7a Medium Access Control (MAC) procedures for EC-GSM-IoT on (EC-)CCCH

3GPP44.060General Packet Radio Service (GPRS)Mobile Station (MS) - Base Station System (BSS) interfaceRadio Link Control / Medium Access Control (RLC/MAC) protocolRelease 17TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

7a.1 General

The establishment of an EC Temporary Block Flow (EC TBF), for a mobile station that has enabled EC operation, is performed on the EC-CCCH. It can be initiated by either the mobile station or the network. The establishment of an EC TBF can also be performed on the CCCH if the mobile station has selected Coverage Class 1 in both the uplink and downlink directions, see 3GPP TS 45.008 and 3GPP TS 44.018, and is allowed to use the CCCH for its packet access procedure. The request for establishment of an EC TBF on the EC-CCCH or on the CCCH is described in 3GPP TS 44.018.

Establishment of an EC TBF in the direction from the mobile station to the network can also be initiated using the EC-PACCH if an EC TBF for transfer of upper-layer PDUs in the direction from the network to the mobile station is already established (see sub-clause 9.3.2.6). Establishment of an EC TBF for transfer of upper-layer PDUs in the direction from the network to the mobile station can also be done on the EC-PACCH if an EC TBF in the direction from the mobile station to the network has been released with an EC PACKET UPLINK ACK/NACK message indicating that the mobile station shall continue to monitor the EC-PACCH for a limited time (see sub-clause 9.3.2.4.3).

7a.2 TBF establishment initiated by the mobile station for EC-GSM-IoT on (EC-)CCCH

The packet access procedure using the EC-CCCH or the CCCH wherein a mobile station is assigned an uplink EC TBF using fixed uplink allocation (see sub-clause 8.1.1.3b) is described in 3GPP TS 44.018.

The following sub-clauses describe the contention resolution procedure and the timing advance handling at the establishment of an EC TBF for a mobile station that has enabled EC operation.

7a.2.1 Contention Resolution

The TLLI is used to uniquely identify the mobile station when sending on the uplink. A mobile station, that has enabled EC operation, includes its TLLI in one or several of the uplink blocks that are transmitted during the establishment of an EC TBF, depending on what packet access procedure is used.

The contention resolution is described for the different packet access procedures in the following sub-clauses:

– using Access Burst procedure, with inclusion of the full TLLI in each RLC data block that is sent on the TBF until contention resolution is completed, described in 7a.2.1.1;

– using Enhanced Access Burst procedure, with inclusion of the full TLLI in only the first RLC data block that is sent on the TBF and then inclusion of a limited part of the TLLI in the subsequent RLC data blocks that are sent until contention resolution is completed, described in 7a.2.1.2.

The network indicates in the EC Immediate Assignment message which of the procedures that shall be used for the contention resolution, see 3GPP TS 44.018.

7a.2.1.1 Contention resolution at packet access procedure using Access Burst procedure

Every RLC data block that is sent on the TBF shall include the TLLI of the mobile station, until the contention resolution is completed on the mobile station side. If MCS-7, MCS-8 or MCS-9 is used for the transmission of the TLLI (i.e. the RLC/MAC block is carrying two RLC data blocks), the TLLI shall be inserted in both RLC data blocks.

The retransmission of an RLC data block shall include the TLLI, if the RLC data block was originally transmitted including the TLLI, also if the retransmission occurs after the completion of the contention resolution.

After the last allocated RLC data block has been transmitted according to the initial fixed uplink allocation (received in the EC Immediate Assignment message), the mobile station shall start timer T3226. When timer T3226 expires the mobile station shall start timer T3228 and start continuously monitoring the EC-PACCH for reception of an RLC/MAC control message, see sub-clause 8.1.1.3b.

When the network has correctly received an RLC data block that comprises the TLLI, it shall include the TLLI in an EC PACKET UPLINK ACK/NACK or an EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION message that it sends to the mobile station (i.e. to allow for contention resolution on the mobile station side). The network may, after successful reception of the TLLI, include the reduced TLLI (rTLLI) of the mobile station in an EC PACKET UPLINK ACK/NACK message that it sends to the mobile station. The rTLLI consists of the 4 least significant bits of the TLLI of the mobile station.

After the last allocated RLC data block of a fixed uplink allocation, the network shall start timer T3227. The mobile station is only reachable on the EC-PACCH once timer T3227 has expired. When timer T3227 expires, the network shall start timer T3229 and send the EC PACKET UPLINK ACK/NACK or the EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION message to the mobile station. The network may send additional EC PACKET UPLINK ACK/NACK or EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION messages to the mobile station while timer T3229 is running. The network should then however take into account that the mobile station will stop monitoring the EC-PACCH at reception of a matching EC PACKET UPLINK ACK/NACK or a matching EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION message containing a fixed uplink allocation. If the network receives uplink data from the mobile station, on the resources that are part of the fixed uplink allocation, the network shall stop timer T3229, if running.

