Re: [Bloat] Skype

[Dave Taht <dave.taht@gmail.com>]

On Mon, Nov 19, 2012 at 11:27 AM, Ingemar Johansson S
<ingemar.s.johansson@ericsson.com> wrote:
> Hi
>
> Been a year or so since I read about the inner secrets of Skype so this may be old..
> I would suspect that your Skype session runs over TCP (via a Relay). This may happen e.g when a firewall blocks UDP.
> TCP (possibly in combination with a lossy WiFi connection) is what creates the high latencies.

I recently tried to use both skype and google voice on a concall to
the US during the recent strike and riots in barcelona. Power and
regular internet were down, so I hacked my way into a local mesh node
with a spare directional antenna to make the call.

The connection was quite lousy,

Skype was unusable. Google voice sort of worked, but exhibited classic
symptoms of overbuffering and wifi retries, sometimes playing back
seconds of audio at a very high rate, and otherwise dropping out
frequently.

I got packet traces of the google voice call, but regrettably cannot
share them due to the contents of the call. They are "interesting",
and if I get a chance I'll write up what I learned.

It did inspire me harder, to try and find a rtp based test tool
(anyone?), so that the next time I or someone else is in a situation
like that, a good analysis can be made.

>
> /Ingemar
> ------------------------------
>
> Message: 2
> Date: Sun, 18 Nov 2012 15:57:53 +0100
> From: Michael Welzl <michawe@ifi.uio.no>
> To: bloat <bloat@lists.bufferbloat.NET>
> Subject: [Bloat] Skype
> Message-ID: <647D57F5-24CE-4006-AD2A-74141C84C3CB@ifi.uio.no>
> Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes
>
> Hi,
>
> I have repeatedly noticed that Skype sometimes, in a long conversation involving video, can create massive audio delays (in the order of multiple seconds). This has happened to me in a conversation from a hotel room in the US to my home in Oslo (where, apologies, I haven't yet looked into de-bloating my modem and access point), and from my office in Oslo to someone else's office in the US.
>
> I'm wondering: was that always due to bloated equipment along the path (including the end hosts), or does Skype poorly handle its internal buffers?
>
> Any experiences? I suppose the way to find out is to run Skype over a verifiably de-bloated path. If, then, the problem never occurs, the fault is with the equipment and not with Skype (and vice versa).
>
> Cheers,
> Michael
>
>
>
> ------------------------------
>
> Message: 3
> Date: Sun, 18 Nov 2012 08:09:03 -0800 (PST)
> From: Alex Burr <ajb44.geo@yahoo.com>
> To: bloat <bloat@lists.bufferbloat.NET>
> Subject: Re: [Bloat] Skype
> Message-ID:
>         <1353254943.93761.YahooMailNeo@web126202.mail.ne1.yahoo.com>
> Content-Type: text/plain; charset=us-ascii
>
> I have noticed delays - although I don't think multiple seconds - but I think that it may be skype trying to make the best of a bad connection. I don't have any knowledge of the internals of the skype client, but I suspect that they take the view that delayed audio is better than incomprehensible audio - I think I have even heard it actually repeating the last bit of audio before a glitch, to give you a better chance to understand the next bit, and presumably catching up when the opportunity arises.
>
> So, an experiment to rule out skype might need to use not just a de-bloated path, but one with known packet loss.
>
>
> Alex
>
>
>
> ----- Original Message -----
>> From: Michael Welzl <michawe@ifi.uio.no>
>> To: bloat <bloat@lists.bufferbloat.NET>
>> Cc:
>> Sent: Sunday, November 18, 2012 2:57 PM
>> Subject: [Bloat] Skype
>>
>> Hi,
>>
>> I have repeatedly noticed that Skype sometimes, in a long conversation
>> involving video, can create massive audio delays (in the order of
>> multiple seconds). This has happened to me in a conversation from a
>> hotel room in the US to my home in Oslo (where, apologies, I haven't
>> yet looked into de-bloating my modem and access point), and from my
>> office in Oslo to someone else's office in the US.
>>
>> I'm wondering: was that always due to bloated equipment along the path
>> (including the end hosts), or does Skype poorly handle its internal buffers?
>>
>> Any experiences? I suppose the way to find out is to run Skype over a
>> verifiably de-bloated path. If, then, the problem never occurs, the
>> fault is with the equipment and not with Skype (and vice versa).
>>
>> Cheers,
>> Michael
>>
>> _______________________________________________
>> Bloat mailing list
>> Bloat@lists.bufferbloat.net
>> https://lists.bufferbloat.net/listinfo/bloat
>>
>
>
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>
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>
> End of Bloat Digest, Vol 23, Issue 10
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-- 
Dave Täht

Fixing bufferbloat with cerowrt: http://www.teklibre.com/cerowrt/subscribe.html