Phone is unreachable, changed or SMS memory is available - Notification Request and Answer (NOR-NOA )

NOR/NOA (Notification Request and Answer) is one of the simplest of message over S6a/S6d interface. Basic idea of this message is to inform HSS about change in Network and User Equipment information, when there is not change in user's location implies update location shall not triggered. So that HSS shall have latest information about subscriber and can notify to other entities that require received information.

Following information are share by MME to HSS with the help of NOR and HSS replies with Successful NOA if HSS has stored shared information successfully.

-*- Update of Terminal Information
    if user's device is changed then IMEI of it shall be sent to HSS

-*- If UE (Subscriber/User) become reachable to network.

-*- If UE (User-Equipment) has created space to receive one or more Messages (SMS).

-*- To inform about Support of IMS voice session over PS session in given Tracing Area and Routing Area.

-*- If there is change in UE's SRVCC capabilities.

-*- If there is change in dynamically allocated PDN-GW for an APN.

Message format of NAR-NOA shall be as following.

< Notify-Request> ::= < Diameter Header: 323, REQ, PXY, 16777251 >
                      < Session-Id >
                      [ Vendor-Specific-Application-Id ]
                      { Auth-Session-State }
                      { Origin-Host }
                      { Origin-Realm }
                      [ Destination-Host ]
                      { Destination-Realm }
                      { User-Name }
                    * [ Supported-Features ]
                      [ Terminal-Information ]
                      [ MIP6-Agent-Info ]
                      [ Visited-Network-Identifier ]
                      [ Context-Identifier ]
                      [ Alert-Reason ]
                      [ UE-SRVCC-Capability ]
                      [ NOR-Flags ]
                   [Homogeneous-Support-of-IMS-Voice-Over-PS-Sessions ]
                    *[ AVP ]

< Notify-Answer> ::= < Diameter Header: 323, PXY, 16777251 >
                     < Session-Id >
                     [ Vendor-Specific-Application-Id ]
                     [ Result-Code ]
                     [ Experimental-Result ]
                     { Auth-Session-State }
                     { Origin-Host }
                     { Origin-Realm }
                     [ OC-Supported-Features ]
                     [ OC-OLR ]
                    *[ Supported-Features ]
                    *[ AVP ]
                    *[ Failed-AVP ]

Your Comments /Suggestions and Questions are always welcome. We would try to clarify doubts with best of our knowledge. So feel free to put Questions. 


  1. hi Team ,
    What is the importance of MIP6-Agent-Info in APN configuration .

    1. this is the AVP which has the most updated PGW IP address.. so in case of Handovers MME will know which PGW to send Create session request to so that the handover is successful

  2. I am want to run diameter code with kernel sctp. but while compiling diameter code I am getting this error:

    error: netinet/sctp.h: No such file or directory

    Please help me to get out from this error.

  3. This comment has been removed by the author.

  4. Hi, Please suggest for below query.
    Is it expected that NOR should be sent whenever a user roams to new location?

    Thanks in Advance!

    1. Hi Rajesh Ji,

      For change in location there shall be Update location procedure. NOR shall be triggered by MME for one of the above stated reasons.

      Thanks for your query.
      Happy to help you again.