Senior VoIP Engineer — SIP & Media Plane Lead

Tin Can; Seattle (WA); On-site; USD 140,000 - 190,000; Full time

Job summary

Tin Can is building a safer, screen-free world for kids, and we’re hiring a Senior VoIP Engineer to own the SIP and media plane that carries every call. You’ll work with Kamailio, FreeSWITCH, and AWS, shaping routing, dialplans, and reliability across regions.

You’ll debug live calls, write tests, and contribute to scalable voice architecture while collaborating with a small, high-trust team.

Qualifications

• 5+ years building and operating real-time voice systems in production.
• Hands-on Kamailio and FreeSWITCH depth.
• Experience with SIP, RTP, NAT traversal, and call routing.
• Ability to debug live production calls from a packet capture and a SIP trace.
• Treat config as code and infrastructure as reproducible.
• Fluency using AI as a multiplier across diagnosis, analysis, and testing.
• Clear communicator who writes things down.

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

Skills

Kamailio

FreeSWITCH

SIP

RTP

Call routing

Packet capture

Infrastructure as code

AI for diagnosis

Tools

rtpengine

Homer/HEP

SIPp

Prometheus exporters

Job description

Tin Can is building a safer, screen-free world for kids, and we’re hiring a Senior VoIP Engineer to own the SIP and media plane that carries every call. You’ll work with Kamailio, FreeSWITCH, and AWS, shaping routing, dialplans, and reliability across regions.

You’ll debug live calls, write tests, and contribute to scalable voice architecture while collaborating with a small, high-trust team.