Monday, March 1, 2010

Non-Blocking Colorless/Directionless Architecture - The Future of Optical Networking

In our last blog, we discussed the options that carriers are considering to enhance the flexibility and reliability of their optical infrastructures.  These architectural improvements are based on the foundation laid by ROADMs, and are designed to extend existing ROADM benefits of maximizing network resources while reducing operating and capital costs, to new levels. 

Again, the definitions of the three options for optical architectures are:

  • Colorless - any color wavelength on a single fiber can connect to any add/drop transponder associated with that fiber.

  • Partial Colorless/Directionless - a compromise architecture with some level of blocking such that not all waves on all fibers can connect to all transponders.
  • Colorless/Directionless/Non-Blocking - extends the concept to any color wavelength on any fiber from any direction  - all can be connected to any add/drop transponder.

A quick comparison of the features of these architectures is illustrated in the table below.

 By choosing a Colorless/Directionless/Non-Blocking architecture, carriers will increase network flexibility and agility - allowing them to offer new services while increasing network reliability, efficiency, and utilization.  Additionally, this architecture will significantly reduce operational costs - adding the ability to perform "low touch" maintenance (see our blogs of February 15 and 16 for more information) and layer one automatic protection switching as well.

However, this architecture is only realizable using an optical switch component (like those from Polatis) that includes key capabilities  - such as low loss and low power consumption - that allow it to integrate easily and without impact to the existing infrastructure.  In our next blog, we'll detail how Polatis can help make Colorless/Directionless/Non-Blocking architures a reality - today.

Thursday, February 25, 2010

Colorless Wavelength Switching - Is It Enough?

Service providers have traditionally used ROADMs (Reconfigurable Add-Drop Multiplexer) for colorless wavelength switching. ROADM's allow optical network operators to switch any color wavelength on a single fiber to connect to any add-drop transponder that is associated with that fiber.  Using Wavelength Selective Switches (WSS's) some service providers have added directionless capabilities.  However the complexities of implementation, provisioning, management and maintenance have severely limited this architecture. 

Ever increasing bandwidth demand (at a lower cost per bit), more stringent customer demand for network services that are reconfigurable and even more reliable, and continuing operational cost pressures are forcing service providers to seek even more flexibility, servicablity and reliability from their optical infrastructures.  As a result, they are continuing to pursue new ways to make their networks more efficient and cost effective.

At this juncture, service providers are looking a three possible architectures. 

  1. Colorless (Status Quo)- any color wavelength on a single fiber can connect to any add/drop transponder associated with that fiber. 
  2. Partial Colorless/Directionless - a compromise architecture with some level of blocking such that not all of the waves on all of the fibers can always connect to all transponders. A cost reduction only solution.
  3. Colorless/Directionless/Non-Blocking - extends the concept to any color wavelength on any fiber from any direction. All can be connected to any add/drop transponder, with no blocking.
Each approach has its strengths and weaknesses.  In our next blog, we'll review the plusses and minuses of each approach, and why we believe that Colorless/Directionless/Non-Blocking is the ultimate goal. 

Monday, February 22, 2010

Working in the Dark

Many optical switch systems require light on a fiber in order to maintain a connection.  The optical power is required to provide the feedback for position control.  There are several operational disadvantages in using this method.  For example:

  • Fiber connections cannot be pre-provisioned.  The need for optical power monitoring means that unlit fibers cannot be connected.  This is a severe limitation in protection switching and planned maintenance operations where fiber paths may need to be set up in advance of carrying traffic.
  • Transient signals are not readily handled.  In remote fiber test applications, OTDRs (Optical Time-Domain Reflectometers) are vital characterization tools.  For successful operation, the ability to hold a connection while - i) optical power radily varies and ii) the fiber path is unlit; is essential for any optical switch used to enable fiber test access.
  • Bidirectional signals are not fully supported.  Optical power monitoring is direction sensitive and consequently so is signal transmission through the switch.  Bidirectional operation is a prerequisite for many applications - including break location using OTDRs.
In contrast, the Polatis Direct BeamSteering (TM) method uses collimator position sensing to maintain fiber to fiber connections.  There is no requirement for optical power to be monitored or indeed for light to be present at all.  Consequently, this technology produces a true dark fiber switch, capable of handling bidirectional and transient signals.  Polatis optical switches are therefore ideal for protection switching planned maintenance and remote fiber test access applications.

