· 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