The purpose of the dedicated EPS bearer context activation procedure is to establish an EPS bearer context with specific QoS and TFT between the UE and the EPC.
The dedicated EPS bearer context activation procedure is initiated by the network, but may be requested by the UE by means of the UE requested bearer resource allocation procedure.
Default EPS bearer is established during the Attach procedure. It will remain connected throughout the lifetime of ODN connection.
If the attach procedure or the default EPS bearer context activation procedure fails, the UE shall consider that the dedicated bearer activation has implicitly failed.
The dedicated EPS bearer can be either guaranteed bit rate (GBR) or non-GBR.
The messages exchanged between UE and Network during Dedicated EPS bearer context activation procedure are:
ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST
ACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT
ACTIVATE DEDICATED EPS BEARER CONTEXT REJECT
ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST
This message is sent by the network to the UE to request activation of a dedicated EPS bearer context associated with the same PDN address(es) and APN as an already active default EPS bearer context.
The MME shall initiate the dedicated bearer context activation procedure by sending an ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST message, start the timer T3485, and enter the state BEARER CONTEXT ACTIVE PENDING
This procedure can be part of the attach procedure or be initiated together with the Default EPS bearer context activation procedure when the UE initiates a stand-alone PDN connectivity procedure.
The MME allocates the EPS bearer identity and includes it in the ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST message.
The MME shall include the EPS bearer identity of the associated default bearer as the linked EPS bearer identity in the ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST message.
If this procedure was initiated by a UE requested bearer resource allocation procedure or a UE requested bearer resource modification procedure, the ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST shall contain the procedure transaction identity (PTI) value received by the MME in the BEARER RESOURCE ALLOCATION REQUEST or BEARER RESOURCE MODIFICATION REQUEST respectively.
ACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT
This message is sent by the UE to the network to acknowledge activation of a dedicated EPS bearer context associated with the same PDN address(es) and APN as an already active EPS bearer context.
Upon receipt of the ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST message, the UE shall stop timer T3396.
Then the UE shall send an ACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT message and enter the state BEARER CONTEXT ACTIVE.
The ACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT message shall include the EPS bearer identity.
IE Protocol configuration options is included in the message when the UE wishes to transmit data.
Upon receipt of the ACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT message, the MME shall stop the timerT3485 and enter the state BEARER CONTEXT ACTIVE.
ACTIVATE DEDICATED EPS BEARER CONTEXT REJECT
This message is sent by UE to the network to reject activation of a dedicated EPS bearer context.
UE to network
Upon receipt of the ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST message, the UE may reject the request from the MME by sending an ACTIVATE DEDICATED EPS BEARER CONTEXT REJECT message.
The message shall include the EPS bearer identity and an ESM cause value indicating the reason for rejecting the dedicated EPS bearer context activation request.
The ACTIVATE DEDICATED EPS BEARER CONTEXT REJECT message contains an ESM cause that typically indicates one of the following ESM cause values:
#26: insufficient resources;
#31: request rejected, unspecified;
#41: semantic error in the TFT operation;
#42: syntactical error in the TFT operation;
Reference 3GPP TS 24.301
