7 GA-CSR elementary procedures

3GPP44.318Generic Access Network (GAN)Mobile GAN interface layer 3 specificationRelease 17TS

7.1 GA-CSR Connection establishment

The GA-CSR connection is a logical connection between the MS and the GANC. It is established when the upper layers in the MS request GA-CSR to enter dedicated mode. The MS initiates GA-CSR connection establishment by sending the GA-CSR REQUEST message to the network. When a successful response is received from the network, GA-CSR replies to the upper layer that it has entered dedicated mode. The upper layers have then the possibility to request transmission of messages to the network. These messages are sent to the network using GA-CSR UPLINK DIRECT TRANSFER messages as defined in sub-clause 7.2.1.

Note that in the case of a network-initiated CS session, the GA-CSR connection is implicitly established when the MS responds to the GA-CSR PAGING REQUEST message from the GANC with the GA-CSR PAGING RESPONSE message (see sub-clause 7.3).

Also, in the case of CS handover from GERAN or UTRAN to GAN A/Gb mode, the GA-CSR connection is implicitly established when the MS sends the GA-CSR HANDOVER ACCESS message to the GANC (see sub-clause 7.7).

Two service access points are defined which are discriminated by their Service Access Point Identifiers (SAPI):

SAPI 0: supports the transfer of signalling information including user-user information;

SAPI 3: supports the transfer of user short messages.

Figure 7.1.1 Initiation of GA-CSR connection, successful case

Figure 7.1.2 Initiation of GA-CSR connection, failure case

7.1.1 Initiation of GA-CSR connection establishment by the MS

The MS initiates the establishment of the GA-CSR connection when the upper layers request the GA-CSR to enter dedicated state.

Before initiation of GA-CSR connection establishment request, the MS shall check for access permission based on Access Control Class bits returned within GA-RC REGISTER ACCEPT message as defined in [12].

If it is allowed for the MS to access the network, it shall send a GA-CSR REQUEST message to the GANC on the established TCP connection and include the Establishment Cause IE and start timer TU3908

7.1.2 Reception of GA-CSR REQUEST by GANC

When GANC receives GA-CSR REQUEST message, the GANC may either accept or reject the GA-CSR connection establishment request.

7.1.2.1 GA-CSR connection establishment request accepted

If the GANC accepts the GA-CSR connection establishment request, it shall send the GA-CSR REQUEST ACCEPT message to the MS.

7.1.2.2 GA-CSR connection establishment request rejected

If the GANC rejects the GA-CSR connection establishment request, it shall send the GA-CSR REQUEST REJECT message to the MS.

7.1.3 GA-CSR connection establishment response handling in the MS

7.1.3.1 GA-CSR connection establishment request accepted

When the MS receives the GA-CSR REQUEST ACCEPT message, it shall:

– if timer TU3908 is active:

– stop timer TU3908,

– move into GA-CSR-DEDICATED state,

– indicate to upper layers that GA-CSR has entered dedicated state and

– send the initial GA-CSR UPLINK DIRECT TRANSFER message to the network

– if timer TU3908 is not active:

– ignore the GA-CSR REQUEST ACCEPT message and

– continue with any ongoing procedure as if the GA-CSR REQUEST ACCEPT message was not received

7.1.3.2 GA-CSR connection establishment request rejected

When the MS receives the GA-CSR REQUEST REJECT message, it shall:

– if timer TU3908 is active:

– stop timer TU3908,

– remain in GA-CSR-IDLE state and

– indicate to upper layers that GA-CSR was not able to enter dedicated state

– if timer TU3908 is not active:

– ignore the GA-CSR REQUEST REJECT message and

– continue with any ongoing procedure as if the GA-CSR REQUEST REJECT message was not received

7.1.4 Failure cases

7.1.4.1 Timer TU3908 expiry

If timer TU3908 expires in the MS, the MS shall remain in GA-CSR-IDLE state and indicate to upper layers that GA-CSR was not able to enter dedicated state

7.2 Upper layer message transmission

The GA-CSR UPLINK DIRECT TRANSFER message is used for the transfer of upper layer messages from the MS to the GANC while the GA-CSR DOWNLINK DIRECT TRANSFER message is used for the transfer of upper layer messages from the GANC to the MS. The first GA-CSR UPLINK DIRECT TRANSFER message received by the GANC triggers the establishment of the signalling connection to the CN for that MS.

