Friday, January 18, 2013

lte Emergency Call Secrets

                                      LTE - Emergency Call Secrets:

          Dial Emergency numbers like 112,999,111 etc.
          Known Emergency numbers are already stored in the USIM/UE.
          MME can also provide the Emergency number List in Attach accept or TAU accept.
          If Emergency number list is provided by the MME, it is stored in the USIM and when the user initiate a call            to one of the number provided in the list then UE treat it as a Emergency number and initiate Attach procedure with Type Emergency_attach.

  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. In that case MME provides its default APN and Qos and procced the emergency call.

  1. MME rejects the emergency call when APN received from UE is not configured in MME      Emergency APN list.

  1. MME rejects the emergency call only when HSS sends Authentication failure with cause ‘IMSI unknown’ in case of MME is configured to contact the HSS. For all other authentication failure cause MME proceed with the call successfully.
  1. When a UE attached normally(non-emergency) with the Lte network it can also calls for emergency services by sending PDN connectivity request with request type emergency.

  1. UE can not create two emergency default bearers. It can be one default and other is dedicated.
  1. UE can create any no. of dedicated bearer with emergency default bearer but the ARP(Qos) value should be same for all the bearers and the IMSI authentication is mandatory.

  1. Bearer modification is not possible for emergency bearers.

  1. 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).

  1. Once the call is completed UE need not to detach. As soon as UE goes into idle mode, MME automatically release the call.

To know about MME configuration for Emegency Click  MME EmergencyConfiguration Data


  1. About the point 6. UE can create dedicated bearer
    if it is only authenticated. Could you refer the spec and section please?

  2. About point 3, why the unknow IMSI can not make an emergency call?

    1. Because all the IMSI's are registered & known to the HSS before its use. If HSS does not have any information about the IMSI that means it is invalid.
      Authentication failure can be acceptable due to any reason for Emergency Call.

  3. Could you please provide the reference for point 7?

    1. 3GPP TS 23.401 version 11.3.0
      Section Handling of PDN Connections for Emergency Bearer Services

    2. Could you please provide the reference for points 1 and 2?