[CII] Advocatus Diaboli

[John Osmon]

On Tue, Dec 01, 2009 at 04:03:19PM +0000, bmanning at vacation.karoshi.com wrote:
[...] 
> 	Lets face it - at any given point in time, some parts of the Internet
> 	are not functionally working/connected  to other parts of the Internet.
> 	Its -always- partially broken.  

Yep.  Any end2end connection can be characterized as:
   - working
   - impaired
   - not working

When it is not working, there's typically a path problem.  Get more
paths, or decide that there are times the "critical" application won't
be available.  With satellite connections, you almost always have a
backup path available -- if you're willing to spend the money.

Impaired channels could have any number of problems, but most will
exhibit either limited bandwidth or high packet loss.  Two methods
of countering either can be:
  - QOS enforcement -- give "critical" traffic across the impaired link
    preferential access
  - protocol changes -- use TCP instead of UDP, or even use text instead
    of pictures on web pages to conserve packets


As Bill indicates:

> 	The critical (imho) components of this best-effort service are:
> 
> 	:: triage - who gets cut off and why
> 	:: restoration - who gets added first and why


Your best bet is multiple paths for the traffic you consider critical.
Then you have a multitude of options when problems occur.  Your options
collapse to "restoration" only when your channel fails completely.