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packet capture guide

PCAP Troubleshooting Checklist

A packet capture is strongest when you know what question you are asking. Start with time, direction, protocol, and the closest capture point to the reported issue.

Start With Scope

  • Confirm the capture time overlaps the problem.
  • Identify client, server, PBX, SBC, or gateway addresses.
  • Check whether the capture point can see both directions.
  • Filter down before drawing conclusions.

For SIP And RTP

  • Read the SIP ladder before judging media.
  • Check SDP connection addresses and ports.
  • Compare RTP packet counts in both directions.
  • Review sequence gaps, jitter, duplicates, and out-of-order packets.

For DNS And TCP

  • Look for DNS response codes and answer records.
  • Check TCP handshakes, resets, and retransmissions.
  • Separate server delay from network packet loss.