[asterisk-dev] TDMOE protocol

Andrew Kohlsmith (Mailing List Account) aklists at mixdown.ca
Fri Dec 11 06:44:16 CST 2009

On December 11, 2009 06:54:37 am Andrew Latham wrote:
> As Miguel mentioned the source code is filled with notes and comments
> that can help you understand how things work.  You do not need to be a
> programmer to understand comments in the source files.  Things like
> TDMoE go back many years and may require you to learn about the origin
> of the technology to form a good "frame" or knowledge base.

Actually TDMoE is pretty straightforward.

Aside from the ethernet header, there is a very thin TDMoE header which 
describes type, sub-address (span # basically), number of channels, format, 
signalling, alarms and the ever-important sequence number.  The rest of the 
payload is just a linear array of DAHDI_CHUNKSIZE (8 bytes) channel data.

The sequence number (seqno) is just a number which is ever-incrementing and is 
used by the receiving side to ensure that no frames were missed.

The rest of it is VERY much like normal TDM circuits. The alarms operate the 
same way, the signalling operates the same way... if all it is that you're 
interested in is the bits on the wire, ztdynamic.c is what you're after (not 
sure what it's called in DAHDI offhand.)

I did a fair amount of work with this a number of years back. If you have any 
specific questions I'd be happy to help.


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