Network Design Life Cycle (NDLC) is a set of strategies for upgrading or replacing an organization’s network system. Network Design Life Cycle (NDLC) is derived from the well known System Analysis and Design Life Cycle (SDLC), which is a structured analysis technique that is used to plan and manage the systems development process. Although there is not yet a standard established for NDLC that is universally agreed upon, many network designers are convinced that it should replace the established SDLC because the design and development process must take less time, and the cost of the process must be less to justify the frequency of NDLC. This is because the cost of network installation is decreasing continuously, and network systems need to be replaced more frequently than other systems due to rapid changes and expansion in network technology, in terms of increased demands for more access network resources and bandwidth (FitzGerald & Dennis).

The NDLC has six stages namely analysis, design, simulation, implementation, monitoring, and management: and it depends on previously completed development processes such as strategic business planning, applications development life cycle, and data distribution analysis. And a top-down approach is often employed to efficiently deliver the information systems that will fulfill strategic business goals.

The purpose of the analysis phase is to understand the business requirements and build a logical model, which describes the business processes for the new system or system to be upgraded. This can basically be termed as requirement modeling, a sort of an investigation and fact-finding techniques, such as sampling and observing the organization or business structure. First, the existing system is analyzed; a process called baselining, and then the need for a new system is analyzed. Analyzing technical business goals such as capacity, performance, reduced costs, improved market share, increased revenues and profit etc, can aid you to propose a network design that will be approved by the users. At the end of this phase, you should produce a systems requirements document that describes management and user requirements, alternative plans and costs, and a recommendation such as whether the new system must be developed in-house or just modify the existing one (Oppenheimer, 2004).

In design phase, the network designers create a blue print of the logical and physical network designs for the new system based on the requirements gathered during the analysis phase. ‘Physical network designs involve the arrangement and inter­connection of the physical network circuits and devices, while Logical network designs involve configuration and definition of services that will run over that physical network such as addressing schemes, routing schemes, traffic prioritization, security, and management.’ In this phase, all the necessary outputs, inputs, interfaces, and processes are identified. And internal and external control factors are designed i.e. features that make the system reliable, accurate, maintainable, and secure. The design is documented and presented to management and users foe review and approval (buy-in). This is crucial because it eliminates misunderstandings about what the new system will do, how, and at what cost. With the aid of computer assisted network engineering (CANE) tools, design errors are minimized, interoperability and accuracy of the network design is ensured, improved quality of design and documentation, and existing network components are easily and automatically discovered (Goldman & Rawles, 2004).

Once the initial design has been completed, it can be tested for proper operations by running a simulation that describes how the actual network devices behave under various real-world conditions. Simulation modeling allows the new system or proposed changes to an existing system to be quickly evaluated before committing to a course of action. Thus, it outlines the detail implications and consequences of the proposed network or change to an existing one. Running simulations or prototypes of the system before its implemented can be beneficial to the designers in that it identifies network congestion/bottlenecks such as overworked serves, network failures, or disk capacity problems; it has the ability to recreate circumstances that might reproduce network problems; and it aids in test piloting new applications and network configurations before the actual deployment. With projected loads, it becomes easier to determine whether the current system can handle unexpected or expected traffic growth and/or to determine how much longer the current system would last before being upgraded. However, with simulations, its easy to make mistakes and very hard to discover those mistakes. And that one mistake can throw those projections off by a wide margin resulting in complicated and costly actual system implementation process.

The implementation phase begins after the design has been approved. The network is then built according the design specifications, tested, documented, and the whole system is installed. If some components of the system were purchased as a package, the network analysts will perform any necessary modifications and configurations. The objective of the implementation phase is to delivery a completely functional and documented information system. As stated, the purpose of this phase is self-explanatory. That is, complete equipment installation, perform actual transition to the new system, complete procedure manuals and conduct training, perform acceptance tests and system assurance evaluation, and determine whether the system operates properly and if costs are within expectations.

The next phase is monitoring the progress of the network system, and many organizations use network management software to monitor and control their networks. Network monitoring involves the ability to monitor and capture SNMP, RMON, and RMON2 data from multi-vendor networking technology with abilities to analyze the captured data and report on trends and exceptions. Network monitoring tools also track network performance over a long period of time and report anomalies from the accumulated baseline data. The parameters monitored by a network management system fall into two distinct categories:  physical network statistics, which includes monitoring the operation of the networks, modems, multiplexers, circuits linking the various hardware devices, and any other network device. And logical network information, which includes performance measurement systems that keep track of user response times, the volume of traffic on a specific circuit, statistics about degrading performance of certain nodes, current network volume by day or week, the destination of data routed around various network, and any other indices showing the level of service provided by the network.

Management phase, like other related technology-based solutions, can only be effectively implemented when combined with other processes, management staff, and procedures (Goldman & Rawles, 2004). Network Management activities can be broken down into numerous sections including:
·    Accounting management, which enables charges to be established for the use of managed objects and costs to be identified for the use of those managed objects;
·    Configuration management, which involves managing the network’s hardware and software configuration and documenting it, for example, adding and deleting user accounts;
·    Performance management, which ensures that the network is operating efficiently;
·    Fault management, which involves preventing, detecting, and correcting faults in the network circuits, hardware, and software.

Network management also has device, system, and application management tools (software) that are designed to provide automated support for some or all of the network management functions. Furthermore,
Network Management Standards ensure that hardware devices from different vendors can interoperate with each other with common network management protocols such as the Simple Network Management Protocol (SNMP) and Common Management Interface Protocol (CMIP) (FitzGerald & Dennis).

NDLC is a continuous cycle that is practical for identifying the logical processes involved in network development. But it lacks an established standard that is universally agreed upon. Besides, there are no clear steps within the cycle that identify how each stage is precisely completed compared to SDLC. Hence, it relies on the network analysis and design methodology, which is a practical, step-by-step approach to network analysis and design to compliment its logical framework.


Reference:
Amato, V. (2000). Cisco Networking Academy Program: Companion Guide.

FitzGerald, J. & Dennis, A. Business Data Communications and Networking, 6th Ed. John Wiley & Sons, Inc

Goldman, E.J. & Rawles, T.P. (2004). Applied Data Communications: A Business-Oriented Approach. Wiley

Held, G. (2001). Understanding Data Communications: Wiley

Oppenheimer, P. (2004). Top-Down Network Design:  Cisco Press

Slone, P.J. (200). Local Area Network, HandBook. Auerbach

White, C. (2004). Data Communications & Computer Networks: A Business User’s
Approach. Thompson Course Tech