Hello:
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.
Regards,
Srihari Varada
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
circuit.
- 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
circuit.
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
> >
+----------STM1----------+
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
===== ======
> >
+----------STM1----------+
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
SDH.
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.
Actually, most of the largest holders of fiber in the U.S. have started to
offer unprotected SONET (and Lambda) service. Apparently, a few months ago
OC-48 and OC-192 speed Unprotected Wavelength services caught on like
wildfire, and customers started clamoring for lower speed Unprotected SONET
service.
I know of at least six of the biggest carriers here who offer it at OC-12,
and every one willing to guarantee a particular path - you just have to work
path diversity into your design. Some may even offer OC-3, though I haven't
checked that.
I can say that the price point on Unprotected SONET services is great - if
you're building redundancy into your physical topology anyway, you may not
need APS. The savings can be huge.
Likewise, I agree that there can be great cost savings for "Preemptable"
service, though I wouldn't use it for a mission-critical network. I only
know offhand of one major U.S. carrier who offers this, but I'm sure others
do, or will - it just makes sense. There are plenty of services that can
stand an occasional outage.
- Jeb