Is it necessary to assign an ip address during the attach procedure ?

Question

This query come out to give answer one of the query. Is really UE should perform combined attach procedure( EPS and non-EPS) for handover between LTE to other 3GPP technology like UMTS/GERAN ?

Answer 1

LTE network supports always on IP connectivity. It means UE should have an IP address until it gets de-registered.
Attach is the procedure by which UE gets registered with MME/Network. I always saw an IP address assignment done by either PGW or MME and sends to UE on attach accept message.

Comments

+1. Just adding to Vimal's answer. As part of Attach Procedure, the UE sends an attach request. This request msg also contains a NAS pdu inside it which is nothing but the "PDN Connectivity Request" for the establishment of default bearer. PGW assigns the IP address and MME forwards it to the UE in the Attach accept msg.