4 Overview/General

3GPP44.056CTS radio interface layer 3 specificationGSM Cordless Telephony System (CTS), Phase 1Release 17TS

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

4.1 Overview

4.1.1 General

CTS-Radio Resource management procedures include the functions related to the management of the common transmission resources, e.g. the physical channels and the data link connections on control channels.

The general purpose of CTS-Radio Resource procedures is to establish, maintain and release RR connections that allow a point-to-point dialogue between the CTS‑FP and a mobile station. Moreover, Radio Resource management procedures at the CTS‑MS side include the reception of the uni-directional CTSBCH and CTSPCH when no RR connection is established. This permits automatic cell selection/reselection.

4.1.2 Services provided to upper layers

A CTS‑RR connection is a physical connection used by the two peer entities to support the upper layers’ exchange of information flows.

4.1.2.1 CTS-Idle mode

In CTS-idle mode no CTS-RR connection exists.

The RR procedures include (on the mobile station side) those for automatic cell selection/reselection. The RR entity indicates to upper layers the unavailability of a CTSBCH/CTSPCH and the cell change when decided by the RR entity. Upper layers are advised of the CTSBCH broadcast information when a new cell has been selected, or when a relevant part of this information changes.

In Idle mode, upper layers can require the establishment of an CTS-RR connection.

In Idle-mode, RR procedures provide the following service:

– alive check (CTS‑FP side);

– hunting;

– connectionless group alerting;

– CTS system information broadcasting.

Connectionless group alerting is a point-to-multipoint unidirectional transmission on the CTSPCH. It can only be initiated by the CTS‑FP.

4.1.2.2 Dedicated mode

In dedicated mode, the CTS‑RR connection is a physical point-to-point bi-directional connection, and includes a SAPI 0 data link connection operating in multiframe mode on the main DCCH. If dedicated mode is established, RR procedures provide the following services:

– establishment/release of multiframe mode on data link layer connections other than SAPI 0, on the main DCCH or on the SACCH associated with the channel carrying the main signalling link;

– transfer of messages on any data link layer connection;

– indication of temporary unavailability of transmission (suspension, resuming);

– indication of loss of CTS-RR connection;

– setting/change of the transmission mode on the physical channels, including change of type of channel, change of the coding/decoding/transcoding mode and setting of ciphering;

– release of an CTS-RR connection.

4.1.3 Services required from data link and physical layers

The CTS-RR sublayer uses the services provided by the data link layer as defined in GSM 04.05.

Moreover, the RR sublayer directly uses services provided by the physical layer such as CTSBCH searching, as defined in GSM 04.04.

4.1.4 Change of dedicated channels

NOTE: for this version of the protocol, no intra-cell handover is to be defined.

4.1.4.1 Change of dedicated channels using SAPI = 0

In case a change of dedicated channels is required using a dedicated assignment procedure, the RR sublayer will request the data link layer to suspend multiple frame operation before the mobile station leaves the old channel. When the channel change has been completed, layer 3 will request the data link layer to resume multiple frame operation again. The layer 2 suspend/resume procedures are described in GSM 04.05 and 04.06.

These procedures are specified in such a way that a loss of a layer 3 message cannot occur on the radio interface. However, messages sent from the mobile station to the CTS‑FP may be duplicated by the data link layer if a message has been transmitted but not yet completely acknowledged before the mobile station leaves the old channel (see GSM 04.06).

As the RR sublayer is controlling the channel change, a duplication of RR messages does not occur. However, there are some procedures for which a duplication is possible, e.g. DTMF procedures. For all upper layer procedures using the transport service of the RR sub-layer (e.g. MM and CM procedures), the request messages sent by the mobile station contain a sequence number in order to allow the CTS‑FP to detect duplicated messages, which are then ignored by the CTS‑FP. The procedures for sequenced transmission on layer 3 are described in subclause 4.1.4.2.

4.1.4.2 Change of dedicated channels using other SAPIs than 0

For SAPIs other than 0, the data link procedures described in GSM 04.06 do not provide any guarantee against message loss or duplication.

Therefore, if an application uses a SAPI other than 0 and if this application is sensitive to message loss or duplication, then it has to define its own protection mechanism. No general protection mechanism is provided by the protocol defined in the present document.

4.1.4.3 Sequenced message transfer operation

Upper layer messages sent using the RR sub-layer transport service from the mobile station to the CTS-FP can be duplicated by the data link layer in the following case:

– a channel change of dedicated channels is required (assignment procedure) and the last layer 2 frame has not been acknowledged by the peer data link layer before the mobile station leaves the old channel.

In this case, the mobile station does not know whether the CTS-FP has received the message correctly. Therefore, the mobile station has to send the message again after the new dedicated channel is established (see GSM 04.06).

The CTS-FP must be able to detect the duplicated received message. Therefore, each concerned upper layer message must be marked with a send sequence number.

For historical reasons (see GSM 04.08), messages sent with the CC, SS and MM PDs share the same sequence numbering.