7.2.1 Upper layer message forwarding by the MS

Figure 7.2.1.1 Uplink Direct Transfer, normal flow

The MS shall initiate the Uplink Direct Transfer procedure in GA-CSR-DEDICATED state when the upper layers request a transfer of a non-access stratum message.

The MS shall include the contents of the received upper layer message in the IE "L3 Message" and set the SAPI used in the IE "SAPI ID".

7.2.2 Reception of GA-CSR UPLINK DIRECT TRANSFER by GANC

When the GANC receives GA-CSR UPLINK DIRECT TRANSFER message from an MS in GA-CSR-DEDICATED state for which there is no signalling connection to the core network (i.e. this is the first GA-CSR UPLINK DIRECT TRANSFER after GA-CSR Connection establishment) the GANC should trigger the normal A-interface procedures towards the Core network to establish a signalling connection. GANC should transfer the contents of the IE "L3 Message" to the CN. The GANC should transfer the contents of the IE "SAPI ID" to the CN.

7.2.3 Upper layer message forwarding by the GANC

Figure 7.2.3.1 Downlink Direct Transfer, normal flow

The Downlink Direct Transfer procedure is initiated by the GANC, when the GANC receives a request from the upper layers to transfer a non-access stratum message, after the establishment of the GA-CSR connection to the MS.

On receiving a request from the upper layers the GANC should include the contents of the upper layer message in the IE "L3 Message".

7.2.4 Reception of GA-CSR DOWNLINK DIRECT TRANSFER by the MS

When the MS receives the GA-CSR DOWNLINK DIRECT TRANSFER message it shall forward the contents of the message to the upper layers.

7.2.4.1 Invalid GA-CSR DOWNLINK DIRECT TRANSFER

If the MS receives a GA-CSR DOWNLINK DIRECT TRANSFER message and MS is not in GA-CSR-DEDICATED state, the MS shall:

– ignore the contents of the GA-CSR DOWNLINK DIRECT TRANSFER message;

– transmit a GA-CSR STATUS message as follows:

– set the IE "RR Cause" to "Message type not compatible with protocol state"

– include the received message contents in the IE "PDU in error"

– continue with any ongoing procedure and act as if the GA-CSR DOWNLINK DIRECT TRANSFER message was not received.

7.3 Paging for CS domain

Figure 7.3.1 Paging, normal flow

7.3.1 Initiation of Paging

The GANC initiates this procedure when it receives a PAGING REQUEST message over the A-interface or a Paging CS message over the Gb-interface. The MS to be paged is identified by the identity received in the request from the CN. If the request includes the TMSI then the GANC should include the TMSI as the mobile identity else it should include the IMSI received in the request.

7.3.2 Reception of GA-CSR PAGING REQUEST by the MS

If the mobile identity in the GA-CSR PAGING REQUEST message matches any of the valid identities of the MS and the MS is in GA-CSR-IDLE state, the MS shall:

– if timer TU3908 is not active and access to the network is allowed;

– send a GA-CSR PAGING RESPONSE message to the GANC and

– enter GA-CSR-DEDICATED state.

– if timer TU3908 is active;

– discard the received GA-CSR PAGING REQUEST message.

7.3.3 Reception of GA-CSR PAGING RESPONSE by the GANC

On receiving the GA-CSR PAGING RESPONSE message the GANC should establish the signalling connection to the MSC and forward the contents of the GA-CSR PAGING RESPONSE message to the MSC.

7.3.4 Abnormal Cases

If the MS receives a GA-CSR PAGING REQUEST message and MS is in GA-CSR-DEDICATED state or GA-RC-REGISTERED state, the MS shall:

– ignore the GA-CSR PAGING REQUEST message

– continue with any ongoing procedure as if the GA-CSR PAGING REQUEST was not received.

If the MS receives a GA-CSR PAGING REQUEST and the mobile identity included in the message does not match any of the valid identities assigned to the MS, the MS shall:

– ignore the GA-CSR PAGING REQUEST message

– continue with any ongoing procedure as if the GA-CSR PAGING REQUEST message was not received.

