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Ethernet <strong>and</strong> TCP/IP networks 317<br />

transmitting at the same time) but rather waited for an acknowledgment back within a<br />

predefined time.<br />

The initial system installed by Xerox was so successful that they soon applied the<br />

system to their other sites typically connecting office equipment to shared resources such<br />

as printers <strong>and</strong> large computers acting as repositories of large databases, for example.<br />

In 1980, the Ethernet Consortium consisting of Xerox, Digital Equipment Corporation<br />

<strong>and</strong> Intel (sometimes called the DIX consortium) issued a joint specification based on the<br />

Ethernet concepts <strong>and</strong> known as the Ethernet Blue Book 1 specification. This was later<br />

superseded by the Ethernet Blue Book 2 specification, which was offered to the IEEE as<br />

a st<strong>and</strong>ard. In 1983, the IEEE issued the 802-3 st<strong>and</strong>ard for Carrier Sense; Multiple<br />

Access; Collision Detect LANs based on the Ethernet st<strong>and</strong>ard which gave this networking<br />

st<strong>and</strong>ard even more credibility.<br />

As a result of this, there are three st<strong>and</strong>ards in existence. The first – often termed<br />

Ethernet Version 1 – can be disregarded as very little equipment based on this st<strong>and</strong>ard is<br />

still in use. Ethernet Version 2 or ‘Blue Book Ethernet’ is, however, still in use <strong>and</strong> there<br />

is a potential for incompatibility with the IEEE 802.3 st<strong>and</strong>ard. Despite the generic term<br />

‘Ethernet’ being applied to all CSMA/CD networks, it should be reserved for the original<br />

DIX st<strong>and</strong>ard. This manual will continue with popular use <strong>and</strong> refer to all the LANs of this<br />

type as Ethernet, unless it is important to distinguish between them.<br />

Ethernet uses the CSMA/CD access method. This gives a system that can operate with<br />

little delay, if lightly loaded, but the access mechanism can fail completely if too heavily<br />

loaded. Ethernet is widely used commercially, <strong>and</strong> the network interface cards (NICs) are<br />

relatively cheap <strong>and</strong> produced in vast quantities. Because of its probabilistic access<br />

mechanism, there is no guarantee of message transfer <strong>and</strong> messages cannot be prioritized.<br />

It is becoming more widely used industrially despite these disadvantages.<br />

12.2 Physical layer<br />

The 802.3 st<strong>and</strong>ard defines a range of cable types that can be used for a network based on<br />

this st<strong>and</strong>ard. They include coaxial cable, twisted pair cable <strong>and</strong> fiber optic cable.<br />

In addition, there are different signaling st<strong>and</strong>ards <strong>and</strong> transmission speeds that can be<br />

utilized. These include both baseb<strong>and</strong> <strong>and</strong> broadb<strong>and</strong> signaling, <strong>and</strong> speeds of 1 Mbps<br />

<strong>and</strong> 10 Mbps. The st<strong>and</strong>ard is continuing to evolve, <strong>and</strong> this manual will look at<br />

100 Mbps <strong>and</strong> gigabit Ethernet systems later.<br />

The IEEE 802.3 st<strong>and</strong>ard documents (ISO 8802.3) support various cable media <strong>and</strong><br />

transmission rates up to 10 Mb/s as follows:<br />

• 10Base2<br />

Ethernet <strong>and</strong> TCP/IP networks thin wire coaxial cable (0.25 inch diameter),<br />

10 Mbps, single cable bus<br />

• 10Base5<br />

Thick wire coaxial cable (0.5 inch diameter), 10 Mbps, single cable bus<br />

• 10BaseT<br />

Unscreened twisted pair cable (0.4 to 0.6 mm conductor diameter), 10 Mbps,<br />

twin cable bus<br />

• 10BaseF<br />

Optical fiber cables, 10 Mbps, twin fiber bus

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