05 Ethernet

8/8/2019 05 Ethernet

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Ethernet is a network standard of communication

using either coaxial or twisted pair cable.Engineers Bob Metcalfe and D.R. Boggs developed

Ethernet beginning in 1972 and through the efforts of

Digital, Intel and Xerox DIX Ethernet became thestandard model for LANs worldwide..

Industry standards based on their work were

established in 1980 under the IEEE 802.3 set ofspecifications and the most widely used for of LAN

communication. Original Ethernet used coaxial wiring,

while now also used in twisted-pair cabling. Different

Ethernet, include 10Base2 (10 Mbps, 200 meters),

10BaseT (10 Mbps, 100 meters, twisted-pair), and

100BaseT (100 Mbps, 100 meter, twisted-pair).


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Ethernet Technologies

In the OSI model, Ethernet technologyoperates at the physical and data link layers -Layers 1 and 2 respectively. Ethernet

supports all popular network and higher-levelprotocols, principally IP.Ethernet supports data transfers at the rate of

10 Megabits per second (Mbps). Over time, asthe performance needs of LANs haveincreased, the industry created more Ethernetspecifications for Fast Ethernet and GigabitEthernet. Fast Ethernet extends traditionalEthernet performance up to 100 Mbps andGigabit Ethernet up to 1000 Mbps speeds.


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Ethernet cables are manufactured to any of

several standard specifications. The mostpopular Ethernet cable in current use,Category 5 or CAT5, supports both traditional

and Fast Ethernet. The Category 5e (CAT5e)cable supports Gigabit Ethernet.

To connect Ethernet cables to a computer, a

person normally uses a network adapter(Network Interface Card - NIC). Ethernetadapters interfaces directly with a computer's

system bus. The cables, in turn, utilizeconnectors that in many cases look like the RJ-45 connector used with modern telephones.


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A NIC is installed in each computer, and is assigned a

unique address. An Ethernet cable runs from each NICto the central switch or hub. The switch or hub will actas a relay (to handle network traffic), receiving anddirecting packets of data across the LAN. Ethernet

networking creates a communications system thatallows the sharing of data and resources, includingprinters, fax machines and scanners.

Ethernet networks can also be wireless. Rather thanusing Ethernet cable to connect the computers,wireless NICs use radio waves for two-waycommunication with a wireless switch or hub. Ethernet

ports, wireless NICs, switches and hubs each feature asmall antenna. Wireless networks can be more flexibleto use, but also require extra care in configuringsecurity.


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Types of Ethernet

The industry used Thicknet, 10Base5 Ethernettechnology until in the 1980s, 10Base2 Thinnetappeared. Thinnet offered better advantage of

thinner (5 millimeters vs 10 millimeters) andmore flexible cabling, making it easier to wireoffice buildings for Ethernet.

The most common form of traditional Ethernet,is 10Base-T, offers better electrical propertiesthan Thicknet or Thinnet, because 10Base-T

cables utilize unshielded twisted pair (UTP)wiring rather than coaxial. It also proved morecost effective than alternatives like fiber optic.


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Name Segment Length (Max.) Cable

10Base5 500m / 1640ft. RG-8 or RG-11 coaxial

10Base2 185m / 606ft. RG 58 A/U or RG 58 C/Ucoaxial

10Base-T 100m / 328ft. Category 3 or betterunshielded twisted pair

Following table has details about traditional Ethernet

technologies. The segment length is also an important aspect of

Ethernet networking.

A segment is a network connection made by a single unbroken

network cable. Ethernet cables/segments can only span a limited

physical distance, after which transmissions will likely fail due to

line noise, reduced signal strength and other degradation.

Other Ethernet standards including 10Base-FL, 10Base-FB, and

10Base-FP for fiber optic networks and 10Broad36 for broadband

(cable television) cabling.


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Fast Ethernet

In the mid-1990s, Fast Ethernet technologybegan to be widely deployed and matured asthe need for greater LAN performance. It met

its design goals ofIncreasing the performance of traditional

Ethernet

Avoiding the need to completely re-cableexisting Ethernet networks

Fast Ethernet comes in two major varieties:

100Base-T (using unshielded twisted paircable)

100Base-FX (using fiber optic cable)


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Fast Ethernet supports a maximum data rate

of 100 Mbps. The most popular is 100Base-T,a standard that includes 100Base-TX(Category 5 UTP), 100Base-T2 (Category 3 or

better UTP), and 100Base-T4 (100Base-T2cabling modified to include two additional wirepairs).A key element of Fast Ethernet's success wasits ability to coexist with existing networkinstallations. Now, many network adapterssupport both traditional and Fast Ethernet.These so-called "10/100" adapters can usuallysense the speed of the line automatically andadjust accordingly.


