The present document includes references to features which are not part of the Phase 2+ Release 96 of the GSM Technical specifications. All subclauses which were changed as a result of these features contain a marker (see table below) relevant to the particular feature.
The following table lists all features that were introduced after GSM Release 96.
The present document specifies the procedures used at the radio interface core network protocols within the 3rd generation mobile telecommunications system and the digital cellular telecommunications system.
It specifies the procedures used at the radio interface (Reference Point Um or Uu, see TS 24.002 or TS 23.002) for Call Control (CC), Mobility Management (MM), and Session Management (SM).
When the notations for "further study" or "FS" or "FFS" are present in this TS they mean that the indicated text is not a normative portion of the present document.
These procedures are defined in terms of messages exchanged over the control channels of the radio interface. The control channels are described in TS 44.003 and TS 25.301.
The structured functions and procedures of this protocol and the relationship with other layers and entities are described in general terms in TS 24.007.
The present document specifies functions, procedures and information which apply to GERAN Iu mode. However, functionality related to GERAN Iu mode is neither maintained nor enhanced.
The procedures currently described in this TS are for the call control of circuit-switched connections, session management for GPRS services, mobility management and radio resource management for circuit-switched and GPRS services.
3GPP TS 24.010 contains functional procedures for support of supplementary services.
3GPP TS 24.011 contains functional procedures for support of point-to-point short message services.
3GPP TS 24.012  contains functional description of short message - cell broadcast.
3GPP TS 44.060 contains procedures for radio link control and medium access control (RLC/MAC) of packet data physical channels.
3GPP TS 44.071 contains functional descriptions and procedures for support of location services.
The procedures defined in the present document apply to the interface structures defined in TS 44.003 and TS 25.301. They use the functions and services provided by lower layers defined in TS 44.005 and TS 44.006 or TS 25.331, TS 25.322 and TS 25.321. TS 24.007 gives the general description of layer 3 (A/Gb mode) and Non Access Stratum (Iu mode and S1 mode) including procedures, messages format and error handling.
A building block method is used to describe the layer 3 procedures.
The basic building blocks are "elementary procedures" provided by the protocol control entities of the three sublayers, i.e. radio resource management, mobility management and connection management sublayer.
Complete layer 3 transactions consist of specific sequences of elementary procedures. The term "structured procedure" is used for these sequences.
The logical control channels are defined in TS 45.002. In the following those control channels are considered which carry signalling information or specific types of user packet information:
Broadcast Control CHannel (BCCH): downlink only, used to broadcast Cell specific information;
Synchronization CHannel (SCH): downlink only, used to broadcast synchronization and BSS identification information;
Paging CHannel (PCH): downlink only, used to send page requests to Mobile Stations (MSs);
Random Access CHannel (RACH): uplink only, used to request a Dedicated Control CHannel;
Access Grant CHannel (AGCH): downlink only, used to allocate a Dedicated Control CHannel;
Standalone Dedicated Control CHannel (SDCCH): bi-directional;
Fast Associated Control CHannel (FACCH): bi-directional, associated with a Traffic CHannel;
Slow Associated Control CHannel (SACCH): bi-directional, associated with a SDCCH or a Traffic CHannel;
Cell Broadcast CHannel (CBCH): downlink only used for general (not point to point) short message information;
Notification CHannel (NCH): downlink only, used to notify mobile stations of VBS (Voice Broadcast Service) calls or VGCS (Voice Group Call Service) calls.
Two service access points are defined on signalling layer 2 which are discriminated by their Service Access Point Identifiers (SAPI) (see TS 44.006):
SAPI 0: supports the transfer of signalling information including user-user information;
SAPI 3: supports the transfer of user short messages.
Layer 3 selects the service access point, the logical control channel and the mode of operation of layer 2 (acknowledged, unacknowledged or random access, see TS 44.005 and TS 44.006) as required for each individual message.
The elementary procedures can be combined to form structured procedures. Examples of such structured procedures are given in clause 7. This part of the present document is only provided for guidance to assist implementations.
Clause 8 specifies actions to be taken on various error conditions and also provides rules to ensure compatibility with future enhancements of the protocol.
