New networks, new T&M approach: a new breed of multi-layer test and measurement equipment has emerged that promises to accelerate service deployment and reduce network operational expenditure - T&M - Monitoring Network Performance

Telecommunications International, August, 2002 by Jim Nerschook

The ability to deploy new services and respond to changing customer requirements quickly -- as well as to reduce operational expenses -- are key requirements for on operator's success. This being so, an increasingly complex network architecture has emerged and, with it, the need for test and measurement (T&M) equipment to match that development.

Reducing costs and increasing network efficiency - seemingly disparate objectives at the best of times -- are made more difficult by complex optical networks. And that complexity will increase (Figure 1) as networks are optimised for bandwidth, new services and QoS.

Bandwidth improvements from 2.5Gbps to 10Gbps and 40Gbps will require accurate characterisation of both chromatic and polarisation mode dispersion in order to properly engineer dispersion compensation schemes within the network. Provisioning of services, such as SONET/SDH and ethernet, will not only require a simple measurement of bit-error rate, but will also require the ability to isolate the network element or application that is the root cause of the network impairment in order to establish ownership (carrier or customer) for its resolution. Whether implementing a SONET/SDH network with forward error correction (FEC) or a network incorporating MPLS technology to seamlessly route lambdas across a network, the need for knowledgeable traffic engineering skills has never been greater.

In the past, the responsibility of qualifying a network for these services has, for the most part, been handled by different personnel within a carrier's organisation but now, due to resource reduction and the blurring of traditional network boundaries between the core, metro and access parts of the network, an individual test technician may be faced with not only characterising the physical medium, but also ensuring services are delivered to end-users in a timely and error-free manner. With network complexity continually increasing, service providers have turned to T&M equipment manufacturers to deliver simple, cost-effective tools to accelerate the deployment of new services while reducing operational expenses.

The multi-layer approach to T&M

In response to the demand for test equipment to address these multiple objectives of service providers, a new category has emerged -- multi-layer T&M. Designed to address specifically the needs of service providers, multi-layer T&M promises to speed up network deployment and reduce operating expenses.

The design criteria of a multi-layer T&M solution is a platform that has the ability and flexibility to characterise multiple layers of a communication network (Figure 2). The physical construction of the platform consists of a controller and an application bay or adapter. The term application is used to describe the T&M functionality contained within the unit. The controller design is usually based upon PC technology, utilising an industry standard operating system such as Windows or LINUX.

The interface to the application bay is also an industry standard, such as cPCI, to simplify integration between the controller and the application bay. The industry standard interface also serves as an open-architecture to allow applications to be quickly developed and integrated in response to emerging network requirements.

The fundamental challenge facing the T&M manufacturer is how to address the needs of both unskilled and skilled technicians. With respect to this objective, the instrument needs to be both a 'brick with a button' and a high performance T&M solution that allows maximum flexibility for skilled users with broad T&M expertise. This task can be accomplished by designing the test equipment with two parallel user interfaces. For the unskilled user, the application must not only report impairment but also recommend corrective actions to resolve the issue.

As an example, consider the pre-qualification of optical return loss (ORL) of a complex DWDM system. It is widely understood that high return loss can contribute to instability in system transmitters. Once the ORL is reported as a pass or fail to the technician, the test equipment may also provide a list of corrective actions to implement to decrease the overall ORL. This may be as simple as cleaning connector interfaces or contacting the DWDM system vendor for further diagnostics.

It is also imperative that the instrument has a consistent look and feel between user interfaces from one application to the next application. Familiarity with a measurement reduces not only the amount of time required to perform a measurement but also reduces the amount of training expenditures within an organisation while increasing the quality of the test results.

The economic arguments

There are compelling financial reasons for service providers to consider the use of multi-layer T&M solutions within their network. The design of the multi-layer solution allows users not only to reduce test time but also to reduce their T&M equipment inventory.

As an example, consider an organisation responsible for fibre characterisation either within a carrier or as a contractor to a carrier. The main responsibility of this organisation is to verify that the optical characteristics (attenuation and dispersion) of the network are within predetermined limits to support desired data rates. To accomplish this task the organisation is usually equipped with the following measuring equipment: inspection microscope, power meter and light source, optical return loss (ORL) meter, OTDR, OSA (optical spectrum analyser), and chromatic and polarisation test systems. Each of these systems would normally require a separate controller (or base system) to operate the system. For the more expensive test systems the price of the controller ranges from US$5,000 ([euro]4,900) to US$7,500 ([euro]7,350).