Network Media

The media used in a network configuration refers to the medium used to convey packets of data between hosts on the network. The most common form of network media today is cable, which is covered in the next section. Wireless networks are also beginning to increase in popularity, but these are not discussed in this book because they are not relevant to the Sun Certified Network Administrator Exam for Solaris 9. The Institute of Electrical and Electronics Engineers (IEEE, pronounced eye triple E ) is a professional body responsible for the majority of network media standards.

Network Cables

Cables used in a network configuration carry electrical or light signals to enable a host to communicate with another host. There are three major cable types in use today: coaxial, twisted-pair, and fiber- optic .

Coaxial

This type of cable was the mainstay of earlier ethernet networks before the introduction of twisted-pair and fiber-optic cables. Coaxial cable uses a central core wire that is insulated and wrapped into a conductive cladding. All this is then wrapped into an outer plastic coating. Coaxial cable is still used in environments with electromagnetic interference because it is well- insulated . The two types of coaxial cable are thick and thin. Thick cable is used for distances up to 500 meters , and thin is used for distances up to 185 meters. Coaxial cable uses a special connector at each end of the cable, called a terminator . Terminators possess the same resistance as the cable itself and effectively absorb the signals, preventing them from reflecting back along the cable.

Twisted-Pair

Twisted-pair is the most commonly used cable for LANs and consists of four pairs of twisted wire, all wrapped into a plastic insulator. The two types of twisted pair cabling are shielded twisted-pair (STP) and unshielded twisted-pair (UTP). An STP cable has a metallic shield surrounding the four pairs of wires, providing much better resistance to electromagnetic interference. STP is also more expensive, so it is used only in environments in which electromagnetic noise levels are high. A UTP cable has no such shield.

Fiber-Optic

Unlike coaxial and twisted-pair cables, fiber-optic signals are sent as light waves. These have a much higher capacity because greater bandwidth is available. Fiber-optic networks can also span larger geographical areas compared to the other cables. The two main modes of fiber-optic are single mode fiber ( SMF ) , in which only one signal can be sent along the cable at a time, and multimode fiber ( MMF ) , in which multiple signals can be sent along the cable simultaneously at different angles of reflection. Fiber-optic cables are popularly used as backbones in larger campus networks, with FDDI being the most common.

IEEE Ethernet Standards

The IEEE has developed and maintained a number of media standards for use with its 802.3 (ethernet) network type. Which one you use for your network depends on the following factors:

• The physical distance the network has to cover

• Security requirements of the media itself

• The cost of the media and of installing it

• Whether the media is supported by current technologies

The following sections describe the various IEEE media standards along with their properties, capacities , and distances where appropriate.

10BASE Types

The 10BASE family of media types has a maximum capacity of 10Mbps and uses baseband signaling. The properties of each is described in the following:

• 10BASE-2 ” Thin coaxial cable that was the most popular, and cheapest, implementation prior to the introduction of twisted-pair. 10BASE-2 networks have a distance limit of 185 meters. The 2 in the designation is rounded up to 200 meters.

• 10BASE-5 ” A thick (half inch) coaxial cable was the first media type to be used in the ethernet standard of 1980. This cable was quite inflexible , although still cheap to install given that it provided electrical shielding, too. It was frequently used as backbone cabling with a maximum distance of 500 meters.

• 10BASE-T ” The most widely used cabling for desktop connections, this was the first twisted-pair specification introduced in 1990. Hubs and switches are used to interconnect network segments, unlike the coaxial cable connections, which could be connected together directly using BNC connectors. Two pairs of twisted wires are used, one for receiving signals and one for sending over a distance of approximately 100 meters.

100BASE Types

The 100BASE family of media types has a maximum capacity of 100Mbps and uses baseband signaling. The properties of each are as follows :

• 100BASE-TX ” Twisted-pair cabling using two pairs of wires. It enables the use of both STP and UTP but can be implemented only on CAT-5 cabling. The maximum distance is approximately 100 meters.

• 100BASE-T4 ” Twisted-pair cabling using four pairs of wires. Although CAT-5 cabling is normally used, it enables the use of both CAT-3 and CAT-4 UTP cabling: one pair for receiving, one pair for sending, and two bidirectional pairs. The maximum distance is approximately 100 meters.

• 100BASE-FX ” Fiber-optic cable consisting of two multimode fibers. The optional full-duplex mode enables a maximum distance of 2000 meters for a network segment. Fiber is inherently more secure because the signal cannot be tapped easily; it is also nonconductive, making it immune to hazards such as lightning.

1000BASE Types

The 1000BASE family of media types has a maximum capacity of 1000Mbps and uses baseband signaling. The properties of each is described in the following:

• 1000BASE-T ” IEEE Standard 802.3ab, a subset of the 802.3 Ethernet standard, was introduced in 1999. This standard is Gigabit Ethernet over four pairs of UTP CAT-5 cabling. Sun's implementation of 1000BASE-T supports distances of up to 100 meters.

• 1000BASE-X ” IEEE Standard 802.3z, a subset of the 802.3 Ethernet standard, was standardized in 1998. This standard provides Gigabit Ethernet over single- and multimode fiber-optic cable, as well as one using copper wire. This standard refers to three implementation types ”namely 1000BASE-SX, 1000BASE-LX and 1000BASE-CX, which are described next.

• 1000BASE-SX ” This standard uses short wavelength lasers to send data on fiber-optic cable. Sun's implementation of this standard supports distances of 300 meters (using MMF 62.5-micron fiber) and 550 meters (using MMF 50-micron fiber).

• 1000BASE-LX ” This standard uses long wavelength lasers to send data on fiber-optic cable. Sun's implementation of this standard supports distances of 550 meters (using MMF 62.5- and 50-micron fiber) and 3,000 meters (using SMF 9-micron fiber).

• 1000BASE-CX ” This standard uses copper cables to connect short distances up to 25 meters. It is primarily used in computer rooms, specifically within wiring cabinets to connect networking equipment in close proximity.