SMPP, SIP & USSD, from the field
Answer-first troubleshooting: the errors every integrator hits, with the causes and fixes — and a link to the tool that shows you the problem.
The first articles are in draft and publishing soon. Previews below.
Drafts in progress
SMPP bind failed: ESME_RBINDFAIL, ESME_RINVPASWD and connection refused
The first wall every SMPP integrator hits. A checklist for diagnosing bind failures — system_id, password, interface_version, IP whitelisting and TLS — with links to the PDU decoder.
Handling ESME_RTHROTTLED: SMPP throttling, window size and backoff
Ops-grade guidance on SMPP throttling — TPS negotiation, window size tuning, retry/backoff patterns and queue design so ESME_RTHROTTLED stops costing you throughput.
Why your SMS is garbled or split: GSM 7-bit, UCS-2 and the DCS byte
Accented characters, emoji and unexpected message splits explained — GSM 03.38 septets, when a message drops to UCS-2, and how the data_coding (DCS) byte decides it all.
SIP 403 Forbidden: causes and per-scenario triage
A 403 on a SIP call or registration is a refusal, not a challenge. Triage the real causes — auth-user mismatch, ACLs, from-user spoofing checks and fraud blocks — with the message analyzer.
One-way audio in SIP: NAT, SDP and the RTP media path
One-way or no audio after the call connects is almost always a media-path/NAT problem, not signalling. How private IPs in SDP c= lines break RTP, and how to debug the media path.