4 Layered overview of radio interface
3GPP44.160General Packet Radio Service (GPRS)Mobile Station (MS) - Base Station System (BSS) interfaceRadio Link Control / Medium Access Control (RLC/MAC) protocol Iu modeRelease 16TS
4.0 Protocol architecture
The protocol architecture for the radio interface is shown in figure 4.1 where the flexible layer one (FLO) is not represented. Figure 4.2 represents the protocol architecture in relation to FLO only.
The RLC/MAC function provides a service to PDCP for User plane data, to RRC for Control plane data and to the application layer of the CS User plane.
Figure 4.1: Radio Interface Protocol architecture
Figure 4.2: Radio Interface Protocol architecture with FLO only
4.1 Layer services
The RLC/MAC sublayer provides services for the transfer over the physical layer between the network and mobile station of upper layer PDUs for one mobile station when operating on a dedicated basic physical subchannel, or for one or more mobile stations when operating on a shared basic physical subchannel.
The RLC function provides the following services to the upper layers:
– Transparent data transfer: This service transmits higher layer PDUs without adding any protocol information.
– Acknowledged data transfer: This service transmits higher layer PDUs and guarantees delivery to the peer entity.
– Unacknowledged data transfer: This service transmits higher layer PDUs without guaranteeing delivery to the peer entity.
– Notification of unrecoverable errors: RLC notifies the upper layer of errors that cannot be resolved by RLC itself by normal exception handling procedures.
– Notification of discard: RLC notifies the upper layer of the higher layer PDUs (RLC SDUs) it discards.
– Suspend: The RLC entity does not transmit any new RLC PDUs to the lower layer.
– Resume: The RLC entity resumes data transmission.
– Stop: The RLC entity does not transmit any RLC PDUs to the lower layer and does not receive any PDUs from the lower layer.
– Continue: The RLC entity resumes data transmission and reception.
– Re-establishment: The RLC entity is re-established.
The MAC function provides the following service to the upper layer:
– Data transfer.
4.2 Layer functions
4.2.1 RLC function
The functions provided by the RLC are given in table 4.2.1.1. Transparent RLC mode provides no functionality.
Table 4.2.1.1: RLC Functions
|
Acknowledged mode RLC |
Unacknowledged mode RLC |
Transparent mode RLC |
|
|
Segmentation of upper layer PDUs into RLC data blocks |
X |
X |
|
|
Concatenation of upper layer PDUs into RLC data blocks |
X |
X |
|
|
Padding to fill out RLC data block |
X |
X |
|
|
Backward Error Correction (BEC) procedure enabling the selective retransmission of RLC data blocks |
X |
||
|
Discard of RLC SDUs not yet segmented into RLC PDUs, according to the delay requirements of the associated Radio Bearers |
X |
||
|
Reassembly of RLC data blocks into upper layer PDUs |
X |
X |
|
|
In-sequence delivery of upper layer PDUs |
X |
X |
|
|
Link Adaptation |
X |
X |
|
|
Ciphering |
X |
X |
|
|
Sequence number check to detect lost RLC blocks |
X |
X |
4.2.2 MAC layer function
The functions of the MAC layer include:
– Configuring the mapping between logical channels and basic physical subchannels: The MAC layer is responsible for configuring the mapping of logical channel(s) onto the appropriate basic physical subchannel(s).
– Mapping between TBFs and transport channels. When FLO is used, the MAC layer is responsible for mapping TBF(s) onto the appropriate transport channel(s).
– Selecting logical channels to be used for each signalling radio bearer service: The MAC layer is responsible for mapping SRBs onto logical channels. There are a set of rules defined for this mapping (see sub-clause 5.6) which shall be used in the uplink and should be used in the downlink. The mapping is dependent on the SRB to be sent, the MAC state, and the logical channels available. The SFACCH may be selected in preference to the PDTCH if a TBF is not already established for the SRB. In the downlink there is an additional requirement that the PHYSICAL INFORMATION message is always sent on the FACCH.
