Re: SONET ring questions

[Sean Donelan <SEAN () SDG DRA COM>]

pete () cobra BRass COM (Peter Polasek) writes:
> 1) Bell Atlantic assures us that, because of the redundancy, we can
>   expect 100% uptime from the OC-12.  I would like feedback as to 
>   whether this is a realistic portrayal of the SONET environment.

100% uptime meaning Bell Atlantic will pay you some small token amount
when it fails? or 100% uptime meaning it will never fail?  Figure out
how much Bell Atlantic will pay you, and compute your risk factor.  However,
you are getting into the insanity region of availability vs. disaster
planning, category 5 hurricane, regional firestorm, sabotage or
terroist attack, etc.  Yes, all have happened, and will happen again.
But paying a bigger insurance premium may be cheaper for these extremes.

Even a perfectly functioning SONET ring will have some delay as the
APS switches to the protect circuit.  So make sure your application
can tolerate whatever the maximum switching delay.  Most carriers
consider SONET outages of less than 60ms 'normal' and an overall
SONET end-user restoral of 2 seconds 'acceptable.'

SONET also has its own set of hardware failures (e.g. APS controller
failure), user errors (e.g. improper provisioning, improper maintenance),
and the dreaded multiple failure modes (e.g. a fiber cut during a
Forced Switched, double Forced Switches in the same ring at the same
time, and other types of ring partitions), and software/firmware bugs.
Humans are always a single point of failure in any system.

In the last carrier summary report I saw the number of SONET failures
was very small, but was greater than zero.  The number of carriers
reporting was also small, making any statistical relevance of the
numbers virtually nill.  On average less than 5.5 SONET outages a
year were reported across 7 carriers.

> 2) We have the option of using either single-mode or multi-mode fiber 
>   OC-3 connections - what factors should be considered in selecting
>   the fiber media type.

Distance and equipment.

> 3) Which routers should be used.  The options are 3com NB-II's DPE+
>   (dual CPU), Cisco 7200 series, or Cisco 7500 (each router will 
>   have at least two 100Base-T LAN ports).  OK, I know the 3com 
>   suggestion is a loaded question for this list, but has anybody
>   used the 3com's in this capacity?  We are a 3com shop that is 
>   considering switching to Cisco - this is a significant decision 
>   because switching will require us to continue to maintain the 
>   existing 3com environment (~500 routers) and the new Cisco 
>   routers.

3com is more likely to jump when when a customer with 500 3com routers
has a problem than cisco will jump for someone with only a couple of
cisco routers.  Assuming cisco will even agree to sell their favored
products to anyone without their seal of approval.  And you already
know the capabilities and operation of 3com.

On the other hand, cisco's SONET products have had the extensive
testing and feedback from a number of noted luminaries/customers
who haven't been shy about encourging cisco to rectify any apparent
shortcomings.  So you won't be the leading edge trailblazing customer.
And since its a good bet Bell Atlantic will blame any problems you
encounter on your CPE equipment, using the CPE equipment which Bell
Atlantic 'related subsidaries' resells may cut short at least one round
of finger-pointing.
-- 
Sean Donelan, Data Research Associates, Inc, St. Louis, MO
  Affiliation given for identification not representation