[Freeswitch-dev] FreeSwitch + ISDN + analog phone adapters - status

Jan Berger janvb at live.com
Fri Jan 30 08:03:01 PST 2009

It's an old hand-rule, nothing more.
The ideal situation would be 1 byte - 0.125 ms latency in switching, but this means a computer masturbating at 8000 interrupt a second - and can you imagine what this will do with your CPU?
Write a small test application that perform memcpy operations and calculate the transer rate.
When test on 1 byte, 5 bytes, 10 bytes 25 bytes 50 bytes
What you will see is that the transfer rate increase with the size of the packet - 50 byte is ca 50 byte faster than 1 byte in x-fer.
Now test with 100 bytes 250 bytes 500 bytes 1000 bytes etc
And you will see that little has changed from ca 50 bytes in xfer rate.
48 byte basicaly is a good trade between latency and cpu usage. The test might vary dependent on processor , but....
10 ms is however more or less the same, and might be a better number today. It goes for 711, 729 and 723 ...

From: brian at freeswitch.orgTo: freeswitch-dev at lists.freeswitch.orgDate: Fri, 30 Jan 2009 09:35:44 -0600Subject: Re: [Freeswitch-dev] FreeSwitch + ISDN + analog phone adapters - statusCan you elaborate on this G.711 at 6ms?  I have never seen this odd number.


On Jan 30, 2009, at 9:30 AM, Jan Berger wrote:
hi Hans, The standard for a PABX on G.711 is 6ms packaging of data - this is 48 byte per channel. If you go higher than this you start getting to much latency, if you go lower than this you start using to much CPU. 400 byte is 50ms, meaning we have spent a lot of the latency budget already here, but this shoud be run-time configurable per channel as per need. - G.711 6 ms- IVR is 250 ms- 729 10 ms- 723 30 ms etc. You need to take into consideration that you are on a system with 8, 16 or 32 E1's of whick some is running IVR, others SIP, others swicthing back out on a different E1 etc. Jan 
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