Local Area Network

Define common networking terms for LAN's and WAN's Networks, LAN's and WAN's

 A network can be defined as "a group of interconnected computers that share information and resources". In it's simplest form, a network can consist of two computers communicating over a single cable.

 The term LAN stands for Local Area Network. A LAN is a group of computers networked within an office, building or campus.

 A WAN or Wide Area Network usually consists of computers in separate geographical areas interconnected by means of leased lines, telephone lines or microwave, radio and satellite links. A good example of a WAN could be a company with offices in two different cities who's LAN's share information over an ISDN line.

Network Topology

You will come across the term Network Topology many times in the Networking Essentials exam. Network Topology refers to the physical layout of a network. These are the topologies you will need to be familiar with. They will be described in full under the objective "Select the appropriate topology for various Ethernet and Token Ring networks":

Bus Topology: Single cable connecting all computers on the network in a line.

Star Topology: All computers on the network are connected directly to a central hub.

Ring Topology: Each computer is connected to the next in a ring with no end to the network.

Mesh Topology: Each computer is connected to every other computer on the network forming a mesh.

Protocols

 In order to communicate with each other computers must follow a common set of communication rules. These rules are referred to as protocols. There are many different network protocols currently in use but the ones you will need to be familiar with for the exam include; TCP/IP, IPX/SPX, NetBEUI, AppleTalk and DLC. If you don't know what the acronyms mean, don't worry, protocols will be covered in greater detail later under the objective "Select the appropriate network and transport protocols for various Ethernet and Token Ring networks".


Local Area Network :

A local area network (LAN) is a group of computers and associated devices that share a common communications line and typically share the resources of a single processor or server within a small geographic area (for example, within an office building). Usually, the server has applications and data storage that are shared in common by multiple computer users. A local area network may serve as few as two or three users (for example, in a home network) or many as thousands of users (for example, in an FDDI network).

The main local area network technologies are:

• Ethernet

• token ring

• ARCNET

• FDDI (Fiber Distributed Data Interface)

 Typically, a suite of application programs can be kept on the LAN server. Users who need an application frequently can download it once and then run it from their local hard disk. Users can order printing and other services as needed through applications run on the LAN server. A user can share files with others at the LAN server; read and write access is maintained by a LAN administrator.

What Is a WAN?

A WAN is a data communications network that covers a relatively broad geographic area and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer. Figure 3-1 illustrates the relationship between the common WAN technologies and the OSI model.

WANs can created with satellite links, packet radio, or microwave transceivers. These options are generally for more expensive than leased telephone lines, but they can operate in areas where leased lines are not available.
Most WANs are private and owned by the business that operates with them. Recently, however, the Internet has emerged as both the largest and the least expensive WAN in the world. Many companies are now forming private WANs through encrypted communication over the Internet.
WANs suffer from extremely limited bandwidth. The fastest commercially feasible wide area data links are many times slower than the slowest local area links. This makes the sharing of resources over a WAN difficult. Generally, WAN links are used only for interprocess communications to route messages, such as email or HTML (World Wide Web) traffic.


Point-to-Point Links

A point-to-point link provides a single, pre-established WAN communications path from the customer premises through a carrier network, such as a telephone company, to a remote network. Point-to-point lines are usually leased from a carrier and thus are often called leased lines. For a point-to-point line, the carrier allocates pairs of wire and facility hardware to your line only. These circuits are generally priced based on bandwidth required and distance between the two connected points. Point-to-point links are generally more expensive than shared services such as Frame Relay.




A Typical Point-to-Point Link Operates Through a WAN to a RemotNetwork

Circuit Switching

Switched circuits allow data connections that can be initiated when needed and terminated when communication is complete. This works much like a normal telephone line works for voice communication. Integrated Services Digital Network (ISDN) is a good example of circuit switching. When a router has data for a remote site, the switched circuit is initiated with the circuit number of the remote network. In the case of ISDN circuits, the device actually places a call to the telephone number of the remote ISDN circuit. When the two networks are connected and authenticated, they can transfer data. When the data transmission is complete, the call can be terminated. Figure 3-3 illustrates an example of this type of circuit.

Figure 3-3: A Circuit-Switched WAN Undergoes a Process Similar to That Used for a Telephone Call

WAN Devices

WANs use numerous types of devices that are specific to WAN environments. WAN switches, access servers, modems, CSU/DSUs, and ISDN terminal adapters are discussed in the following sections. Other devices found in WAN environments that are used in WAN implementations include routers, ATM switches, and multiplexers.

WAN Switch

A WAN switch is a multiport internetworking device used in carrier networks. These devices typically switch such traffic as Frame Relay, X.25, and SMDS, and operate at the data link layer of the OSI reference model. Figure 3-5 illustrates two routers at remote ends of a WAN that are connected by WAN switches.


Figure 3-5: Two Routers at Remote Ends of a WAN Can Be Connected by WAN Switches