S6a/S6d [MME/SGSN <-->HSS]


Some times S6a/S6d interfaces are treated as two separate interfaces but here we treat them as single because both have same application identifier(16777251).S6a interface is between MME-HSS and S6d interface between SGSN-HSS.

This section gives abstrace of s6a/s6d interface. In LTE network HSS (Home Subscriber Server) is a database that contains Authentication Information and Subscriber's Data  such as Services associated, Location Information etc. Where MME shall take care of mobility of UE/Subscriber. This interface is used to Authenticate Subscriber, providing services to subscriber, to store location information of subscriber sent by MME.There are eight messages are exchanged between MME/SGSN and HSS. Four of them are invoked by MME and rest four are invoked by HSS.

1)AIR/AIA (Authentication-Information-Request/Answer):- MME fetches Authentication data from HSS to authenticate subscriber.

2)ULR/ULA (Update-Location-Request/Answer):- MME stores its own identity at HSS, and feteches subscription data from HSS.

3)NOR/NOA (Notification-Request/Answer):- MME stores PDN address and other attach information at HSS.

4)PUR/PUA (Purge Request/Answer):- MME informs the HSS that UE is inactive for a long period that why MME has deleted the Subscription Data received in previous ULR from its end. 

5)IDR/IDA(Insert-Subscription-Data-Request/Answer):- It is invoked by HSS only when a subscriber is attached and there is change in subscriber profile at HSS end then same change to be reflected at Subscriber profile at MME (sent in ULA) end as well.

6)DSR/DSA (Delete-Subscriber-Data-Request/Answer):- It is invoked by HSS only when Subscriber is attached and some data is deleted at HSS. Now HSS informs MME with this message that some part of subscription data is deleted at HSS.

7)CLR/CLA(Cancel-Location-Request/Answer):- Invoked by HSS to detach the subscriber.

8)RSR/RSA(Reset-Request/Answer):- Invoked by HSS, to inform MME that HSS goes down for some time, kindly sync the data and send fresh location/PDN information at HSS.

Detail behavior with example
2. ULR/ULA (Update-Location-Request/Answer)
3. NOR/NOA (Notification-Request/Answer)
6. DSR/DSA (Delete-Subscriber-Data-Request/Answer)
8. RSR/RSA(Reset-Request/Answer)


Your Comments /Suggestions and Questions are always welcome. I would try to clear your doubts with best of my knowledge. So feel free to put Questions.

28 comments:

  1. Not sure you are right, S9 Application ID is 16777267, please check
    http://www.iana.org/assignments/aaa-parameters/aaa-parameters.xml

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  2. This section talks about S6 and not S9

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  3. Hi,

    Could you please provide me diameter traces for ULR/ULA message?

    Regards,
    Chandra

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  4. Hi,
    I could not find detailed explanation of how CLR/IDR work from foreign HSS to home MME when there is a Diameter relay in the middle with topology hiding. Could you pls put a reference or detailed explanation?

    Thanks,
    Dave

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    Replies
    1. Hi Dave

      HSS can't be of Foreign, It MUST be of Home. That is why it is Home Subscriber Server.

      Only Home/operator knows what all subscriber I have.

      Thanks for your query.
      Happy to help you again.
      Team-Diameter

      Delete
  5. Hi Parashar,
    Thanks for replying.
    In roaming case, you have a roamer belonging to operator A, visiting a PLMN of operator B, but therefore the local MME (of OP A) authenticates the sub. with a foreign HSS (OP B). Yes the HSS is a Home subscriber Server which is exactly what it is doing with the subscriber, granting service to its UE. So I was interested in the very details of the CLR transaction when the foreign HSS send a CLR after a while or when the subs authenticates thorough another MME then F-HSS sends CLR to the previous MME...

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    Replies
    1. Hi Dave

      Following link shall help you.

      http://diameter-protocol.blogspot.in/2013/04/clrclacancel-location-requestanswer.html

      Delete
  6. Hi

    Can I get the S6a, S6d, S9 message list each other?
    Or Could you tell me how can I classify the message?

    Thanks.
    Kim.

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    Replies
    1. Hi Kim

      S6a/S6d have same eight (8) messages that are discussed above.
      We can uniquely identify message with the help of Command-Code and Application-Identifier.

      Following link might help you.
      (Diameter Message Structure and Message Flow)
      http://diameter-protocol.blogspot.in/2011/05/diameter-message-structure-and-message.html

      Delete
  7. Priyadarshi,
    Superb reference. Thanks very much!

