Documentation on writing a custom socket

Julian Elischer julian at
Sun Mar 9 16:33:31 UTC 2008

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.

> --HPS
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