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Senior VoIP Engineer

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Senior VoIP Engineer in USA

  • Tin Can
  • Full time
  • Email
  • Seattle, WA

Responsibilities

  • Own Tin Can’s production SIP and media plane, including Kamailio, FreeSWITCH, and carrier trunking.
  • Review call-path changes and author SIP test scenarios that gate voice changes before release.
  • Write and maintain Kamailio routing logic, including dispatcher, registrar, usrloc, htable, DMQ replication, and TLS configuration.
  • Build FreeSWITCH dial plans and integrations using ESL, mod_xml_curl, Lua, and Sofia profiles.
  • Measure and operationalize call quality metrics including MOS, jitter, packet loss, and setup time.
  • Model and load-test concurrent calls, calls per second, and trunk capacity against peak demand.
  • Extend the SIP and media layer into new countries with market-specific codec and emergency-calling requirements.
  • Harden signaling and media using SIP over TLS, SRTP, rate limiting, toll-fraud prevention, and topology hiding.
  • Improve team fluency through documentation, runbooks, and technical reviews.

Requirements

  • 5+ years of experience building and operating real-time voice systems in production.
  • Hands-on depth with Kamailio and FreeSWITCH.
  • Strong knowledge of SIP and RTP, including location services, dialog state, transfers, Path routing, NAT traversal, and late-packet media behavior.
  • Ability to debug live production calls from packet captures and SIP traces through root cause and resolution.
  • Experience treating configuration as code and infrastructure as reproducible.
  • Fluency using AI for diagnosis, analysis, and testing.
  • Clear written and verbal communication skills and a collaborative, low-ego working style.
  • Preferred experience with rtpengine, Homer/HEP, SIPp regression suites, Prometheus exporters, STIR/SHAKEN, or carrier interconnect.
  • Additional preferred experience with WebRTC internals, including ICE, DTLS-SRTP, and TURN, and with bridging WebRTC to SIP.

Benefits

  • Opportunity to build technology intended to give children a safer, more analog way to connect.
  • End-to-end ownership of Tin Can’s voice call path and its technical direction.
  • Small, high-trust, mission-driven team with room to explore and challenge assumptions.

Salary: $175k - $195k/yr

Tin Can

Tin Can is a screen-free phone for kids that gives them the independence to call friends and family—without giving them a smartphone. Built like a modern landline, Tin Can connects over Wi-Fi and uses a simple mobile app for parents to control who can call in and out. There’s no browser, no app s...

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