Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

Why wrong LINE rate could cost dear

Why wrong LINE rate could cost dear

1.	Cost JUMPS as bit rate goes up.
Faster IC technologies, more heat, possibly substantial extra complexity
around the optoelectronics.

Lasers don't follow Moore's Law.
Unlike transistors, there is no virtuous circle of smaller -> faster and
cheaper -> better.  The guts of a laser are sized for the wavelength. 
Laser speed has increased slowly and unevenly, but until now, they were
fast enough (for 2.5 Gbit/s line rate).  Optical modulator type
transmitters as used in OC-192 are very expensive.

Picking a line rate that's faster than the state of the art will delay
product availability and cause extra costs into the future (25% to 150%
more? make your own guess).

2.	Standards are good.
Line clock ICs take time and money to design.  Other parts
(multiplexers, receivers, whatever) may be in the market now for ~9.95
Gbit/s, a very few at OC-192+FEC rates, none for 12.5 Gbit/s.  Analog
parts are rarely right first time, respins add to the delays...

Picking a non-standard line rate could cause delay and further fragment
the market for parts which we believe are currently too expensive but
where volumes are driving costs down.

So, I believe that raising the line rate of optical transmitters
four-fold is a worthwhile achievement, and then we attach ourselves to
the nearest standard, the OC-192 line rate of 9.95328 Gbit/s.  Raising
the line rate of optical transmitters five-fold, out ahead of the state
of a slow-moving art and away from any standard, will cost money and
delay and needs very good justification.  There's an obvious direct hit
on link length too (dispersion limited) but what I'm talking about is
more severe than that.

Can we get back the difference between what's desired and what's
affordable by looking at line codes, interframe gap or what?  Maybe
settle for 95% of what we would like and get a good-enough job done on
time and affordably?

"Keep it simple, follow standards, keep it cheap."

Piers Dawe
	Phone	+44 (0)1473 465654 or Telnet (31)25654
	Fax	+44 (0)1473 464965
	Hewlett-Packard Ltd   White House Road   Ipswich
	Suffolk   England   IP1 5PB