Media converters are sometimes used to add a point-to-point fiber-optic
link between buildings for ground isolation and noise immunity. Media
converters may be more cost effective than an entire hub or switch fitted with
a fiber-optic transceiver on both ends of the link. Sometimes, small form
factor Ethernet switches are used as media converters and are often a better
choice than a typical media converter.
Consider the following guidelines when choosing between a media
converter and switches with small form factors:
- With Ethernet media
converters, the entire link must operate at the same speed and duplex or severe
communication problems can occur. This means that both fiber-optic and twisted
pair devices must operate at the same speed and duplex. For example, the
twisted pair link cannot operate at 100Mbit while the fiber-optic link operates
at 10Mbit. The lower speed of the two attached devices determines the maximum
speed for the link. Likewise, the twisted pair port of the media converter
cannot operate at half duplex while its fiber-optic port operates at full
duplex. For 100Mbit half duplex operation between a half duplex controller and
a half duplex fiber-optic media converter attached to a switch’s fiber-optic
port, fiber-optic distance is limited to less than 300 meters because the
entire link is half duplex. The actual fiber cable distance must be calculated
on a case-by-case basis depending upon the manufacturer’s specifications for
propagation delay through the media converter.
- With Ethernet switches with
small form factors such as the DeltaV Single Port Fiber Switch and DeltaV Four
Port Fiber switch, the twisted pair port on the switch operates with
independent collision domain timing from all other ports including the
fiber-optic ports. This ensures that the fiber-optic distance can always be two
kilometers and the twisted pair distance can always be 100 meters. Due to
advances in switch technology and new components, the cost of a multi-port
small form factor switch is about the same as a two port media converter. In
addition, more devices can be added to this small switch as the system grows.