1.10 Network Supportability

The ability of the customer to sustain the required level of performance (that architected and designed into the network) over the entire life cycle of the network is an area of networking that is often neglected. It is a mistake to assume that a successful network architecture and design meets the requirements only on the day that it is delivered to the customer and that future requirements are the responsibility of the customer.

Experience indicates that 80% of the life cycle costs of a system are the operations and support costs, and only 20% is the cost incurred to develop, acquire, and install it. Good network architects/designers will take into account the major factors that affect operability and supportability as they make their decisions. Knowledgeable customers will insist that they understand the operations and support implications of a network architecture and design. At times, such issues may be of more concern than the feasibility of a new technology.

The postimplementation phases of a network's life cycle can be broken into three elements: operations, maintenance, and human knowledge. The operations element focuses on ensuring that the network and system are properly operated and managed and that any required maintenance actions are identified. The maintenance element focuses on preventive and corrective maintenance and the parts, tools, plans, and procedures for accomplishing these functions. The human knowledge element is the set of documentation, training, and skilled personnel required to operate and maintain the network and system. Design decisions affect each of these factors and have a direct impact on the ability of the customer to sustain the high level of service originally realized upon implementation of the network.

Failure to consider supportability in the analysis, architecture, and design processes has a number of serious consequences. First, a smart customer, when faced with a network architecture/design that obviously cannot be operated or maintained by his or her organization, will reject the network project or refuse to pay for it. Second, a customer who accepts the architecture/design and subsequent implementation will have inadequate resources to respond to network and system outages, experience unacceptable performance after a period of time, and may suffer adverse effects in his or her operation or business (e.g., a loss of their customers or revenue). Other customers will be highly dissatisfied with their networks and either require the architect/designer to return and repair it by providing adequate materials to sustain its required performance level or will prematurely replace it. None of these cases reflects positively on the network architect/designer or implementation team and often lead to finger pointing that can be more painful than any acceptance test.

Key characteristics of a network architecture and design that affect the postimplementation costs include:

Network and system reliability
Network and system maintainability
Training of the operators to stay within operational constraints
Quality of the staff required to perform maintenance actions

Some examples of key network architecture/design decisions that affect these characteristics include:

Degree of redundancy of critical-path components in network architecture/design
Quality of network components selected for installation
Location and accessibility of components requiring frequent maintenance
Implementation of built-in test equipment and monitoring techniques

Supportability must be considered throughout the life cycle of the network. An accurate assessment of the requirements for continuous service at full performance level must be included in the requirements analysis process, along with a statement of specific, measurable requirements. During the architecture and design processes, trade-offs must take into account the impact of supportability and the concept of operations must be formulated. Last, during implementation, two major tasks must be accomplished to ensure supportability:

Conformance to the network architecture and design must be validated and nonconformance corrected or (at least) documented to ensure that performance is adequate and that maintenance can be performed.
Operations and maintenance personnel must understand and be trained in the technologies that are being deployed, including how to operate the network and system properly, when to perform maintenance, and how to most quickly restore service in the event of a fault.

A detailed discussion of how supportability fits into the overall architecture and design processes is provided in Chapter 2.