Cisco 2650 - 2650 Router Specifications download pdf (Page 171)

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Cisco IOS Telephony Service, Version 2.02

Chapter 5 Command Reference

loopback-dn (ephone-dn)

Command History

Usage Guidelines The loopback-dn command is used to configure two ephone-dn virtual voice ports as

back-to-back-connected voice-port pairs. A call presented on one side of the loopback-dn pair is

reoriginated as a new call on the opposite side of the loopback-dn pair. The forward, prefix, and suffix

keywords can be used to manipulate the original called number that is presented to the incoming side of

the loopback-dn pair to generate a modified called number to use when reoriginating the call at the

opposite side of the loopback-dn pair. For loopback-dn configurations, you must always configure

ephone-dn virtual voice ports as cross-coupled pairs.

Note Use of loopback-dn configurations within a VoIP network should be restricted to resolving critical

network interoperability service problems that cannot otherwise be solved. Loopback-dn configurations

are intended to be used in VoIP network interworking situations in which the only other alternative would

be to make use of back-to-back-connected physical voice ports. Loopback-dn configurations emulate the

effect of a back-to-back physical voice-port arrangement without the expense of the physical voice-port

hardware. A disadvantage of loopback-dn configurations is that, because digital signal processors

(DSPs) are not involved in a loopback-dn arrangement, the configuration does not support interworking

or transcoding between calls that use different voice codecs. In many cases, the use of back-to-back

physical voice ports that do use DSPs to resolve VoIP network interworking issues is preferred, because

it introduces fewer restrictions in terms of supported codecs and call flows. Also, loopback-dns do not

support T.38 fax relay.

Note Cisco recommends that you create the basic ephone-dn configuration for both ephone-dn entries before

configuring the loopback-dn option under each ephone-dn. The loopback-dn mechanism should be used

only in situations where the voice call parameters for the calls on either side of the loopback-dn use

compatible configurations; for example, compatible voice codec and DTMF relay parameters.

Loopback-dn configurations should only be used for G.711 voice calls.

The loopback-dn arrangement allows an incoming telephone call to be terminated on one side of the

loopback-dn port pair and a new pass-through outgoing call to be originated on the other side of the

loopback-dn port pair. The loopback-dn port pair normally works with direct cross-coupling of their call

states; the alerting call state on the outbound call segment is associated with the ringing state on the

inbound call segment.

Release Modification

12.2(2)XT This command was introduced on the following platforms: Cisco 1750,

Cisco 1751, Cisco 2600 series, Cisco 3600 series, and

Cisco IAD2420 series.

12.2(2)XT3 The suffix keyword was added.

12.2(8)T This command was integrated into Cisco IOS Release 12.2(8)T and

implemented on the Cisco 3725 and Cisco 3745 routers. The auto-con

keyword was added.

12.2(8)T1 This command was implemented on the Cisco 2600-XM and Cisco 2691

routers.

12.2(11)T This command was integrated into Cisco IOS Release 12.2(11)T and

implemented on the Cisco 1760 routers. The suffix keyword was added.

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