IEEE 802.3 and IEEE 802.5 Media

IEEE 802.3 and IEEE 802.5 Media

IEEE 802.2(topology independent), IEEE 802.3 (based on Ethernet), and IEEE 802.5 (based on Token Ring) are the most commonly used IEEE 802 standards. Carefully read the following overview of the media each uses—Microsoft expects you to describe “the characteristics and purpose of the media used in IEEE 802.3 and IEEE 802.5” for the Networking Essentials exam. (Chapters 3 and 4 discuss Ethernet and Token Ring media in greater detail.)

The IEEE 802.3 Physical layer definition describes signaling methods (both baseband and broadband), data rates, media, and topologies. Several Physical layer variants also have been defined. Each variant is named following a convention that states the signaling rate (1 or 10) in Mbps, baseband (BASE) or broadband (BROAD) mode, and a designation of the media characteristics.

The following list details the IEEE 802.3 variants:

1BASE5. This 1-Mbps network utilizes UTP cable with a signal range up to 500 meters (250 meters per segment). A star physical topology is used.
10BASE5. Typically called Thick Ethernet, or Thicknet, this variant uses a large diameter (10 mm) “thick” coaxial cable with a 50-ohm impedance. A data rate of 10 Mbps is supported with a signaling range of 500 meters per cable segment on a physical bus topology.
10BASE2. Similar to Thicknet, this variant uses a thinner coaxial cable that can support cable runs of 185 meters. (In this case, the “2” only indicates an approximate cable range.) The transmission rate remains at 10 Mbps, and the physical topology is a bus. This variant typically is called Thin Ethernet, or Thinnet.
10BASE-F. This variant uses fiber-optic cables to support 10-Mbps signaling with a range of 4 kilometers. Three subcategories include 10BASE-FL (fiber link), 10BASE-FB (fiber backbone), and 10BASE-FP (fiber passive).
10BROAD36. This broadband standard supports channel signal rates of 10 Mbps. A 75-ohm coaxial cable supports cable runs of 1,800 meters (up to 3,600 meters in a dual-cable configuration) using a physical bus topology.
10BASE-T. This variant uses UTP cable in a star physical topology. The signaling rate remains at 10 Mbps, and devices can be up to 100 meters from a wiring hub.
100BASE-X. This proposed standard is similar to 10BASE-T but supports 100 Mbps data rates.

Some disagreement exists in the industry regarding the proper use of the name “Ethernet.” Xerox has placed the name “Ethernet” in the public domain, which means that no one can claim authority over it. Purists, however, often claim that “Ethernet” refers only to the original Digital-Intel-Xerox standard. More frequently, however, the term designates any network based on CSMA/CD access-control methods.

Usually, it is necessary to be specific about the standard that applies to a given network configuration. The original standard is called Ethernet version 2 (the older version 1 is still in occasional use) or Ethernet-II. The IEEE standard is distinguished by its committee title as 802.3.

This distinction is important because Ethernet version 2 and 802.3 Ethernet use incompatible frame types. Devices using one frame type cannot communicate with devices using the other frame type.

The IEEE 802.5 standard does not describe a cabling system. Most implementations are based on the IBM cabling system, which uses twisted-pair cable wired in a physical star. See Chapter 3 and Chapter 4 for more information on Token Ring cabling and topologies.