asterisk users - Sep 2010 - Mixing ISDN and R2 in the same card...

I have a project where I need to connect two E1 links from different
providers.  One will be PRI ISDN (Telefonica) and the other MFC/R2
(Telmex).  There should not be any problem supporting both types of link
on a single TE220B card but my concern is more about who will be the
primary timing source.  Since the links come from different companies
how do I choose the clock source?

-- 
Carlos Chavez
Director de Tecnolog?a
Telecomunicaciones Abiertas de M?xico S.A. de C.V.
Tel: +52-55-91169161 Ext 2001