User's Manual
V34bis Fax-modem - AJ 2885 P
AJ 2885 P - Page 11
The answer is carried out automatically if the command
ATS0 = 2
was sent to the modem by
the local PC. A training sequence is then initiated. A training sequence is the hand-shake
sequence between modems to establish a communication link. It establishes speed, modes...
1.4. Leased
line
A leased line is a permanent communication link dedicated between two modems. This kind of
link is used for:
•
High
usage,
•
Secure
communications,
•
Privately managed networks.
The leased line, can be a:
•
4-Wire type where there is:
1 transmit pair,
1 receive pair.
•
2-Wire type where:
the same pair of wires is used for transmit & receive.
For a leased line, a modem is designated:
•
Originating modem (ORIGINATE or MASTER),
•
The other as the answering modem (ANSWER or SLAVE).
Modems in leased line mode always try to connect when power is on, in order to provide
permanent a link.
The
AJ 2885
modem can establish leased line connections in the following speeds:
V22 1200
bps
V22bis 2400
bps
V32
9600 bps/4800 bps
V32bis
14400 bps/12000 bps
V34
33600 bps down to 2400 per steps of 2400 bps
In case of failure on the leased line, the
AJ 2885
modem performs automatic switch-over to the
dial-up PSTN. It then monitors continuously the leased line until it can connect again on leased
line. The AJ2885P modem is provided with an internal real time clock and calendar, to disable
dial backup when the link is not of use and then optimise the PSTN cost .
1.5. Protocols
Two types of protocols can be used to improve communication performance between two
modems:
•
Error
correction:
MNP4 or V42 detect errors which occurred during data transmission, and either correct
them or re-transmit the data.
•
Data
compression:
MNP5 or V42bis compress the data and thus transmit at a higher effective speed.
These two types of protocols improve efficiency and reliability of a connection.
1.6. Memory
Beyond these basic principles, the modem offers other functions, aimed at improving
performance and ease of use.
These functions are controlled via the memory (S-Registers) of the modem, and are available
via the extended AT command set.