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Gigabit Ethernet

Gigabit Ethernet is an extension to the family ofEthernet computer networking and communicationstandards.

The Gigabit standard takes Ethernet to the next levelof performance beyond Fast Ethernet. It boasts thesame order-of-magnitude improvement over FastEthernet by offering speeds of 1000 Megabits (1

Gigabit).Gigabit Ethernet was first made to travel over opticaland copper cabling, but the 1000Base-T standardsuccessfully supports it as well.

1000Base-T uses Category 5 cabling similar to 100Mbps Ethernet, although achieving gigabit speedrequires the use of additional wire pairs.


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Migration of existing computer networks from

100 Mbps Fast Ethernet to Gigabit Ethernet ishappening slowly. Gigabit Ethernet can only befound mainly in research institutions.

A decrease in cost, increase in demand, andimprovements in other aspects of LANtechnology will be required before Gigabit

Ethernet surpasses other forms of wirednetworking in terms of adoption.

Cisco Systems technology brief describing the

Gigabit Ethernet architecture, standards effort,comparison with ATM, and migrationstrategies.


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Ethernet Topologies and Protocols

Traditional Ethernet employs a bus topology, meaningthat all devices or hosts on the network use the same

shared communication line. Each device possesses an

Ethernet address, also known as MAC address.Sending devices use Ethernet addresses to specify the

intended recipient of messages.

Data sent over the Ethernet exists in the forms of

frames. An Ethernet frame contains a header, a data

section, and a footer having a combined length of no

more than 1518 bytes. The Ethernet header contains

the addresses of both the intended recipient and the

sender.


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Data sent over the Ethernet is automatically broadcast

to all devices on the network. By comparing theirEthernet address against the address in the frameheader, each Ethernet device tests each frame todetermine if it was intended for them and reads or

discards the frame as appropriate. Network adaptersincorporate this function into their hardware.

Devices wanting to transmit on the Ethernet first

perform a preliminary check to determine whether themedium is available or whether a transmission iscurrently in progress. If the Ethernet is available, thesending device transmits onto the wire. It's possible,

however, that two devices will perform this test atapproximately the same time and both transmitsimultaneously.


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By design, the Ethernet standard does not preventmultiple simultaneous transmission. These so-calledcollisions, when they occur, cause both transmissionsto fail and require both sending devices to re-transmit.Ethernet uses a algorithm based on random delay

times to determine the proper waiting period betweenre-transmissions.

The network adapter also implements this algorithm(Protocol) for broadcasting, listening, and detectingcollisions is known as CSMA/CD (Carrier Sense MultipleAccess / Collision Detection). Some newer forms ofEthernet do not use CSMA/CD. Instead, they use the

so-called full duplex Ethernet protocol, which supportspoint-to-point simultaneous sends and receives with nolistening required.


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Ethernet Devices

As mentioned earlier, Ethernet cables arelimited in their reach, and these distances (asshort as 100 meters) are insufficient to cover

medium-sized and large network installations.A repeater in Ethernet networking is a devicethat allows multiple cables to be joined and

greater distances to be spanned. A bridgedevice can join an Ethernet to another networkof a different type, such as a wireless network.

One popular type of repeater device is anEthernet hub. Other devices sometimesconfused with hubs are switches and routers.


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Ethernet network adapters also exist in multiple forms.

Newer personal computers often include a built-inEthernet adapter. Otherwise, one can purchase and

install an add-in card. PCI cards are most popular for

desktop computers and PCMCIA ("credit card")

adapters most popular for notebooks. USB Ethernet

adapters also exist for both desktops and laptops.

Wireless Ethernet adapters can also be configured to

work with newer computers.

Summary

Ethernet is one of the Internet's key technologies. It

continues to power many of the world's local area

networks and continually is improving to meet future

needs for high-performance networking.

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05 Ethernet