not apply the DL TBF is released as normal and no further actions are performed. When applicable, and after a certain time period, a retry to setup the DL TBF is performed. If successful the transfer continues with the kept buffer, which makes the temporary interrupt less noticeable by the end-user. If unsuccessful a new retry is performed after a certain time period. At each retry to setup the DL TBF all LLC-PDUs where the PDU lifetime has expired are discarded and SGSN is informed. When the buffer is kept for a certain time period and no successful DL TBF has been setup the remaining parts of the buffer is discarded and the SGSN is informed by sending 48.018 LLC-DISCARDED. 206/1553-HSC 103 12/7 Uen B 2005-08-18 37 User Description, GPRS/EGPRS Connection Control and Transfer 3.12 Related Statistics 3.12.1 Impact on Legacy Counters The counters DLTHP1GTHR, DLTHP2GTHR, DLTHP3GTHR, DLBGGTHR are expected to have an increased value when the AQM feature is activated. The counters DLTHP1EGTHR, DLTHP2EGTHR, DLTHP3EGTHR, DLBGEGTHR are expected to have an increased value when the AQM feature is activated. 3.12.2 Statistics for Performance Management Two counters related to the AQM feature: 3.13 38 AQMDELIVDATA Total amount of data delivered to the MS by AQM. This is generated per BSC. AQMRECDATA Total amount of data received from SGSN by AQM. This is generated per BSC. Main Changes in Ericsson GSM System R12/BSS R12 • AQM, see Section 3.4.10 on page 24 • Change of TBF mode, see Section 3.10 on page 32 • Acquisition of MS RAC, see Section 3.2.3 on page 7 and Section 3.2.2 on page 6 • Improved RLC polling, see Section 3.4.3 on page 19 • EGPRS Access on CCCH, see Section 3.2.3 on page 7 • Improved UL/DL handling, see Section 7 on page 49 • GPRS Load Optimization, see Section 3.5 on page 25 • Simultaneous reconfigure, see Section 3.7.2 on page 29 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer 4 Engineering Guidelines ESDELAY defines the time a downlink TBF is kept alive after it was set up. The intention of the parameter value is to keep the downlink TBF alive until the response, which is triggered by the uplink TBF, arrives from the core network. The parameter is set per BSC. Scenarios to consider when setting this parameter are: • TCP handshakes • WAP requests • Other MS originated requests Keeping the downlink TBF alive: • too long is a waste of radio resources and TFIs • too short makes the response from the core network to be set up on PCCCH or CCCH, which takes significantly much more time than setting up the response on PACCH. DLDELAY defines the time a downlink TBF is kept alive after there is no more real data to send in downlink. The intention of the parameter value is to keep the downlink TBF alive between arrival of consecutive LLC-PDUs from the core network. The parameter is set per BSC. Scenarios to consider when setting this parameter are: • General downlink transfers, just one downlink TBF should be used • TCP handshakes • FTP in uplink (one downlink TBF to carry all the TCP acknowledgements in downlink) • PING benchmarking, one downlink TBF to carry all the PINGs Keeping the downlink TBF alive: • too long is a waste of radio resources and TFIs • too short results in too many unnecessary TBFs has to be set up on PACCH, PCCCH or CCCH. TFILIMIT parameter is set per BSC and defines a minimum number of available TFIs that has to be available in the following two cases: 206/1553-HSC 103 12/7 Uen B 2005-08-18 39 User Description, GPRS/EGPRS Connection Control and Transfer • Early setup of downlink TBF, the TFILIMIT defines a minimum number of TFIs that have to be available for a PSET if a setup of a downlink TBF is to be performed. • TBF keep alive mechanisms, the TFILIMIT defines a minimum number of TFIs that have to be available for a PSET if an uplink/downlink TBF is to be kept alive if no real data is to be transferred. TFILIMIT=0 means that a check for available TFIs is not performed, i.e. real data can be blocked due to that identifiers are used to keep TBFs alive. For this to occur the cell has to have a