LTE: What will happen if MME fails to send modify bearer request message to SGW during the attach procedure ?

Question

In case of SGW relocation, MME sends CSRequest to new SGW, now question how does a SGW come to know that CS Request is received as part of attach procedure or handover procedure ?

Answer 1

Modify Bearer Request message is sent from MME to SGW as part of attach procedure. This message carries information of tunnel ids which are created at eNodeB to receive the downlink data from the SGW. If MME gets failed to send MBR to SGW, SGW would not be able to send downlink data for UE. However, eNodeB would be able to forward uplink data to SGW for an UE.