5.1 Overview

24.0083GPPCore network protocolsMobile radio interface Layer 3 specificationRelease 18Stage 3TS

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

5.1.1 General

This subclause describes the call control (CC) protocol, which is one of the protocols of the Connection Management (CM) sublayer (see 3GPP TS 24.007 [20]).

Every mobile station must support the call control protocol. If a mobile station does not support any bearer capability at all then it shall respond to a SETUP message with a RELEASE COMPLETE message as specified in subclause 5.2.2.2.

In Iu mode only, integrity protected signalling (see subclause 4.1.1.1.1 of the present document and in general, see 3GPP TS 33.102 [5a]) is mandatory. In Iu mode only, all protocols shall use integrity protected signalling. Integrity protection of all CC signalling messages is the responsibility of lower layers. It is the network which activates integrity protection. This is done using the security mode control procedure (3GPP TS 25.331 [23c] and 3GPP TS 44.118 [111]).

In the call control protocol, more than one CC entity are defined. Each CC entity is independent from each other and shall communicate with the correspondent peer entity using its own MM connection. Different CC entities use different transaction identifiers.

With a few exceptions the present document describes the call control protocol only with regard to two peer entities. The call control entities are described as communicating finite state machines which exchange messages across the radio interface and communicate internally with other protocol (sub)layers. This description is only normative as far as the consequential externally observable behaviour is concerned.

Certain sequences of actions of the two peer entities compose "elementary procedures" which are used as a basis for the description in this subclause. These elementary procedures may be grouped into the following classes:

– call establishment procedures;

– call clearing procedures;

– call information phase procedures;

– miscellaneous procedures.

The terms "mobile originating" or "mobile originated" (MO) are used to describe a call initiated by the mobile station. The terms "mobile terminating" or "mobile terminated" (MT) are used to describe a call initiated by the network.

Figure 5.1a/3GPP TS 24.008 gives an overview of the main states and transitions on the mobile station side.

The MS side extension figure 5.1a.1/3GPP TS 24.008 shows how for the Network Initiated MO call the MS reaches state U1.0 from state U0 $(CCBS)$.

Figure 5.1a.2/3GPP TS 24.008 illustrates the additional state transitions possible in the MS due to SRVCC handovers from PS to CS or 5G-SRVCC handover from NG-RAN to UTRAN.

Figure 5.1a.3/3GPP TS 24.008 illustrates the additional state transitions possible in the MS due to SRVCC handovers from CS to PS.

Figure 5.1b/3GPP TS 24.008 gives an overview of the main states and transitions on the network side.

The Network side extension figure 5.1b.1/3GPP TS 24.008 shows for Network Initiated MO Calls the Network reaches state N1.0 from state N0 $(CCBS)$.Figure 5.1b.2/3GPP TS 24.008 illustrates the additional state transitions possible in the network due to SRVCC handovers from PS to CS or 5G-SRVCC handover from NG-RAN to UTRAN.

Figure 5.1b.3/3GPP TS 24.008 illustrates the additional state transitions possible in the network due to SRVCC handovers from CS to PS.

Figure 5.1a/3GPP TS 24.008: Overview call control protocol/MS side

Figure 5.1a.1/3GPP TS 24.008: Overview call control protocol/MS side, extension

Figure 5.1a.2/3GPP TS 24.008: Overview call control protocol/MS side, extension for SRVCC from PS to CS or 5G-SRVCC handover from NG-RAN to UTRAN

Figure 5.1a.3/3GPP TS 24.008: Overview call control protocol/MS side, extension for SRVCC from CS to PS

Figure 5.1b/3GPP TS 24.008 Overview call control protocol/Network side

Figure 5.1b.1/3GPP TS 24.008 Overview call control protocol/Network side, extension

Figure 5.1b.2/3GPP TS 24.008: Overview call control protocol/Network side, extension for SRVCC from PS to CS or 5G-SRVCC handover from NG-RAN to UTRAN

Figure 5.1b.3/3GPP TS 24.008: Overview call control protocol/Network side, extension for SRVCC from CS to PS

5.1.2 Call Control States

5.1.2.1 Call states at the mobile station side of the interface

The states which may exist on the mobile station side of the radio interface are defined in this subclause.

NOTE: States U0.1, U0.2, U0.3, U0.4, U0.5, U0.6, U26, and U27 are 3GPP specific. All other states are ITU-T defined.

5.1.2.1.1 Null (State U0)

No call exists.

5.1.2.1.2 MM Connection pending (U0.1)

This state exists for a mobile originating call, when the mobile station requests the establishment of a MM connection.

5.1.2.1.2a CC prompt present (U0.2) $(CCBS)$

This state exists for a mobile originating call when the network has prompted the mobile station to establish a CC connection but the mobile station has not yet responded.

NOTE: This state is transient.

5.1.2.1.2b Wait for network information (U0.3) $(CCBS)$

This state exists for a mobile originating call when the mobile station has responded to the prompt from the network to establish a CC connection and the mobile station is waiting for further information from the network.

5.1.2.1.2c CC-Establishment present (U0.4) $(CCBS)$

This state exists for a mobile originating call when the mobile station has received a CC-establishment request but has not yet responded.

NOTE: This state is transient.

5.1.2.1.2d CC-Establishment confirmed (U0.5) $(CCBS)$

This state exists for a mobile originating call when the mobile station has sent the acknowledgement that the mobile station has received all the CC information that is needed.

5.1.2.1.2e Recall present (U0.6) $(CCBS)$

This state exists for a mobile originating call when the mobile station has received a recall request but has not yet responded.

