Cisco Cisco IOS Software Release 12.4(4)T

The IP SLAs RTP-based VoIP operation provides an enhanced capability to measure voice quality using 
DSP-based calculations to determine MOS scores. For customer scenarios where the destination gateway 
does not have DSP hardware, statistical information is gathered only from the DSP of the source 
gateway. In this case, the RTP data stream is looped back from the destination to the source gateway.

The statistics gathered by the IP SLAs RTP-based VoIP operation will vary depending on the type of 
DSP module (see 

 and 

Interarrival jitter 
(destination-to-source 
and 
source-to-destination)

Interarrival jitter is the mean deviation (smoothed absolute value) of the 
difference in packet spacing for a pair of packets.

The source-to-destination value is measured by sending RTP packets to the IP 
SLAs Responder. No values are obtained from the DSP for this measurement.

For more information about interarrival jitter, see RFC 3550 (RTP: A 
Transport Protocol for Real-Time Applications).

Estimated R factor 
(destination-to-source 
and 
source-to-destination)

Estimated transmission rating factor R.

This value is based on one-way transmission delay and standard default 
values. No values are obtained from the DSP to calculate the estimated 
transmission rating factor R.

For more information about the estimated R factor, see International 
Telecommunication Union Telecommunication Standardization Sector 
(ITU-T) Recommendation G.107 (The E-model, a computational model for 
use in transmission planning).

MOS-CQ 
(destination-to-source 
and 
source-to-destination)

Mean Opinion Score for Conversational Quality.

This value is obtained by conversion of the estimated R factor to Mean 
Opinion Score (MOS) using ITU-T Recommendation G.107 conversion 
tables.

The source-to-destination value is measured by sending RTP packets to the IP 
SLAs Responder. No values are obtained from the DSP for this measurement.

Round-trip time (RTT) 
latency

Round-trip time latency for an RTP packet to travel from the source to the 
destination and back to the source.

Packet loss 
(destination-to-source 
and 
source-to-destination)

Number of packets lost.

The source-to-destination value is measured by sending RTP packets to the IP 
SLAs Responder. No values are obtained from the DSP for this measurement.

Packets missing in 
action 
(source-to-destination)

Number of missing packets.

The source-to-destination value is measured by sending RTP packets to the IP 
SLAs Responder. No values are obtained from the DSP for this measurement.

One-way latency 
(destination-to-source 
and 
source-to-destination)

Average, minimum, and maximum latency values.

These values are measured by sending RTP packets to IP SLAs Responder. 
The RTP data stream is then looped back from the destination to the source 
gateway.