Renee
Have you tried just connecting the circuit to see if it will work. I'm not sure I understand the difference between D3 and D4 but I got this off the web doing a search:
Framing
For a receiving multiplexer to recognize what is what in the incoming bitstream some smart things are done. First of all from every channel only 8 bits at a time are send. Each of those 8 bits is called a time slot, so T1 consists of 24 time slots in the frame. The entire frame is thus 192 (24 x 8) bits and 1 control bit (the framing bit) which makes up 193 bits in total. At a repeat speed of 8000 times per second you get the T1 rate of 1.544 Mbps.
The modern T1 lines use one of two framing schemes: SuperFrame (SF) or Extended SuperFrame (ESF).
SF
Also known as D3/D4 frame (CCITT: G.733). Each superframe consists of 12 frames. The 193rd bit has different meanings. In the odd-numbered frames it acts as a terminal framing bit (FT), but in the even-numbered frames it acts as a signaling framing bit (FS).
FT frames are used for synchronization.
When I looked at the mode selections on my Bert tester it shows the following options: T1-D1D, T1-D2, T1-D4, T1-ESF, etc. There is no T1-D3.
Larry
