Dialup modem transmission protocols and reates (client and server)

Does anybody know why when connecting two dial-up modems the maximum protocol you can use to stablish the communication is V.34 -33.6K?

I've read that you can connect with th开发者_如何学编程e server modems of the ISP using V.92 or V.90 and I would like to know if there is any explanation to this.

Thanks in advance.

V.92/V.90 requires one end of the link (in this case the ISP) to have digital access to the telephone network to work.

Your two modems will be connecting in analogue and so can only support V.34 at most.

If you have a bad connection line, e.g. noise in the line, so the established speed will drop down to values as the V.34. The connection speed is established at the handshake process (the beginning of transmission).

A comprehensive list of connections speeds can be found at: http://en.wikipedia.org/wiki/List_of_device_bandwidths .

To achieve the maximum speed (56K over telephone line) you must have a very good quality line (no noise).