token-bus

What Is Token Bus 802.4?

Hello friends, In this blog post I am going to let you know about a LAN network standard that is token Bus which is also known as 802.4.

The standard 802.4(Token Bus) describes a LAN which is known as a token bus. Physically, the token bus is a linear or tree-shaped cable onto that station that is attached.

Logically, stations are organized into a right with each station knowing the address of the station to its right and left. if the logical ring is initialized, then the highest-numbered station may transmit the first frame.

After it is done, it passes permission to its closest neighbor by transmitting the neighbor a special control frame known as a token.

The token propagates around the logical ring, with the only token holder being allowed to send frames. Collision does not occur because only one station at a time holds the token.

logical-ring-token-bus
Token Bus 802.4

The important thing to realize is that the physical order in which the stations are connected to the cable is not important. Because the cable is inherently a broadcast medium, every station receives every frame, discarding those not to address it.

If a station passes the token, then it transmits a token frame specifically addressed to its logical neighbor in the ring, irrespective of the physical location of that station on the cable.

It is also important to be noted that when stations are first powered on, They will not be in the ring. Therefore, the MAC protocol has provisions for adding stations to and deleting stations from the ring.

The 75-ohm broadband coaxial cable, used for cable television, is used by the token bus for the physical layer. Both single and double cable systems are permitted with or without head-ends.

Three different analog modulation methods are allowed- phase-coherent frequency shift keying, phase continuous frequency-shift keying, and multilevel duobinary amplitude modulated phase shift keying.

speeds of 1, 5 or 10 MBPS are possible. In addition, the modulation method not only provides ways to denote 0, 1 and idle on the cable, but also three other symbols used for network control.

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