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Monitoring RTP and RTCP Traffic

To monitor Real-Time Transport Protocol (RTP) and Real-Time Control Protocol (RTCP) packets on media gates, the VPG uses RTP and RTCP application layer gateway (ALGs) that are attached to flows when the PGC installs media gates on the VPG.

The RTP ALG uses the sequence number of each RTP packet on that flow to record the number of lost packets. Each RTP packet contains a 16-bit sequence number field that is incremented for every packet sent. The starting sequence number is randomly selected.

The RTCP ALG monitors the Sender Report and Receiver Report packet types. For the sender, the ALG records the Synchronization Source (SSRC) value and the number of invalid packets, sender packets, and sender octets.

For the receiver, the RTCP ALG records monitors lost packets, the fraction of lost packets, and jitter. When the ALG tracks multiple receiver reports (that is, when a sender is listening to media from multiple sources), it tracks the statistics for up to four sources. When more than four sources are available, the ALG overwrites the statistics for the source with the oldest record.

Enabling Monitoring of RTP and RTCP Traffic

You can enable RTP and RTCP ALGs for twice NAT flows created when the PGC installs media gates on the VPG. The ALGs monitor packets on the gate and provide statistics.

You can enable these ALGs only for flows created by the VPG. You cannot enable them within standalone NAT rules.

Step-by-Step Procedure

You can choose to monitor either RTP or RTCP, or both. To enable monitoring of RTP and RTCP media flows:

Access the configuration of your VPG.[edit services pgcp] user@host#edit gateway vpg-1
Enable monitoring of both RTP and RTCP for media flows.[edit services pgcp gateway vpg-1] user@host#set monitor media
Enable monitoring of only RTP media flows.[edit services pgcp gateway vpg-1] user@host#set monitor media rtp
Enable monitoring of only RTCP media flows. [edit services pgcp gateway vpg-1] user@host#set monitor media rtcp

In operational mode, view statistics gathered for RTP and RTCP.

user@host> show services pgcp gates
gate-id 352187384065 statistics

Gate Statistics:
================
Output packets: 582
Input packets: 582
Dropped packets: 0
Lost RTP packets: 0

RTCP statistics:

SSRC           : 32270
Sender octets  : 7500
Sender packets : 375
Invalid packets: 9

RTCP Receiver statistics:

SSRC        Lost packets   Lost fraction         Jitter
13043                  0           0.000              0
16487                  0           0.000              0
5655                   0           0.000              0

. . .

Monitoring RTP and RTCP Traffic

Enabling Monitoring of RTP and RTCP Traffic

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