4. OTN switching
4
OTN switching is more a hype than a reality. This is quite evident from the low
number of OTN switching deployments currently in the world.
Prime advantage: sub-lambda grooming at intermediate sites.
Industry trend(both suppliers and operators): Start WITHOUT OTN switching and go
for OTN switching in the future if all the lambdas run out/close to run out (aka
Wave-length blocking).
This requires that you select a vendor who's capable of OTN switching but you need
NOT purchase OTN switching components (cards) on day one.
You do NOT need OTN switching to achieve mesh protection. What is then required
is ASON/GMPLS.
(c) Anuradha Udunuwara
5. Available options
5
1. Fixed Optical Add Drop Multiplexers (FOADM)
2. Re-configurable OADM (ROADM)
3. Tunable ROADM (TROADM) (Wave-length Selective Switching (WSS)): supports Color-Less and
Direction-less)
Cost increases
4. FOADM with Automatically Switched Optical Networks (ASON)/ Generalized Multi-Protocol Label
Switching (GMPLS) control plane
5. ROADM with ASON/GMPLS control plane
6. TROADM with ASON/GMPLS control plane
7. FOADM with ASON/GMPLS control plane and OTN switching
8. ROADM with ASON/GMPLS control plane and OTN switching
9. TROADM with ASON/GMPLS control plane and OTN switching
Note: All options need to support OTN wrapper
(c) Anuradha Udunuwara
6. Good features to have on WSS system
6
Color-Less
Direction-less
Contention-less
(c) Anuradha Udunuwara
7. 3 CAPEX components
7
Cost of adding OTN switching capability vs. loosing sub-lambda grooming at
intermediate sites need to be properly analyzed based on your current and future
traffic matrix.
CAPEX I CAPEX II CAPEX III
When you have OTN switching, If you do not do sub-
When you want to the earlier Point-to-Point lambda
passed through several lambda grooming at the
do sub-lambda intermediate nodes at the optical intermediate site, you will
grooming at domain (OOO) now need to go to have to have a separate
electrical domain to do grooming
lambda at the
intermediate sites, (OEO) making it multi-segment.
This requires several OTN ports . intermediate site, though
you'll have to have However, you use only one
lambda. Some call the latter as
the traffic goes to the
OTN switching Layer 1-ASON and former as same destination.
Layer 0-ASON.
(c) Anuradha Udunuwara
8. How to select a good solution?
8
A good approach, adopted by many operators when publishing
Request For Proposal (RFP)s for Optical Transport Networks is
keeping the RFP open for all the options given above.
It's required to give the fiber characteristics, locations and the traffic
matrix (current and future). Based on these inputs the vendors can
come out with the least Total Cost of Ownership (TCO) option.
The evaluation should also be based on lowest TCO (this covers both
initial Capital Expenditure (CAPEX), future expansion CAPEX and
the running Operational Expenditure (OPEX) such as site rentals,
power etc.).
(c) Anuradha Udunuwara
9. Recommended options
9
Following options are recommended to be used as
ASON/GMPLS is better to have. This will also make sure
that the comparison is more balanced.
FOADM with ASON/GMPLS control plane
ROADM with ASON/GMPLS control plane
TROADM with ASON/GMPLS control plane
FOADM with ASON/GMPLS control plane and OTN switching
ROADM with ASON/GMPLS control plane and OTN switching
TROADM with ASON/GMPLS control plane and OTN switching
(c) Anuradha Udunuwara
10. About the Author
10
Eng. Anuradha Udunuwara is a Chartered Engineer by profession based in Sri Lanka. He has nearly a decade
industry experience in strategy, architecture, engineering, design, plan, implementation and maintenance of CSP
Networks using both packet-switched (PS) and Circuit-Switched (CS) technologies, along with legacy to NGN
migration. Eng. Anuradha is a well-known in the field of CSP industry, both locally and internationally.
Graduated from University of Peradeniya, Sri Lanka in 2001 with an honors in Electrical & Electronic Engineering,
Eng. Anuradha is a corporate member of the Institution of Engineers Sri Lanka, a professional member of British
Computer Society, a member of Institution of Electrical & Electronic Engineers, a member of Institution of
Engineering & Technology (formerly Institution of Electrical Engineers), a member of the Computer Society of Sri
Lanka, a life member of Sri Lanka Association for the Advancement of Science, senior member of the Carrier
Ethernet Forum, member of the Internet Society, member of the Internet Strategy Forum, member of the Internet
Strategy Forum Network, member of the Ethernet Academy, member of the NGN/IMS forum and member of the
Peradeniya Engineering Faculty Alumni Association. He is also an ITIL foundation certified and the only MEF-CECP in
the country.
In his spare time Anuradha enjoys spending time with his family, playing badminton, photography, reading and
travelling.
He can be reached at udunuwara@ieee.org
(c) Anuradha Udunuwara
