Are Virtex-II Pro RocketIO transceivers fully Gigabit Ethernet Compliant?
Virtex-II Pro RocketIO transceivers are electrically compliant with 1000-Base-SX and 1000-Base-LX Gigabit Ethernet standards.
Virtex-II Pro RocketIO can be used for the 1000-Base-T Gigabit Ethernet Standard as an SGMII interface to an external PHY that is compliant with the 1000-Base-T specification.
1000-Base-T uses PAM5 signaling; whereas 1000-Base-SX, and 1000-Base-LX use NRZ signaling.
Virtex-II Pro RocketIO transceivers are compliant with all Gigabit Ethernet standards except latency.
The CRC and the elastic buffer (used to handle channel bonding and large frame sizes) cause an additional delay that makes it impossible to meet the latency specification (even if CRC is not used).
The CRC and channel bonding were never meant to be in the Physical Layer, so the specification does not take them into account.
The latency specification is related to the Pause function of Gigabit Ethernet. "Pause" is an optional feature that instructs the other side to stop sending for a desired multiple of 512 ns.
A latency miss will cause less than one 512 ns unit of difference in the response to a Pause command. Most systems will not even notice the extra latency.
In addition, jumbo frames can still be sent without modification of the core.