7 Examples of structured procedures
23.1083GPPMobile radio interface layer 3 specification, core network protocolsRelease 17Stage 2TS
Clause 7 is informative.
7.1 General
Clause 7 contains examples of how the network may group together the elementary procedures (i.e. the procedures defined in clauses 3 to 5) in order to provide normal service.
The layer 3 signalling at the radio interface may be divided into so-called structured procedures which consist of specific combinations of elementary procedures. In subclause 7.3, selected examples of structured procedures are described. A structured procedure consists of (not necessarily all) components shown in figure 7.1. These components are characterized by the purpose of their use in structured procedures and their message flow in the following subclauses 7.1.1 to 7.1.7.
+- -+
│ Paging request │ RR connection
│ Immediate assignment │ establishment
+- -+
+- -+
│ Service request and │
│ Contention resolution │
+- -+
+- -+
│ Authentication │
+- -+
+- -+
│ Ciphering mode setting │
+- -+
+- -+
│ Transaction phase │
+- -+
+- -+
│ Channel release │ RR connection
+- -+ release
Figure 7.1/3GPP TS 23.108: Components of structured procedures
7.1.1 Paging request
The paging procedure is used to locate a mobile station to which a connection shall be established.
Upon receipt of a PAGING REQUEST message the addressed mobile station initiates the immediate assignment procedure.
Mobile Station Network
PAGING REQUEST
<——————-
Figure 7.2/3GPP TS 23.108: Paging request
7.1.2 Immediate assignment
The immediate assignment procedure is always initiated by the mobile station. It may be triggered by a paging request or by a mobile originating service request.
The mobile station sends a CHANNEL REQUEST message on the Random Access Channel. The network responds with an IMMEDIATE ASSIGNMENT message which causes the mobile station to seize the indicated dedicated channel.
Mobile Station Network
CHANNEL REQUEST
————————->
IMMEDIATE ASSIGNMENT
<————————
Figure 7.3/3GPP TS 23.108: Immediate assignment
7.1.3 Service request and contention resolution
The initial service request message (a PAGING RESPONSE, LOCATION UPDATING REQUEST, IMSI DETACH, CM SERVICE REQUEST, or CM RE-ESTABLISHMENT REQUEST message) is sent by the mobile station to the network piggy-backed in the L2 SABM frames establishing the main signalling link. Its purpose is:
– to provide non-confidential information relevant to the service requested for the RR and MM sublayer in the network;
– in particular to identify the user in the network without jeopardising the confidentiality of the user’s identity; this is achieved by using as mobile identity the TMSI, which was never before transmitted un-encrypted over the radio interface;
– to allow for contention resolution;
– optionally, in the CM SERVICE REQUEST message to inform the network of the priority level associated with the call.
Contention resolution provides a resolution process when more than one MS try to seize a channel allocated during the immediate assignment procedure (because they happened to use the same random reference at the same time during random access). This is achieved by the network including in a L2 UA frame the same information field as that one received in the L2 SABM frame to which the UA frame responds. By comparing the two information fields the MS can verify whether it was the originator of the L2 establishment, because the service request contains the mobile identity.
Mobile Station Network
SABM(service request)
————————->
UA(service request)
<————————
Figure 7.4/3GPP TS 23.108: Service request and contention resolution
7.1.4 Authentication
The purpose of authentication is to validate the identity provided by the mobile station . It is initiated by the network. The authentication procedure also provides the mobile station with information from which a new ciphering key can be derived. The network decides whether or not to use authentication. This may depend on the context.
Mobile Station Network
AUTHentication REQuest
<————————–
AUTHentication RESponse
—————————>
Figure 7.5/3GPP TS 23.108: Authentication
7.1.5 Ciphering mode setting
Ciphering mode setting is initiated by the network. Its purpose is to instruct the mobile station whether or not to use ciphering and which algorithm to use.
Where ciphering is used, this procedure synchronizes the start of ciphering at the mobile station and in the network.
Mobile Station Network
CIPHer MODE CoMmanD
<———————-
CIPHer MODe COMplete
———————–>
Figure 7.6/3GPP TS 23.108: Ciphering mode setting
7.1.6 Transaction phase
A variety of elementary procedures described in clauses 3 to 5 may be performed during the transaction phase. In this subclause, only the channel mode modify procedure is characterized.
7.1.6.1 Channel mode modify
The channel mode modify procedure may be used when a traffic channel has been assigned e.g.:
– during the in-call modification procedure in order that the channel mode of the TCH be changed to that one requested by call control;
– during call establishment with very early assignment in order that the channel mode of the TCH be changed from signalling only to the mode requested by call control;
– during the active phase of a data call in order that the speed of the data transmission be changed.
