8.9 RR connection establishment in packet transfer mode

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

8.9.0 General

The initiation of the procedure and the assignment of resources for the establishment of the RR connection are described in sub-clauses 8.9.1 and 8.9.2, respectively. A mobile station that has enabled PEO may use mobile originated RR connection establishment for GSM services (see 3GPP TS 23.060 [19]) while in packet transfer mode in which case it shall abort the ongoing TBFs, leave packet transfer mode and enter packet idle mode when the RR connection is released.

The establishment of the main signalling link and the completion of the establishment of the RR connection are described in 3GPP TS 44.018.

8.9.1 Initiation

8.9.1.1 Initiation by the mobile station

8.9.1.1.1 Transmission of the PACKET CS REQUEST message

The RR connection establishment procedure is initiated by the RR entity of the mobile station. Initiation is triggered by request from the MM sublayer to enter dual transfer mode. The request from the MM sublayer to establish the RR connection specifies an establishment cause.

The RR entity in the mobile station shall not request the establishment of an RR connection while in packet transfer mode from the point where it receives a PS HANDOVER COMMAND message until the PS handover procedure has been completed (see sub-clause 8.10).

On receipt of the RR connection establishment request from upper layer the mobile station shall start timer T3196. At expiry of timer T3196, the mobile station shall release all ongoing TBFs and start RR connection establishment as specified in 3GPP TS 44.018. If a mobile station that supports PS handover receives a PS HANDOVER COMMAND message while T3196 is running it shall stop T3196, abort its current attempt to establish an RR connection and not make another attempt to establish an RR connection until completion of the PS handover procedure.

If the contention resolution is not solved, the mobile station shall delay the transmission of the PACKET CS REQUEST message until contention resolution is solved.

If the countdown procedure has been started on all the ongoing uplink TBFs, none of those TBFs is operating in extended uplink TBF mode and there is no downlink TBF in progress, the mobile station may either send the PACKET CS REQUEST message, or may immediately release the ongoing TBF(s) and start an RR connection establishment as specified in 3GPP TS 44.018.

The mobile station shall initiate the RR connection establishment by sending PACKET CS REQUEST messages on the PACCH. The mobile station is allowed to retransmit the PACKET CS REQUEST message once while timer T3196 is running. The second sending occurrence of this message shall take place at the first suitable opportunity at least 0.75 s after the first transmission of that message.

8.9.1.1.2 Answer from the network

Upon receipt of a PACKET CS REQUEST message, the network shall answer to the mobile station by encapsulating one of the following RR messages in the PACKET CS COMMAND message, and sending the PACKET CS COMMAND message on PACCH:

– DTM ASSIGNMENT COMMAND message (see sub-clause 8.9.2.1); or

– IMMEDIATE ASSIGNMENT message (see sub-clause 8.9.2.2); or

– IMMEDIATE ASSIGNMENT REJECT message (see sub-clause 8.9.2.3).

Upon receipt of PACKET CS COMMAND message encapsulating one of the above messages the mobile station shall stop timer T3196.

8.9.1.2 Initiation by the network

The network initiates the RR connection establishment procedure by sending a PACKET CS COMMAND message to the mobile station on PACCH, encapsulating one of the following RR messages:

– DTM ASSIGNMENT COMMAND message (see sub-clause 8.9.2.1); or

– IMMEDIATE ASSIGNMENT message (see sub-clause 8.9.2.2).

After sending the mobile station a PS HANDOVER COMMAND message the network shall not initiate the establishment of an RR connection for that mobile station until the PS handover procedure has been completed (see sub-clause 8.10).

8.9.2 Assignment

8.9.2.1 Assignment of both dedicated and packet resource

The network may allocate both a dedicated channel and radio resources on one or more PDCHs to be used by the mobile station and shall in this case send a DTM ASSIGNMENT COMMAND encapsulated in a PACKET CS COMMAND message. Having sent the DTM ASSIGNMENT COMMAND message, the network starts timer T3107, specified in 3GPP TS 44.018. The allocated dedicated channel shall be of TCH type. The network may also reallocate radio resources (PDCH(s)) in the DTM ASSIGNMENT COMMAND message. If both the RR Packet Uplink Assignment and the RR Packet Downlink Assignment information elements are omitted in the DTM ASSIGNMENT COMMAND the network implicitly indicates that the current radio resources shall be maintained. The mobile station shall act on the DTM ASSIGNMENT COMMAND message as specified in 3GPP TS 44.018.

On receiving an encapsulated DTM ASSIGNMENT COMMAND message, the mobile station shall establish the main signalling link using the procedure described in 3GPP TS 44.018.

The completion of the establishment of the RR connection is described in 3GPP TS 44.018.

If timer T3107 elapses before the successful establishment of the main signalling link on the new channel, both the new CS channel and new PS resources are released. If the encapsulated DTM ASSIGNMENT COMMAND message was sent in response to a PACKET CS REQUEST message received from the mobile, then the old PS resources are also released.

NOTE: If timer T3107 expires and the procedure was initiated by the network, the subsequent network behaviour with respect to the old PS resources is implementation dependent.

8.9.2.2 Assignment of dedicated resource only

The network may allocate only a dedicated channel to the mobile station and shall in this case send an IMMEDIATE ASSIGNMENT encapsulated in a PACKET CS COMMAND message. Having sent the IMMEDIATE ASSIGNMENT message, the network starts timer T3101, specified in 3GPP TS 44.018.