really high GPRS/EGPRS load. In this case the end-user throughput will be bad no matter what TFILIMIT is set to. ULDELAY defines the time an uplink TBF, in extended uplink TBF mode, is kept alive after there is no more real data to send in uplink. The intention of the parameter value is to keep the uplink TBF alive between transmission of consecutive LLC-PDUs for the mobile station. The parameter is set per BSC. Scenarios to consider for the setting of this parameter are: • General downlink transfers, one uplink TBF to carry all the TCP acknowledgements in uplink • TCP handshake • General uplink transfers, just one uplink TBF should be used • PING benchmarking, one uplink TBF to carry all the PINGs Keeping the uplink TBF alive: • too long is a waste of radio resources, TFIs and USFs • too short results in too many TBFs set up on PACCH, PCCCH or CCCH. USFLIMIT defines the minimum number of available USFs for a PDCH that have to be available if an uplink TBF is to be kept alive on that PDCH. The parameter is set per BSC. USFLIMIT=0 means that a check for available USFs is not performed before keeping an uplink TBF alive, i.e. real data can be blocked due to that identifiers are used to keep TBFs alive. PULSCHEDINT defines if Persistent Uplink Scheduling is active or not. When active it also defines the scheduling periods for a TBF in Extended UL TBF mode and Delayed release of Downlink TBF mode. The intention with the feature is to reduce roundtrip times by scheduling the mobile frequently for uplink responses. The parameter is set per BSC. Scheduling the mobile for uplink responses: 40 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer • more frequently may significantly reduce roundtrip times for traffic such as TCP handshakes and Ping benchmarking, but reduces battery lifetime in the mobiles • less frequently increases roundtrip times for traffic such as TCP handshakes and Ping benchmarking, but does not reduce the battery lifetime in the mobiles. Since Persistent Uplink Scheduling is used when it does not affect any ongoing active data transfer(s) there are no negative affects from schedule the mobile more frequently except for possibly shorter battery lifetime in the mobiles. An important note is that setting the parameter to any of the values 6–10 will increase roundtrip times compared to having the feature deactivated. PULSCHEDINT=99 and =1 uses the same scheduling frequency, but the parameter set to 99 schedules the mobile on all assigned PDCHs UL. For example a mobile with 2 slot UL will be scheduled 2 times every 20 ms with the parameter set to 99 but only 1 time with the parameter set to 1. This means that the parameter set to 99 will increase battery consumption compared to the parameter set to 1, but the reduced roundtrip times with the parameter set to 99 compared to the parameter set to 1 is neglectible. Also, QoS scheduling can have a negative impact on the mobile with lower QoS weight when the parameter is set to 99, since the mobile with higher QoS weight (absolute priority) will be scheduled all the time. Therefore if the choice is between parameter setting 1 and 99, then 1 is the recommended setting. Note that for EIT it is important to consider the parameter settings for ESDELAY, DLDELAY and ULDELAY. To keep a constant flow of data during an EIT transfer, high values of the mentioned parameters give benefits for the end-users running EIT. This is important to avoid noise for the end-user caused by temporary interrupts in the data flow, for example from temporary periods of silence. With low values for the mentioned parameter this may lead to unnecessary releases of TBFs and thus extra delays from having to setup TBFs again. Note that for the feature Dual Transfer Mode (DTM) it is important to consider the parameter settings for ESDELAY, DLDELAY and ULDELAY. If the TBF(s) for a mobile in DTM mode is released a re-allocation of the complete DTM connection might be necessary. Therefore a too short setting of the three parameters may have negative impact on the DTM service. A higher value than the default value of the parameter AQMRTTCONST results in that LLC-PDUs will be discarded earlier. 