Dialing

Computer to Computer: Software

Protocols

How Device Speeds Compare

The table below will help you see just how much faster the different transfer rates are. To read the table, look at the speed in the top row, which is in kilobytes per second. Below it you will see how long it takes to transfer 1 MB, 10 MB, and 1000 MB at that speed. Check out the last row. This one really shows the difference between analog modems and the digital kind. The times go down from days to hours or even minutes!

Remember that just because your device is able to send and receive at a certain rate does not mean that it will ever actually work that fast. There are many other factors in the communications channel that can reduce the transmission speed from the maximum.

Throughput (Kbps)	14.4	28.8		ISDN 128		Cable 1544	ADSL 8000
File Size	Download Time
1 MB	9.26 min	4.63 min	2.6 min	1 min	31.25 s	5.18 s	1 s
10 MB	1.54 hr	46.3 min	26.6 min	10.4 min	5.2 min	51.8 s	10 s
1000 MB (gigabyte)	6.4 days	3.2 days	1.85 days	17.4 hr	8.6 hr	1.4 hr	16.6 min

To talk to each other, modems have to exchange a good bit of information, since there are so many different types and speeds of modems around. That's what the high pitched squeals and squawks are that you can hear when an analog modem is trying to connect. It's modem talk for "So, who are you? Do you speak my language? Well, maybe we can find a common language so these guys can get connected."

A digital modem does not make noises (an advantage!) but it must do the same kind of negotiation with the device at the other end to come up with a common language, called a protocol.

A protocol defines what information is exchanged and in what order. The names of the protocols are of the form v.##. So you'll see things like v.25bis, v.34, and v.120. Some protocols are more stable or faster than others at certain tasks.

You can't just hook up your computer to a network or a modem and start sending and receiving data. The computer needs instructions on how to do this. You need some kind of communications software. Since there are a number of different communications tasks, there are different kinds of programs that manage those tasks.

Dialing software tells the computer how to place a call on the phone line connected to it. It also displays messages about the progress of the call or lack thereof. A list of phone numbers for frequently called, or frequently forgotten, numbers is an important feature.
These capabilities are often included in other software packages.

Дата добавления: 2014-12-23