Packet captures for VoIP troubleshooting
Use a small, repeatable packet-capture method to diagnose SIP failures, missing RTP, DTMF problems, and call-quality symptoms.
From the blog
VoIP Fundamentals
Clear explanations of VoIP, SIP, RTP, codecs, phone numbers and the technologies behind modern voice.
SIP trunking fundamentals: how business calls reach the carrier
Learn what a SIP trunk is, how a PBX connects to a carrier, and which signalling, media, numbering, and security checks matter.
RTP port ranges and media planning for VoIP
Plan RTP and RTCP port ranges, firewall rules, NAT behaviour, and concurrent call capacity without confusing signalling and media.
DTMF guide: how phone keypad tones work in VoIP
Understand in-band, RFC 2833 or RFC 4733, and SIP INFO DTMF methods, including when IVR keypad tones fail.
DNS and SRV records for VoIP
Learn how A, AAAA, NAPTR, and SRV records help phones and SIP systems find services, choose transports, and fail over.
VoIP protocol guide
Understand the roles of SIP, SDP, RTP, RTCP, TLS, SRTP, STUN, TURN, ICE, DNS, and related protocols in an IP call.
Voice codec guide
Compare common voice codecs by payload rate, speech bandwidth, interoperability, delay, and practical deployment considerations.
SIP response codes: a practical troubleshooting guide
Understand common SIP status codes, what they mean, and what to check when registration or call setup fails.
VoIP QoS: latency, jitter, packet loss, and capacity
Learn how delay, jitter, packet loss, and congestion affect voice calls, and use a practical checklist to improve call quality.
Networking layers for voice troubleshooting
Map common VoIP symptoms and evidence to the physical, data-link, network, transport, session, presentation, and application layers.
NAT and firewall troubleshooting for VoIP
Diagnose registration failures, one-way audio, and dropped calls caused by NAT, firewalls, and incorrect SIP or RTP address handling.
IP and networking cheat sheet
Use a compact reference for IP addressing, subnets, routing, DNS, ports, NAT, and network checks relevant to VoIP.