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Senior VoIP Engineer

Tin Can· Technology
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SeattleFull-timePosted 2mo ago

About the role

Senior VoIP Engineer to own the SIP and media plane used for all Tin Can calls (Kamailio, FreeSWITCH) on AWS. Hands-on role focusing on routing, dial plans, testing, and reliability of voice communication across carrier trunks and device fleet.

Responsibilities

  • Own our production SIP and media plane end to end — Kamailio, FreeSWITCH, and the carrier trunking behind every call to the outside world
  • Be the reviewer of record for call-path changes, and author the SIP test scenarios that gate a voice change before it ships
  • Write and maintain the Kamailio routing logic behind every call — dispatcher, registrar and usrloc tuning, htable, DMQ replication, TLS
  • Build FreeSWITCH dialplans and integrations (ESL, mod_xml_curl, Lua, Sofia profiles), and keep call state correct across boxes, transfers, and NAT
  • Produce the packet-level truth about call quality — MOS, jitter, packet loss, setup time — and make it trustworthy enough to alarm on
  • Model and load-test call capacity — concurrent calls, calls per second, trunk headroom — against our holiday peak, using scenarios built on real call flows
  • Extend the SIP and media layer into new countries as we expand, where codec support and emergency-calling rules change market to market
  • Harden the signaling and media path: SIP over TLS, SRTP, rate limiting, toll-fraud prevention, and topology hiding
  • Raise the team’s voice fluency: the documentation, runbooks, and reviews that make this stack legible to every engineer here

Qualifications

  • 5+ years building and operating real-time voice systems in production, with hands-on Kamailio and FreeSWITCH depth
  • You can hold your own on SIP and RTP: location services, dialog state, transfers, Path routing, NAT traversal, and what happens to media when a packet arrives late
  • You’ve debugged live production calls from a packet capture and a SIP trace to root cause
  • You treat config as code and infrastructure as reproducible
  • Fluency using AI as a multiplier across diagnosis, analysis, and testing
  • A clear communicator who writes things down
  • A collaborative, low-ego approach — everyone here sweeps the floor
  • Bonus: rtpengine, Homer/HEP for capture and call-leg correlation, SIPp regression suites, Prometheus exporters for the voice plane, or STIR/SHAKEN and carrier interconnect
  • Extra bonus: WebRTC internals (ICE, DTLS-SRTP, TURN) and bridging WebRTC to SIP

Benefits

  • Full benefits package
  • Offers Equity
Last updated Aug 26, 2026. Interested? Apply on the company site.
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About Tin Can

The super-magical Wi-Fi landline for kids

The super-magical Wi-Fi landline for kids. No screens, no texting, no strangers — just real conversation with Grandma, besties, and contacts you approve. Plug in, twirl that cord, and time-travel to pure voice fun.

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