The channel mode modify procedure is initiated by the network sending a CHANNEL MODE MODIFY message and completed by the mobile station changing the mode of the TCH and sending back a CHANNEL MODE MODIFY ACKNOWLEDGE message.
Mobile Station Network
CHANNEL MODE MODIFY
<———————————–
CHANNEL MODE MODIFY ACKNOWLEDGE
————————————>
Figure 7.7/3GPP TS 23.108: Channel mode change
7.1.7 Channel release
Once the transaction phase has been completed, the channel is released by the channel release procedure. The data link layer is released explicitly as described in 3GPP TS 44.006 [19]. After the channel release is completed, the radio resources which were in use may be reallocated by the network.
Mobile Station Network
CHANNEL RELEASE
<———————-
Figure 7.8/3GPP TS 23.108 Channel release
7.2 Abnormal cases
Abnormal cases are not described in the examples of clause 7. They may arise from:
a) failure at a lower layer (e.g. loss of radio connection);
b) failure of an elementary procedure;
c) errors in an elementary procedure.
7.3 Selected examples
The following examples are considered:
– location updating;
– mobile originating call establishment;
a) without OACSU (early assignment);
b) with OACSU;
c) with very early assignment;
– mobile terminating call establishment;
a) without OACSU (early assignment);
b) with OACSU;
– call clearing:
a) network initiated;
b) mobile initiated;
– DTMF protocol control.
– handover:
a) between finely synchronized cells;
b) between non-synchronized cells;
c) handover failure, where reconnection of the old channel is possible;
– in-call modification;
– call re-establishment;
– network initiated MO call, e.g. CCBS Recall $(CCBS)$:
a) assignment before A party alerting;
b) assignment before B party alerting;
c) assignment after A and B party alerting.
7.3.1 Location updating
The location updating procedure is always initiated by the mobile station e.g. when it finds itself in a different location area from the one in which it was registered before. The cases where the procedure is triggered are described in clause 4.
The procedure is shown in figure 7.9/3GPP TS 23.108. The network may decide whether to allocate a new TMSI during location updating, and this option is reflected in this example.
The mobile station initiates immediate assignment, service request using the LOCATION UPDATING REQUEST message, and contention resolution.
The network requires authentication (this again is an option).
As the network intends to allocate a new TMSI, it should activate ciphering. The network includes the new TMSI in the LOCATION UPDATING ACCEPT message (it could also use the explicit TMSI reallocation procedure, see clause 4). The mobile station sends a TMSI REALLOCATION COMPLETE message to the network to acknowledge the receipt of the new TMSI. Upon receipt of the TMSI REALLOCATION COMPLETE message the network initiates the channel release if no further transactions are scheduled.
Mobile Station Network
+- -+
│ CHANNEL REQUEST │ RR connection
│ —————————————> │ establishment
│ │ (MO)
│ │
│ IMMEDIATE ASSIGNMENT │
│ <————————————– │
+- -+
+- -+
│ │
│ LOCATION UPDATING REQUEST │
│ —————————————-> │ Service request
│ │
│ │
│ │
│ │
+- -+
+- -+
│ AUTHENTICATION REQUEST │
│ <————————————— │ Authentication
│ │
│ AUTHENTICATION RESPONSE │
│ —————————————-> │
+- -+
+- -+
│ │
│ CIPHER MODE COMMAND │
│ <————————————— │ Ciphering mode
│ │ setting
│ CIPHER MODE COMPLETE │
│ —————————————–>│
+- -+
+- -+
│ LOCATION UPDATING ACCEPT │
│ <————————————— │
│ │
│ TMSI REALLOCATION COMPLETE │
│ —————————————> │
+- -+
+- -+
│ CHANNEL RELEASE │ RR connection
│ <————————————— │ release
│ │
+- -+
Figure 7.9/3GPP TS 23.108: Location updating: successful case
7.3.2 Mobile originating call establishment
The mobile station initiates immediate assignment, service request using the CM SERVICE REQUEST message, and contention resolution. The network may initiate authentication and may start the ciphering mode setting.
After sending the CIPHERING MODE COMPLETE message, the mobile station initiates call establishment by sending the SETUP message to the network. The network answers with a CALL PROCEEDING message.
a) Non-OACSU option (early assignment):
With this option the network allocates a traffic channel to the mobile station before it initiates call establishment in the fixed network.
If call queuing is applied, it may cause variable delay in the traffic channel assignment.
When user alerting has been initiated at the called side, an ALERTING message is sent to the mobile station. The network may optionally instruct the MS to attach the user connection at this stage of the call, by means of the progress indicator information element set to the value #1 or #8 (if the ringing tone will be sent by the remote end) in the ALERTING message. In that case, an alerting ringing tone has to be generated by the network.
NOTE: The speech codec is transparent for supervisory tones.