If timer T3249 is not used, i.e. it has the value 0, the network may release the TBF and reuse the TFI resource when timer T3229 has expired and no uplink data has been received in a fixed uplink allocation sent to the mobile station in EC PACKET UPLINK ACK/NACK or EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION messages before expiry of timer T3229. If timer T3249 is used, i.e. it has a value > 0, it shall be started at expiry of T3229. The network may send EC PACKET UPLINK ACK/NACK or EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION messages to the mobile station using the next higher DL Coverage Class, compared to the last assigned DL Coverage Class, while T3249 is running, see sub-clause 8.1.1.3b. When timer T3249 has expired and no uplink data has been received in a fixed uplink allocation allocated to the mobile station in EC PACKET UPLINK ACK/NACK or EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION messages before expiry of timer T3249 (or preceding T3229), the network may release the TBF and reuse the TFI resource.

When the mobile station receives an EC PACKET UPLINK ACK/NACK or an EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION message addressing the mobile station with the TFI value associated with the uplink TBF, the mobile station shall stop timer T3228, if running, and act on the received message, unless it included a TLLI value other than that the mobile station included in the RLC header of the RLC data blocks sent during the initial fixed uplink allocation or an rTLLI value which does not consist of the 4 least significant bits of the TLLI. If timer T3248 was running at reception of the EC PACKET UPLINK ACK/NACK or EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION message (and thus not T3228), the timer T3248 shall be stopped.

The contention resolution is successfully completed on the mobile station side when the mobile station receives an EC PACKET UPLINK ACK/NACK or an EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION message addressing the mobile station with the TFI value associated with the uplink TBF and including the same TLLI value that the mobile station has included in the RLC header of the RLC data blocks sent during the initial fixed uplink allocation. The TLLI shall thus be included in all RLC data blocks that are sent as part of the initial fixed uplink allocation.

The mobile station has entered the packet transfer mode upon a successful contention resolution.

The contention resolution has failed on the mobile station side when timer T3228 expires, if timer T3248 (sent in EC SI) is not used. If timer T3248 is used, i.e. it has a value > 0, it shall be started when timer T3228 expires. The contention resolution has failed on the mobile station side when timer T3248 expires. The contention resolution also fails, if the mobile station receives an EC PACKET UPLINK ACK/NACK or an EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION message addressing the mobile station with the TFI associated with the uplink TBF and including a TLLI value other than that the mobile station included in the RLC header of the RLC data blocks sent during the initial fixed uplink allocation or including an rTLLI value which does not consist of the 4 least significant bits of the TLLI; in such a case, the mobile station shall not transmit on any of the uplink resources that are allocated in the EC PACKET UPLINK ACK/NACK or EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION message, nor shall it transmit an EC PACKET CONTROL ACKNOWLEDGEMENT or EC PACKET CONTROL ACKNOWLEDGEMENT HIGHER CC in the uplink resources specified if a valid RRBP field is received as part of the EC PACKET UPLINK ACK/NACK or EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION message.

In case of a contention resolution failure on the mobile station side, the mobile station shall stop timer T3228, if running, stop transmitting on the TBF and enter packet idle mode. If timer T3248 was running when the contention resolution failure occurred (and thus not T3228), the timer T3248 shall be stopped. It shall then reinitiate the packet access procedure, unless the maximum allowed number of packet access procedure has already been attempted, see 3GPP TS 44.018. In that case, a TBF failure has occurred, see sub-clause 7a.2.4.

7a.2.1.2 Contention resolution at packet access procedure using Enhanced Access Burst procedure

When the Enhanced Access Burst procedure is used, only the first RLC data block that is sent on the TBF shall include the TLLI of the mobile station. If MCS-7, MCS-8 or MCS-9 is used for the transmission of the TLLI (i.e. the RLC/MAC block is carrying two RLC data blocks), the TLLI shall be inserted in both RLC data blocks that are included in the first RLC/MAC block. Every RLC data block that is sent on the TBF, except the first one, shall include the reduced TLLI (rTLLI) of the mobile station until the mobile station receives an EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION message or an EC PACKET UPLINK ACK/NACK message addressing the mobile station with the TFI value associated with the uplink TBF and containing either the TLLI or the rTLLI of the mobile station. The reduced TLLI (rTLLI) consists of the 4 least significant bits of the TLLI of the mobile station. The rTLLI shall not be included in the RLC/MAC header if the TLLI is included in the RLC Data block. The rTLLI value shall thus not be included in the RLC/MAC header of the first RLC Data block of a TBF, with BSN=0 and, if MCS-7, MCS-8 or MCS-9 is used for the transmission, with BSN=1, since the TLLI of the mobile station is included in the RLC data block(s).

