when i had a 56k modem one thing always popped into my mind, how come this thing never connects at 56k but at the max 49.3k i never found the answer and was seeking it here.
56000 bits per second (bps) is the maximum speed the modem can receive data at. That is the hardware limitation of the modem.
53,333 bps is the maximum obtainable rate on phone lines in the US due to crosstalk considerations. This would be a 'perfect' phone line.
In reality, very few phone lines are 'perfect'. Most have one or more impairments that most likely do not appreciably affect the phones lines ability to carry a voice conversation, but these impairments do limit the ability of the line to carry high speed data.
V.90/v.92 modems have the ability to 'probe' the phone line and determine what the maximum connect rate is that will yield an acceptably error free connection. The modem will connect at a rate that it feels will give you the greatest thoughput for the given line connections. Valid v.90/v.92 downlink connect rates are:
53,333
52,000
50,666
49,333
48,000
...
32,000
Oh, and v.90/v.92 connect rates are not static. They can vary as phone line conditions change. Your initial rate my be 49,333, but that rate may vary up or down during the connect.
Dave Lyle
2 Intern
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1952 Posts
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Posted October 3rd, 2004 03:00
53,333 bps is the maximum obtainable rate on phone lines in the US due to crosstalk considerations. This would be a 'perfect' phone line.
In reality, very few phone lines are 'perfect'. Most have one or more impairments that most likely do not appreciably affect the phones lines ability to carry a voice conversation, but these impairments do limit the ability of the line to carry high speed data.
V.90/v.92 modems have the ability to 'probe' the phone line and determine what the maximum connect rate is that will yield an acceptably error free connection. The modem will connect at a rate that it feels will give you the greatest thoughput for the given line connections. Valid v.90/v.92 downlink connect rates are:
53,333
52,000
50,666
49,333
48,000
...
32,000
Oh, and v.90/v.92 connect rates are not static. They can vary as phone line conditions change. Your initial rate my be 49,333, but that rate may vary up or down during the connect.
Message Edited by ddeerrff on 10-02-2004 11:45 PM