Ref: 99980067
Title: New Products/Broadband Network Systems
Date: 8/1/86

Copyright 3Com Corporation, 1991.  All rights reserved.

Overview

The Bridge Communications Broadband products provide multi-vendor
communications in pure broadband and hybrid broadband/baseband
applications.  They use 5M bps, Carrier Sense Multiple Access/
Collision Detection (CSMA/CC) local area network (LAN) technology
on a single 6MHz channel.

Bridge's Broadband servers use the Transmission Control Protocol/
Internet Protocol (TCP/iP) high-leve protocols.  They provide
network access to a wide variety of devices and offer
interoperability in multi-vendor environments.

Multiple data channels can be established to allow separate
networks to share the same physical cable, yielding a very high
aggregate data rate.  These multiple channels can include other
broadband services such as video and voice on other data
channels.

The Bridge Broadband frequency allocations is compatible with the
IEEE 802 standard.  The network can also operate on a midsplit or
highsplit cable plant up to 10 miles long.  Bridge Modems are
frequency agile and support six channel pairs; they use duo-
binary Amplitude Modulation Phase Shifted Key (AM PSK)
modulation.  These modems can be configured for single-cable or
dual-cable translated systems.

Features

*   Provides communication and resource sharing between
terminals, workstations, personal computers, peripherals, and
host computers.

*   Connects Ethernet segments through a broadband backbone that
operates independently of high-level protocols.

*   Supports speeds up to 5M bps and implements full CSMA/CD.  In
addition, the channl remodulator detects collisions for the
entire network.

*   Provides compatability with all of Bridge's TCP/IP Ethernet
products, including network control servers for bootloading,
configuration management, monitoring, and control.

*   Offers self-adjusting modems that eliminate much of the
routine alignment and maintenance associated with a broadband
cable plant.  Operating frequency is software controlled
for reconfiguration ease and sparing.

*   Includes closed-loop control mechanism allowing Bridge Modem
self-adjust transmit signal levels to compensate for changes
in the environment; therefore, the Bridge network stays
operational when others may fail.

*   Permits the broadband modem transmitter to shut itself off
after a timer expires to prevent malfunctioning equipment
from transmitting continuously.

The Bridge Communications Broadband Network System consists of
the Internetworking Bridge/1, Communications Server/200-B,
Communications Server/1-B, RFM/5 Modem, and CR/5 Channel
Remodulator.  The following list describes these broadband
products in more detail.

.h1;Internetwork Bridge/1

Overview

The IB/1 is a high-performance broadband-to-baseband internetwork
bridge that provides protocol-transparent routing.  It
interconnects a standard Ethernet (IEEE 802.3) and Bridge's 5M
bps CSMA/CD Broadband network to form an extended campus hybrid
network that covers a radius of up to 10 mles.

The IB/1 is a data link level (ISO Layer 2) bridge that routes
packets based on Ethernet addresses only.  It continuously
monitors traffic on the LAN, filters and discards messages
addressed to local stations, and forward any inter-LAN packets.
It can pass data between a baseband Ethernet and a broadband
network even when they are running incompatible high-level
protocol sets such as XNA, TCP/IP, DECnet, or ISO.

Features

The IB/1 and IB/2 run the same software.  Therefore, the
following features apply to both the IB/1 and IB/2.

*   A programmable, generalized filtering capability to isolate
excess inter-LAN traffic and to protect network security.  In
addition, customer filers can be set up to discard packets
based on Ethernet addresses.  They can also be set up to
filter traffic based on arbitrary masks on any packet byte,
word, or double words.  This feature allows the network
manager to fine-tune network performance and to restrict
internetwork access by user stations.

*   An integrated network management system.  Users can access
network management functions through a local console port or
through Bridge's XNS-based Communications Servers.

*   System parameters, routing information, and performance and
throughput statistics can be set, specified, or displayed via
the user interface commands.

*   Continuous adaptive learning of the network configuration.
The IB recognized the local and remote status of the
stations.  This feature greatly simplifies the installation
and reconfiguration of network stations.

*   Operation at the data link level as well as protocol
transparency.  A multi-vendor network can be set up to pass
data between a standard Ethernet and Bridge's Broadband
network.

*   With the addition of a Multiport Transceiver Unit (MTU), the
IB/1 becomes a Multiport Bridge/1, which can be used as a
front-end for up to seven Ethernet-compatible hosts and
devices on the broadband network.

