In IPTV testing and monitoring, several MPEG metrics are calculated and reported by Netrounds. This is done by the Test Agents inspecting the headers of the MPEG stream, including RTP headers.
MPEG loss: This is the MPEG packet loss calculated from the Continuity Count field (4 bits) in the MPEG transport stream header.
Values in the Continuity Count field are required to be sent in order (starting at 0, going up to 7 in increments of one, then wrapping around to 0 and beginning a new cycle). A continuity count error indicates that one of three possible errors has occurred:
- A continuity count value was skipped in the sequence of packets.
- Continuity count values arrived out of order.
- The same continuity count value arrived twice in a row.
Program Clock Reference (PCR) jitter: To enable a decoder to present synchronized content, a Program Clock Reference (PCR) is transmitted in the adaptation layer of the MPEG transport stream. Netrounds uses this timestamp field to calculate the PCR jitter (delay variation) for the received MPEG stream.
Program Allocation Table (PAT) errors: The Program Allocation Table (PAT) lists all programs available in the transport stream, where each individual program is identified by its PID and points to a PMT (see below).
According to the standards, a PAT should be received every half second on a multicast group. If no PAT is received within that interval, a PAT error is triggered.
Program Map Table (PMT) errors: The Program Map Table (PMT) contains information about the programs in the stream. There is one PMT for each program.
According to the standards, a PMT should be received every half second on a program. If no PMT is received within that interval, a PMT error is triggered.
Packet identifier (PID) errors: On regular audio/video streams, the standards stipulate that a frame should be received once every 5 seconds. If no frame is received for 5 seconds, Netrounds starts counting PID errors (one for every second during which no frame is received).
RTP jitter, loss and misorders: If the IPTV streams contain RTP headers, Netrounds will also calculate RTP jitter, loss, and misorderings, all of which are analogous to the corresponding metrics for IP. Whether or not the stream contains RTP headers depends on the encoder at the TV head-end.