Cisco 2650 - 2650 Router Specifications download pdf (Page 172)

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Cisco IOS Telephony Service, Version 2.02

Chapter 5 Command Reference

loopback-dn (ephone-dn)

The loopback-dn mechanism allows for call operations (such as call transfer and call forward) that are

invoked for the call segment on one side of the loopback-dn port pair to be isolated from the call segment

that is present on the opposite side of the loopback-dn port pair. This approach is useful when the

endpoint devices associated with the two different sides have mismatched call transfer and call

forwarding capabilities. The loopback-dn arrangement allows for call transfer and call forward requests

to be serviced on one side of the loopback-dn port pair by creating hairpin-routed calls when necessary.

The loopback-dn arrangement avoids the propagation of call transfer and call forward requests to

endpoint devices that do not support these functions.

The loopback-dn command provides options for controlling the called-number digits that are passed

through from the incoming side to the outgoing side. The available digits can be manipulated with the

forward, prefix, and suffix keywords.

The forward keyword defines the number of digits in the original called number to forward to the other

ephone-dn in the loopback-dn pair. The default is set to forward all digits. The forward keyword can be

used with any combination of the prefix and suffix keywords.

The prefix keyword defines a string of digits to add in front of the forwarded number.

The suffix keyword is most commonly used to add a terminating “#” (pound-sign) character to the end

of the forwarded number to indicate that no more digits should be expected. The pound-sign character

indicates to the call-routing mechanism that is processing the forwarded number that the forwarded

number is complete. Providing an explicit end-of-number character also avoids a situation in which the

call-processing mechanism waits for the interdigit timeout period to expire before routing the call

onward using the forwarded number.

Note The Cisco IOS command-line interface (CLI) requires that arguments with character strings that start

with the pound-sign (#) character be enclosed within quotation marks; for example, “#”.

The retry keyword is used to suppress a far-end busy indication on the outbound call segment. Instead

of returning a busy signal to the call originator (on the incoming call segment), a loopback-dn presents

alerting or ringing tone to the caller and then periodically retries the call to the final far-end destination

(on the outgoing call segment). This is not bidirectional. To prevent calls from being routed into the idle

outgoing side of the loopback-dn port pair during the idle interval that occurs between successive

outgoing call attempts, configure the outgoing side of the loopback-dn without a number so that there is

no number to match for the inbound call.

The auto-con keyword is used to configure a premature trigger for a connected state for an incoming

call segment while the outgoing call segment is still in the alerting state. This setup forces the voice path

to open for the incoming call segment and support the generation of in-band call progress tones for busy,

alerting, or ringback. The disadvantage of the auto-con keyword is premature opening of the voice path

during the alerting stage and also triggering of the beginning of billing for the call before the call has

been answered by the far end. These disadvantages should be considered carefully before you use the

auto-con keyword.

Examples The following example creates a loopback-dn configured with the forward and prefix keywords:

Router(config)# ephone-dn 7

Router(config-ephone-dn)# loopback-dn 15 forward 5 prefix 41

The following example creates a loopback-dn that appends the pound-sign (#) character to forwarded

numbers to indicate the end of the numbers:

Router(config)# ephone-dn 7

Router(config-ephone-dn)# loopback-dn 16 suffix “#”

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