Breaking the Gigabit Distance Barrier of Multimode Fiber
What do you do if you have a legacy backbone installed over multimode fiber and you
want to migrate to Gigabit Ethernet ? This is a typical question asked by a lot of
companies, schools, and government agencies who installed FDDI technology in the
1980’s because of it’s high-speed, redundancy features and widespread market
acceptance.
Only until recently have there been compelling reasons to consider newer and faster
technologies, such as Gigabit Ethernet. The main reason is obvious: the need for
increased bandwidth in today’s constantly growing networks. Explosive growth in
streaming audio and video, larger and larger e-mail attachments, and emerging voiceover-IP applications are but a few of the reasons to consider migrating to Gigabit
Ethernet. In addition, FDDI is a legacy technology and most manufacturers have
discontinued production of FDDI equipment. The costs of maintaining these networks is
increasing as parts availability is decreasing.
FDDI vs. Gigabit Ethernet
Gigabit Ethernet has become the leading enterprise backbone technology and is
considered to be much more economical and superior in performance than other
technologies.
FDDI was installed in a lot of Local Area Network backbones because it was the first
technology to bring about a solid physical-layer standard. This standard guaranteed
interoperability between manufacturers if the physical plant (fiber) was installed properly
to a set of rules governing fiber cable type (62.5/125 micron, multimode fiber), distance
(maximum of 2 kilometers), and optical budget. Unfortunately, little thought was given
to the future need for more bandwidth over this fiber at anything other than the FDDI
speed of 100Mbps.
Migrating to Gigabit Ethernet using Multimode Fiber
One of the characteristics of fiber cable is that the bandwidth rating of the cable is
proportional to the distance, the higher demand for bandwidth results in a reduction of
distance. For Gigabit Ethernet speed, the distance is limited over multimode fiber cable
(220 meters for 62.5/125 micron and 550 meters for 50/125 micron). To overcome the
bandwidth limitations of multimode fiber, products such as the AT-EX1001SC/GM1
have been developed which allow a high-speed, standards-based, multimode Gigabit
Ethernet port (1000Base-SX) and grooms the optical properties so that it can function
over the older legacy fiber in use by FDDI networks. Low-cost multimode Gigabit
Ethernet interfaces can now take advantage of multimode fiber distances up to 2
kilometers.
Without using the AT-EX1001SC/GM1, the only alternative to supporting Gigabit
Ethernet over distances greater than 550 meters is to install single-mode fiber at a
significantly higher cost. The increased cost does not stop with the new fiber, however,
since the switch or router equipment has to support the more expensive single-mode
optics.
Using the AT-EX1001SC/GM1 to Migrate
Migration to Gigabit Ethernet using the AT-EX1001SC/GM1 is quick and easy. In most
cases, removal of the existing FDDI system isn’t necessary since most installations
provided extra fiber pairs as backup for future growth. To prepare for installation of the
AT-EX1001SC/GM1, survey your fiber system to determine the availability of unused
fiber pairs and the kind of optical connectors that were installed in your optical patch
panels. With this information, you can now install your Gigabit Ethernet switch, router,
or NIC. You will need to connect the AT-EX1001SC/GM1 to your local Gigabit host
device and then connect one end of your fiber cable to the AT-EX1001SC/GM1. Please
note that this has to be done on BOTH ends of the fiber cable that you are migrating to
Gigabit (THE AT-EX1001SC/GM1 MUST BE USED IN PAIRS).
Once the installation is complete, you will have completed your migration to Gigabit
Ethernet since the existing fiber which supported FDDI up to 2 kilometers will support
Gigabit Ethernet when using the AT-EX1001SC/GM1.
EX1001
1000Base-SX (SC)
Gigabit
Host A
2 kilometer, multimode
fiber
EX1001
1000Base-SX (SC)
Gigabit
Host B
Application of the AT-EX1001SC/GM1 for NEW Gigabit Installations
The AT-EX1001SC/GM1 can also be considered as a viable, low-cost solution for new
Gigabit Ethernet installations where the distance between Gigabit host devices is less
than 2 kilometers. Again, the cost of the AT-EX1001SC/GM1 products along with
1000Base-SX devices would be considerably less expensive than the alternative of going
to the more expensive single-mode fiber and optics (1000Base-LX) solution.