Ref: 10820008
Title: History of 3Com's Communications Server Models
Date: 6/11/91

Copyright 3Com Corporation, 1991.  All rights reserved.


Bridge Communications Inc. began producing Communications Servers in 1981.
They were first designed to give terminals access to the Ethernet, but
are now used to accomplish a number of different tasks.  In addition to
giving terminals access to the Ethernet, they can provide modem
connections, inbound or outbound, single or pooled.  They can also
provide a network front-end to a host computer.  All of these functions
are supported in the XNS, TCP/IP, or OSI software packages.

When thinking of the Comm Server in the network, think of it as glass;
connections go through it.  Connections are not made to the Comm Server
itself, but to devices that are on the other side of it.  Applications
do not run on the Comm Server, but through it.

Following is a description of each Comm Server model.


CS/1:

The first Comm Server was the CS/1.  Its purpose was to enable terminals
to make connections via Ethernet to host computers which have Ethernet
access.  The CS/1 consisted of 4-7 boards:

  *  the Main Central Processing Unit (MCPU)--designed around the
     Motorola 68000 microprocessor, with a clock speed of 8 MHz.

  *  the Ethernet Transceiver Interface (ETI)--along with the ESB, the
     ETI controlled access to the Ethernet.  The ETI provided access to
     the transceiver, and ultimately to the physical Ethernet cable.  It
     had no microprocessor.

  *  the Ethernet Shared Buffer (ESB)--designed to provide memory space
     for DMA (Dynamic Memory Allocation) of the Ethernet data.  The ESB
     had an 8 MHz 68000 microprocessor.

  *  the Serial Input/Output (SIO) board(s)--designed to provide serial
     line (RS-232) interface to the unit.  There could be from one to
     four SIO boards, depending on the customer's needs.  The SIO boards
     were tied together by the MBI (MultiBus Interface) board in the
     bottom of the CS/1 chassis.

One important feature of the CS/1 chassis was its versatility.  Through
the years, many changes were made to the basic unit.  The MCPU board was
upgraded from 8 MHz to 10 MHz, to 12 MHz, and finally to the Motorola
68020 microprocessor, with a 16 MHz clock speed.  CPU memory size
increased from 256 KB to 512 KB, and finally to the current size of 384
KB.  Also, Ethernet control, initially provided by the ETI and ESB
working together, was later provided by the Intelligent Ethernet Control
Module (IEC/M), sometimes called the EC2.  (For broadband networks, the
Intelligent Broadband Control Module [IBC/M], can be installed instead
of the IEC/M network interface.)

The first serial input/output board was the SIO-A, designed around the
Motorola 68000.  It supported eight RS-232 async ports.  When it was
discovered that customers needed sync and SM support, Engineering
designed the SIO-A/U (async/universal) board, which could be modified to
support a multitude of serial interface protocols, including RS-232 SM,
V.35, and Honeywell 422.  All of these provided sync and async support.

The SIO-A/U was a single board that could be modified into 14 different
loading options to fit customers' needs.  With various combinations of
SIO boards and software, the CS/1 chassis can be a Communications
Server, an Internetwork Bridge, a Bridging Router, or a Gateway Server.
Loading options also enable the CS/1 to act as an SIO board for
Internetwork Bridge and Bridging Router applications.

Initially, all CS/1s had 48tpi floppy drives.  The FDC (Floppy Drive
Controller) was a daughter board attached to the MCPU board.  When the
68020-based MCPU (MCPU20) was released, the code image had grown
sufficiently to require a 96tpi drive to support it.  Sometime between
the last of the SIO-A/U developments and the beginning of the MCPU-20,
as a result of the need for a lower cost-per-port solution, the SIO-16
was developed.  This board provides limited RS-232 support for 16 ports
per board (up to 64 async ports on a CS/1).  The SIO-16 does not
support RTS/CTS flow control.

There was a token ring network controller for the CS/1 line.  Not many
token ring network controllers were sold, presumably because at the
time, token ring was slow, and most of Bridge's customer base were
mainframe shops not interested in token ring.


