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

[Michael Jerris]

Another useful advantage without the latency tradeoff is to read a  
full span or card every 1ms  (or whatever sane interval) and chop up  
the bytes in userland.  The latency argument dies if you are bridging  
to voip, so if you can handle bridging the tdm to tdm channels in  
kernel space, you could easily get away with 10ms reads to user space  
as well.

Mike



On Jan 30, 2009, at 11:11 AM, Anthony Minessale wrote:

> That is one of the benefits of sangoma hardware.
> They have an mtu value in the driver you can set to 80 (10ms) which  
> despite the interval the channel is using
> it will operate at 10ms interrupts.  Digium's zaptel, umm i mean  
> dahdi uses the aforementioned masturbation technique and any  
> hardware that interfaces to it must comply.  Since most of use do  
> not want to be forced to masturbate with dahdi we are seeking an  
> alternative, hence OpenZAP
>
> OpenZAP so far is only a user land interface with plug-ins for i/o  
> and signaling.
> Eventually the goal is to make a cross-platform kernel layer  
> interface as well that can abstract TDM and RTP hardware alike and  
> allow the creation of handles that can be cross-connected inside the  
> kernel as well as in and out of userland depending on the needs.
>
>
>
>
> On Fri, Jan 30, 2009 at 10:03 AM, Jan Berger <janvb at live.com> wrote:
> 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 ...
>
> Jan
>
>
>
> From: brian at freeswitch.org
>
> To: freeswitch-dev at lists.freeswitch.org
> Date: Fri, 30 Jan 2009 09:35:44 -0600
> Subject: Re: [Freeswitch-dev] FreeSwitch + ISDN + analog phone  
> adapters - status
>
>
> Can you elaborate on this G.711 at 6ms?  I have never seen this odd  
> number.
>
> /b
>
> 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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>
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>
> -- 
> Anthony Minessale II
>
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