LTE: When the ESM Information Request message is sent by the MME to the UE ?

Question

What is the objective to send the ESM Information Request message to UE ? Does it part of attach procedure ?

Answer 1

When UE wants to provide the ESM information security protected, it enables a flag "ESM information security protected" in the PDN connectivity req(as a part of Initial Attach). Therefore the MME can obtain ESM info only after it establishes the NAS security context, which, once done, MME sends a ESM information req to UE to obtain ESM related information such as the PCO, APN, ECGI,TAI.

Answer 2

In ESM Information Request message, this signaling used to check the imei info; firstly will check with the old mme, if the old mme doesn't have this info, then it will send to ue in order to get imei info, this is part of the attach procedure.

Answer 3

In attach request message if UE set ESM information transfer flag ( The UE shall include this IE in the PDN CONNECTIVITY REQUEST message sent during the attach procedure if the UE has protocol configuration options (PCO) that need to be transferred security protected or wishes to provide an access point name(APN) for the PDN connection to be established during the attach procedure) ,before proceeding create session request MME will send ESM information request to UE .Yes its part of attach procedure