Connecting With Other Data Modems - IBM Aptiva Handbook

28,800 bps (V.34) modem that connects with a
14,400 bps (V.32bis) modem will only be able to send
and receive data at 14,400 bps.
The transmission rate at which two modems agree to
communicate can also be affected by a noisy telephone
line. If the phone line that connects the two modems is
noisy, the modems may negotiate to communicate
using a slower modulation protocol so the integrity of
the transmitted data is preserved.
Telephone line noise can cause loss of data and
connection when modem speeds rise above 9600 bps.
Over time, many different file transfer protocols have
been developed solely to detect and correct the errors
caused by phone line noise.
Connecting with other data
modems
When you use your computer's data modem functions
to communicate with another computer or
communications service, you may need to choose a file
transfer protocol in your software communications
program. For example, when you connect to a bulletin
board, you must choose a file transfer protocol before
downloading a file.
The file transfer protocol determines how the data that
travels between computers is packaged and transferred
through the lines. This protocol ensures that the data is
interpreted the same way at both ends of the line. For
example, the protocol determines how the data might
be broken up into chunks (called "blocks" or "frames")
154 Appendix C: Modem information
and how the communications software finds and
corrects transmission errors.
Your data modem and the data modem on the other end
of the line must use the same file transfer protocol to
transfer data. For example, if your data modem uses
Z-modem, the modem you are connecting to must also
use Z-modem.
Many different file transfer protocols are commonly
used today. Examples of these protocols include
X-modem, Y-modem, and Kermit. Z-modem is currently
the most commonly used transfer protocol.
Z-modem is also the only file transfer protocol
supported by the DOS TSR program that is required for
operating DOS communications programs or DOS
Note:
games that use the modem. For more information
about this TSR program, see "Operating the modem
without Windows 95" on page 150.
Microcom Network Protocol (MNP) levels 1 through 4
were created to correct errors caused by noisy
telephone lines. V.42, which was adopted later, more
effectively corrects these errors.
MNP 5 and V.42bis were established to provide high
data throughput. With V.42bis, it is possible to achieve a
4:1 data compression ratio. MNP 5, however, should be
used only with uncompressed data. MNP 5 attempts to
compress data that has already been compressed and
this slows the transfer process significantly.
If you cannot connect to another modem, it may be
because the file transfer protocol you are using is not
compatible with the protocol used by the other modem.