In the mad rush to increase
network speed, it is important to stop, take a deep breath, and consider where
you are going.
For good business reasons,
most companies are committed to building a high-speed backbone and extending it
to the desktop. However, the road to successful high-speed deployment is full
of curves and hazards. This white paper is a roadmap that points out some of
the potential rough spots. It highlights seven costly errors IS and IT people
make when moving to fiber. Some are strategic errors. Others are tactical
errors. Whether they arise from incorrect planning or installing correct
technology, these errors cost a lot of money. It is simple to avoid stumbling
as long as you are aware of where the pitfalls are located.
Rest assured that it is not
vital that you do everything exactly as outlined below. While we are sure you
can avoid making fiber flubs by following these proven strategies for success,
in some cases, there may be sound business reasons for doing things a different
way. Just be sure you have a good reason for deviating.
Even if they accept the
argument that fiber is the way to future-proof their network, too many managers
see migration to fiber as an all-or-nothing proposition. That is an expensive
strategy. In fact, the cost of a massive upgrade is the main reason so many
companies are going with the "nothing" strategy and are still installing
Category 5E, Category 6 or looking at Category 7 cable. The common complaint is
that, while they see the advantage of going to fiber, they simply cannot do a
forklift upgrade or throw out so many miles of installed copper.
So what's the problem? Do
the upgrade on the installment plan, a department at a time. There is no reason
to toss the installed copper base along with all of its associated electronics.
Keep it in place, let it do its job, and plan to keep downgrading the
importance of the copper plant as technology advances.
Meantime, install optical fiber each and every time the network has to be
upgraded. Simply link the copper cable with the fiber cable (using media
conversion technology) and rest assured that those on the network are enjoying
the best and fastest networking available without worrying about a call from
the financial department about wasting money.
Before the advent of media
conversion, this was a bigger deal. However, in the past couple of years many
people who are upgrading to high speed backbones have discovered that media
converters work, work well and work cheaply. Since humans began using
machinery, they have been adapting one thing to another. Media converters can
solve the problem by providing a transparent link between twisted pair
horizontal cable and the fiber backbone without requiring new cable or
replacement of expensive equipment.
For most applications, the
economical answer to linking fiber, copper and/or coax is media conversion.
Media conversion is the means by which one media type is converted to another
media type. Changes in networking equipment driven by the ongoing quest for
increased bandwidth, and structured cabling limitations, have helped define the
need for media conversion technology. As routers, switches and other network
devices evolve at a furiously fast pace, network administrators must develop
ways to keep up. This constant migration places demands on both human and
Put simply, media converters
make one cable "look" like another cable—without changing the nature of
your network. A media converter is a small device with two media dependent
interfaces and a power supply. They can be installed almost anywhere in your
network environment, expanding, rather than limiting your options. Your
networking infrastructure, and thus, your investment is protected. Adapting new
media types, such as fiber optics, does not require costly hardware
The end user has an
investment in fiber or twisted pair and is understandably reluctant to toss
that investment out the window to achieve a faster network. Even going from
copper to fiber or copper to copper presents a challenge. Most enterprises are
not financially prepared to put in an entire new infrastructure to meet the
needs of a new application. Media converters ease that transition by converting
a variety of media to another: coax to twisted pair; coax to fiber; twisted
pair to fiber and single mode to multimode fiber.
The device itself has two
media dependent interfaces and a power source. The style of connector depends
on the selection of media to be converted by the unit. For example, in a Fast
Ethernet environment a 100BASE-TX to 100BASE-FX Media Converter connects a
100BASE-TX twisted pair device to a 100BASE-FX compliant single or multimode
fiber port that has either a ST or SC fiber optic connector. Converters are
small enough to fit in a hand and can be stand-alone units on their own. Don't
be one of those network managers who says, "I wish I'd known last month that it
was possible to link TX and FX."
Check into media conversion.
Prioritize the network links which will be upgraded. Use media conversion to
bring the different technologies together, keeping the installed base while
upgrading on a pay-as-you-go basis. Even if you don't save money on the actual
fiber run, you will save a considerable amount by using the existing
The alternative to using
media converters would be expensive; to put many more hubs out in the network,
run new fiber plant, and make sure it would transition from one hub to the
other while still maintaining the purity of the signal.
