I have seen many wireshark logs and found mainly two types of attach request, one is known as "EPS attach" and another one is known as "Combined attached". I want to know, how does UE nas layer decide on "attach type" in attach request ?
Does UE send APN information while registering with network using the "Attach request" message ? How MME come to know that UE should attach to APN "XYZ" ?
From UE point of view, I want to know when UE triggers integrity protected Attach request and when it sends as plain message ?
An LTE UE can attach to network without having any IMSI. Does there any call flow change or handling diffence w.r.t attach procedure ?
