Networking

Media converters interconnect different cable types such as twisted pair, fiber, and coax within an existing network. They are often used to connect newer Ethernet equipment to legacy cabling. They can also be used in pairs to insert a fiber segment into copper networks to increase cabling distances and enhance immunity to electromagnetic interference (EMI).

Traditional media converters are purely Layer 1 devices that only convert electrical signals and physical media. They don’t do anything to the data coming through the link so they’re totally transparent to data. These converters have two ports—one port for each media type. Layer 1 media converters only operate at one speed and cannot, for instance, support both 10-Mbps and 100-Mbps Ethernet.

Some media converters are more advanced Layer 2 Ethernet devices that, like traditional media converters, provide Layer 1 electrical and physical conversion. But, unlike traditional media converters, they also provide Layer 2 services—in other words, they’re really switches. This kind of media converter often has more than two ports, enabling you to, for instance, extend two or more copper links across a single fiber link. They also often feature autosensing ports on the copper side, making them useful for linking segments operating at different speeds.

Media converters are available in standalone models that convert between two different media types and in chassis-based models that connect many different media types in a single housing.

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Standalone converters convert between two media. But, like a small apartment, they can be outgrown. Consider your current and future applications before selecting a media converter. Standalone converters are available in many configurations, including 10BASE-T to multimode or single-mode fiber, 10BASE-T to Thin coax (ThinNet), 10BASE-T to thick coax (standard Ethernet), CDDI to FDDI, and Thin coax to fiber. 100BASE-T and 100BASE-FX models that connect UTP to single- or multimode fiber are also available. With the development of Gigabit Ethernet (1000 Mbps), media converters have been created to make the transition to high-speed networks easier.

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Chassis-based or modular media converters are normally rackmountable and have slots that house media converter modules. Like a well-planned house, the chassis gives you room to grow. These are used when many Ethernet segments of different media types need to be connected in a central location. Modules are available for the same conversions performed by the standalone converters, and 10BASE-T, 100BASE-TX, 100BASE-FX, and Gigabit modules may also be mixed.

Although sharing printers is one of the primary reasons for installing networks, networks didn’t manage this chore very well until the print server was developed. A print server is a specialized network device that enables network users to share one or more printers. It accepts print jobs from users and manages these jobs on each printer. Print servers are easy to install, use, and maintain.

Typically a print server is a freestanding device that’s connected between the network and the printer; some print servers are so tiny they sit directly on the parallel port of the printer. And some newer printers are even equipped with embedded or internal print servers, so you don’t need to purchase a separate print server at all—just connect the printer to the network. Most print servers support multiple protocols and operating systems. You can also get print servers with multiple ports to connect more than one printer.

When a print job arrives at a print server, it’s entered into a queue where it waits until the desired printer becomes available. Print jobs are normally served in a first-in, first-out order, however many print servers enable users to prioritize print jobs so important jobs can be moved to the front of the queue.

For a print server to manage this entire lineup of print jobs, it must have a place to store them—either in memory (a buffer) or, if the buffer isn’t large enough, sometimes on a hard disk. When a print job arrives at the print server, it sends the job to the printer immediately if the printer is free. Because the print job usually arrives faster than the printer can handle it, data waiting to be printed is stored temporarily in the buffer. If the print job is very large or if multiple print jobs start arriving, the buffer fills up. In this case, the print job is often spooled to a hard disk.

A Gigabit Interface Converter (GBIC) is a transceiver that converts digital electrical currents to optical signals and back again. GBICs support speeds of 1 Gbps or more and are typically used as an interface between a high-speed Ethernet or ATM switch and a fiber backbone. GBICs are hot-swappable, so switches don’t need to be powered down for their installation.