NSAPI changes Acct-Session-Id from upstream provider

[Gabriel Marais]

Hi Guys

This might be off topic but I was wondering if someone with more
knowledge than me, would be able to confirm the following :-

In a mobile network scenario with thousands of IoT devices

On our radius servers, we've been noticing a lot of 0-byte sessions on
our databases and upon investigation, we've seen the following
behaviour :-

> Authentication Request Received
< Access Accept sent back
> Accounting Start Packet Received with a Acct-Session-Id
< Acknowledgement sent back
> Interim Accounting Packet Received - This time with a different Acct-Session-Id for the same connection

** At this point, things start going bad as we are not able to update
the original DB entry created with the Acct Start Packet, since the
Acct-Session-Id differs between the packet received in the Accounting
Start Packet and the Interim Accounting Packet.

This results in a 0-session entry in the DB for the Accounting Start
Packet entry as a new entry is written into the DB based on the new
Acct-Session-Id received in the Interim Accounting packet.

Any subsequent packets received with a different Acct-Session-Id,
results in writing a new DB entry when the Interim Accounting Packet
is received.

We queried this with the upstream provider, and they advised that the
3GPP-NSAPI number changes when packets are received and they claim
that the Acct-Session-Id on their side would change based on the
3GPP-NSAPI value that could (and in most cases) changes.

< Acknowledgement Sent back

>From what I've been reading, The Acct-Session-Id should remain
constant for the entire PDP context/session, even when the NSAPI
changes because the Acct-Session-Id is meant to uniquely identify the
entire user session. NSAPI changes are considered sub-sessions within
the main PDP context and keeping the same Acct-Session-Id helps
maintain session continuity for billing and tracking purposes, which
is exactly our use case for accounting which is not working as
expected.

Any thoughts and insights would be appreciated if someone faced a
similar situation.


Many thanks, Gabriel