CS/100:

Engineering developed the CS/100 to meet the continuing need for a lower
cost-per-port solution.

The first version was based on the Motorola 68000 processor.  For this
use, an 8 MHz clock speed was fast enough.  As a cost saving measure, a
single-board unit was developed.  There are two 68000s, one for the MCPU
function, and another for SIO functions.  Ethernet access is
accomplished via a SEEQ Ethernet coprocessor, with discrete DMA.  All
three of the coprocessors are "mated" at memory; that is, they all use
the same 256 KB (or, in later versions, 512 KB) of RAM.

The first CS/100 offered four RS-232 ports.  Engineering soon developed
a daughter board that provided another six ports, and, later, an
additional four-port daughter board.  Real estate and processing speed
dictated that this be the end of the additions--almost.

It had become apparent that there was a need for a Network Management
product.  Engineering responded with a modified CS/100 which has a real-time
clock board and an expanded capacity floppy drive.  This unit offered
audit trail, remote configuration of Comm Servers, and network
booting capabilities.  The network booting capability was the cause of a
near doubling of the product line by offering diskless Comm Servers as a
cost saving measure.

CS/100s run either XNS or TCP/IP.  There is no broadband option.

A major shortcoming of the CS/100 product line was the SEEQ.  The SEEQ
had two major problems:  it was not capable of transmitting and
receiving at the same time, and it did not have the ability to perform
DMA.  As a result, a large, inelegant discrete circuit was required,
which eventually caused Engineering to develop a new model of Comm
Server.


CS/200 and CS/210:

After the shortcomings of the CS/100 had become apparent, Engineering
chose an entirely new approach in the CS/200.  The CS/200 had a single
68000, plus the Intel 82586 Ethernet coprocessor.  The 82586 addressed
both of the major problems in the SEEQ, the simultaneous TX/RX, and the
ability to do its own DMA.  The CS/200 gives full RS-232 support on ten
async ports, and ports 0 and 1 provide limited support to sync RS-232.
As a cost saving measure, the CS/200 has no disk drive, so it had to be
booted from an NCS.

Although the CS/200 was successful, customers also wanted to be able to
do a local boot.  Thus, Engineering provided the CS/210.  Because there
was no room in the chassis for a disk drive, Engineering moved the power
supply to a mounting bracket that "bridged" over the main board.  At the
time it was agreed that this was a less than optimum solution, but the
design was implemented in order to deliver the product to market in a
timely fashion.

After the merger of 3Com and Bridge Communications, Marketing wanted a
new look for the CS/200 and CS/210.  At the same time, Manufacturing was
looking to reduce costs by using as much common hardware as possible.
These conditions led to the development of the CS/2000 and CS/2100.
Both units used the CS/210 board, the modular power supply from the
NETBuilder, and a redesigned chassis which allowed Manufacturing to
reduce the number of parts required for stock.


CS/50:

3Com designed the CS/50 primarily for the U.S. government, to provide a
two-port, diskless Comm Server.  The CS/50 eliminated the need to string
RS-232 cables along with the Ethernet in installations where users are
separated by long distances.  The CS/50 used the Motorola 68000 (a lot
of processor for a two-port Comm Server!) and the 82586 microprocessor.


General Information:

All of the products designed by Bridge Communications Inc. use a
proprietary format for the floppy drives.  The software cannot be copied
on a standard PC.

All of the products designed by Bridge Communications Inc. except
the ESPL/100 product line have loading options to provide support to a
broadband network.

Configuration needs to be broken into two parts:  how the Comm Server
acts on the network (through SYSGEN), and how the serial port acts.
These characteristics are defined in each port's default parameters
(DP).  This is different in the 4.x release of TCP and TCP/LAT.  In
both of these packages, the menuing system addresses SYSGEN and serial
port parameters.  Note that in these releases, the term SYSGEN now is a
read-only term.  The actual SYSGEN parameters are addressed throughout
the menuing scheme.