Cisco Cisco IOS Software Release 12.2(2)XA
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Cisco IOS Release 12.2(2)XA
PSTN Fallback Enhancement
Feature History
This document describes an enhancement to the PSTN Fallback feature that is the call fallback
reject-cause-code command. This document includes the following sections:
reject-cause-code command. This document includes the following sections:
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Feature Overview
The PSTN Fallback feature monitors congestion in the IP network and redirects calls to the Public
Switched Telephone Network (PSTN) or rejects calls on the basis of network congestion. The fallback
subsystem has a network traffic cache that maintains the Calculated Planning Impairment Factor (ICPIF)
or delay/loss values for various destinations. Performance is improved because each new call to a
well-known destination does not have to wait on a probe to be admitted and the value is usually cached
from a previous call.
Switched Telephone Network (PSTN) or rejects calls on the basis of network congestion. The fallback
subsystem has a network traffic cache that maintains the Calculated Planning Impairment Factor (ICPIF)
or delay/loss values for various destinations. Performance is improved because each new call to a
well-known destination does not have to wait on a probe to be admitted and the value is usually cached
from a previous call.
ICPIF calculates an impairment factor for every piece of equipment along the voice path and then adds
them up to get the total impairment value. Refer to International Telecommunication Union (ITU)
standard G.113 for more information. The ITU assigns a value to the types of impairment, such as noise,
delay, and echo.
them up to get the total impairment value. Refer to International Telecommunication Union (ITU)
standard G.113 for more information. The ITU assigns a value to the types of impairment, such as noise,
delay, and echo.
The ICPIF method of determining the impairment value was introduced for compatibility with Cisco H.323
applications. Part of ICPIF includes a concept of Total Impairment Value that is a function of loss of
packets, delay of packets, and codecs used based on the round-trip reports from Service Assurance Agent
(SAA).
applications. Part of ICPIF includes a concept of Total Impairment Value that is a function of loss of
packets, delay of packets, and codecs used based on the round-trip reports from Service Assurance Agent
(SAA).
Release
Modification
12.1(3)T
The PSTN Fallback feature was introduced on Cisco 2600 series and
Cisco 3600 series routers and Cisco MC3810 multiservice concentrators.
Cisco 3600 series routers and Cisco MC3810 multiservice concentrators.
12.2(2)T
The call fallback command was introduced.
12.2(2)XA
The call fallback reject-cause-code command was introduced.