AT&T makes Ethernet switching as easy as a "Seabreeze"

August 22, 1995 -- BERKELEY HEIGHTS, N.J. -- AT&T Microelectronics has made
it possible to design a cost-effective, expandable 12-port, four-segment
Ethernet switching system which enables users to reconfigure port-switched
hubs virtually on the fly.

With the combination of the newly-introduced ATT1S04 Seabreeze switching
device and three ATT1RX04 Forespar quad single-port repeaters, system
designers can now offer customers flexible network management features
like per-port switching and port mobility.

"The Seabreeze switch is an ideal building block because its scaleable
design allows it to be cascaded to support up to 192 ports among multiple
segments," noted Clarence Joh, AT&T's Ethernet IC marketing manager. "It
solves the OEM's concerns about time-to-market while matching the user's
investment closely to current, as opposed to future needs."

While governing collision detection and data-path switching for each
segment on a port-by-port basis, the Seabreeze device enables network
managers to use software to reassign a port to a different segment,
thereby eliminating the need for hardware changes.

Per-port segmentation and port mobility improves network management by
enabling the network administrator to better balance traffic loads, set
aside certain segments for redundancy and reliability -- all without
costly hardware moves and rearrangements. Additional management features
are possible through the Forespar's microprocessor interface, providing
access to status and configuration registers, on-chip security options,
and a packet postprocessor with an associated 32-bit event counter for
statistical monitoring. Moreover, AT&T's hardware-based patented security
feature is a selectable option for automatic protection from eavesdropping
and intrusion.

The new Seabreeze switching device helps further reduce design costs by
integrating miscellaneous board-level circuitry. Among on-chip functions
are address decoding for three Forespar repeater devices, powerup reset
and a software-controlled hardware reset to the repeaters. The Seabreeze
device conditions a system-level hardware reset to the Forespar repeater
and also indicates completion of any reset operation.

Packaged in a 132-pin bumpered plastic quad flat pack (BQFP), the ATT1S04
Seabreeze chip is available now at $9.15 each in 10K quantities.

For product literature, customers may call the AT&T Microelectronics
Customer Response Center, 1-800-372-2447, Dept. P65 (in Canada,
1-800-553-2448, Dept. P65); fax number +1-610-712-4106 (especially for
callers outside of North America); or write to AT&T Microelectronics, Room
21Q-133BA, 555 Union Boulevard, Allentown, Pa., 18103.

AT&T Microelectronics offers a full line of high performance integrated
circuits, electronic systems and optoelectronic components for
applications in network computing, telecommunications, wireless and
messaging products and multimedia workstations.

MULTI-PORT ICS MAKE ETHERNET SWITCHES COST EFFECTIVE FOR MAINSTREAM USE

Local Area Network (LAN) switches are slowly moving from specialty to
mainstream status due to their ability to extend the functionality and
baseline capacity (number of nodes) of a LAN. Unfortunately, the low-cost,
widely-available ICs used to implement the single-port LAN interface in
workstations or passive hubs aren't cost effective for use in multi-port
active LAN switches. Therefore switch manufacturers require an entire new
class of VLSI devices to continue and drive down the cost of switching
technology. Ethernet has come a long way from the early days of bus
topologies using shared coaxial media. First, the computing community
devised the 10BaseT Ethernet derivative that took advantage of both the
more easily maintained star topology and lower-cost, twisted-pair
cabling.

Both, coax and 10BaseT Ethernet installations, however, share a similar
problem -- bandwidth limitations. Both topologies rely on shared media and
use collision detection and rebroadcast techniques as a media-access
scheme. As the number of users on a network grows more collisions occur
causing more data packets to be broadcast multiple times thereby resulting
in degraded performance.

One way to increase performance in a LAN is to move to faster communication
schemes. The ongoing 100BaseT and 100VG efforts, for example, are both
techniques that extend Ethernet transmission speed from 10 Mbits/sec to
100 Mbits/sec. AT&T, in fact, supports both new standards.

