[asterisk-users] Re: Bandwidth requirements

[omar parihuana]

Unfortunately cRTP is not supported by Asterisk, and normally it is
implemented between routers that support it.

On 10/5/06, Dan Austin <Dan_Austin at phoenix.com> wrote:
> J. Oquendo wrote:
> > Benny Amorsen wrote:
> >>>>>>> "rJ" == raphael Jacquot <sxpert at sxpert.org> writes:
> >>>>>>>
> >>
> >> rJ> ATM cell tax is actually 10% as there's 5 header bytes for each
> 53
> >> rJ> bytes cell,
> >>
> >> For VoIP the cell tax is much larger. In the example, each RTP packet
> >> contains 20 useful bytes and 40 bytes IP overhead. 60 bytes doesn't
> >> fit in one cell, so you end up with 106 bytes at the ATM layer to
> >> transport 20 bytes of G.729. The ATM-caused overhead is thus 46 bytes
> >> per voice packet, thereby making the needed bandwidth 77% larger.
> >>
> >>
>
> > CRTP solves this issue (40byte waste)
> cRTP is a great idea that is not widely implimented.  Not very
> many endpoint support it, and Asterisk currently does not.
>
> In version 1.4, Asterisk will support configurable RTP packetization.
> So you could use 40ms for your G729 payload and reach a 50/50
> split between payload and overhead (before ATM encapsulation for
> DSL).  At 50ms for g729, you get a nice fit into two ATM cells, while
> a small bump to 60ms will force you into three ATM cells.
>
> Of course you need to be mindful of the latency between endpoints
> when you start increasing the payload, but a healthy network and
> tuning the payload can greatly reduce bandwidth requirements.
>
> AND most endpoints do support configurable RTP packetization.
> If Asterisk and more endpoints supported cRTP, then combining that
> feature with larger RTP payloads would result in very low
> overhead numbers.
>
> Dan
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-- 
Omar E.P.T
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