[LINK] VDSL/FTTN alternative to NBN-GPON - variation in temperature and reliability

[Robin Whittle]

Further to what I wrote in the thread: "No batteries required in new
broadband plan", placing a lot of electronics (VDSL transceivers, 10GBps
or greater WDM (Wavelength Division Multiplexing) fibre optoelectronics
and switches between them) in street cabinets, with backup batteries, is
a really bad idea.

In addition to being bulky, flood-prone and subject to being hit by
cars, the cabinets and their electronic equipment will be subject to
daily temperature cycling and being frequently extremely hot due to high
atmospheric temperatures and the impact of the Sun on the cabinet.  To
have refrigerated cooling systems in these boxes would make them
extremely expensive in terms of power, and would make them even noisier
than if they were cooled by ambient air with fans.

A quick look at:

  "Temperature Management in Data Centres: Why Some (Might) Like it
   Hot"  Nosayba El-Sayed, Ioan Stefanovici, George Amvrosiadis, Andy
   Hwang, Bianca Schroeder

   ACM special interest group for the computer systems performance
   evaluation (SIGMETRICS/Performance) 2012

   http://www.cs.toronto.edu/~nosayba/temperature_cam.pdf

indicates that temperature cycling is a problem, at least for disk
drives in large data centres, where the ambient air is often cooled to
the low 20s, and where I assume that humidity would be carefully
controlled too.  (There would be no disk drives in an FTTN node.)

  Observation 2: The variability in temperature tends to
  have a more pronounced and consistent effect on latent sector
  error rates than mere average temperature.

These are variations within a large data centre - not the more extreme
variations, every day, which would occur in a street cabinet.

Electronic devices are now full of ball-grid array packages, where the
balls are tin-based solder, which is more brittle than ordinary tin-lead
solder.  BGA solder joints can't be visually inspected or repaired in
any reasonable manner.

  http://www.google.com/search?q=%22ball+grid+array%22&tbm=isch

BGA devices themselves typically get hot due to their own power
dissipation.  Other electronic devices such as regulators and power
transistors dissipate more heat, and while they don't use BGA solder
joints, they still use (typically, though not necessarily in Australia)
lead-free tin-based solder which is more subject to fracture than
lead-based solder.

High temperatures, uncontrolled humidity variations, temperature cycling
will all contribute to failures, including intermittent faults.  The
cabinets might work OK for a few years, but who wants to have their
Internet and phone services dependent on 10 or 15 year old electronics
sitting out in a street cabinet?  Dust, insects, plant material etc.
might also be problems.

  - Robin