Well, found part of my standards documents, and thought I'd follow-up on our  
original discussion.

Q.390 is the layer 3 protocol used for ISDN signaling across the  
user-interface (SS7 is the inter-switch protocol defined by the Q.700-series).  
 Basic Call Control defined by Q.391 identifies specific ISDN Information  
Elements (IE) for transmission on the D channel in order to support  
connections that will be established on the B or H channels.  One of them is  
the IE defined by 010 1001 (Date/Time).  It is 64 bit wide and it appears as  
if you can request this IE arbitrarily at any time.

I'm right now digging through the Q.700-series of documents which are  
defining SS7, since the Q.390 documents are inconclusive about the timing on  
the signaling channel.  Perhaps the SS7 definition, which contains elements  
similiar to the IE's defined by Q.391 thru Q.393, my give some pointers as to  
what exactly the answer regarding the speculation around ISDN signaling  
latency characteristics.

Best regards,
Chris

PS: Please include me on the Cc: if you want me to participate in replies,  
since I'm currently not subscribed to tech-kern@netbsd.org due to the  
tremendous workload at my end.

--
Christian Kuhtz <ckuhtz@paranet.com>                          MIME/NeXTmail Ok 
UNIX/Network Specialist   "A German in the U.S., speaking for himself *gasp*"
Paranet, Inc., Rocky Mountain Branch                   http://www.paranet.com/