New developments in fibre connections have made this high capacity
medium an even more attractive proposition in the networking
technology marketplace
Media conversion products are products for evolving networks.
Simply put, they convert from one network media type ( defined by
cable and connector types and bandwidth ( to another. By performing
this transition, the media convertor makes it possible to extend
legacy networks with the latest technology, instead of the
alternative of being tied to what the network was started with or,
even worse, tearing it out and starting over. Alternatively,
convertors allow the use of less expensive, lower bandwidth desktop
connections from a state of the art fibre optic backbone. The
ability to mix media and speeds on a network is critical to
achieving optimal price/performance goals. Media conversion devices
further the flexibility and extensibility of the network by:
Facilitating upgrades to the network to better, faster, more secure
technology ( as with fibre cabling without requiring a full network
retrofit Legacy copper cabling can be left in place, while fibre is
used for additions and extensions to the network Providing a means
by which to extend network distancesUsing a media convertor to
integrate fibre allows the network to support the longer cable
distances available through the use of fibre Making it easier to
add a host of new devices to the network ( including the newer
high-end, high-bandwidth switches and hubs ( regardless of
connector restrictions Maximising efficiency and economy in new
networks. The media convertor can help the network manager optimise
capital for efficiency by enabling a high-bandwidth fibre optic
backbone to feed copper to workgroups and desktops Being flexible.
Media convertors can be inserted almost anywhere in the network To
the network architect or the network manager, a pure media
convertor is best described as two transceivers or MAUs (Media
Attachment Units) that can pass data to and from each other, and a
power supply. Each of the MAUs has a different, industry standard,
connector to join the different media: one medium goes in, the
other comes out. The connectors themselves are standardised to IEEE
specifications and, as IEEE-compliant devices, they utilise
standard data encoding rules and link tests. Media convertors
facilitate the connection of a multitude of devices as a result of
the flexibility they lend to the network. They support connections
to and from switches, hubs, routers and even direct to servers.
Currently, the most commonly used media convertors support twisted
pair to fibre connections. Standard fibre connectors of today
typically are classified as either ST (simple-twist) or SC
(subscriber-channel). New technology in connectors is coming to
market in the form of 'next generation' small form factor fibre
connectors. These new fibre connectors are the MT-RJ, the VF-45 and
the LC. The media convertors most widely used today, though, are
designed for quick, reliable, cost-effective connections
between:10Mb/s twisted pair cable segment or device and 10Mb/s
fibre optic, singlemode or multimode (10Base-T to 10Base-FL) 10Mb/s
10Base-T segment or device and 10Mb/s Ethernet coaxial cable
(10Base-T to 10Base2) 100Mb/s twisted pair cable segment or device
and 100Mb/s fibre optic, single-mode or multimode (100Base-TX to
100Base-FX)
Speed conversionThere is another choice emerging
within media conversion itself, and that is the small, 2-port
switch. Low-cost, two-port unmanaged switches upgrade, extend and
relieve network congestion where it's needed, and cost-effectively.
The switches not only provide a means for connecting new network
media or speed, but they further improve performance by providing a
means to segment networks into smaller, connected sub-nets. While
convertors are simple pass-through devices, these small switches
provide media conversion that is supplemented with security and
store and forward capability. These switches' connector options
follow the conventions of the media convertors described above, but
in a more feature-rich tool. Sometimes the application is worthy of
the extra features; sometimes the simple convertor is all that is
needed.
The real worldMedia convertors can be used in a
variety of applications; they are used from the heart of the
network, the server, to its end, the workstation or DTE.
The
marketIn addition to the general heterogeneous nature of
network installations built over time, the increasing use of fibre
optics in networking is one of the key drivers of growth in the
media conversion market. The benefits of fibre are compelling:
increased security, increased bandwidth and greater supported
network distances. Distance specifications drive the argument for
using fibre as the backbone medium ( in standard Ethernet and Fast
Ethernet networks, fibre specifications prescribe maximum distance
of 2000m versus the twisted pair limit of 110m. Gigabit Ethernet, a
fibre-only specification, supports singlemode fibre in addition to
the multimode fibre supported by its other Ethernet cousins. The
same 2000m limit applies to multimode fibre, but singlemode fibre
is supported for Gigabit Ethernet to a distance of 3000m. Cost
considerations drive the need to link other media to the fibre
backbone ( having achieved the goals of greater distances, security
and bandwidth in the backbone; network managers can often justify a
step-down approach to the desktop for economy. A fibre-to-coaxial
or fibre-to-twisted pair media convertor between the backbone and
the desktop run makes it all possible. The growing use of Ethernet
and Fast Ethernet switches in the network infrastructure is also a
factor. Switches solve many of the problems that are common to
larger networks, but the majority of Ethernet and Fast Ethernet
switches on the market today are equipped with twisted pair
connectors. Where the entire network is built of twisted pair
cabling, the switches are easy to integrate ( just plug one in.