Sunday, February 21, 2010

Is Now the Right Time to Integrate O-O-O Switching Into Your Hosting Centers and Peering Sites?

According to the Yankee Group, server and storage virtualization have already helped more than 75 percent of all corporations to improve utilization of their systems from an average of approximately 20 percent to more than 40 percent.  However, server and storage virtualization and cloud computing gains will not be realized without a network infrastructure prepared to meet the demands of faster processors and more robust virtualization and cloud computing systems.

Larry Smar of UCSD predicts that network bandwidth is growing by an order of magnitude every 5 years and states, "Grid-intensive applications will require an international distributed cyber infrastructure based on petascale computing, exabyte storage, and terabit networks."  This growth is faster than the well known Moore's Law which states the number of transistors that can be placed inexpensively on an integrated circuit doubles approximately every two years.   And Infonetics reports that the 10, 40 and 100 Gbps markets are expected to total a cumulative $105 billion US between 2008 and 2013.

This all points to new network architectures in the data center and peering sites that deliver increased speed and reliability, while decreasing management complexity, and power and space requirements.  New architectures are required that use copper and O-E-O technologies as transition points to legacy systems and where Layer 2 and Layer 3 traffic management features are required - and O-O-O Layer 1 switching where speed, reliability, and super fast network recovery are required for connections between server and storage racks and between the data center/peering site and service provider WAN.

O-O-O Layer 1 switching is protocol and bit rate independent and can therefore seamlessly transition from 10G to 40G and 100G speeds today, without requiring a forklift switch upgrade layer.  Polatis O-O-O switches support dark fiber switching, which allows the pre-provisioning of M:N sparing of protection fibers, should a failure occur on the primary fiber.

Polatis O-O-O switches are compact, consume less than 1 watt per fiber, are simple to install, operate, and maintain, and help improve the bottom line for any data center green metric.  This results in a significant savings when compared to copper and/or O-E-O based solutions.

And, Polatis switches are cost competitive with today's O-E-O switches.

Common applications for O-O-O switches in the data hosting center and peering sites include automatic protection switching, enhanced network monitoring and management, intelligent fiber distribution, and colorless/directionless wavelength switching.

Isn't it time for you to consider including O-O-O switching at your hosting and peering sites?

Saturday, February 20, 2010

Protection Switching at the Physical Layer - Fast and Resilient

Automatic protection switching at the physical layer can greatly improve network resilience.  There are a number of small switches available, mainly based on PLC (Planar Lightwave Circuit) technology, which can handle simple "one for one" sparing of fibers or even 1:N protection.  However, the power of an optical matrix switch is the ability to enable rapid physical layer N for M protection switching.  In this concept, a pool of fibers can be shared between diverse routes and allocated automatically in response to a fiber path failure, as shown below.


The Polatis switch is ideal for this application because its low loss enables diverse routing through multiple nodes.  Integrated power monitors enable the system to automatically respond to loss of light without reference to a higher level control plane.  The Polatis technology does not require light on a fiber in order to hold a connection, so dark fiber routes can be pre-provisioned.  Combining this pre-provisioning capability with Polatis fast switching time enables the Polatis system to reconfigure a complete fiber network in approximately 20ms.

Wednesday, February 17, 2010

"...The mirror cracked from side to side....."

