[Asterisk-Users] Zaptel DACS and FDL

[Jerry]

>
> Yes, but does FDL run over the per channel robbed bit signalling or 
> does it run over the T-1 signaling.  i.e. Does FDL run using ESF 
> (applies to the whole T-1) or does it run on the robbed bit signaling 
> for specific channels?
>

FDL is carried in some surplus bits within the ESF frame, not within 
the payload. Follow this link for a good article describing T1/E1s.

http://www.commsdesign.com/showArticle.jhtml?articleID=16501900