5 Elementary procedures for Mobility Management

04.563GPPGSM Cordless Telephony System (CTS), (Phase 1) CTS Radio Interface Layer 3 SpecificationTS

5.1 General

This section describes the procedures used for mobility management at the CTS radio interface (Reference Point Um*).

The general purpose of CTS Mobility Management sublayer is to support the mobility of the mobile stations, such as informing the fixed part of its presence and providing user identity confidentiality. The CTS‑MM sublayer provides also connection management services to the different entities of the upper Connection Management (CM) sublayer.

All the CTS‑MM procedures can only be performed if a CTS-RR connection has been established between the mobile station and the fixed part. If no CTS‑RR connection is currently established, the CTS‑MM sublayer has to initiate such establishment.

Depending of the CTS‑MM procedure, they can be initiated either by the mobile station or by the fixed part or even indifferently by one of the two parties.

The CTS-FP may also start all mobility management procedures defined in GSM 04.08, including:

– the GSM authentication procedure,

– the GSM identity request procedure.

The messages defined in GSM 04.08 shall be used for these procedures.

5.1.1 Type of CTS-MM procedures

Depending on how they can be initiated, two types of CTS-MM procedures can be distinguished:

(i) CTS-MM common procedures:

A CTS-MM common procedure can always be initiated whilst a CTS-RR connection exists. The procedures belonging to this type are:

Initiated by the fixed part:

– CTS mutual authentication procedure;

– CTSMSI update procedure;

– CTS de-enrolment procedure.

Initiated by the mobile station:

– CTS detach procedure

(ii) CTS-MM specific procedures:

A CTS-MM specific procedure can only be initiated if no other MM specific procedure is running or no MM connection exists. The procedures belonging to this type are:

Initiated by the mobile station:

– CTS enrolment procedure;

– CTS attach procedure;

– CTS re-attach procedure.

Initiated by the fixed part:

– CTS periodic attach update procedure.

These running procedures do not preclude from running procedures defined in the CTS supervising system layer 3 specification.

5.1.2 CTS-MM sublayer states

5.1.2.1 CTS-MM sublayer states in the mobile station

An additional machine describes the states related to the CTS.

5.1.2.1.1 Main states

1. WAIT FOR CTS-RR ACTIVE

The CTS-MM sublayer has requested activation of the CTS-RR sublayer.

2. WAIT FOR CTS-RR CONNECTION (ENROLMENT OR ATTACH)

The CTS-MM sublayer has requested CTS-RR connection establishment for starting the enrolment procedure or the attach one.

3. ATTACH INITIATED

The attach procedure has been started and the CTS-MM awaits a response from the fixed part. The timer TC3250 is running.

4. ENROLMENT INITIATED

The enrolment procedure has been started and the CTS-MM awaits a response from the fixed part. The timer TC3254 is running.

5. ATTACH REJECTED

The attach procedure has been rejected and CTS-RR connection release is awaited. The timer TC3256 is running.

6. ENROLMENT REJECTED

The enrolment procedure has been rejected and CTS-RR connection release is awaited.

7. AUTHENTICATION INITIATED

The mutual authentication procedure has been started by the fixed part.

8. CTS-MM IDLE

There is no MM procedure running and no RR connection exist. This is a compound state.

5.1.2.1.2 Substates of the CTS-MM IDLE state

8.1 NORMAL SERVICE

The mobile station is attached to a fixed part and it is reachable.

8.2 FP SEARCH

The mobile station is searching for fixed parts on which the mobile station is enrolled.

8.3 NO FP AVAILABLE

No fixed part can be selected. This state is entered after a first intensive search failed. Fixed parts are searched at a low rhythm. No CTS services are offered.

5.1.2.2 CTS-MM sublayer states in the fixed part

1. IDLE

The CTS-MM sublayer is not active.

2. WAIT FOR CTS-RR CONNECTION

The CTS-MM sublayer has requested activation of the CTS-RR sublayer.

3. CTS-MM CONNECTION ACTIVE

The CTS-MM sublayer has a CTS-RR connection to a mobile station. One or more MM connections are active.

4. CTS AUTHENTICATION INITIATED

The authentication procedure has been started by the fixed part.

