| 单词 | Figure T-4 |
| 释义 | Figure T-4 If a station has no data to transmit, it passes the token to the next station on the ring, perhaps after holding it for a brief period of time established and limited by the master control station. If a station has data to transmit, and its priority level meets or exceeds the priority level established in the Access Control field, it seizes the token and changes one bit of the Start Delimiter field to a start-of-frame sequence, fills out the balance of the frame control fields, inserts the payload into the data field, and transmits the frame to the next station on the ring. A Token Ring command/data frame is formatted as follows: • Start Delimiter (SD): A field of one octet that denotes the beginning of the token.The bit pattern JK0JK000 intentionally violates the Manchester coding scheme used elsewhere in the frame, thereby firmly establishing its identity. ( Note: J indicates the intentional violation of a 1 bit, and K indicates the intentional violation of a 0 bit.) • Access Control (AC): A field of one octet in the bit sequence PPPTMRRR.The P bits are Priority bits.The T bit is a Token bit that, when set at a 1 value, indicates that the frame is a token frame rather than a data or command frame. The M bit is a Monitor bit set by the active monitor (AM) 74570c20.qxd 9/12/07 12:44 AM Page 492 |
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