IMS Engineer

Telnyx is an industry leader building the future of global connectivity. We're seeking an IMS Engineer to 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.

Requirements

• 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.