Advanced optical diagnostics: Relieving the opex burden

By KARL TOOMPUU, Ceyba Inc.--The new optical core requires unique diagnostic capabilities that are embedded within the network itself and remotely accessible to ensure that significantly lower capital expenditures of next-generation core networks are not eroded by an increased opex burden.

Th 118702
Th 118702

The new optical core requires unique diagnostic capabilities that are embedded within the network itself and remotely accessible to ensure that significantly lower capital expenditures of next-generation core networks are not eroded by an increased opex burden.

Ceyba Inc.

Not surprisingly, several trends in optical network management are driven by the current market conditions. As carriers struggle to save money and maximize assets, operational expenses have moved to the forefront.

Traditionally, most aspects of operations expenses (opex) have been viewed as "soft" expenses since they are difficult to quantify. Carrier business cases are now taking a harder look at opex for two reasons.

First, in the current market, carriers have already significantly lowered their capital expenditure (capex) spending, often by creatively redeploying existing equipment. There are limits to how far these cuts can be taken, thus driving the need to look to other expenses to lower the total cost of network ownership.

The second reason to pay more attention to opex involves how optical networks have evolved. Major capex reduction occurred in the 1990s when the introduction of optical amplifiers significantly reduced the need for expensive optical-electrical-optical (OEO) regeneration in the network. However, these same OEO points sectionalized the network, allowing for efficient fault isolation and diagnosis.

Each time the optical signal was converted back to electrical, SONET performance metrics could be used to help monitor and maintain the network. New optical systems that remain optical end-to-end, however, offset their reduced capex through an increase in the cost of operating and maintaining the network. These new networks can also take significantly longer to commission and add new wavelengths. So even though capex has been significantly reduced, the total cost of ownership of the network can actually increase.

There are various ways to partition the operational costs in a network, with a typical breakdown as follows:

Equipment space requirements10%
Equipment power requirements13%
System commissioning time & effort16%
Channel turn-up time & effort22%
Network maintenance26%
Customer service8%

Equipment space and power requirements are easily quantifiable, and billing and customer service have similar costs regardless of the network equipment. Therefore, quantification of opex should focus on the cost of commissioning a new network or network segment, turning up new channels, and network maintenance. These items account for approximately 64% of total opex.

A number of tools are currently used to commission, provision, and maintain networks. For example, an optical time domain reflectometer (OTDR) is used to detect fiber breaks as well as dirty connectors or bad splices that could affect network traffic. An optical spectrum analyzer (OSA) is used to determine wavelength activity and to measure optical signal-to-noise ratio (OSNR). Bit-error rate testers (BERTS) are used to test new circuits for errors, and eye diagram analyzers (EDAs) are used for advanced diagnostics by viewing the actual received optical signal.

There are many advantages to integrating these capabilities directly into the network equipment. First, field technicians do not always have access to all of these tools, especially when working in remote amplifier sites. Secondly, integrating these test functions into the equipment is less expensive than using external test sets because existing network element components can do double duty for testing. Finally, an integrated set of tools can be accessed remotely. This allows faster resolution of problems, and also allows for less skilled field personnel since tests can be performed and analyzed at a central location.

Looking at the individual tools mentioned above, an integrated OTDR performs two tasks. First, during commissioning, the end-to-end fiber can be scanned to find dirty connectors, or poor splices. The fact that the OTDR is integrated ensures that the fiber is tested from faceplate to faceplate so, before the field technician leaves the site, there is a record of clean fiber. The integrated OTDR also allows remote isolation of a fiber break down to centimeters, enabling a faster repair time.

The integrated OSA can assist in the turn-up of individual wavelengths by checking their integrity through the entire network. The OSA can also be used to remotely isolate problems by viewing the optical signal at separate points in the network. In this way, a field technician can be sent directly to the appropriate site.

Typically, more than one service is turned up at a time. Often in these cases, the field technician has a single BERT tester and must loop back the new circuits to allow all of them to be tested. If there are bit errors, the technician must then test each circuit individually to find the problem. Given that operational procedures can require a BERT to run error free for 48 or 72 hours, this process can become very long. By integrating the BERT into each interface, all circuits can be tested in parallel and, if there is a problem, it is immediately isolated to the bad circuit.

A study was performed to estimate the cost impact of integrated diagnostic tools over the life of a network. Every carrier has different methods and procedures that will vary the results of this type of study, however, feedback from multiple carriers has contributed to the evolution of this model.

The network parameters are:

Network length5,800 km
Span length100 km
Technicians hour rate$100 US
Average site visit travel3 hours
Length of study5 years
Fiber breaks/1,000 km/yr3
Wavelengths provisioned/yr12
Interest rate8%

The results illustrate that over a five-year period, integrated diagnostic tools can save more than 53% in operational costs.

In summary, advancements in the field of optical networking have significantly reduced the capital costs to carriers. However, at the same time, these new networks have become more difficult and more expensive to manage and maintain. Without new tools suited to advances in optical networking, the operational costs will continue to rise, negating the initial capital savings. Integrated optical diagnostic tools not only save significant money, but also make next generation networks viable to deploy and maintain.

Karl Toompuu is director of product line management at Ceyba Inc., headquartered in Ottawa, ON. He may be reached via the company's Web site at

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