– Selecting transport channel to be used for signalling radio bearer service: When FLO is used, the MAC layer is responsible for mapping some SRBs onto transport channels. There is a set of rules defined for this mapping (see sub-clause 5.6) which shall be used in the uplink and should be used in the downlink. The mapping is dependent on the SRB to be sent, the MAC state, and the logical channels and transport channels available. When SRB data is sent using FLO on a DBPSCH/F, the signalling TFC shall be used. When SRB data is sent using FLO on a DBPSCH/H, the MAC layer shall send every RLC/MAC block for data transfer twice in a row. The corresponding first and second transport blocks shall use the signalling TFC.
– Selecting logical channels to be used for each user radio bearer service: The logical channels used by the MAC for user radio bearers are set up by configuration from RRC.
– Selecting transport channels to be used for each user radio bearer service: When FLO is used, the transport channels used by the MAC for user radio bearers are set up by configuration from RRC.
– Selection of the appropriate transport format per transport channel. When FLO is used, the MAC layer is responsible for selecting the appropriate transport format for each transport channel within the transport format set configured by RRC for each transport channel so that the resulting transport format combination belongs to the transport format combination set configured by RRC.
– Assignment, reconfiguration and release of shared radio resources for a TBF: The MAC layer may handle the assignment of radio resources needed for a TBF including needs from both the control and user plane. The MAC layer may reconfigure radio resources of a TBF.
– MS measurement reporting and control of the reporting: The MAC layer is responsible for sending information that control the MS measurement reporting when using PBCCH or PACCH channels. The MAC layer also performs the reporting of the measurements from the MS to the network using PACCH.
– Broadcasting/listening of/to PBCCH and PCCCH: The MAC layer broadcasts/listens (to) the PBCCH of the serving cell for the sending/decoding of packet system information messages. The MAC layer also sends paging information on the PCCCH or and monitors the paging occasions according to the DRX cycle. Within the Mobile Station, the MAC layer notifies the RRC layer when receiving a paging message; within the network, it is responsible for aggregating and sending paging messages addressed to one or more Mobile Stations when received from the RRC layer.
– Timing advance control: The MAC layer controls the operation of timing advance on shared basic physical subchannels.
– Ciphering and deciphering (only in combination with transparent RLC mode).
– Priority handling between data flows of one MS. When FLO is used, the MAC layer is responsible for prioritization between data flows of one MS on DBPSCH.
When the MAC layer is providing services to a non-transparent RLC mode entity, the MAC layer supports the following additional functions:
– Ciphering.
– Identification of different traffic flows of one or more MSs on the basic physical subchannels: Inband identification is needed to address a flow to an MS in the downlink or identify a flow from an MS in the uplink.
– Multiplexing/demultiplexing of higher layer PDUs: This may include priority handling between data flows of one or more mobile stations, e.g. by attributes of Radio Bearer services.
– Multiplexing/demultiplexing user and control plane data to/from the physical layer for PDTCHs: The MAC layer is responsible for multiplexing/demultiplexing RLC data blocks carried on PDTCH and RLC/MAC control blocks carried on PACCH.
– Scheduling of RLC/MAC data and control PDUs delivered to the physical layer on shared basic physical subchannels: This includes USF and RRBP field monitoring for uplink transfer and sharing radio resources on the downlink.
– Splitting/recombining: This includes splitting/recombining of the RLC/MAC PDU flow belonging to one or more TBF(s) onto/from several shared logical channels. This function does not apply for RLC/MAC control blocks.
4.3 Service primitives
4.3.1 MAC to Physical Layer Primitives
These are defined in 3GPP TS 44.004.
4.3.2 PDCP to RLC Primitives
4.3.2.1 Primitives
The primitives between PDCP and RLC are shown in table 4.3.2.1.1.