A CONNECT message and its acknowledgement CONNECT ACKNOWLEDGE complete the call establishment when the called party has answered.
The mobile originating call setup with early assignment is shown in figure 7.10a/3GPP TS 23.108.
b) OACSU option (late assignment):
The network determines when the traffic channel is to be assigned. The assignment may be performed at any time after call establishment has been initiated in the fixed network. In the following the case is considered where the network will only allocate a traffic channel after the called party has answered the call (late assignment).
As in a) an ALERTING message is sent to the mobile station when user alerting has been initiated at the called side. If the ringing tone is needed, it has to be generated locally at the mobile station as no traffic channel is allocated. When the called party has answered, the network will initiate the channel assignment procedure in order to allocate a traffic channel to the mobile station. If call queuing is applied, it may cause variable delay in the traffic channel assignment. Once the channel assignment has been completed the network will send a CONNECT message to the mobile station. The MS attaches then the user connection. The CONNECT ACKNOWLEDGE message will complete the call setup.
The mobile originating call setup with late assignment is shown in figure 7.10b/3GPP TS 23.108.
c) Very early assignment:
The network assigns the traffic channel at the earliest possible moment, i.e. in the immediate assignment procedure. The mode of the traffic channel is changed from signalling only to the mode necessary for the call by means of the channel mode change procedure. An appropriate moment for that change is after the network has sent the CALL PROCEEDING message, when the call is established towards the called user.
With this option, call queuing is never applied.
The further establishment of the call is as in a).
The mobile originating call setup with very early assignment is shown in figure 7.10c/3GPP TS 23.108.
ß
Mobile Station Network
+- -+
│ CHANNEL REQUEST │ RR connection
│ ————————-> │ establishment
│ IMMEDIATE ASSIGNMENT │ (MO)
│ <———————— │
+- -+
+- -+
│ CM SERVICE REQUEST │
│ ————————-> │ Service request
│ │
+- -+
+- -+
│ AUTHENTICATION REQUEST │ Authentication
│ <————————- │
│ AUTHENTICATION RESPONSE │
│ ————————–> │
+- -+
+- -+
│ CIPHER MODE COMMAND │
│ <————————- │ Ciphering
│ CIPHER MODE COMPLETE │ mode setting
│ ————————–> │
+- -+
+- -+
│ SETUP │
│ ————————–> │ Call initiation
│ CALL PROCEEDING │
│ <————————- │
+- -+
+- -+
│ ASSIGNMENT COMMAND │
│ <————————– │ Assignment of
│ ASSIGNMENT COMPLETE │ a traffic
│ ————————–> │ channel
+- -+
+- -+
│ ALERTING │
│ <————————– │ User alerting
+- -+
+- -+
│ CONNECT │
│ <————————– │ Call accepted
│ CONNECT ACKNOWLEDGE │
│ ————————–> │
+- -+
Figure 7.10a/3GPP TS 23.108: Mobile originating call establishment without OACSU (early assignment)
Mobile Station Network
+- -+
│ CHANNEL REQUEST │ RR connection
│ ————————-> │ establishment
│ IMMEDIATE ASSIGNMENT │ (MO)
│ <———————— │
+- -+
+- -+ Service indication
│ CM SERVICE REQUEST │
│ ————————-> │
│ │
│ │
+- -+
+- -+
│ AUTHENTICATION REQUEST │ Authentication
│ <————————- │
│ AUTHENTICATION RESPONSE │
│ ————————–> │
+- -+
+- -+
│ CIPHER MODE COMMAND │
│ <————————- │ Ciphering
│ CIPHER MODE COMPLETE │ mode setting
│ ————————–> │
+- -+
+- -+
│ SETUP │
│ ————————–> │ Call initiation
│ CALL PROCEEDING │
│ <————————- │
+- -+
+- -+
│ ALERTING │
│ <————————– │ User alerting
+- -+
+- -+
│ ASSIGNMENT COMMAND │
│ <————————- │ Assignment of
│ ASSIGNMENT COMPLETE │ a traffic
│ ————————–> │ channel
+- -+
+- -+
│ CONNECT │
│ <————————– │ Call accepted
│ CONNECT ACKNOWLEDGE │
│ ————————–> │
+- -+
Figure 7.10b/3GPP TS 23.108: Mobile originating call establishment with OACSU (late assignment)
Mobile Station Network
+- -+
│ CHANNEL REQUEST │ RR connection
│ ————————–> │ establishment
│ IMMEDIATE ASSIGNMENT(TCH) │ (MO)
│ <————————- │
+- -+
+- -+
│ CM SERVICE REQUEST │
│ ————————–> │ Service request
│ │
+- -+
+- -+
│ AUTHentication REQuest │ Authentication
│ <————————– │
│ AUTHENTICATION RESPONSE │
│ —————————> │
+- -+
+- -+
│ CIPHER MODE COMMAND │
│ <————————– │ Ciphering
│ CIPHer MODe COMplete │ mode setting
│ —————————> │
+- -+
+- -+
│ SETUP │
│ ————————–> │ Call initiation
│ CALL PROCeeding │
│ <————————– │
+- -+
+- -+
│ CHANNEL MODE MODIFY │
│ <————————— │ Transmission
│ CHANNEL MODE MODIFY ACKNOWLEDGE │ mode
│ —————————> │ change
+- -+
+- -+
│ ALERTING │
│ <—————————- │ User alerting
+- -+
+- -+
│ CONNect │
│ <————————— │ Call accepted
│ CONNect ACKnowledge │
│ —————————> │
+- -+
Figure 7.10c/3GPP TS 23.108: Mobile originating call establishment with very early assignment
7.3.3 Mobile terminating call establishment
Mobile terminating call establishment is initiated by the network sending a PAGING REQUEST message (see figure 7.11a/3GPP TS 23.108). Upon receiving this message the mobile station initiates the immediate assignment procedure and responds to the network by sending the PAGING RESPONSE message within a layer 2 SABM frame. The network returns a layer 2 UA frame containing the same information field as was sent in the SABM frame.
