Twilio posts packet captures (.pcap files) for calls placed and received with Elastic SIP Trunking, and SIP Domains. This guide will walk you through viewing these packet captures for your calls.
Download Twilio SIP Call Packet Captures
- Access the Call Logs page in Console.
- Navigate to and click the desired SIP call.
- Click the "SIP PCAP LOG" Download link.
View Packet Captures
Once downloaded, your packet capture file can be examined with software that supports .pcap files. Some examples include Wireshark, tcpdump, and more.
Outbound Calls (SIP Termination): Your pcap should show a SIP
INVITE from your SIP infrastructure (PBX, SBC, Proxy, etc.) or SIP phone IP address to Twilio. One of Twilio's SIP signaling IPs should respond back. A successfully connected call should generate a
200 OK response.
Incoming Calls (SIP Origination): Your pcap hsould show a SIP
INVITE from one of Twilio's SIP signaling IPs. Your SIP infrastructure (PBX, SBC, Proxy, etc.) or SIP phone IP should respond back. A successfully connected call should generate a
200 OK response.
For a more in-depth explanation of how SIP connections work, please see the following resources:
- SIP Spec (RFC3261): Overview of operation (ietf.org)
- Session Initiation Protocol: SIP Messages (wikipedia.org)
Common Response Codes
The following table contains common SIP response codes for calls that do not complete.
Proxy Authentication Required
|The request requires user authentication.||These responses should be automatically responded to with an ACK and another INVITE that includes the required credentials. If not, verify your SIP Trunk or Domain credentials are correct.|
|The request can't be fulfilled.||Request is valid, but the destination may have rejected or blocked the incoming call. Have the callee check their side to make sure calls aren't blocked.|
|The destination doesn't exist, or can't be found.||The destination number may not be valid, or not in service. Double check the destination number.|
|The destination is currently unavailable.||The destination number is not answering, or unable to answer. They may be out of service, roaming, or not accepting calls. Often seen when calling wireless phones that don't answer and don't have voicemail.|
|The destination is busy.||The destination number is returning a busy signal. Try again later.|
Additional information on SIP response codes can be found at the following resources: