9.3 Protocol states

25.3223GPPRadio Link Control (RLC) protocol specificationRelease 17TS

The content presented in this subclause is intended to support the definition of the RLC protocol states only, and is not meant to specify or constrain the implementation of the protocol.

9.3.1 State model for transparent mode entities

Figure 9.16 illustrates the state model for transparent mode RLC entities (both transmitting and receiving). A transparent mode entity can be in one of the following states.

9.3.1.1 NULL State

In the NULL state the RLC entity does not exist and therefore it is not possible to transfer any data through it.

Upon reception of a CRLC-CONFIG-Req from upper layers indicating establishment, the RLC entity:

– is created; and

– enters the DATA_TRANSFER_READY state.

9.3.1.2 DATA_TRANSFER_READY State

In the DATA_TRANSFER_READY state, transparent mode data can be exchanged between the entities according to subclause 11.1.

Upon reception of a CRLC-CONFIG-Req from upper layer indicating release, the RLC entity:

– enters the NULL state; and

– is considered as being terminated.

Figure 9.16: The state model for transparent mode entities

9.3.2 State model for unacknowledged mode entities

Figure 9.17 illustrates the state model for unacknowledged mode RLC entities (both transmitting and receiving). An unacknowledged mode entity can be in one of the following states.

9.3.2.1 NULL State

In the NULL state the RLC entity does not exist and therefore it is not possible to transfer any data through it.

Upon reception of a CRLC-CONFIG-Req from upper layer indicating establishment the RLC entity:

– is created; and

– enters the DATA_TRANSFER_READY state.

9.3.2.2 DATA_TRANSFER_READY State

In the DATA_TRANSFER_READY state, unacknowledged mode data can be exchanged between the entities according to subclause 11.2.

Upon reception of a CRLC-CONFIG-Req from upper layer indicating release, the RLC entity:

– enters the NULL state; and

– is considered as being terminated.

Upon reception of a CRLC-CONFIG-Req from upper layer indicating modification, the RLC entity:

– stays in the DATA_TRANSFER_READY state;

– modifies only the protocol parameters and timers as indicated by upper layers.

Upon reception of a CRLC-SUSPEND-Req from upper layers, the RLC entity:

– enters the LOCAL_SUSPEND state.

9.3.2.3 LOCAL_SUSPEND State

In the LOCAL_SUSPEND state, the RLC entity is suspended, i.e. it does not send UMD PDUs with "Sequence Number" greater than or equal to a certain specified value (see subclause 9.7.5).

Upon reception of a CRLC-CONFIG-Req from upper layer indicating release, the RLC entity:

– enters the NULL state; and

– is considered as being terminated.

Upon reception of a CRLC-RESUME-Req from upper layers, the RLC entity:

– enters the DATA_TRANSFER_READY state; and

– resumes the data transmission.

Upon reception of a CRLC-CONFIG-Req from upper layer indicating modification, the RLC entity:

– stays in the LOCAL_SUSPEND state;

– modifies only the protocol parameters and timers as indicated by upper layers.

Figure 9.17: The state model for unacknowledged mode entities

9.3.3 State model for acknowledged mode entities

Figure 9.18 illustrates the state model for the acknowledged mode RLC entity (both transmitting and receiving). An acknowledged mode entity can be in one of the following states.

9.3.3.1 NULL State

In the NULL state the RLC entity does not exist and therefore it is not possible to transfer any data through it.

Upon reception of a CRLC-CONFIG-Req from upper layer indicating establishment, the RLC entity:

– is created; and

– enters the DATA_TRANSFER_READY state.

9.3.3.2 DATA_TRANSFER_READY State

In the DATA_TRANSFER_READY state, acknowledged mode data can be exchanged between the entities according to subclause 11.3.

Upon reception of a CRLC-CONFIG-Req from upper layer indicating release, the RLC entity:

– enters the NULL state; and

– is considered as being terminated.

Upon detection of an initiating condition for the RLC reset procedure described in subclause 11.4.2, the RLC entity:

– initiates the RLC reset procedure (see subclause 11.4); and

– enters the RESET_PENDING state.

Upon reception of a RESET PDU, the RLC entity responds according to subclause 11.4.3.

Upon reception of a RESET ACK PDU, the RLC entity takes no action.

Upon reception of CRLC-SUSPEND-Req from upper layer, the RLC entity is suspended and enters the LOCAL_SUSPEND state.

9.3.3.3 RESET_PENDING State

In the RESET_PENDING state the entity waits for a response from its peer entity and no data can be exchanged between the entities.

Upon reception of a CRLC-CONFIG-Req from upper layer indicating release, the RLC entity:

– enters the NULL state; and

– is considered as being terminated.

Upon reception of a RESET ACK PDU with the same RSN value as in the corresponding RESET PDU, the RLC entity:

– acts according to subclause 11.4.4; and

– enters the DATA_TRANSFER_READY state.

Upon reception of a RESET ACK PDU with a different RSN value as in the corresponding RESET PDU, the RLC entity:

– discards the RESET ACK PDU (see subclause 11.4.4); and

– stays in the RESET_PENDING state.

Upon reception of a RESET PDU, the RLC entity:

– responds according to subclause 11.4.3; and

– stays in the RESET_PENDING state.

Upon reception of CRLC-SUSPEND-Req from upper layer, the RLC entity:

– enters the RESET_AND_SUSPEND state.

Figure 9.18: The state model for the acknowledged mode entities

9.3.3.4 LOCAL_SUSPEND State

In the LOCAL_SUSPEND state, the RLC entity is suspended, i.e. it does not send AMD PDUs with "Sequence Number" greater than or equal to certain specified value (see subclause 9.7.5).

Upon reception of CRLC-RESUME-Req from upper layers in this state, the RLC entity:

– resumes the data transmission; and

– enters the DATA_TRANSFER_READY state.

Upon reception of CRLC-CONFIG-Req from upper layers indicating release, the RLC entity:

– enters the NULL state; and

– is considered as being terminated.

Upon detection of an initiating condition for RLC reset procedure described in subclause 11.4.2, the RLC entity:

– initiates the RLC reset procedure (see subclause 11.4); and

– enters the RESET_AND_SUSPEND state.

9.3.3.5 RESET_AND_SUSPEND State

In the RESET_ AND_SUSPEND state, the entity waits for a response from its peer entity or a primitive (CRLC-RESUME-Req) from its upper layer and no data can be exchanged between the entities.

Upon reception of CRLC-CONFIG-Req from upper layer indicating release, the RLC entity:

– enters the NULL state; and

– is considered as being terminated.

Upon reception of a RESET ACK PDU with the same RSN value as in the corresponding RESET PDU, the RLC entity:

– acts according to subclause 11.4.4; and

– enters the LOCAL_SUSPEND state.

Upon reception of CRLC-RESUME-Req from upper layer in this state, the RLC entity:

– is resumed, i.e. releases the suspend constraint; and

– enters the RESET_PENDING state.