Content Overview A wide-area network (WAN) is a data communications network that spans a large geographic area. WANs have several important characteristics that distinguish them from LANs. The first lesson in this module will provide an overview of WAN technologies and protocols. It will also explain how WANs and LANs are different, and ways in which they are similar. It is important to have an understanding of the physical layer components of a router. This understanding builds a foundation for other knowledge and skills needed to configure routers and manage routed networks. This module provides a close examination of the internal and external physical components of the router. The module also describes techniques for physically connecting the various router interfaces. Students completing this module should be able to:

Identify organizations responsible for WAN standards
Explain the difference between a WAN and LAN and the type of addresses each uses
Describe the role of a router in a WAN
Identify internal components of the router and describe their functions
Describe the physical characteristics of the router
Identify common ports on a router
Properly connect Ethernet, serial WAN, and console ports

Content 1.1 WANs 1.1.1 Introduction to WANs A wide-area network (WAN) is a data communications network spanning a large geographic area such as a state, province, or country. WANs often use transmission facilities provided by common carriers, for example, telephone companies. These are the major characteristics of WANs:

They connect devices that are separated by wide geographical areas.
They use the services of carriers such as the Regional Bell Operating Companies (RBOCs), Sprint, MCI, VPM Internet Services, Inc., and Altantes.net.
They use serial connections of various types to access bandwidth over large geographic areas.

A WAN differs from a LAN in several ways. For example, unlike a LAN, which connects workstations, peripherals, terminals, and other devices in a single building or other small geographic area, a WAN makes data connections across a broad geographic area. Companies use a WAN to connect various company sites so that information can be exchanged between distant offices. A WAN operates at the physical layer and the data link layer of the OSI reference model. It interconnects LANs that are usually separated by large geographic areas. WANs provide for the exchange of data packets and frames between routers and switches and the LANs they support. The following devices are used in WANs:

Routers offer many services, including internetworking and WAN interface ports.
Switches in the WAN provide connectivity for voice, data, and video communication.
Modems include interface voice-grade services, channel service units/digital service units (CSU/DSUs) that interface T1/E1 services, and Terminal Adapters/Network Termination 1 (TA/NT1s) that interface Integrated Services Digital Network (ISDN) services.
Communication servers concentrate dial-in and dial-out user communication.

WAN data link protocols describe how frames are carried between systems on a single data link. They include protocols designed to operate over dedicated point-to-point, multipoint, and multi-access switched services such as Frame Relay. WAN standards are defined and managed by a number of recognized authorities, including the following agencies:

International Telecommunication Union-Telecommunication Standardization Sector (ITU-T), formerly the Consultative Committee for International Telegraph and Telephone (CCITT).
International Organization for Standardization (ISO).
Internet Engineering Task Force (IETF).
Electronic Industries Association (EIA).

Interactive Media Activity Drag and Drop: Identifying Network Devices After completing this activity, the student will be able to understand WANs.

Content 1.1 WANs 1.1.2 Introduction to routers in a WAN A router is a special type of computer. It has the same basic components as a standard desktop PC. It has a CPU, memory, a system bus, and various input/output interfaces. However, routers are designed to perform some very specific functions that are not typically performed by desktop computers. For example, routers connect and allow communication between two networks and determine the best path for data to travel through the connected networks. Just as computers need operating systems to run software applications, routers need the Internetwork Operating System software (IOS) to run configuration files. These configuration files contain the instructions and parameters that control the flow of traffic in and out of the routers. Specifically, by using routing protocols, routers make decisions regarding the best path for packets. The configuration file specifies all the information for the correct set up and use of the selected, or enabled, routing and routed protocols on the router. This course will demonstrate how to build configuration files from the IOS commands in order to get the router to perform many essential network functions. The router configuration file may at first glance appear complex, but it will seem much less so by the end of the course. The main internal components of the router are random access memory (RAM), nonvolatile random-access memory (NVRAM), flash memory, read-only memory (ROM), and interfaces. RAM, also called dynamic RAM (DRAM), has the following characteristics and functions:

Stores routing tables
Holds ARP cache
Holds fast-switching cache
Performs packet buffering (shared RAM)
Maintains packet-hold queues
Provides temporary memory for the configuration file of the router while the router is powered on
Loses content when router is powered down or restarted

NVRAM has the following characteristics and functions:

Provides storage for the startup configuration file
Retains content when router is powered down or restarted

Flash memory has the following characteristics and functions:

Holds the operating system image (IOS)
Allows software to be updated without removing and replacing chips on the processor
Retains content when router is powered down or restarted
Can store multiple versions of IOS software
Is a type of electronically erasable, programmable ROM (EEPROM)

Read-only memory (ROM) has the following characteristics and functions:

Maintains instructions for power-on self test (POST) diagnostics
Stores bootstrap program and basic operating system software
Requires replacing pluggable chips on the motherboard for software upgrades

Interfaces have the following characteristics and functions:

Connect router to network for frame entry and exit
Can be on the motherboard or on a separate module

Web Links Core WAN http://www.cisco.com/warp/public/779/largeent/ select_ products/ wan/ WAN_routers.html

Content 1.1 WANs 1.1.3 Router LANs and WANs While a router can be used to segment LANs, its major use is as a WAN device. Routers have both LAN and WAN interfaces. In fact, WAN technologies are frequently used to connect routers and these