Unified PMD vs. Unified PHY
I was intending to ask you why you did not ask about unified PMDs
separate from a unified PHY as part of your survey but did not get a
chance. At the 10GEA technical meeting you were very adamant about
getting consensus for a small set of PMDs. I agree that having a small
group of PMDs is preferable. Having a unified PHY in order to have a
small set of PMDs may not be preferable.
The cost of the unified PHY, as presented, so far has been very high in
the form of lost transfer rate. As it is, the unified PHY, as
presented, does not meet the objective to have a 10.000 Gigabit MAC
data transfer rate (Gb-Mtr). Separate PHYs, LAN and WAN do meet the
objectives. Additionally, one of the scramble encoded WAN PHY
presentations was able to achieve an average 10.000 Gb-Mtr transfer rate
by using IPG compression, which can be inferred to meet the 10.000
Gb-Mtr objective in addition to the 9.548 Gb-Mtr objective.
A unified PMD set can support the block encoded LAN PHY and the scramble
encoded WAN PHY, allowing both to meet the 10.000 Gb-Mtr objective.
This will allow the PMD people to concentrate on the technologies of the
PMDs with the consideration of a signaling range to support both PHYs.
It will also simplify the marketing of 10GbE by reducing the confusion
about distances and fiber types.
As was demonstrated in some of the previous presentations (SUPI and OIF
SERDES), it is possible to have unified PMDs without having a unified
PHY. If the question had been asked, would it have made a difference to
separate the issues? If they are separate issues, as a I believe they
are, then should the survey be redone with that segregation? Would this
have put less pressure on group to have a unified PHY and changed the
scaling of the responses?