The retransmission of an RLC data block shall include the TLLI, if the RLC data block was originally transmitted including the TLLI. The retransmission of an RLC Data block shall include the rTLLI in the RLC/MAC header if the RLC Data block was initially transmitted including the rTLLI in the RLC/MAC header.

When the network has correctly received an RLC data block that comprises the TLLI, it shall include the TLLI in an EC PACKET UPLINK ACK/NACK or an EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION message that it sends to the mobile station (i.e. to allow for contention resolution on the mobile station side). If the network has received an RLC Data block with the rTLLI included in the RLC/MAC header but no RLC Data block comprising the TLLI, the network shall include the rTLLI in the next EC PACKET UPLINK ACK/NACK message that it sends to the mobile station.

The contention resolution is completed on the network side when the network receives an RLC data block that comprises the TLLI value that identifies the mobile station and the TFI value associated with the TBF. The subsequent RLC Data blocks that are part of the initial fixed uplink allocation are identified by the reduced TLLI (rTLLI) included in the RLC/MAC header and the TFI value associated with the TBF.

When the mobile station receives an EC PACKET UPLINK ACK/NACK or an EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION message addressing the mobile station with the TFI value associated with the uplink TBF, the mobile station shall stop timer T3228, if running, and act on the received message, unless it included a TLLI value other than that the mobile station included in the RLC header, or a rTLLI value other than that the mobile station included in the RLC/MAC header, of the RLC data blocks sent during the initial fixed uplink allocation. If timer T3248 was running at reception of the EC PACKET UPLINK ACK/NACK or EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION message (and thus not T3228), the timer T3248 shall be stopped.

The contention resolution is successfully completed on the mobile station side when the mobile station receives an EC PACKET UPLINK ACK/NACK message addressing the mobile station with the TFI value associated with the uplink TBF and including the same TLLI value that the mobile station has included in the RLC header of the first RLC data block.

The mobile station has entered the packet transfer mode upon a successful contention resolution.

The contention resolution has failed on the mobile station side when timer T3228 expires, if T3248 (sent in EC SI) is not used. If timer T3248 is used, i.e. it has a value > 0, it shall be started when timer T3228 expires. The contention resolution has failed on the mobile station side when timer T3248 expires. The contention resolution also fails, if the mobile station receives an EC PACKET UPLINK ACK/NACK or an EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION message addressing the mobile station with the TFI associated with the uplink TBF and including a TLLI value other than that which the mobile station included in the RLC header of the first RLC data block sent during the initial fixed uplink allocation or including an rTLLI other than that which the mobile station included in the RLC/MAC header of subsequent RLC Data blocks sent during the initial fixed uplink allocation; in such a case, the mobile station shall not transmit on any of the uplink resources that are allocated in the EC PACKET UPLINK ACK/NACK or EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION message, nor shall it transmit an EC PACKET CONTROL ACKNOWLEDGEMENT or EC PACKET CONTROL ACKNOWLEDGEMENT HIGHER CC in the uplink resources specified if a valid RRBP field is received as part of the EC PACKET UPLINK ACK/NACK or EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION message.

7a.2.2 RLC/MAC procedures during contention resolution

During the contention resolution, the only non-distribution RLC/MAC control message that the mobile station shall accept are the EC PACKET UPLINK ACK/NACK and EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION messages. Any other non-distribution RLC/MAC control message shall not be accepted by the mobile station.

If a valid RRBP field is received as part of the RLC/MAC control block containing the EC PACKET UPLINK ACK/NACK or EC PACKET UPLINK ACK/NACK AND CONTENTION RESOLUTION message addressing the mobile station, the mobile station shall transmit an EC PACKET CONTROL ACKNOWLEDGEMENT or EC PACKET CONTROL ACKNOWLEDGEMENT HIGHER CC message in the uplink resources specified (see sub-clause 10.4.5).

7a.2.3 Timing Advance

Initial timing advance is provided in the EC Immediate Assignment messages, in the TIMING_ADVANCE_VALUE field, when the packet access is performed using the EC-RACH or RACH.

Thereafter the timing advance is updated with an EC PACKET POWER CONTROL/TIMING ADVANCE message or an EC PACKET UPLINK ACK/NACK message, containing a TIMING_ADVANCE_VALUE field, on the EC-PACCH.

