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DDR (Dial-on-Demand Routing)

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DDR provides a way to link two sites over a public network and provide needed bandwidth by setting up additional lines as required. DDR is a feature of routers from Cisco and other vendors. It allows a device to establish a circuit-switched asynchronous modem connection, an ISDN digital connection, or Switched 56 connections to a remote location. Switched connections can provide secondary links that back up primary communication lines when they become overloaded or when they fail. Switched lines are ideal for handling peaks in traffic, fax transmissions, backup sessions, bulk e-mail transfers, and temporary remote office connections.

A Cisco router running the DDR utility issues a dial-up command to the connected DCE (data circuit-terminating equipment) when it receives packets destined for remote networks. The network administrator can designate which packets can initiate a dial-on-demand sequence. Cisco routers use the CCITT V.25 bis protocol to initiate calls on automatic calling devices. DDR provides an alternative to leased lines that can help managers when making decisions about adding bandwidth for remote links.

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