Table 4.3.2.1.1: Primitives between RLC and upper layers
|
Generic Name |
Parameters |
|||
|
Req. |
Ind. |
Resp. |
Conf. |
|
|
RLC-AM-DATA |
Data, CNF, MUI |
Data |
Not Defined |
Status, MUI |
|
RLC-UM-DATA |
Data |
Data |
Not Defined |
Not Defined |
|
RLC-TM-DATA |
Data |
Data, Error_Indicator |
Not Defined |
Not Defined |
Each Primitive is defined as follows:
RLC-AM-DATA-Req/Ind/Conf
– RLC-AM-DATA-Req is used by upper layers to request transmission of an RLC SDU in acknowledged mode.
– RLC-AM-DATA-Ind is used by the AM RLC entity to deliver to upper layers an RLC SDU that has been transmitted in acknowledged mode.
– RLC-AM-DATA-Conf is used by the AM RLC entity to confirm to upper layers the reception of an RLC SDU by the peer-RLC AM entity or to inform the upper layers of a discarded RLC SDU.
RLC-UM-DATA-Req/Ind/Conf
– RLC-UM-DATA-Req is used by upper layers to request transmission of an RLC SDU in unacknowledged mode.
– RLC-UM-DATA-Ind is used by the UM RLC entity to deliver to upper layers an RLC SDU that has been transmitted in unacknowledged mode.
RLC-TM-DATA-Req/Ind/Conf
– RLC-TM-DATA-Req is used by upper layers to request transmission of an RLC SDU in transparent mode.
– RLC-TM-DATA-Ind is used by the TM RLC entity to deliver to upper layers an RLC SDU that has been transmitted in transparent mode.
4.3.2.2 Primitive parameters
The following parameters are used in the primitives:
1) The parameter Data is the RLC SDU that is mapped onto the Data field in RLC PDUs.
2) The parameter Confirmation Request (CNF) indicates whether the transmitting side of the AM RLC entity needs to confirm the reception of the RLC SDU by the peer-RLC AM entity. If required, once all AMD PDUs that make up the RLC SDU are positively acknowledged by the receiving AM RLC entity, the transmitting AM RLC entity notifies upper layers.
3) The parameter Message Unit Identifier (MUI) is an identity of the RLC SDU, which is used to indicate which RLC SDU that is confirmed with the RLC-AM-DATA-Conf. Primitive.
4) The Error_Indicator parameter indicates that the RLC SDU is erroneous.
5) The parameter Status is only applicable for AM operation. This parameter indicates whether a RLC SDU is successfully transmitted or discarded.
4.3.3 RRC to RLC Primitives
4.3.3.1 Primitives
The primitives between RRC and RLC are shown in table 4.3..3.1.
Table 4.3.3.1: Primitives between RRC and RLC
|
Generic Name |
Parameters |
|||
|
Req. |
Ind. |
Resp. |
Conf. |
|
|
RLC-AM-DATA |
Data, CNF, MUI, DiscardReq |
Data |
Not Defined |
Status, MUI |
|
RLC-UM-DATA |
Data |
Data |
Not Defined |
Not Defined |
|
CRLC-CONFIG |
E/R, Stop (UM/AM only), Continue (UM/AM only), Ciphering Elements (UM/AM only), TM_parameters (TM only), UM_parameters (UM only-SDU discard, EGPRS window size), AM_parameters (AM only –SDU discard, resegment bit, EGPRS window size) |
Not Defined |
Not Defined |
Not Defined |
|
CRLC-SUSPEND (UM/AM only) |
N |
Not Defined |
Not Defined |
V(S) (AM/UM only) |
|
CRLC-RESUME (UM/AM only) |
No Parameter |
Not Defined |
Not Defined |
Not Defined |
Each Primitive is defined as follows:
RLC-AM-DATA-Req/Ind/Conf
– RLC-AM-DATA-Req is used by upper layers to request transmission of an RLC SDU in acknowledged mode.
– RLC-AM-DATA-Ind is used by the AM RLC entity to deliver to upper layers an RLC SDU that has been transmitted in acknowledged mode.
– RLC-AM-DATA-Conf is used by the AM RLC entity to confirm to upper layers the reception of an RLC SDU by the peer-RLC AM entity.
RLC-UM-DATA-Req/Ind/Conf
– RLC-UM-DATA-Req is used by upper layers to request transmission of an RLC SDU in unacknowledged mode.
