A switching system includes a plurality of line cards and a switch card. The line card or cards notifies the switch card about whether or not the line card or cards is in the FDB learning enabled state. The switch card includes a learning information storage unit that holds in store the FDB learning information received from the multiple line cards and an FDB learning arbitration unit that, when all of the line cards are in an FDB learning enabled state, selects and sends the FDB learning information, stored in the learning information storage unit, to the respective line cards, based on a notification from each of the line cards.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A switching system, comprising: a plurality of line cards each including an FDB (forwarding database), an FDB search unit and an FDB learning unit; the FDB search unit searching the FDB for an entry matched to a frame received to make a decision on whether or not FDB learning is necessary; the FDB search unit sending FDB learning information to a switch card in case the decision is made that FDB learning is necessary; the FDB learning unit registering the FDB learning information received from the switch card in the FDB; the line card(s) notifying the switch card about whether or not the line card(s) is in the FDB learning enabled state; and the switch card; the switch card including a learning information storage unit that holds in store the FDB learning information received from the plurality of the line cards, and an FDB learning arbitration unit; the FDB learning arbitration unit selectively sending the FDB learning information stored in the learning information storage unit to the line cards if, based on a notification from each of the line cards, the total of the line cards are in the FDB learning enabled state. 2. The switching system according to claim 1, wherein, as long as the FDB learning information is being written in the FDB(s), the line card(s) notifies the switch card that the line card(s) is not in the FDB learning enabled state. 3. The switching system according to claim 1, wherein, the line card(s) notifies whether or not it in an FDB learning enabled state depending on whether or not a numerical value representing a load state of the own device has exceeded a preset threshold value. 4. The switching system according to claim 1, wherein, the line card(s) includes a frame processing unit that causes the information being sent to the switch card to be stored in a preset frame; and wherein, the switch card takes out the FDB learning information from the frame based on a flag contained in the frame; the switch card registering the FDB learning information thus taken out in the learning information storage unit. 5. The switching system according to claim 4, wherein, the frame received and the FDB learning information are sent on the same physical line using the preset frame. 6. The switching system according to claim 1, wherein, the switch card commences sending the FDB learning information to the switch card based on a logical sum or a logical product of signals received from each line card; the signals indicating whether or not each line card is in an FDB learning enabled state. 7. A line card(s), connected to a switch card; the switch card including a learning information storage unit that holds in store FDB learning information received from the line card(s) and an FDB learning arbitration unit that sends the FDR learning information stored to the line card(s) if, based on a notification from each of the line cards, the total of the line cards are in the FDB learning enabled state; the line card(s) including: an FDB search unit that searches an FDB (forwarding database) for an entry matched to a frame received to make a decision on whether or not FDB learning is necessary; the FDB search unit sending the FDB learning information to the switch card in case the decision is made that FDB learning is necessary; and an FDB learning unit that registers the FDB learning information received from the switch card in the FDB; the line card(s) notifying the switch card about whether or not the line card(s) is in the FDB learning enabled state. 8. A switch card, comprising: a learning information storage unit that holds in store FDB (forwarding database) learning information received from a plurality of line cards and an FDB learning arbitration unit; the FDB learning arbitration unit sending the FDB learning information stored to each of the line cards if, based on a notification from each of the line cards, the total of the line cards are in the FDB learning enabled state. 9. A method for learning FDB information comprising: a line card(s) connected to a switch card; the switch card including a learning information storage unit that holds in store FDB learning information received from the line card(s) and an FDB learning arbitration unit; the FDB learning arbitration unit sending the FDB learning information stored to each of the line cards if, based on a notification from each of the line cards, the total of the line cards are in the FDB learning enabled state; searching an FDB (forwarding database) for an entry matched to a frame received to make a decision on whether or not FDB learning is necessary; sending the FDB learning information to the switch card in case the decision is time that FDB learning is necessary; and registering the FDB learning information received from the switch card in the FDB when the total of the line cards are in the FDB learning enabled state. 10. A method for arbitrating FDB learning, comprising: a switch card connected to a plurality of line cards each including an FDB search unit and an FDB learning unit; the FDB search unit searching FDB (forwarding database) for an entry matched to a frame received to make a decision on whether or not FDB learning is necessary; the FDB search unit sending FDB learning information to the switch card in case the decision is made that FDB learning is necessary; the FDB learning unit registering the FDB learning information received from the switch card in the FDB; the line card(s) notifying the switch card about whether or not the line card(s) is in the FDB learning enabled state; storing the FDB learning information received from the line card(s); and sending the FDB learning information stored to each of the line cards if, based on a notification from each of the line cards, the total of the line cards are in the FDB learning enabled state. 11. The switching system according to claim 2, wherein, the line card(s) notifies whether or not it is in an FDB learning enabled state depending on whether or not a numerical value representing a load state of the own device has exceeded a preset threshold value. 12. The switching system according to claim 2, wherein, the line card(s) includes a frame processing unit that causes the information being sent to the switch card to be stored in a preset frame; and wherein, the switch card takes out the FDB learning information from the frame based on a flag contained in the frame; the switch card registering the FDB learning information thus taken out in the learning information storage unit. 13. The switching system according to claim 3, wherein, the line card(s) includes a frame processing unit that causes the information being sent to the switch card to be stored in a preset frame; and wherein, the switch card takes out the FDB learning information from the frame based on a flag contained in the frame; the switch card registering the FDB learning information thus taken out in the learning information storage unit. 14. The switching system according to claim 12, wherein, the frame received and the FDB learning information are sent on the same physical line using the preset frame. 15. The switching system according to claim 13, wherein, the frame received and the FDB learning information are sent on the same physical line using the preset frame. 16. The switching system according to claim 2, wherein, the switch card commences sending the FDB learning information to the switch card based on a logical sum or a logical product of signals received from each line card; the signals indicating whether or not each line card is in an FDB learning enabled state. 17. The switching system according to claim 3, wherein, the switch card commences sending the FDB learning information to the switch card based on a logical sum or a logical product of signals received from each line card; the signals indicating whether or not each line card is in an FDB leaning enabled state. 18. The switching system according to claim 4, wherein, the switch card commences sending the FDB learning information to the switch card based on a logical sum or a logical product of signals received from each line card; the signals indicating whether or not each line card is in an FDB learning enabled state. 19. The switching system according to claim 5, wherein, the switch card commences sending the FDB learning information to the switch card based on a logical sum or a logical product of signals received from each line card; the signals indicating whether or not each line card is in an FDB learning enabled state.