WANs connect remote sites. Connection requirements vary depending on user requirements, cost, and availability.

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WAN Review

A WAN makes data connections across a broad geographic area so that information can be exchanged between distant sites. This topic defines the characteristics of a WAN.

A WAN is different from a LAN. 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 the WAN to connect various company sites so that information can be exchanged between distant offices.

Because the cost of building a global network to connect remote sites can be astronomical, WAN services are generally leased from service providers. You must subscribe to an outside WAN provider to use network resources that your organization does not own. The service provider will use the portion of its network that you leased to transport the information.

Note A metropolitan-area network (MAN) leverages the high-speed communication infrastructure built around large cities. A MAN supports higher bandwidth than is typically afforded by a WAN, but is limited in scope to the high-speed infrastructure contained in the metropolitan area.

WAN Overview

• WANs connect remote sites.

• Connection requirements vary depending on

user requirements, cost, and availability.

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WAN Connection Types

Some of the WAN connection types available are leased line, circuit-switched, and packet- switched. This topic describes the different WAN connection types and the components that provide the connection.

Some of the WAN connection types that you can select are as follows:

Leased line: A leased line, also known as a point-to-point or dedicated connection, provides a single, preestablished WAN communications path from the customer premises, through a service provider network, to a remote network. The service provider reserves this connection for private use by the client. Leased lines eliminate the issues that arise with a shared connection, but they are costly. Leased lines are typically employed over

synchronous serial connections up to T3 speeds, operating at 45 Mbps.

Circuit-switched: Circuit switching is a switching system in which a dedicated circuit path must exist between sender and receiver for the duration of the “call.” Service provider networks use circuit switching to provide basic telephone service or ISDN. Circuit-

switched connections are commonly used in environments that require only sporadic WAN usage. Basic telephone service is typically employed over an asynchronous serial

connection.

WAN Connection Types: Layer 1

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When your organization subscribes to an outside WAN service for network resources, the provider assigns your organization the parameters for making the WAN link. Commonly used terms for the main physical parts are as follows:

Customer premises equipment (CPE): Devices physically located on subscriber premises. The equipment includes devices that are owned by the subscriber and devices that are leased to the subscriber by the service provider.

Demarcation (or demarc): The juncture at which the CPE ends and the local loop portion of the service begins. It often occurs at a telecommunication closet.

Local loop (or “last-mile”): Cabling (usually copper wiring) that extends from the demarcation point into the WAN service provider central office (CO).

CO switch: A switching facility that provides the nearest point of presence (POP) for the provider WAN service. Inside the long-distance toll network are several types of COs.

Toll network: The collective switches and facilities (called trunks) of the WAN provider.

The call may cross a trunk to a primary center and then go to a sectional center and then to a regional or international carrier center as the call travels the long distance to its

destination. Switches operate in provider offices, with toll charges based on tariffs or authorized rates.

•Provider assigns connection parameters to subscriber.

Interfacing Between

WAN Service Providers

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WAN Cabling

Cisco routers support the EIA/TIA-232, EIA/TIA-449, V.35, X.21, and EIA/TIA-530 standards for serial connections. This topic describes the cabling available for WAN connections.

To make a synchronous serial leased-line or packet-switched WAN connection, such as a Frame Relay connection, Cisco devices support the following serial standards:

EIA/TIA-232

EIA/TIA-449

V.35

X.21

EIA/TIA-530

When you order the cable, you will receive a shielded serial transition cable that has the appropriate connector for the standard that you specify. The router end of the shielded serial transition cable has a DB-60 connector, which connects to the DB-60 port on a serial WAN interface card (WIC). Because five different cable types are supported with this port, it is

Serial Point-to-Point Connections

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port is configured as DTE (the default setting), it will require external clocking from the CSU/DSU or other DCE device.

Note To support higher densities in a smaller form factor, Cisco has introduced a smart serial cable. The serial end of the smart serial cable is a 26-pin connector that is much smaller than the DB-60 connector used to connect to a five-in-one serial port. These transition cables support the same five serial standards, are available in either DTE or DCE configuration, and are used with the two-port serial and two-port asynchronous and/or synchronous WICs.

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Layer 2 Encapsulation Protocols

To encapsulate data for crossing a WAN link, you can choose from a variety of Layer 2

protocols, including High-Level Data Link Control (HDLC), PPP, Serial Line Internet Protocol (SLIP), X.25 and/or Link Access Procedure, Balanced (LAPB), Frame Relay, and ATM. This topic describes the different encapsulation protocols.

On each WAN connection, data is encapsulated into frames before crossing the WAN link. To ensure that the correct protocol is used, you will need to configure the appropriate Layer 2 encapsulation type. The choice of protocol depends on the WAN technology and the communicating equipment. Typical WAN protocols include the following:

HDLC: The Cisco default encapsulation type on point-to-point connections, dedicated links, and circuit-switched connections. It is used typically when communicating between two Cisco devices. It is a bit-oriented synchronous data-link layer protocol. (HDLC is covered in more detail later in this lesson.)

PPP: Provides router-to-router and host-to-network connections over synchronous and asynchronous circuits. PPP was designed to work with several network-layer protocols, such as IP. PPP also has built-in security mechanisms such as Password Authentication

Typical WAN Encapsulation Protocols:

Layer 2

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Frame Relay: Industry standard, switched data-link layer protocol that handles multiple VCs. It is a successor to X.25 that is streamlined to eliminate some of the time-consuming processes (such as error correction and flow control) that were employed in X.25 to compensate for older, less-reliable communication links.

ATM: The international standard for cell relay in which multiple service types (such as voice, video, or data) are conveyed in fixed-length (53-byte) cells. ATM, a cell-switched technology, uses fixed-length cells, which allow processing to occur in hardware, thereby reducing transit delays. ATM is designed to take advantage of high-speed transmission media such as T3, E3, and SONET.

Note SLIP, X.25, and ATM are not covered further here.

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Summary

This topic summarizes the key points discussed in this lesson.

References

For additional information, refer to these resources:

Cisco IOS Configuration Guides

Cisco IOS Command Reference Guides

Summary

• A WAN makes data connections across a broad geographic area so that information can be exchanged between distant sites.

• Some of the WAN connection types available are leased line, circuit-switched, and packet-switched.

• Cisco routers support the EIA/TIA-232, EIA/TIA-449, V.35, X.21, and EIA/TIA-530 standards for serial connections.

• To encapsulate data for crossing a WAN link, you can choose from a variety of Layer 2 protocols, including HDLC, PPP, SLIP, X.25/LAPB, Frame Relay, and ATM.