4.1.4.3.1 Variables and sequence numbers

4.1.4.3.1.1 Send state variable V(SD)

The RR sublayer of the mobile station shall have one associated send state variable V(SD) ("Send Duplicated") for each upper layer message flow. The send state variable denotes the sequence number of the next in sequence numbered message in the flow to be transmitted. The value of the corresponding send state variable shall be incremented by one with each numbered message transmission. Arithmetic operations on V(SD) are performed modulo 2.

4.1.4.3.1.2 Send sequence number N(SD)

At the time when such a message to be numbered is designated for transmission, the value of N(SD) for the message to be transferred is set equal to the value of the send state variable V(SD). See GSM 04.07.

4.1.4.3.2 Procedures for the initiation, transfer execution and termination of the sequenced message transfer operation

4.1.4.3.2.1 Initiation

The sequenced message transfer operation is initiated by establishing a RR connection. The send state variables V(SD) are set to 0.

4.1.4.3.2.2 Transfer Execution

The CTS-FP must compare the send sequence numbers of pairs of subsequent messages in the same upper layer messages flow. In case the send sequence numbers of two subsequent messages in a flow are not identical, no duplication has occurred. In case the send sequence numbers are identical, the CTS-FP must ignore the second one of the received messages.

4.1.4.3.2.3 Termination

The sequenced message transfer operation is terminated by the RR connection release procedure.

4.1.5 Procedure for Service Request and Contention Resolution

Upon seizure of the assigned dedicated channel, the mobile station establishes the main signalling link on this channel by sending a layer 2 SABM frame containing a layer 3 service request message. The data link layer will store this message to perform the contention resolution. The service request message will be returned by the CTS‑FP in the UA frame.

The data link layer in the mobile station compares the content of the information field (i.e. the layer 3 service request message) received in the UA frame with the stored message and leaves the channel in case they do not match. This procedure resolves contentions in the case where several mobile stations have accessed at the same random access slot and with the same random reference and one has succeeded due to capture. The full description of the procedure is given in GSM 04.06.

The purpose of the service request message is to indicate to the CTS‑FP which service the mobile station is requesting. This then allows the CTS‑FP to decide how to proceed (e.g. to authenticate or not).

The service request message must contain the identity of the mobile station and may include further information which can be sent without encryption.

CTS-MS CTS-FP

┌──────────────────────────────────────────┐

│ │

│ SABM ("layer 3 service request message") │

│ ───────────────────────────────────────› │

│ │

│ UA ("layer 3 service request message") │

│ ‹─────────────────────────────────────── │

│ │

└──────────────────────────────────────────┘

Figure 4.1/GSM 04.56: Service request and contention resolution

4.2 Idle mode procedures

4.2.1 Mobile Station side

4.2.1.1 CTSBCH and CTSPCH monitoring

In CTS-idle mode, a MS which has recognised a known FPBI, listens to the CTSBCH and to the CTSPCH when CTSPCH indicator flags indicates "CTSPCH to decode".

4.2.1.2 Alive check response

When the CTSPCH contains an CTS ALIVE CHECK REQUEST message, the addressed CTS‑MS shall send a CTS ALIVE CHECK RESPONSE message. A CTS ALIVE CHECK RESPONSE message shall be send by the CTS‑MS in response to each CTS ALIVE CHECK REQUEST message received with the corresponding CTSMSI.

The CTS ALIVE CHECK RESPONSE messages are sent on the CTSARCH and contain as parameters:

– an establishment cause which corresponds to "attachment update" given by the RR entity in response to a CTS ALIVE CHECK REQUEST message;

– the CTS‑MS Mobile Subscriber Identity.

4.2.2 CTS-FP side

4.2.2.1 CTSBCH information broadcasting

FPBI and CTS-FP status are regularly broadcast by the CTS-FP on the CTSBCH. Based on this information, the CTS-MS is able to decide whether it may gain access to the CTS-FP.

The information broadcast may be grouped in the following classes:

– information giving unique identification of the current CTS-FP cell;

– information describing the Training Sequence Code to be used in dedicated mode;

– information describing the Radio Resource availability at the CTS-FP side;

– information describing the presence of a Paging Channel;

– information describing the timeslot number to be used by the CTSCCH except CTSBCH (i.e. CTSARCH, CTSPCH and CTSAGCH);

– information describing the shifting status of the CTSBCH.

4.2.2.2 CTSPCH information broadcasting

In pure idle mode, the Paging Channel is not used. The CTS-FP shall set the CTSPCH indicator flag to "no CTSPCH" value.

4.2.2.3 Alive check

The CTS-FP initiates the alive check procedure by broadcasting a CTS PAGING REQUEST message with an indication of Alive Check, and start timer TC3101. The CTSPCH indicator flag shall be set to "CTSPCH to decode" and the CTSBCH‑SB Status field shall be set to idle. The alive check procedure shall not be triggered if the CTS‑FP is in a busy state (no radio resources available); i.e. CTS‑FP RR layer shall reject upper layer alive check procedure initiation request.

When receiving a CTS PAGING REQUEST with an indication of Alive Check, the CTS-MS shall send 2 CTS ACCESS REQUEST messages.