7.4 Traffic Channel assignment

Figure 7.4.1 Channel Activation, successful case

7.4.1 Initiation of Channel Assignment

The GANC configures a traffic channel by transmitting the GA-CSR ACTIVATE CHANNEL message on receiving an Assignment Request from the MSC. The GA-CSR ACTIVATE CHANNEL message can be sent to the MS only in GA-CSR-DEDICATED state. The Channel Assignment procedure is always activated by the network.

7.4.2 Reception of GA-CSR ACTIVATE CHANNEL by MS

The MS shall act on the received GA-CSR ACTIVATE CHANNEL message when in GA-CSR-DEDICATED state as follows:

– Code and decode the CS payload samples according to the IE "Channel Mode";

– If the IE "Bandwidth-efficient Mode Indicator" is received, use the RFC 4867 [48] bandwidth-efficient payload format to code and decode the CS payload samples; otherwise, use the RFC 4867 [48] octet-aligned payload format.

– Use the value indicated by the IE "Sample Size" as the minimum sampling size for the coding and decoding of the CS payload samples, if the MS is not able to use the indicated value. If AMR is used with FEC by sending redundant frames, the sample size is defined as the size of the new speech sample in each RTP packet, not including any redundant speech sample.

– Configure the uplink CS payload stream to be transmitted to the UDP port identified by the IE "UDP Port";

– Configure the uplink CS payload stream to be transmitted to the IP address identified by the IE "IP address";

– If received, use the configuration included in the IE ‘Multi-rate Configuration’ for the CS payload stream;

– If received, use the configuration included in the IE "RTP Redundancy Configuration" for the CS payload stream. The redundancy policy is defined for each of the AMR modes to use. The level of redundancy can span from no redundancy to double redundancy. In the same active codec set, a lower codec mode shall not be associated with a lower redundancy level then a higher codec mode. For example, the highest mode in the set is used with no redundancy, the next lower with single redundancy and rest of the modes with double redundancy;

– If received, use the Payload Type included in the IE ‘Payload Type’ for the PT field in the RTP header for the CS downlink and uplink payload streams;

On successful configuration of the channel, the MS shall:

– Start timer TU3911.

– Transmit a GA-CSR ACTIVATE CHANNEL ACK message and include the UDP port number in the IE ‘UDP Port" for the downlink CS payload stream to be used by the GANC.

– Include the selected RTP sample size, to be used uplink and downlink, in the IE Sample Size.

– if the IE ‘RTCP UDP Port’ was received in the GA-CSR ACTIVATE CHANNEL message and the MS is capable of supporting RTCP, activate the uplink RTCP stream and include the IE ‘RTCP UDP Port’ for the downlink RTCP stream to be used by the GANC.

7.4.3 Reception of GA-CSR ACTIVATE CHANNEL ACK by GANC

If the call uses a TDM-based A-interface: The GANC shall configure itself for transmission of RTP packets to the MS to the indicated UDP port and RTCP packets to the MS, if the IE ‘RTCP UDP Port’ is included by the MS, and transmit a GA-CSR ACTIVATE CHANNEL COMPLETE message to the MS.

If the call uses a TDM-based A-interface: To enable downlink quality measurements in the MS, the GANC shall send at least one RTP frame each 480 ms. During periods of discontinuous transmission (DTX), each RTP frame transmitted by the GANC shall bear a format in the AMR payload Table of Contents that either (a) omits all NO_DATA indications and contains only the next AMR speech or SID frame that is available, or (b) includes a single NO_DATA frame should no AMR speech or SID frame become available for 480 ms. The RTP timestamp shall indicate the time of that speech or SID or NO_DATA frame. See Section A.1.2 of Annex A for examples of the RFC 4867 [48] octet-aligned payload format.

If the call uses a IP-based A-interface: The GANC sends a GA-CSR ACTIVATE CHANNEL COMPLETE message to the UE.

7.4.4 Reception of GA-CSR ACTIVATE CHANNEL COMPLETE by MS

The RTP channel is available for use by upper layers. To enable uplink quality measurements in the GANC, the MS shall send at least one RTP frame each 480 ms. During periods of discontinuous transmission (DTX), each RTP frame transmitted by the MS shall bear a format in the AMR payload Table of Contents that either (a) omits all NO_DATA indications and contains only the next AMR speech or SID frame that is available, or (b) includes a single NO_DATA frame should no AMR speech or SID frame become available for 480 ms. The RTP timestamp shall indicate the time of that speech or SID or NO_DATA frame. See Section A.1.2 of Annex A for examples of the RFC 4867 [48] octet-aligned payload format.