5. CTS DE-ENROLMENT INITIATED

The de-enrolment procedure has been started by the fixed part.

6. CTS CIPHERING MODE INITIATED

The cipher mode setting procedure has been requested to the CTS-RR-sublayer.

5.2 CTS-MM common procedures

5.2.1 CTS detach procedure

The purpose of the CTS detach procedure is to detach a mobile station from a fixed part. The mobile station may launch the detach procedure during the CTS mode deactivation (e.g. at the power off, when the SIM is extracted, when the mobile station is set in GSM mode only).

The CTS detach procedure is always initiated by the mobile station.

5.2.1.1 CTS detach initiation by the mobile station

The mobile station initiates the CTS detach procedure by sending a CTS DETACH INDICATION to the fixed part. The mobile station then starts timer TC3253.

If no RR connection exists, the MM sublayer within the mobile station will request the RR sublayer to establish a RR connection. If a RR connection exists, the MM sublayer will release locally any ongoing MM connections before the CTS DETACH INDICATION message is sent.

5.2.1.2 CTS detach procedure in the fixed part

On reception of a CTS DETACH INDICATION, the fixed part shall consider the mobile station as detached. No response is returned to the mobile station. After reception of the CTS DETACH INDICATION message, the fixed part shall release locally any ongoing MM connections, and start the normal RR connection release procedure.

5.2.1.3 CTS detach completion by the mobile station

Timer TC3253 is stopped when the RR connection is released. The mobile station should, if possible, delay the local release of the channel to allow a normal release from the fixed part until TC3253. If this is not possible (e. g. detach at power down) the RR sublayer on the mobile side should be aborted.

5.2.1.4 Abnormal cases

If establishment of an RR connection is not possible, or the RR connection is lost, the CTS detach procedure is aborted by the mobile station.

5.2.2 CTS de-enrolment procedure

The purpose of the CTS de-enrolment procedure is to inform a CTS MS that it is no more enrolled on this CTS-FP.

The CTS de-enrolment procedure is always launched by the fixed part.

This procedure shall be launched when the mobile station has no more right to be enrolled (e.g. expiration of validity period, de-enrolment requested by the CTS operator). Any reference to this mobile station should be removed in the fixed part.

5.2.2.1 CTS de-enrolment initiation by the fixed part

The fixed part initiates the CTS de-enrolment procedure by sending a CTS DE-ENROLMENT INDICATION to the mobile station. Then the fixed part will request the RR sublayer to release the RR connection.

5.2.2.2 CTS de-enrolment procedure in the mobile station

On reception of a CTS DE-ENROLMENT INDICATION, the CTS-MS shall remove the corresponding CTS-FP of the list of the fixed parts on which the mobile station is enrolled.

The mobile station should inform the user that it is no more enrolled on this CTS-FP.

5.2.2.3 Abnormal cases

If establishment of an RR connection is not possible, or the RR connection is lost, the CTS de-enrolment procedure is aborted by the fixed part. Nevertheless, any reference to the corresponding mobile station should be removed in the fixed part.

5.2.3 CTS mutual authentication procedure

The purpose of the CTS mutual authentication procedure is:

– to permit the fixed part to check whether the identity provided by the mobile station is acceptable or not (see GSM 03.20 Annex E);

– to permit the mobile station to check whether the identity provided by the fixed part is acceptable or not (see GSM 03.20 Annex E);

– to agree on required parameters between the fixed part and mobile station to calculate a new ciphering key (see GSM 03.20 Annex E).

The authentication procedure uses the CTSMSI if it is available. If it is not available or if the authentication fails using this identity, the authentication procedure shall be started again using the IMSI.

The CTS authentication procedure is always initiated by the CTS-FP on the radio interface.

This procedure shall be used each time an enrolment procedure or an attach procedure is started.

5.2.3.1 CTS authentication initiation by the fixed part

The fixed part initiates the CTS authentication procedure by sending a CTS MS AUTHENTICATION REQUEST message to the CTS-MS and starts the timer TC3211.

The CTS MS AUTHENTICATION REQUEST message specifies the authentication parameter.