Fiber can be connected to almost any legacy environment. Equipment equipped
with an AUI or MII port can also make use of fiber transceivers. Media
converters can also be used to link single mode to multimode fiber.
Media converters are as
simple to install as patch cables and connectors. Media converters function as
physical layer devices. As such, they do not interfere with any upper level
protocol information. This allows them to support both QoS (quality of service)
and Layer 3 Switching.
A fiber media converter can
reliably and inexpensively extend the distance between two 10BASE2 devices or
two 10BASE-T devices up to 2,000 meters. This function is done without the
monetary expense of a repeater or the use of a portion of your network repeater
Using media converters in a
100BASE-TX to 100BASE-FX back to back configuration, provides a single method
of extending the distance between a full duplex switch and a fileserver up to
2,000 meters. The same strategy will work between two switches. In fact, media
converters can function in either half-duplex or full-duplex mode. Full-duplex
Ethernet over UTP runs at 20 or 200 Mbps, while half-duplex Ethernet over UTP
runs at either 10 or 100 Mbps. Full-duplex Ethernet is especially valuable in
linking two switches or connecting a switch to a file server. No adjustments
are necessary when using either mode. A media converter will automatically
sense which mode is in operation.
Fast Ethernet offers two
fiber options. 100BASE-FX is the most common. It supports distances of up to
2,000 meters over multimode fiber but offers no 10/100 negotiation. To address
the need for 10/100 auto-negotiation and to lower the cost of fiber
connectivity, the industry is developing the 100BASE-SX standard. 100BASE-SX is
limited to deployments of 300 meters or less, but since it allows using both 10
and 100 Mbps, conversion technology can be used to run the link at whatever
speed is required.
Step 1: Install new fiber utilizing existing copper-based workstations and
Step 2: Upgrade workstation performance by simply replacing the 10Mbps
copper NIC with a 100BASE-SX NIC.
Using a 10/100 SX converter
allows you to future-proof your install. Take, for example, a 10/100 NIC (network
interface card) plugged into a 10BASE-T hub with SX converters at either end, and
the link runs at 10 Mbps. Replacing the 10BASE-T should cause the whole link to
come up at 100 Mbps if the 10/100 SX media converter is used. The alternative is
to buy a 10 Mbps converter for the 10 Mbps link and replace it when the upgrade
is made. Although a bit more expensive than a 10 Mbps converter, an SX converter
costs less than a 100BASE-FX converter.
While Fast Ethernet is good
for now, mixed network topology eventually will have to be scaled to Gigabit
Ethernet. Using a Gigabit Ethernet Media Converter enables converting one or
more 1000BASE-SX ports on a Gigabit Ethernet switch or 1000BASE-LX for use in
campus area networks or other applications requiring the distance advantages of
single mode fiber. It is only necessary to convert those ports required for
Ironically, it is often less
expensive to purchase a multimode switch and an external multimode to single
mode media converter, than it is to buy a switch with single mode installed
internally. Additionally, some Gigabit Ethernet electronics are only compatible
with multimode fiber. In such an instance, a single mode to multimode media
converter makes the connection.
With single mode fiber in
the backbone, copper or another medium to the desktop and media conversion
tools providing connectivity between disparate technologies, the network
manager can confidently plan for a future network incorporating Gigabit
domains is key when designing an efficient, robust Fast Ethernet networking
system. A collision domain is a group of Ethernet or Fast Ethernet devices that
are directly connected by repeaters. Collision domains are separated by
switches and routers that allow separate collision domains to communicate with
each other. Only one device within a collision domain may transmit at any one
time. When a device is transmitting, all other devices in the collision domain
listen. Both Ethernet and Fast Ethernet use a collision sensing standard
protocol that allows multiple devices to access a shared Ethernet or Fast
Ethernet network. This is known as CSMA/CD (Carrier Sense Multiple
For each collision domain,
the CSMA/CD determines which device has access to the network. The CSMA allows
a node to transmit if there is no existing traffic on the network. The CD will
detect simultaneous transmissions and stop all traffic. All devices will then
re-send at random intervals, allowing each node to retransmit successfully
unless another collision is detected. However, collision domain size is
limited. Collision domain size is not measured in terms of distance, but in
terms of bit time. This is because a signal on the network has a constant speed
relating to the type of media it is traversing-fiber or twisted pair. Bit time
is measured by the time it takes the smallest allowable packet to make the
round trip from the transmitting node to the furthest node in the collision
domain. The smallest allowable packet size in Ethernet and Fast Ethernet is 64
bytes or 512 bits.
