Cisco Cisco IOS Software Release 12.2(2)XA

PSTN fallback does not provide assurances that a VoIP call that proceeds over the IP network is 
protected from the effects of congestion. This is the function of the other Quality of Service (QoS) 
mechanisms such as IP Real-Time Transport Protocol (RTP) priority or low latency queuing (LLQ).

PSTN fallback includes the following features:

Offers flexibility to define the congestion thresholds based on the network.

Defines a threshold based on Calculated Planning Impairment Factor (ICPIF), which is derived 
as part of International Telecommunication Union (ITU) G.113. 

Defines a threshold based solely on packet delay and loss measurements.

Uses Response Time Reporter (RTR) probes to provide packet delay, jitter, and loss information for 
the relevant IP addresses. Based on the packet loss, delay, and jitter encountered by these probes, an 
ICPIF or delay and loss values are calculated.

Is supported by calls of any codec. Only G.729 and G.711 have accurately simulated probes. Calls 
of all other codecs are emulated by a G.711 probe.

For details, please see 
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122limit/122x/122xa/122
xa_2/ft_pfavb.htm.

The Cisco H.323 Scalability and Interoperability Enhancements feature upgrades the Cisco H.323 
Gatekeeper (GK) and Cisco H.323 Gateway to comply with H.323 Version 3. The enhancements in this 
release include:

Support for mandatory H.323 Version 3 elements in the gateway and GK, including:

multipleCalls

maintainConnection

alternateTransportAddresses 

useSpecifiedTransport 

Support for H.225 call signalling over UDP.

Address resolution using border elements (BE). 

Support for bandwidth request (BRQ) messages. 

Support for concurrent calls over a single H.225 call signalling channel. 

For details, please see 
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122limit/122x/122xa/122
xa_2/ft323sca.htm.