DUAL-SPEED WORKGROUP HUBS

Are you looking for flexibility, low cost and a good price-performance ratio in a
workgroup hub? Who isn’t, you say? Your search is over. A move to dual-speed 10/100
Ethernet/Fast Ethernet autosensing hubs is the way to go to fold 10-Mbps LANs into a
high-speed 100-Mbps Fast Ethernet system.

10-Mbps Ethernet is the most widely used network standard in the world for good
reasons. It is cost-effective and has evolved to support a wide range of inexpensive
media.

But contention-based 10-Mbps Ethernet schemes can no longer keep up with heavy LAN
traffic. Even the smallest workgroups usually connect to client-server network
architectures via high-end servers and powerful PCs. Memory-intensive applications and
Internet access are the rule, not the exception, for most users.

Designed to deliver better performance for network servers and high-end users, 100-Mbps
Fast Ethernet is rapidly becoming the network scheme of choice for even small workgroup
LANs.

Fast Ethernet is an extension of the 10-Mbps Ethernet standard but runs up to 10 times
faster. Like Ethernet, it is stable and cost-effective to install and operate. But while
many would like to move to an all-100-Mbps network, they cannot do so without sacrificing
support for legacy 10-Mbps equipment. That gap generated the need for bridge technology
that lets 10-Mbps Ethernet and 100-Mbps Fast Ethernet systems coexist.

Combined 10/100 Ethernet/Fast Ethernet technology is based on dual-speed 10/100 network
equipment, including hubs, switches and network interface cards or network adapters. Such
dual-speed devices promise to span conventional 10Base-T Ethernet devices and high-speed
100Base-TX devices.

10/100 switches, which provide dedicated bandwidth to connected devices, perform better
than hubs, but that performance comes at a high price. Many listed hubs come with built-in
switches that eliminate the need for expensive external 10/100 switches.

The accompanying chart features dual-speed workgroup hubs that can serve up between
four and 32 ports at 10-Mbps Ethernet or 100-Mbps Fast Ethernet speeds. Some are designed
as standalone units that operate separately as small workgroup hubs or can daisychain to
serve dozens of users.

Stackable hubs can be cascaded via specialized high-speed cables to form logical hubs
with higher port densities than single units. Just about all the listed hubs are
autosensing units. They can tell whether the NICs or adapters at the other end of the
connection operate at 10-Mbps or 100-Mbps and can automatically match the data rates.

Despite its appeal, mixing 10-Mbps and 100-Mbps speeds within a single network device
is a challenge for both network users and equipment designers. Ethernet and Fast Ethernet
standards are fundamentally compatible, but each technology uses different cabling schemes
and topologies.

Ethernet uses two-pair Category 3 unshielded twisted-pair cables for its 10-Mbps
throughput rates; 100Base-TX Fast uses Category 5 shielded twisted-pair.

Distance limits are less important to 10-Mbps Ethernet than to Fast Ethernet. Fast
Ethernet’s higher transmission speeds and need for shorter collision-detection
response times require a maximum of five meters between hubs and a total network diameter
limit of 205 meters.

Usually, simply swapping new 10/100-Mbps units for slower old hubs isn’t enough to
turn a 10-Mbps Ethernet LAN into a 10/100 LAN. You first must ensure that Category 5
cabling is used throughout the network and that the basic topological limits of Fast
Ethernet are observed.

Although a few desktop dual-speed hubs, such as D-Link Systems Inc.’s four-port
DFE-904, rely on manual switch-setting to change operating speeds between 10 Mbps and 100
Mbps, most are autosensing. That is, each port on the hub can automatically detect and
adjust to the 10-Mbps or 100-Mbps speed of the equipment linked to it. Autosensing lets
dual-speed hubs not only serve up 100-Mbps Fast Ethernet speeds but protect users’
investments in legacy 10-Mbps Ethernet equipment.

Each dual-speed hub holds two independent 10-Mbps or 100-Mbps segments. Signals coming
from attached devices into the hub go first to a multiplexer. The multiplexer determines
to which segment the signal should go. Usually, an internal bridge links the two
independent segments, allowing attached 10-Mbps or 100-Mbps devices to communicate. The
bridge can also link 10-Mbps and 100-Mbps devices in cascaded, or stacked, hubs.

