Hello All,
I have some basic knowledge about E&M, and have practically used it. But concept wise, I am not very clear... So i am posting a few queries related to E&M to get a better picture.
- Normally I have used E&M in a back-toback configuration. i.e. I have an E&M interface set to say type 4, and another interface also set to type 4. Both of these are on the same VoIP gateway. And hence no PBX coming into picture here. Thus, I guess I am using two signaling units, rather than a signaling unit and a trunk unit ( Hope I am right here !!!!). I connect the two using a cross E&M cable ( i.e. EM, ME, .........). My query is that will the cross cable be still used if, instead of the other interface on the VoIP gateway, I connect it to a PBX. Or will it HAVE to be a straight cable.
- With using the circuit diagramof Type II, i tried to visualise the back to back configuration. What diagram I obtained was as follows:
___________________________________ Signaling Unit 1 Signaling Unit 2 ___________________________________
E ( open)------------------------M ( GND) | SG--------------------------------SB ( -48V) ___________________________________
M ( GND)------------------------E ( open) | SB ( -48V)-----------------------SG
My Question is if either side has to indicate Offhook, then it will always be that E Lead has to be asserted. Have I understood it right. Whereas the basic working principle of E&M ( be it E&M Wink or immediate) states that once the side that is initiating the call asserts the M Lead, and then dials the digits, the Recieving end will assert the E Lead to indicate the call is connected. So i am not able to correlate this principle with the figure shown above.
Thanks in advance, Regards Sandeep