Avaya Configuring Dial Services Uživatelský manuál stáhnout pdf (Strana 144)

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Configuring Dial Services

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308621-14.00 Rev 00

Standby Circuits

The expansion of enterprise networks to remote branch sites requires reliable

access to these sites. Therefore, it is important to have more than one connection

to the remote sites in case a primary connection fails.

To provide additional connections, you can use standby circuits. A standby circuit

is a special type of demand circuit that gives the router another path to the

destination. The destination can be a different interface at the primary circuit’s

original site, or an entirely different site.

Standby circuits support asynchronous (RS-449), synchronous (RS-449, V.35,

RS-422, and X.21), and ISDN interfaces. PPP is the only data link layer protocol

that you can configure over a standby circuit; you cannot use frame relay.

Comparing Standby Circuits with Dial Backup Circuits

Both standby circuits and dial backup circuits can back up failed primary circuits;

however, they differ in the following ways:

• Each standby circuit has a unique configuration; it does not adopt the primary

circuit’s configuration. In contrast, most dial backup circuits inherit the

primary circuit’s configuration.

This unique standby configuration offers flexibility when setting up other

paths to remote sites. For example, you may want the standby circuit to have a

different destination than the primary circuit, or you may enable compression

on the standby circuit but not on the associated primary circuit.

• Standby circuits let you control when the router switches from the standby

circuit back to the recovered primary circuit. You do not have this option with

dial backup circuits. In dial backup configurations, the router terminates the

backup circuit when the primary circuit recovers. For example, to ensure the

stability of a recovered primary circuit before bringing down the standby

circuit, you can delay the return of data to the primary circuit.

• Standby circuits support PPP multilink.

You can assign a bandwidth-on-demand pool to the hot standby circuit to

relieve congestion. Bandwidth-on-demand connections use PPP multilink,

which lets the router use multiple dial-up lines simultaneously to transmit

data. You do not have this option with dial backup circuits.

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