45. Token Ring

Introduction to Data Communications
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45o. IEEE 802.5 Frames

IEEE 802.5 Token Ring Standard has 3 frames specified:

Abort Sequence
Token
Token Frame

Abort Sequence

The Abort Sequence is used to indicate to stations on the ring that a temporary internal error has occurred. The Source NIC has discovered a soft error during transmission and is aborting the transmission. It is a broadcast frame that goes to every station on the local ring.

The Abort Sequence consists of

Start Delimiter (SD)
End Delimiter (ED)

Token

The Token, sometimes called the free token, is used for Bus Arbitration in Token Ring. Whichever station claims the Token has the right to transmit its information/data (Token Frame) on the ring. The Token consists of 24 bits:

Start Delimiter (SD)
Access Control Field (AC)
End Delimiter (ED)

It is a broadcast frame that goes to every station on the local ring.

Token Frame

The Token Frame is used for transmitting information/data on the ring. It is the only frame with Source and Destination addresses. The Token Frame consists of the following fields:

Start Delimiter (SD)
Access Control (AC)
Frame Control (FC)
Destination Address (DA)
Source Address (SA)
Information Field (INFO)
Frame Check Sequence (FCS)
End Delimiter (ED)
Frame Status (FS)

Introduction to Data Communications
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