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WebRTC Metrics

A comprehensive overview of WebRTC statistics, derived indicators, and observable signals, to better understand call quality, connectivity, and user experience in rtcStats

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inboundaudiovideonetwork

Packets out of order

NACK requests were sent while no packets were reported as lost. This suggests packets were reordered in the network.

Description

This observation detects when the receiver requests retransmissions via NACK (Negative ACKnowledgement) while the packetsLost metric reports zero packets lost for the same time interval.

When does it trigger?

When packets arrive out of order, the receiver may send NACK requests to ask for retransmission of sequence numbers it hasn't received yet. However, if those packets eventually arrive (just later), they are not counted as lost. This pattern suggests:

  • Network paths: Packets take different network paths and arrive out of sequence.
  • Buffering equipment: Buffers in intermediate network equipment (routers, switches, or firewalls) can temporarily store packets and cause reordering.
  • Network instability: Fluctuations in network conditions can also impact packet ordering.

Interpretation

A high number of out-of-order packets can be a sign that something is wrong in the network.

From a quality perspective, this phenomenon triggers a large number of retransmissions, increasing network pressure, and slows down the media pipeline while the receiver waits for missing packets.

See also