*   With the multiple high-speed 68000 processors, the IB filters
local traffic at up to 7,000 packets per second and forward
inter-LAN traffic up to 2,500 packets per second.

*   Fully compatible with the entire Bridge family of
Communications Servers, Gateway Servers, PC network products.
and Network Control Servers.

.h1;Communications Server/1-B

The CS/1-B is a Communications Server that is installed on the
broadband network.  Since its hardware is based on a standard CS/
1, the CS/1-B can connect up to 64 asynchronous terminals, 3270
terminals, PCs, printer, modems, or host ports to the Bridge
broadband network.  The hardware interface options include RS-
232, RS-422, and 3270 Category A coax.

The CS/1-B can be a disk-based on diskless unit.  For the
diskless unit, operating software is loaded from a Bridge NCS/150
across the Internetwork Bridge/1.  The CS/1-B supports the audit
trail server, which gathers and records session information such
as conections attempted, whether successfully completed,
unsuccessful, or disconnected.

The CS/1-B runs standard TCP/IP software; therefore, it has the
same features as other Bridge TCP/IP products.

.h1;Communicaitons Server/200-B

The CS/200-B is a compact, diskless Communications Server that
connects four or ten RS-232 interface terminals, personal
computers, printers, modems, or host ports to the Bridge
Broadband network.

The CS/200-B runs TCP/IP software.  Its operating software is
loaded from a Bridge NCS/150 across the Internetwork Bridge/1.
The CS/200-B supports the audit trail service, which gathers and
records session information such as connections attempted,
whether successfully completed, unsuccessfuly, or disconnected.

The CS/1-B and CS/200-B require an RFM/5 to connect to the
broadband network.  Refer to the RF Modem/5 section or a more
detailed description of the RFM/5.

.h1;TCP/IP Features

The CS/1-B and CS/200-B described above are based on TCP/IP
protocols.  Bridge's TCP/IP implementation includes the following
features.

*   Server Telnet and User Telnet support.

*   Subnet support.

*   Passive-end or host-side RLOGIN.  The RLOGIN feature allows a
login from a UNIX host to a non-UNIX host front-ended by the
CS/1-B.

*   Primary and secondard name server support.  This feature
allows the secondary name server to be queried if the primary
name server does not yield a name to address resolution.

*   Default gateway support.  This feature allows all remote
network packets to be sent to a specified gateway.  The
gateway, however, should be able to return an Internet
Control Message Protocol (ICMP) REDIRECT if it is not the
optimal first hop.

*   The number of physical ports can be limited via the system
generation program allowing the number of shared sessions per
port to be increased.

*   The amount of system buffer allocated during initialization
time can be controlled via the system generation program.

*   Permanent Virtual Circuits support allowing automatic circuit
reestablishment upon disconnection.  Note that this feature
is only available in the CS/200 and CS/200-B.

*   Service Port Listener support allowing the TCP interface to
be exported to the serial line.  Refer to Application Note
number 12 for more detailed descriptions of these service
ports.

.h1;RF Modem/5

The RFM/5 is an external, frequency-agile modem that connects a
communications server or internetwork bridge to the broadband
cable and is powered by the server.  One of six operating channel
pairs can be selected through software commands.  The modem
supports adjacent channel operation to maximize use of the cable
bandwidth.  It also provides connections for single- or dual-
cable translataed systems.

Directed by the channel remodulator, the microprocessor-
controlled RFM/5 will automatically and continuously self-adjust
transmit levels to compensate for environemtnal changes.  The
Channel Remodulator/5 (CR/5) measures the signal levels of each
incoming packet, and sends a command to the transmitting modem to
increase or decrease the level whenever it drifts outside the
selected range.  This self-correcting feature makes the Bridge
Broadband network ideal for applications where up-time is
critical, and also greatly simplifies routine broadband
maintenance.

A jabber-inhibit feature automatically turns off the modem
transmitter when the maximum transmit time is up.  This prevents
a malfunctioning station from transmitting continuously and tying
up the entire channel.  The modem can also be taken off-line
remotely.

.h1;Channel Remodulatoor/5

The CR/5 is located at the cable headend to handle frequency
translation and packet regeneration for each Bridge Broadband
channel, filtering out any noise in the process.

The CR/5 detects collisions for the broadband network.  It
examines each incoming packet for framing errors or illegal bit
transitions.  To allow collision detection, the CR/5 broadcasts a
jamming signal to alert all modems so that the CSMA/CD protocol
can operate effectively.



