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Implementing Basic DDR 141
ISDN Call Release
Any party in the network can release the call for whatever reason. Whether the release of the
call is intentional or accidental (that is, due to some type of failure in the network), the call is
torn down completely.
When either the calling or called party is ready to disconnect a call, that party issues a disconnect
(DISC) message. The disconnect is not negotiable. If necessary, the call can be re-established,
but once a disconnect is issued, the call comes down.
When a DISC is issued, it is acknowledged with a release message (RELEASED). The switch
forwards the RELEASED message, which should be followed by a Release Complete
(RELEASE COMPLETE) message. Figure 6-8 depicts the ISDN call release process.
Figure 6-8
ISDN Call Release
Implementing Basic DDR
Dial-on-demand routing (DDR) is a feature available on ISDN-capable Cisco routers. It was
created to enable users to save money on usage-based ISDN. Use-based ISDN occurs when
charges are assessed for every minute of ISDN circuit connect time.
Obviously, in a charge-by-the-minute scenario, the connection should be down during no or
low-volume traffic times. DDR provides that capability and offers a wide array of commands
and configuration variations. Many of those configuration options are covered in the remainder
of this chapter.
Calling
party
Release complete
Called
party
Disconnect
Provider switch network
Released
Disconnect
Release
Released
Release complete