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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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inboundvideonetwork

Incoming video disrupted

Unusual number of NACK requests sent during the session for retransmitting video packets.

Description

Sending NACKs means the receiver is asking the sender to retransmit specific RTP sequence numbers - usually because packets are late or missing. When the number of NACK messages is large relative to how many media packets actually arrived, it usually means the network is frequently reordering packets, triggering retransmission requests that may resolve when late packets show up, or it reflects sustained loss/repair behavior. Either way, it stresses the link and the media pipeline.

When does it trigger?

When packets are disrupted and not received when expected, the receiver may send NACK requests to ask for retransmission of RTP packets with sequence numbers it hasn't received yet. However, if these packets eventually arrive (retransmission), 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