Ethernet seminar

8/7/2019 Ethernet seminar

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History A loca l area network [LAN] is a data commu nicatio n system that a llow a number of ind epe nd e nt device to commu nicate direct ly with each other in a limite d g eo graphic area .Ether net ,Toke n B us , Toke n R ing are sta nd ar d of the IEEE a nd are part of its P roject 802.P roject 802 set sta nd ar ds to e nab le intercommu nicatio n betwee nequipme nt from a variety of ma nufacturers .P roject 802 d oes nt seek to rep lace a ny part of the OSI mo de l ,instea d it is a way of specifyi ng functio ns of P hysica l layer , the

Data link layer , a nd to a lesser exte nd , the network layer to a llow inter co nn ectivity of major LAN protoco ls .IEEE has sub divide d the data link layer in to two sub layers

1) Logic Link Contro l [LLC]2) Me dium Access co ntro l [MAC]


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Deve lope d by Bob Metca lfe at Xerox PARC in mid-197 0

S ta nd ar dize d by Xerox , DEC, a nd In te l in 197 8

LAN sta nd ar ds define MAC a nd physica l layer co nn ectivity

IEEE 802.3 (CSMA/CD - E ther net) sta nd ar d origina lly 2MbpsIEEE 802.3 u sta nd ar d for 100M bps Ether net

IEEE 802.3 z sta nd ar d for 1,000M bps Ether net


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W he never mu ltiple users have unre gulate d access to a singl e line ,there is a da ng er of sign a l over lappi ng a nddestroyi ng each other , such over lap , which tur n the sign a ls in to unusab le noise are ca lle d co llisio n.

The access mecha nism use d in a n E ther net is ca lle dcarrier se nse mu ltiple access with co llisio n d etectio n[CSMA/CD] .

CSMA/CD is the resu lt of evo lutio n from mu ltiple access [MA] to carrier se nse mu ltiple access [CSMA] a nd fina lly to CSMA/CD.


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In Multiple Access there was no provisio n for traffic coor dinatio n ,the access to the line was ope n to a ny node at a ny time ,with the assumptio n that the odd of two devices , access at same time were sma ll e nou gh to be unimporta nt.

In CSMA system a ny work statio n wishi ng to tra nsmit must first liste n for existi ng traffic on the line . A d evice liste n by checki ng for a vo lta ge , if no vo lta ge is detecte d , the line is co nsidere d idle a ndthe tra nsmissio n is initiate d.

In CSMA/CD the statio n wishi ng to tra nsmit first liste n to make certai n the link is free , the n tra nsmits its data , the n l iste n a gain. I f co llisio n is detecte d , the statio n quits the curre nt tra nsmissio n a ndwaits for a pre determi ne d amou nt of time for the line to clear ,the nse nd its data a gain.


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A B

A B

Collisio ns are cause d whe n two a daptors tra nsmit at the same time (a daptors se nse co llisio n base d on volta ge differe nces)

Both fou nd l ine to be idle

A starts attime 0

Message almost

there at time T whenB starts collision!


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S e nd jammi ng sign a l after co llisio n is detecte d to insure a ll hosts see co llisio n

4 8 bit sign a l


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P reamb le SFD D esti natio na dd ress

S ource Add ress

Le ng thPDU

DATA CRC

P reamb le :- 7 bytesS tart Frame De limiter [SFD] :- 1 byteDesti natio n Add ress :- 6 bytesS ource Add ress :- 6 bytesLe ng th :- 2 bytesData :- 4 6 to 15 00 bytesCRC :- 4 bytes


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PREAMBLE :- I t is the first field of the frame it co nsist of seve nbytes of a lter nate zero a nd one , it a lerts the receivi ng n ode to the comi ng frame a nd e nab le it to sy nchro nize .

SFD :- T he seco nd field(10101011) it is one byte long .T he SFDte lls the receiver that everythi ng that follows it is data

Desti natio n Add ress :- The thir d field it is 6 byte long a nd co ntainthe physica l a dd ress of the packets next desti natio n.


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S ource Add ress :- The fourth field it is a lso 6 bytes long co ntain the physica l a dd ress of the last node that forwar d the packet

Le ng th :- The fifth field of the frame it is 2 byte long . I t ind icates the number Of bytes in comi ng DATA.

Data :- The sixth field is the data field a nd it is 4 6 to 15 00 bytes long.

CRC :- T he last field of the frame it is 4 byte long use d for error detectio n


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DSAP SSAP CONTROL INFORMATION

DSAP :- D esti natio n S ervice Access P oint. The first bit ind icate whether the frame is inte nd e d for a n ind ividua l or a group .

0 Ind ividua l1 -- G roup

SSAP :- S ource S ervice Access P oint. The first bit ind icate whether the commu nicatio n is a Comma nd or Respo nse .

0 Comma nd1 -- R espo nse

CONTROL :- 1 byte or 2 byte se gme nt of the frame use d for f low ma na geme nt.INFORMATION :- I t co ntain user data .


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Name SegmentLength (Max.)

Cable

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

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

58 C/U coaxial10Base-T 100m / 328ft. Category 3 or

better unshieldedtwisted pair


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In thick Ether net a loca l area ca n be divide d into se gme nts by co nn ecti ng d evicesThe le ng th of each se gme nt is limite d to 500 meters .Each statio n is attache d by a n AUI [A ttachme nt Un it Interface ] cab le to a n interme diate device ca lle d a me dium attachme nt unit [MAU] or more commo nly , a tra nsceiver .The tra nsceiver performs the CSMA/CD functio n of checki ng for vo lta ge a nd co llisio ns on the line .It a lso serves as the co nn ector that attaches a statio n to the thick

coaxia l cab le itse lf via a tap .It uses bus topo logy.


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10B ase 2 - U ses Thinn et coaxia l cab leUse a BNC T co nn ector ,it is T shape d with three port one for the NIC a nd one for the input a nd output e nd of the cab le .The cab le require d to imp leme nt the 10 BASE 2sta nd ar d is RG- 58.The maximum le ng th of one se gme nt is 185 meters .It uses bus topo logy.


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10 BASE- T use a star topo logy .It use a unshie lde d twiste d pair cab le instea d of coaxia l cab le .It supports a data rate of 10 Mbps a nd has a maximum le ng th of 100 meters .10 B ase -T E ther net places a ll of its networki ng operatio ns in a ninte llige nt hub with a port for each statio n.S tatio ns are linke d in to the hub by four -pair RJ- 4 5 cab le .Logic in the NIC assures that the only statio n to ope n a nd rea d a give n frame is the situatio n to which that frame is a dd resse d.


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The migratio n from 10 M bps to 100 M bps e ncoura ge d the IEEE802.3 committee to desi gn G igabit Ether net ,which has a data rate of 1000M bps or 1Gbps .

The strate gy is same ,the MAC layer a nd the access metho d remai nthe same , but the co llisio n d omai n is re duce d.


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Data Communication and Networking(second edition )

Behrouz A. Forouzan

Internet Working With TCP/ IP(Fifth edition )Douglas E. Comer

http://en.wikipedia.org/wiki/Ethernet


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Ethernet seminar

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Transcript of Ethernet seminar