NOTE: This state is transient.

5.1.2.1.3 Call initiated (U1)

This state exists for a mobile originating call, when the MS requests call establishment from the network.

5.1.2.1.4 Mobile originating call proceeding (U3)

This state exists for a mobile originating call when the mobile station has received acknowledgement that the network has received all call information necessary to effect call establishment.

5.1.2.1.5 Call delivered (U4)

This state exists for a mobile originating call, when the calling mobile station has received an indication that remote user alerting has been initiated.

5.1.2.1.6 Call present (U6)

This state exists for a mobile terminating call when the mobile station has received a call establishment request but has not yet responded.

5.1.2.1.7 Call received (U7)

This state exists for a mobile terminating call when the mobile station has indicated alerting but has not yet answered.

5.1.2.1.8 Connect Request (U8)

This state exists for a mobile terminating call, when the mobile station has answered the call and is waiting to be awarded the call.

5.1.2.1.9 Mobile terminating call confirmed (U9)

This state exists for a mobile terminating call when the mobile station has sent acknowledgement that the mobile station has received all call information necessary to effect call establishment.

5.1.2.1.10 Active (U10)

This state exists for a mobile terminating call when the MS has answered the call. This state exists for a mobile originating call when the MS has received an indication that the remote user has answered the call..

5.1.2.1.11 Disconnect request (U11)

This state exists when the mobile station has requested the network to clear the end-to-end connection (if any) and is waiting for a response.

5.1.2.1.12 Disconnect indication (U12)

This state exists when the mobile station has received an invitation to disconnect because the network has disconnected the end-to-end connection (if any).

5.1.2.1.13 Release request (U19)

This state exists when the MS has requested the network to release and is waiting for a response.

5.1.2.1.14 Mobile originating modify (U26)

This state exists when the mobile station has sent a request to the network for a new mode but has not yet received an answer.

5.1.2.1.15 Mobile terminating modify (U27)

This state exists when the mobile station has received a request from the network for a new mode and has not yet sent a response to this request.

5.1.2.2 Network call states

NOTE: States N0.1, N0.2, N0.3, N0.4, N0.5, N0.6, N26, N27, N28, N3a, N4,a, N7a, and N9a are 3GPP specific. All other states are ITU-T defined.

The call states that may exist on the network side of the radio interface are defined in this subclause.

5.1.2.2.1 Null (State N0)

No call exists.

5.1.2.2.2 MM connection pending (N0.1)

This state exists for a mobile terminating call, when the network requests the establishment of a MM connection.

5.1.2.2.2a CC connection pending (N0.2) $(CCBS)$

This state exists for a mobile originating call when the network has requested the mobile station to establish a CC connection.

5.1.2.2.2b Network answer pending (N0.3) $(CCBS)$

This state exists for a mobile originating call when the mobile station has established a CC connection upon the request of the network, but the network has not yet informed the mobile station of the reason for the network’s action.

5.1.2.2.2c CC-Establishment present (N0.4) $(CCBS)$

This state exists for a mobile originating call when the network has sent a CC establishment request but has not yet received a satisfactory response.

5.1.2.2.2d CC-Establishment confirmed (N0.5) $(CCBS)$

This state exists for a mobile originating call when the network has received acknowledgement that the mobile station has received all call information necessary to effect call establishment.

5.1.2.2.2e Recall present (N0.6) $(CCBS)$

This state exists for a mobile originating call when the network has sent a recall request but has not yet received a satisfactory response.

5.1.2.2.3 Call initiated (N1)

This state exists for a mobile originating call when the network has received a call establishment request but has not yet responded.

5.1.2.2.4 Mobile originating call proceeding (N3)

This state exists for a mobile originating call when the network has sent acknowledgement that the network has received all call information necessary to effect call establishment.

5.1.2.2.5 Call delivered (N4)

This state exists for a mobile originating call when the network has indicated that remote user alerting has been initiated.

5.1.2.2.6 Call present (N6)

This state exists for a mobile terminating call when the network has sent a call establishment request but has not yet received a satisfactory response.

5.1.2.2.7 Call received (N7)

This state exists for a mobile terminating call when the network has received an indication that the mobile station is alerting but has not yet received an answer.

5.1.2.2.8 Connect request (N8)

This state exists for a mobile terminating call when the network has received an answer but the network has not yet awarded the call.

5.1.2.2.9 Mobile terminating call confirmed (N9)

This state exists for a mobile terminating call when the network has received acknowledgement that the mobile station has received all call information necessary to effect call establishment.

5.1.2.2.10 Active (N10)

This state exists for a mobile terminating call when the network has awarded the call to the called mobile station. This state exists for a mobile originating call when the network has indicated that the remote user has answered the call.

5.1.2.2.11 Not used

5.1.2.2.12 Disconnect indication (N12)

This state exists when the network has disconnected the end- to-end connection (if any) and has sent an invitation to disconnect the mobile station to network connection.

5.1.2.2.13 Release request (N19)

This state exists when the network has requested the MS to release and is waiting for a response.

5.1.2.2.14 Mobile originating modify (N26)

This state exists when the network has received a request from the mobile station for a new mode but has not yet sent a response.

5.1.2.2.15 Mobile terminating modify (N27)

This state exists when the network has sent a request to the mobile station for a new mode but has not yet received an answer.

5.1.2.2.16 Connect Indication (N28)

This state exists for a mobile originating call when the network has indicated that the remote user has answered the call and the network is waiting for acknowledgement by the mobile station.