The purpose of this procedure is to modify an EPS bearer context with a specific QoS and TFT.
This procedure is initiated by network, it may also be initiated as part of the UE requested bearer resource allocation procedure.
The network may also initiate the EPS bearer context modification procedure to update the APN-AMBR of the UE
There are 3 messages exchanged in EPS bearer Context Modification Procedure:
Modify EPS bearer context request
Modify EPS bearer context accept
Modify EPS bearer context reject
Modify EPS bearer context request
The MME shall initiate the EPS bearer context modification procedure by sending a MODIFY EPS BEARER CONTEXT REQUEST message to the UE, starting the timer T3486, and entering the state BEARER CONTEXT MODIFY PENDING
The MME shall include an EPS bearer identity that identifies the EPS bearer context to be modified in the MODIFY EPS BEARER CONTEXT REQUEST message.
IE’s present in this message are:
EPS bearer identity
Modify EPS bearer context request message identity
New EPS QoS
TFT
New QOS
Modify EPS bearer context accept
Upon receipt of the MODIFY EPS BEARER CONTEXT REQUEST message, the UE shall stop timer T3396 if it is running for the APN associated with the PDN connection, check the received TFT before taking it into use and then send a MODIFY EPS BEARER CONTEXT ACCEPT message to the MME.
The UE shall use the received TFT to apply mapping of uplink traffic flows to the radio bearer if the TFT contains packet filters for the uplink direction.
IE’s present in this message are:
EPS bearer identity
Procedure transaction identity
Modify EPS bearer context accept message identity
Modify EPS bearer context reject
Upon receipt of the MODIFY EPS BEARER CONTEXT REQUEST message, the UE may reject the request from the MME by sending a MODIFY EPS BEARER CONTEXT REJECT message to the MME.
The message shall include the EPS bearer identity and an ESM cause value indicating the reason for rejecting the EPS bearer context modification request.
The ESM Cause can be:
#26: insufficient resources;
#41: semantic error in the TFT operation;
#42: syntactical error in the TFT operation;
IE’s present in this message are:
EPS bearer identity
Procedure transaction identity
Modify EPS bearer context reject message identity
ESM cause
Reference 3GPP TS 24.301
