Model FMC-ST RS stock no. 288-5847
Model FMC-SC RS stock no. 288-5853
Issued March 1998 10774
Fast Ethernet
Media Converters
Instruction Leaflet
Table of contents
1.0 Introduction ____________________________________________________1
1.1 Inspecting the package and product ________________________________________1
1.2 Product description ______________________________________________________1
1.3 Features and benefits ____________________________________________________2
1.4 Applications ____________________________________________________________2
2.0 Installation ____________________________________________________3
2.1 Locating the media converter unit __________________________________________3
2.2 Calculating segment distance ______________________________________________3
2.2.1 Segment distance, full-duplex ______________________________________3
2.2.2 Segment distance, half-duplex ____________________________________4
2.3 Connecting fast ethernet media ____________________________________________6
2.3.1 Connecting twisted pair (RJ-45) ____________________________________6
2.3.2 Connecting fibre optic (SC and ST) ________________________________6
3.0 Operation ______________________________________________________7
3.1 Power requirements, power supply types ____________________________________7
3.2 Front panel LEDs ________________________________________________________7
3.3 Up-link switch on TX port__________________________________________________7
4.0 Troubleshooting ________________________________________________7
5.0 Technical specification __________________________________________7
1.0 Introduction
This section describes the RS Fast Ethernet Media Converters, including features and possible
applications.
1.1 Inspecting the package and the product
Inspect the contents of the package for any signs of damage and ensure that the items listed
below are included.
This package should contain:
1 RS Media Converter Unit
1 External Power Supply, 230Vac 50Hz
1 Set of two metal mounting clips with screws
1 Velcro® tape section, approximately 3 inches in length
1 User guide
1.2 Product description
RS Fast Ethernet Media Converters offer a compact, cost-effective way to convert and transmit data
among twisted pair, and fibre network cabling environments. They allow the use of fibre media with
full-duplex devices such as Fast Ethernet switching hubs, and may sometimes be used with shared
(half-duplex) fast ethernet segments as well.
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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
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collision domain. Regardless of the actual network topology, the Collision Domain diameter must be
less than 510 BT (Bit Times). Bit Times are related to media type as shown in the table below.
Table 2.2.2a:Worst case round-trip delay for Fast Ethernet media*
*Worst case delays taken from IEEE Std 802.3u-1995, actual delays may be less for a particular cable.
Each shared Fast Ethernet network device also has an associated BT delay. Table 2.2.2b shows
typical Fast Ethernet device components and the associated BT delay.
Note: There is only one DTE pair associated with any device-to -device path.
Table 2.2.2b:Worst case round-trip delay for Fast Ethernet device components*
* Worst case delays taken from IEEE Std 802.3u1995
To determine whether a prospective network topology adheres to the collision domain diameter
specification, the following formula should be applied to worst case path through the network. The
worst case path is the path between the two Fast Ethernet devices (DTEs) which have the longest
round trip delay time.
PDV = (sum of cabling delays) + (sum of repeater and media
converter delays) + (DTE pair delays) + (safety margin)
PDV is the Path Delay Value of the worst case path. For the network to adhere to IEEE 802.3u
standard,this value must be less than 512 BT. The safety margin is specified in BT and may be a value
between 0 and 5. This margin can be used to accommodate unexpected delays, such as an extra
long patch cable. A safety margin of at least 4 BT is recommended.
”Rules-of thumb” Collision domain calculations
Rules-of-thumb, while inexact, may be helpful in planning network topology. As a rule-of-thumb, a
Class 11 Repeater has a PDV of about 90 to 95 BTs, and twisted-pair or fibre media has a PDV of
about 1 BT per meter of length. The RS Media Converters has a PDV of 80 BT. Therefore, in shared
Fast Ethernet applications, the converters uses about 80 meters of equivalent cable distance to
convert from TX media to fibre FX media, i.e., it consumes almost as much of the available PDV as a
Class 11 repeater. Since a 512BT collision domain will almost always include at least one repeater
and two media segments, the remaining amount of Bit Times left after allowing for a Converter and
a length of fibre media indicates that the available fibre length will be much less than the 412 meters
that is the known maximum for fibre. Therefore, in shared environments, the RS Media Converters
will be of benefit when they allow the user of fibre media, but not to gain distance by facilitating use
of fibre media instead of twisted pair.
