IMS Engineer

Telnyx is productizing a carrier-grade IMS core on Kamailio. You’ll design implement and operate P-/I-/S-CSCF functions at a global scale— with VoLTE expertise and the ability to modify Kamailio’s C codebase when needed .

What you’ll 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 you’ll 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 29.xx) CSCF roles registration service routing.

• Kamailio mastery: Confident authoring kamailio.cfg 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.

#LI-REMOTE #LI-KG1