Consider again the case shown in Requirement for the Receive Elastic Buffer with the following exception; assume that the clock sources used are both 50 ppm. Now the maximum frequency difference between the two devices is 100 ppm. It can be shown that this translates into a full clock period difference every 10000 clock periods, resulting in a requirement for 16 FIFO entries above and below the half-full point. This provides reliable operation with the device-specific transceiver receive elastic buffers. Again, however, check the PHY data sheet to ensure that the PHY device sources the receiver SGMII stream synchronously to its reference oscillator.