Cisco IOS IP SLA Responder is a Cisco IOS Software component whose functionality is to respond to Cisco IOS IP SLA request packets. The IP SLA source sends control packets before the operation starts to establish a connection to the responder. Once the control packet is acknowledged, test packets are sent to the responder. The responder inserts a time-stamp when it receives a packet and factors out the destination processing time and adds time-stamps to the sent packets. This feature allows the calculation of unidirectional packet loss, latency, and jitter measurements with the kind of accuracy that is not possible with ping or other dedicated probe testing. Reference: UDP Jitter measures the delay, delay variation (jitter), corruption, misordering and packet loss by generating periodic UDP traffic. This operation always requires IP SLA responder. The command to enable UDP Jitter Operation is "ip sla responder udp-echo {destination-ip-address} [destination-port]