Specifications

Longer distance through fiber

Sometimes a network may need to span a long distance but there is no practical need for hubs distributed along

the way. The computer networking industry, on whom we’re already relying for an economical and rugged

transport medium, has an answer to this need also: fiber optics.

Data signals sent over optical fiber don’t degrade as much as they do over copper wiring, and they are immune

to induced interference from electromagnetic and RF sources, fluorescent lighting fixtures, etc. Consequently,

a Fast Ethernet fiber optic network segment (100baseFX) can be up to 2 kilometers (6560 feet, or 1.24 miles) long,

twenty times longer than what is possible with CAT-5 UTP copper wire.

Due largely to increased economies of scale, fiber optic cable pricing has become more economical in recent years,

so even 62.5 µm multimode fiber is no longer painfully more expensive than CAT-5 UTP. However, because of

the added cost of media conversion, it’s usually most cost-effective to use fiber only when distance or

electromagnetic conditions require it.

This illustration at right shows a simple 2-node

network similar to the “hubless” one decribed

before, except nearly all of the interconnect-

ing UTP cable between the RAVE devices has

been replaced by a couple 100baseTX-to-

100baseFX converters and a length of fiber

optic cable. The fiber optic medium allows you

to increase the distance between the RAVE

units by 2 kilometers. Some hubs, including

certain QSC FE models, have both UTP and

fiber ports and can thus perform the media

conversion themselves.

*Although any one fiber segment can be up

to 2000 meters long, and any single UTP seg-

ment can be up to 100 meters long, it may be

necessary to impose shorter limits, in con-

sideration of cumulative delays caused by

devices and cabling. See text for more in-

formation.

If you opt for the “hubless” topology shown in the illustration, beware of certain types of media converter that

don’t have a Fast Ethernet chipset for communication but instead “passively” convert electrical pulses to light

pulses and vice-versa. Such converters might not pass the network start-up transmissions that the RAVE units

and other Fast Ethernet hardware use to set up 100 Mbps communication, and the network will fail. If you

encounter such a problem, there are several solutions you can try:

1. At one or both ends, insert a Fast Ethernet hub in the network between between the RAVE unit and

the media converter.

2. Replace the media converters with ones that have true Fast Ethernet communication capability.

3. Replace the media converters with media-converting hubs, such as some of the QSC FE models.

The other network topologies described earlier also can be upgraded with optical fiber. This can be done with

media conversion on individual network segments (opposite page, top) or by using fiber to interconnect hubs

(opposite page, center), or combinations thereof. You can further simplify the networks by using hubs that have

built-in media conversion capability, such as certain QSC FE models.