The purpose of the default bearer context activation procedure is to establish a default EPS bearer context between the UE and the EPC.
The default EPS bearer context activation procedure is initiated by the network as a response to the PDN CONNECTIVITY REQUEST message from the UE.
The default bearer context activation procedure can be part of the attach procedure, and if the attach procedure fails, the UE shall consider that the default bearer activation has implicitly failed.
The default EPS bearer context does not have any TFT assigned during the activation procedure. This corresponds to using a match-all packet filter. It means the default bearer is a non GBR.
ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST
The MME shall initiate the default bearer context activation procedure by sending an ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message and enter the state BEARER CONTEXT ACTIVE PENDING
When the default bearer is activated as part of the attach procedure, the MME shall send the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message together with ATTACH ACCEPT and shall not start the timer T3485.
When the default bearer is activated as the response to a stand-alone PDN CONNECTIVITY REQUEST message apart from the attach procedure, the MME shall send the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message alone, and start the timer T3485.
The MME shall assign and include an EPS bearer identity in the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message.
The MME shall retrieve the PTI from the PDN CONNECTIVITY REQUEST message and include it in the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message.
IE’s include:
EPS bearer identity
Activate default EPS bearer context request message identity
EPS QoS
Access point name
PDN address
ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT
This message is sent by the UE to the network to acknowledge activation of a default EPS bearer context.
Upon receipt of the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message, the UE shall stop timer T3396 if it is running for the APN indicated in the message and send an ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT message and enter the state BEARER CONTEXT ACTIVE.
When the default bearer is activated as part of the attach procedure, the UE shall send the ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT message together with ATTACH COMPLETE message.
When the default bearer is activated as the response to the stand-alone PDN CONNECTIVITY REQUEST message, the UE shall send the ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT message alone.
Upon receipt of the ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT message, the MME shall enter the state BEARER CONTEXT ACTIVE and stop the timer T3485, if the timer is running
If the PDN CONNECTIVITY REQUEST message included an NAS signalling low priority indication set to “MS is configured for NAS signalling low priority”, the MME shall store the NAS signalling low priority indication within the default EPS bearer context.
IE’s include:
EPS bearer identity
Activate default EPS bearer context accept message identity
ACTIVATE DEFAULT EPS BEARER CONTEXT REJECT
This message is sent by UE to the network to reject activation of a default EPS bearer context.
If the default EPS bearer context activation is not part of the attach procedure, the UE shall send an ACTIVATE DEFAULT EPS BEARER CONTEXT REJECT message and enter the state BEARER CONTEXT INACTIVE.
The ACTIVATE DEFAULT EPS BEARER CONTEXT REJECT message contains an ESM cause that typically indicates one of the following cause values:
#26: insufficient resources;
#31: request rejected, unspecified; or #95 – 111: protocol errors.
IE’s include:
EPS bearer identity
Activate default EPS bearer context reject message identity
Reference 3GPP TS 24.301