Token Passing - Token Ring (IEEE 802.5)

• Needs that station take turns sending data
• Token passing coordinates process
• Token is a especially formatted three-byte frame that circulates station wishing to transmit must first have possession
• Token passes from NIC to NIC in sequence if station has data to send and station takes token and sends data frame if not passes to neighbour
• Every station receives the frame one by one and examines the destination address
• If it matches frame is copied station checks the frame for errors changes bits to indicate the frame was received and copied
• Packet continues around the ring also is passed back to originating station
• Once the sender receives the frame in addition to recognizes its address in the sender field it examines the address-recognized bits
• If they are set it recognizes the frame was received and copied
• Sender subsequently discards the frame and releases the token back to the ring