Client-Side SIP Trace Decoder

What the decoder reads

The parser reads the request or response start line, Via, From, To, Contact, Call-ID, CSeq, P-Asserted-Identity, Reason, User-Agent or Server, Content-Type, Identity presence and SDP connection/media lines. It does not transmit the pasted value and does not use localStorage or sessionStorage.

Important limitations

This utility does not validate an Identity signature, reconstruct every folded header, decrypt TLS or decide which party is commercially responsible. Confirm findings with the original capture and the system that emitted the message.

Related engineering resources

What the decoder can and cannot establish

The decoder extracts start line, Via, From, To, Contact, Call-ID, CSeq, P-Asserted-Identity, Reason/Q.850, User-Agent or Server, content type, SDP connection/media fields and Identity presence. It can show that a field exists and help correlate a sanitized message. It cannot validate digest credentials, determine the owner of an internal policy, verify a PASSporT signature or prove that an advertised media address was reachable.

Before pasting, remove the Authorization header, replace real numbers with +12025550123, replace hosts with example domains, replace addresses with RFC documentation ranges and redact the full Identity token. Keep Call-ID structure only when it is synthetic; real identifiers can correlate customer activity. Do not paste decrypted TLS traffic from a production call into an untrusted workstation.

A detected 403 should lead to the hop-attribution guide. Detected SDP should lead to the 488 and NAT/RTP guides. Missing Identity is neutral until the applicable trust and policy context is established. The decoder deliberately makes no remote lookup and stores no history.

Use the result to create an evidence worksheet, then verify it against the protected original. Parser output can be incomplete when a trace is truncated, folded unusually or contains multiple messages. The original packet order and capture boundary remain authoritative.

Verify parsed fields against packet order

Check that the pasted text contains one complete message or clearly ordered messages. Header folding, compact SIP header forms, malformed packets and truncation can affect extraction. Compare Call-ID and CSeq in the decoder result with the protected original, then identify whether the message was transmitted or received at the capture point. Direction cannot be derived reliably from header text alone.

If SDP is present, inspect whether the connection line is session-level or media-level and whether later re-INVITEs supersede it. If Identity is present, use an authorized verifier; the decoder intentionally reports presence without fetching a certificate or validating a signature. Clear the text area after use.

Operational assurance

Because processing is client-side, closing or refreshing the page clears the visible input, but browser extensions, clipboard history and screen capture remain outside the tool’s control. Use a managed workstation for operational evidence. Validate every extracted field against the source line before escalation. If several SIP messages were pasted together, parse them separately when ordering or direction matters. The decoder never sends a probe, verifies a remote server or stores a case identifier.

Limitations

Parsing is intentionally deterministic and limited. A malformed line may be displayed without correction, and encrypted network packets must first be inspected in an authorized endpoint log. Do not paste binary pcap data. Export only a sanitized text message containing the headers and SDP required for the question. When a header occurs multiple times, verify the applicable topmost or dialog value in the original protocol context.

Close the triage safely

Copy only the sanitized field summary into the case record, clear the input and keep the protected original in its authorized location. Document parser limitations when a message was incomplete or nonstandard.