Authentication and ciphering are treated by the network in the same way as defined for the mobile originating call establishment (subclause 7.3.2). After ciphering has been started, the network sends a SETUP message to the mobile station. The capability of the mobile station (at that time) to accept the call is confirmed when the mobile station returns a CALL CONFIRMED message to the network.
a) Non-OACSU option (early assignment):
With this option the network initiates the assignment of a traffic channel upon receiving the CALL CONFIRMED message.
The signal IE is not included in the SETUP message, therefore user alerting is initiated only after a traffic channel has been allocated. An ALERTING message will be sent to the network.
When the called user answers, the mobile station sends a CONNECT message to the network. Upon receiving the CONNECT message the network completes the through connection of the communication path and sends a CONNECT ACK message to the mobile station.
b) OACSU option (late assignment):
In that option, the signalling IE is included in the SETUP message. Consequently, user alerting is initiated as soon as the MS has accepted the call.
The network determines when the traffic channel is to be assigned. The assignment may be performed at any time after user alerting has been initiated. In the following the case is considered where the network will only allocate a traffic channel to the mobile station after having received the CONNECT message sent from the mobile station (see figure 7.11b).
Upon receiving the ASSIGNMENT COMPLETE message from the mobile station, the network completes the through connection of the communication path and sends a CONNECT ACKNOWLEDGE message to the mobile station.
Mobile Station Network
+- -+
│ PAGING REQUEST │
│ <————————- │
│ CHANNEL REQUEST │ RR connection
│ ————————-> │ establishment
│ IMMEDIATE ASSIGNMENT │ (MT)
│ <———————— │
+- -+
+- -+
│ PAGING RESPONSE │
│ ————————-> │ Service request
+- -+
+- -+
│ AUTHENTICATION REQUEST │ Authentication
│ <————————- │
│ AUTHENTICATION RESPONSE │
│ ————————–> │
+- -+
+- -+
│ CIPHer MODe COMMAND │
│ <————————- │ Ciphering
│ CIPHER MODE COMPLETE │ mode setting
│ ————————–> │
+- -+
+- -+
│ SETUP │
│ <————————– │ Call initiation
│ CALL CONFIRMED │
│ ————————–> │
+- -+
+- -+
│ ASSIGNMENT COMMAND │
│ <————————– │ Assignment of
│ ASSIGNMENT COMPLETE │ a traffic
│ ————————–> │ channel
+- -+
+- -+
│ ALERTING │
│ ————————-> │ User alerting
+- -+ information
+- -+
│ CONNECT │
│ ————————–> │ Call accepted
│ CONNECT ACKNOWLEDGE │
│ <————————– │
+- -+
Figure 7.11a/3GPP TS 23.108: Mobile terminating: call establishment without OACSU (early assignment)
Mobile Station Network
+- -+
│ PAGING REQUEST │
│ <————————- │
│ CHANNEL REQUEST │ RR connection
│ ————————-> │ establishment
│ IMMEDIATE ASSIGNMENT │ (MT)
│ <———————— │
+- -+
+- -+
│ PAGING RESPONSE │
│ ————————-> │ Service request
+- -+
+- -+
│ AUTHENTICATION REQUEST │ Authentication
│ <————————- │
│ AUTHENTICATION RESPONSE │
│ ————————–> │
+- -+
+- -+
│ CIPHer MODe COMMAND │
│ <————————- │ Ciphering
│ CIPHER MODE COMPLETE │ mode setting
│ ————————–> │
+- -+
+- -+
│ SETUP │
│ <————————– │ Call initiation
│ CALL CONFIRMED │
│ ————————–> │
+- -+
+- -+
│ ALERTING │
│ ————————-> │ User alerting
+- -+ information
+- -+
│ CONNECT │
│ ————————-> │
+- -+
+- -+
│ ASSIGNMENT COMMAND │
│ <————————– │ Assignment of
│ ASSIGNMENT COMPLETE │ a traffic
│ ————————–> │ channel
+- -+
+- -+
│ CONNECT ACKNOWLEDGE │
│ <————————– │
+- -+
Figure 7.11b/3GPP TS 23.108: Mobile terminating: call establishment with OACSU (late assignment)
7.3.4 Call clearing
a) initiated by the network
The network initiates the clearing of a call by sending a DISCONNECT message to the mobile station (see also subclause 5.4.4).
