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Looking at this issue, there seems to be a need for 3 things:
1) to provide a MAC data rate of 10 Gb/s to make this an easier sell into the existing Ethernet marketplace and to simplify uplinks for existing Ethernet products
2) to provide a low cost LAN solution (part of the PAR and 5 criteria)
3) to provide a WAN solution using the OC-192 installed base
The problem, as everyone is probably well aware of, is the difference in data rates between 10 Gb/s MAC/PHY combinations for the LAN, and the OC-192 data rate of 9.58464 Gb/s. To resolve this data rate matching issue, I believe their are 3 possible solutions:
1) Use a local 802.3x flow control between the WAN PHY and the MAC. The advantage is that there is an existing standard to perform this operation. The disadvantage is that there would need to be a mechanism to distinguish between local and remote flow control messages.
2) Use deference with the indication of CRS/HOLD signal. The advantage is that it would operate as a local flow control. The disadvantage is that there would be an impact on the standard to add this capability and there may be an issue with backwards compatibility, especially if a 1/10 Gb/s MAC is designed.
3) Use of PHY management registers and management layer. This solution would require the management layer to read the PHY management registers (probably register 15) prior to data transmission to determine what the data rate is for the PHY. The management layer would indicate the PHY's data rate to the MAC, which would then alter its IPG to compensate. The advantage is that this is a relative simple change to the MAC. The disadvantage is that this depends on a management layer.
Those are my thoughts. Comments, thoughts? Any other solution that could be implemented?
Thanks,
Brad
Brad Booth
bbooth@xxxxxxxxxx