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A customer contacted me with an inbound call issue. Inbound calls were taking at least 30 seconds to connect, and some would not connect at all. While I've experienced call delays before, the root cause was different each time I investigated. Since the issue was happening so frequently, I took a SIP trace from their Audio Codes Gateway. I noticed the following pattern in the SIP trace: INVITE SIP 183 INVITE SIP 183 CANCEL 200 OK If everything was working correctly, *I should* see the SIP 183 answered with a '200 OK' rather than an additional SIP 183. My initial thought was, "Why isn't the carrier answering my 183 message?" I spoke with an engineer from the carrier (AT&T) and he provided logs from his end showing they were, in fact, answering my SIP 183. The customer side, however, was not sending the SIP 200 back to them. What's going on here? The carrier's log proved they weren't causing the problem. The other time I've exper...
