Gigabit Ethernet

The jump from Ethernet to Fast Ethernet gave users 10 times more available bandwidth. Gigabit Ethernet, with a data rate of 1000 Mbps, offers the same proportioned jump for Fast Ethernet users, but the difference is 900 Mbps more available bandwidth as opposed to 90 Mbps. This substantial increase in bandwidth places a strain on developers who must solve network diameter issues and cabling issues. Gigabit Ethernet has two main areas:

• 1000BASE-T— Like its 10BASE-T and 100BASE-TX brethren, 1000BASE-T supports UTP cabling at a distance of up to 100 m.
  

• 1000BASE-X— 1000BASE-X has three subcategories:
  

1000BASE-SX— A fiber-optic–based medium designed for use over standard multimode fiber for short-haul runs up to 200 m.
1000BASE-LX— A fiber-optic–based medium designed for use over singlemode fiber for long runs of up to 10 km, although it is possible to use modeconditioned multimode fiber in some cases.
1000BASE-CX— A shielded copper medium designed for short patches between devices. 1000BASE-CX is limited to distances of 25 m.


802.3ab 1000BASE-T

The development of the 1000BASE-T standard stemmed from the efforts of Fast Ethernet development. The search for the ideal Fast Ethernet copper solution drove the adoption of 100BASE-TX. Although not well known, there were two other standards: 100BASE-T4 and
100BASE-T2. 100BASE-T4 was not a popular solution because it required the use of all four pairs of Category 3 or 5 cabling. Some installations wired only two-pair Category 3 or 5 cabling in accordance with the requirements of 10BASE-T. 100BASE-T4 also missed the mark by not supporting full-duplex operation.

100BASE-T2 was a more far-reaching specification, enabling 100 Mbps operation over Category 3 cabling using only two pairs. The problem is that no vendor ever implemented the standard. When the time came to develop the gigabit solution for the Ethernet standard, developers took the best of all the 100 Mbps standards and incorporated them into the 1000BASE-T specification.


802.3z 1000BASE-X

802.3z was ratified in 1999 and included in the 802.3 standard. 1000BASE-X is the specification for Gigabit Ethernet over a fiber-optic medium. The underlying technology itself is not new because it is based on the ANSI Fibre Channel standard (ANSI X3T11). 1000BASEX comes in three media types: 1000BASE-SX, 1000BASE-LX, and 1000BASE-CX. 1000BASESX is the most common and least expensive media, using standard multimode fiber. The low cost is not without shortcomings; 1000BASE-SX has a maximum distance of 220 m (compared with full-duplex 100BASE-FX at 2 km). 1000BASE-LX generally utilizes singlemode fiber and can span distances up to 5 km.

1000BASE-CX is the oddball of the three media types. It is a copper-based solution that requires precrimped shielded twisted-pair cabling. The connector is not the familiar RJ-45 of 10/100/1000BASE-T. Instead, you use either a DB-9 or HSSDC connector to terminate the two pairs of wire. 1000BASE-CX can span lengths of up to 25 m, relegating it to wiring closet patches. 1000BASE-CX is not all that common because 1000BASE-T provides the same function for a fraction of the price, and four times the cable length, using standard four-pair, Category 5 cabling.

Ethernet has evolved to support new requirements that users and network administrators demand. It continues to evolve beyond Gigabit Ethernet with its next iteration, 10 Gigabit Ethernet, on the horizon. Table 1-3 gives a summary of the Ethernet family of topologies and their media types. Each topology has a place in networking today, determined by requirements such as cost, required data rate, distance, and existing cable plant. Wired Ethernet shows that backward compatibility is what allows new topologies to prosper, develop, and become accepted standards.