4 General

25.3313GPPProtocol specificationRadio Resource Control (RRC)Release 17TS

If not specified differently, descriptions are relevant for both FDD and TDD. Descriptions for TDD only are relevant for both 1.28 Mcps TDD and 3.84 Mcps TDD and 7.68 Mcps TDD if not specified differently.

4.1 Overview of the specification

This specification is organised as follows:

– subclause 4.2 contains the description of the model of the RRC protocol layer;

– clause 5 lists the RRC functions and the services provided to upper layers;

– clause 6 lists the services expected from the lower layers and specifies the radio bearers available for usage by the RRC messages;

– clause 7 specifies the UE states for the Access Stratum, and also specifies the processes running in the UE in the respective states;

– clause 8 specifies RRC procedures, including UE state transitions;

– clause 9 specifies the procedures for the handling of unknown, unforeseen, and erroneous protocol data by the receiving entity;

– clause 10 describes the message in a Tabular format; these messages descriptions are referenced in clause 8;

– clause 11 specifies the encoding of the messages of the RRC protocol. This is based on the Tabular description in clause 10.

– clause 12 specifies the transfer syntax for RRC PDUs derived from the encoding definition;

– clause 13 lists the protocol timers, counters, constants and variables to be used by the UE;

– clause 14 specifies some of the processes applicable in UTRA RRC connected mode e.g. measurement processes, and also the RRC information to be transferred between network nodes. Note that not all the processes applicable in UTRA RRC connected mode are specified here i.e. some UTRA RRC connected mode processes are described in [4] e.g. cell re-selection;

– Annex A contains recommendations about the network parameters to be stored on the USIM;

– Annex B contains informative Stage 2 description of the RRC protocol states and state transitions.

The following figure summarises the mapping of UE states, including states in GSM and E-UTRA, to the appropriate UTRA, GSM and E-UTRA specifications that specify the UE behaviour.

Figure 4.1-1: Mapping of UE state to 3GPP Specifications

4.2 RRC Layer Model

The functional entities of the RRC layer are described below:

– Routing of higher layer messages to different MM/CM entities (UE side) or different core network domains (UTRAN side) is handled by the Routing Function Entity (RFE).

– Broadcast functions are handled in the broadcast control function entity (BCFE). The BCFE is used to deliver the RRC services, which are required at the GC-SAP. The BCFE can use the lower layer services provided by the Tr-SAP and UM-SAP.

– Paging of UEs that do not have an RRC connection is controlled by the paging and notification control function entity (PNFE). The PNFE is used to deliver the RRC services that are required at the Nt-SAP. The PNFE can use the lower layer services provided by the Tr-SAP and UM-SAP.

– The Dedicated Control Function Entity (DCFE) handles all functions specific to one UE. The DCFE is used to deliver the RRC services that are required at the DC-SAP and can use lower layer services of UM/AM-SAP and Tr-SAP depending on the message to be sent and on the current UE service state.

– In TDD mode, the DCFE is assisted by the Shared Control Function Entity (SCFE) location in the C-RNC, which controls the allocation of the PDSCH and PUSCH using lower layers services of UM-SAP and Tr-SAP.

– The Transfer Mode Entity (TME) handles the mapping between the different entities inside the RRC layer and the SAPs provided by RLC.

NOTE 1: Logical information exchange is necessary also between the RRC sublayer functional entities. Most of that is implementation dependent and not necessary to present in detail in a specification.

Figure 4.2-1 shows the RRC model for the UE and Figure 4.2-2 and Figure 4.2-3 show the RRC model for the UTRAN.

NOTE 2: The figure shows only the types of SAPs that are used. Multiple instances of Tr-SAP, UM-SAP and AM-SAP are possible. Especially, different functional entities usually use different instances of SAP types.

Figure 4.2-1: UE side model of RRC

Figure 4.2-2: UTRAN side RRC model (DS-MAP system)

Figure 4.2-3: UTRAN side RRC model (DS-41 System)

4.3 Protocol specification principles

This protocol specification is based on the applicable general guidelines given in [14].

In this specification, a notation of variables is used. The variables are defined in subclause 13.4. Variables are typically used to represent a status or a result of an action, such as reception of an information element in a message, which is used to specify a behaviour somewhere else in the specification, such as when setting the value of an information element in a transmitted message. The variables only serve the purpose of specifying the protocol, and do not therefore impose any particular implementation.

When specifying the UE behaviour at reception of messages, the behaviour that is tied to reception or non-reception of individual information elements, and in some cases combinations of information elements, is specified in one location (subclause 8.6).