What level is the modem?

Question

System administration

What level is the modem?

Answer 1

If you are talking about the seven-layer OSI model, then it looks something like this:
4..7 standard
3 IP
2 SLIP, PPP
1 Modem
0 transmission medium (telephone cable)
I said "approximately", because the seven-layer OSI model is not very adequate for describing network reality , so that it is pulled on reality with difficulty, it often warps. For example, UDP and ICMP are usually placed at the fourth level, while at their core they are datagrams, so they should be at the third - but IP already sits there tightly. And protocols / services that work without establishing a connection (UDP-based DNS, Ping, DHCP, ARP) do not fit into this model at all.
As a rule, to squeeze reality into this model - for each protocol, they look at which protocol it works on top of, and who works on top of it. The modem works over a telephone cable; SLIP (long out of date) or PPP (the most current modem protocol - to the extent that modems are generally relevant) works on top of the modem; IP works over SLIP or PPP. The mosaic came together quite accurately, the modem turned out to be at the first level.
But such protocols as X / Y / Z-modem or UUCP - in the seven-level OSI model fall extremely clumsily. Let's start with the fact that there is no separation of the second and third levels - there is only one level of datagrams.

Answer 2

l2 + l3