Neo,
indeed the value-added feature ist what you mentioned in your post:
> AFAIK if a card supports E1/T1 that means it can handle either data or voice ,
> then whats the added advantage of supporting Unstructured E1 (G.703)
G.703 is an ITU formerly known as CCITT (telephony)-Standard for 2048000 bit/s PDH services.
One device must supply clocking, the other device picks the clocking from the line.
So the clock-generators on the VWIC...-G.703 must be more accurate than on the without -G.703,
which gets reflected in the pricing (and tells you why you should not use an el-cheopo-lookalike module).
G.704 is also an ITU standard. It is based on G.703, slices it (under lost of 64000bit/s) into 31 64000bit/s "Frames".
Normally this is used for ISDN/PRI Telephone access.
It picks the clocking allways from the line.
In Europe (E1 :-) on an PMX (PRI) one of the frames is used for signalling
(here it is the frame 15 in the middle, not frame 0 !) the calls
and the other Frames ar for one telephone-call (or even isdn-data-calls).
For Data Communication, you can order both.
The G.703 Version is cheaper, the G.704 version is more expensive.
But, hidden in the framing of G.704, the carrier can do some kind of diagnostics to see where the circuit fails.
A Special Data-Application is to map just one or a few Frames to a destionation.
Here, the VWIC-MFT... ist not so good as the good old NM-1CE1B.
The VWIC can only have two "channelgroups" while the NM-1CE1B can have 31 (one for each frame)
so your telco can map ISDN-BRI-Datachannel from Remote-Location to one Frame/channel on the central site onto one PRI .
Strange that the Voice application of that VWic _can_ use each channel seperately.
But those are historicall issues, with broadband and xdsl those technique is disappearing.
We did prefer external Modem G703/G704 to X.21 for data applications and a WIC-1T
since the overvoltage from a lightning storm kills just that modem
and not the complete router with the VWIC inside.
