Documentation on writing a custom socket

Alexander Leidinger Alexander at
Mon Mar 10 09:59:00 UTC 2008

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?


--    Alexander @ PGP ID = B0063FE7       netchild @  : PGP ID = 72077137

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