If a node is too distant
from other nodes in its collision domain, then packet transmissions may not be
able to make the entire round trip distance needed to ensure that collisions
are heard by all devices on the network. This is referred to as a late
collision. Late collisions increase the possibility of lost packets and overall
The 512-Bit Rule says that
the total bit times between any two devices in the same collision domain cannot
be greater than 512 bit times in a round trip.
To eliminate the guesswork,
here are three simple guidelines to follow:
1) Between two hubs: (2)
Fast Ethernet Bridging Media Converters
2) Between a hub and a
switch: (1) Fast Ethernet Bridging Media Converter on the hub side and (1) Fast
Ethernet Media Converter on the switch side
3) Between two switches: (2)
Fast Ethernet Media Converters
Look for a media conversion
product which is auto-negotiation enabled. Believe us – it's a lot easier
to let well-designed components negotiate speed and compatibility automatically
than it is to do it by hand, on a piecemeal basis. This holds whether setting
up speeds and resolving full/half-duplex issues, or sorting out which cable
pair has the transmit and which the receive function.
Here's how auto-negotiation
works. Whenever two copper 10/100 ports talk to one another there is a
negotiation process. Each port broadcasts its capabilities. It may say it can
do 10 Mbps or 100 Mbps or both; or that it can handle full-duplex or only
half-duplex, or both. A typical switch can do either 10 or 100, either full or
half. If both have similar capabilities, they resolve to the highest performing
common denominator (in this case 100 Mbps full-duplex). However, if a 10/100
switch is being connected to a dual-speed hub, the switch will come up and say
it can do 10 or 100, full or half-duplex; the hub will say it can do 10 or 100,
but can only do half-duplex. The result will be a 100 Mbps half-duplex
Lastly, consider a switch
talking to an old, legacy NIC (network interface card). It may be a 100BASE-T
NIC which does not have auto-negotiation. It is fixed at 100 Mbps. Again, the
switch tries to establish a contact. But the NIC ignores the requests, since it
has no idea what the switch is requesting. The NIC does not respond in
auto-negotiation language. The answer to the conundrum is "parallel detection."
When it does not get an auto-negotiation response, but rather discovers a
legacy device, it has to respond in kind.
Parallel detection allows
the intelligent device to detect the speed (in this case 100 Mbps), but has to
take the safer road and set up a link based on the lowest common denominator:
The same scenario works for
media conversion. Take the same intelligent server. Put an auto-negotiating
10/100 NIC card at the other end and both will be fully capable of
auto-negotiation, with the result being a link running at the highest
performing common denominator. A plain-jane media converter, without
auto-negotiation, will have the same problem the dumb NIC had, and will give
similar results—a link with the correct speed but the wrong duplex mode.
The result is a three-aspirin headache for the network manager.
If the media converter does
not understand auto-negotiation, the switch will fall back on parallel
detection and the network ends up with the right speed, but an unwanted
half-duplex link. The media converter has to be intelligent enough to allow the
link to be set up at the desired state (in most cases, full-duplex).
converters (on the copper port) will broadcast ability to do 100 Mbps. There is
a DIP (dual in-line package) switch which can be set either to allow the
converter to broadcast ability to run in full-duplex or ability to run at
The advantage of having this
capability on media converters is that the converter will never give the other
end a choice. It will either broadcast ability to do 100 Mbps full-duplex, or
100 Mbps half-duplex…nothing else. Think of this as ability to do just
enough auto-negotiation to get by for the job at hand. The media converter can
not negotiate to 10 Mbps and can not change on the fly—it is somewhat
fixed. But the advantage is that, given this level of intelligence, the media
converter can sit between the server and the NIC and the link will come up
properly, never realizing there is a converter in between them.
