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
About the job
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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