Upon receiving the DISCONNECT message from the network the mobile station sends a RELEASE message to the network.
Upon receiving the RELEASE message from the mobile station, the network sends a RELEASE COMPLETE to the mobile station and, if the traffic channel is longer needed (e.g. last activity on the traffic channel), performs the channel release procedure as described in subclause 7.1.7.
Upon receiving the RELEASE COMPLETE message and if the cleared call was the last activity on the traffic channel, the mobile station waits for the release of the channel which is always initiated by the network.
When there exist multiple traffic channels in the Multicall environment the network does not release (i.e. retains) a traffic channel even if the cleared call was the last activity on the traffic channel under the condition as follows;
– a waiting call exists and the mobile station does not indicates to the network which bearer will be used for accepting the waiting call yet; and
– there exists no retained bearer for the waiting call.
When the mobile station receives SETUP message with Signal IE indicating Call Waiting, which means the network cannot provide any additional traffic channel, then:
– the MS shall not request a new SI value before releasing any other call (that leads to release any other bearers than the retained bearer);
– If the mobile station indicates the different SI value from the retained bearer after releasing any other calls (that leads to release any other bearer than the retained bearer), the network allocates a new TCH for the call, and releases the retained bearer.
Call clearing initiated by the network is shown in figure 7.12a.
b) initiated by the mobile station:
The mobile station initiates the clearing of a call by sending a DISCONNECT message to the network (see also subclause 5.4.3).
Upon receiving the DISCONNECT message from the mobile station the network sends a RELEASE message to the mobile station.
Upon receiving the RELEASE message from the network, the mobile station sends a RELEASE COMPLETE to the network, which, if the traffic channel is no longer needed (e.g. last activity on the traffic channel), performs the channel release procedure as described in subclause 7.1.6.
When there exist multiple traffic channels in the Multicall environment the network does not release (i.e. retains) a traffic channel even if the cleared call was the last activity on the traffic channel under the condition as follows:
– a waiting call exists and the mobile station does not indicates to the network which bearer will be used for accepting the waiting call yet; and
– there exists no retained bearer for the waiting call.
When the mobile station receives SETUP message with Signaling IE indicating Call Waiting, which means network cannot provide any additional traffic channel, then:
– The MS shall not request a new SI value before releasing any other call (that leads to release any other bearers than the retained bearer);
– If the mobile station indicates the different SI value from the retained bearer after releasing any other calls (that leads to release any other bearer than the retained bearer), the network allocates a new TCH for the call, and releases the retained bearer.
Call clearing initiated by the mobile station is shown in figure 7.12b.
Mobile Station Network
+- -+
│ DISCONNECT │
│ <———————— │ Call clearing
│ RELEASE │
│ ———————–> │
│ RELEASE COMPLETE │
│ <———————– │
+- -+
+- -+
│ CHANNEL RELEASE │ RR connection
│ <———————— │ release
+- -+
a) Call clearing initiated by the network
Figure 7.12a/3GPP TS 23.108: Call clearing
a)
Mobile Station Network
+- -+
│ DISCONNECT │
│ ————————> │ Call clearing
│ RELEASE │
│ <———————— │
│ RELEASE COMPLETE │
│ ———————–> │
+- -+
+- -+
│ CHANNEL RELEASE │ RR connection
│ <———————— │ release
+- -+
b) Call clearing initiated by the MS
Figure 7.12b/3GPP TS 23.108: Call clearing
7.3.5 DTMF protocol control
Figure 7.13 shows the structured procedure for DTMF protocol control.
Mobile Station Network
+- -+
│ │ active call
│ │
+- -+
.