When receiving a valid CTS ACCESS REQUEST, the CTS‑FP shall stop timer TC3101.

The CTS‑FP RR sublayer shall end the alive check procedure when:

– a CTS ACCESS REQUEST with a valid cause has been received from the polled CTS‑MS; or

— timer TC3101 expires; or

– an end of alive check procedure is triggered by the upper layer; or

– a paging procedure requiring a new PAGING REQUEST message to be started; or

– a busy state occurs (i.e. no more radio resource available).

The CTS‑FP shall ignore unsolicited or out of sequence CTS ACCESS REQUEST.

CTS-MS CTS-FP

┌──────────────────────────────────────────┐

│ │

│ CTS PAGING REQ(CTSMSI, AC ind) │

│ <──────────────────────────────[CTSPCH] │ Start TC3101

│ │

│ CTS ACCESS REQUEST (CTSMSI) │

│ [CTSARCH]─────────────────────────────> │ Stop TC3101

│ │

└──────────────────────────────────────────┘

Figure 4.2/GSM 04.56: alive check sequence

4.2.2.4 Hunting

The CTS-FP initiates the hunting procedure by continuously broadcasting CTS HUNTING REQUEST messages on the CTSPCH channel, and start timer TC3102. The CTSPCH indicator flag shall be set to "CTSPCH to decode". The value of TC3102 is manufacturer dependant, but shall be less than 120 s. The hunting procedure shall not be triggered if the CTS‑FP is in a busy state (no radio resources available); i.e. CTS‑FP RR layer shall reject upper layer hunting procedure initiation request.

Upon receipt of a CTS HUNTING REQUEST, the CTS‑MSs shall act as following:

– if group alerting was requested, the CTS‑MS shall alert if the received connectionless group CTSMSI is equal to its assigned connectionless group CTSMSI (if any);

– if collective alerting was requested, the CTS‑MS shall start alerting.

Hunted CTS‑MS are required to receive and analyse the message sent on the next CTSPCH occurrence. The CTS‑MSs shall consider that the hunting procedure has been ended by the CTS‑FP when no CTS HUNTING REQUEST message has been received within the 3 latest occurrences of the CTSPCH. The CTS-MSs shall stop alerting.

The CTS‑FP shall end the hunting procedure when:

– T_C3102 expires; or

– a paging procedure is to be started; or

– an end of hunting procedure is triggered by the CTS‑FP user; or

– a busy state occurs (i.e. no more radio resource available).

A CTS‑MS shall stop alerting when requested by the user.

USER CTS-MS CTS-FP

┌───────────────────────────────────────────────────────┐

│ │

│ CTS HUNTING REQUEST │

│ <──────────────────────────────[CTSPCH] │

│ │

│ USER ALERTING │

│<───────────── │

│ │

│ CTS HUNTING REQUEST │

│ <──────────────────────────────[CTSPCH] │

│ │

│ [NO HUNTING REQUEST WITHIN THE] │

│ [3 LATEST OCCURRENCES OF THE CTSPCH] │

│ │

│ STOP ALERTING │

│<───────────── │

│ │

└───────────────────────────────────────────────────────┘

Figure 4.3/GSM 04.56: hunting sequence

4.2.2.5 Connectionless group alerting

On receipt of a request for an incoming call, the CTS‑FP may decide to alert part or all enrolled CTS‑MSs.

In this case the CTS‑FP shall request the RR sublayer to send a request for alerting indicating which CTS‑MSs shall alert. Either the group mask shall be used to alert all CTS‑MSs having an assigned connectionless group CTSMSI matching the group mask, or the connectionless CTSMSI shall be used to alert the CTS‑MSs having this connectionless CTSMSI assigned, or the Collective Broadcast Identifier shall be used to alert all CTS‑MSs.

This Connectionless CTS-MS paging procedure should be used for group or collective connectionless alerting service when the number of paged CTS‑MS is greater than the number of available CTS‑FP radio resources.

The CTS-FP initiates the connectionless group alerting procedure by broadcasting continuously a GROUP ALERTING REQUEST message on the CTSPCH subchannel.. The CTSPCH indicator flag shall be set to "CTSPCH to decode" and the CTSBCH‑SB Status field shall be set to idle. Only connectionless group CTSMSI or Connectionless Broadcast Identifier are allowed in a CTS GROUP ALERTING REQUEST message.

Upon receipt of a CTS GROUP ALERTING REQUEST, the CTS‑MS shall react as following:

– if group alerting was requested, the CTS‑MS shall alert if the received connectionless group CTSMSI is equal to its assigned connectionless group CTSMSI (if any);

– if collective alerting was requested, the CTS‑MS shall start alerting.

Alerted CTS‑MSs are required to receive and analyse the message sent on the next CTSPCH. Unless the user accept the call, the CTS‑MS shall not answer to this paging. When the user accept the call, the "off hook" shall trigger an outgoing call request. The CTS-FP shall initiate the immediate assignment procedure as specified in subclause 4.3.1. The CTS‑FP shall suspend the connectionless paging procedure. The establishment of the main signalling link is initiated by the use of an SABM. The SETUP message shall be then passed to the CTS‑FP.

