Media converters: of round holes and square pegs

While sometimes overlooked, media converters can solve last-minute installation problems and extend the usefulness of legacy equipment.

John Lillywhite imc Networks Inc.

Welcome to the world of networking, where cabling and protocol permutations abound at every turn and newly installed cabling is already obsolete. Even the most sophisticated network administrators find it difficult to remain ahead of the emerging technologies. In fact, more than 20% of cable installed between 1990 and 1995 was never used due to increased data throughput requirements that made the existing cable unusable.

Manufacturers of the new local area network/wide area network (lan/ wan) equipment typically spend little time considering how the implementation of their new equipment will affect the existing cabling infrastructure. Cabling is not as easily replaced as a server, a switch, or a hub, and can create complex and expensive problems if the capabilities of the lan/wan equipment and the cabling are not considered concurrently. Stuck deep within some basement telco room, most replaced lan/wan equipment can at least find a humbler second-generation function. Unused or obsolete copper cabling, however, is rarely, if ever, removed from a facility and reused.

Given the growing variety of legacy lan/wan equipment and cabling media, how can a network manager cope? Media converters offer an extremely cost-effective solution, though they are sometimes overlooked because they are not recognized as a mainstream technology.

Media converters are often seen as short-term, quick fixes to network cabling problems. Yet, to the dismay of every network manager, virtually every piece of networking or communications equipment is a short-term fix. A server is obsolete almost as soon as it`s put into service. Buy a router today, and by tomorrow, an intelligent switch will do more for less. The server purchased only three years ago is antiquated and collecting dust in some back room because the owner doesn`t know quite what to do with it.

A converter for every occasion

Media converters are purely iso Protocol Stack Layer-One Physical devices. They simply take the signal from the upstream side of one cable medium and send it downstream to another. No frame or packet retiming or error checking is performed.

Although media converters convert virtually every type of medium (10Base-2 to 10Base-T, 10Base-2 to 10Base-FL, 10Base-T to 10Base-FL, 100Base-TX to 100Base-FX, for example), the most popular models connect twisted-pair copper cable to fiber cable. This is a result of the greater price/performance benefits of fiber combined with the large installed base of twisted pair.

Multimode- to singlemode-fiber conversion is also popular and has wide-ranging functional and cost advantages. Singlemode fiber offers distance advantages of much more than 50 km. Relative to singlemode, multimode fiber`s advantages are its low cost, but maximum fiber distances are dramatically reduced. Expect the presence of both singlemode- and multimode-fiber cabling to increase dramatically, especially in OC-3 (155-Mbit/sec) and gigabit-per-second data networks. Higher-speed technologies are not conducive to copper cabling and will no doubt accelerate the implementation of fiber. Fiber-mode media converters allow both types of fiber to communicate transparently at a relatively low cost.

Network connectivity problems are especially prevalent in companies experiencing radical change and growth. Several manufacturers have addressed this problem by offering modular media converter solutions. The primary benefit of modularity is that it allows adaptation to change with very little cost. Other advantages of modular media converter products include fewer power cords, higher density, multiple redundant power supplies, and greater centralization. These products usually support between 2 and 20 modules and install in enclosures that provide redundant power and cooling. Enclosures are usually rack-mountable for use in telephone and computer rooms.

Media converters are the unsung heroes of many last-minute networking projects. Connectivity problems typically arise in the final phases of cut-over when a cable type is incompatible with the lan/wan equipment. The traditional resolution is to contact the manufacturer of the switch or router and purchase a product to offset the compatibility problem. These decisions are usually quite expensive.

Companies that manufacture enterprise connectivity products, such as Cisco, 3Com, Bay, and Cabletron, often use media converters as a way to reduce their own equipment costs. In many cases they offer router and switch modules that create end-to-end solutions and eliminate the need for a media converter. However, this can be expensive, as their conversion hardware is tightly integrated into their switch and router products. Consequently, large switch and router manufacturers tend not to make media conversion a part of their core business. In fact, many of these companies usually recommend media converters in their proposals to maintain flexibility and reduce the solution costs.

Managing media converters

A common rule of thumb is that data is only as available as the least reliable component is able to make it. This applies to media converters as well. Fault tolerance, health monitoring, and system management play important roles in enterprise-level media converters, just as they do when implemented at the hub, switch, router, or server.