+- -+
│ START DTMF │ DTMF generation
│ ——————————> │ started
│ START DTMF ACKNOWLEDGE │
│ <—————————– │
+- -+
+- -+
│ STOP DTMF │ DTMF generation stopped
│ ——————————-> │
│ STOP DTMF ACKNOWLEDGE │
│ <——————————- │
+- : -+
:
+- -+
│ │ active call
│ │
+- -+
Figure 7.13/3GPP TS 23.108: DTMF protocol control
7.3.6 Handover
Figure 7.14 shows the structured procedure for handover to a finely synchronized cell, successful case.
Figure 7.15 shows the structured procedure for handover to a non-synchronized cell, successful case.
Figure 7.16 shows the structured procedure for handover failure, and reconnection to the old traffic channel.
Mobile Station Network
+- -+
│ │
│ │ RR connection established
│ │
+- -+
+- -+ handover
│ HANDOVER COMMAND │ old channel,
│ <———————— │ old cell
-│- – – – – – – – – – – – – -│– – – – – – – – – –
│ HANDOVER ACCESS │ new channel,
│ ————————>│ new cell
│ │
│ HANDOVER ACCESS │
│ ————————>│
│ │
│ HANDOVER ACCESS │
│ ————————>│
│ │
│ HANDOVER ACCESS │
│ ————————>│
│ │
│ HANDOVER COMPLETE │
│ ————————>│
+- -+
Figure 7.14/3GPP TS 23.108: Handover to a finely synchronized cell, successful case
Mobile Station Network
+- -+
│ │
│ │ RR connection established
│ │
+- -+
+- -+ handover
│ HANDOVER COMMAND │ old channel,
│ <———————— │ old cell
-│- – – – – – – – – – – – – -│– – – – – – – – – –
│ HANDOVER ACCESS │ new channel,
│ ————————>│ new cell
│ . │
│ . │
│ . │
│ HANDOVER ACCESS │ new channel,
│ ————————>│ new cell
│ │
│ PHYSICAL INFORMATION │
│ <———————– │
│ HANDOVER COMPLETE │
│ ————————>│
+- -+
+- -+
│ . │
│ . │
│ . │
+- -+
Figure 7.15/3GPP TS 23.108: Handover to a non-synchronized cell, successful case
Mobile Station Network
+- -+
│ │
│ │ RR connection established
│ │
+- -+
+- -+ handover
│ HANDOVER COMMAND │ old channel,
│ <———————— │ old cell
-│- – – – – – – – – – – – – -│- – – – – – – –
│ T3124 expiry or │ new channel,
│ lower layer failure │ new cell
-│- – – – – – – – – – – – – -│- – – – – – – – –
│ HANDOVER FAILURE │ old channel,
│ ————————>│ old cell
+- -+
+- -+
│ . │
│ . │
│ . │
+- -+
Figure 7.16/3GPP TS 23.108: Handover failure, reconnection to the old traffic channel
7.3.7 In-call modification
Figure 7.17/3GPP TS 23.108 shows the structured procedure for in-call modification.
Mobile Station Network
+- -+
│ │ active call
│ │
+- -+
.
+- -+
│ MODIFY │
│ ——————————> │ in-call modification
│ │ e.g. from speech
│ │ to data
+- -+ channel
│ │ mode modify
│ │
+- -+
│ │
│ MODIFY COMPLETE │
│ <—————————– │
+- -+
+- -+
│ │ active call
│ │
+- -+
Figure 7.17/3GPP TS 23.108: In-call modification
7.3.8 Call re-establishment
Figure 7.18/3GPP TS 23.108 shows the structured procedure for call re-establishment.
Mobile Station Network
+- -+
│ │ active call
│ │
+- -+
————————————– radio link failure
+- -+
│ CHANNEL REQUEST │ RR connection
│ ————————-> │ establishment
│ IMMEDIATE ASSIGNMENT │ (MO)
│ <———————— │
+- -+
+- -+
│ CM RE-ESTABLISHMENT REQUEST │
│ ————————-> │ Service request
+- -+
+- -+
│ CIPHer MODe COMMAND │
│ <————————- │ Ciphering
│ CIPHER MODE COMPLETE │ mode setting
│ ————————-> │
+- -+
+- -+
│ ASSIGNMENT COMMAND │
│ <————————- │ assignment of
│ ASSIGNMENT COMPLETE │ a traffic channel
│ ————————-> │
+- -+
+- -+
│ │ active call
│ │
+- -+
Figure 7.18/3GPP TS 23.108: Call re-establishment
7.3.9 Network initiated mobile originating call $(CCBS)$
Network initiated mobile originating call establishment (which is used, for example, for CCBS Service) is initiated by the network sending a PAGING REQUEST message. Upon receiving this message the mobile station initiates the immediate assignment procedure and responds to the network by sending the PAGING RESPONSE message within a layer 2 SABM frame. The network returns a layer 2 UA frame containing the same information field as was sent in the SABM frame.
