What is WAN

Posted on November 12, 2009. Filed under: CCNA, ICND1 break down |


wan

Wide Area Network (WAN) is a computer network that covers a broad geographical area. On the contrary, Local Area Networks (LAN) are usually limited to a small physical area, like a home, office, building  or campus.  The largest and most well-known example of a WAN is the Internet.

WANs are used to connect LANs and other types of networks together. Many WANs are built for one particular organization and are private. Others, built by Internet Service Providers (ISP), provide connections from an organizations’s LAN to the internet. In order to provide connections over large geographical arears, WANs often use public networks, such as the telephone system, leased lines (ISDN), satellite, microwave, or other connection method.

Typical WANs use serial connections of various types to access bandwidth over large geographic areas.

So, who is managing the WANs today? The following organizations defined and managed the WAN access standards:

  • International Organization for Standardization (ISO)
  • Telecommunications Industry Association (TIA)
  • Electronics Industry Alliance (EIA)

WAN access standards are primarily resides in OSI reference model Layer 1 and Layer 2. WAN access standards decribe physical layer and data link layer requirements such as physical addressing, flow control, and encapsulation. The following picture shows the popular WAN solutions today.

fig15

As shown above, at OSI model layer 1, WAN protocols describe how to provide electrical, mechanical, operational, and functional connections to the services of a communications service provider.

At OSI model layer 2,WAN protocols define encapsulation of data for transmission toward a remote location and the mechanisms for transferring the resulting frames. The WAN data link layer protocols include:

  • HDLC
  • PPP
  • Frame Relay (Link Access Procedure for Frame Relay [LAPF])
  • ATM

Serial connections support WAN services such as dedicated leased line, above which the PPP or Frame Relay runs.

Other WAN services, such as ISDN or dial-up modem, offer low cost dial-on-demand connection. An ISDN BRI is composed of two 64-kbps bearer channels (B channels) for data, and one 16-kbps data channel(D channel) for link-management purposes.

DSL and cable modem connections dominates today’s residential broadband service market. A typical residential DSL service can offer up to 1.5 Mbps connection speed over the existing telephone line. Cable services can offer higher speed connection over the existing coaxial cable TV line.

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