WAN Technologies Overview (2.1)
As an organization expands, WAN connections are necessary. This section discusses the purpose of WANs, introduces WAN terminology, WAN devices, and circuit-switch / packet-switch networks.
Why a WAN? (188.8.131.52)
A WAN operates beyond the geographic scope of a LAN. As shown in Figure 2-1, WANs are used to interconnect the enterprise LAN to remote LANs in branch sites and telecommuter sites.
Figure 2-1 WANs Interconnect Users and LANs
A WAN is owned by a service provider. An organization must pay a fee to use the provider’s network services to connect remote sites. WAN service providers include carriers, such as a telephone network, cable company, or satellite service. Service providers provide links to interconnect remote sites for the purpose of transporting data, voice, and video.
In contrast, LANs are typically owned by the organization and used to connect local computers, peripherals, and other devices within a single building or other small geographic area.
Are WANs Necessary? (184.108.40.206)
Without WANs, LANs would be a series of isolated networks. LANs provide both speed and cost-efficiency for transmitting data over relatively small geographic areas. However, as organizations expand, businesses require communication among geographically separated sites. The following are some examples:
- Regional or branch offices of an organization need to be able to communicate and share data with the central site.
- Organizations need to share information with other customer organizations. For example, software manufacturers routinely communicate product and promotional information to distributors that sell their products to end users.
- Employees who travel on company business frequently need to access information that resides on their corporate networks.
Home computer users also need to send and receive data across increasingly larger distances. Here are some examples:
- Consumers now commonly communicate over the Internet with banks, stores, and a variety of providers of goods and services.
- Students do research for classes by accessing library indexes and publications located in other parts of their country and in other parts of the world.
It is not feasible to connect computers across a country, or around the world, with physical cables. Therefore, different technologies have evolved to support this communication requirement. Increasingly, the Internet is being used as an inexpensive alternative to enterprise WANs. New technologies are available to businesses to provide security and privacy for their Internet communications and transactions. WANs used by themselves, or in concert with the Internet, allow organizations and individuals to meet their wide-area communication needs.
Evolving Networks (220.127.116.11)
Every business is unique, and how an organization grows depends on many factors. These factors include the type of products or service the business sells, the management philosophy of the owners, and the economic climate of the country in which the business operates.
In slow economic times, many businesses focus on increasing their profitability by improving the efficiency of their existing operations, increasing employee productivity, and lowering operating costs. Establishing and managing networks can represent significant installation and operating expenses. To justify such a large expense, companies expect their networks to perform optimally and to be able to deliver an ever increasing array of services and applications to support productivity and profitability.
The example used in this chapter is of a fictitious company called SPAN Engineering. The following topics provide an example of how the network requirements of SPAN Engineering change as the company grows from a small local business into a global enterprise.
Small Office (18.104.22.168)
SPAN Engineering is an environmental consulting firm that has developed a special process for converting household waste into electricity. SPAN Engineering is developing a small pilot project for a municipal government in its local area. The company, which has been in business for 4 years, has grown to include 15 employees: 6 engineers, 4 computer-aided drawing (CAD) designers, a receptionist, 2 senior partners, and 2 office assistants.
SPAN Engineering’s management is working to win full-scale contracts after the pilot project successfully demonstrates the feasibility of their process. Until then, the company must manage its costs carefully.
For their small office, SPAN Engineering uses a single LAN to share information between computers, and to share peripherals, such as a printer, a large-scale plotter (to print engineering drawings), and fax equipment. They have recently upgraded their LAN to provide inexpensive Voice over IP (VoIP) service to save on the costs of separate phone lines for their employees.
The SPAN Engineering network consists of a small office as shown in Figure 2-2.
Figure 2-2 Connecting a Small Office
Connection to the Internet is through a common broadband service called digital subscriber line (DSL), which is supplied by their local telephone service provider. With so few employees, bandwidth is not a significant problem.
The company cannot afford in-house IT support staff, and uses support services purchased from the DSL provider. The company also uses a hosting service rather than purchasing and operating its own FTP and email servers.
Campus Network (22.214.171.124)
Five years later, SPAN Engineering has grown rapidly. The company was contracted to design and implement a full-size waste-conversion facility soon after the successful implementation of their first pilot plant. Since then, SPAN has won other projects in neighboring municipalities, and in other parts of the country.
To handle the additional workload, the business has hired more staff and leased more office space. It is now a small- to medium-size business with several hundred employees. Many projects are being developed at the same time, and each requires a project manager and support staff. The company has organized itself into functional departments, with each department having its own organizational team. To meet its growing needs, the company has moved into several floors of a larger office building, as shown in Figure 2-3.
Figure 2-3 Connecting a Campus Network
As the business has expanded, the network has also grown. Instead of a single small LAN, the network now consists of several subnetworks, each devoted to a different department. For example, all the engineering staff is on one LAN, while the marketing staff is on another LAN.
These multiple LANs are joined to create a company-wide campus network which spans several floors of the building.
The business now has in-house IT staff to support and maintain the network. The network includes dedicated servers for email, data transfer, and file storage, and web-based productivity tools and applications. There is also a company intranet to provide in-house documents and information to employees. An extranet provides project information to designated customers.
Branch Networks (126.96.36.199)
Another 6 years later, SPAN Engineering has been so successful with its patented process that demand for its services has skyrocketed. New projects are underway in multiple cities. To manage those projects, the company has opened small branch offices closer to the project sites.
This situation presents new challenges to the IT team. To manage the delivery of information and services throughout the company, SPAN Engineering now has a data center, which houses the various databases and servers of the company. To ensure that all parts of the business are able to access the same services and applications regardless of where the offices are located, the company must now implement a WAN, as shown in Figure 2-4.
Figure 2-4 Connecting Branch Networks
Connecting to its branch sites may occur over dedicated private lines or by using the Internet. For its branch office that is in a nearby city, the company decides to use private dedicated lines through their local service provider. However, for its regional office and remote office located in another country, the Internet is an attractive WAN connection option. Although connecting offices through the Internet is economical, it introduces security and privacy issues that the IT team must address.
Distributed Network (188.8.131.52)
SPAN Engineering has now been in business for 20 years and has grown to thousands of employees distributed in offices worldwide. The cost of the network and its related services is a significant expense. The company is looking to provide its employees with the best network services at the lowest cost. Optimized network services would allow each employee to work at a high rate of efficiency.
To increase profitability, SPAN Engineering must reduce its operating expenses. It has relocated some of its office facilities to less-expensive areas. The company is also encouraging teleworking and virtual teams. Web-based applications, including web conferencing, e-learning, and online collaboration tools, are being used to increase productivity and reduce costs. Site-to-site and remote access virtual private networks (VPNs) enable the company to use the Internet to connect easily and securely with employees and facilities around the world. To meet these requirements, the network must provide the necessary converged services and secure Internet WAN connectivity to remote offices and individuals, as shown in Figure 2-5.
Figure 2-5 Connecting a Global Enterprise Network
As seen in this example, network requirements of a company can change dramatically as the company grows over time. Distributing employees saves costs in many ways, but it puts increased demands on the network. Not only must a network meet the day-to-day operational needs of the business, but it must also be able to adapt and grow as the company changes. Network designers and administrators meet these challenges by carefully choosing network technologies, protocols, and service providers, and by optimizing their networks using many of the network design techniques and architectures described in this course.