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Re: Utilization of the redundant ring in SONET

  • From: Glen Turner
  • Date: Tue Jul 17 23:04:26 2001

srihari varada wrote:
> I would like to know how typical it is to have the redundant ring
> in SONET used for the transport of data while still providing
> protection switching features. Also, could any one give me 
> insight into a few vendors that does it. I would appreciate,
> if some one could provide input on the above.

We looked into SDH/SONET for our Australia-US capacity
and backhaul.

The SDH/SONET products you can buy are:

 - protected SDH/SONET presented to customer on a single

 - protected SDH/SONET presented to customer on two circuits
   (called "interface protection").

 - protected SDH/SONET with both Main and Protect circuits
   presented to the customer.

 - "extra traffic channel" which is the Protect circuit of
   another customer.  Obviously when that other customer
   requires the protection, you see Alarm Indication.
   This can be viewed as being an unprotected SDH/SONET

What you can't buy is two unprotected diversely-routed
circuits.  You can simulate that by purchasing a
protected circuit with a single customer interface
and an extra traffic channel.

If your vendor has a multi-ring archiecture, you may
also be able to purchase multi-drop capacity.  For
example, our Southern Cross Network capacity is

        +-STM1--- Hawaii ---STM1-+
        |                        |
    Sydney                      Oregon
        |                        |

We then used protected (shown by ===) and extra traffic
circuits (shown by ~~~) to backhaul that three-drop ring
to the PoPs.

                      Hawaii PoP
                      =        =
              +-STM1---        ---STM1-+
              |         Hawaii         |
          ~~~~~                        ~~~~~~
Sydney PoP     Sydney            Oregon      Washington PoP
          =====                        ======
              |                        |

Other architecuters were possible, but cost more.

The backhaul providers were PowerTel (Sydney),
WCI (Oregon-Washington) and Verizon (Hawaii).
All were more than willing to meet our rather odd
backhaul requirements, although Verizon could
only offer protected capacity.  The engineering
staff were all wonderful to deal with.  We
did have issues with provisioning, and I would
encourage you to check that:

 - the round-trip time is within expectation
 - the bit error rate is low, as a high rate
   is a symptomm of configuration error
 - the protection works

We also had additional issues where international
standards vary from US practice, these mainly
lead to SONET being provisioned where we intended

We use MPLS to load share and to provide end-to-end
protection.  Note that using end-to-end protection
has significantly more delay then using SDH's native
segment protection on long undersea links.  But
the ability to load share and get 310Mbps out of
155Mbps of expensive undersea capacity swayed the
decision towards MPLS.

 Glen Turner                                 Network Engineer
 (08) 8303 3936      Australian Academic and Research Network
 The revolution will not be televised, it will be digitised

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