As for most networking equipment, networking downtime can be minimized using several approaches:

redundant components to increase

component fault tolerance,

modular and hot-swappable compo-

nents to minimize downtime during replacement,

and fault notification through health

monitoring.

Enterprise-level media converters address all of these in some fashion.

Fault-resilient media converters, like most other enterprise-level networking components, are usually managed via simple network management protocol (snmp). snmp communication with media converters occurs via a separate out-of-band connection. This connection can be an RS-232, RS-485, or 10Base-T port. The information available from a managed media converter varies by manufacturer, but usually includes link-good/link-lost information. Depending upon the type of media converter used, other information might include power supply health, power supply redundancy status, media converter type, and location within a larger rack-mounted system. snmp-managed products can send fault warnings to a centralized snmp console where the network administrator can take further action to preempt a failed connection.

Currently, only a few manufacturers provide snmp-managed media converters. snmp-management design implementation as well as remote monitoring and control techniques vary greatly from vendor to vendor.

The inclusion of a media converter can increase the complexity of cable fault isolation by essentially doubling the number of cables between the equipment. Therefore, in managed environments, using a managed media converter is highly recommended. Adding management to the media converter between two managed switches or routers enables the network administrator to isolate the fault to any of the pieces of cable between them (see figure). Without management, the network administrator would have little idea whether a fault between switches was located before or after the media converter, or within the media converter itself.

Cable fault isolation and diagnosis can get tricky over long-haul cable runs. Many media converters provide a means to simplify the task. Some media converters can be configured to stop sending link pulses to the downstream destination if they stop receiving link pulses from the upstream source. This feature, combined with snmp services, can be extremely useful to isolate faults if the media converter is at a remote location or when human intervention and monitoring are difficult.

Considering the relatively low cost of media conversion (between $400 and $1000 per port depending on the media), managed and fault-tolerant media-converter implementation can easily pay for itself by rapid resolution and minimized downtime during the first cable fault.

Given the growing complexity of today`s networking infrastructures, media converters give network administrators a cost-effective buffer between legacy products and those that change rapidly. Media converters save money by extending the life of cabling or equipment that might otherwise be replaced before its time. u

John Lillywhite manages the product marketing department at imc Networks Inc. (Irvine, CA).

Justifying fiber

Significant advances in signaling techniques and the ability to run 100 Mbits/sec (and 1000 Mbits/sec, though at far shorter distances) over twisted-pair cabling will likely shape the future technology of choice for many companies. For various reasons, however, fiber will remain the only viable option in many applications.

As bandwidth requirements increase and fiber costs decrease, network managers are finding it easier to justify the implementation of fiber beyond the computer room to the desktop. Therefore, these implementations are becoming more frequent, especially in government installations. However, with the increased use of fiber comes the increased complexity of attaching non-fiber lan/wan equipment. Converting a computer room to fiber or implementing a fiber backbone is relatively simple when compared to the time and costs associated with running fiber to the desktop.

Many companies, in an attempt to save money and stay ahead of the cable-obsolescence curve, are "futureproofing" their premises cabling by installing fiber when laying new data cable. No other medium is expected to replace fiber, which is also expected to provide all the bandwidth necessary for the foreseeable future. Media converters simplify this fiber-only "futureproofing" and allow the network manager to implement a fiber-only cabling strategy today without implementing fiber-only networking equipment.

The following are several of the most compelling reasons network administrators are increasing the use of fiber:

Extended distance requirements: Fiber offers

distance capabilities far surpassing those supported by copper media.

Centralized architectures: Due to the dis-

tance restrictions of copper-based networks, lan hubs and switches are usually required throughout a large organization. Fiber`s distance advantages enable network administrators to consolidate the equipment of many smaller server and switch rooms into fewer clusters.

Resistance to electromagnetic interference:

Photons are wonderful things. Not only do they go farther for less energy, but they are also immune to the arcs and sparks that create unwanted noise and errors in copper cabling.

Reduced voltage-potential problems: Ground

loops between long distances can create large voltage potentials with copper wiring. Not only can these potentials cause bodily harm, but they can also create problems in the equipment connected to the long-reach copper cabling. Fiber eliminates this problem.