At the CTS‑FP, this outgoing call is directly mapped to the awaiting incoming call.

The CTS-FP shall stop the connectionless group alerting procedure when:

– the awaiting call is answered by a paged CTS-MS; or

– the fixed line end user hangs up before the call is answered; or

– the call is answered by another device (e.g. answering machine); or

– the paging timer expires.

The connectionless group alerting procedure could be resumed if the call establishment failed.

The CTS‑MSs shall consider that the connectionless group alerting procedure has been ended by the CTS‑FP when CTS GROUP ALERTING REQUEST message has not been received within the 3 latest occurrences of the CTSPCH. The CTS-MSs shall stop alerting.

USER CTS-MS CTS-FP

┌───────────────────────────────────────────────────────┐

│ │

│ CTS GROUP ALERTING REQUEST │

│ <──────────────────────────────[CTSPCH] │

│ │

│ USER ALERTING │

│<───────────── │

│ │

│ CTS GROUP ALERTING REQUEST │

│ <──────────────────────────────[CTSPCH] │

│ │

│OFF HOOK │

│─────────────> │

│ │

│ CTS ACCESS REQUEST(CTSMSI) │

│ [CTSARCH]─────────────────────────────> │

│ │

│ CTS IMMEDIATE ASSIGNMENT │

│ <─────────────────────────────[CTSAGCH] │

│ │

│ SABM(CM SERVICE REQUEST) │

│ [DCCH] ───────────────────────────────> │

│ │

│ UA(CM SERVICE REQUEST) │

│ <────────────────────────────────[DCCH] │

│ │

│ {AUTHENTICATION & CIPHERING} │

│ │

│ CC SETUP │

│ [DCCH]────────────────────────────────> │

│ │

│ {//} │

│ │

│ CC CONNECT │

│ <────────────────────────────────[DCCH] │

│ │

└───────────────────────────────────────────────────────┘

Figure 4.4/GSM 04.56: connectionless group alerting and response sequence

4.2.2.5 CTS system information broadcasting

CTS SYSTEM INFORMATION TYPE 1, 2 or 3 may be broadcast by the CTS‑FP on the CTSPCH channel.

CTS SYSTEM INFORMATION TYPE 1, 2 or 3 may be sent to the attached CTS‑MSs when the TFH list or the TFH parameters need to be changed.

The information broadcast may be group in the following classes:

– information about the frequency list to used;

– information about the Total Frequency Hopping parameters to used.

4.3 RR connection establishment

4.3.1 RR connection establishment initiated by the mobile station

The purpose of the immediate assignment procedure is to establish an RR connection between the mobile station and the CTS‑FP.

4.3.1.1 Entering the dedicated mode: immediate assignment procedure

The immediate assignment procedure can only be initiated by the RR entity of the mobile station. Initiation is triggered by request from the MM sublayer to enter the dedicated mode or by the RR entity in response to a CTS PAGING REQUEST message. Upon such a request:

– if access to the CTS‑FP is allowed (as defined in subclause 4.3.1.1.1), the RR entity of the mobile station initiates the immediate assignment procedure as defined in subclause 4.3.1.1.2;

– otherwise, it rejects the request.

The request from the MM sublayer to establish an RR connection specifies an establishment cause. Similarly, the request from the RR entity to establish a RR connection in response to a paging message specifies one of the establishment causes "answer to paging".

4.3.1.1.1 Permission to access the CTS‑FP

Access to the CTS-FP is allowed to any enrolled CTS‑MS when the CTSBCH status field indicates idle. CTS‑MS shall not try to access the CTS‑FP when the status field indicates busy and it shall continue to decode CTSBCH and if needed CTSPCH or CTSAGCH.

4.3.1.1.2 Initiation of the immediate assignment procedure

The RR entity of the CTS‑MS initiates the immediate assignment procedure by scheduling the sending on the CTSARCH and leaving idle mode. It then send maximally M_CTS + 1 CTS ACCESS REQUEST messages on the CTSARCH.

The CTS ACCESS REQUEST messages are sent on the non-hopping CTSARCH for the enrolment and attachment MM-procedures and on the hopping CTSARCH for the other cases. They contain as parameters:

– an establishment cause which corresponds to the establishment causes given by the MM sublayer or which corresponds to one of the establishment causes "answer to paging" given by the RR entity in response to a CTS PAGING REQUEST message;

– the CTS‑MS Mobile Subscriber Identity.

After sending the first CTS ACCESS REQUEST, the CTS‑MS shall start listening continuously to the CTSAGCH. After having sent M_CTS + 1 CTS ACCESS REQUEST messages, the CTS‑RR entity of the CTS‑MS shall start timer T_C3150. At expiry of this timer, the immediate assignment procedure is aborted. If the immediate assignment procedure was triggered by a request from the CTS‑MM sublayer, a access failure is indicated to the CTS‑MM sublayer.

