Understanding Skew in 100GBASE-R4 applications

Tim Warland, AppliedMicro
EETimes (12/14/2011 3:35 PM EST)

The 100GBASE-R4 physical layer device converts 10-lanes running 10Gbps (CAUI) to 4-lanes running 25Gbps. The conversion process is data agnostic with no provision for rate adaptation, consequently skew management is an integral part of end-to-end system performance.

Recently ratified, the 100Gigabit Ethernet Standard, (IEEE802.3ba) defines a 100GBASE-LR4 and 100GBASE-ER4 interface for optical interfaces on single-mode fiber. The architecture includes the Physical Coding sub layer (PCS), connected on one side to the reconciliation sub-layer (RS) and MAC and to the PMA/PMD on the other side. Actually implementations are more likely to combine the PCS and PMA with the RS and MAC and interface to a second PMA and PMD (referred to as the PHY)

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