Five models are defined for Layer 3, one model for non-GPRS services, one for GPRS services supporting Class C MSs only, one model for GPRS-services supporting Class A and Class B MSs, one model for EPS services and one model for 5GS services over either 3GPP access or over non-3GPP access. (The third model is a combination of the first two models listed). In the present document GPRS services and EPS services will be used as synonyms.
The layer 3 for non-GPRS services provides the functions necessary:
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for Radio Resource (RR) management;
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for Mobility Management (MM); and
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for the Connection Management (CM) functions, i.e. functions for the control, provision, and support of services offered by the network; among which there are, e.g.:
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the functions to establish, maintain and terminate circuit-switched connections across a GSM PLMN and other networks to which the GSM PLMN is connected;
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supporting functions for supplementary services control;
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supporting functions for short messages service control;
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supporting functions for location services control (only for a type A LMU).
The layer 3 for non-GPRS services is composed of three sublayers comprising:
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the Radio Resource Management (RR) functions;
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the Mobility Management (MM) functions; and
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the Connection Management (CM) functions.
When CTS services are added to non-GPRS services, the following functions are added:
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CTS Radio Resource Management (CTS-RR) functions to RR; and
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CTS Mobility Management (CTS-MM) functions to MM.
The layer 3 for GPRS services is composed of four sublayers comprising:
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the Radio Resource Management (RR) functions;
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the Mobility Management (GMM);
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for the Logical Link Control (LLC);
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the Connection Management (CM) functions.
The Connection Management (CM) sublayer is composed of functional blocks for:
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Call Control (CC) for non-GPRS services;
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Short Message Service Support (SMS) for non-GPRS services;
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GPRS Short Message Service Support (GSMS) (for GPRS services supporting Class A, B and C MSs);
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Session Management (SM) (for GPRS services supporting Class A, B and C MSs);
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Supplementary Services Support (SS) for non-GPRS services;
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Group Call Control for non-GPRS services;
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Broadcast Call Control (BCC) for non-GPRS services;
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Connection Management of Packet Data on Signalling channels for non-GPRS services;
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Location Services support (LCS) for non-GPRS services (only for a type A LMU).
Within the context of LCS, for GSM LCS, the services defined for an MS are equally applicable to a type A LMU, unless otherwise stated. However, services defined specifically for a type A LMU are not applicable to an MS. The following is a list of services essential for a type A LMU.
The layer 3 for non-GPRS services provides the functions necessary:
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for Radio Resource (RR) management;
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for Mobility Management (MM); and
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supporting functions for location service control.
The layer 3 for non-GPRS services is composed of three sublayers comprising:
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the Radio Resource Management (RR) functions;
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the Mobility Management (MM) functions; and
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the Connection Management (CM) functions.
The Connection Management (CM) sublayer is composed of a functional block for:
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location services support (LCS) for non-GPRS services.
The present document does not consider the distribution of signalling functions among the different network equipments. The signalling functions are described between two systems which represent the MS side and the network side of the radio interface of layer 3. Only the functions in the network for signalling communication with one MS is considered.
For GPRS services, in addition to the signalling functions also the user data transfer is included in the present document.
The layer 3 for EPS services is composed of three sublayers comprising:
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the EPS Radio Resource Management (RR) functions;
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the EPS Mobility Management (EMM) functions; and
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the Connection Management (CM) functions.
The Connection Management (CM) sublayer is composed of a functional block for:
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the EPS Session Management (ESM) functions.
The layer 3 for 5GS services is composed of three sublayers comprising:
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the 5GS radio resource management (5GRR) functions for NAS over 3GPP access or the non-3GPP access functions for NAS over non-3GPP access;
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the 5GS mobility management (5GMM) functions; and
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the 5GS connection management (5GCM) functions.
The 5GS mobility management (5GMM) sublayer is composed of a functional block for:
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the 5GS mobility management (5GMM) functions.
The 5GS connection management (5GCM) sublayer is composed of a functional block for:
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the 5GS session management (5GSM) functions.
Not for all functional blocks listed in
clause 4.1, support in the MS or in the network is mandatory:
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Support of Group Call Control is optional in the MS and in the network.
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Support of Broadcast Call Control is optional in the MS and in the network.
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Connection Management of Packet Data on Signalling channels. is optional in the MS and in the network.
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Support of GPRS services is optional in the MS and in the network.
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Support of CTS services is optional in the MS. CTS services are not applicable to the network.
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Support of LCS services is optional in the MS and in the network, but not optional in LMU.
