100GbE Ethernet Alliance – San Jose TEF
June 14, 2011 – San Jose, CA – The Ethernet Alliance held a technical forum on the topic of 100GbE and some of the issues on the proposed standard. The event at the Techmart in Santa Clara was well attended with a full house and some standing attendees for the full day of sessions. The current method of achieving 100Gb throughput is with 10 lanes of 10Gb connections. This configuration is becoming an issue due to the number of high speed connections needed in an HPC or large data center application. The 10 lane method is being supplanted by 4 lanes of 25Gb connections in upcoming technology standards.
One of the main issues for these high speed connections is insertion loss and cabling issues. Cable variability is such that tested and qualified 10M cable, are generally use for 3M-6M applications. Recently (April ‘11) both Molex and NSC demo’d cables and connectors that would operate for the 10M at 25Gb data rates.
The insertion loss for backplane connections is also a major issue. Standard loss is 0.92dB/inch. Tyco has create a new material that is low loss at 0.67dB/inch. A standard backplane with connectors is currently 43.6dB/meter of loss. The KR form of the specification, includes equalization for only 20db of loss. To address the real requirement,NRZ equalization with FFC (Feed Forward Compensation) is needed as it can address the 42db/M specification. This method also supports the shift in Bit Error Rate (BER) from 10 -12 to 10 -16.
To address these new connections backplane design is also changing. A new Z-Plane backplane architecture from Z-Plane Inc . This is a press fit backplane method that employs microstrip connections and minimizes stubs. The method is tested at 40Gb/s (4 lanes of 10G) and soon to be released for 100G as 4 lanes of 25Gb/s. These new architectures are essential as the current backplane methods cannot support the needs of always connected mobile.
Inphi is currently working on 10GbaseKR and extended-KR connectivity. Their solution follows the KR spec for 10Gb and has been extended to 25Gb/s using crosstalk cancellation techniques. Broadcom is following a similar path, but is focusing on using a receiver with 4 level PAM in current technology CMOS to achieve 25.78Gb/s connections on a path to single channel 40Gb. The 25.78G channels can be dualed and quaded in a single die to achieve a 4 lane wide 100G device in the future.
All of these formats include power down as part of the EEE compliance, and focus on the SERDES / channel / control logic being at the higher data rates but the same or lower power budget than the prior generation device. There is an updated specification coming from the Optical Interconnect Forum (OIF) Common Electrical I/O (CEI) group for 100G in late 2011 that is version 3.0. An interim working document on the 28G specification is available from the Ethernet Alliance at CEI-28G_rev8
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