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Adsl and Frame Relay


I am asking this question because there are so many different information about in which layer frame relay and adsl operate.

I was sure that Frame Relay operates just in Layer - 2, has nothing to do with Layer - 1. But some web pages say that FR operates both Layer - 2 and Layer - 1.

Also I was sure that ADSL is a Layer - 1 technology, has nothing to do with Layer - 2. Also, End-to-End ADSL Architectures book says that:

"Like analog modems, cable modems, wireless, and T1 lines, DSL by itself  is a transmission technology, not a complete end-to-end solution. End  users don't buy DSL. They buy services such as high-speed Internet  access, an intranet, a leased line, voice over DSL, a virtual private  network (VPN), and video on demand (VoD)."

But some web pages say that ADSL is layer - 2 technology.

So my questions are:

1-) Can you please tell me in which layer do Frame Relay and ADSL are?

2-) If I am right, that FR is just Layer-2 protocol and ADSL is Layer - 1. So Frame relay wan connection can communicate over ADSL. Right?

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VIP Super Bronze

Adsl and Frame Relay


Layer-1 is the physical layer.  So in DSL the phone cable itself is layer-1 but there is also layer-2 (data link layer).

As for frame relay, that is an encapsulation type and can't be layer-1. It is layer-2.  Most frame relay connections communicate over T1s, or sub-rate T1s (256, 512, etc..)