Gigabit Ethernet

Gigabit Ethernet

Gigabit Ethernet

Vijay Moorthy, (moorthy@cis.ohio-state.edu)

Ethernet is the world's most pervasive networking technology. Gigabit Ethernet is the latest version of Ethernet. It offers 1000

Mbps ( 1 Gbps ) raw bandwidth, that is 100 times faster than the original Ethernet, yet is compatible with existing Ethernets, as it

uses the same CSMA/CD and MAC protocols. When Gigabit Ethernet enters the market it will compete directly with ATM. This

paper presents a survey of Gigabit Ethernet technology.

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Table of Contents

1. Introduction

1.1 History of Ethernet

1.2 Gigabit Ethernet Alliance

2. Physical Layer

2.1 1000Base-X

2.2 1000Base-T

3. MAC Layer

3.1 Carrier Extension

3.2 Packet Bursting

4. GMII ( Gigabit Media Independent Interface )

4.1 PCS (Physical Coding Sublayer)

4.2 PMA (Physical Medium Attachment)

4.3 PMD (Physical Medium Dependent)

5. Buffered Distributor

6. Topologies

6.1 Upgrading server-switch connections

6.2 Upgrading switch-switch connections

6.3 Upgrading a Fast Ethernet backbone

6.4 Upgrading a Shared FDDI Backbone

6.5 Upgrading High Performance Workstations

7. ATM vs. Gigabit Ethernet

8. Summary

9. Bibliography and Links

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Gigabit Ethernet

1. Introduction

Ethernet is the world's most pervasive networking technology , since the 1970's. It is estimated that in 1996, 82% of all networking

equipment shipped was Ethernet. In 1995 ,the Fast Ethernet Standard was approved by the IEEE. Fast Ethernet provided 10 times

higher bandwidth, and other new features such as full-duplex operation, and auto-negotiation. This established Ethernet as a

scalable technology. Now, with the emerging Gigabit Ethernet standard, it is expected to scale even further.

The Fast Ethernet standard was pushed by an industry consortium called the Fast Ethernet Alliance. A similar alliance, called the

Gigabit Ethernet Alliance was formed by 11 companies in May 1996 , soon after IEEE announced the formation of the 802.3z

Gigabit Ethernet Standards project. At last count, there were over 95 companies in the alliance from the networking, computer and

integrated circuit industries.

A draft 802.3z standard was issued by IEEE in July 1997. The last technical changes are expected to be resolved by September.

The standard is expected to be adopted by March 1998.

The new Gigabit Ethernet standards will be fully compatible with existing Ethernet installations. It will retain Carrier Sense

Multiple Access/ Collision Detection (CSMA/CD) as the access method. It will support full-duplex as well as half duplex modes

of operation. Initially, single-mode and multi mode fiber and short-haul coaxial cable will be supported. Standards for twisted pair

cables are expected by 1999. The standard uses physical signalling technology used in Fiber Channel to support Gigabit rates over

optical fibers.

Initially, Gigabit Ethernet is expected to be deployed as a backbone in existing networks. It can be used to aggregate traffic

between clients and "server farms", and for connecting Fast Ethernet switches. It can also be used for connecting workstations and

servers for high - bandwidth applications such as medical imaging or CAD.

1.1 History of Ethernet

Today, Ethernet is synonymous with the IEEE 802.3 standard for a "1-persistent CSMA/CD LAN". The 802.3 standard has an

interesting history. The beginning, is generally considered to be the University of Hawaii ALOHA network. This system is the

ancestor of all shared media networks. The original Ethernet, developed by Xerox was based on the ALOHA system. It was a 2.94

Mbps CSMA/CD system and was used to connect over 100 personal workstations on a 1 Km cable. It was so successful, that

Xerox, DEC and Intel came up with a 10 Mbps standard. The IEEE 802.3 standard was based on the 10 Mbps Ethernet.

CSMA/CD refers to the protocol used by stations sharing the medium, to arbitrate use of the medium. A sender has to "listen" to

the medium. If no one else is transmitting, then the sender may transmit. If two senders start transmitting at the same time, then a

collision is said to have occurred. Transmitting stations, therefore, have to listen to the medium for collisions while transmitting,

and