Ethernet has evolved to meet the increasing demands of packet-switched networks. Now see what Gigabit Ethernet has to offer. by Mahesh Rathod

Since its inception, Ethernet has been a popular networking protocol. High-speed data, voice and video transactions on a single network are becoming the choice of enterprises. They are looking for cost-effective solutions that will provide greater speed and more bandwidth. A favorable option is to move to Gigabit Ethernet.

What is Gigabit Ethernet?

Gigabit Ethernet is an expansion of the popular 10 Mbps (10BASE-T) Ethernet and 100 Mbps (100BASE-T) Fast Ethernet standards for network connectivity. It builds on top of the Ethernet protocol, and increases speed tenfold over Fast Ethernet to 1000 Mbps, or one gigabit per second (Gbps). This protocol was introduced by the 10 GEA (Gigabit Ethernet Alliance) in June 1998, mainly for use in high-speed local area network backbones and server connectivity.

The main purpose of Gigabit Ethernet is to build on the existing installed base of Ethernet and Fast Ethernet. The idea is to facilitate a high-speed network without forcing customers to throw away existing networking equipment. The earlier Ethernet specification mainly defined frame format and support for CSMA/CD (Carrier Sense Multiple Access/Collision Detection) protocol, flow control, full duplex and management objects, as defined by the IEEE 802.3 standard. Gigabit Ethernet conforms to all these specifications.

Why is Gigabit Ethernet necessary?

The main circumstances that are driving enterprises or organizations to move to Gigabit Ethernet is the increase in Internet and Intranet traffic. Some of the factors that are contributing to this explosive growth are:

• A rapid increase in the number of network connections
• Deployment of bandwidth-intensive applications such as high-quality video and voice
• Rise in Web hosting and application hosting traffic
• Increase in the connection speed of each end-station architecture

Gigabit Ethernet makes use of a combination of proven protocol technologies like the original IEEE 802.3 Ethernet specification and the ANSI X3T11 Fiber Channel standard. Leveraging these two technologies helped in taking advantage of the existing high-speed physical interface technology of Fiber Channel while maintaining the IEEE 802.3 Ethernet frame format, backward compatibility for installed media, and use of full- or half-duplex CSMA/CD.

To support the ever increasing bandwidth needs, Gigabit Ethernet also incorporates enhancements that enable fast optical fiber connections at the physical layer of the network. It also provides a tenfold increase in MAC (Media Access Control) layer data rates to support video and voice, complex imaging and other data-intensive applications.

What media will support Gigabit Ethernet?

Gigabit Ethernet standards call for media support for multimode fiber-optic cable, single-mode fiber-optic cable, and a special balanced shielded 150-ohm copper cable.

1000BaseSX (short-wave laser) and 1000BaseLX (long-wave laser) laser standards are supported over multimode fiber. Two types of multimode fiber are available: 62.5 and 50 micron-diameter fibers. Long-wave lasers will be used for single-mode fiber, mainly because this fiber is optimized for long-wave laser transmission. There is no support for short-wave laser over single-mode fiber.

In case of shorter cable runs of 25 meters or less, Gigabit Ethernet will allow transmission over a special balanced shielded copper 150-ohm cable. This is a new type of shielded cable and should not be confused with unshielded twisted pair (UTP).

Differences

There are two main differences between Gigabit Ethernet and previous versions of Ethernet. First is the inclusion of a long-haul (40+ km) optical transceiver or physical medium dependent (PMD) interface for single-mode fiber that can be used with either the LAN physical layer (PHY) or wide area network (WAN PHY) for building metropolitan area networks (MANs). The second is the WAN PHY option, which allows 10-Gigabit Ethernet to be transparently transported across existing SONET (synchronous optical network) OC-192c or SDH (synchronous digital hierarchy) VC-4-64c infrastructures.

What after Gigabit Ethernet?

The 10-Gigabit Ethernet standard extends the 802.3 protocols to an operating speed of 10 Gbps and also expands the Ethernet application space to include WAN links. This new standard will provide for a significant increase in bandwidth while maintaining maximum compatibility with the installed base of 802.3 interfaces.

Similar to 1000BASE-X and 1000BASE-T Ethernet model,

10-Gigabit Ethernet continues the natural progression of Ethernet in distance and speed. Since it is a full-duplex only and fiber-only technology, it does not need the carrier-sensing multiple-access with CSMA/CD protocol that defines slower, half-duplex Ethernet technologies. Overall 10-Gigabit Ethernet remains true to the original Ethernet model.

While Gigabit Ethernet is currently being deployed over tens of kilometers in private networks,

10-Gigabit Ethernet will be mainly used by network administrators as a cornerstone for network architectures that encompass LANs, MANs and WANs using Ethernet as the end-to-end, Layer 2 transport method.

As with Gigabit Ethernet, the 10-Gigabit standard supports both single-mode and multi-mode fiber mediums. But in 10-Gigabit Ethernet, the distance for single-mode fiber has been expanded from the 5km that Gigabit Ethernet supports to 40km in 10-Gigabit Ethernet.

Application areas

Lets take a look at some of the areas were 10-Gigabit Ethernet can be put into use:

Higher performance in LANs: Traditionally, Ethernet technology has been deployed for high performance LAN environments. Now with 10-Gigabit Ethernet, the LAN can reach farther and support bandwidth starved applications.

With 10 Gigabit backbones installed, enterprises will be able to provide Gigabit Ethernet service to workstations and, eventually, to the desktop in order to support hungry applications such as high-end graphics, streaming video, medical imaging, and centralized applications. This technology will also provide lower network latency due to the speed of the link and over-provisioning bandwidth to compensate for the bursting nature of data in enterprise applications.

Increased velocity in MANs and SANs: Deployment of Gigabit Ethernet as a backbone technology for fiber metropolitan networks has already been seen. Now with 10-Gigabit Ethernet interfaces, optical transceivers and single-mode fiber, service providers will be able to build links reaching 40 km or more.

Additionally, 10-Gigabit Ethernet, can now offer superior data carrying capacity at similar latencies to many other storage networking technologies including 1 or 2 Gigabit Fiber Channel, ATM OC-3, OC-12 & OC-192,Ultra 60 and HIPPI (High Performance Parallel Interface). Applications like remote backup, disaster recovery and storage on demand can be easily extended to 10-Gigabit Ethernet.

WANs: Using 10-Gigabit Ethernet, network service providers and ISPs will be able to create high-speed links at a very low cost, between co-located, carrier-class switches and routers and optical equipment that is directly attached to the SONET/SDH cloud. Along with 10-Gigabit Ethernet, the WAN PHY will also allow the construction of WANs that connect geographically scattered LANs between campuses or POPs (points of presence) over existing SONET/SDH/TDM networks.

	Ethernet 10 Base T	Fast Ethernet 100 Base T	Gigabit Ethernet 1000 Base x
Data Rate	10 Mbps	100 Mbps	1000 Base Mbps
CAT UTP	100 m	100 m	100 m
STP / Coax	500 m	100 m	25 m
Multimode fiber	2 km	412 m (hd) 2 km (fd)	550 m
Single-mode fiber	25 km	20 km	5 km
Ethernet Technology Comparison

Mahesh Rathod can be reached at rathodmp@hotmail.com