Stop timer TU3911.

7.4.5 Failure to establish channel by MS

If the MS fails to establish the channel indicated in the GA-CSR ACTIVATE CHANNEL message or timer TU3911 expires the MS shall:

– transmit a GA-CSR ACTIVATE CHANNEL FAILURE message;

– act as if the GA-CSR ACTIVATE CHANNEL message was not received.

7.5 Release of GA-CSR

7.5.1 Initiation of GA-CSR connection release by MS

If the MS needs to release the GA-CSR connection and signalling connection to the core network, it shall send the GA-CSR CLEAR REQUEST message to the GANC and start timer TU3909. The MS shall include the ‘RR Cause’ IE.

Figure 7.5.1.1 Initiation of GA-CSR connection release by MS

7.5.2 Reception of GA-CSR CLEAR REQUEST by GANC

The GANC will request core network to initiate the procedure to release of dedicated resources.

7.5.3 Initiation of GA-CSR connection release by GANC

Figure 7.5.3.1 Initiation of GA-CSR connection release by network

The GANC initiates this procedure to command the MS to release the GA-CSR and any traffic channel resources and instruct the MS to leave GA-CSR-DEDICATED state.

The GA-CSR RELEASE message will include an RR cause indication as follows:

#0: normal release, e.g. at the end of a call.

#1: unspecified abnormal release.

#65: if e.g. a handover procedure is stopped because the call has been cleared.

7.5.4 Reception of GA-CSR RELEASE by MS

When the MS receives the GA-CSR RELEASE message, it shall:

– transmit a GA-CSR RELEASE COMPLETE message to the GANC and release all GA-CSR and any traffic channel resources,

– stop timer TU3909 (if running), and

– enter GA-CSR-IDLE state.

A mobile station not supporting "GPRS" shall consider the IE "GPRS Resumption" as unknown in the GA-CSR RELEASE message and perform the GA-CSR Release procedure as normal.

For a MS supporting the "GPRS" option:

– if the GA-CSR RELEASE message includes the IE "GPRS Resumption":

– if the GPRS Resumption information element indicates that the network has resumed GPRS services, the GA-CSR sub-layer of the mobile station shall indicate a GA-CSR GPRS resumption complete to the MM sub-layer.

– if the GPRS Resumption information element indicates that the network has not successfully resumed GPRS services, the GA-CSR sub-layer of the mobile station shall indicate a GPRS resumption failure to the MM sub-layer.

– if the mobile station has performed the GPRS suspension procedure (sub-clause 8.10) and the GPRS Resumption information element is not included in the message, the GA-CSR sub-layer of the mobile station shall indicate a GPRS resumption failure to the MM sub-layer.

– if the mobile station has not performed the GPRS suspension procedure and the GPRS Resumption information element is not included in the message, the mobile station shall perform the channel release procedure as normal

7.5.5 Failure cases

7.5.5.1 Timer TU3909 expiry

If timer TU3909 expires in the MS, the MS shall release all GA-CSR and any traffic channel resources and enter GA-CSR-IDLE state.

7.6 Classmark Indication

7.6.1 Initiation of classmark interrogation by GANC

Figure 7.6.1.1 Classmark change

The GANC initiates the classmark interrogation procedure by transmitting the GA-CSR CLASSMARK ENQUIRY message to the MS when it desires more information about the MS’s capabilities. The GA-CSR CLASSMARK ENQUIRY message can be sent to a MS only in GA-CSR-DEDICATED state.

7.6.2 Transmission of classmark information by MS

On receipt of the GA-CSR CLASSMARK ENQUIRY message or in case of "early classmark sending" procedure based on the system information indication received in GA-RC REGISTER ACCEPT message, the mobile station sends a GA-CSR CLASSMARK CHANGE message to the GANC.

The MS shall include the IE "Mobile Classmark 2" in the GA-CSR CLASSMARK CHANGE message. It may also contain a IE "Mobile Classmark 3" depending on the MS capabilities.