206/1553-HSC 103 12/7 Uen B 2005-08-18 41 User Description, GPRS/EGPRS Connection Control and Transfer 42 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer 5 Parameters 5.1 Main Controlling Parameters There are STS counters available for surveillance of the setting of ESDELAY, DLDELAY, ULDELAY, TFILIMIT and USFLIMIT, see Reference [10]. GPRSAQM is used to activate and deactivate the optional feature AQM PULSCHEDINT is used to activate and deactivate the feature Persistent Uplink Scheduling. The parameter is set per BSC. The parameter GPRSPULS must be switched on (1) to be able to activate the feature. When active it also defines the scheduling periods for a TBF in Extended UL TBF mode (EUL) and Delayed release of Downlink TBF mode (DDL) according to the table below: Table 1 5.2 PULSCHEDINT Feature Minimum insertion interval per TBF, EUL [ms] Minimum insertion interval per TBF, DDL [ms] No of TSs scheduled, EUL 0 deactive NA NA NA 1 active 20 40 1 2 active 40 40 1 3 active 60 80 1 4 active 80 80 1 5 active 100 120 1 6 active 120 120 1 7 active 140 160 1 8 active 160 160 1 9 active 180 200 1 10 active 200 200 1 99 active 20 40 all assigne d Parameter for Special Adjustments AQMMAXIPSIZE 206/1553-HSC 103 12/7 Uen B 2005-08-18 The BSC Exchange Property indicates the upper limit of the IP packet size. 43 User Description, GPRS/EGPRS Connection Control and Transfer AQMMINBUFF This BSC Exchange Property gives the value of Tminwhich ensures that at least a few IP packets are buffered at very low peak rate. AQMMINSIZE The BSC Exchange Property indicates the lower limit of the IP packet size. AQMRTTCONST The BSC Exchange Property indicates the constant part of the roundtrip time. This includes delays in server, core network, BSC, MS and laptop as well as transmission delays on the air interface such as Gn, Gb and Abis. The parameter is changed in steps of 10 ms. AQMSUPPORT Support of AQM 0 = AQM not activated 1 = AQM activated LOADOPT Support for GPRS Load Optimization 0 = Feature Off 1 = Feature On for Background 2 = Feature On for Background and Interactive LOPTETHR Radio link bit rate threshold for EGPRS TBFs. The threshold defines when an EGPRS TBF is considered to be in a bad radio environment. The radio link bit rate is measured per PDCH. Valid for both UL and DL. LOPTGTHR Radio link bit rate threshold for GPRS TBFs. The threshold defines when an GPRS TBF is considered to be in a bad radio environment. The radio link bit rate is measured per PDCH. Valid for both UL and DL. MSRACREQCCCH The BSC Exchange Property indicates if MS RAC Acquisition on CCCH is activated or not. 0 = MS RAC Acquisition on CCCH not activated 1 = MS RAC Acquisition on CCCH activated MSRACREQPCCCH The BSC Exchange Property indicates if MS RAC Acquisition on PCCCH is activated or not. 0 = MS RAC Acquisition on PCCCH not activated 1 = MS RAC Acquisition on PCCCH activated 44 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer TBFMODEACT The BSC Exchange Property defines if Change of TBF Mode for QoS traffic classes Streaming, Interactive and Background is activated or not. 0 = OFF 1 = Streaming 2 = Interactive and Background 3 = Streaming, Interactive and Background 5.3 Value Ranges and Default Values Table 2 Parameter name Default value AQMMAXIPSIZE Value range Unit 1700 100–2000 byte s AQMMINBUFF 4 1–200 Kbyt es AQMMINIPSIZE 300 100–2000 byte s AQMRTTCONST 600 100–4000 ms AQMSUPPORT 0 0–1 MSRACREQCCCH 0 0–1 MSRACREQPCCCH 0 0–1 DLDELAY 2200 2200 0-5000 ms ESDELAY 750 750 0–2000 ms LOADOPT 0 0–2 LOPTETHR 10 0–60 kbps LOPTGTHR 8 0–20 kbps PULSCHEDINT 0 TBFMODEACT 0 TFILIMIT 4 4 0–31 ULDELAY 1000 1500 0–5000 USFLIMIT 2 2 0–6 206/1553-HSC 103 12/7 Uen B 2005-08-18 Recommended value 2 0–10,99 0–3 ms 45 User Description, GPRS/EGPRS Connection Control and Transfer 46 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer 6 Appendix - 206/1553-HSC 103 12/7 Uen B 2005-08-18 47 User Description, GPRS/EGPRS Connection Control and Transfer 48 