However, for many new installations, network managers are looking
to fibre optic for their cabling infrastructure because of its
security features, bandwidth capabilities and its ability to span
longer distances. For older installations that use BNC connectors,
the same incompatibility arises. A simple fibre to twisted pair
media convertor or a BNC to twisted pair connector can make these
devices work on incompatible networks.
The future is
nowMoving forward, the market is heating up with the
introduction of three new, next-generation, small form-factor,
fibre connectors. These new connectors are being promoted as the
future device of choice for all network hardware vendors: the
MT-RJ, the LC and the VF-45. These new connectors are an extremely
positive addition to the technology base because they solve some of
the common shortfalls of SC and ST connectors in the areas of port
density and termination. Some hardware vendors have already stated
their commitment to one or another of these connector types ( it is
only a matter of time before any one of them becomes the de facto
industry standard. These connectors are being put to use on various
types of network hardware, including the latest in hubs and
switches. The connectors represent a significant advance in that,
because of their size, more ports can be placed in a given device.
This higher port density has the potential to deliver cost savings
to the consumer, so early adoption is highly attractive. Without an
accepted standard, however, early adoption can be risky.These new
connectors were developed to resolve certain issues inherent in the
current ST and SC fibre connectors (i.e., port density and
termination issues), and as switches and hubs are starting to
utilise more and more fibre, the issues became more and more
critical. Prior to the introduction of the next generation small
form factor connectors, a switch or hub could support no more than
12 fibre ports stacked one-high in a rack-mount unit. The new fibre
connectors double the capacity, accommodating as many as 24 ports
in the same size chassis as today's 12 port device. These new
connectors have the added benefit of being easier to use and thus
decreasing cable installation time. In the time that precedes the
emergence of a single standard, Allied Telesyn is committed to
providing media conversion products for all three of the connector
types so that network administrators and architects are able to
continue to purchase network building and expansion products with
confidence. Through its introduction of media conversion devices
for all three of the "next generation" small form-factor connector
types, Allied Telesyn is making it possible for consumers to
proceed with purchases, taking advantage of the economies that come
with the new small form-factor connectors that they use. Consumers
can make these purchases without worrying about whether they have
made the right choice from among the new small form-factor fibre
connectors ( no matter what they choose, the network will retain
flexibility and connectivity options without risk of early
obsolescence as the de facto standard shakes out.
Link integrity
status monitoringNetwork managers need to know that the
physical network infrastructure is intact and operational, whether
it is fibre, twisted pair or coax. In the case of twisted pair,
link integrity is usually tested by sending a signal past the
transmitter electronics when the cable is not in use. If link
integrity is not confirmed, the link is assumed to be lost. In the
case of fibre optics, link integrity is monitored via the power of
the light being received. If it drops beneath a certain threshold,
link is lost. The loss of a link is normally indicated by a link
LED somewhere on the network hardware device. If the link LED is
on, the assumption is made that the cabling has a clean connection
with the other side. If the link LED is off, the user knows there
is a cable connection problem.Link status can be checked either by
observation of the link LED, or, as is more common in larger
networks, through the use of network management software (i.e.,
SNMP). Allied Telesyn offers a link test switch with each of its
media convertors. This switch allows network managers to determine
whether or not a clean link has been established. When the switch
is in test mode, the network manager can determine if any
corruption is present in the fibre link. With the presence of a
clean connection established, the manager can set the link test
switch to normal mode and the media convertor will work in normal
fashion. Other products with SNMP software management can
interrogate the manageable switches that are in use and display the
link status of a segment, in either a graphical or a tabular
format. In addition, the SNMP manageable switch may also support
the ability to be configured so that an alert is sent to the
management workstation when link is lost. Allied Telesyn's
MissingLink is an extremely useful tool for monitoring. MissingLink
provides the host (router, hub, switch or server) attached to
either end of a convertor critical information about the status of
the other (remote) segment link. If either link fails, the
convertor interacts with both hosts, making each instantly aware of
the link fault. Either host can then execute a pre-programmed,
redundant transmission path selection.
Rackmountable
designThe option of mounting media convertors is a rackmount
chassis is useful where multiple convertors are in use, or where
they are anticipated in the future. All of the media conversion
products that are available from Allied Telesyn can be rack mounted
using the optional AT-MCR12 Media Convertor Rackmountable Chassis.
The chassis holds 12 media convertors and/or two port switches, has
an internal power supply and fits into a standard 19in network
rack.
Compiled by Mike BurkittCopyright (c) 1998 Allied
Telesyn International Corp