Re: [Ekiga-devel-list] 3.2.5 release

[yannick <sevmek free fr>]

Damien Sandras a écrit :
> Le vendredi 10 juillet 2009 à 10:49 +0200, yannick a écrit :
>>>>> That's what I thought. By default, only a few codecs are enabled.
>>>> The bug is strange, since 
>>>> https://launchpadlibrarian.net/24407094/ekiga_3.2.0-0ubuntu1.diff.gz 
>>>> does not show any change related to enabled codecs in ekiga...
>>>>
>>> I guess people enable everything.
>> I have done some limited search on the MTU topic and it seems the MTU
>> can vary along the patch. Beside large bandwidth can greatly benefit for
>> a larger MTU than 1500 and some people are pushing to have larger MTU in
>> this case. (I have a report with this case at hand here:
>> https://bugs.launchpad.net/ubuntu/+source/ekiga/+bug/380091 )I do not
>> know how the choice if 1500 is made inside OPAL; if it is hardcoded it
>> is probably a source of frame dropping in some case (and it happen
>> probably in silence). Around 1400 seems more safe but it seems to not
>> cover all cases.
>>
>> AFAIK a proper fix for this situation is to use a discovery mechanism
>> for the MTU: fortunately this exist in RFC:
>> http://tools.ietf.org/html/rfc4821
> 
> OPAL does not touch the MTU.
> 
> The MTU setting on a machine is an OS thing, not a user program thing.

(ARGH I only answered to Damien, reposting to the list, sorry Damien for
the noise...)

It does not matter, even if your host has a 1500 MTU, the next hop in
the path can have a 1400 MTU (I agree this should be a rare case), thus
if you only take your host in account you'll be screwed.

e.g. the AOL ISP use a 1450 MTU:
"MTU (Maximum Transfer Unit) defines the largest data packet size you
can transmit in one go across a network. Any messages larger than the
MTU are divided into smaller packets before being sent. The industry
standard follows the principle that in order to transmit the largest
amount in one go, an MTU should be set to a high value, such as 1500.

However, the AOL Broadband network runs at an MTU of 1450. Many modem
routers have inbuilt auto-configurations where the hardware identifies
that the AOL Broadband traffic has an MTU of 1450 and dynamically
adjusts. If the modem router hardware does not have this facility, the
MTU setting can manually be changed on the computer."
Source:
http://help.aol.co.uk/what-is-an-mtu-setting-and/article/20060802093009990042