LTE: Activate Default EPS Bearer Context Request

·          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 is a non-Guaranteed Bit Rate (GBR) bearer. A dedicated bearer can be either a GBR or a non-GBR bearer.

·           The default bearer remains established throughout the lifetime of the PDN connection to provide the UE with IP connectivity to the PDN

·           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

·           Once the UE is successfully attached, the UE can request the MME to set up connections to additional PDNs. For each additional connection, the MME will activate a separate default EPS bearer context

·           The MME shall initiate the default bearer context activation procedure by sending an ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message

·           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

·           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 (Procedure Transaction Identity) from the PDN CONNECTIVITY REQUEST message and include it in the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message

·           Typical IEs in  ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message include EPS bearer identity, Procedure transaction identity (PTI), EPS QoS, Access point name (APN), PDN address, Negotiated QoS, Negotiated LLC SAPI, Packet flow Identifier, APN-AMBR (APN aggregate maximum bit rate), ESM cause, and Protocol configuration options etc…

·           The network shall include the IE ESM cause, if the network allocated a PDN address of a PDN type which is different from the PDN type requested by the UE

Reference 3GPP TS 24.301

Example: ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST with Attach Accept message