In addition a MS supporting UTRAN sends a GA-CSR UTRAN CLASSMARK CHANGE message.

The Classmark Enquiry Mask information element in the GA-CSR CLASSMARK ENQUIRY message indicates the type of request. If the Classmark Enquiry Mask information element is not included in the GA-CSR CLASSMARK ENQUIRY message, this indicates a request for GA-CSR CLASSMARK CHANGE message.

In the "early classmark sending" case the GA-CSR UTRAN CLASSMARK CHANGE message shall not be sent by the MS if prohibited by the 3G Early Classmark Sending Restriction received as system information in GA-RC REGISTER ACCEPT message.

The GA-CSR UTRAN CLASSMARK CHANGE and GA-CSR CLASSMARK CHANGE message shall only be sent by a MS in GA-CSR-DEDICATED state

When an GA-CSR CLASSMARK CHANGE message and an GA-CSR UTRAN CLASSMARK CHANGE message are to be sent, the GA-CSR CLASSMARK CHANGE message shall be sent first.

7.7 CS handover to GAN A/Gb mode

Figure 7.7.1: CS handover to GAN A/Gb mode, successful case 7.7.1 Initiation

The procedure is initiated when the source radio access technology (e.g. GERAN) orders the MS to make CS handover to GAN A/Gb mode.

The procedure is applicable in GA-RC-REGISTERED state provided the conditions described in Annex C.1: "(Source-RAT) Measurement Report for Handover and Cell Change Order to GAN A/Gb mode" are met.

The handover order in the source radio access technology mode is sent via the (RR) HANDOVER COMMAND message. If the ARFCN and BSIC parameters included in the Cell Description IE in the (RR) HANDOVER COMMAND message (specified in [12]) match those of the GAN cell, the MS shall:

– send a GA-CSR HANDOVER ACCESS message to the network including the complete (RR) HANDOVER COMMAND message in the Handover To GAN Command IE and enter GA-CSR-DEDICATED state;

NOTE: sending the complete (RR) HANDOVER COMMAND message in the Handover To GAN Command IE instead of the Handover Reference IE allows for more than 256 concurrent handover requests

– if non-signalling mode is indicated in Channel Mode IE, the MS shall:

– start timer TU3920;

– otherwise, the MS shall:

– immediately send a GA-CSR HANDOVER COMPLETE message to the network;

– switch to GAN A/Gb mode; i.e. attach the GA-CSR entity to the RR-SAP.

7.7.2 Reception of GA-CSR HANDOVER ACCESS by the GANC

If non-signalling mode is indicated in the Channel Mode IE, the GANC shall initiate traffic channel assignment as specified in sub-clause 7.4.

7.7.3 Successful completion of the CS handover to GAN A/Gb mode

If the traffic channel assignment was successfully completed within timer TU3920, the MS shall:

– stop timer TU3920;

– send a GA-CSR HANDOVER COMPLETE message to the network;

– switch to GAN A/Gb mode; i.e. attach the GA-CSR entity to the RR-SAP.

In addition the MS shall send upper layer messages for which LAPDm has not yet received acknowledgement from the network to the network using the GA-CSR entity.

7.7.4 Reception of GA-CSR HANDOVER COMPLETE by the GANC

The GANC should indicate handover detection and completion to CN.

7.7.5 MS fails to complete requested handover

If the traffic channel assignment procedure fails or the timer TU3920 expires before traffic channel assignment is completed, the MS shall:

– terminate the procedure including release of the associated GA-CSR resources;

– resume the connection in the source radio access technology used before the handover;

– indicate the failure to the source radio access technology.

7.8 CS handover from GAN A/Gb mode

Figure 7.8.1: Handover from GAN, successful case

Figure 7.8.2: Handover from GAN, failure case

7.8.1 Initiation

The purpose of this procedure is to transfer, upon request from the MS (and under the control of the GAN), a connection between MS and GAN to another radio access technology (e.g. GERAN).

The procedure is applicable in GA-CSR-DEDICATED state.