– RLC-UM-DATA-Ind is used by the UM RLC entity to deliver to upper layers an RLC SDU that has been transmitted in unacknowledged mode.
CRLC-CONFIG-Req
This primitive is used by upper layers to establish, re-establish, release, stop, continue or modify the RLC. Ciphering elements are included for UM and AM operation.
CRLC-SUSPEND-Req/Conf
– CRLC-SUSPEND-Req is used by upper layers to suspend the UM or AM RLC entity.
– CRLC-SUSPEND-Conf is used by the UM or AM RLC entity to confirm that the entity is suspended.
CRLC-RESUME-Req
This primitive is used by upper layers to resume the UM or AM RLC entity after the UM or AM RLC entity has been suspended.
4.3.3.2 Primitive parameters
Following parameters are used in the primitives:
1) The parameter Data is the RLC SDU that is mapped onto the Data field in RLC PDUs.
2) The parameter Confirmation Request (CNF) indicates whether the transmitting side of the AM RLC entity needs to confirm the reception of the RLC SDU by the peer-RLC AM entity. If required, once all AMD PDUs that make up the RLC SDU are positively acknowledged by the receiving AM RLC entity, the transmitting AM RLC entity notifies upper layers.
3) The parameter Message Unit Identifier (MUI) is an identity of the RLC SDU, which is used to indicate which RLC SDU that is confirmed with the RLC-AM-DATA-Conf. Primitive.
4) The parameter E/R indicates establishment, re-establishment, release or modification of an RLC entity, where re-establishment is applicable to AM and UM RLC entities only.
5) The parameter Ciphering Elements are only applicable for UM and AM operations. These parameters are Ciphering Key, Activation Time (Sequence Number (BSN) to activate a new ciphering configuration) and HFN (Hyper Frame Number).
6) The AM_parameters are only applicable for AM operation.
7) The Stop parameter is applicable to AM and UM RLC entities only and indicates to the RLC entity to not transmit nor receive any RLC PDUs.
8) The Continue parameter is applicable to AM and UM RLC entities only and indicates to the RLC entity to continue transmission and reception of RLC PDUs.
9) The UM_parameters are only applicable for UM operation.
10) The TM_parameters are only applicable for TM operation.
11) The N parameter indicates that an RLC entity will not send a PDU with "Sequence Number"V(S)+N for UM/AM RLC entities where N is a non-negative integer.
12) The V(S) parameter indicates the value of the Send State Variable for the case of the AM/UM RLC entities.
13) The parameter Status is only applicable for AM operation. This parameter indicates whether a RLC SDU is successfully transmitted or discarded.
14) The parameter DiscardReq indicates whether the transmitting RLC entity needs to inform the upper layers of the discarded RLC SDU. If required, the transmitting RLC entity notifies upper layers when the RLC SDU is discarded..
4.3.4 RRC to MAC Primitives
4.3.4.1 Primitives
The primitives between MAC and RRC are shown in table 4.3.4.1.
Table 4.3.4.1: Primitives between RRC sub-layer and MAC
|
Generic Name |
Parameter |
|||
|
Request |
Indication |
Response |
Confirm |
|
|
CMAC-CONFIG |
MS information elements, RB information elements, Ciphering elements, |
|||
|
CMAC-SYS-INFO |
System Information Elements |
|||
|
PAGING |
MS Identity, CN Domain Identity, Paging Cause, Paging Record Type Identifier |
MS Identity, CN Domain Identity, Paging Cause, Paging Record Type Identifier |
NA |
NA |
|
HANDOVER |
Handover Reference Value |
Handover Reference Value |
NA |
NA |
|
PHYSICAL-INFO |
Timing Advance Value |
Timing Advance Value |
NA |
NA |
CMAC-CONFIG-Req
– CMAC-CONFIG-Req is used to request for setup, release and configuration of a logical channel, G-RNTI allocation, mapping between radio bearer and logical channel, setup, release and configuration of transport channels and mapping between radio bearers and transport channels.
