CCNA - What Layer Does v.34, 56x, and v.90 Reside?

Author

What Layer Does v.34, 56x, and v.90 Reside?

2000-12-28, 4:39 am

Hey all.

I'm thinking these protocols reside at the physical layer, but don't know for sure.

Any thoughts?

2000-12-28, 5:26 am

Firechicken, V.34, k56flex, x2, and v.90 are all modem transmission standards, not networking protocols. I have never seen them referred to in any OSI model I have studied.
A modem is a device that modulates digital data from a computer to an analog format that can be sent over telephone wires, then demodulates it back into digital form.
Modems also perform error correction and are similar to a network interface card but are used for dial up networking. From this perspective, they should be regarded as a data link layer device. Just my 2 cents worth. Anyone think differently?

2000-12-28, 5:36 am

correct, layer 1

2000-12-28, 8:29 am

quote:
Originally posted by firechicken:
Hey all.

I'm thinking these protocols reside at the physical layer, but don't know for sure.

Any thoughts?

These protocols rule how data is encoded on the line. They govern such things as timing, voltages and so on. All of this is physical layer stuff.

Grollo mentions error correction in his answer, but that is not done by any of the protocols you mention. Error correcting modems nowadays use V.42. Earlier error correcting protocols are MNP2, MNP3 and MNP4. These protocols fits on the LLC sublayer of the data link layer.

Most modems nowadays also has a presentation layer component. They can do data compression by V.42bis or MNP5. Note that this does not fit perfectly in the OSI model as we usually run network and transport layer protocols on top of that. This is just another example of non-ISO protocols not fitting the OSI model. The OSI model is still a usefull tool however and questions like the one you pose are usefull not least as a learning tool.

Hm. Perhaps I should not include that last paragraph?

Terje

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