calculation

The most common way to build a network is to construct a local area network (LAN) using networking equipment such as switches and hubs. On a LAN, all the computers and servers that are connected to the common infrastructure are able to communicate with one another, although it cannot be assumed that they can communicate with computers on other LANs. In order to do that, a router must be configured to link the LAN to either an Internet Service Provider or another LAN.

Some features of LANs to remember are:

· Often restricted to a single physical location

· Requires a switch (most common) or a hub to connect each device

· May provide very fast connectivity relative to other environments

· In some business environments LANs may be restricted by a firewall or completely disconnected from the Internet for security reasons

Wide Area Networks (WANs)

For a large organization that may have several LANs, routers and similar devices may be used to create a Wide Area Network (WAN). WANs are used to connect LANs and similar networks in order to make private information systems available to people throughout the organization. When WANs are constructed for permanent use advanced network technologies such as leased lines, ATM, frame really, or ISDN may be used to connect one LAN to the next.

Some features of a WAN to remember are:

· Used to connect more than one physical location

· Requires additional network equipment, typically using routers at each location

· Requires special connections such as leased lines

· Typically provides much slower connectivity than LAN connections

In modern business networks, it is common to accommodate workers who are traveling or who wish to access information systems from their homes by extending the WAN to them temporarily. Dial-up connections used to be the only way to accomplish this, although this worked by permitting a user to connect via a phone line directly to a server on a specific LAN. More common today is a Virtual Private Network (VPN) connection, which permits the user to connect over the public Internet and establish a secure tunnel through which it is possible to access private information services.

Intranet Networking and Systems Maintenance

When planning to install an important information system on a local area network, it is critical that some approach be planned for measuring the quality of service that the users should be able to expect from that service. Because of the dependencies involved in a complex information system - server performance, network performance, availability of electricity, for example - different measures must be used in order to form a complete picture of how well the service is working. These finite measures may guide the IT staff and the organization as a whole towards making decisions about upgrades, improvements, and other changes.

Calculating Uptime

Uptime is a measure of the availability of a specific service, regardless of dependencies. This is often the most important metric that system administrators track because it is a clear indication of to what degree they've been able to provide their services to the end users. Uptime is typically calculated as a percentage of time per week. A system whose uptime is 99.7%, therefore, is only down for 30 minutes per week:

(7 days x 24 hours x 60 minutes ) * .003 = 30.24 minutes

More often than not uptime is established as a target expectation, and may be expressed as a technical requirement when building a new system. Doing so allows the people who are designing a complex information system to plan for the need for redundant systems so that the uptime target is achievable.

Calculating Network Performance

Because most information systems are accessed via the local area network, it is valuable to measure the capabilities of that network to see its impact on the quality and availability of those systems. Network performance is typically measured in these terms:

Capacity - The actual capability of the network to carry data. Expressed in bits per second (bps).

Utilization - The percentage of the capacity of the network being used over a specific period of time.

Throughput - The quantity of error-free traffic sent over the network. On a perfect network this value would be the same as the capacity, but too many additional factors affect data transmission for this to be possible. The most common measurement of throughput is packets per second (PPS).