CMAC-SYS-INFO-Req
– CMAC-SYS-INFO-Req is used to pass information elements needed for the generation of system information messages within the MAC entity.
PAGING-Req/Ind:
– PAGING-Req is used by RRC to page a MS.
– PAGING-Ind is used by the MS to inform the RRC of the reception of a PACKET PAGING REQUEST message.
HANDOVER-Req/Ind:
– HANDOVER-Req is used by the mobile station’s RRC to trigger the transmission of the HANDOVER ACCESS message to the network
– HANDOVER-Ind is used by the network to inform the RRC of the reception of a HANDOVER ACCESS message
PHYSICAL-INFO-Req/Ind:
– PHYSICAL-INFO-Req is used by the network’s RRC to trigger the transmission of the PHYSICAL INFORMATION message to the mobile station
– PHYSICAL-INFO-Ind is used by the mobile station to inform the RRC of the reception of the PHYSICAL INFORMATION message
4.3.4.2 Primitive Parameters
The MAC configuration primitives use the following parameters. See 3GPP TS 44.118 for a detailed description of the MS, and RB information elements.
1) MS information elements
G-RNTI
SRNC identity
Activation time
2) RB information elements
RB multiplexing info (Logical channel identity, radio priority, mapping of reduced radio bearer id to radio bearer id, transport channel identity)
3) Ciphering elements
Ciphering key
Activation Time (TDMA Frame Number) HFN
The system information primitives use the following parameter:
1) System Information elements
See 3GPP TS 44.118
The paging primitives use the following parameters:
1) The MS Identity parameter is the IMSI, TMSI, PTMSI, or G-RNTI.
2) The CN Domain Identity parameter indicates whether a CN-initiated page is from the packet domain or circuit domain.
3) The Paging Cause parameter indicates the reason for the page.
4) The Paging Record Type Identifier parameter indicates the type of MS identity used by the CN in a CN-initiated page, e.g. IMSI (GSM), IMSI (DS-41), TMSI/PTMSI (GSM).
The handover primitives use the following parameter:
1) The Handover Reference Value parameter indicates the handover reference value used for access identification in the HANDOVER ACCESS message
The physical info primitives use the following parameter:
1) The Timing Advance Value parameter indicates the timing advance value in the PHYSICAL INFORMATION message to be applied by the mobile station
4.4 Services required from lower layers
The RLC/MAC function uses the services provided by the physical link layer as defined in 3GPP TS 44.004.
The following services are required of the physical layer:
– Access capabilities: In configurations where FLO is not used, the physical layer offers logical channels and the transmission services associated to higher layers. Logical channels are multiplexed either in a fixed predefined manner (multiframe structure) or dynamically by the MAC layer on basic physical subchannels. In configurations where FLO is used, the physical layer offers transport channels and the transmission services associated to higher layers. Transport channels are multiplexed in a dynamic manner on dedicated basic physical subchannels. Basic physical subchannels are the units scheduled on the radio medium. Some are reserved by the network for common use (e.g. for use by a combination of CCCH and BCCH), others are assigned to dedicated connections with MSs (dedicated basic physical subchannels), or are assigned to a shared usage between MSs (shared basic physical subchannels).
– Error detection: The physical layer offers an error protected transmission service, it includes error detection functions and to a lower level, error correction functions. Erroneous received frames may be notified to upper layers and, depending on the need of the upper layer, offered to it. The probability of one or more errors in a physical block transferred by the physical layer is defined in 3GPP TS 45.005. Due to non-specified methods of quality detection, the probability of residual errors in transferred blocks may vary between implementations.
– Measurement of the signal strength of neighbouring base stations. Measurements are transferred to RRC.
– Measurement of the signal quality of the basic physical subchannel used. Measurements are transferred to the MAC layer for reporting to the base station.
– Cell/PLMN selection in MAC-Idle state. In MAC-Idle state the physical layer selects the best cell with its BCCH in close co‑operation with layer 3, meeting requirements for PLMN selection specified in 3GPP TS 42.011.