Adapters
Modems
www.networking.ibm.com
53
A
Product Overview
Flexible operations in both
synchronous and asynchronous
mode
The 7858 provides flexible operation in
synchronous and asynchronous mode
over switched and 2- or 4-wire leased
telecommunication lines.
Each 7858 modem can be controlled and
configured from the front panel, from a
DTE using AT commands, or NetView
®
using LPDA commands.
The following command sets are
available:
• Hayes Attention (AT) command set
• ITU V.25bis asynchronous command
set
•ITU V.25bis synchronous command set
• IBM's LPDA commands.
The modem can be configured to
operate in asynchronous or synchro-
nous mode:
• Asynchronous mode:
- AT Command mode / Hayes
Autosynch
- Asynchronous V.25bis Command
mode
- Dumb mode (The modem does not
accept any command from the DTE.)
• Synchronous mode:
- Asynchronous Command mode and
Synchronous Data mode
- Synchronous Command mode and
Synchronous Data mode
- Synchronous V.25bis Command mode
- LPDA-2 mode.
Standards compliance
The 7858 modem supports a wide
range of ITU and industry standards:
Digital Interface standards:
•ITU V.24
•ITU V.28
Modulation Mode standards:
• ITU V.21
• ITU V.22 alternative A/B with V.25
autoanswer
• ITU V.22bis
• ITU V.23
• ITU V.32
• ITU V.32 bis and V34
Other standards:
• ITU V.14 Async/Sync conversion with
overspeed range selection
• ITU V.42 Asynchronous error checking
compatible with the Microcom Net-
working Protocol (MNP) class 4 service.
With this error checking, the data
integrity in asynchronous operation is
as good as typical synchronous
protocols.
• ITU V.42bis data compression compat-
ible with MNP class 5 service
• ITU V.54 loop testing capabilities
• ITU AT and ITU V.25bis Automatic
Calling Interfaces
• IBM LPDA-2 command set for network
management
• Fax support Group 3 Class 1 ITU V.29,
V.27 ter, and V.17
Automatic adaptation to a
network environment
The 7858 supports functions that
automatically adapt to the changing
network environment. For example, it
supports auto-mode capability to
automatically select the modulation
scheme at connection setup. This
function determines the appropriate
modulation scheme (V.34, V.32bis,or V.32)
based on compatibility with remote
modem capabilities.
The 7858 also has an adaptive line rate
facility that automatically decreases or
increases the transmission speed to
constantly achieve the highest
performance compatible with the line
quality. It adjusts the speed if telecom-
munication line conditions degrade or
improve and according to the transmis-
sion protocol negotiated at connection
setup.
Switched Network Backup (SNBU)
capability establishes a switched
connection when a leased line is down.
A SNBU connection is associated with
a timer selected at modem setup.
With
leased line monitoring
one of the
following actions can occur after a time
out, depending on the modem configu-
ration:
• The active SNBU line is released and
the modem switches back to a leased
line. If the leased line is still down, a new
SNBU call is set up.
• The modem switches back to the
leased line operation without releasing
the SNBU line. If the leased line
communication is operational for one
minute, then the SNBU line is released;
otherwise the communication is
resumed through the SNBU line.
The 7858 also incorporates asynchro-
nous speed buffering, which allows the
DTE speed to remain constant even
when the modem-to-modem line speed
changes from call to call. For example,
the DTE speed might be 115.2 Kbps
while the line speed is 33.6 Kbps.
High-throughput telecommuni-
cations over switched and
leased lines
The 7858 modem operates on switched
and 2- and 4-wire leased lines. The
supported line and DTE speeds are
listed in the Supported Line and DTE
Speeds table.
