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10 Gb to 9.58 Gb rate adjuster

Title: 10 Gb to 9.58 Gb rate adjuster

Ok, barring any math mistakes, here is the first cut of the block diagram for speed matching between 10.000 Gb/s ethernet and the 9.58 Gb/s Sonet payload data rate.

To match speeds, FIFOs are needed to absorb the rate difference. On the transmit side, the FIFO only has to be big enough to prevent underruns during a single packet transmission on to the ethernet side. 2K is too big unless we change to really jumbo frames.

On the receive side, the FIFO has to be big enough to hold incoming data while the 802.3x pause frame is sent and the link partner stops sending data. The primary variable is the propagation delay down the cable.

Assuming the speed in cable is roughly 2/3 of the speed of light in vacuum, there is approximately 50 bits per meter of cable. Therefore, once the receiver detects the FIFO has filled to an upper water mark, it sends a pause frame to the link partner. The link partner will continue to transmit while the pause frame propagates down the cable.

For a 3km cable, this time is 150,000 bits or just over 18K bytes.

Walter Thirion
Level One Communications

<<10 Gig to Sonet speed adapter.pdf>>

10 Gig to Sonet speed adapter.pdf