[Asterisk-Users] frames/packet

[Paul Lambert]

Steve Underwood wrote:
> 
> Paul Lambert wrote:
> 
> >"Not yet." implies that it is coming.
> >
> Look at the latency it causes, and you will see its not that useful.
> 
> >I know it would help on Internet
> >connections such as fixed wireless and cable modem where packet rate is
> >an issue. 20ms translates to 50 packets/sec.
> >
> 30ms per block codec aren't bad. Going beyond that gets nasty. 2 x 20ms
> blocks per packet about the most people will tolerate.
> 

2 x 20ms cuts the packet rate in half. That means a fixed wireless ISP
could fit twice the calls on a single access point.


> >I believe cable modem
> >upstream packet rates cap at 150-200 packets/sec. G729 gets the bit rate
> >down to 8kbits.
> >
> G.729 gets the rate down to 8kbps. Then RTP puts it back up to several
> times that.
> 
> >So based on a bit rate of 256K the theory is that the
> >link could handle 32 calls. But, that would produce packets coming out
> >at a rate of 1600 packets/sec beyond the limitation of most Internet
> >connections including a T1.
> >
> >
> A T1 has no particular packet limit. It is just limited to 1544kbps.
> Some routers choke on large numbers of small packets, but that is not a
> T1 problem.

There has to be a limit. You can't send 1 bit packets. As I think about
it more, I'm sure it's higher than 1600 packets/sec probably closer to
3000 packets/sec. So with 20ms blocks/packet your limit on a T1 with IP
would be 60 calls. Go 2 x 20ms and then you get 120 calls all with the
same IP overhead. I think an extra 20ms latency could be worth it.

> 
> Regards,
> Steve
> 
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