Network Design

Before you begin designing a new network or adding on to an existing network, you need to have a clear picture of what you need the network to accomplish.
1.     What do you expect the network to do?
2.     What do the users expect the network to do?
3.     What applications do you need to support?
4.     How many users will be using the system?
5.     How complex are the applications; is this e-mail or a multimedia database?
6.     What kinds of Internet access will you need?
7.     Will you need servers for each application, or can applications share servers?
8.     Will you need web servers, file servers, print servers or CD servers?

When you have considered the needs of the network (and have talked to some of your users), write all of the information down and begin assigning priorities to each item. Determine the importance of each item and the resources needed to support it. As you begin to budget and build a deployment plan, you may find that some items will have to wait. With this process, you’ll know up front what has be delayed and what must be done first due to its critical nature.

Communication
If designing a network, good communication between the network administrators, the server administrators and the users is critical. Talking to each group will allow you to hear what each thinks they need, what they think is most critical and how they measure “success.” This information is critical in order to meet the needs as well as the expectations of the users.
In addition to design criteria, regular briefings help keep everyone informed of the progress of the project and any impending issues. By bringing the users into the process, you can use their advice and help when you need to modify the plan due to budget, time or other issues and will have their support in making the changes.

Sizing the Network
To properly size the network, consider the capacity of the network in terms of users, bandwidth and functionality.
-   Users: How many users will use the network in the beginning? How many new users will be added each year for the next five years?
-   Bandwidth: How much bandwidth does the network require? Consider the applications the users will run, as well as where the data will be stored and used. Concurrent users, high-bandwidth applications (usually multimedia) and special-needs applications (low latency, low jitter) will place heavy demands on bandwidth.
-   Functionality: What network-based features do you need? Network-based storage, print servers, DNS, DHCP and web servers all impact network design. In addition, Quality of Service (QoS) methods may be required to ensure the applications function properly. Your network needs to be designed to grow easily and to be able to incorporate new or enhanced technologies. One of the most commonly used designs is a hierarchical model, which allows for incremental upgrades of specific sections without requiring an upgrade to the entire network. Troubleshooting and problem isolation are also simplified.

Standards
It is important that a network be designed around industry standards. By using standards-based, proven components and systems you will increase the reliability of the network and be able to select hardware and software from various manufacturers as price and function dictate. Many of the standards you will need to adhere to are Internet-based, such as TCP/IP, DNS, H.323, etc. Appendix A lists the standards bodies that create, modify, approve and disseminate standards for companies to implement in their hardware or software.

Connectivity
There are essentially four different network types:
-   Local Area Network (LAN): Network for a single building.
-   Metropolitan Area Network (MAN): A network between buildings, all in the same area (generally a single city).
-   Wide Area Network (WAN): A network between buildings, connected over long distances (usually between cities)

In addition to the types listed above, remote access and connectivity to the Internet should also be considered.
For all connectivity, consider several factors.
-   Speed: How fast does the network link need to be?
DNS: Domain Name Service. Maps a name in the format “name.domain.tld” to an IP address.
DHCP: Dynamic Host Configuration Protocol. Assigns IP addresses to machines on a “lease” basis. Allows machines to get an IP address, gateway and other information without having to be manually configured.
-   Cost: How much does the network link cost (generally a function of speed vs. distance)?
-   Quality of Service: What guarantee of data delivery exists?
Different technologies offer different QoS levels, and can affect the price, sometimes more so than speed. Consider the needs of the applications carefully when choosing a link type.

General Design
Once you have the functional requirements and an idea of the network scale, you can begin the design. The network is comprised of layers, and decisions will need to be made on several things per layer.
-   Network Type: For a LAN, Ethernet at 10, 100 or 1,000 Mbps is the generally accepted standard. Some details involve switching vs. hubs and UTP vs. fiber. You will need to examine the bandwidth the network needs in order to support the applications. Multimedia (audio or video) demands more network resources and will consequently require a faster, higher-quality network, which usually costs more. For a CAN, the same network standards that are common in LANs are usually sufficient. For a MAN and WAN, however, networks based on Frame Relay or ATM are the most common choices.
-   Physical Network: The physical network covers everything from network cabling to faceplates and patch panels. The type of cabling you select depends on the type of network you need to support.