In defense applications that require the speed, security, and capacity native to optical switching, 3D MEMS technology that uses mirror and fixed collimator beams, just isn't good enough.  
Switches using 3D MEMS are fragile.  There is the potential for the "mirrors to crack from side to side" (with apologies to Alfred, Lord Tennyson).  In defense applications, a cracked, distorted or marred mirror could result in degraded performance or switch failure.  But reliability isn't the only reason that 3D MEMS aren't the best solution for defense applications.  They also:

  • Have relatively high insertion loss - from 2.5dB to 4dB
  • Require light to make connections
  • Support single mode fiber only
  • Require integrated optical power meters
  • Modulate power during switching
  • Have relatively high return loss - from 30 to 35dB.
For defense systems that are often deployed in environmentally and maintenance unfriendly environments but must still deliver very high performance, 3D MEMS don't measure up.

A better solution for defense applications requiring reliable, stable, fast, and ultra-low loss optical switching is available in Polatis DirectLight (TM) technology.  Polatis steers light using piezoelectric actuators (not mirror arrays) to direct light paths.  As a result, Polatis switches can not only stand up to the toughest physical environments, they also:

  • Have very low insertion loss - 0.4dB typical, 1.0dB max
  • Use integral position sensors
    • Control is independent of the light level
    • Switch dark fiber in <10ms
    • Are fully transparent and bi-directional
  • Have no unwanted signal modulation
  • Support both single mode and multimode fiber
  • Support optical power monitors - but don't need them
  • Have low return loss - 55 dB
  • Consume very little power.
For defense applications that require the most reliable, best and most flexible optical switch - even under the most difficult physical environments - Polatis' DirectLight (TM) beam steering technology is the answer. 

Want to learn more?  Contact us at:

Tuesday, February 16, 2010

"Low Touch" Optical Network Maintenance and the End of Downtime

Performing maintenance on optical network infrastructure doesn't need hours of planning, re-routing of traffic, customer notifications, and "touching" transmission equipment (transponders, ROADMs, OTN terminals, SONET ADMs).  Using compact, low cost Polatis 1000 series optical switches, network operators can simplify maintenance processes, make them faster and more efficient, and safer for maintenance personnel.  The result is a reduction in network downtime and operational costs, and an improvement in network and human resource utilization.  Here's how we can help you do it.

Small form factor Polatis 1000 series switches are inserted at the end point of each fiber span (after Raman amplifiers).  The switches are connected to primary and secondary spare fibers which can be "lit" or "dark".  When the primary fibers require maintenance, network operators can simply switch to the secondary or spare fiber using Polatis' easy to use graphic user interface (GUI) over the supervisory channel of most DWDM equipment.  Or the switch can happen automatically (Automatic Protection Switching - APS), when the Polatis optical switch senses a loss of light on the fiber.  Loss of light, and an APS event, triggers an SNMP alarm to operations personnel.  However, transmission equipment sees, in most cases, only a low power alarm that clears after the switching event is complete (<20msec). 

Polatis has performed extensive testing that has demonstrated:
  • Switching to spare or secondary fibers using the Polatis switch does not cause amplifiers of any type (pre-, booster, amplifier, Raman amplifier) to shut down nor trigger other service effecting events in transmission equipment.
  • The switches inject <1dB loss.
  • Switches can support very high optical power - >30dBm.
  • Protection switching that supports "dark" or "unlit" fiber.
Using Polatis optical switches, network operators can now simply automatically, or manually, switch to a spare fiber whenever maintenance needs to be performed on a fiber span.  Maintenance events are isolated to each unique span, and no longer impact network transmission equipment and other routes in the optical infrastructure.  Additionally, the operational complexity of maintenance events is reduced and maintenance personnel are shielded from potentially harmful exposure to high power lasers.

The bottom line for network operators - using Polatis Series 1000 optical switches, network maintenance can be fast, efficient, and safe.  Our "low touch" approach means the end of downtime for maintenance and an better use of valuable network and human resources.

Interested in learning more about how Polatis can make maintenance a "low touch" operation in your network?  Contact us at: