Several special Token Ring MAC frames are essential to the operation of a Token Ring network:
• LLC frames— These are frames that carry user data and carry an LLC header.
• MAC frames— These are frames that carry various types of Token Ring protocol messages.
• Active Monitor Present (AMP) frames— These are frames that the Active Monitor periodically sends out to announce that it is still doing its job of monitoring ring operations. If these messages cease, the standby monitors (any other host attached to the ring) initiate an election process to select the new active monitor.
• Ring Purge frames— These are the first frames that a newly elected active monitor will transmit onto the ring to clean out all old data. Each host that receives a Ring Purge frame resets all its timers and becomes quiet, simply repeating the bit stream it receives across the ring. When the active monitor receives back its Ring Purge frame after it has circled the ring, the active monitor removes the Ring Purge frame and initiates normal operation by transmitting a token.
• Claim Token frames— These are frames sent by a host that detects that the active monitor is not functioning properly. Claim Token frames initiate the election process for a new active monitor on the ring.
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