Voice Group Call Service and Voice Broadcast Service are applicable in A/Gb mode only.
For mobile stations supporting the Voice Group Call Service or the Voice Broadcast Service, it is explicitly mentioned throughout the present document if a certain procedure is applicable only for such a service and, if necessary, how mobile stations not supporting such a service shall behave.
For VGCS and VBS, the following possible mobile station implementations exist:
support of listening to voice broadcast calls (VBS listening);
support of originating a voice broadcast call (VBS originating);
support of listening to voice group calls (VGCS listening);
support of talking in voice group calls (VGCS talking. This always includes the implementation for VGCS listening);
support of originating a voice group call (VGCS originating. This always includes the implementation for VGCS talking).
Apart from the explicitly mentioned combinations, all possible combinations are optional and supported by the present document.
The related terms are used in the present document, if information on these implementation options is required.
For mobile stations supporting the General Packet Radio Service (GPRS), it is explicitly mentioned throughout the technical specification if a certain procedure is applicable only for such a service and, if necessary, how mobile stations not supporting such a service shall behave.
A GPRS MS may operate in one of the following MS operation modes, see TS 23.060:
MS operation mode A;
MS operation mode B; or
MS operation mode C.
The MS operation mode depends on the services that the MS is attached to, i.e., only GPRS or both GPRS and non-GPRS services, and upon the MS's capabilities to operate GPRS and other GSM services simultaneously. Mobile stations that are capable to operate GPRS services are referred to as GPRS MSs.
It should be noted that it is possible that for a GPRS MS, the GMM procedures currently described in the ETS do not support combinations of VGCS, VBS and GPRS. The possible interactions are not studied yet.
An MS attached to packet switched domain may operate in one of the following MS operation modes, see TS 23.060:
CS/PS mode of operation; or
PS mode of operation.
The terms 'CS/PS mode of operation' and 'PS mode of operation' are not used in the present document with some exceptions. Instead the terms 'MS operation mode A' and 'MS operation mode C' are used.
In network operation mode I and II (see TS 23.060), an MS in CS/PS mode of operation shall use the same
procedures as for a GPRS MS operating in MS operation mode A, unless it is explicitly stated for A/Gb mode only or
Iu mode only.
In network operation mode I and II, an MS in PS mode of operation shall use the same procedures as for a GPRS MS operating in MS operation mode C, unless it is explicitly stated for A/Gb mode only or Iu mode only.
An MS configured for NAS signalling low priority (see TS 24.368, TS 31.102) indicates this by including the Device properties IE in the appropriate NAS message and setting the low priority indicator to "MS is configured to NAS signalling low priority" except for the following cases in which the MS shall set the low priority indicator to "MS is not configured for NAS signalling low priority":
the MS is performing an attach for emergency bearer services;
the MS has a PDN connection for emergency bearer services established and is performing mobility management procedures, or is establishing a PDN connection for emergency bearer services;
the MS configured for dual priority is requested by the upper layers to establish a PDN connection with the low priority indicator set to "MS is not configured for NAS signalling low priority";
the MS configured for dual priority is performing session management procedures related to the PDN connection established with low priority indicator set to "MS is not configured for NAS signalling low priority";
the MS configured for dual priority has a PDN connection established by setting the low priority indicator to "MS is not configured for NAS signalling low priority" and is performing mobility management procedures;
the MS is establishing or re-establishing an MM connection for an emergency call;
the MS is an MS configured to use AC11 - 15 in selected PLMN; or
the MS is responding to paging.
The network may use the NAS signalling low priority indication for NAS level mobility management congestion control on a per core network node basis and APN based congestion control.
If the NAS signalling low priority indication is provided in an ACTIVATE PDP CONTEXT REQUEST message, the SGSN stores the NAS signalling low priority indication within the default PDP context activated due to this request.
Independently of what is stated elsewhere in this and other 3GPP specifications, mobile station support for PBCCH and PCCCH is optional for A/Gb-mode of operation. The network shall never enable PBCCH and PCCCH. This makes use of network operation mode III obsolete.