Hello,
We have a system which sends radius accounting messages to our radius.
Based on this accounting we charge subscribers. Interim accounting is
enabled so for a normal session we get one Start, zero or more
Interim-Update and one Stop packets. Every accounting packet except
Start contains Acct-Session-Time which is "how many seconds the user has
received service for" according to rfc2866. That means that it's always
incrementing during a session. To charge a session in chunks we
calculate a difference between the recent value and the previous one. In
our case we get Interim-Update records every 15 minutes, so this
difference between 2 sequential Interim-Update records is 900 secs +/-
2-3 secs. What happens when for some reason one Interim-Update records
is lost? In such case we get diff - 1800 secs and everything is fine.
However recently we discovered that a system which is sending accounting
records will resend unconfirmed packets after some time (I do not mean
Retransmit-Interval/Retransmit-Count feature which exists on most if not
all NAS-es). The later means that in some cases we can get an
Interim-Update packet with Acct-Session-Timeout = 1800 calculate a
difference against a Start record (that is 1800 secs) and charge it,
later get Interim-Update with Acct-Session-Timeout = 900. So my
questions can be stated like this:
1. Is it better to charge the whole difference between current and
previous Session-Timeout values and later ignore any previous packets
which arrive out of order, or it's better to charge last 15 minutes (I
get Interim-Update records every 15 minutes as already stated above) and
do not care about missing parts (if any) of a session?
2. Is it a correct behavior of a NAS to store accounting information on
it's internal disk if it can't get acknowledgment for accounting
request/s and resend it later?
Best Regards,
George Chelidze
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