13-8
C
HAPTER
13: H
ANDSHAKING
,
ERROR
CONTROL
,
DATA
COMPRESSION
,
AND
THROUGHPUT
Data Compression
Courier V.Everything modems employ different data compression
techniques during data connections.
Example:
Sending
AT&K3
is used to transfer compressed files. The
modem will only negotiate for V.4
bis
compression. This command also
will disable MNP Level 5 (MNP5) compression.
If a Courier V.Everything modem successfully establishes a V.42 error
control connection with a remote device, it also negotiates for V.42
bis
data compression.
If a Courier V.Everything modem successfully establishes an MNP
connection with a remote device, it also negotiates for MNP5 data
compression.
The type of compression for a call, if any, is reported in the ATI6 display
and in the CONNECT message if the modem is set to &A3
V.42
bis
versus MNP5
Data Compression
Courier V.Everything modems using V.4
bis
compression negotiate the
following options and report them in the ATI6 display
■
Dictionary size, that is, the amount of memory available for
compression table entries. (Entries are codes devised for redundant
data. The data is packed into shorter data units, called code words,
and unpacked by the receiving device.)
For the modem to
Command
Disable data compression
AT&K0
Auto-enable/disable data compression. The Courier
V.Everything mode
enables compression if the serial
port rate is fixed (&B1) and disables compression if the
serial port rate follows the connection rate (&B0).
AT&K1
(Default)
Always enable data compression
AT&K2
Selective data compression. Use this setting to transfer
compressed files. The Courier V.Everything modem
negotiates only for V.42
bis
compression, and disables
MNP Level 5 (MNP5) compression.
AT&K3
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 ...