PUR/PUA (Purge Request/Answer)

As the literal meaning of Purge implies is to remove. When MME/SGSN shall remove the data of a subscriber from its (temporary) storage because of following reasons then MME/SGSN shall trigger PUR toward HSS to notify that subscriber is in-active for several days or by MMI (Man Machine Interface) from MME/SGSN.

Before PUR message it was assumed that subscriber is attached atleast once (i.e. Subscriber Profile is downloaded to MME or SGSN) and PUR comes from the same MME/SGSN on which subscriber is attached (i.e ULR is triggered). If it is received form other MME/SGSN then HSS shall return success no need to freeze temporary identity.

When MME send PUR to HSS then HSS marks(set a flag) that subscriber is Purged from MME, similarly for SGSN, HSS marks that subscriber is purged from SGSN. In response HSS shall send an indication to freeze the M-TMSI (Temporary Identity) to MME for some time so that same temporary identity can be used when subscriber became active, similarly to HSS sends freeze P-TMSI indication to SGSN.

When Combined MME-SGSN sends deletes a specific section of data then it shall use PUR-Flag to inform HSS that only MME or only SGSN specific data is deleted.

Following cases shall be performed.


STAND-ALONE MME




STAND-ALONE SGSN


COMBINED MME-SGSN without PUR Flags


COMBINED MME-SGSN Only MME data is deleted.


COMBINED MME-SGSN Only SGSN data is deleted.

Your Comments /Suggestions and Questions are always welcome,  shall clarify with best of knowledge. So feel free to put Questions.

12 comments:

  1. Wow. Awesome article. Please do more articles like this in the future. Very informational and knowledgeable. I will expect more from you in the future. For now i will just bookmark your page and surely I'm gonna come back later to read more. Thank you to the writer!


    Rica
    www.imarksweb.org

    ReplyDelete
  2. Hello. Now we have an issue in our network. We are testing LTE roaming. When our sim in a visited plmn make a location update, after the location update is successful, the visited MME sends a PUR to our HSS. We don't know why ?

    ReplyDelete
    Replies
    1. If (new) Visited MME is sending PUR just after successful Location Update(ULR/ULA). It is to share EPS-Location-Information with HSS. Kindly manage to check Supported feature AVP and PUR-FLAG AVP in trace.

      Delete
    2. Hello, we have exactly same problem. Did you able to resolve this issue? if yes, please tell us how did you do that?

      Delete
    3. Hi Aakash

      As you know Purge is sent by MME when UE is not active for a longer period of time. hence MME deletes data sent by HSS from its-end and notify the same to HSS.


      if you are getting purge very frequently for an IMSI please check followings
      -- Purge timer @ MME configuration
      -- Check in previous messages of that IMSI EPS-LOCATION-INFO is not asked by HSS.
      -- Please share the trace if possible.


      Regards.

      Delete
  3. hi all,, we are also facing the same issue in LTE attach as while testing with roaming SIM's after successful ULA we are seeing purge initiated from MME. can anyone help or provide your feedback to fix this issue.

    ReplyDelete
    Replies
    1. If (new) Visited MME is sending PUR just after successful Location Update(ULR/ULA). It is to share EPS-Location-Information with HSS. Kindly manage to check Supported feature AVP and PUR-FLAG AVP in trace.

      Delete
  4. Hi all,
    Could you tell what we should check with more detail? we do not know why our MME is sending this Purge. what we should check.

    ReplyDelete
    Replies
    1. Hello, we have exactly same problem. Did you able to resolve this issue? if yes, please tell us how did you do that?

      Delete
    2. Hi Aakash

      As you know Purge is sent by MME when UE is not active for a longer period of time. hence MME deletes data sent by HSS from its-end and notify the same to HSS.


      if you are getting purge very frequently for an IMSI please check followings
      -- Purge timer @ MME configuration
      -- Check in previous messages of that IMSI EPS-LOCATION-INFO is not asked by HSS.
      -- Please share the trace if possible.


      Regards.

      Delete
    3. Hi,
      We have the same problem but the PURGE is just sent after the LU, no after a long period.
      Could you please help us?

      Delete
    4. Hi Victor & Aakash,

      After analyzing above scenario, we have reached to a point that there could be a case.
      Where HSS sends a data that is not supported/limited by MME (may be one of the supported feature bit, or and configuration feature @MME) and MME is unable to process ( or failure during processing) Subscription data even after DIAMETER_SUCCESS in ULA i.e. not initiating message toward Gateway.

      In this case MME left with only PURGE message to notify HSS that IMSI is not even registered with NETWORK and remove MME name that showing IMSI is Attached/Registered in HSS.

      Kindly manage to share complete trace on teamdiameter@gmail.com

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

      Delete