>.
ATDT*70,1234567
Also, adding 1170 after the ATDP dial command can be used to disable
callwaiting on some pulsedialing phone systems. Check with your phone company
to see if these features are supported.
In general, set the parameters to 8-N-1. If you are calling a commercial
online service (such as GEnie), you may need to set the parameters to 7-E-1.
The only popular online service that uses half duplex is GEnie.
If you are using an IBM compatible, choose IBM PC or ANSI. Otherwise, try
VT102, VT100, VT52, TTY.
For your computer to talk to your modem, you need to tell the software where
to find the modem. If you use a PC with an external modem, you need to specify
which serial port the modem is connected to. If you have an internal modem,
you need to configure the modem and tell the software which COM port the modem
is configured for.
If you use a Macintosh, specify whether your modem is connected to the modem
port or the printer port.
Errors that occur during file transfer are automatically detected and
corrected by file transfer protocols. If a block of data is received
incorrectly, the receiving system sends a message to the sending system and
requests the retransmission. This process is automatic. When errors occur
during file transfer, the communication program shows an error in the file
transfer status window.
This is designed to work with ASCII text files only. Notice that you do not
have to use this protocol when transferring text files. The ASCII protocol is
useful for uploading a text file when you are composing e-mail online.
Xmodem is one of the most widely used file transfer protocols. The original
Xmodem protocol uses 128-byte packets and a simple "checksum" method of error
detection. A later enhancement, XmodemCRC, uses a more secure Cyclic
Redundancy Check (CRC) method for error detection. Xmodem protocol always
attempts to use CRC first. If the sender does not acknowledge the requests for
CRC, the receiver shifts to the checksum mode and continues its request for
transmission.
Xmodem-1K is essentially Xmodem CRC with 1K (1024 byte) packets. On some
systems and bulletin boards it may also be referred to as Ymodem. Some
communication software programs, most notably Procomm Plus 1.x, also list
Xmodem-1K as Ymodem. Procomm Plus 2.0 no longer refers to Xmodem-1K as Ymodem.
Ymodem is essentially Xmodem-1K that allows multiple batch file transfer. On
some systems it is listed as Ymodem Batch.
Ymodem-g is a variant of Ymodem. It is designed to be used with modems that
support error control. This protocol does not provide software error
correction or recovery, but expects the modem to provide the service. It is a
streaming protocol that sends and receives 1K packets in a continuous stream
until instructed to stop. It does not wait for positive acknowledgement after
each block is sent, but rather sends blocks in rapid succession. If any block
is unsuccessfully transferred, the entire transfer is canceled.
This is generally the best protocol to use if the electronic service you are
calling supports it. Zmodem has two significant features: it is extremely
efficient and it provides crash recovery.
Like Ymodem-g, Zmodem does not wait for positive acknowledgement after each
block is sent, but rather sends blocks in rapid succession. If a Zmodem
transfer is canceled or interrupted for any reason, the transfer can be
resurrected later and the previously transferred information need not be
resent.
Kermit was developed at Columbia University. It was designed to facilitate the
exchange of data among very different types of computers (mainly minicomputers
and mainframes). You probably will not need to use Kermit unless you are
calling a minicomputer or mainframe at an educational institution.
In general, I recommend Zmodem. If Zmodem is not supported by the system you
are calling, use Ymodem-g. (If you are connecting to a UNIX system in a
university, you may have to use Kermit or Xmodem to transfer files.)
Here are the test results obtained by downloading the files using various file
transfer protocols. The number before the parentheses is the transfer speed
(in cps) and the number in the parentheses is the time elapsed (in seconds).
Filename Xmodem Xmodem1K Ymodem Ymodem-g Zmodem
-------------------------------------------------------------------------
the-wave.txt 429(334) 1508(95) 1527(94) 3261(44) 3296(43)
dayrpt.arc 314(26) 758(11) 761(11) 1042(8) 1025(8)
dayrpt.wks 415(47) 1252(15) 1244(15) 2314(8) 2337(8)
sunset.arc 337(15) 771(6) 745(6) 987(5) 965(5)
sunset.pic 399(41) 1337(12) 1297(12) 2594(6) 2588(6)
text109k.arc 343(86) 817(36) 814(36) 1089(27) 1064(27)
text109k.txt 410(271) 1379(80) 1351(82) 2812(39) 2885(38)
Copyright (c) 1991-92
Patrick Chen.
All rights reserved.