How MME handles Attach Req for emergency or non-emergency call ?

Question

Does there any difference of handing Attach Request for these two scenarios ?

Comments

Check the Following Links - should be useful
http://www.leliwa.com/downloads/VoLTE_Emergency.ppsx
http://www.lteandbeyond.com/2012/01/lte-attach-procedure.html

Answer 1

Default Emergency APN should be configured in MME in case where UE does not send APN in attach request and also HSS does not provide it in Subscription data for Emergency attached UE or Authentication is optional.
1. MME rejects the emergency call when APN received from UE is not configured in MME Emergency APN list.
2. MME rejects the emergency call only when HSS sends Authentication failure with cause ‘IMSI unknown’.

If any one of the attach type or the request type in Attach Request is non-emergency then call is considered as normal call(non-emergency call).

Answer 2

Initial UE Message on the S1 interface has a RRC Establishment IE, which will indicate whether the call is an emergency call or other priority. Consequently the MME can take appropriate action e.g. decide whether to accept USIM-free calls/IMEI identity allocate ARP to the E-RAB(s), and anything it wishes to do.

Some countries allows call to be made without a USIM present, in which case the NAS identity presented by the UE will be the IMEI.