LANs can be classified as large-building LANs, campus LANs, or small and remote LANs. A large-building LAN typically contains a major data center with high-speed access and floor communications closets; it is usually the headquarters in a larger company. Campus LANs provide connectivity between buildings on a campus. Redundancy is usually a requirement in large-building and campus LAN deployments. Small and remote LANs provide connectivity to remote offices with a relatively small number of nodes.
Campus design factors include the following categories:
- Network application characteristics: Different application types
- Infrastructure device characteristics: Layer 2 and Layer 3 switching and hierarchy
- Environmental characteristics: Geography, wiring, distance, space, power, and number of nodes
Network Requirements for Applications
A business dictates which applications need to be used, and the network must be able to support them. Applications may require high bandwidth or may be time sensitive. Infrastructure devices influence the design. Decisions on switched or routed architectures and port limitations influence the design. The actual physical distances affect the design. The selection of copper or fiber media may be influenced by the environmental or distance requirements. Table 7-2 describes different application types.
Table 7-2 Application Types
| Application Type | Description |
| Peer-to-peer | Peer-to-peer applications include instant messaging, file sharing, IP phone to IP phone, and video conferencing. |
| Client/local servers | Servers are located in the same segment as the clients or close by, normally on the same LAN. According to the legacy 80/20 workgroup rule, 80% of traffic is local, and 20% is not local. This rule is not followed today. |
| Client/data center | Mail servers, file servers, database servers, and business applications are located in the data center. The network needs to be reliable and provide adequate bandwidth to the data center. |
| Client/enterprise edge | External servers such as mail, web, business-to-business (B2B), and public servers are located in the enterprise-edge where off-net connectivity is located. |
There is a wide range of network requirements for applications, depending on the application type. Networks today are switched and not shared. Data centers require high-capacity links to the servers and redundant connections on the network to provide high availability. With servers now located in data centers, the 20/80 rule is applied. With 20/80, 20% of traffic is local traffic, and 80% of the traffic communicates with servers in the data center.
Costs are lower for peer-to-peer applications and become higher for applications that traverse the network with high redundancy. Table 7-3 summarizes network requirements for applications.
Table 7-3 Network Requirements for Application Types
| Requirement | Peer-to-Peer | Client/Local Servers | Client/Data Center | Client/Enterprise Edge |
| Connectivity type | Switched | Switched | Switched | Switched |
| Throughput required | Medium to high | Medium | High | Medium |
| Availability | Low to high | Medium | High | High |
| Network costs | Low to medium | Medium | High | Medium |