Why split physical and data link when they are so closely related? You can't use vpi/vci on an ethernet port, you can't use MAC addresses on a frame relay port. Bundle that shit together.

Presentation, application, and session are all dealt with by the application anyway so why bother splitting them out from a network point of view?

[–] rtxn@lemmy.world 7 points 2 days ago* (last edited 2 days ago) (1 children)

Why split physical and data link when they are so closely related?

You can run Ethernet on any medium that has the capacity to transmit digital signals. It can be copper, optical, over-air laser, radio, on top of an analog carrier wave (ASK, FSK, PSK). The Ethernet traffic can be completely independent from the physical medium by using encapsulation (L2TP or any other protocol that encapsulates Layer-2). It can be pigeons carrying printouts of the Ethernet frames, scanned and reassembled at the destination. The same can be said about most Layer-2 protocols.

As long as the proper interfaces are present, the physical layer is completely transparent to the data link layer.

(edit) I should point out that Ethernet, specifically, transmits extra data before and after the frame (the preamble and inter-packet gap) that are used to configure the Rx circuit for reception, but the Layer-2 frame will be identical regardless of the medium.

[–] ulterno@programming.dev 0 points 1 day ago

RFC 2549

[–] Blue_Morpho@lemmy.world 7 points 2 days ago

Why split physical and data link when they are so closely related?

100 mb Ethernet can be run over cat 5e, Cat 6, etc. You can even have Ethernet frames running over coax. (Not just the original standard which was coax but there are modern bridges for using cable TV coax in your house to reach rooms where you can't pull cat5.)