On Monday 09 July 2001 02:37, Tony Alfrey wrote:
> Is the modem smart enough to know when the phone line is capable
> (bandwidth-wise) of supporting a high data rate?
It's a two part answer. The modems negotiate between themselves, to
'discover' what speed each can handle and which protocol the other can use.
It is why you hear a series of escalating 'scratchy sounds' as the modems
test each other for ever increasing speed. (read speed as various forms of
modulation)
Secondly modems nowadays use dynamic negotiation. If the line quality drops,
as it can and will over time, they re-negotiate with each other to accomodate
the changed conditions.
They don't sense the telephone line itself as much as they simply go for
broke, between themsevles, and as a consequence, the copper cable is
accounted for. In _addition_, for 56kbs speeds, the telco exchange itself
must become involved. In that sense, yes, the modems are smart enough to ask
the exchange to increase it's bandwidth from the standard 3k voice channel to
'something else'.
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