Further conditions and constraints are defined in other Technical Specifications.
Layer 3 and its sub-layers are specified by:
Descriptions in
clause 3 to
clause 10 are not maintained actively.
The services of signalling layer 3 and its sublayers are described in terms of:
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services provided to upper (sub-)layers at the service access points;
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services assumed from lower (sub-)layers at the service access points.
Layer 3 and its supporting lower layers provide the Mobile Network Signalling (MNS) Service and User Data Transfer (UDT) Service (for GPRS services only) to the upper layers.
The service provided/assumed at the service access points are described by means of abstract service primitives and parameters as recommended in
ITU-T Recommendation X.200 [18].
The abstract service primitives consist of requests, responses, indications and confirmations. The general syntax of a primitive is specified in
TR 21.905.
By use of the services provided by lower (sub-)layers, peer entities in a (sub-)layer in the MS and the network exchange information. Exchange of information between two peer entities is performed according to the corresponding (sub-)layer protocols. A protocol is a set of rules and formats by which the information (control information and user data) is exchanged between the two peers. The information is exchanged by use of messages which are defined in the protocol. (Therefore, the messages are also called Protocol Data Units, PDUs).
There are several protocols of the RR sublayer, one protocol of the LLC sublayer, three protocols of the MM sublayer, and several protocols of the CM sublayer. For each functional block of the CM sublayer as defined in
clause 4.1 there is one protocol. The CM protocols are specified in the Technical Specifications identified in
clause 4.3.4.
In the model used in the present document, there are:
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for non-GPRS services:
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one RR sub-layer entity in the MS and one RR sub-layer entity in the network;
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one MM sub-layer entity in the MS and one MM sub-layer entity in the network;
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for each functional block of the CM sublayer as defined in clause 4.1 which is supported in the MS (in the network), there are, depending on the protocol, one or more entities in the MS (in the network). Two different entities of the same functional block in the MS (in the network) are called parallel entities. The entities of the same functional block in the MS correspond in a one-to-one relation to the entities of the functional block in the network. The corresponding entities are called peer entities;
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for CTS services (in addition to non-GPRS services):
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one RR sub-layer entity in the MS and one in the CTS fixed part. These RR sub-layers include one CTS-RR sub-entity on each side;
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one MM sub-layer entity in the MS and one in the CTS fixed part These MM sub-layers include one CTS-MM sub-entity on each side;
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for each functional block of the CM sublayer as defined in clause 4.1 which is supported in the MS (in the fixed part), there are, depending on the protocol, one or more entities in the MS (in the fixed part). Two different entities of the same functional block in the MS (in the fixed part) are called parallel entities. The entities of the same functional block in the MS correspond in a one-to-one relation to the entities of the functional block in the fixed part. The corresponding entities are called peer entities;
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for GPRS services supporting Class C MSs:
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one RR sublayer entity (RR) in the MS and one RR sublayer entity in the network;
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six LLC sublayer entities (QoS1-QoS4, signalling, SMS) in the MS and six LLC sublayer entities in the network;
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one MM sublayer entity (GMM) in the MS and one MM sublayer entity in the network (GMM);
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one SM entity in the MS's CM sublayer and one SM sublayer entity in the network's CM sublayer;
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one or more GSMS functional blocks in the CM sublayer if supported;
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for non-GPRS and GPRS services supporting Class A and Class B MSs:
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two RR sublayer entities (RR) in the MS and two RR sublayer entities in the network;
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six LLC sublayer entities (QoS1-QoS4, signalling, SMS) in the MS and six LLC sublayer entities in the network;
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two MM sublayer entities (GMM + MM) in the MS and one or two MM sublayer entities in the network (GMM or MM);
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one SM entity in the MS's CM sublayer and one SM entity in the network's CM sublayer;
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for each functional block of the CM sublayer as defined in clause 4.1 which is supported in the MS (in the network), there are, depending on the protocol, one or more entities in the MS (in the network). Two different entities of the same functional block in the MS (in the network) are called parallel entities. The entities of the same functional block in the MS correspond in a one-to-one relation to the entities of the functional block in the network. The corresponding entities are called peer entities;
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for EPS services:
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one RR entity in the MS and one RR entity in the network;
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one EMM entity in the MS and one EMM entity in the network;
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for each functional block of the CM sublayer as defined in clause 4.1 which is supported in the MS (in the network), there are, depending on the protocol, one or more entities in the MS (in the network). Two different entities of the same functional block in the MS (in the network) are called parallel entities. The entities of the same functional block in the MS correspond in a one-to-one relation to the entities of the functional block in the network. The corresponding entities are called peer entities.
