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minus 10 BT for two short TP cables from the hubs to the Converters leaves 202 BTs.
minus 160 BT for two Media Converters leaves 42 BTs for fibre cable, Which indicates a fibre
cable length of about 40 meters.
It is obvious that using twisted pair wiring to connect the hubs would enable the interconnect length
to be the 100 meters maximum for twisted pair media, and this would still leave about a hundred BTs
as a safety margin. In other words, use of Media Converters and fibre in this case did not gain
allowable maximum cable distance vs. TP cable without the Media Converters.
Consider a more typical use of the Media Converters in a shared Fast Ethernet segment. A stack of
Fast Ethernet hubs comprises the only repeater in a collision domain, and the users and servers in
the local work group are connected via category 5 twisted pair cable, a maximum of 30 meters (100
ft.) in length. It is desired to connect one remote user with a fibre NIC via fibre cable, using the Media
Converters circuit. How long can the fibre cable be?
The solution is:
512 = total available Bit Times in a collision domain diameter,
minus 100 BT for two DTEs on each end leaves 412 BTs,
minus 90 BT for class 11 stackable repeater leaves 322 BTs,
minus 30 BT for one 30-meter TP cable from hub to user leaves 292 BTs
minus, 5 BT for a short TP cable from the hub to the Converters leaves 287 BTs,
minus 80 BT for one Converter leaves 207 BTs for fibre cable, which indicates a fibre cable
length of about 200 meters.
2.3 Connecting Fast Ethernet media
Connecting Ethernet Media to the Media Converter is very simple and straightforward. Using a
properly terminated media segment, simply attach the cable end to the appropriate connector.
2.3.1 Connecting twisted pair (RJ-45)
The following procedure describes how to connect a 100BASE-TX twisted pair segment to the RJ-45
port on the Media Converters. The procedure is the same for both unshielded and shielded pair
segments.
1.
Using standard 100BASE-TX media, insert either end of the cable with an RJ-45 plug into the RJ-
45 connector of the Media Converter.
2.
Connect the other end of the cable to the corresponding device.
3.
Use the LINK LED to ensure proper connectivity by noting that the LED will be illuminated when
the unit is powered and proper connection is established. If the LINK LED is not illuminated,
change the setting of the up-link switch (see section 3.3 for the up-link switch information.) If this
does not help, ensure that the cable is connected properly and is not defective.
2.3.2 Connecting fibre optic (ST and SC)
The following procedure applies to 100BASE-FX applications using the Media Converter with ST-
type (twist-lock) and SC-type (snap-in) fibre connectors.
1.
Before connecting the fibre optic cable, remove the protective dust caps from the tips to the
connectors on the converter. Save these dust caps for future use.
2.
Wipe clean the ends of the dual connectors with a soft cloth or lint-free lens tissue dampened in
alcohol. Make certain the connectors are clean before connecting.
Note:
One strand of the duplex fibre optic cable is coded using colour bands at regular intervals;
you must use the colour-coded strand on the associated ports at each end of the fibre optic
segment.
3.
Connect the transmit (TX) port on the Converter to the Receive (RX) port of the remote device.
Begin with the colour-coded strand of the cable for the first “Transmit-to-Receive” connection.
4.
Connect the receive (RX) port to the transmit (TX) port of the remote device. Use the non-colour
coded fibre strand for this.
5.
The LINK LED corresponding to the fibre port on the front of the Media Converters will
illuminate when a proper connection has been established at both ends (and when power is
ON in the unit). If LINK is not lit after cable connection, the normal cause is improper cable
polarity. Swap the fibre cables on the converters fibre connectors to remedy this situation.
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Alternatively, a server with full-duplex NIC needs to be connected via a fibre to a 100Mbps
switching hub with RJ-45 ports. In these and similar situations, the RS Fast Ethernet Media Converters
conveniently converts the twisted pair cable to fibre, allowing use of any available RJ-45 Fast
Ethernet switched port with a new or existing fibre cable.
Where shared Fast Ethernet segments are used, such as with Fast Ethernet hubs with RJ-45 ports, it
may be desirable to connect one or more servers or users via fibre cable. It is necessary to calculate
the PDV of overall collision domain for proper operation when the Media Converter is used in
shared half-duplex applications.
2.0 Installation
This section describes the installation of the Media Converters, including location, segment
distance calculation and media connection.
2.1 Locating the Media Converter unit
The compact and lightweight design of the Media Converter allows it to be easily installed in
most location. A velcro strip and a set of two metal clips and screws are included for
mounting the unit on a vertical surface such as a wall or cabinet, or for securing the unit on a
table-top or shelf. Installation location is dependent upon physical layout of the Ethernet
network. Make sure the unit is installed in a location that will be easily accessible to an AC
power outlet and where convection cooling is not inhibited.
Note:
Special consideration must be given to maximum segment lengths on each side of the
Media Converter. It is recommended that IEEE 802.3 specification for overall maximum
segment distances be adhered to in order to maintain optimum network performance.
2.2 Calculating segment distances
The media distance considerations are quite different for full-duplex and for half-duplex (standard
Fast Ethernet) installations.
2.2.1 Segment distance, full-duplex
Full-duplex ports, as found in switching hubs and some NICs, can receive and transmit signals
simultaneously and do not experience collisions accordingly.
There may be only two nodes present on a full-duplex segment. Media distance rules are not the
same as for standard (half-duplex) Fast Ethernet because collision distance limitations are not a
factor. Specially, fibre segments can be up to 2Km for multi-mode and up to 15Km for single mode.
100 Mbps
LINK
PWR
LINK
100 Mbps
LINK
PWR
LINK
100 Mbps
LINK
PWR
LINK
10BASE-TX
wiring segment
100BASE-TX
wiring segment
100BASE-FX
wiring segment
Two fast Ethernet media converters provide connectivity for switched 100Mbps hubs via fibre
Fast Ethernet media converters provides connectivity to servers or users via fibre
100BASE-FX
wiring segment
100BASE-TX
wiring segment
