Documentation on writing a custom socket

Julian Elischer julian at
Mon Mar 10 18:13:02 UTC 2008

Hans Petter Selasky wrote:
> ISDN can have more than 2-data channels per logical unit. There is something 
> called E1 and T1 which has 30 and 24 B-channels respectivly per D-channel.

I know, but neither of these represent any challenge to modern hardware.

> --HPS
> On Monday 10 March 2008, Alexander Leidinger wrote:
>> Quoting Julian Elischer <julian at> (from Sun, 09 Mar 2008
>> 09:33:36 -0700):
>>> Hans Petter Selasky wrote:
>>>> On Saturday 08 March 2008, Robert Watson wrote:
>>>>> On Sat, 8 Mar 2008, Hans Petter Selasky wrote:
>>>>> For example, do you
>>>>> anticipate using or even needing the routing facilities, and how might
>>>>> you map ISDN telephony parts into the normal network stack
>>>>> infrastructure of addresses, routing, interfaces, etc?
>>>> Hi Robert,
>>>> ISDN is very simple. In the ISDN world there is a term called TEI
>>>> which is the Terminal Entity Identifier. This kind of like an IP
>>>> address.
>>>> Besides from the signalling there are 2 B-channels which can
>>>> transport data or audio. One of my goals is to achive zero copy
>>>> when moving data to/from an ISDN line and also in combination to
>>>> Voice over IP. Currently data is moved through userland (Asterisk
>>>> typically) which is usable in the short term, but in the long run I
>>>>  want this extra copying removed. The idea is that I can route [IP]
>>>>  packets (mbufs) through various filters in the kernel without the
>>>> need for copy.
>>> Given the speed of ISDN connections, It is not worth doing zero copy
>>> on ISDN unless you have more than 1000 of them,  which seems unlikely.
>>> given a total throughput of 128000 b/s and the speed of current
>>> hardware, the number of packets per second is probably not high
>>> enough to make the difference even noticable.
>> What about low-power embedded systems and a high count of small
>> packets (VoIP)? Where do you draw the line between powerful enough and
>> how do you chose this line?
>> Bye,
>> Alexander.

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