LTE attach procedure after random access

After random access, UE acquired some RRC dedicated configuration, but in order to establish DRB, UE has to follow NAS protocol and make connection with MME to setup signaling channel.

NAS protocol is in 3GPP 24.301, to search certain IE from ASN decoded log in 24.301, add space between each word. I.E. Search "MMEGroupID", use string "MME Group ID"

Following NAS procedure is quoted from http://www.sharetechnote.com/

Following is a very good chart explained all channels of all layers. Also quoted from http://www.sharetechnote.com/

Comments regarding UE attach procedure
1. IE ESMInformationTransferFlag in attachRequest (RRCConnectionComplete) has to be set to '01'H in order for MME to send ESMInformationRequest. UE has to respond ESMInformationRequest with ESMInformationResponse which contains requested APN information.
2. After proper detach, when attach again, UE will not need to be authenticated again for certain amount of times depending on MME's configuration.
3. If UENetworkCapability is included in attachRequest or trackingAreaUpdateRequest, MME will send authenticationRequest to UE.