As a sample calculation, consider the question of what fibre cable distance (connected by a pair of
Media Converters on each end) can be obtained that will interconnect two 100Mbps hubs where the
twisted pair cables to the user nodes are 10 meters in length. 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 180 BT for two Class 11 repeaters leaves 232 BTs,
minus 20 BT for two 10-meter TP cables for hubs to users leaves 212 BTs.
Component
Round-trip delay in
Bit Times (BT)
2 TX DTEs 100
2 FX DTEs 100
1 FX and 1 TX DTE 100
2 T4 DTEs 138
1 T4 and 1 TX or FX DTE 127
Class 1 repeater 140
Class 11 repeater with any combination of TX and FX ports 92
Class 11 repeater with T4 ports 67
Media type
Round-trip delay in
Bit Time per meter (BT/m)
Fibre optic 1.000
Shielded TP cable 1.112
Category 5 cable 1.112
Category 4 cable 1.140
Category 3 cable 1.140
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3.0 Operation
This section describes the operation of the Media Converters including power supply requirements,
up-link switch functionality, and a description of all LEDs.
3.1 Power requirements
Both Media Converters require 5 watts of power and are designed to be used with an external power
supply. Both units are supplied with 230Vac, 50Hz mains adaptor with an integral 3 pin mains plug
and a lightweight DC power cord to plug in to the power jack on the Media Converter.
3.2 Front panel LEDs
LED Description
PWR Illuminates GREEN to indicate the unit is receiving DC power.
LINK (RJ45 port) Illuminates GREEN, to indicate proper connectivity on the 100BASE-TX network
segment. LINK will turn off in the event of connectivity being lost between the ends of the
twisted pair segment or a loss of power occurs in the unit or remote device.
LINK (Fibre port) Illuminates GREEN, to indicate proper connectivity on the 100BASE-FX network
segment. LINK will turn off in the event connectivity is lost between the ends of the fibre
segment or a loss of power occurs in the unit or remote device.
3.3 Up-link switch (on TX port)
RS Media Converters are equipped with an up-link slide switch to accommodate repeater-toconverter connections without a special cross-over cable.
When set to the UP position (=), the Media Converter is wired for normal twisted pair connection to
a user device. When set to the DOWN position (X), the Media Converter is wired with cross-over
functionality for direct up-link to a network hub or connector.
4.0 Troubleshooting
Important: RS Media converters contain no user serviceable parts. Attempted service by
unauthorised personnel shall render any and all warranties null and void.
Should problems develop during installation or operation, this section should help to locate, identify
and correct such problems. Please follow the suggestions listed below prior to contacting RS.
However, if you are unsure of any procedure described in this section, or if the Media Converter is
not operating as expected, do not attempt to repair or alter the unit. Contact RS Technical Helpline
for assistance.
Before calling for assistance, observe the following steps
1. If difficulty is encountered when installing or operating the Media Converter, refer back to
section 2.0, Installation and section 3.0, operation. Check to make sure that the various
components of the network are operable.
2. Check the cables and connectors to ensure that they have been properly connected, and the
cables/wires have not been crimped or in some way impaired during installation.
3. Make sure that the external DC power supply is properly attached to the unit, and that it is
plugged into a functioning electrical outlet. Use the PWR LEDs to verify the unit is receiving
proper power.
4. If the problem is isolated to a network device other than the Media Converter, it is
recommended that the problem device be replaced with a known good device. Verify whether
or not the problem is corrected. If not, go to Step 5 below. If the problem is corrected, the Media
Converter and its associated cables are functioning properly.
5. If the problem continues after completing Step 4 above, contact the RS Technical Helpline on Tel:
01536 402888 or Fax: 01536 401588
5.0 Technical specification
Performance:
Data rate: 100Mbps Half-or full-duplex, auto-sensing 800ms (80 bit times) Path Delay
Value (PDV) for conversion delay.
Network standards:
Fast Ethernet IEEE 802.3u: 100BASE-TX, 100BASE-FX
(RS Media Converters are physical layer standard Fast Ethernet products, and operate
independently of all software).
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