13-6
C
HAPTER
13: H
ANDSHAKING
,
ERROR
CONTROL
,
DATA
COMPRESSION
,
AND
THROUGHPUT
.
Example:
Sendin
AT&M4
allows your modem to operate in Normal Mode
if an ARQ connection can’t be made.
Error control is available for calls at 1200 bps and above. It can be
disabled, although high-speed calls (9600 bps or higher) should always
be under error control. The operations defined in an error-control
protocol include:
■
Establishing compatibility.
■
Formatting data frames.
■
Detecting errors using Cyclic Redundancy Checking (CRC).
■
Retransmitting corrupt data frames
The Courier V.Everything modem is set at the factory to try for a
error-control connection and, if that isn't possible, to proceed with the
call in Normal mode. This means that &M4 is set.
For your modem to
Command
Have no error control (Normal Mode)
Due to the nature of phone line channels, this is never
recommended for analogue calls above 2400 bps
AT&M0
Enter Online Synchronous Mode without V.25
bis
.
External Courier V.Everything modems only
AT&M1
Operate in Normal mode if an ARQ connection can’t be
made (Normal/ARQ mode)
AT&M4
Hang up if it can’t make an ARQ connection (ARQ
Asynchronous Mode)
AT&M5
Start V.25
bis
synchronous mode, using the BISYNC
protocol.
AT&M6
Start V.25
bis
synchronous mode, using the HDLC link
protocol.
AT&M7
Summary of Contents for Courier
Page 12: ......
Page 28: ...1 14 CHAPTER 1 CONNECTING TO YOUR ISP ...
Page 36: ...3 4 CHAPTER 3 UPGRADING YOUR MODEM ...
Page 58: ...6 6 CHAPTER 6 WORKING WITH MEMORY ...
Page 64: ...8 4 CHAPTER 8 CONTROLLING EIA 232 SIGNALING ...
Page 72: ...9 8 CHAPTER 9 ACCESSING AND CONFIGURING THE COURIER V EVERYTHING MODEM REMOTELY ...
Page 80: ...10 8 CHAPTER 10 CONTROLLING DATA RATES ...
Page 96: ...12 6 CHAPTER 12 FLOW CONTROL ...
Page 108: ...13 12 CHAPTER 13 HANDSHAKING ERROR CONTROL DATA COMPRESSION AND THROUGHPUT ...
Page 112: ...14 4 CHAPTER 14 DISPLAYING QUERYING AND HELP SCREENS ...
Page 122: ...15 10 CHAPTER 15 TESTING THE CONNECTION ...
Page 142: ...17 8 CHAPTER 17 TROUBLESHOOTING ...
Page 156: ...A 14 APPENDIX A S REGISTERS ...
Page 172: ...B 16 APPENDIX B ALPHABETIC COMMAND SUMMARY ...
Page 178: ...C 6 APPENDIX C FLOW CONTROL TEMPLATE ...
Page 186: ...E 4 APPENDIX E V 25 BIS REFERENCE ...