Jim, FWIW: Last time I had company money to deal with this issue I bought a similar model of this: A Viking DLE-200 https://www.amazon.com/Viking-DLE-200B-Two-Way-Line-Simulator/dp/B004PXK314 Dave. Sent from Mail for Windows 10 Message: 18 Date: Tue, 3 Dec 2019 22:35:40 -0600 From: Jim Brain <brain at jbrain.com> ? To continue validating modem functionality, I think it makes sense to set up a closed loop phone system in my lab that will function well enough to allow modems to connect to each other (dial tone, ringing, busy signal, etc.). I know I can probably whip something up with a 9 v battery and a piece of cable with rj11s, but I think that will fall short. That said, I went out to eBay to see if I could source a 2-8 line something to help, and got smacked around with my lack of telephone system knowledge. So, any ideas (or links to eBay auctions) of brands/models/etc. I should focus on? Also, if anyone has any modems lying around gathering dust, I probably should source a few more models. tcpser handles Hayes "+++" spec correctly, but I should probably support TIES as well, to cite one example. Jim -- Jim Brain brain at jbrain.com www.jbrain.com