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for 5GS services:
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one 5GRR entity in the MS and one 5GRR entity in the network for NAS over 3GPP access;
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one non-3GPP access management entity in the MS and one non-3GPP access interworking entity in the N3IWF for the NAS over non-3GPP access;
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one 5GMM entity in the MS and one 5GMM entity in the network;
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for each functional block of the 5GCM sublayer as defined in clause 4.1 which is supported in the MS (in the network), there are, depending on the protocol, one or more entities in the MS (in the network). Two different entities of the same functional block in the MS (in the network) are called parallel entities. The entities of the same functional block in the MS correspond in a one-to-one relation to the entities of the functional block in the network. The corresponding entities are called peer entities.
As each sub-layer entity is specified by one and only one protocol, it is also called a protocol entity or protocol control entity.
For GPRS-services supporting Class A and Class B MSs, the MM entities of the MM-sublayer are able to exchange information by means of GMM PDUs as well as MM PDU's. This means if a mobile is GPRS attached, non-GPRS mobility management procedures may make use of GRPS mobility management messages.
When two peer protocol entities exchange PDUs, a transaction is said to be established (or: to be active; or: to exist). It depends from the protocol when exactly a protocol entity considers the transaction to be active, normally this is the case:
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from the moment when it has passed the first suitable message to lower (sub-) layers or received the first suitable message from its peer entity;
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up to the moment when it has released the transaction.
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The Radio Resource (RR) management protocol is defined in TS 44.018;
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the Mobility Management (MM) protocol is defined in TS 24.008;
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the Session Management (SM) protocol is defined in TS 24.008;
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the Call Control (CC) protocol is defined in TS 24.008;
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the Supplementary Services (SS) protocol is defined in TS 24.010, 3GPP TS 24.08x, 3GPP TS 24.09x, and TS 24.030;
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the Short Message Service (SMS) protocol is defined in TS 24.011;
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the Group Call Control (GCC) protocol is defined in TS 44.068;
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the Logical Link Control (LLC) protocol is defined in TS 44.064;
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the GPRS Radio Resource (GRR) protocol is defined in TS 44.060 and TS 24.008;
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the CTS Radio Resource (CTS-RR) sub-protocol is defined in TS 44.056;
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the CTS Mobility Management (CTS-MM) sub-protocol is defined in TS 44.056;
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the CTS additions to the Call Control (CC) protocol are defined in TS 44.056;
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the Location Services (LCS) protocol for a type A LMU is defined in TS 23.271 and TS 44.071;
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the EPS Radio Resource (RR) management protocol is defined in TS 36.331;
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the EPS Mobility Management (EMM) protocol is defined in TS 24.301;
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the EPS Session Management (ESM) protocol is defined in TS 24.301;
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the 5GS Radio Resource management (5GRR) protocol is defined in TS 38.331;
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the 5GS Mobility Management (5GMM) protocol is defined in TS 24.501;
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the UE policy delivery service is defined in TS 24.501;
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the 5GS Session Management (5GSM) protocol is defined in TS 24.501;
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the non-3GPP access management protocol is defined in TS 24.502;
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the PC5 signalling protocol for V2X communication for 5GS is defined in TS 24.587;
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the Time-Sensitive Networking (TSN) Application Function (AF) to Device-Side TSN Translator (DS-TT) and Network-Side TSN Translator (NW-TT) protocol is defined in TS 24.519;
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the Performance Measurement Function (PMF) protocol is defined in TS 24.193;
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the PC3 and PC5 signalling protocol for Proximity-based Services (ProSe) are defined in TS 24.334;
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the PC3a and PC5 signalling protocol for 5G Proximity-based Services (ProSe) are defined in TS 24.554;
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the signalling protocol between the Application Client on the constrained UE and the MSGin5G Client on the MSGin5G Gateway UE for Enabling MSGin5G Service is defined in TS 24.538;
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the Location Services User Plane (LCS-UP) protocol is defined in TS 24.572;
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the User Plane Positioning Connection Management (UPP-CM) protocol is defined in TS 24.572;
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the extended PC5 signalling protocol and supplementary RSPP signalling protocol over PC5-U for ranging and sidelink positioning are defined in TS 24.514; and.
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the PC5 signalling protocol for aircraft-to-everything (A2X) communication is defined in TS 24.577.