VoIP packet-capture methodology

Capture where the question is observable

A normal switch port does not show all other ports' unicast traffic. Use an authorized endpoint capture, switch mirror, network TAP or supported virtual capture path. For a border or relaying-PBX problem, paired observations on the relevant sides can reveal where addresses change or packets disappear. Record which direction each point can see; inside, outside, PBX and phone are locations, not media directions.

Confirm mirror direction and capacity. An overloaded mirror destination can drop copies even when production packets arrive successfully, and host offload can create checksum or segmentation artifacts not present on the wire. A capture gap is evidence about the capture until corroborated by another vantage point, interface counter or endpoint statistic.

Compare observations on both sides of a boundary

Set scope before starting

Record the authorized test endpoints, incident window, expected signaling transport and likely topology before starting. A SIP-port-only capture filter can omit RTP, SRTP and signaling on another port. A host-only filter can miss direct media between endpoints. Begin broad enough to retain the complete call, then use display filters after collection; a display filter does not recover packets excluded at capture time.

Use synchronized clocks, a bounded duration and a rotating or size-limited output. Leave enough packet data for the intended decoder; truncated packets can prevent SDP or RTP interpretation. Record the interface, filter, snap length, file format, tool version and capture-drop counters with the file. Wireshark's pcapng format may be required when collecting multiple interfaces.

Correlate signaling and media

Preserve one exact dialog and match packets by Call-ID, tags, branches and content while allowing for NAT and back-to-back user agent transformations. Read the final SDP offer and answer on every call leg, then compare advertised receive addresses with observed packet sources and destinations. For RTP, separate streams by address, port, SSRC and payload mapping; inspect sequence progression and timestamps rather than treating a packet count as audio proof. Wireshark's VoIP Calls, RTP Streams and Stream Analysis views organize captured evidence but do not validate the endpoint's playout or microphone.

Keep encryption and absence claims bounded

SRTP is designed to add confidentiality, authentication and replay protection. A capture without the applicable keying context can still show useful network and timing metadata, but payload playback or decryption is not an expected acceptance step. Do not weaken the production security policy just to make a trace readable.

If an expected stream is absent, state not observed at this capture point rather than not sent until the interface, mirror direction, filter, dropped-packet counters and actual direct-media or relay path have been checked at a second point.

Protect and close the evidence

Stop the capture after the controlled test, record the incident time range and secure the original. SIP headers, SDP, numbers, addresses, credentials and media can be sensitive even when some transport is encrypted. Share only an access-controlled, minimally sufficient redacted extract, preserving an integrity hash or immutable original when the incident process requires it. Document what each vantage point could not see before using the capture to justify a configuration change.

Validate a dialplan header against one bounded response

The PJSIP response-header diagnostic correlates the function result with one sanitized 200 response by Call-ID and CSeq before changing dialplan ownership.

Correlate stored contact evidence with one signaling exchange

The PJSIP AoR/contact diagnostic compares the stored URI and lifecycle with bounded REGISTER, OPTIONS or INVITE evidence while keeping each transaction distinct.

Correlate endpoint policy with the exact SIP session

The PJSIP endpoint diagnostic compares loaded fields with bounded identification, SIP and SDP evidence on the same channel and Call-ID.

Distinguish RFC 4733, SIP INFO and in-band evidence

Use the PJSIP DTMF override diagnostic to compare the runtime mode with the exact SDP, RTP event, INFO request or audio observation on the same leg.

Keep SIP transfer signaling beside ARI and bridge evidence

Use the Asterisk transfer diagnostic to align REFER, 202, NOTIFY and new-dialog messages with the matching ChannelTransfer event and bridge actions.

Compare From placement at Asterisk and the next hop

Use the PJSIP_HEADER_PARAM diagnostic to distinguish dialplan output from SBC or provider rewriting.

Use one bounded capture for the NOTIFY transaction

Follow the Asterisk PJSIP NOTIFY diagnostic to preserve request URI, Event, content type, body boundary and response before moving to device evidence.

Capture both phases of a forced re-registration

Use the Asterisk registration-control diagnostic to preserve any unregister exchange and the later registration attempt instead of sampling only one packet.

Do not use an encrypted payload as peer-identity proof

For a Linphone security symptom, preserve sanitized SDP and transport evidence but keep it separate from ZRTP SAS verification. The Linphone encryption diagnostic treats capture visibility, negotiated media protection and authenticated peer identity as different states and warns against exposing SDES key material.