5.2.3.2 CTS authentication response by the mobile station

The mobile station shall be ready to respond upon a CTS MS AUTHENTICATION REQUEST message at any time whilst a CTS-RR connection exists.

On reception of a CTS MS AUTHENTICATION REQUEST from the fixed part, the mobile station shall send a CTS MS AUTHENTICATION RESPONSE and starts the timer TC3260.

The CTS MS AUTHENTICATION RESPONSE message specifies the authentication parameter CH2 and the authentication parameter SRES1.

5.2.3.3 CTS authentication processing by the fixed part

On reception of the CTS MS AUTHENTICATION RESPONSE from the mobile station, the fixed part shall stop the timer TC3211 and shall check the validity of the response (see GSM 03.20 Annex E).

The fixed part shall respond with a CTS FP AUTHENTICATION RESPONSE message. This message specifies the authentication parameter SRES2.

5.2.3.4 CTS authentication completion by the mobile station

On reception of the CTS FP AUTHENTICATION RESPONSE from the fixed part, the mobile station shall stop the timer TC3260 and shall check the validity of the response (see GSM 03.20 Annex E).

5.2.3.5 Unsuccessful authentication

If mobile station authentication fails, i.e. the response given by the mobile station is not valid, the fixed part may distinguish between the two different ways of identification: IMSI or CTSMSI. If the mobile station identifies itself using the CTSMSI, the fixed part may request the IMSI using the identity request procedure and may start a new mutual authentication procedure using the IMSI.

If the fixed part does not start a new authentication procedure, it shall sent a CTS MS AUTHENTICATION REJECT message to the mobile station. After having sent this message, the fixed part shall release any ongoing MM connections and shall initiate the RR connection release procedure. If fixed part authentication fails, i.e. the response given by the fixed part is not valid, the mobile station may abort the RR connection. In this case, the CTS-MS shall abort any MM ongoing procedure.

5.2.3.6 Abnormal cases

Fixed part side

(a) CTS-RR connection failure

Upon a detection of a CTS-RR connection failure before the CTS MS AUTHENTICATION RESPONSE is received, the fixed part shall release all MM connections (if any) and abort any ongoing MM specific procedure.

(b) Expiry of timer TC3211

The mutual authentication procedure is supervised on the fixed part by the timer TC3211. At expiry of this timer the fixed part may release the CTS-RR connection. In this case the fixed part shall abort the mutual authentication procedure and any ongoing MM specific procedure, release all MM connections if any, and initiate the CTS-RR connection release procedure described in section 4.4.13.

Mobile station side

(a) CTS-RR connection failure

Upon a detection of a CTS-RR connection failure before the CTS FP AUTHENTICATION RESPONSE is received, the mobile station shall release all MM connections (if any) and abort any ongoing MM specific procedure.

(b) Expiry of timer TC3260

The mutual authentication procedure is supervised on the mobile station by the timer TC3260. At expiry of this timer the mobile station may abort the CTS-RR connection. In this case the mobile station shall abort the mutual authentication procedure and any ongoing MM specific procedure, release all MM connections if any, and initiate the CTS-RR connection release procedure described in section 4.4.13.

5.2.4 CTSMSI update procedure

The purpose of the CTSMSI update procedure is to provide identity confidentiality, i.e. to protect a user against being identified and located by an intruder (see GSM 03.20 Annex E).

The CTSMSI update procedure is always initiated by the CTS-FP on the radio interface.

The structure of the CTSMSI is specified in GSM 03.03. The CTSMSI has significance only for a specific CTS-FP.

The CTSMSI update procedure shall be performed after each access to the fixed part done by a mobile station

5.2.4.1 CTSMSI update initiation by the fixed part

The fixed part initiates the CTSMSI update procedure by sending a CTSMSI UPDATE COMMAND message to the CTS-MS and starts the timer TC3202.

The CTSMSI UPDATE COMMAND message specifies the new CTSMSI of the mobile station. The CTSMSI UPDATE COMMAND message shall be sent to the mobile station using a CTS-RR connection in ciphering mode (see GSM 03.20 Annex E).

5.2.4.2 CTSMSI update response by the mobile station

Upon receipt of the CTSMSI UPDATE COMMAND message the mobile station stores the new CTSMSI related to the corresponding fixed part in the SIM.

