PAM-5 4-WDM deskewing
At the end of my presentation in Albuquerque,
over Multimode Fiber for 10 GbE"
one of the members in the audience asked me
about how we manage the deskewing since the
group velocities of the four streams of data
are different for different wavelengths.
PAM-5 4-WDM at 1.25 Gbaud manages the deskewing
in exactly the same way as its sister proposal
8b/10b 4-WDM at 3.125 Gbaud.
In fact, PAM-5 4-WDM at 1.25 Gbaud shares a lot
of common with 8b/10b 4-WDM at 3.125 Gbaud,
because both are 4-WDM systems.
Hence, encoding, serializing, deserializing
and decoding of both systems is done exactly in
the same way, as described in the presentation:
"10Gig MII update"
by Howard Frazier
Kauai, Nov 99
the only differences being:
1) one uses the 1000BASE-X PCS (8b/10b)
and the other uses the 1000BASE-T PCS
(scrambling, convolutional and PAM-5 encoding).
2) one uses a SERDES at 3.125 GHz and the
other uses a SERDES at 1.25 GHz
3) one uses a baud rate of 3.125 Gbaud
in the fiber and the other uses a baud rate
of 1.25 Gbaud in the fiber.
4) one uses the K-R characters of the 8b/10b
to perform byte synchronization at the receiver
and the other uses the IDLE properties of the
1000BASE-T PCS to do the same task.
Deskewing in PAM-5 4-WDM is handled in exactly
the same way as deskewing in 8b/10b 4-WDM,
by realigning the octets of data of the four lanes
after decoding in the receiver, using the
low frequency 312.5 MHz clock.
Also Open Fiber Control is dealt identically
in both systems, since both are 4-WDM.
Jaime E. Kardontchik
San Jose, CA 95131