Some hubs have a built-in switch. For example, the ED-1508X, ED-1516S and ED-1524S hubs
from Edimax Computer Co. automatically switch traffic between devices running at different
speeds, facilitating communication between ports running at 10 Mbps and those running at
100 Mbps.

Several technologies can expand a single hub’s port capability beyond its basic
four-, eight-, 16- or 24-port capacity. Simple desktop standalone hubs, such as
D-Link’s DSH-5 hub or Ovislink Technologies Corp.’s palm-sized Ether-FH8DS,
aren’t designed to be expanded. Other standalone hubs, including 3Com Corp.’s
OfficeConnect Dual Speed Hub 8, Addtron Technology Co. Ltd.’s ADH-508, Cisco Systems
Inc.’s 1528 Micro Hub 10/100 and Hewlett-Packard Co.’s HP ProCurve series, may
easily be daisychained to achieve multiples of their native port capacities.

You can link dual-speed stackable hubs that have internal switches, including
Edimax’s ED series, to form larger logical 10-Mbps and 100-Mbps hubs and connect
those hubs via the switch.

Like the ED series, IBM Corp.’s 8245 dual-speed series has separate 10-Mbps and
100-Mbps backplanes, or segments, and uses an optional bridge that functions as a
three-port switch to prevent bottlenecks. A stack of 12-port or 24-port 8245 models holds
up to six hubs and automatically supports 10-Mbps and 100-Mbps throughput by using the
bridge to join segments.

A hub with an internal switch used as a link to outside equipment also replaces an
expensive external switch while providing a high-end server, for example, with a dedicated
high-bandwidth connection of up to 200 Mbps.

Not all dual-speed hub designs require an internal switch in all hubs. To cut down on
costs while providing expandability, D-Link’s DFE-26xx 16-and 24-port hubs come with
master units equipped with built-in switches and slave units without them. Trendware
International Inc.’s T100 hubs are similarly designed.

Are managed hubs worth the extra money? For small- to medium-sized workgroup LANs,
exotic hub management technology usually is not necessary. As LANs expand and proliferate
into larger networks, however, hubs with built-in Simple Network Management Protocol and
remote monitoring (RMON) can prove worth the money.

Network Peripherals Inc.’s 16-port DH16M is a managed stack master that allows
stacking up to five units for a total of 112 ports in a single stack. The unit supports
industry-standard SNMP, RMON Groups 1 through 4, Telnet and Hypertext Transfer Protocol
server management and monitoring functions. It comes with Hewlett-Packard Co.’s
SNMP-compliant HP OpenView for Microsoft Windows. You can use any Web browser to monitor
the hub or stack. Trivial File Transfer Protocol , a version of the TCP/IP File Transfer
Protocol that has no directory or password capability, allows firmware downloads without
changing hardware.

A dual-speed 10/100 workgroup hub will include some of these features and options:

Bargain-hunters in search of a good buy on dual-speed hubs will pounce on NDC
Communications Inc.’s new eight- and 16-port SOHOware Dual-Speed SuperFlex Hubs.

Both the NDS108 at $349 and the NDS316 at $699 have a surprisingly complete range of
features. Both are autosensing, standalone, unmanaged units and come with internal switch
ports—one in the NDS108 and three in the NDS316—that eliminate the need for an
external 10/100 network switch when the hubs are used.

The three-port NDS316 can provide an astounding 600-Mbps of bandwidth for full-duplex
switched connections to servers, high-end workstations or backbone switches.

They also solve the 205-meter cabling restrictions of Fast Ethernet by providing an
unlimited uplink cable length via the integrated switch ports.

Because the NDS108 and NDS316 are autosensing units, you can simply plug in the network
cable and they will automatically and with no user intervention determine whether the
connection is 10 Mbps or 100 Mbps.

Both models enable store-and-forward switching between 10-Mbps and 100-Mbps networks to
protect against bad packets and enhance the flow of error-free traffic. LEDs on all the
ports indicate whether or not the port is active.

NDC spokesmen estimate that, before month’s end, the street price of the NDS108
will be $239 and the NDS316 will be $499.

Check out the hubs on the company’s Web site at http://www.ndclan.com.

Contact NDC Communications Inc. of Sunnyvale, Calif., at 408-730-0888.
    

J.B. Miles writes about communications and computers from Carlsbad, Calif.