4.3.1.1.3 Answer from the CTS-FP

4.3.1.1.3.1 On receipt of a CTS ACCESS REQUEST message

The CTS‑FP may allocate a dedicated channel to the CTS‑MS by sending an CTS IMMEDIATE ASSIGNMENT message in unacknowledged mode. Timer T_C3103 is then started by the CTS‑RR layer of the CTS‑FP.

The CTS IMMEDIATE ASSIGNMENT message contains:

– the access request reference (cause, CTSMSI);

– the description of the dedicated channel;

– optionally the multiframe number reference.

4.3.1.1.3.2 Assignment rejection

If no channel is available for assignment, the CTS‑FP may send to the CTS-MS a CTS IMMEDIATE ASSIGNMENT REJECT in unacknowledged mode in the CTSAGCH channel. This message contains an access request reference and a wait indication.

4.3.1.1.4 Assignment completion

The immediate assignment procedure is terminated on the CTS‑FP side when the main signalling link is established. Timer T_C3103 is stopped and the MM sublayer on the CTS-FP side is informed that the RR entity has entered the dedicated mode.

On the mobile station side, the procedure is terminated when the establishment of the main signalling link is confirmed. The MM sublayer is informed that the RR entity has entered the dedicated mode.

4.3.1.1.4.1 Early classmark sending

Early classmark sending consists in the mobile station sending as early as possible after access a CTS CLASSMARK CHANGE message to provide the CTS-FP with additional classmark information.

A mobile station which implements the "Controlled Early Classmark Sending" option shall indicate it in the classmark (ES IND bit).

4.3.1.1.5 Abnormal cases

If a lower layer failure occurs on the mobile station side on the new channel 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 failure is due to information field mismatch in the contention resolution procedure, see subclause 4.1.5, and no repetition as described in this paragraph has been performed, the immediate assignment procedure shall be repeated.

– If the failure is due to any other reason or if a repetition triggered by a contention resolution failure has been performed. The mobile station returns to idle mode (RR connection establishment failure), transactions in progress are aborted and cell reselection then may take place.

4.3.2 Paging procedure for RR connection establishment

The CTS-FP can initiate the establishment of an RR connection by the paging procedure for RR connection establishment. Such a procedure can only be initiated by the CTS‑FP.

4.3.2.1 Paging initiation by the CTS-FP

The CTS-FP initiates the paging procedure by broadcasting a CTS PAGING REQUEST message on the CTSPCH subchannel and starts timer T_C3104. The CTSPCH indicator flag shall be set to "CTSPCH to decode" and the CTSBCH‑SB Status field shall be set to idle.

A CTS PAGING REQUEST message may include more than one CTS‑MS identification. Only Assigned Individual CTSMSIs or are allowed in a CTS PAGING REQUEST message.

The CTS‑MS is required to receive and analyse the paging messages sent on the CTSPCH according to the multiframe paging period.

4.3.2.2 Paging response

Upon receipt of an CTS PAGING REQUEST, the addressed CTS-MS shall initiate the immediate assignment procedure as specified in subclause 4.3.1 The establishment of the main signalling link is then initiated by the use of an SABM with information field containing the paging response message. The MM sublayer in the CTS‑MS is informed that an CTS‑RR connection exists.

Upon receipt of the paging response message, timer T_C3104 is stopped and the MM sublayer in the CTS‑FP is informed that a CTS‑RR connection exits.

4.3.2.3 Abnormal cases

The CTS-FP shall abort the paging procedure when:

– an end of paging procedure is triggered by the upper layer i.e.:

– the fixed line end user hangs up before the call is answered; or

– the call is answered by another device (e.g. answering machine); or

– the call is forwarded; or

– the paging timer expires.

If timer T_C3104 expires and a valid CTS PAGING RESPONSE message has not been received, a specific failure indication shall be triggered to the upper layer and the CTS‑FP upper layer may repeat the paging procedure.

CTS-MS CTS-FP

┌──────────────────────────────────────────┐

│ │

│ CTS PAGING REQUEST(CTSMSI) │ Start TC3104

│ <──────────────────────────────[CTSPCH] │

│ │

│ CTS ACCESS REQUEST(CTSMSI) │

│ [CTSARCH]─────────────────────────────> │

│ │

│ CTS IMMEDIATE ASSIGNMENT │

│ <─────────────────────────────[CTSAGCH] │ Start TC3103

│ │

│ SABM(CTS PAGING RESPONSE) │

│ [DCCH]────────────────────────────────> │ Stop TC3103

│ │ Stop TC3104

└──────────────────────────────────────────┘

Figure 4.5/GSM 04.56: individual paging sequence

4.4 Procedures in dedicated mode

Procedures described in this subclause apply to the dedicated mode.

Direct transition between dedicated mode and group transmit mode is possible in both directions by use of the following procedures:

– Channel assignment procedure;

– Channel mode modify procedure.

