We Claim:
1. A transfer device comprising:
a calculation unit to calculate a first code that is a frame check sequence code of a received frame; 5 a first comparison unit to compare the first code with a second code that is a frame check sequence code stored in the received frame, and to output a first comparison result indicating a match or no match between two codes compared with each other;
10 a second comparison unit to compare the first code with a third code obtained by inverting each bit of the second code, and to output a second comparison result indicating a match or no match between two codes compared with each other;
15 an error determination unit to determine an error state of the received frame on a basis of the first comparison result and the second comparison result; and an update unit to update, if the second comparison result indicates no match, the second code with a fourth
20 code obtained by inverting each bit of the first code at a time when the received frame is transferred to a subsequent device.
2. The transfer device according to claim 1, wherein when
25 the first comparison result indicates no match and the
second comparison result indicates no match, the error determination unit determines that a fault has occurred on a transmission path between the transfer device itself and a preceding device having outputted the received frame. 30
3. The transfer device according to claim 1 or 2, wherein
when the first comparison result indicates no match and the
second comparison result indicates a match, the error
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determination unit determines that a fault has not occurred on a transmission path between the transfer device itself and a preceding device having outputted the received frame, but a fault has occurred at a previous transmission phase 5 to the preceding device.
4. The transfer device according to any one of claims 1 to 3, wherein when the transfer device comprises a plurality of input ports and output ports, the transfer 10 device comprises the calculation unit, the first comparison unit, the second comparison unit, and the error determination unit for each of the input ports, and comprises the update unit for each of the output ports.
15 5. The transfer device according to any one of claims 1 to 4, comprising:
a frame identification unit to determine whether the subsequent device is capable of using the third code; and an input-side buffer to store therein the received 20 frame in order to transfer the received frame in store-and-forward mode when the subsequent device is incapable of using the third code.
6. The transfer device according to claim 5, wherein
25 when the first comparison result indicates no match, the error determination unit outputs an error signal indicating that an error has occurred in the received frame, and
when the input-side buffer obtains the error signal
30 along with the received frame, the input-side buffer discards the received frame.
7. The transfer device according to claim 5 or 6, wherein
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when the transfer device comprises a plurality of input ports, the transfer device comprises the frame identification unit and the input-side buffer for each of the input ports. 5
8. A frame transfer method comprising:
a calculating step of, by a calculation unit, calculating a first code that is a frame check sequence code of a received frame;
10 a first comparing step of, by a first comparison unit, comparing the first code with a second code that is a frame check sequence code stored in the received frame, and outputting a first comparison result indicating a match or no match between two codes compared with each other;
15 a second comparing step of, by a second comparison unit, comparing the first code with a third code obtained by inverting each bit of the second code, and outputting a second comparison result indicating a match or no match between two codes compared with each other;
20 a determining step of, by an error determination unit, determining an error state of the received frame on a basis of the first comparison result and the second comparison result; and
an updating step of, by an update unit, updating, if
25 the second comparison result indicates no match, the second code with a fourth code obtained by inverting each bit of the first code at a time when the received frame is transferred to a subsequent device.
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