Compare Asterisk output with intermediary header policy

Use the PJSIP inheritable-header diagnostic to distinguish source-channel inheritance, duplicate dialplan stores and later SBC or carrier rewriting.

Capture the complete in-dialog offer-answer exchange

Use the Asterisk session-refresh diagnostic to compare request and response SDP with both RTP directions before and after the transaction.

Validate one inventory against the bounded INVITE

The PJSIP header-list diagnostic correlates Asterisk output with one sanitized request by Call-ID, CSeq and channel before interpreting missing names.

Capture one bounded hold and resume exchange

The PJSIP hold diagnostic correlates channel state, re-INVITE, offer-answer direction, RTP owner and audible result without treating one packet as the whole call.

Correlate Linphone ICE state with the captured media tuple

For a Linphone traversal failure, preserve sanitized candidate types, checklist state and the selected pair, then compare them with packet source and destination and media counters. The focused diagnostic warns against exposing ICE passwords, TURN credentials or unnecessary payloads.

Capture both sides when a PJSIP rejection appears rewritten

The PJSIPHangup diagnostic keeps the Asterisk-side final response, intermediary behavior and caller-side result distinct; a translated cause alone cannot prove the wire code.

Match PJSIP channel context to the same wire leg

The focused diagnostic compares Call-ID, tags, URI meaning, transport security and socket direction with the corresponding SIP exchange.

Choose a capture point from the active media topology

The PJSIP RTP context workflow explains why an Asterisk-host capture may not see endpoint-to-endpoint packets during remote native bridging.

Do not expect a phone-side SIP capture to contain the push hop

A Linphone background-call investigation needs adjacent proxy, platform, device and SIP evidence. The focused diagnostic uses timestamps and bounded identifiers to correlate them without exposing a full push token, credential or unnecessary payload.

Capture Request-URI, headers and body boundaries for MESSAGE

The Asterisk MessageSend diagnostic compares final routing and identity fields, full request size and response without publishing message content unnecessarily.

Correlate DIDWW packets with provider attempt records

A local capture can show which endpoint received an INVITE and what it returned, but DIDWW records each routing attempt separately. The DIDWW diagnostic joins packet evidence to routing_attempt, is_last_cdr, destination and disconnect fields.

Do not substitute internal frames for wire packets

Use the FRAME_TRACE diagnostic to correlate channel-internal frames with the exact signaling or media capture point without collapsing those evidence layers.

Join SessionTalk SIP evidence to the out-of-band push stages

A phone-side packet capture cannot by itself prove APNs or FCM delivery. The SessionTalk diagnostic correlates PBX, push-server, platform, device and direct-media evidence by timestamp without exposing full tokens or credentials.

Correlate one SIPStation attempt across signaling and media

The SIPStation inbound workflow uses one timestamped capture to distinguish absent delivery, rejected signaling, DID mismatch and RTP failure while keeping payload and customer data protected.

Choose the observation point before collecting SIP

The PJSIP History guide distinguishes messages retained inside the Asterisk PJSIP stack from packets observed on one network interface.

Capture only the VoIPstudio failure interval

The VoIPstudio Desktop diagnostic narrows evidence to one application session, endpoint record, call identifier, offer and answer, and RTP interval. Credentials, customer numbers and audio remain sensitive, and product encryption claims are not represented as end-to-end capture results.

Capture one VoIP Much registration and failed call interval

The VoIP Much workflow correlates one REGISTER exchange, INVITE, response, SDP and RTP interval while keeping credentials and personal numbers redacted.

Capture one VoIPline transaction without exposing identity data

The VoIPline workflow correlates registration or diversion, INVITE, response, SDP and RTP while redacting credentials and personal numbers.

Protect Webex diagnostics and trace exports

The Webex App workflow correlates a narrow call interval with local and administrator evidence while treating exported diagnostic ZIPs as confidential network data.

Capture the exact Voip Unlimited inbound attempt

The Voip Unlimited workflow correlates the provider log, edge packet, Request-URI, endpoint identity, response, route and media while protecting credentials and caller data.

Correlate the SignalWire log with one bounded SIP and media trace

The SignalWire workflow preserves provider resource IDs, edge receipt, SIP result, SDP and both media directions while redacting secrets and personal data.

Correlate a Telnyx route with the observed provider edge

Capture the selected region, current DNS or voice.json evidence, packet source, request, response and next attempt. The Telnyx diagnostic preserves the current first-party Canada-address disagreement instead of silently choosing one list.

