Senior VoIP Engineer

Newfund; Seattle (WA); On-site; USD 175,000 - 195,000; Full time

Job summary

Tin Can is hiring a Senior VoIP Engineer to own the SIP and media plane that carries every call. You will manage Kamailio and FreeSWITCH deployments on AWS, implement dialplans, and ensure high-quality voice paths across carrier trunks and devices.

You’ll work hands-on with routing, tracing, and test scenarios, expanding to new markets while hardening TLS, SRTP, and call-security controls. Join a small, mission-driven team focused on safe, screen-free family communication.

Qualifications

• 5+ years building and operating real-time voice systems in production.
• Hands-on Kamailio and FreeSWITCH depth and SIP/RTP expertise.
• Experience debugging live calls from packet captures and SIP traces.

Responsibilities

• Own the production SIP and media plane end to end — Kamailio, FreeSWITCH, and carrier trunking.
• Review call-path changes and author SIP test scenarios before changes ship.
• Write and maintain Kamailio routing logic (dispatcher, registrar, usrloc, TLS).
• Build FreeSWITCH dialplans and integrations (ESL, mod_xml_curl, Lua).
• Provide packet-level call quality metrics (MOS, jitter, packet loss) and alert on issues.
• Model and load-test call capacity against peak traffic using real call flows.
• Extend SIP and media layer as we expand to new countries with different rules.
• Harden signaling and media paths (TLS, SRTP, rate limiting, STIR/SHAKEN).
• Improve team docs, runbooks, and code reviews for the voice stack.

Skills

Kamailio

FreeSWITCH

SIP

RTP

Packet capture

Troubleshooting

Documentation

Tools

rtpengine

Homer/HEP

Prometheus exporters

SIPP

Job description

About Tin Can

Tin Can is building a safer, simpler way for kids to connect — without smartphones. We’re creating screen‑free, delightful devices and services that let families call the people who matter most, free from the noise of today’s digital world. We’re building a bold, authentic, nostalgic, and kinda quirky brand that resonates with folks who want something simpler & better for their kids than the tech‑infused lives we’re currently living (and who have a sense of humor about it). As we gear up to scale to thousands of families, we’re ready to bring on an engineer to help make it happen.

The Role

A call either connects or it doesn’t — there’s no partial credit when a kid picks up a Tin Can to reach Grandma, or to dial 911. We’re hiring a Senior VoIP Engineer to own the SIP and media plane that carries every one of those calls: how it routes, how it sounds, and how we know it works. It’s the first role dedicated entirely to that stack. Our production stack is Kamailio (SIP proxy and registrar) and FreeSWITCH (media and voicemail), running on AWS across carrier trunks and our own device fleet. This is a deeply hands‑on role: routing logic, dial plans, and packet captures every day. You’ll report to the Head of Engineering and own the call itself. You’ll set the direction for how the voice plane is designed and tuned and when a registration flaps at 3am, you’re the person who can go from a SIP trace to root cause and out the other side with a fix.

What You’ll Do

• 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

What We’re Looking For

• 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

Why Join Tin Can

• We’re building tech that protects childhood: We’re on a quest to give kids a more analog childhood — one with real conversations, real connection, and way less screen time. No doomscrolling, data mining, or dopamine traps — just a simpler, better way for kids to stay in touch. This is a rare opportunity to build something that truly matters.
• You’ll own the call path outright: This is the first role dedicated entirely to our voice stack — the systems that decide whether a kid’s call connects and how it sounds. You’ll set the direction for how calling works as we scale.
• Small, high‑trust team: Every company says “team,” but at Tin Can it means something different. We’re a small, mission‑driven group that genuinely has each other’s backs — professionally and personally. You’ll be joining a tight‑knit crew where your ideas and instincts matter from day one.
• Room to explore, not just execute: You’ll have the space to challenge assumptions, solve hard problems, and build systems that reflect our values of trust, simplicity, and care.

If you’re excited by the idea of owning the systems that carry a kid’s voice to the people who matter most, and making them so dependable that nobody has to think about them, we’d love to meet you.

Compensation Range: $175K - $195K