If a mobile station receives an encapsulated IMMEDIATE ASSIGNMENT message which either does not specify a starting time or specifies a starting time which has already elapsed, the mobile station shall immediately:

– perform an abnormal release without retry (see sub-clause 8.7.1), if no uplink TBF is in progress, or,

– perform an abnormal release with access retry (see sub-clause 8.7.2), if one or more uplink TBFs are in progress.

On receiving an encapsulated IMMEDIATE ASSIGNMENT message which specifies a starting time which has not yet elapsed, the mobile station shall wait until the specified start time. If, at that time, no uplink TBF is in progress, the mobile station shall perform an abnormal release without retry (see sub-clause 8.7.1); else (i.e. one or more uplink TBFs are in progress) the mobile station shall perform an abnormal release with access retry (see sub-clause 8.7.2).

The mobile station shall proceed with the assignment by establishing the main signalling link using the procedure described in 3GPP TS 44.018. In respect of the RR connection, the mobile station shall act on the starting time information element, if present, as specified in 3GPP TS 44.018.

The completion of the establishment of the RR connection is described in 3GPP TS 44.018.

If timer T3101 elapses before the main signalling link is established, the new CS channel is released. If the encapsulated IMMEDIATE ASSIGNMENT message was sent in response to a PACKET CS REQUEST message received from the mobile, the old PS resources are also released.

NOTE: If timer T3101 expires and the procedure was initiated by the network, the subsequent network behaviour with respect to the old PS resources is implementation dependent.

8.9.2.3 Rejection of the mobile station request

If no dedicated channel is available for assignment, the network may send to the mobile station an IMMEDIATE ASSIGNMENT REJECT message encapsulated in a PACKET CS COMMAND message.

On receipt of the encapsulated IMMEDIATE ASSIGNMENT REJECT message the mobile station shall stop sending PACKET CS REQUEST messages, starts timer T3122 with the indicated value ("wait indication" information element, specified in 3GPP TS 44.018) and continue in packet transfer mode.

The behaviour of the mobile station while timer T3122 is running is specified in 3GPP TS 44.018.

8.9.3 (void)

8.9.4 Abnormal cases

8.9.4.1 RR connection establishment initiated by the mobile station

If a failure occurs on the mobile station side before the successful establishment of the main signalling link, the allocated channels are released; the subsequent behaviour of the mobile station depends on the type of failure and previous actions:

– If the radio resources have been dropped before the network has a chance to respond to the PACKET CS REQUEST, the network shall abort the current DTM procedure.

– If the mobile station does not receive the PACKET CS COMMAND message after it has sent a corresponding PACKET CS REQUEST message (i.e. expiry of timer T3196), the mobile station shall perform an abnormal release with the RR connection establishment retry (see sub-clause 8.7.4).

– If the mobile station receives the DTM ASSIGNMENT COMMAND or the IMMEDIATE ASSIGNMENT message specifying frequencies that are not all in one frequency band then the mobile station shall perform an abnormal release with RR connection establishment retry (see sub-clause 8.7.4).

– If the mobile station receives the DTM ASSIGNMENT COMMAND or the IMMEDIATE ASSIGNMENT message specifying a frequency that is in a frequency band not supported by the mobile station then the mobile station shall perform an abnormal release with RR connection establishment retry (see sub-clause 8.7.4).

– If the information in the DTM ASSIGNMENT COMMAND message does not properly specify an uplink PDCH or specifies a multislot configuration that the mobile station does not support (see 3GPP TS 45.002), the mobile station shall perform an abnormal release with RR connection establishment retry (see sub-clause 8.7.4).

– If the information in the DTM ASSIGNMENT COMMAND message does not properly specify an uplink and downlink PDCH or specifies a multislot configuration that the mobile station does not support (see 3GPP TS 45.002), the mobile station shall perform an abnormal release with RR connection establishment retry (see sub-clause 8.7.4).

– If a failure in the assignment message (e.g. DTM ASSIGNMENT COMMAND or the IMMEDIATE ASSIGNMENT message) is due to any other reason, the mobile station shall perform an abnormal release with RR connection establishment retry (see sub-clause 8.7.4).

– If the mobile fails to establish the main signalling link, it shall perform an abnormal release with RR connection establishment retry (see sub-clause 8.7.4).

8.9.4.2 RR connection establishment initiated by the network

– If the information in the DTM ASSIGNMENT COMMAND message does not properly specify an uplink and downlink PDCH, the mobile station shall perform an abnormal release with access retry (see sub-clause 8.7.2).

– If the mobile station has been reassigned a TBF in EGPRS TBF mode and the MS does not support EGPRS, or has been reassigned an MCS (e.g. 8-PSK in the uplink) that the MS does not support, the MS shall enter to dedicated mode and notify higher layers (TBF establishment failure).

– On expiry of timer T3190, the mobile station shall enter dedicated mode.

– If a failure in the DTM ASSIGNMENT COMMAND message is due to any other reason, the mobile station shall return to packet idle mode.

– If there is a failure in the IMMEDIATE ASSIGNMENT message the mobile station shall continue in packet transfer mode.

– If the mobile fails to establish the main signalling link, it shall perform an abnormal release with RR connection establishment retry (see sub-clause 8.7.4).