For those who might be interested, The Society of
St. James now has an Asterisk system in service at
one of its projects.
The system consists of a small Dell PowerEdge
server [1], currently running Asterisk 1.2.16.
There's two BT Featureline Compact analogue lines
terminated in a Sangoma A200 [2] with a single
dual-line FXO module. The A200 is the cheaper
model, without hardware echo-cancellation.
On the client side, there's nine Atcom AT-530 [3]
VoIP phones, using SIP to talk to the Asterisk
box. They use straight a-law PCM codec, to keep
the load on the server low.
The dial-plan is quite simple, with all incoming
calls being directed to a reception desk. There is
automatic diversion to a group of office phones if
the reception line is busy or not answered. Out-
going calls can use either line, but prefer the
second. I did have an auto-attendant initially,
but it seemed to confuse the clients.
There were some teething problems to start with -
I think they've mostly been solved. Having ten
days (real time) to set the project up didn't
help, so the first proper testing was when the
whole network went live on the Monday morning!
The two main problems we experienced were with the
analogue lines - detecting answer and hang-up, and
spurious disconnections.
Initially, the Asterisk system couldn't detect
answers and hang-ups on out-going calls. Calls
worked, but time-outs had to be removed from the
dial-plan, as Asterisk didn't know the call had
been answered. The solution to this was to
persuade BT to enable Line Polarity Reversal on
both analogue lines, and enable the relevant
settings...
answeronpolarityswitch=yes
hanguponpolarityswitch=yes
in zapata.conf. The latter was easy; the former
required several fun hours on the phone to BT,
before I was able to speak to an Engineer in
person, and discover the magic incantation:
"Called-Party Answer". One call to the sales line
later, and I had polarity reversal.
The other problem, of spurious disconnections, has
been a little more difficult to track down. The
reports of problems have ceased, so I think it has
gone away. Enabling polarity reversal certainly
helped, but I also disabled 'busydetect' and
'callprogress', which are marked as being
potentially unreliable.
The Asterisk system is working surprisingly well,
given how little time and concentration I've spent
on it. The project uses the phones heavily - two
lines aren't really enough - with calls to and
from clients and other agencies. The whole system
cost about UKP 800, including server, analogue
card, phones, and networking, and still has a good
bit of head-room for more lines or extensions.
Nick.
[1] Dell PowerEdge specs:
(Refurbished system from Jamie's)
Dual P3 866MHz processors
256MB PC-133 memory
Single 18GB 10k RPM SCSI disk
Debian Sarge, with Asterisk compiled from
source
[2]
http://www.sangoma.com/datasheets/p_a200-specs
[3]
http://www.atcom.cn/En_products_At530.html
--
Nick Chalk ................. once a Radio Designer
Confidence is failing to understand the problem.