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer 7 Concepts Contention Resolution A procedure used to uniquely identify a GPRS/EGPRS MS during an MS originated access procedure. The procedure is completed in the network side at reception of the TLLI of the GPRS/EGPRS MS. The procedure is completed in the GPRS/EGPRS MS side when the same TLLI is returned in a PACKET UPLINK ACK/NACK or in a PACKET UPLINK ASSIGNMENT message. Dedicated PDCH A dedicated PDCH is allocated from the CSD to the PSD, and will be dedicated for GPRS/EGPRS traffic only. The allocation of dedicated PDCHs will be made by the system according to operator request (ordered number of PDCHs). The operator sets the number of dedicated PDCHs in a cell. Dual Transfer Mode An MS in dual transfer mode has simultaneously a PS and a CS connection. The allocated radio resources are co-ordinated by BSS. EDGE Enhanced Data for Global Evolution. An add on to GPRS which uses different modulation (8–PSK or GMSK) and/or coding schemes to allow greater bandwidth and thus provide greater spectral efficiency. EGPRS Enhanced GPRS (EGPRS) supports the GMSK and 8–PSK modulation methods and defines nine modulation and coding schemes. EGPRS increases the bitrate over the radio interface up to 59.2 kbit/s per timeslot and offers increased system capacity. GPRS GPRS is a feature that makes it possible to send packet data over the GSM network with GMSK coding schemes (CS-1 to CS-4). GPRS supports net bit rates up to 20.0 kbps per timeslot. GPRS Attach A GPRS/EGPRS MS shall perform a GPRS Attach to the network in order to obtain access to the GPRS/EGPRS services. GPRS/EGPRS MS Class Mode of Operation • Class A mode of operation allows a GPRS/EGPRS MS to have a CS connection at the same time as it is involved in a packet transfer. • Class B mode of operation allows a GPRS/EGPRS MS to be attached to both CS and PS connections, but it cannot use both services at the same time. 206/1553-HSC 103 12/7 Uen B 2005-08-18 49 User Description, GPRS/EGPRS Connection Control and Transfer However, a GPRS/EGPRS MS that is involved in a packet transfer can receive a page for a CS connection which requires the Gs Interface between the MSC/VLR and SGSN to be present. The GPRS/EGPRS can then suspend the packet transfer for the duration of the CS connection and afterwards resume the packet transfer. • GPRS/EGPRS MS States and Modes Class C mode of operation allows a GPRS/EGPRS MS only to be attached to one service at a time. There are three GPRS/EGPRS MM states: • Idle state, when the GPRS/EGPRS MS is turned on but not GPRS Attached. The GPRS/EGPRS MS is “invisible” to GPRS/EGPRS, e.g. when the GPRS/EGPRS MS is outside of the coverage area for GPRS/EGPRS. • Standby state, the GPRS/EGPRS MS is GPRS Attached and sends RA updates to the SGSN every time it changes RA. The SGSN has to page the GPRS/EGPRS MS since only the RA is known in the SGSN. • Ready state, a packet transfer is ongoing or has recently ended. A ready timer defines how long time the GPRS/EGPRS MS shall remain in ready state after a packet transfer has ended. The time is decided by the SGSN where the value range is from zero to infinity. If timer is set to ’infinity’, the GPRS/EGPRS MS shall never go back to Standby state. The GPRS/EGPRS MS sends cell update to SGSN every time it changes cell. In ready state there is no need to send a PS page to the GPRS/EGPRS MS. SGSN sends the LLC frames to the PCU and the PCU sends an assignment immediately to the GPRS/EGPRS MS since the location is known. The SGSN knows the MM states of the GPRS/EGPRS MSs. The MM state is not known in the BSS. There are two GPRS/EGPRS RR MS states, which are known only in the BSS: 50 • Packet Idle mode, when no packets are transferred. • Packet Transfer mode, a packet transfer is ongoing in uplink, downlink or in both directions simultaneously. 