4.4.1 SACCH procedures

4.4.1.1 General

In RR connected mode, the SACCH is used in signalling at least for measurement results transmission from the CTS‑MS. Continuous transmission must occur in both directions. For that purpose, in CTS‑MS to CTS‑FP direction, measurement result messages are sent at each possible occasion when nothing else has to be sent. Similarly, empty UI frames are sent in the CTS‑FP to CTS‑MS direction when nothing else has to be sent.

4.4.1.2 Measurement report

When in RR connected mode, the CTS‑MS regularly sends CTS MEASURMENT REPORT messages to the CTS‑FP. These messages contain measurement results about reception characteristics from the current cell. They are sent on the slow ACCH, in unacknowledged mode. If no other message is scheduled on the SACCH at the instant when a layer 2 frame is due to be sent, then the CTS‑MS shall send a CTS MEASUREMENT REPORT message. The interval between two successive layer 2 frame containing CTS MEASUREMENT REPORT messages shall not exceed one layer 2 frame.

4.4.2 Transfer of messages and link layer service provision

When in dedicated mode or in group transmit mode, upper layers can send messages in multiframe or unacknowledged mode on SAPI 0.

Moreover, but only when in dedicated mode, upper layers have access to the full link layer services for SAPIs other than 0, with the exception of the error indication and local end release that are directly treated by the RR sublayer, as specified in particular places of clause 4.

4.4.3 Intracell handover procedure

In dedicated mode, an intracell change of channel can be requested by upper layers for changing the channel type, or decided by the RR sublayer, e.g. for an internal handover. This change may be performed through the dedicated channel assignment procedure.

The purpose of the channel assignment procedure is to completely modify the physical channel configuration of the mobile station without frequency redefinition or change in synchronisation while staying in the same CTS-cell.

This procedure shall not be used for changing between dependent configurations, i.e. those sharing Radio Resource for the main signalling link. An example of dependent channels is a full rate channel and one of the corresponding half rate channels. In multislot operation however, it is allowed to use the same timeslots before and after the assignment, as long as the main signalling link has been changed. The only procedures provided for changing between dependent configurations for the main signalling link are the additional assignment and the partial release procedures.

The channel assignment procedure happens only in dedicated mode. This procedure cannot be used in the idle mode; in this case the immediate assignment procedure is used.

The channel assignment procedure includes:

– the suspension of normal operation except for RR management (layer 3);

– the release of the main signalling link, and of the other data links as defined in subclause 4.1.4, and the disconnection of TCHs if any;

– the deactivation of previously assigned channels (layer 1);

– the activation of the new channels and their connection if applicable;

– the triggering of the establishment of the data link connections for SAPI = 0.

The channel assignment procedure is always initiated by the CTS‑FP.

4.4.3.1 Intracell handover initiation

The CTS‑FP initiates the intracell handover procedure by sending a CTS INTRACELL HANDOVER COMMAND message to the CTS‑MS on the main signalling link. The CTS‑FP then starts timer T_C3105. When sending this message on the CTS‑FP side, and receiving it on the CTS‑MS side, all transmission of signalling layer message except for those RR messages needed for this procedure and for abnormal cases is suspended until resumption is indicated.

Upon receipt of the CTS INTRACELL HANDOVER COMMAND message, the CTS-MS initiates a local end release of link layer connections, disconnects the physical channels, commands the switching to the assigned channel and initiates the establishment of lower layer connections.

The CTS‑MS shall wait up to the starting time before accessing the channel. If the starting time has already elapsed, the CTS‑MS shall access the channel as an immediate reaction to the reception of the message.

4.4.3.2 Intracell handover completion

After the main signalling link is successfully established, the CTS‑MS returns a CTS INTRACELL HANDOVER COMPLETE message specifying cause "normal event” to the CTS‑FP on the main DCCH.

The sending of this message on the CTS‑MS side and its receipt on the CTS‑FP side allow the resumption of the transmission of signalling layer messages other than those belonging to RR management.

At the receipt of the CTS INTRACELL HANDOVER, the CTS‑FP releases the previously allocated resources and stops timer TC3105.

4.4.3.3 Abnormal cases

If the CTS INTRACELL HANDOVER COMMAND instruct the CTS‑MS to use a parameter that it is not capable of, then the CTS-MS shall return a CTS INTRACELL HANDOVER FAILURE message, and the CTS-MS shall remain on the current channel(s) and use the old channel description or channel mode.

When receiving a CTS INTRACELL HANDOVER FAILURE message, the CTS‑FP stops TC3105.

On the CTS‑FP side, if timer T_C3105 elapses before either the CTS INTRACELL HANDOVER COMPLETE message has been receive on the new channel or a CTS INTRACELL HANDOVER FAILURE message is received or the CTS‑MS has re-established the call, the old and the new channels are released and all contexts related to the connection with that CTS‑MS are cleared.

4.4.4 Intercell handover procedure

Intercell handover is a CTS phase 2 issue.

