2004-06-02 01:31:20 GMT
In a message dated May 27, 2004 Mpierce1 <at> aol.com writes:
I believe this remains as one of the major
open questions for the application of SIP or H.323 in a large, managed network.
I've heard of speech clipping (on answer), but I don't know what "ring-clipping" is. I presume you are referring to call setup delay (or delay to ring). The issue is signaling delay in general (call setup and release), but speech clipping has always been the most serious impact of delay.
It seems to me that this issue is really not related to "interfacing to a TDM telephony switch", but occurs equally within a fully IP environment.
Ring-clipping can occur if SS7 signaling path from the softswitch to the TDM CO is much faster than the signaling path from softswitch to IP gateway that interfaces to the TDM CO were the ringing tone is generated. Speech-clipping can occur if the signaling path from the call answered phone to the softswitch and back to the IP gateway that enables the audio path takes longer then for the person answering the phone to say hello.
No matter what service class is used for
signaling (above, below, or same as speech bearer) there must be guaranteed
bandwidth for the expected signaling traffic to provide sufficient low latency
and almost zero discard rate independent from the amount of speech bearer
traffic. In effect, if signaling is in a separate class and is guaranteed, say
5% of the bandwidth on an outgoing link and speech bearer (EF) is guaranteeed
50%, then it isn't really necessary to think of one being above or below or the
same as the other. The forwarding algorithm guarantees a minimum bandwidth to
both in what is effectively "time-division multiplexing", but we
don't call it that since it is not based on strict timing. The result is that
the signaling does not experience "higher latency", but probably has
"higher delay variation", mostly due to the varying packet sizes.
Agree. Putting signaling traffic into a distinct class and engineering that class so that queuing dose not occur does work. In next draft (03) I will total separate telephony signaling from telephony bearer traffic.
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