IMS Engineer

About Telnyx

Telnyx is an industry leader thats not just imagining the future of global connectivitywere building it. From architecting and amplifying the reach of a private global multi-cloud IP network to bringing hyperlocal edge technology right to your fingertips through intuitive APIs were shaping a new era of seamless interconnection between people devices and applications.

Were driven by a desire to transform and modernize whats antiquated automate the manual and solve real-world problems through innovative connectivity solutions. As a testament to our success were proud to stand as a financially stable and profitable company. Our robust profitability allows us not only to invest in pioneering technologies but also to foster an environment of continuous learning and growth for our team.

Our collective vision is a world where borderless connectivity fuels limitless innovation. By joining us you can be part of laying the foundations for this interconnected future. Were currently seeking passionate individuals who are excited about the opportunity to contribute to an industry-shaping company while growing their own skills and careers.

Telnyx is productizing a carrier-grade IMS core on Kamailio. Youll design implement and operate P-/I-/S-CSCF functions at a global scalewith VoLTE expertise and the ability to modify Kamailios C codebase when needed.

What youll do

• Design & build: Own P-/I-/S-CSCF call flows; configure Kamailio modules (ims* dispatcher topos tm usrloc permissions); integrate HSS/UDM/UDR.
  
  
• Productize: Turn prototypes into supportable services with versioned configs CI/CD and observability.
  
  
• Performance & scale: Tune throughput dialog/state handling NAT traversal DNS/SRV TLS/mTLS; benchmark CPS/latency.
  
  
• Reliability: Architect HA/DR; lead load tests game days incident reviews.
  
  
• Security: Implement abuse/DoS controls (pike/htable/rate limiters) auth encryption and audit-grade logging.
  
  
• Upstream: Contribute fixes/patches and collaborate with the Kamailio community.
  
  
• On-call (shared): Keep the voice core healthy.
  
  

What youll bring (must-haves)

• VoLTE expertise: Hands-on IR.92 (voice/SMS) registration/attach flows SIP/SDP (AMR-WB/EVS) QoS/bearers via PCRF/PCF emergency calling multi-vendor interop.
  
  
• Core IMS/SIP: 5 years with SIP/IMS; strong grasp of 3GPP (TS 23.228 24.229 ) CSCF roles registration service routing.
  
  
• Kamailio mastery: Confident authoring routing logic; registrar/dialog/topology hiding; IMS modules in production.
  
  
• Software engineering to modify Kamailio (required):
  
  
• Proficient in C for high-performance network services (memory management concurrency lock-free/atomic patterns).
  
  
• Experience building and changing Kamailio core/modules (parsers transaction/dialog layers ims*) adding/adjusting AVPs/headers and writing new module logic.
  
  
• Tooling: gcc/clang make gdb valgrind/AddressSanitizer perf/flamegraph packet tools (pcap sngrep ngrep).
  
  
• Strong unit/functional testing habits; familiarity with Kamailio test approaches and CI.
  
  
• Comfortable proposing and landing upstream PRs engaging in code review and maintaining forks/patch sets.
  
  
• Systems & SRE: Linux networking DNS (NAPTR/SRV) TLS/mTLS observability (Prometheus/Grafana ELK/Loki/OpenTelemetry).
  
  
• Automation: Git workflows CI/CD Docker/Kubernetes IaC (Terraform/Helm) scripting (Python/Bash/Lua).
  
  
• Communication: Clear design docs and incident write-ups.
  
  

Nice to have

• FreeSWITCH/Asterisk; RTP/RTCP; media relays (rtpengine/rtpproxy); SBC concepts.
  
  
• Diameter (Cx/Sh/Gx) ENUM/NP; VoWiFi/VoNR; SRVCC/eSRVCC exposure.
  
  
• Prior upstream contributions to Kamailio or related SIP projects.
  
  
• Telecom fraud mitigation and signaling security patterns.
  
  

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