We have a small office installation running over a cable modem. (8M down, 500k up confirmed with numerous speed test sites) When a single call is up, call quality is fine. When a second call is up, outbound audio is immediately choppy. We're using ulaw, and confirmed that traffic with 2 calls is <175kbps in/out. (IAX connection out) Asterisk doesn't report any dropped frames, the internet connection looks fine, etc. We have a linux router in place running wondershaper that seems to be running fine (same as our other installations). Can someone suggest where to look? Could this be the ITSP?
Philipp von Klitzing
2010-Oct-15 15:07 UTC
[asterisk-users] Audio problems on cable modem link
Hi!> Can someone suggest where to look? Could this be the ITSP?- turn off IAX trunking mode - test with SIP to find if it IAX causing the trouble - capture the RTP traffice on the other side and let wireshark have a look at that stats (loss, jitter) Philipp
On Fri, Oct 15, 2010 at 8:53 AM, Michelle Dupuis <mdupuis at ocg.ca> wrote: When a single call is up, call quality is fine. When a second call is up,> outbound audio is immediately choppy. We're using ulaw, and confirmed that > traffic with 2 calls is <175kbps in/out. (IAX connection out) > > Asterisk doesn't report any dropped frames, the internet connection looks > fine, etc. We have a linux router in place running wondershaper that seems > to be running fine (same as our other installations). > > Can someone suggest where to look? Could this be the ITSP? >It could be your traffic shapper, the ITSP, your local network, the ISP's network, or the internet backbone - basically anywhere in-between. You only have control over your local network, so I'd start there. Look for duplex mismatches (hint: if one end is set to "auto" or not able to be set manually, the other end should also be auto, never full [don't worry, they'll negotiate full, but only if both ends are set to auto; otherwise, the auto end will negotiate half due to the end running full not broadcasting capabilities when hardset]). That said, I've never felt great about using the internet for phone calls - you can't controll anything else in the chain, so the possibility of problems is huge - and most of the time you can't fix it. I know lots of people here do it, but it's going to be problematic. If you want toll-quality voice, you still need either TDM lines or dedicated (non-internet) bandwidth. -------------- next part -------------- An HTML attachment was scrubbed... URL: http://lists.digium.com/pipermail/asterisk-users/attachments/20101015/7c7617a6/attachment.htm
On Fri, Oct 15, 2010 at 11:07 AM, Philipp von Klitzing <klitzing at pool.informatik.rwth-aachen.de> wrote:> - turn off IAX trunking mode >I would disagree, you want to enable trunking with multiple call. It will reduce patch overhead, leading to less bandwidth. OP could enable jitterbuffer, if not already enabled. -- Paul Belanger | dCAP Polybeacon | Consultant Jabber: paul.belanger at polybeacon.com | IRC: pabelanger (Freenode) blog.polybeacon.com
I've had to rip out VoIP in two cable-modem situations because the call
quality was too poor.
Bandwidth isn't the main characteristic you are looking for; most Internet
connections have plenty of that. Latency and jitter matter far more. Latency
describes how long each packet travels from your Asterisk system to the other
end of the IAX connection. The easiest way to measure it is with ping. Jitter
describes how consistent the data transfer speed is. Cable modems are to some
extent designed for burst data. This will obviously kill call quality.
You can go to http://myvoipspeed.visualware.com/ to get an idea. Run the same
test multiple times, both with no traffic on the cable modem, and with a VoIP
call going on. Then compare the jitter numbers. What I found was that on my
connection (also cable modem) the average jitter was supposedly acceptable, but
it was highly variable - in three tests with minimal other traffic all in the
middle of the night, the jitter was 1.6, 3.5 and 4.6 milliseconds. 4.6 is in the
borderline quality area. And if there is more traffic, quality may well go down
further, into the poor-quality zone.
-----Original Message-----
From: asterisk-users-bounces at lists.digium.com [mailto:asterisk-users-bounces
at lists.digium.com] On Behalf Of Michelle Dupuis
Sent: Friday, October 15, 2010 7:53 AM
To: Asterisk Users List
Subject: [asterisk-users] Audio problems on cable modem link
We have a small office installation running over a cable modem. (8M down, 500k
up confirmed with numerous speed test sites)
When a single call is up, call quality is fine. When a second call is up,
outbound audio is immediately choppy. We're using ulaw, and confirmed that
traffic with 2 calls is <175kbps in/out. (IAX connection out)
Asterisk doesn't report any dropped frames, the internet connection looks
fine, etc. We have a linux router in place running wondershaper that seems to
be running fine (same as our other installations).
Can someone suggest where to look? Could this be the ITSP?
--
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