The mobile station sends a CTSMSI UPDATE COMPLETE message to the fixed part.

5.2.4.3 CTSMSI update completion in the fixed part

Upon receipt of the CTSMSI UPDATE COMPLETE message the fixed part stops the timer TC3202 and considers the new CTSMSI as valid.

5.2.4.4 Abnormal cases

Mobile station side:

Any CTS-RR connection failure after storage of the new CTSMSI value in the SIM does not have any impact on this storage.

Fixed part side

  1. CTS-RR connection failure:

If the CTS-RR connection is lost before the CTSMSI UPDATE COMPLETE message is received, all MM connections (if any) shall be released and both the old and the new CTSMSIs should be maintained in order to be able to recover from unsuccessful CTSMSI update.

  1. No response from the mobile station (expiry of timer TC3202):

The fixed part should maintain the old and the new CTSMSI in order to be able to recover from unsuccessful CTSMSI update.

5.3 CTS-MM specific procedures

5.3.1 CTS enrolment procedure

The purpose of the CTS enrolment procedure is:

– to define an association between a certain CTS-MS and a certain CTS-FP;

– to ensure the rights of the CTS-MS to use CTS services on this CTS-FP.

The CTS enrolment procedure is always initiated by the mobile station.

The user shall provide the CTS-PIN (see 03.20 Annex E) on the mobile station and shall take a physical action on the CTS-FP.

5.3.1.1 CTS enrolment initiation by the mobile station

The mobile station initiates the CTS enrolment procedure by sending a CTS ENROLMENT REQUEST message to the CTS-FP. The mobile station shall start the timer TC3254.

5.3.1.2 CTS enrolment completion by the fixed part

After mutual authentication, the fixed part shall request the mobile station identity to perform the verification of its rights to use CTS services on this fixed part. This verification is done either locally by the fixed part or by the CTS operator via the Cf interface (see GSM 03.20 Annex E). Upon these rights are verified, the CTS-FP shall enrol the CTS-MS and shall send a CTS ENROLMENT ACCEPT to the mobile station. The CTS ENROLMENT ACCEPT contains the identity of the fixed part (IFPSI or IFPEI), and the first CTSMSI value of the mobile station.

5.3.1.3 CTS enrolment completion by the mobile station

On reception of a CTS ENROLMENT ACCEPT, the CTS-MS shall stop the timer TC3254 and enters in CTS MM IDLE state.

5.3.1.4 Unsuccessful enrolment

If the mobile station has not the rights to be enrolled, the fixed part shall send a CTS ENROLMENT REJECT message to the mobile station. This message contains a reject cause and the identity of the fixed part.

On reception of a CTS ENROLMENT REJECT, the CTS-MS shall stop the timer TC3254 and enters in ENROLMENT REJECTED state.

5.3.1.5 Abnormal cases

(a) CTS-RR connection failure:

If the CTS-RR connection is lost before the CTS ENROLMENT ACCEPT message is received, the enrolment procedure has failed. A new enrolment attempt may be done by the user.

(b) No response from the fixed part (expiry of timer TC3254):

The mobile station should warn the mobile station user. A new enrolment attempt may be done by the user.

5.3.2 CTS attach procedure

The purpose of the CTS attach procedure is to attach the corresponding mobile station to a specific fixed part. Before performing the attach procedure, the corresponding mobile station has to be enrolled on this fixed part.

The attach procedure is always initiated by the mobile station.

5.3.2.1 CTS attach initiation by the mobile station

The mobile station initiates the CTS attach procedure by sending a CTS ATTACH REQUEST message to the CTS-FP and starts the timer TC3250.

The CTS ATTACH REQUEST message specifies the CTSMSI, and the classmark of the mobile station.

5.3.2.2 CTS attach completion by the fixed part

If the mobile identity corresponds to an enrolled mobile station on the CTS-FP, the fixed part shall send a CTS ATTACH ACCEPT to the mobile station.

If the mobile station sends its CTSMSI as identity and it does not correspond to any enrolled mobile station, the fixed part could use the identity request procedure (see GSM 04.08) to obtain the IMSI of the mobile station. If the IMSI corresponds to an enrolled mobile station, the fixed part shall complete the attachment as described before.

