[asterisk-dev] H.263 Buffer size

[John Lange]

On Tue, 2006-07-18 at 08:29 +0200, Sergio García Murillo wrote:
> John Martin wrote:
> > Hi Devs,
> >   I was just watching the SVN commits going by and I was wondering
> > why the H.263 buffer size in format_h263.c had to be increased to
> > 32kB?  
> 
> I really don't see the point if it either (perhaps someone can enlighten us).
> I don't know if there is any special case in which it's needed, but if you
> work with rtp you shouldn't exceed the MTU to avoid problems. 

Since MTU is a network layer 2 feature, and since you may traverse any
number of different networks on your way from point A to point B, I
don't see how anything at the application layer could possibly know what
the MTU is.

When developing at the application layer you are supposed to be able to
safely ignore the layer 2 stuff and let the network(s) do its job. If
that involves fragmenting and reassembling packets then so be it; it
should be 100% transparent to the application layer.

Now I suppose your point is that in the real world you do have to pay
attention to MTU when coding RTP because it impacts performance. I will
grant you that. Its a shame to have to "corrupt" an application with
issues it shouldn't be concerned with. For one thing if you subsequently
put it on a properly optimized network (larger MTU) it will not perform
optimally.

By the way, which phones are you guys using to test video?

John