4A: Don’t Get Crossed Up
If the cable pair running
through the media converter does not match what the system expects, the system
will not operate properly. This is because the transmitter of the one interface
should talk to the receiver at the other end. If the lines are not setup
properly, this will not happen.
The solution is
AutoCross—a feature which saves time and money during installation.
Whenever a tech plugs in cables to any hub there should be an automatic
transmission delineating which cable pair has the transmit and which pair has
the receive capability. At this point, the system automatically re-configures
itself on the fly and the link starts to work properly. This allows you to plug
in a straight-through cable or a cross-over cable and it will sense the proper
configuration for the link.
While this sounds simple
(and, indeed, it really is), this AutoCross capability is a feature which can
eliminate much of the backtracking through an installation. It is a huge
time-saver for the technicians. All new Transition Networks media converters
will have this ability; existing converters are being redesigned to include
Even with auto-negotiation
and other sophisticated features, it is possible to create confusion on links
running through media converters which are between router pairs. It is
important to maintain link integrity. Transition Networks offers a feature
called LinkAlert™ which does just that.
LinkAlert monitors 100% of
physical uplink & downlink failures, ensuring that hubs, converters,
repeaters, transceivers & NICs can detect Link status.
A common problem on trunked
networks is that the network on each side of the media converter may begin to
act independently of the other. Take a link where there is conversion from
copper to fiber and back to copper. When the copper link goes down on one
switch the fiber is not dropped.
Some switches may run a
trunking algorithm, splitting traffic across multiple ports. If, at the
physical layer, the switch does not see the that the port has gone down, the
box becomes confused. It sees that it is not getting data through, yet it
thinks the port is there.
Spanning tree also can be
tricked the same way. If the spanning tree does not see the physical link go
down, it will not be able to re-route it to another path, even though the
primary path is bad. The physical layer appears intact.
The answer is simple: a
media converter that says, in effect, if the copper side goes down then the
fiber side goes down as well; or, vice versa. LinkAlert accomplishes this
simply and elegantly, allowing either trunked or spanning tree-based networks
to "see" that the physical layer has been broken. The result is an alert sent
to the network manager who can proceed to make whatever correction is
A well-designed network
management system allows network managers to respond to problems quickly
– often before the people using the network know there has been a
degradation of service. Proactive management means catching problems before
they become service-disrupting.
Network management has been
standardized around SNMP and is used by virtually every network management
system as a means to communicate information. Network management requires
information to be passed from the SNMP agent to the management station and vice
versa. Because each managed item is unique, there needs to be a standard way to
define it so that any SNMP management system can "talk" to it. This is
accomplished by using a Management Information Base, (MIB) which defines status
and control items that are available in a particular piece of equipment and
does it in a very structured method. As an example, a MIB might define a media
converter as having a status item called "FiberLink" or "CopperLink." With
these links, any SNMP software would know that this status information is
available, and understands how to obtain it from the media converter.
This exchange of information
can happen in one of two ways, in-band and out-of-band. Most managed items
support both in-band and out-of-band connections. The in-band method can be
done using SNMP, telnet or recently with HTTP (Web browser based management).
Out-of-band management typically utilizes an RS-232 port and a dumb terminal
While SNMP management has
been around in high-end LAN equipment for several years, the physical plant has
been largely neglected, primarily due to cost issues. Previously, it was
expensive to install equipment that manages the cable plant. When fiber started
being deployed, people often used media converters to connect it to legacy
copper equipment. These devices were typically not managed and further
complicated the issue of managing the physical plant.
Now several manufacturers of
media conversion products offer managed conversion solutions. These are
typically in the form of a chassis that can manage up to sixteen media
converters, allowing them to be placed in critical locations within the
In managed media conversion
systems the primary piece of information that is gathered is a port link
status. Simply put, it is the link up or down. This information is available
upon request (like when looking at a graphical representation of the product)
or as a trap. Traps are sent to the management system as soon as the SNMP agent
detects that the link is down. When the link is restored, another trap can be
sent which notifies the administrator that the problem has been solved.
For example, if there is a
physical loss of a patch cord going to a managed media converter, the media
converter senses that the link has been lost and sends a trap to the network
management system. Even though the problem could not be prevented, the network
manager is able to fix the problem before anyone realizes that the network is
down. Without management, there is no indication of a problem until someone
calls the help desk complaining that he/she can not log onto the server.