The procedure may be initiated by the MS based on:

– local measurements of GAN coverage signal quality;

– reception of a GA-CSR UPLINK QUALITY INDICATION message indicating poor uplink quality in the UL Quality Indication IE; If the UL Quality Indication IE indicates "Network problem" a handover out to GERAN or UTRAN should be attempted. In case the UL Quality Indication information element shows "Radio problem" or "Undetermined problem" a search for a new access point should be done before the handover out is initiated;

– reception of RTCP packets indicating poor uplink quality;

– excessive loss or delay in the received RTP packets

When the MS decides to trigger the handover from GAN A/Gb mode, it shall:

– send a GA-CSR HANDOVER INFORMATION message to the network including a list of candidate/ target cell identifiers ranked in order of preference which is the most recent list available from the other radio access technology (e.g. GSM RR) and including the received signal strength for each identified GERAN or UTRAN cell. The MS may include GERAN cells, UTRAN cells or both, as permitted by the Handover Reporting Control IE (see sub-clause 11.2.113). If no Handover Reporting Control IE was included in the most recently received GA-RC REGISTER ACCEPT message, there is no restriction on the cells that may be listed.

7.8.2 Reception of GA-CSR HANDOVER INFORMATION by the GANC

The GANC should signal the need for handover to the CN.

If the CN grants the handover request, GANC should send a GA-CSR HANDOVER COMMAND message to the MS.

The GA-CSR HANDOVER COMMAND message should only indicate a target cell which was reported by the MS in the GA-CSR HANDOVER INFORMATION message.

7.8.3 Reception of GA-CSR HANDOVER COMMAND by the MS

The MS shall:

– suspend all NAS layer signalling transmissions;

– start the connection establishment to the target radio access technology (e.g. GERAN) by using the contents of the Handover From GAN Command IE. This message carries information about the candidate/ target cell identifier and radio parameters relevant for the target radio access technology;

A MS that is simultaneously operating in GPRS and CS modes over GAN shall follow the procedure as outlined in 3GPP TS 43.055 when it switches to target cell.

NOTE: The requirements concerning the establishment of the radio connection towards the target radio access technology (e.g. GERAN) and the signalling procedure are outside of the scope of this specification.

7.8.4 Successful completion of the CS handover from GAN A/Gb mode

Upon successfully completing the CS handover from GAN A/Gb mode, the GANC should:

– release all radio resources associated with the GAN connection.

Upon successfully completing the CS handover, the MS shall:

– switch to target radio access technology (e.g. GERAN) mode i.e. detach the GA-RR entity from the RR-SAP;

– enter GA-RC-REGISTERED state.

NOTE: The release of the GAN radio resources is initiated from the target RAT. The MS may deregister from the GANC (as defined in sub-clause 6.4) after successfully completing the handover. If the MS chooses to deregister from the GANC, it may do so either immediately after successfully completing the handover or after sending the GA-CSR RELEASE COMPLETE message to the GANC in response to the GA-CSR RELEASE message from the GANC.

7.8.5 MS fails to complete requested handover

If the MS does not succeed in establishing a connection to the target radio access technology, the MS shall:

– revert back to the GAN configuration;

– return a GA-CSR HANDOVER FAILURE message and resume normal operation as if the GA-CSR HANDOVER COMMAND message has not been received. The cause shall be set as specified in 3GPP TS 44.018.

7.8.6 Reception of GA-CSR HANDOVER FAILURE by the GANC

The GANC may initiate the release of resources in the target radio access technology.

7.8.7 Abnormal Cases

If the GA-CSR HANDOVER COMMAND message instructs the MS:

– to perform a non-supported scenario, or

– to use a non-supported configuration,

the MS shall return a GA-CSR HANDOVER FAILURE message with cause as defined in 3GPP TS 44.018 and resume normal operation as if the GA-CSR HANDOVER COMMAND message has not been received.

7.9 Ciphering configuration procedure

The ciphering configuration procedure is used by the network to set the ciphering mode, i.e. whether or not the transmission is ciphered, and if so which algorithm to use. This information is not used when the GA-CSR-layer is the serving entity in the MS, but shall be stored in the MS for possible future use after a handover from GAN during the same upper layer transaction (i.e. RR-layer becomes the serving entity during this upper layer transaction).

This procedure applies only for a MS in GA-CSR-DEDICATED state.

The procedure shall only be used to change from "not ciphered" mode to "ciphered" mode, or vice-versa, or to pass a GA-CSR 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 network.