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer Low Scheduling Mode A TBF that is in Low Scheduling Mode is scheduled with lower frequency than a similar TBF that is not in Low Scheduling Mode. Master PDCH A PDCH carrying the Packet Broadcast Control Channel and the Packet Common Control Channel. PS traffic can also be carried on the Master PDCH. The Master PDCH is a dedicated PDCH. MCS A Modulation and Coding Scheme (MCS) is a specific coding scheme in combination with a modulation method. MS multislot class MS capability to handle multiple time slots. The multislot classes 1-45 are defined. They are all supported but multislot classes 30–45 are mapped into lower multislot classes, 33–45 if the feature Five Downlink Timeslots is available. MS RAC The purpose of the MS RAC is to provide the BSS with additional information concerning the radio capabilities of the GPRS/EGPRS MS. The contents of the MS RAC affects the way in which the BSS handles the GPRS/EGPRS MS. On-demand PDCH A PDCH which is set up and released dynamically depending on the need for GPRS/EGPRS traffic. An on-demand PDCH may be PDCH pre-empted by CS traffic. PCU The Packet Control Unit (PCU) is a logical unit in the BSS which is responsible for the handling of the RLC/MAC and parts of the physical link layers of the radio interface. PDCH A logical channel used to transfer packet data and related control signalling. The PDCHs can have different capabilities. The different PDCH types are: • B-PDCH, CS-1 to CS-2 capable • G-PDCH, CS-1 to CS-4 capable • E-PDCH, CS-1 to CS-4 and MCS 1–9 The B-PDCH requires a 16 kbit/s Abis connection per timeslot The G-PDCH and the E-PDCH require a 64 kbit/s Abis connection per timeslot. PDCH Reservation 206/1553-HSC 103 12/7 Uen B 2005-08-18 When a TBF is to be set up in order to support a certain service for a mobile user, transmission resources will be 51 User Description, GPRS/EGPRS Connection Control and Transfer reserved on one or more PDCHs. Among other things, the PDCH reservation is taking the GPRS/EGPRS MS capabilities (Multislot Class, and support for EGPRS) and the requested QoS Class for the service into account. 52 PSET A set of PDCHs possible to use together in a TBF. A PSET can contain up to 16 on-demand and/or dedicated and/or semi-dedicated PDCHs. Maximum one PSET can be allocated on the same TCHGRP. R97 QoS Quality of Service as specified in the 3GPP TS R97. Includes the attributes Precedence class, Peak Throughput etc. R99 QoS Quality of Service as specified in the 3GPP TS R99. Includes the PFM procedure and the classes Conversational, Streaming, Interactive and Background. RA A Routing Area consists of one or a number of cells. The RA is identical to the LA in the Ericsson BSS. RLC/MAC Radio Link Control (RLC) and Medium Access Control (MAC) are protocols responsible for segmentation of data and multiplexing of users. RTT The time for a peer to receive an answer for a transmitted message. Semi-dedicated PDCH A semi-dedicated PDCH is permanently allocated in a cell by operator command but not always activated. That is, a hardware device is not tied to the channel until the PS traffic requires it. A semi-dedicated PDCH can not be preempted by CS traffic, but it can be deallocated by operator command. Pre-emption is possible though at Abis congestion if the feature Flexible Abis is available. TAI individual The PDCH, among the PDCHs used by a TBF, that is chosen to carry the TAI. The TAI is actually sent to GPRS/EGPRS MSs sharing the PTCCH on the same PDCH. TBF A Temporary Block Flow (TBF) is a logical connection between the BSS and the MS. A TBF is set up when there is data to send at the BSS or MS side. TBF MODE Indicates whether an MS is using GPRS or EGPRS. TCHGRP All deblocked TCHs are grouped into TCHGRPs. All channels within the group are located in the same cell or subcell, and have the same channel type. The 206/1553-HSC 103 12/7 Uen B 2005-08-18 User Description, GPRS/EGPRS Connection Control and Transfer TCHs within a TCHGRP shall have the same frequency capabilities. Non Frequency Hopping Channels shall have the same Training Sequence Code and ARFCN. Frequency Hopping Channels shall have the same Training Sequence Code, Hopping Sequence Number and MAIO. A TCHGRP can contain maximum one PSET. PDCHs can only be allocated