Once the network has been
installed, operability testing is always a challenge. If the network is not
performing correctly it could due to any one of a variety of problems: it could
be the media converter slowing the packet down, the cable itself, a problem
with the patch cord or the NIC card. There may be a difficulty with the
application itself. Or, the server might simply be too slow. Troubleshooting
follows standard Ethernet procedures.
The keys are being proactive
in management or, alternatively, responding rapidly when a problem does strike.
In the media conversion sense, this usually means the latter – a trap
will show when a link goes down. It may warn of the loss of a fiber link on a
given port. Management can work around the problem, thus preserving
Once the decision to do
media conversion is reached, it is important to know what kind of media
converter platform will be used for the application. There are three types of
platforms to consider:
1) chassis mount
2) fixed-port unit
For management, a chassis is
the best way to go. Fixed-port units have six or twelve of the same type of
media converter in one enclosure. They are not modules which can be slid in or
out. The structure is more like a hub. In an application that requires
redundant power, the chassis also is the platform of choice. In many networks,
an hour of downtime costs the organization hundreds of thousands of dollars. A
redundant power system costs about $300, making this the classic example of a
"no-brainer" for companies involved in fail-safe networking, such as those
requiring meeting service level guarantees, electronic commerce, EDI
(electronic data interchange), banking and similar pursuits.
A company which does not
need redundant power or is not concerned about continuous management on every
link, but which will do a lot of conversion, should look at a fixed-port unit.
Fixed port units have six or twelve of the same type of media converter in one
enclosure. They are not modules which can be slid in or out. The mechanical
structure is more like a hub. This is especially indicated when a lot of the
same type of conversion is going to be done in the same spot. Take, for
example, a network converting twelve 10BASE-T's to fiber or six 100BASE-TX to
fiber, the fixed port unit will provide the required number of media converters
in a single enclosure. These fixed-port units are smaller, so they save rack
space. Typically you can fit twelve converters in a space one rack unit high.
If racking economy is important, this is probably the way to go. The old
"cheaper by the dozen" rule applies, too – racks are cheaper than buying
For single end node
conversion, the stand-alone product is the answer. The right media converter
will allow linking one type of media to another. Page 12 shows a number of
common conversions and which converter will do the job. This is not an
exhaustive list, but does show the versatility of media converters.
No matter who you chose to
deal with, there are several basic questions you should ask any media
conversion provider. First, look at their demonstrated commitment to quality.
This includes not only the reliability of their existing products, but also
their commitment to upgrading those products and to introducing new, useful
features on future devices.
Second, look at the
company's range of product line. It is rare that a network will have only one
kind of fiber or only a single type of connectivity need. As you upgrade
different segments of the network to increase network speed or versatility,
you'll encounter the need for different types of converters. There is
copper-to-fiber, copper-to-coax, coax-to-fiber and many other permutations. It
is much easier to find a full-line media conversion vendor at the outset than
it is to hunt for a new supplier every time you encounter a new conversion in
Lastly, be sure your vendor
is committed to media conversion. This may sound like a given, but it is not.
Do business with a company which is focused on media conversion, which has a
primary engineering and technical background in media conversion, and where the
sales staff speaks conversion as a first language, not something picked up on
Economics, more than
electronics, often determines the way a network ends up being designed.
By continuing to use as much
of the installed copper as possible, designing around 100BASE-SX to gain 10/100
based functionality over fiber, being aware of collision domains, letting the
components transparently do as much of the work as possible, and staying on top
of network management issues you will be able to keep the economics under
Lastly, deal with
forward-looking, reliable vendors who design with the future of your network in
mind. With these elements in choice, you're ready to pick the correct
converters for the job, install them on the platform of your choice, and
proceed to enjoy the benefits of an easy, economical, evolutionary upgrade to
Transition Networks offers a
complete line of media converters that give you the highest price-performance
available in the industry. We are continually expanding our product offering.
Check our web site for the most current product information. Transition
Networks offers copper to fiber (multimode & single mode) media converters
as well as single mode to multimode media converters for the following