Project Network Design

One of the first steps in starting a network design project is to determine its scope. Some of the most common network design projects these days are small in scope— for example, projects to allow a few people in a sales office to access the enterprise network via a VPN. On the other hand, some design projects are large in scope. Ask your customer to help you understand if the design is for a single network segment, a set of LANs, a set of WAN or remote-access networks, or the entire enterprise network. Also ask your customer if the design is for a new network or a modification to an existing one.

Explain to your customer any concerns you have about the scope of the project, including technical and business concerns. Subsequent sections in this chapter discuss politics and scheduling, which are tightly linked to the scope of a network design project. (Many network designers have learned the hard way what happens when you don’t help your customers match the schedules of their projects to the scope.

Make sure your customers tell you everything they can about the network and the design project. You may want to poke around outside the stated scope of the project, just to make sure nothing essential has been omitted. Double-check that you have gathered all the requirements and that you have accurate information about sites, links, and devices. If the project addresses network security, make sure you know about all external links, including dial-in access.

Designers rarely get a chance to design a network from scratch. Usually a network design project involves an upgrade to an existing network. However, this is not always the case. Some senior network designers have developed completely new next-generation networks to replace old networks. Other designers have designed networks for a new building or new campus. Even in these cases, however, the new network usually has to fit into an existing infrastructure—for example, a new campus network that has to communicate with an existing WAN. Where there is an existing network, the design project must include plans for migrating to the new design with minimal disruption and risk.

When analyzing the scope of a network design, you can refer to the seven layers of the OSI reference model to specify the types of functionality the new network design must address. For example, you might decide that the design project is concerned only with network layer concerns such as routing and IP addressing. Or you might decide that the design also concerns the application layer because the focus is on voice applications, such as Interactive Voice Response (IVR), which directs customers to the correct location in a call center, or unified messaging, where e-mail can be retrieved via voice mail and text messages can be converted into speech. Figure shows the OSI reference model.

Figure: The Open Systems Interconnection (OSI) Reference Model

In addition to using the OSI reference model, this book also uses the following terms to define the scope of a network and the scope of a network design project:

• Segment- A single network based on a particular Layer 2 protocol. May include Ethernet hubs and repeaters, and multistation access units (MAUs) if Token Ring is still in use.
• LAN- A set of switched segments, usually based on a particular Layer 2 protocol (although mixed LANs are possible). May have one or more Layer 3 protocols associated with it, although most networks are standardizing on IP.
• Building network- Multiple LANs within a building, usually connected to a building-backbone network.
• Campus network- Multiple buildings within a local geographical area (within a few miles), usually connected to a campus-backbone network.
• Remote access- Networking solutions that support individual remote users or small remote branch offices accessing the network.
• WAN- A geographically dispersed network including point-to-point, Frame Relay, ATM, and other long-distance connections.
• Enterprise network- A large and diverse network, consisting of campuses, remote-access services, and one or more WANs or long-range LANs. An enterprise network is also called an internetwork.