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  8. How is the MME and HSS are configured to connect to a external Diameter Router? Rightnow MME and HSS are connected via S6a. that needs to be broken and connected to Diameter router.

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    Replies
    1. Hi Orral Sezer,

      I hope by Diameter Router you are referring to Diameter Relay.

      from your comment i have understood that; you are looking what interface shall be used between Relay and MME , Relay and HSS.

      MME <----- s6a ----> Relay <----s6a----> HSS


      I hope my information shall help you. if not,
      Kindly explain your query again; because not able to understand what exactly you are looking for.

      Delete
    2. Sounds like a roaming question. vMME to hHSS is usually via an IPX provider.

      Delete
  9. Anyone know how to simulate (open source SW) the MME s6a interface to test diameter SCTP against HSS

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  10. Hi,
    Could you please provide some trace of these packets which can be opened in Wireshark?

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  11. Hi, Any one can help me, where can i get the test case or testing scenarios for s6a & s6d interface,functional & non functional also.

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  12. Seagull simulator will help you to test s6a interface

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    Replies
    1. Hi Prasant,

      Are you sure that seagull can be used to simulate the below S6a/S6d interface messages.

      1)AIR/AIA (Authentication-Information-Request/Answer)
      2)ULR/ULA (Update-Location-Request/Answer)
      3)NOR/NOA (Notification-Request/Answer)
      4)PUR/PUA (Purge Request/Answer)
      5)IDR/IDA(Insert-Subscription-Data-Request/Answer)
      6)DSR/DSA (Delete-Subscriber-Data-Request/Answer)
      7)CLR/CLA(Cancel-Location-Request/Answer)
      8)RSR/RSA(Reset-Request/Answer)

      Delete
  13. home plmn to visitor plmn moving hss sending what information to the mme

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  14. In Case of Roaming MME will send AIR to authenticate subscriber first to Home HSS or directly send a ULR to Home HSS to update its location and to know what are the services granted

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    Replies
    1. Hi

      MME shall send AIR first, as PLMN id is changed. PLMN id is a mandatory parameter to generate Authentication credentials (Vectors) in LTE

      Thanks for your query.
      Happy to help you again.
      Team-Diameter

      Delete
  15. hi all..can anyone help or provide your feedback as while performing LTE attach after successful ULR we can see purge initiated from MME.

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  16. Hi Site Author, thanks for a good, simple article that explains DSR. If a DSR flag "Trace-Data-Withdrawal" bit is set to 1, what might this indicate, I referred to 29.272 but as usual its just not that easy to figure out from specs alone. I'd appreciate some feedback.

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    Replies
    1. Hey Nik,

      Trace-Data AVP received in the subscriber data (of ULR or IDR) shall inform the MME/SGSN to start a trace session for the subscriber in question. More about the tracing can be found is TS 32.422. The DSR flag indicates to MME/SGSN to stop the active tracing and clear the trace data, if any, for the trace-reference-id provided in the Trace-Reference AVP, for the given subscriber. In case of multiple active tracing sessions, there needs to be multiple DSR messages with different Trace-Reference AVPs. Absence of Trace-Reference AVP will mean that all active tracing-sessions needs to be aborted/stopped and their data deleted.

      Hope that helps.

      Delete
  17. Thanks a lot for theoretical explanation!
    Could anybody share appropriate configuration file for freeDiameter ULR/ULA transmission? Is the test_app.fdx sufficient?

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  18. Hi
    after MME send PUR to HSS, MME purge the EMM and ESM of the user. if the user wanna connect to network again, does he send the attach request?

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  19. Hi,

    I would like to know whether the Seagull simulator will support the simulation of S6a/S6d interface messages.
    Can you please let me know whether it's possible to simulate the below list of S6a/S6d interface messages.
    1)AIR/AIA (Authentication-Information-Request/Answer)
    2)ULR/ULA (Update-Location-Request/Answer)
    3)NOR/NOA (Notification-Request/Answer)
    4)PUR/PUA (Purge Request/Answer)
    5)IDR/IDA(Insert-Subscription-Data-Request/Answer)
    6)DSR/DSA (Delete-Subscriber-Data-Request/Answer)
    7)CLR/CLA(Cancel-Location-Request/Answer)
    8)RSR/RSA(Reset-Request/Answer)

    ReplyDelete