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We are working on an HSS project for a client, and are stuck on a strange issue. Right now we are in POC stage.

When we send ULA to MME, right after it, MME sends PUR to us for the same subscriber and the UE does not attach to 'network' (obviously). MME is not under our control (roaming partner), so we cannot get the logs from it.

We have tried to imitate ULA as per another working UE in the same roaming partner network (this connects to live HSS, not ours), and it did not work.

Can anyone please guide me what could be wrong?

Please let me know if you need more information.

Aakash
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2 Answers2

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Take a good look at your ULA. Could be that you include in the ULA some unsupported data by MME

I would suggest to check 3GPP TS 29.229 there is an AVP called Supported-Features which is included in the ULA and might be problematic to the MME.

Oded Itzhaky
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  • thank you for answer. However, as I said, we have tried to simulate the ULA as per another working ULA with same roaming partner's MME, with same value of Supported-Features avp. It didn't work. Right now, we are trying to configure our test sim on live network and trace the messages. – Aakash Jan 25 '18 at 06:22
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Location update procedure normally helps to update MME or SGSN with user subscription data and also to provide the HSS with other user data, such as terminal information, identity of the MME or SGSN currently serving the user.

In the scenario where issue is occurring, the IE 'Supported Features' could have different info which is not acceptable at this particular MME and hence it could be one potential reason for triggering PUR for the subscriber.

One another reason could be that somehow it is being determined that the UE has been inactive for several days and hence PUR is used to indicate subscriber's profile deletion of the same. You may also need to check the timer configured for PUR at MME and whether any issue is causing it to override and send the same.

In general, once ULR is received, the HSS shall checks for subscription details and accordingly HSS shall send ULA with subscription data , else an error shall be returned in ULA. Subscription data have list of APNs and other details.

Check for proper diameter logs and result codes (success/error codes). Also, there are lot of access related data (restriction, access) in subscriber data and also barring details which should be checked bit by bit as per your deployment scenario. You may need to dump the ULA message , AVPs and cross-check which could be a source for triggering PUR.

Once the ULA is success, MME shall initiate tunnel establishment procedure using GTP-C (create session request) with SGW and PGW. If the tunnel creation procedure fails, the purge request (PUR) shall be sent by MME to delete the roaming data in HSS.

Enabling logs in MME, HSS and UE can help to take closure to the root cause. Can you kindly share the logs of the same (if issue persists).

Karthik Balaguru
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