telephoneterminal
I am making an Eagle Cad library for this part, and I want to make sure I am making my part correctly. On this datasheet, http://www.switchcraft.com/Drawings/35rapc2av_cd.pdf, I am assuming that:
Testing the wiring is an interesting project in and of itself, but there may be a simpler and more effective way to address the overall system, at least before resorting to that: Can you take the DSL modem and a laptop to the service entry point and try it right there, thus eliminating the wiring issue? If it works there, then you work on testing your wiring; if it doesn't the problem would seem to be either with the carrier/drop or with the modem itself.
The analogue circuit is known as a "two-wire hybrid" and does exactly what you are doing with your DSP. Strictly speaking this is just sidetone elimination rather than echo cancellation which Kellenjb's link addresses. Below is a simple example (which is a discrete replacement for an obsolete Mitel part). This arrangement only works if the load impedance is precisely controlled - in this case 754\$\Omega\$.
Best Answer
"Tip spring" would be the inverted "V" on the schematic, and "shunt terminal is the downwards-pointing arrow. "Terminal" would be the body of the mating plug, and "Tip spring" would contact the tip of the plug.
"Shunt terminal" is a switch contact that is normally connected to the Tip Spring, and is disconnected when the plug is inserted in the jack.