4.4.5 Frequency hopping definition procedure

This procedure is used by the CTS‑FP to update the Total Frequency Hopping List and Total Frequency Hopping parameters in the MS. The CTS‑FP send a CTS FREQUENCY HOPPING DEFINITION message containing the new parameters together with a reference time indication. The TFH parameters are split in general static parameters and current dynamic parameters which are valid for a given TDMA frame number. The values indicated by the current parameters IE are those used by the TFH algorithm at the frame number indicated by the reference time. These parameters shall be used after the RR connection is released when the MS is returning in idle mode.

4.4.6 Channel mode modify procedure

In dedicated mode, higher layers can request the setting of the channel mode.

The channel mode modify procedure allows the CTS‑FP to request the mobile station to set the channel mode for one channel or one channel set. The channel mode covers the coding, decoding and transcoding mode used on the indicated channel.

This procedure is always initiated by the CTS‑FP.

NOTE: Direct transitions between full rate speech coder version 1 and full rate speech coder version 2 (and vice versa) may cause unpleasant audio bursts.

4.4.6.1 Normal channel mode modify procedure

4.4.6.1.1 Initiation of the channel mode modify procedure

The FP initiates the procedure by sending a message CTS CHANNEL MODE MODIFY to the CTS‑MS. This message contains:

– a channel description of the channel(s) on which the specified mode shall be applied; and

– the mode to be used on that channel.

4.4.6.1.2 Completion of channel mode modify procedure

When it has received the CTS CHANNEL MODE MODIFY message, the CTS‑MS sets the mode for the indicated channel, and if that is in a multislot configuration, the whole channel set and then replies by a CTS CHANNEL MODE MODIFY ACKNOWLEDGE message indicating the ordered channel mode.

This applies whether the mode commanded by the CTS CHANNEL MODE MODIFY message is different from the one used by the CTS‑MS or whether it is already in use.

4.4.6.1.3 Abnormal cases

No specific action for a lower layer failure is specified in this subclause. If the mobile station does not support the indicated mode, it shall retain the old mode and return the associated channel mode information in CTS CHANNEL MODE MODIFY message.

4.4.7 Ciphering mode setting procedure

In dedicated mode, the ciphering mode setting procedure is used by the FP to set the ciphering mode, i.e. whether or not the transmission is ciphered, and if so which algorithm to use. The procedure shall only be used to change from "not ciphered" mode to "ciphered" mode, or vice-versa, or to pass a CTS CIPHERING MODE COMMAND message to the mobile station while remaining in the "not ciphered" mode. The ciphering mode setting procedure is always triggered by the FP and it only applies to dedicated resources.

4.4.7.1 Ciphering mode setting initiation

The CTS‑FP initiates the ciphering mode setting procedure by sending a CTS CIPHERING MODE COMMAND message to the mobile station on the main signalling link, indicating whether ciphering shall be used or not, and if yes which algorithm to use.

The new mode is applied for reception on the CTS‑FP side after the message has been sent.

4.4.7.2 Ciphering mode setting completion

Whenever the CTS‑MS receives a CTS CIPHERING MODE COMMAND message, it shall, if a SIM is present and considered valid by the mobile equipment and the ciphering key sequence number stored on the SIM indicates that a CTS ciphering key is available, load the ciphering key stored on the SIM into the ME. A valid CTS CIPHERING MODE COMMAND message is defined to be one of the following:

– one that indicates "start ciphering" and is received by the mobile station in the "not ciphered" mode;

– one that indicates "no ciphering" and is received by the MS in the "not ciphered" mode; or

– one that indicates "no ciphering" and is received by the mobile station in the "ciphered" mode.

Other CTS CIPHERING MODE COMMAND messages shall be regarded as erroneous, an CTS RR STATUS message with cause "Protocol error unspecified" shall be returned, and no further action taken.

Upon receipt of the CTS CIPHERING MODE COMMAND message indicating ciphering, the mobile station shall start transmission and reception in the indicated mode.

When the appropriate action on the CTS CIPHERING MODE COMMAND has been taken, the mobile station sends back a CTS CIPHERING MODE COMPLETE message. If the "cipher response" field of the cipher response information element in the CTS CIPHERING MODE COMMAND message specified "IMEI must be included" the mobile station shall include its IMEISV in the CTS CIPHERING MODE COMPLETE message.

Upon receipt of the CTS CIPHERING MODE COMPLETE message or any other correct layer 2 frame which was sent in the new mode, the CTS‑FP starts transmission in the new mode.

CTS-MS CTS-FP

CTS CIPH MOD CMD

<──────────────────────────

<──── start reception

start ────> in new mode

transmission and ÷

reception in new mode ÷

CTS CIPH MOD COM

──────────────────────────>

<───── start trans-

mission in new mode

Figure 4.6/GSM 04.56: Ciphering mode setting sequence

4.4.8 [Reserved: Additional channel assignment procedure]

This is a CTS phase 2 issue.

4.4.9 [Reserved: Partial channel release procedure]

This is a CTS phase 2 issue.

4.4.10 Classmark change procedure

In dedicated mode, this procedure allows the mobile station to indicate to the CTS‑FP a change of characteristics reflected in the classmark (e.g. due to addition of power amplification). Furthermore, a mobile station which implements the "controlled early classmark sending" option may also send a CTS CLASSMARK CHANGE message as described in subclause 4.3.1.1.4, even if no change of characteristics has occurred.

