In this curriculum you will be introduced to three LAN technologies: Ethernet, Token Ring, and FDDI. All three have a wide variety of Layer 1 components and devices. The focus of this chapter will be Ethernet 10BASE-T technologies.

When it was developed, Ethernet was designed to fill the middle ground between long distance, low-speed networks, and specialized computer room networks that carried data at high speeds for very limited distances. Ethernet is well-suited to applications in which a local communication medium must carry sporadic, occasionally heavy, traffic at high-peak data rates.

The Ethernet 10BASE-T technologies carry Ethernet frames on inexpensive twisted-pair wiring. You will study four components and three devices that are related to these technologies. The first four components are passive, meaning they require no energy to operate. They are:

• patch panels
• plugs
• cabling
• jacks

The last three are active. They require energy to do their jobs. They are:

• transceivers
• repeaters
• hubs

For more information on other Ethernet, Token Ring, and FDDI components and devices, go to the Web site

The standard 10BASE-T termination (end point, 0 plug, connector) is the registered jack-45 connector (RJ-45).  It reduces noise, reflection, and mechanical stability problems, and resembles a phone plug, except that it has eight conductors instead of four. It is considered a passive networking component because it only serves as a conducting path between the four pairs of Category 5 twisted cable and the prongs of the RJ-45 jack. It is considered a Layer 1 component, rather than a device, because it serves only as a conducting path for bits.

The standard 10BASE-T cable is CAT 5 twisted-pair cable, which is composed of four twisted pairs that reduce noise problems. CAT 5 is thin, inexpensive, and easy to install. The function of CAT 5 cable is to carry the bits, therefore, it is a Layer 1 component.

RJ-45 plugs fit into RJ-45 jacks or receptacles. The RJ-45 jack has eight conductors , which snap together with the RJ-45 plug. On the other side of the RJ-45 jack is a punch down block where wires are separated out and forced into slots with a fork-like tool called a punch-down tool. This provides a copper-conducting path for the bits. The RJ-45 jack is a Layer 1 component.

Patch panels are convenient groupings of RJ-45 jacks. They come in 12, 24, and 48 ports, and are typically rack-mounted. The front sides are RJ-45 jacks ; the back sides are punch-down blocks that provide connectivity or conducting paths. They are classified as Layer 1 devices.

A transceiver is a combination of transmitter and receiver. In networking applications, this means that they convert one form of signal to another form. For example, many networking devices come with an auxiliary unit interface and a transceiver that allows a 10BASE2, 10BASE5, 10BASE-T, or 10\100 BASE-FX to be connected to the port. A common application is the conversion of AUI ports to RJ-45 ports. They are Layer 1 devices. They transmit from one pin configuration and/or media to another. Transceivers are often built into NICs, which are typically considered Layer 2 devices. Transceivers on NICs are called signaling components, which means they encode signals onto the physical medium.

Repeaters regenerate, and retime signals, which then enables cables to extend farther to reach longer distances. They only deal with packets at the bit level, therefore they are Layer 1 devices.

Repeaters are internetworking devices that exist at the physical layer (Layer 1) of the OSI model. They can increase the number of nodes that can be connected to a network, and thus, the distance over which the network can extend. Repeaters re-shape, regenerate, and retime signals before sending them on along the network.

The disadvantage of using repeaters is that they cannot filter network traffic. Data (bits) that arrive at one port of a repeater are sent out on all other ports. The data gets passed along to all other LAN segments of a network regardless of whether or not it needs to go there.

Multiport repeaters combine connectivity with the amplifying and re-timing properties of repeaters. It is typical to see 4, 8, 12, and up to 24, ports on multiport repeaters. This allows many devices to be cheaply and easily interconnected. Multiport repeaters are often called hubs, instead of repeaters, when referring to the devices that serve as the center of a star topology network. Hubs are very common internetworking devices. Since the typical unmanaged hub only requires power and plugged-in RJ-45 jacks, they are great for setting up a network quickly. Like the repeaters on which they are based, they only deal with bits, and are Layer 1 devices.

All of these devices - passive and active - create or act on the bits. They recognize no information patterns in the bits, no addresses, and no data. Their function is simply to move bits around. Layer 1 is fundamental to troubleshooting networks, and should never be underestimated. Many network problems are traceable to bad RJ-45 terminations, jacks, punch-downs, repeaters, hubs, or transceivers.