Service Assurance Agent (SAA) is a network congestion analysis mechanism that provides delay, jitter, and packet loss information
for the configured IP addresses. SAA is based on a client/server protocol defined on the User Datagram Protocol (UDP). UDP
is a connectionless transport layer protocol in the IP protocol stack. UDP is a simple protocol that exchanges datagrams without
acknowledgments or guaranteed delivery, requiring that error processing and retransmission be handled by other protocols.
The SAA probe packets go out on randomly selected ports from the top end of the audio UDP port range.
The information that the SAA probes gather is used to calculate the ICPIF or delay/loss values that are stored in a fallback
cache, where they remain until the cache ages out or overflows. Until an entry ages out, probes are sent periodically for
that particular destination. This time interval is user configurable.
With this feature enhancement, you can also configure codes that indicate the cause of the network rejection; for example,
packets that are lost or that take too long to be transmitted. A default cause code of 49 displays the message qos-unavail , which means Quality of Service is unavailable.
The Cisco SAA functionality in Cisco IOS software was formerly known as Response Time Reporter (RTR). In the How to Configure PSTN Fallback section, note that the command-line interface still uses the keyword rtr for configuring RTR probes, which are now actually the SAA probes.