Jitter

[Lostdog]

Hi,

I have Time Warner Cable and I have jitter problems.  Various voip tester applets peg my MOS at 3.5-3.9 due to the jitter.  I can hear just fine, but folks on the other end are always complaining that I sound garbled to the point of unintelligible. And the lag is noticeable.

The faq says to lower the ChannelRxGain and ChannelTxGain, but they're already 0.  Should I go into negative numbers?  How much?

Would changing to the Google DNS on my modem help anything?  If so, how to go about it?  I looked inside my SBG6580, but didn't see anything likely looking.  NAPT mode is "enabled" and the WAN Connection Type is "DHCP".  As you can probably tell, I don't really know what I'm doing...

Thanks, 

Lostdog

[lk96]

The gain should not have anything to do with the garbled/low MOS score.
It would be strange for these settings to saturate the remote end. I'd leave them at 0 for now.

Also you didn't mention if you use a 100/110 device or a 2xx device. If you are using
a 100 or 110 device you should change the settings for Ethernet to full duplex (by default
it's set to half duplex). So depending on your home traffic/devices a full duplex setting may make
a difference. IF you use a 2xx device, then Ethernet is already set to full duplex so this don't require any changes.

I also don't think that your DNS settings make a difference but if you want to
use a Google DNS server you can set point your DNS to 8.8.8.8 or 8.8.4.4

Your issues most likely are a combination of one or more of the following:
1. you have limited or highly fluctuating uplink bandwidth
2. your provider (TWC) cause packet losses
3. you may have other uplink traffic originating from your home network that you saturate
your uplink and as a result Voip traffic gets dropped.

For #1: you should measure the speed of your uplink. I know that you run some MOS scoring.But
do run some speed test (ie using speedtest.net) to get an idea of where you stand.
(BTW, I believe that audio with 3.5-3.9 MOS scoring is not great that should be kind of legible)

For #2: if we can determine that this is the case, then TWC has to fix. Some times
the cable provide has to fix issues related to weak or very strong signal on the cable.

For #3: try to determine if your router/firewall allow you to prioritize traffic from
the obi over other home traffic. If you use the 2xx device, then you can even use
the obi as a basic firewall: so you can connect your home network to the Obi and use the
obi uplink/WAN to connect to your cablemodem.

L.

[Lostdog]

LK96, thank you for your thorough reply!  Cheers!

I have the OBI 100.  I just discover a firmware update and executed it.  As you suggested, I also changed the OBI to full duplex using directions I found on this forum.  

1:      The speed and quality tests are inconsistent throughout the day and even the hour, but this is representative:
       DL: 12.53 Mbps   UL: 0.71 Mbps  Packet Loss: 0.2%   Latency 105ms   Jitter: 69ms

2:     If this is TWC's fault, what is my recourse?  I've complained before, but nothing seems to change, and they're the only game in town.

3:     Here's my setup:  OBI 100, Motorola SBG 6580, OSX 10.8.5, Google Voice
       The only internet traffic in my house originates with me.  I've check this.  My SBG6580 doesn't have a QoS option, but it does have an advanced options page which looks like this:

WAN Blocking   Enabled
Ipsec PassThrough   Enabled
PPTP PassThrough   Enabled
Remote Config Management   Disabled   
Multicast Enable   Enable
UPnP Enable   Disabled

NAT ALG Status
FTP   Enabled
TFTP   Enabled
Kerb88   Enabled
Kerb1293   Enabled
ICQ   Enabled
ICQTalk   Enabled
IRC666x   Enabled
IRC7000   Enabled
IRC8000   Enabled
H225   Enabled
RSVP   Enabled
NetBios   Enabled
MSN   Enabled
PPTP   Enabled
Net2Phone   Enabled
RTSP   Enabled
IKE   Enabled
SIP   Enabled

[lk96]

Your uplink speed should still be adequate for G711 codec. But I'm afraid that
the inconsistency you experience plus the presence of packet loss degrade things fast.

For a cable modem connection though an uplink of 710 kbps seems really low (not to say pathetic).
When I experienced similar issues with Comcast in the past, they did fix the issues
(they found that in one case their signal was too strong and in another case it was too weak).

Any chance though that the issue may be cabling inside the house? either on the cable side
or on the ethernet side? If you own a network tester I'd suggest you check out all the segments.
if you don't have one, may be you can try replacing the cables.

In terms of options: given the presence of pkt losses and the lower than normal bandwidth,
I'd think that you could benefit from using another codec that supports
pkt loss concealment and requires less bandwidth. This requires though that you
move off the GV service (which btw goes away anyway in May or so).
So for the codecs supported on the Obi, we can try ti figure out which ones
are supported by potential voip providers and see if that alleviates a little your situation.

Another thing you may way to try is to enable silence suppression. The setting
is under the codecs -> codec profile A or B. You should do it at least to G711U.
It may help reducing a bit the uplink bandwidth requirements.

L.

[sdb-]

1:      The speed and quality tests are inconsistent throughout the day and even the hour, but this is representative:
       DL: 12.53 Mbps   UL: 0.71 Mbps  Packet Loss: 0.2%   Latency 105ms   Jitter: 69ms

That looks more like a medium-OK ADSL line than cable internet.

The only number there that really stands out as strange is the UL rate.  Using the standard uncompressed G711 codecs are going to require about 0.10 Mbps (or about 15%) of that upload.  That is a high enough percentage that that alone may be causing your observed issues.  With GV you do not have any choice in codec.  If you can set up QoS in your router to give the OBi highest priority access to about 0.10 to 0.15 Mbps upload it will probably help.

Latency looks about normal for that upload rate.

The Jitter may be caused if your upload and download vary from minute to minute, or if you are using QoS already (or somewhere upstream is QoS'ing you).

The Packet loss of 0.2% is not great, but not bad unless it is sometimes higher (2x is starting to be a problem).  If every packet is 20ms of talk, 50 packets is 1second. 0.5% loss would be almost unnoticeable if it were evenly distributed, but usually packet loss occurs in lumps so you could lose several in a row then be OK for a few seconds.

And the inconsistency you mention...  If the upload speed drops much or the latency or jitter increase much it could be problems.

The OBi110 keeps good stats on the call (jitter buffer, loss, delay, etc).  I think I only saw it with syslog.  I expect the 100 does the same.  (I miss that with my '202.)

Summary:  I'd look at adding QoS to prioritize OBi upload traffic.

[lk96]

That looks more like a medium-OK ADSL line than cable internet.

The OP mentions use of SBG6580 which is a Motorola cable modem if I'm not mistaken.
But regardless of the nature of the connection, the speed asymmetry is pretty high for
either case.