7a.2.4 Abnormal cases

If a failure occurs on the mobile station side of the uplink TBF before the mobile station has successfully entered the packet transfer mode, the reserved resources are released; the subsequent behaviour of the mobile station depends on the type of failure and previous actions.

– If the failure is due to a TLLI or rTLLI mismatch in the contention resolution procedure, the mobile station shall remain in packet idle mode, notify higher layers (TBF establishment failure), transactions in progress shall be aborted and the mobile station shall reinitiate the packet access procedure, unless the maximum number of access retransmissions allowed by the packet access procedure has already been attempted, see 3GPP TS 44.018. If the maximum number of access retransmissions allowed by the packet access procedure has been attempted a change of Coverage Class or cell reselection may be performed (see 3GPP TS 45.008);

– If the failure is due to the expiry of timer T3228 (if timer T3248 is not used) or timer T3248 in the contention resolution procedure, the mobile station shall remain in packet idle mode, notify higher layers (TBF establishment failure), transactions in progress shall be aborted and the mobile station shall reinitiate the packet access procedure, unless the maximum number of access retransmissions allowed by the packet access procedure has already been attempted, see 3GPP TS 44.018. If the maximum number of access retransmissions allowed by the packet access procedure has been attempted a change of Coverage Class or cell reselection may be performed (see 3GPP TS 45.008);

– If the mobile station, in the EC PACKET UPLINK ACK/NACK message has been assigned an MCS that the MS does not support (e.g. with 8-PSK modulation), the MS shall return to packet idle mode and notify higher layers (TBF establishment failure);

– If the failure is due to any other reason, the mobile station shall return to packet idle mode, notify higher layers (TBF establishment failure), transactions in progress shall be aborted and cell reselection may be performed (see 3GPP TS 45.008).

7a.3 TBF establishment initiated by the network for EC-GSM-IoT on EC-CCCH

The purpose of network initiated TBF establishment is to establish a TBF to support the transfer of upper layer PDUs in the direction from the network to the mobile station. The procedure is triggered by a request from upper layers on the network side to transfer an upper layer PDU to a mobile station in packet idle mode that has enabled EC operation. Upon such a request, the network shall initiate a packet downlink assignment procedure on the EC-CCCH as described in 3GPP TS 44.018.

On expiry of timer T3190, the mobile station shall abort the procedure and return to packet idle mode.

The packet downlink assignment procedure is completed when the mobile station receives a valid RLC/MAC block. The mobile station then restarts timer T3190 and enters the packet transfer mode.

7a.3.1 Timing Advance

Initial timing advance can be provided in the EC Downlink Assignment message in the TIMING_ADVANCE_VALUE field. In case valid timing advance for the mobile station is not available, the network may trigger the packet polling procedure (see sub-clause 7a.3.2) by transmitting an EC PACKET POLLING REQUEST message with TYPE_OF_ACK parameter set to access bursts (see sub-clause 11.2.54).

The EC PACKET CONTROL ACKNOWLEDGEMENT or EC PACKET CONTROL ACKNOWLEDGEMENT HIGHER CC message, received from the mobile station, is then used to derive the timing advance of the mobile station.

Thereafter the timing advance in the mobile station is updated with the EC PACKET POWER CONTROL /TIMING ADVANCE message. For the case where a Timing Advance Value is not provided in the EC Downlink Assignment message, the mobile station is not allowed to send normal bursts (e.g. EC PACKET DOWNLINK ACK/NACK message) on the uplink until it receives a valid timing advance in an EC PACKET POWER CONTROL /TIMING ADVANCE message.

7a.3.2 Packet polling procedure

The network may send an EC PACKET POLLING REQUEST message to the mobile station, where the mobile station is addressed with its TFI.

On receipt of an EC PACKET POLLING REQUEST message with the TYPE_OF_ACK parameter set to access bursts (see sub-clause 11.2.54), the mobile station shall send the EC PACKET CONTROL ACKNOWLEDGEMENT or EC PACKET CONTROL ACKNOWLEDGEMENT HIGHER CC message using identical repeated access bursts, on resources allocated by the RRBP field (as defined in sub-clause 10.4.5) and according to its uplink Coverage Class.

The mobile station shall, in the EC PACKET CONTROL ACKNOWLEDGEMENT or EC PACKET CONTROL ACKNOWLEDGEMENT HIGHER CC message, include its latest downlink Coverage Class estimation and, in case the C value is above BT_Threshold_DL (see 3GPP TS 45.008), the latest estimated C value range in the DL_CC_EST field.