On Fri, 9 Mar 2007, Zeeshan Zakaria wrote:
Gordon, thanks for such a detailed and full of information email. It
helped me and must have helped hundreds of others on this mailing list.
It's quite a simplistic approach really - I think it'seasier to do
physical separation at times than dive into the weird and whacky world of
QoS, etc...
In my scenario, for this client whom I am working for, their main issue
has always been echo. They have about 50 extensions, with 20 in the
office, busy office, calls all the time, up to 5 at any given time, 10
remote extensions and other virtual extensions just for voicemail
purposes. 5 IVRs and 4 queues, one VoIP line and main trunk a T1 PRI.
PRI is used for all incoming and outgoing calls except for long distance
calls where VoIP line is used.
I woudln't be sure that the echo is caused by the internal network. I'd be
fairly sure that if you separated the asterisk box from the rest of the
network that you'd still hear echo...
Ethernet switches do switch very well and as long as they don't have
internal issues then 2 devices connecting point to point over the switch
really should look like a bit of wire. You haven't said, but maybe you
have the phones wired in-line? In which case the PC behind the phone
talking to another PC or server on the network might well interrupt the
phone calls, but even then I'm not sure it would introduce echo. If they
are doing P2P down/uploading over the Internet, then unless you have a
very high speed Internet connection (over 10Mb/sec!) then that's unlikely
to interfere with the VoIP traffic, even without QoS.
One thing to do is make sure everything is talking the right speed though
- make sure the ethernet switch realyl is a switch an not a passive hub.
(if it has a collision LED then it's a hub and should be thrown in the
bin) and make sure all ports come up at 100Mb (or 1Gb if it's a Gb switch)
full duplex.
I am thinking of going with HWEC and also using a good QoS switch. Right now
there is only one switch (don't remember the name) and it is handling all
the VoIP and data traffic. Sometimes voice breaks, and it must be because of
interference from data traffic. But this is not a very serious problem and
one switch with QoS should be able to handle it. Am I right here? Even if
someone starts using P2P software.
There is a lot of information on the wiki about Echo. Mostly to do with
analogue lines though and I've as yet, no 1st hand experience with BRI or
PRI circuits
Start here:
http://www.voip-info.org/wiki/view/Asterisk+echo+cancellation
Current router is a linksys WRT54GL - Wireless-G Broadband Router. Is it
good enough if I get a good switch? Can you suggest which switch I should
get. I was looking on the Internet and found switches like Adtran NetVanta
which are very expensive. What do they do which makes them so expensive? And
in my case, is that the type of switch which I need or is there something
cheaper out there too. I am ok without PoE.
That has a 4-port 10/100 switch and I'm guessing your internet connection
is cable (or you have another upstream ADSL modem).
I've had good results with DLink switches and Netgear switches. Even Cisco
switches work ok, if a shade on the expensive side. (but no-one got sacked
for buying cisco ... yet ;-)
If you want a reasonable switch that has most features you need, I'd look
at:
http://www.netgear.co.uk/smart_switch_fs726t.php
but I've no 1st hand experience of them, and they're 10/100 only (with 2
Gb ports - and I'd connect one to the asterisk box, the other to the
router on the 'VoIP' switch, and on the other, one to a server if they
have one and one to the router) So for 20 PCs and 20 phones, you'll need 2
of these.
You typically pay a premium on ethernet switches for "management". This
will give you some sort of command interface to the switch (web, serial,
telnet) to let you fiddle with it - set link type/speeds, enable snmp
monitoring, create VLANs, and so on. I'm not convinced of the requirement
for this in a small office, but it may be features management desire...
If you can get the echo cracked on the office extensions out through the
T1 line, then all ought to be fine. But if you have a lot of remote SIP
users then you might have problems with your internet line - then you need
to see if you can enable QoS on the router - which may help, but theres
almost mothing you can do to shape incoming traffic, as by the time the
rotuer see it to shape it, it's too late, as it's already come over the
wire... So your single SIP outgoing line might suffer, as well as your
incoming remote SIP users if you have a lot of people on the LAN doing
heavy interweb stuff...
You might even want to start monitoring the router, if possible using
traffic graphing software like MRTG, etc.
Good luck!
Gordon
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