on TCHGRPs with multislot capable TCHs. TFI An identity which identifies an uplink or downlink TBF on all PDCHs used by the TBF. TLLI A value assigned to an GPRS/EGPRS MS by the SGSN which uniquely identifies the GPRS/EGPRS MS within a routing area. USF Used on a PDCH to allow multiplexing of UL radio blocks from a number of GPRS/EGPRS MSs. A GPRS/EGPRS MS is allocated a USF value for each PDCH as part of an uplink TBF establishment. When an MS reads its USF value in the header of a downlink RLC/MAC block, it may send data in the next uplink radio block period on this PDCH. 206/1553-HSC 103 12/7 Uen B 2005-08-18 53 User Description, GPRS/EGPRS Connection Control and Transfer 54 206/1553-HSC 103 12/7 Uen B 2005-08-18 Glossary Glossary 8–PSK 8–Phase Shift Keying DDL Delayed Downlink AGCH Access Grant Channel DRX Discontinuous Reception AQM Active Queue Management DTM Dual Transfer Mode ARFCN Absolute Radio Frequency Channel Number EGPRS Enhanced GPRS BCCH Broadcast Control Channel EIT Ericsson Instant Talk BN Block Number EUL Extended Uplink BSC Base Station Controller GBR Guaranteed Bit Rate BSS Base Station System GMSK Gaussian Minimum Shift Keying BSSGP BSS GPRS Protocol GPRS General Packet Radio Service BTS Base Transceiver Station GSL GPRS Signalling Link CCCH Common Control Channel IE Information Element CCU Channel Codec Unit LA Location Area CS Circuit Switched LLC Logical Link Control CS-x Coding Scheme x (Where x is 1 to 4) MAC Medium Access Control CSD Circuit Switched Domain MAIO Mobile Allocation Index Offset CV Countdown Value MCS Modulation and Coding Scheme 206/1553-HSC 103 12/7 Uen B 2005-08-18 55 Glossary MM Mobility Management PTCCH Packet Timing Advance Control Channel MS Mobile Station QoS Quality of Service NACC Network Assisted Cell Change RA Routing Area PACCH Packet Associated Control Channel RAC Radio Access Capability PAGCH Packet Access Grant Channel RACH Random Access Channel PBCCH Packet Broadcast Control Channel RLC Radio Link Control PCCCH Packet Common Control Channel RP Regional Processor PCU Packet Control Unit RR Radio Resource PDCH Packet Data Channel RRBP Relative Reserved Block Period PDTCH Packet Data Traffic Channel RTT Round Trip Time PDU Protocol Data Unit SGSN Serving GPRS Support Node PPCH Packet Paging Channel SI Stall Indicator PRACH Packet Random Access Channel TA Timing Advance PS Packet Switched TAI Timing Advance Index PSD Packet Switched Domain TBF Temporary Block Flow PSET PDCH Set TCH Traffic Channel PSI Packet System Information TCHGRP Traffic Channel Group 56 206/1553-HSC 103 12/7 Uen B 2005-08-18 Glossary TCP Transmission Control Protocol TFI Temporary Flow Identity TLLI Temporary Logical Link Identifier TN Timeslot Number TRU Transceiver Unit UD User Description USF Uplink State Flag 206/1553-HSC 103 12/7 Uen B 2005-08-18 57 Glossary 58 206/1553-HSC 103 12/7 Uen B 2005-08-18 Reference List Reference List Ericsson Documents [1] User Description, Dual Transfer Mode, (User Description), [2] User Description, EGPRS Link Quality Control, (User Description), [3] User Description, Flexible Abis, (User Description), [4] User Description, GPRS/EGPRS Cell Reselection, (User Description), [5] User Description, GPRS/EGPRS Channel Administration, (User Description), [6] User Description, GPRS/EGPRS Idle Mode Behaviour, (User Description), [7] User Description, GPRS/EGPRS Quality of service, (User Description), [8] User Description, GPRS/EGPRS Traffic Timers, (User Description), [9] User Description, GPRS Link Adaptation, (User Description), [10] User Description, Radio Network Statistics, (User Description), Standards [11] 3GPP TS 44.060 — MS - BSS Interface; RLC/MAC Protocol, (GSM Specification), [12] 3GPP TS 48.018 — Base Station System (BSS) - Serving GPRS Support Node (SGSN); BSS GPRS Protocol (BSSGP), (GSM Specification), [13] 3GPP TS 48.058 — (BSC - BTS) interface; Layer 3 specification, (GSM Specification), [14] 3GPP TS 44.018 — Mobile radio interface layer 3 specification, Radio Resource Control Protocol, (GSM Specification), 206/1553-HSC 103 12/7 Uen B 2005-08-18 59