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Dongles

RJ45 BNCLC

CoaxialFiber optic

Wirednetcard

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I n 1973 Robert Metcalfe needed something that was fast, couldconnect hundreds of computers, and span a whole building. To

solve this problem, Metcalfe developed a rudimentary form of LAN and dubbed it Ethernet. The original Ethernet sent roughlya paragraph of data over thick coaxial cable and could handle adistance of one kilometer.

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I n 1975 Xerox filed a patent listing Metcalf, David Boggs,Chuck Thacker and Butler Lampson as inventors. I n 1976

Metcalf wrote a seminal paper that stated the transfer rate was 3Mbits/second. Metcalf left Xerox in 79 to start the company3com.

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I n 1981, 3COM built the first 10 Mbits/sec Ethernet adapter.

In mid 1980s, Tim Rock, Richard Bennett, Pat Thaler, andothers develop StarLAN, the basis for 1BASE5 ethernet

I n late 1980s the twisted pair design started to replace thecoaxial cables.

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How the N

IC transfers data

The app you are using generates the data youwould like to send to another computer.

Your NIC accepts the data from your motherboard and transfers it to a small buffer on

the card.The NI C adds its address (set by themanufacturer) plus the destination address andthe type of data to the buffer.Your NI C calculates the checksum, or CRC, for the data in the buffer.

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How the N

IC transfers data

The information is arranged into a frame.The NI C listens to the network for other transmissions.

I f a transmission is heard, it will wait until the transmissionis complete.The NI C begins to serially transmit the frame over thenetwork.The receiving N I C calculates the checksum for thereceived frame, then compares it to the checksum it

received.I f there are no errors, the receiving station acknowledgesthe received data.

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Translated into 5 stepsThe network application retrieves the data beingsent.

The NI C puts the address of the other computer onto the data.The NI C calculates for errors.The data is arranged into a packet and sent over

the network.The receiving card checks for errors, if there arenone, it acknowledges the data.

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The Network interface cards use differing amounts of

voltage to transport the 1s and 0s of binary across thecable.

For fiber optic cable, different wavelengths of light are passed along.

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Application(Layer 7)

This layer supports application and end-user processes.

Presentation(Layer 6)

Session(Layer 5)

Transport(Layer 4)

Network(Layer 3)

Data Link(Layer 2)

Physical(Layer 1)

This layer translates the data so it can be sent along the network. I t is

sometimes called the syntax layer .This layer establishes, manages and terminates connections between applications.The session layer sets up, coordinates, and terminates connections at each end. I tdeals with session and connection coordination.

This layer provides transparent transfer of data between end systems, or hosts, andis responsible for end-to-end error recovery and flow control. I t ensures complete

data transfer.This layer provides routing technologies, creating paths, known as virtual circuits ,for transmitting data from computer to computer. Routing and forwarding arefunctions of this layer, as well as addressing, internetworking, error handling,congestion control and packet sequencing.

At this layer, data packets are encoded and decoded into bits. The data link layer is

divided into two sub layers: The Media Access Control (MAC) layer and theLogical Link Control (LLC) layer. The MAC layer controls how a computer onthe network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking.

This layer conveys the bit stream - electrical impulse, light or radio signal -- through thenetwork at the electrical and mechanical level. It provides the hardware means of sending and

receiving data on a carrier, including defining cables, cards and physical aspects. FastEthernet, RS232, and ATM are protocols with physical layer components.

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Token Ring ProcessPhase 0 (Lobe Check) The station checks to ensure it can receive these frameswithout error.Phase 1 (Physical Insertion) A station then sends a 5 volt signal to the MSAU to openthe relay.Phase 2 (Address Verification) A station then transmits MAC frames with its ownMAC address in the destination address field of a token ring frame. When the framereturns and if the address copied , the station must participate in the periodic (every 7seconds) ring poll process. This is where stations identify themselves on the network as

part of the MAC management functions.Phase 3 (Participation in ring poll) A station learns the address of its Nearest ActiveUpstream Neighbor (NAUN) and makes its address known to its nearest downstreamneighbor, leading to the creation of the ring map. Station waits until it receives an AMPor SMP frame with the AR I and FC I bits set to 0. When it does, the station flips both

bits (AR I and FC I) to 1, if enough resources are available, and queues an SMP frame for transmission. If no such frames are received within 18 seconds, then the station reports afailure to open and de-inserts from the ring. If the station successfully participates in aring poll, it proceeds into the final phase of insertion, request initialization.Phase 4 (Request Initialization) Finally a station sends out a special request to a

parameter server to obtain configuration information. This frame is sent to a specialfunctional address, typically a token ring bridge, which may hold timer and ring number information with which to tell the new station abort

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How the procedure works.

Main procedure, it states and asksAsks: is the frame ready for transmission.

Is medium idle? If not, wait until it becomes ready and wait the interframe periodStarts transmitting.Asks: did a collision occur? If so, it goes to collision detected procedure.Resets retransmission counters and end frame transmission.If a collision is detected it:

Continues the transmission until minimum packet time is reached to ensurethat all receivers detect the collision.Counts how many times it retransmittedAsks: was the maximum number of transmission attempts reached? If so, aborttransmission.Calculates and wait random back off period based on number of collisionRe-enters main procedure at stage 1.

Simpler than a token ring, the procedure for coaxialis as following:

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H ow long the card waits between retransmission

The card counts how many collisions occurred.

Then, back-off algorithms determine when thecolliding stations retransmit.

2^n -1 Action2^0 - 1 Transmits immediately2^2 - 1 Waits 0, 1, 2, or three slots

2^3 - 1 Waits 0 to 7 slots

N = number of collisions

The card can wait up to 16 collisions, anything higher and it quits.

Slot Time: Twice the time it takes for an electronic pulse to travel thelength of the maximum theoretical distance between two nodes.

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The Frames

A runt frame is a packet smaller than the 64 bytes. This usually occurs because of a collisionor an error.

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Differences in the cardsThe major difference between the cards are theway the data is converted to transmit over the

network. Each type of network has its own type of transceiver (transmitter + receiver). 10baseTnetworks have a specialized transceiver thattranslates the data into 10baseT Ethernet

standards, then transmits it. I t also receivesinformation from the network and translates it

back into a form the N I C card can use.

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Differences in the cards (continued)10base2 Ethernet networks have almost thesame N I C except for the transceiver. Some

NI Cs have two transceivers, normally10baseT and 10base2. These dual type cardsare known as combo N I Cs.

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Major ManufacturersZTECisco Systems

H ewlett-Packard3Com

LinksysBelkinDlink

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F iber Distributed Data Interface

Can support thousands of users

Uses duel token ring setup

Due to their speed, cost and ubiquity, fast Ethernet and (since1998) Gigabit Ethernet have largely made FDD I redundant.

Needs two Token ring supportable cards or two jacks on thecard.

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PriceThe cards can range in price from $10 to$800. Most cards are actually around $20.

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ReferencesWebopedia.com

H owstuffworks.comhttp://everything2.com/title/ H ow+Network+Adapters+Work Wikipedia.comBestbuy.com

http://www.eflnet.com/networking/acrolist.php?firstletter=F