Multi-module switching system

1. A multi-module switching system comprising:

at least two switching modules for receiving data packets from at least one input adapter and transmitting said data packets to at least one output adapter, each of said switching modules comprising a shared buffer for buffering a portion of a data packet received from said at least one input adapter and transmitting said portion of data packet to said at least one output adapter, one of said switching modules being a master module for receiving a portion of a data packet containing a packet header and sending control information contained therein serially to each other switching module as a slave module, each slave module comprising a delay computing structure for computing a first delay needed to transmit said control information from said master module to said slave module and a first storing structure for storing said portion of data packet transmitted from said at least one input adapter to said slave module during said first delay before transmitting said portion of data packet to said shared buffer such that said portion of data packet is not received by said shared buffer before said slave module has received said control information from said master module.

2. The multi-module switching system according to claim 1 , wherein said first delay computed by said delay computing structure is converted into a data latency comprising a number of packet portion cycles corresponding to a time equal to or greater than said first delay.

3. The multi-module switching system according to claim 2 , wherein said data packets are received by said at least one input adapter or transmitted from said at least one output adapter at a speed of about 16 gigabits/second and there are 8 switching modules operating at a speed of about 2 gigabits/second.

4. The multi-module switching system according to claim 1 , further including a speed expansion bus adapted for transmitting said control information serially from said master module to said slave module.

5. The multi-module switching system according to claim 4 , wherein said delay computing structure comprises a counter resettable to zero by said master module at an initialization time and which is incremented until said structure receives a synchro bit transmitted from said master module through said speed expansion bus.

6. The multi-module switching system according to claim 5 , wherein said first storing structure is a FIFO queue in which a time interval between an operation of writing said portion of data packet and an operation of reading said portion of data packet is substantially equal to said first delay.

7. The multi-module switching system according to claim 5 , further comprising a first write pointer and a first read pointer, said first write pointer loaded at said initialization time with a value substantially equal to said first delay and adapted for controlling an operation of writing said portion of data packet into said first storing structure, said first read pointer set to zero at said initialization time and adapted for controlling an operation of reading said portion of data packet.

8. The multi-module switching system according to claim 7 , wherein said slave module further comprises a second storing structure adapted for storing a portion of a data packet transmitted from said shared buffer to said output adapter during a second delay which is substantially equal to a maximum delay minus said first delay such that respective portions of data packet transmitted by said master module and each said slave module reach said output adapter at substantially the same time.

9. The multi-module switching system according to claim 8 , wherein said maximum delay is a delay taken for said control information to be transmitted from said master module to a slave module at the end of said speed expansion bus.

10. The multi-module switching system according to claim 9 , wherein said second storing structure is a FIFO queue in which a time interval between an operation of writing said portion of said data packet and an operation of reading said portion of said data packet is substantially equal to said second delay.

11. The multi-module switching system according to claim 9 , further comprising a second write pointer and a second read pointer, said second write pointer loaded at said initialization time with a value substantially equal to said second delay and adapted for controlling an operation of writing said portion of said data packet into said second storing structure, said second read pointer set to zero at said initialization time and adapted for controlling an operation of reading said portion of said data packet.

12. The multi-module switching system according to claim 11 , wherein processing time of a portion of said data packet by said master module is greater than a timing skew occurring between links in said speed expansion bus such that transmission of said portion of said data packet by said master module does not occur before said portion of said data packet has been stored in said shared buffer of said slave module at the end of said speed expansion bus.