LTE: ESM Information Request Procedure

·        The ESM information request procedure is used by the network to retrieve ESM information, i.e. protocol configuration options, APN, or both from the UE during the attach procedure if the UE has indicated (in the PDN CONNECTIVITY REQUEST) that it has ESM information that needs to be sent security protected.

·        The purpose of this procedure is to provide privacy for the ESM information if ciphering is enabled in the network.

·        The network initiates the ESM information request procedure by sending a ESM INFORMATION REQUEST message to the UE and starts the timer T3489.

·        This message shall be sent only after the security context has been setup, and if the ESM information transfer flag has been set in the PDN CONNECTIVITY REQUEST message.

·        The MME shall set the EPS bearer identity of the ESM INFORMATION REQUEST message to the value "no EPS bearer identity assigned" and include the PTI from the associated PDN CONNECTIVITY REQUEST message.

·        After receiving the ESM INFORMATION REQUEST message, the UE shall send an ESM INFORMATION RESPONSE message to the network.

·        The UE shall include all the protocol configuration options that need to be transferred security protected, and APN if required, to the network in the ESM INFORMATION RESPONSE (see the example below)message.

·        The UE shall set the EPS bearer identity of the ESM INFORMATION RESPONSE message to the value "no EPS bearer identity assigned" and include the PTI from the ESM INFORMATION REQUEST message

Reference 3GPP TS 24.301

Example:   ESM INFORMATION REQUEST message

Example:   ESM INFORMATION RESPONSE message  

LTE: Modify EPS Bearer Context Reject

·        If the MODIFY EPS BEARER CONTEXT REQUEST message cannot be accepted by the UE, then it sends a MODIFY EPS BEARER CONTEXT REJECT message to the MME.

·        This message shall include the EPS bearer identity and an ESM cause value indicating the reason for rejecting the EPS bearer context modification request

·        The MODIFY EPS BEARER CONTEXT REJECT message contains an ESM cause that typically indicates one of the following ESM cause values:

#26: insufficient resources

#41: semantic error in the TFT operation

#42: syntactical error in the TFT operation

#43: invalid EPS bearer identity

#44: semantic error(s) in packet filter(s)

#45: syntactical error(s) in packet filter(s)

#95 – 111: protocol errors

·        Upon receipt of the MODIFY EPS BEARER CONTEXT REJECT message with ESM cause value other than #43 "invalid EPS bearer identity", the MME shall stop the timer T3486 and abort the EPS bearer context modification procedure.

·        If the network receives the MODIFY EPS BEARER CONTEXT REJECT message with ESM cause #43 "invalid EPS bearer identity" the MME locally deactivates the EPS bearer context(s) without peer-to-peer ESM signalling

Reference 3GPP TS 24.301

Example:  MODIFY EPS BEARER CONTEXT REJECT message