No, not directly (i.e., plug an Ethernet device into the T1 jack).
The base signaling is different (different voltage, different frequencies, different pulse trains, different connector pin-outs).
You need an intermediate device to do the signal / level conversion (Ethernet-to-T1/E1) and to encapsulate the Ethernet into a Frame-Relay Frame at each end.
Encapsulation is like putting your paper message into an envelope to mail it; the envelope has the addressing information and routes the message to the correct recipient. When the envelope reaches the destination, the message is removed so it can be read.
With Ethernet / Frame-Relay, the Ethernet "message" is placed into a Frame-Relay "envelope" and routed through the Frame-Relay network. When the FR frame reaches the destination, the router/FRAD at the other end removes the Ethernet frame from the Frame-Relay frame and sends it along.
In addition to routers, there are/were bridge devices called "FRADs" that looked like a large modem. I haven't seen or heard of anyone using FRADS for a long time, I believe they've been dropped in favor of small routers (which offer more options/features than the FRADs did).
So, No, you can't plug Ethernet in directly to the "Frame-Relay Jack," but you can transport Ethernet over Frame-Relay by using (usually) a router.
Good Luck
Scott
