7 Mar
2005
7 Mar
'05
12:20 a.m.
Maxim Sobolev wrote:
Alistair Cunningham wrote:
Maxim,
You're quite correct. I was generalising too much.
--
Alistair Cunningham,
Integrics Ltd,
Telephony, Database, Unix consulting worldwide
+44 (0)7870 699 479
http://integrics.com/
Matt,
Because SER handles SIP messages, not RTP streams, it cannot 100%
accurately record CDRs. For instance, if the BYE message is lost
because a client crashed, SER has no way of knowing when the call
ended or how much it cost. A BTBUA gets round this problem by having
the RTP packets come to it, so if a client crashes, the RTP stream
stops and the BTBUA knows the call has finished. The disadvantage of a
BTBUA is that it adds latency and doesn't scale well, because it needs
to handle all the RTP traffic.
This is not necessarily true. SIP permits building signalling-only
B2BUA, which if designed correctly will be able to handle up to 50-100
call setups/teardowns per second on any modern x86 hardware. This will
provide capacity sufficient for any mid-level ITSP - allowing to bill
more than 10 millions per month. If this is not sufficient then several
of such B2BUA can be installed in parallel to provide more scalable
solution. The problem with using either Cisco or Asterisk as SIP B2BUA
is that they handle both signalling (SIP) and media (RTP), which makes
them less scalable and introduces the problem with increased latency,
losses and jitter.