Authentication and ciphering are treated by the network in the same way as defined for the mobile originating call establishment (subclause 7.3.2). After ciphering has been started, the network sends a CM SERVICE PROMPT message, indicating that the CM protocol is to be started, to the mobile station. The basic capability of the mobile station to accept any form of recall service is confirmed when the mobile station returns a START CC message to the network.
a) assignment before A party alerting:
With this option the network allocates a traffic channel to the mobile station before the mobile station alerts its user.
The network responds to the START CC message with a CC-ESTABLISHMENT message. The MS answers with a CC-ESTABLISHMENT CONFIRMED message indicating the wanted channel characteristics. The network then initiates traffic channel assignment.
When the traffic channel has been assigned, the network indicates a pending recall by sending a RECALL message.
If the calling user accepts the recall, a SETUP message is sent to the network. The network responds with a CALL PROCEEDING message and initiates call establishment in the fixed network.
When user alerting has been initiated at the called side, an ALERTING message is sent to the mobile station. The network may optionally instruct the MS to attach the user connection at this stage of the call, by means of the progress indicator information element set to the value #1 or #8(if the ringing tone will be sent by the remote end) in the ALERTING message. In that case, an alerting ringing tone has to be generated by the network.
NOTE 1: The speech codec is transparent for supervisory tones.
A CONNECT message and its acknowledgement CONNECT ACKNOWLEDGE complete the call establishment when the called party has answered.
The network initiated mobile originating call establishment with assignment before A part alerting is shown in figure 7.19/3GPP TS 23.108.
b) assignment before B party alerting:
With this option the network allocates a traffic channel to the mobile station after the mobile station has alerted its user and after its user has accepted the recall but before the network initiates call establishment in the fixed network.
The network responds to the START CC message with a CC-ESTABLISHMENT message. The MS answers with a CC-ESTABLISHMENT CONFIRMED message indicating the wanted channel characteristics.
The network indicates a pending recall by sending a RECALL message. If the calling user accepts the recall, a SETUP message is sent to the network. The network responds with a CALL PROCEEDING message and initiates traffic channel assignment.
When the traffic channel has been assigned, the network initiates call establishment in the fixed network.
When user alerting has been initiated at the called side, an ALERTING message is sent to the mobile station. The network may optionally instruct the MS to attach the user connection at this stage of the call, by means of the progress indicator information element set to the value #1 or #8(if the ringing tone will be sent by the remote end) in the ALERTING message. In that case, an alerting ringing tone has to be generated by the network.
NOTE 2: The speech codec is transparent for supervisory tones.
A CONNECT message and its acknowledgement CONNECT ACKNOWLEDGE complete the call establishment when the called party has answered.
The network initiated mobile originating call establishment with assignment before B party alerting is shown in figure 7.20/3GPP TS 23.108.
c) assignment after A and B party alerting
With this option, the network determines when the traffic channel is to be assigned. The assignment may be performed at any time after call establishment has been initiated in the fixed network. In the following, the case is considered where the network will only allocate a traffic channel after the called party has answered the call (late assignment).
The network responds to the START CC message with a CC-ESTABLISHMENT. The MS answers with a CC-ESTABLISHMENT CONFIRMED message indicating the wanted channel characteristics.
The network indicates a pending recall by sending a RECALL message. If the calling user accepts the recall, a SETUP message is sent to the network. The network responds with a CALL PROCEEDING message and initiates call establishment in the fixed network.
As in a) and b) an ALERTING message is sent to the mobile station when user alerting has been initiated at the called side. If the ringing tone is needed, it has to be generated locally at the mobile station as no traffic channel is allocated. When the called party has answered, the network will initiate the channel assignment procedure in order to allocate a traffic channel to the mobile station. Once the channel assignment has been completed the network will send a CONNECT message to the mobile station. The MS attaches then the user connection. The CONNECT ACKNOWLEDGE message will complete the call setup.
The network initiated mobile originating call establishment with assignment after A and B party alerting is shown in figure 7.21/3GPP TS 23.108.
Mobile Station Network
+- -+
│ PAGING REQUEST │
│ <————————- │
│ CHANNEL REQUEST │ RR connection
│ ————————-> │ establishment
│ IMMEDIATE ASSIGNMENT │ (MT)
│ <————————- │
+- -+
+- -+
│ PAGING RESPONSE │
│ ————————-> │
+- -+
+- -+
│ AUTHENTICATION REQUEST │ Authentication
│ <————————- │
│ AUTHENTICATION RESPONSE │
│ ————————-> │
+- -+
+- -+
│ CIPHer MODe COMMAND │
│ <————————- │ Ciphering
│ CIPHER MODE COMPLETE │ mode setting
│ ————————-> │
+- -+
+- -+
│ CM SERVICE PROMPT │
│ <————————- │ Service Request
│ START CC │
│ ————————-> │
+- -+
+- -+
│ CC-ESTABLISHMENT │
│ <————————-_ │ Recall initiation
│ CC-ESTABLISHMENT CONFIRMED │
│ ————————-> │
+- -+
+- -+
│ ASSIGNMENT COMMAND │
│ <————————- │ Assignment of
│ ASSIGNMENT COMPLETE │ a traffic channel.