Correlate each Bandwidth route attempt with the packet evidence

Capture the number, route priority, endpoint target, provider source, request, response or timeout and any later attempt. The Bandwidth diagnostic avoids inventing undocumented failover triggers.

Correlate the Voipfone attempt with number and divert state

Pair packet evidence with the dialed number, effective portal route, enabled divert, provider call identifier and first PBX match. The Voipfone diagnostic supplies the bounded sequence.

Correlate a VoIP.ms capture with DID and POP state

Pair packet evidence with the dialed DID, primary route, POP hostname, registration target, delivered number form and failover state. The VoIP.ms diagnostic supplies the sequence.

Correlate each Twilio origination attempt across the edge

Pair the capture with the number, Trunk SID, OriginationUrl SID, priority, weight, selected edge, response and any next attempt using the Twilio diagnostic.

Join Plivo and customer captures by call identity

Use the call UUID, SIP Call-ID, timestamps, trunk ID, URI and hangup evidence to align provider and customer views with the Plivo inbound diagnostic.

Join Vonage and customer evidence by call identity

Use timestamps, SIP Call-ID, selected URI, transport and PBX result to align provider and customer views with the Vonage inbound diagnostic.

Correlate packets and security events without collapsing clocks

Use exact host, interface and timezone evidence when comparing a packet capture with the Asterisk security-event pipeline.

Correlate each Voxtelesys destination attempt

Pair packet evidence with the DID, route profile, destination priority, registration Contact or Customer IP, provider result and any later Transfer. The Voxtelesys diagnostic provides the sequence.

Correlate Amazon Chime routing with the customer-edge trace

Pair AWS call and connector identifiers with the selected origination host, edge receipt, Request-URI, PBX match and media. The diagnostic supplies the evidence sequence.

Correlate the didlogic number destination with the captured INVITE

Use the didlogic diagnostic to connect the purchased-number target, provider attempt, edge packet, Asterisk match, answer and RTP.

A missing Callcentric INVITE may be provider-side precedence

Pair a bounded capture with the DID Forward and Call Treatment export. The Callcentric diagnostic distinguishes provider forwarding from customer-edge loss.

Capture Anveo Direct signaling and direct RTP separately

Pair the DID and URI export with bounded SIP and RTP evidence. The Anveo Direct diagnostic preserves primary and backup attempts, SDP and observed carrier-media endpoints.

Correlate CarrierX object state with packet evidence

Export the effective group and trunks, then pair each provider attempt with bounded edge capture. The diagnostic preserves responses, OPTIONS probes, PBX handling and RTP separately.

Correlate AVOXI portal and edge evidence

Retain the number rule, URI, data center and terminal list, then pair each provider attempt with a bounded edge capture. The diagnostic separates response, PBX and media results.

Pair Easybell portal state with edge evidence

Retain the selected mode, stored address order or FQDN and provider attempt, then pair it with a bounded edge capture. The diagnostic separates PBX and media results.

Correlate SIP.US control state with one call

Capture the provider gateway, selected trunk, customer-edge packet, PBX result and media only after preserving Forward, Backup and identity mode. The diagnostic provides the evidence order.

Pair Flowroute signaling with the negotiated Direct Media ports

Use one Call-ID to join provider edge, route result, SDP, SSRC and packet direction. The Flowroute diagnostic keeps signaling success separate from audio.

Correlate one Bulk Solutions provider attempt with the PBX result

Use the Bulk Solutions diagnostic to join portal assignment, DNS, customer-edge packet, PJSIP match, response, SDP and RTP.

Correlate one Yay.com attempt across signaling and media

Use the Yay.com diagnostic to join number assignment, DNS, customer-edge request, PBX result, SDP and both media directions.

Correlate one ClearlyIP attempt from Location to destination

Use the ClearlyIP diagnostic to join number routing, registration, provider attempt, edge receipt, PBX response and media.

Correlate one Simwood inbound attempt end to end

Use the Simwood diagnostic to join provider evidence, edge receipt, PBX response, answer and media.

Correlate Sinch with call ID and UTC time

The Sinch diagnostic joins callback or CDR evidence to edge receipt, PBX response and media.

Capture one SIPTRUNK attempt from REGISTER through RTP

Use the SIPTRUNK diagnostic to correlate provider evidence, SIP results, SDP and both media directions.

Capture one bounded Blink REGISTER transaction

The Blink registration diagnostic joins client logs, DNS, packet direction, response class and retry timing.