0049-2702-XXX Alliance Series Modems – USER MANUAL
08/05/2010
Rev. A
Page 35 of 197
•
For 600- or 1200/75-bps operation, V.22bis/V.22/V.21/V.23 operating mode fallback
option must be selected. To connect at 1200/75 bps, the minimum and maximum data
rate must both be set at 1200/75 bps on both modems.
Related options: Buffer Mode / Speed Conversion, Speed Matching, Forward Rate
Renegotiation, Asynchronous Overspeed Range, DTE Speed.
Symbol Rate Settings
The minimum and maximum symbol rate settings (“SYM” on the LCD) apply to V.34
connections only. The available selections are
3429, 3200, 3000, 2800, 2743, 2400
sym/s
(symbols per second).
Where analog implemented carrier is used, more calls will connect successfully at symbol rates
of 2743 and 2800 sym/s. On noisy T1 PCM digitally implemented connections, more calls will
connect when the symbol rate is set to 3429-sym/s.
V.42 ERROR CORRECTION OPTIONS
The ALX supports both ITU-T V.42 and V.42bis error correction and Microcom Networking
Protocol (MNP) error correction (classes 1 through 5). V.42 and MNP both provide end-to-end
correction through an automatic repeat-transmission request algorithm. Both types of error
correction enable the ALX to detect data transmission errors and automatically request
retransmission of adversely affected data until it is received correctly.
Either error correction standard (V.42 or MNP) may be enabled for either dial or leased line
operation (except V.33, V.29, V.27 and V.26 modes). However, error correction can only
function if
all
of the following conditions are present:
•
The modem the ALX is communicating with must be equipped with the same type of
error correction (V.42/V.42bis or MNP).
•
Both communicating modems must be configured for
asynchronous
data type.
•
The same type of error correction (V.42/V.42bis or MNP) must be enabled at both ends
of the communication link.
•
The connected systems must support data flow control (data buffering).
Note –
•
Error correction options cannot be changed when the modem is on-line.
•
Disable error correction before running diagnostic tests to ensure valid results.
You can configure the ALX for V.42 (LAPM) error correction only, MNP error correction only,
or V.42 error correction with MNP as the fallback (alternate) error correction protocol. Data
compression may also be enabled by selecting either V.42bis or MNP class 5 error correction.