│ ————————-> │
+- -+
+- -+
│ RECALL │
│ <————————- │ User notified about recall
│ SETUP │
│ ————————-> │ Recall accepted and
│ CALL PROCEEDING │ call initiation
│ <————————- │
+- -+
+- -+
│ ALERTING │
│ <————————- │ Called user alerting
+- -+ information
+- -+
│ CONNECT │
│ <————————- │ Call accepted
│ CONNECT ACKNOWLEDGE │
│ ————————-> │
+- -+
ß
Figure 7.19/3GPP TS 23.108: Network initiated mobile originating call establishment with assignment before A party alerting
Mobile Station Network
+- -+
│ PAGING REQUEST │
│ <————————- │
│ CHANNEL REQUEST │ RR connection
│ ————————-> │ establishment
│ IMMEDIATE ASSIGNMENT │ (MT)
│ <————————- │
+- -+
+- -+
│ PAGING RESPONSE │
│ ————————-> │
+- -+
+- -+
│ AUTHENTICATION REQUEST │ Authentication
│ <————————- │
│ AUTHENTICATION RESPONSE │
│ ————————-> │
+- -+
+- -+
│ CIPHer MODe COMMAND │
│ <————————- │ Ciphering
│ CIPHER MODE COMPLETE │ mode setting
│ ————————-> │
+- -+
+- -+
│ CM SERVICE PROMPT │
│ <————————- │ Service Request
│ START CC │
│ ————————-> │
+- -+
+- -+
│ CC-ESTABLISHMENT │
│ <————————-_ │ Recall initiation
│ CC-ESTABLISHMENT CONFIRMED │
│ ————————-> │
+- -+
+- -+
│ RECALL │
│ <————————- │ User notified about recall
│ SETUP │
│ ————————-> │ Recall accepted and
│ CALL PROCEEDING │ call initiation
│ <————————- │
+- -+
+- -+
│ ASSIGNMENT COMMAND │
│ <————————- │ Assignment of
│ ASSIGNMENT COMPLETE │ a traffic
│ ————————-> │ channel
+- -+
+- -+
│ ALERTING │
│ <————————- │ Called user alerting
+- -+ information
+- -+
│ CONNECT │
│ <————————- │ Call accepted
│ CONNECT ACKNOWLEDGE │
│ ————————-> │
+- -+
ß
ß
Figure 7.20/3GPP TS 23.108: Network initiated mobile originating call establishment with assignment before B party alerting
Mobile Station Network
+- -+
│ PAGING REQUEST │
│ <————————- │
│ CHANNEL REQUEST │ RR connection
│ ————————-> │ establishment
│ IMMEDIATE ASSIGNMENT │ (MT)
│ <————————- │
+- -+
+- -+
│ PAGING RESPONSE │
│ ————————-> │
+- -+
+- -+
│ AUTHENTICATION REQUEST │ Authentication
│ <————————- │
│ AUTHENTICATION RESPONSE │
│ ————————-> │
+- -+
+- -+
│ CIPHer MODe COMMAND │
│ <————————- │ Ciphering
│ CIPHER MODE COMPLETE │ mode setting
│ ————————-> │
+- -+
+- -+
│ CM SERVICE PROMPT │
│ <————————- │ Service Request
│ START CC │
│ ————————-> │
+- -+
+- -+
│ CC-ESTABLISHMENT │
│ <————————-_ │ Recall initiation
│ CC-ESTABLISHMENT CONFIRMED │
│ ————————-> |
+- -+
+- -+
│ RECALL │
│ <————————- │ User notified about recall
│ SETUP │
│ ————————-> │ Recall accepted and
│ CALL PROCEEDING │ call initiation
│ <————————- │
+- -+
+- -+
│ ALERTING │
│ <————————- │ Called user alerting
+- -+ information
+- -+
│ ASSIGNMENT COMMAND │
│ <————————- │ Assignment of
│ ASSIGNMENT COMPLETE │ a traffic
│ ————————-> │ channel
+- -+
+- -+
│ CONNECT │
│ <————————- │ Call accepted
│ CONNECT ACKNOWLEDGE │
│ ————————-> │
+- -+
ß
Figure 7.21/3GPP TS 23.108: Network initiated mobile originating call establishment with assignment after A and B party alerting