But faster data transfers don't get at the crux of the shared-media
limitations. Faster speeds certainly enable applications requiring rich
media streams such as compressed digital video. But faster speeds alone
don't eliminate congestion on the shared media and this congestion
degrades performance regardless of maximum data transfer speed.

Ethernet switches are the best solution for maximizing LAN bandwidth. The
heritage of the LAN switch is the telephone switch. A series of switches
maintain a direct physical connection between two parties for the entire
duration of a telephone call. The connected parties have the full use of
the bandwidth supported by the connection during the call.

A switch that could establish a dedicated link between any two nodes on a
network would be ideal but impractical. Moreover, data flow on an Ethernet
LAN is broken into packets or frames so a pure circuit switch isn't
required to effectively boost capacity. Instead, so-called frame and
segment switches are two different ways to solve the bandwidth problem
using switching technology.

FRAME SWITCHING

Frame switching was the first Ethernet switching technology and was
introduced by Kalpana and others in 1990. In a frame switching
environment, each workstation or node connects directly to one port of the
switch. The workstation Ethernet interface operates just as if it were
connected to a shared-media 10BaseT topology, except, the dedicated switch
port eliminates collisions. The workstation node can broadcast a data
frame anytime it is ready.

In the frame switch, the switch port is responsible for receiving the data
frame and sending the frame to the appropriate destination node. Each port
of the frame switch, therefore, must integrate MAC (media access control)
layer functionality because the port must be capable of examining the
incoming frame and extracting the destination address.

Frame switches use several techniques to move a packet along to the
destination. The most common method is called store-and-forward. In a
store-and-forward switch, the port receives the entire incoming frame,
checks the frame for errors, extracts the destination address, and
forwards the packet to the destination node.

To eliminate the latency of waiting for the entire packet to arrive before
forwarding the frame, some vendors implement a cut-through technology.
Essentially, the frame switch extracts the destination address from the
header of the frame and begins the forward operation immediately. While
this technique reduces latency, it can result in the transmission of an
error-laden frame.

Regardless of the frame-forwarding scheme, all frame switches share the
same basic set of features and characteristics. The key feature of the
switches is the ability to add LAN capacity by adding ports without
degrading performance as long as the bandwidth of the switch isn't
exceeded. The switches typically use RISC processors, a fast backplane,
and a large shared-memory array to process packets.

The most significant drawback of frame switches is cost. The RISC
processors and memory arrays, and the need for a MAC in every port make
the switches relatively expensive -- too expensive for many mainstream
LANs.

SEGMENT SWITCHING

Segment switching takes a different tact to solve the bandwidth problem.
Rather than eliminating the shared-media scheme of connecting nodes,
segment switches attempt to reduce collisions to a negligible level by
breaking the overall network into small segments. Within each segment, the
nodes still rely on shared media and collision detection. But the system
administrator ideally defines the segments so that most of the traffic on
each segment is local to the segment and collisions aren't a problem.

Segmentation is a widely tested concept. System administrators have been
segmenting Ethernet LANs for years, albeit by manually connecting patch
cords in a wiring closet. The administrator would physically connect all
workstations within a segment to the same passive hub, and messages
between hubs would be handled by bridges.

Historically, the downfall of segmenting LANs was the manual effort
involved. Administrators typically provided segments based on departmental
boundaries such as accounting, marketing, or engineering. Problems would
arise when a segment should more logically be formed in a different manner
-- around a project team for example.

Consider a team working on a new product that might include some engineers,
a marketing person, someone from accounting, a purchasing agent, and a
manufacturing engineer. Without segment switching, different physical
locales and the cost of manually wiring segments made it impractical to
physically connect the project team members from different departments.

A project team with regular communication needs and with members connected
to different LAN segments, could increase traffic and degrade performance
throughout the corporate LAN. For example, if the team member from
accounting broadcasted a new budget to everyone on the team, the broadcast
would create traffic on all of the segments rather than a single segment.

