Explain IEEE 802.4 Standard in Detail ?

In a effort to design a standard less prone to collisons then the 802.3,thr IEEE 802.4 sub committee designed a combination bus/ring topology that transmitted information via a token but would use the bus physical topology.
=>The 802.4 standard is designed around to the obvervation that computers are prone to the same fallibility as humans:give i em half a chance and they''''''''ll talk right on top of each other.To get around this problem the 802.4 committee described a token packet that the network could use to decide which machine got to "talk" so it is with the 802.4 standard.
=>Only the workstation that has the token can send information and once the workstation has received acknowledgment of the receipt of that information,it must then pass the token.next workstation in line.How does the network determine who''''''''s next in line ?
=>In 802.4 standard,the network keeps track who gets the token next.Just as the business manager could get the talking stick more often than the person in charge of office decoration,its possible for some workstations to have higher priority to get the token than others.
=>The method of controlling collisions isnt''''''''s the only way in which the 802.4 standar differs from the 802.4 standard.First,the medium is different to some degree.a token bus network runs on either 70-ohm coaxial cable or fiber second,as you can see in figure,an 802.4 ethernet frame in that cantains as following.

1.Preamble

2.Start Frame Delimiter

3.Frame control

4.Destination address

5.Source address

6.Information

7.Frame check sequence

8.Frame delimiter

Figure

Preamble Start Frame Delimiter Frame control .Destination address Source address

Information

Frame check sequence Frame delimiter

An 802.4 Ethernet Frame

Although,the token/bus combination avoids collisions,802.4 that have kept it from common usage.most short falls of the token/busb format come from malfunctioning hardware,which can result in the token being lost,or shadowed tokens that make it look as though there are multiple tokens on the network.Imagine a board meeting with more than one talking stick.


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by MuntazirFatema   Khoja  in Networking  on 9/28/2015 11:21:22 AM  


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