The fixed part shall send a CTS ATTACH REJECT with its identity (IFPSI or IFPEI) when the mobile shall not be attached:

– the mobile station is not enrolled on this fixed part: the reject cause shall be #4 (IMSI unknown in VLR);

– the fixed part is not able to complete all the operations it has to perform at mobile station attachment (e.g. FMC registration).

5.3.2.3 CTS attach completion by the mobile station

On reception of a CTS ATTACH ACCEPT, the mobile station shall stop the timer TC3250 and shall start the timer TC3252.

The CTS-MS enters in CTS MM IDLE state.

5.3.2.4 CTS attach rejection treatment by the mobile station

On reception of a CTS ATTACH REJECT, the mobile station shall verify if the CTS-FP identity (IFPSI or IFPEI) is the expected one and shall stop the timer TC3250.

If the fixed part identity is the expected one and the reject cause is equal to #4 (IMSI unknown in VLR), the mobile station shall not re-attempt to attach automatically to the same fixed part. The CTS-MS should inform the user that it is no more enrolled on this fixed part.

If the fixed part identity is the expected one and the reject cause is different of #4, the mobile station shall not attempt to attach to any fixed part having the same FPBI before expiration of the timer TC3257.

If the fixed part identity is not the expected one, the mobile station shall start the timer TC3256. The mobile shall not attempt to attach to any fixed part having the same FPBI before expiration of the timer TC3256.
This does not forbid attachment attempts to fixed parts having an other FPBI.

5.3.2.5 Abnormal cases

(a) CTS-RR connection failure:

Upon a detection of a CTS-RR connection failure before the CTS ATTACH ACCEPT is received, the mobile station shall abort the ongoing attach procedure and shall stop the timer TC3250.

(b) No response from the fixed part (expiry of TC3250 timer):

The mobile station shall start the timer TC3251. The mobile station shall not re-attempt to attach again to the same fixed part before expiry of timer TC3251.

5.3.3 CTS re-attach procedure

The purpose of the CTS re-attach procedure is to inform the presence of a mobile station to the fixed part on which it is attached.

The CTS re-attach procedure is always started by the mobile station.

This procedure is started at expiry of the timer TC3252.

5.3.3.1 CTS re-attach initiation by the mobile station

The mobile station initiates the CTS re-attach procedure by sending a CTS ATTACH REQUEST message with an indication of re-attachment to the CTS‑FP and starts the timer TC3255.

5.3.3.2 CTS re-attach completion by the fixed part

On reception of a CTS ATTACH REQUEST message with an indication of re-attachment, the fixed part shall respond with a CTS ATTACH ACCEPT and shall start again the CTS periodic attach update procedure (see 5.3.4).

5.3.3.3 Abnormal cases

(a) RR connection failure:

Upon a detection of a RR connection failure before the CTS ATTACH ACCEPT is received, the mobile station shall consider to be detached from the fixed part.

(b) RR not available:

If no radio resource is currently available on the fixed part (STATUS field set to busy in the BCH-SB), the timer TC3252 shall be started again with its initial value.

(c) Expiry of timer TC3255:

The mobile station shall be considered to be detached of the corresponding fixed part.

5.3.4 CTS periodic attach update procedure

The purpose of the CTS periodic attach update procedure is to verify the presence of the attached mobile stations.

The CTS periodic attach update procedure is started by the fixed part when it enters the MM IDLE state.

5.3.4.1 CTS periodic attach update procedure behaviour in the fixed part

At the begin of this procedure, the timer TC3201 is started.

At expiry of TC3201, the MM sublayer shall trigger the RR sublayer to launch the alive check procedure (see 4.2.2.3) with the CTSMSI corresponding to the mobile.

The fixed part can trigger up to NC320 times the alive check procedure using the same CTSMSI. At the next expiry of TC3201, the fixed part shall launch the CTSMSI update procedure instead of the alive check.

5.3.4.2 Abnormal cases

After alive check triggering done by MM, the following abnormal cases may occur:

(a) RR not available

The fixed part shall start again the timer TC3201 with its initial value.

(b) No response from the mobile station

The fixed part shall considered that the mobile station is detached.