Is there any nas signalling/messages before RRC connection in LTE also like to know how enodeb selects MME?

Question

There are couple of procedures are defined which consist of NAS as well as RRC signalling messages exchange.
Some of the NAS message sends to an UE through RRC Connection Reconfiguration message as piggybacked and some as DL Info transfer.

I want to know, Is there any procedure exists in lte when an UE receives RRC Connection Reconfiguration along with NAS message and responds back to network with NAS message first and then Reconfiguration Complete to eNodeB.

Usually, I saw UE sends RRC Connection Reconfiguration Complete message first then NAS response message.

Answer 1

No, as per my information NAS messages does not get exchanged prior to RRC connection setup.

How enodeb selects MME?
eNodeB selects an available MME to serve a particular UE based on typically network topology and location of the UE within the network, so that the best MME is selected e.g. to reduce the probability that the MME is changed.
As part of the UE Attach the eNB will query the DNS Server using the TAI for the address of the MME. Typically the DNS will have a pool of MMEs to select from in response to the query.
The format of the TAI FQDN is constructed as follows:
tac-lb.tac-hb.tac.epc.mnc.mcc.3gppnetwork.org
The DNS may also provide more than one MME address (candidate set) from which the eNB can select a MME.
Please refer for the following threads for more details -
http://tech.queryhome.com/13801/how-enodeb-selects-mme-while-executing-attach-procedure-for
http://tech.queryhome.com/84332/how-enodeb-selects-mme