The mobile station sends a CTS CLASSMARK CHANGE message to the CTS‑FP. This message contains the new mobile station classmark 2 information element. It may also contain a Classmark 3 Information Element. There is no acknowledgement from the CTS‑FP at layer 3.

4.4.11 Classmark interrogation procedure

This procedure allows the CTS‑FP to request additional classmark information from the mobile station (e.g. if the information initially sent by the mobile station is not sufficient for CTS‑FP decisions).

The CTS-FP initiate the classmark interrogation procedure by sending a CTS CLASSMARK ENQUIRY message to the CTS‑MS on the main DCCH.

on receipt of the CTS CLASSMARK ENQUIRY message, the CTS‑MS sends a CTS CLASSMARK CHANGE message to the CTS‑FP on the main DCCH.

4.4.12 [Reserved]

4.4.13 RR connection release procedure

4.4.13.1 Normal release procedure

The release of the RR connection can be requested by upper layers.

The purpose of this procedure is to deactivate all the dedicated channels in use for this RR connection. When the channels are released, the mobile station returns to the idle mode. The channel release procedure can be used in a variety of cases, including TCH release after a call release, and DCCH release when a dedicated channel allocated for signalling is released.

In dedicated mode, the channel release procedure is always initiated by the CTS‑FP.

4.4.13.1.1 Channel release procedure initiation

The CTS-FP initiates the channel release procedure by sending a CTS CHANNEL RELEASE message to the CTS-MS on the main DCCH, starts timer T_C3106 and deactivates the SACCH.

On receipt of a CTS CHANNEL RELEASE message, the CTS-MS starts timer T_C3151 and disconnect the main signalling link. When TC3151 times out or when the disconnection is confirmed, the CTS‑MS deactivates all signalling link, considers the RR connection as released, and returns to idle mode.

On CTS‑FP side, when the main signalling link is disconnected, the CTS-FP stops timer TC3106 and starts timer TC3107. When timer TC3107 times out, the CTS-FP deactivates the channels. If timer TC3106 times out, the CTS‑FP deactivates the channels.

4.4.13.1.2 Abnormal case

Abnormal cases are taken into account in the main part of the description of the procedure.

4.4.13.2 Radio link fai2lure in dedicated mode

The main part of these procedures concerns the "normal" cases, i.e. those without any occurrence of loss of communication means. A separate paragraph at the end of the description of each procedure treats the cases of loss of communication, called a radio link failure. In dedicated mode, in most of the cases the reaction of the mobile station or the CTS-FP is the same. Those reactions are described in this subclause to avoid repetitions.

A radio link failure can be detected by several ways:

1) by analysis of reception at layer 1, as specified in GSM 05.08 and subclause 4.4.1.1;

2) by a data link layer failure as specified in GSM 04.06, on the main signalling link. A data link failure on any other data link shall not be considered as a radio link failure;

3) when a lower layer failure happens while the mobile station attempts to connect back to the old channels in a channel assignment procedure or handover procedure;

4) in some cases where timers are started to detect the lack of answer from the other party, as described in clause 3.

The two first cases are known by the term "lower layer failure".

4.4.13.2.1 Mobile side

When a radio link failure is detected by the mobile station:

‑ the MS shall perform a local end release on all signalling links unless otherwise specified;

‑ the mobile station shall deactivate all channels;

‑ the RR sublayer of the mobile station shall indicate an RR connection failure to the MM sublayer unless otherwise specified.

NOTE: Upper layers may decide on a re-establishment (see subclause 5.5.4).

4.4.13.2.2 CTS-FP side

When a radio link failure has been detected, an indication is passed to the upper sublayer on CTS‑FP side.

The CTS‑FP should release the connection except when otherwise specified, either with the channel release procedure as specified in subclause 4.4.13.1 or with the following procedure. The CTS‑FP start timer TC3106 and deactivates the SACCH and hence stops transmission on the SACCH. When timer TC3106 expires, the CTS-FP can regard the channel as released.

NOTE: The CTS‑FP The network should maintain for a while the transaction context in order to allow call re‑establishment.

4.4.13.3 RR connection abortion in dedicated mode

The mobile station aborts the RR connection by initiating a normal release of the main signalling link, performing local end releases on all other signalling links and disconnecting all traffic channels, if any.

4.4.14 Receiving CTS RR STATUS message by a CTS-RR entity

If the CTS‑RR entity of the mobile station receives a CTS RR STATUS message no transition and no specific action shall be taken as seen from the radio interface, i.e. local actions are possible.

The actions to be taken on receiving a CTS RR STATUS message in the CTS‑FP are defined in GSM 04.08. See also clause 8.

4.4.15 CTS RR parameters update

This procedure allows the CTS-FP to provide mandatory parameters to the mobile station. It shall be initiated during enrolment and attachment MM-procedures.

The CTS-FP sends the CTS RR PARAMETERS UPDATE message containing the relevant parameters.