Figure 7.9.1 Ciphering configuration

7.9.1 Ciphering configuration initiation

The network initiates the ciphering mode setting procedure by sending a GA-CSR CIPHERING MODE COMMAND message to the mobile station, indicating whether ciphering shall be used or not, and if yes which algorithm to use.

Additionally, the network may, by the use of the cipher response information element, request the mobile station to include its IMEISV in the GA-CSR CIPHERING MODE COMPLETE message.

7.9.2 Ciphering configuration completion

Whenever the mobile station receives a valid GA-CSR CIPHERING MODE COMMAND message, it shall, if a SIM is present and considered valid and the ciphering key sequence number stored on the SIM indicates that a ciphering key is available, save information about the ciphering key to use if the MS is later performing Handover from GAN. A valid GA-CSR 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 GA-CSR CIPHERING MODE COMMAND messages shall be regarded as erroneous, and a GA-CSR STATUS message with cause "Protocol error unspecified" shall be returned, and no further action taken.

The MS shall also calculate a MAC (Message Authentication Code). The MAC shall be calculated over the following data:

RAND | IMSI

using "HMAC-SHA1-96" algorithm, as specified in [24] with Kc as authentication key.

In the formulas above, the "|" character denotes concatenation. RAND is the 16-octet random number received from the GANC in the GA-CSR CIPHERING MODE COMMAND message. IMSI is the MS IMSI, in the same format as defined for the Mobile Identity IE as defined in [8] i.e. as a variable-length sequence of digits in BCD format (e.g. the IMSI "123456789098765" is encoded as the following octets (in hexadecimal): "21 43 65 87 09 89 67 F5"). Network byte order is used.

The Kc key is the Kc that has been derived during the last authentication. The length of the MAC is 12 octets.

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

7.10 Channel mode modify procedure

In dedicated mode, the GANC can request a modification of the channel mode, multi-rate configuration, RTP redundancy configuration, sample size, GANC IP address, GANC RTP UDP port and GANC RTCP UDP port used for an active traffic channel.

The channel mode modify procedure allows the network to request the mobile station to modify configuration used for an active channel. The channel mode covers the coding, decoding and transcoding mode as well as the redundancy policy used on the active channel.

This procedure is always initiated by the network.

Figure 7.10.1 Channel mode modify

7.10.1 Normal channel mode modify procedure

7.10.1.1 Initiation of the channel mode modify procedure

The network initiates the procedure by sending a GA-CSR CHANNEL MODE MODIFY message to the mobile station.

7.10.1.2 Completion of channel mode modify procedure

When the MS has received the GA-CSR CHANNEL MODE MODIFY message, the mobile station modifies the configuration, sets the mode and/or the RTP redundancy configuration for the active channel and then replies by a GA-CSR CHANNEL MODE MODIFY ACKNOWLEDGE message indicating the ordered channel mode.

This applies whether the mode and/or redundancy policy commanded by the GA-CSR CHANNEL MODE MODIFY message is different from the one used by the mobile station or whether it is already in use.

When the MS has sent the GA-CSR CHANNEL MODE MODIFY ACKNOWLEDGE message, it shall start transmit RTP packets with the new size. Until RTP packets with the new sample size have been received, the MS should handle the reception of RTP packets with the old sample size. The MS shall also use changed configurations for all other parameters (channel mode, multi-rate configuration, RTP redundancy configuration, etc.) in uplink RTP frames immediately after sending GA-CSR CHANNEL MODE MODIFY ACKNOWLEDGE message. In the downlink direction, MS shall be able to receive RTP packets with the old parameters, until the first RTP packet using the new parameters is received.

The GANC shall only start using the new configuration in downlink RTP frames as of receiving GA-CSR CHANNEL MODE MODIFY ACKNOWLEDGE message. In the uplink direction, the GANC shall be able to receive RTP packets with the old parameters, until the first RTP packet using the new parameters is received.

7.10.1.3 Abnormal cases

If the GA-CSR CHANNEL MODE MODIFY message includes IE "RTP Redundancy Configuration" and MS has indicated that it does not support RTP Redundancy through the GAN Classmark, it shall ignore the IE "RTP Redundancy Configuration".

If the mobile station does not support the indicated channel mode or sample size modifications, it shall retain the old mode and return the used configuration in the GA-CSR CHANNEL MODE MODIFY ACKNOWLEDGE message.