Remotely controllable switches made remote management and configuration of
a segmented LAN possible. The earliest segment switches, however, still
had limitations. For example, the cost of the repeaters that broadcast an
Ethernet packet across the shared media made it impractical to handle the
segment switching on a per-port basis. Instead, a group of four or more
nodes would be multiplexed through a single repeater making segmenting
possible on a small group basis.

PER-PORT SEGMENTING AND VIRTUAL LANS

Newer VLSI ICs, however, now make per-port segmenting or micro-segmenting
cost feasible. To drive the price per port down, for example, AT&T has
introduced ICs that support multiple channels including a repeater
dedicated to each channel. These developments have led segment-switching
proponents to coin a new term -- virtual LANs -- describing the ability to
connect any user to a dedicated LAN segment on an ad hoc basis. The users
connected to each segment have access to reserved bandwidth by being
physically switched onto the segment. Should the organization change, the
administrator can remotely reconfigure the segments.

Specifically, two VLSI ICs from AT&T provide switch vendors with the
capabilities required to build segment switches that can handle per-port
switching. First, the ATT1RX04 Forespar announced as the T7204 in 1994
integrates four independent Ethernet channels. Each channel includes a
transceiver, a repeater, and a NRZ (non return to zero) backplane
interface.

Second, the ATT1S04 Seabreeze includes 12 NRZ ports and can independently
switch each of the 12 ports to one of four circuit segments. The Seabreeze
is being announced in August, 1995.

ATT1RX04 FORESPAR

The Forespar IC implements a comprehensive set of features that allow
switch vendors go beyond offering simple port switching capabilities. The
front-end transceiver interface, for example, directly supports 10BaseT
twisted pair and external AUI (attachment unit interface) transceivers.
The AUI compatibility will allow both coaxial or fiber media to connect to
a segmented network. Each transceiver also supports smart squelch, link
integrity detection, long line length, and automatic polarity reversal
direction and correction. The back-end NRZ backplane interface supports
data, collision, carrier sense, and clock signals.

The repeater core is the heart of the Forespar chip and implements a rich
feature set including:

* Data and clock recovery with +/-18-nsec jitter tolerance.
  Selectable full preamble regeneration.
* Selectable packet fragment extension to 96 bits.
* Per-port auto partition/reconnection state machines.
* Individual port transmit and receive disables.
* Support for segments based on both media and backplanes.

The Forespar IC also includes an AT&T-patented hardware security
controller, port configuration and status registers, management statistic
registers and counters including support for RMON statistics, and status
LED controllers. These functions are linked into each repeater channel and
provide the basis through which a switch vendor can offer robust network
management capabilities. A microprocessor interface allows for remote
monitoring and configuration of each port.

The hardware-based network security controller handles automatic
eavesdropping prevention, and intrusion detection and control. The
controller supports one source address per port, and can learn the source
address automatically or under programmable control. The security features
work with broadcast and multicast packets. And the intrusion detector can
lock the last source address for management notification.

In addition, the ATT1RX04 optionally supports two universal media ports for
10BaseT, AUI, 10BaseFL, and 10BaseFB. For 10BaseFL and FB, the
twisted-pair and AUI interface logic is bypassed to reduce the latency
through the repeater core.

ATT1S04 SEABREEZE

A single ATT1S04 Seabreeze IC is the ideal companion to a set of three
Forespar ICs. Together, the four chip set can implement a complete
12-port, 4-segment switch.

The Seabreeze is an equally robust complement to the Forespar, providing
data path switching, collision detection, and address decoding for a
glueless interface to the quad-repeater ICs. The Seabreeze also supports
system-level reset functions including power-up reset, and
software-controlled hardware reset of attached Forespar repeaters.

Switch vendors can also cascade Seabreeze ICs to design hubs supporting
more than 12 ports. A 4-bit ID allows for expansion to 192 ports.
Moreover, the IC also includes provisions to support more than four
segments when cascaded.

The ATT1RX04 Forespar and ATT1S04 Seabreeze provide switch vendors with the
first truly cost-effective solution for reconfigurable, port-switched
hubs. The ICs support flexible configurations, and allow the vendors to
meet the intense time-to-market pressures that are prevalent in today's
computer industry.
 
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