IMS Engineer (VoLTE/Kamailio)

TL;DR

IMS Engineer (VoLTE/Kamailio): Designing, implementing, and operating P-/I-/S-CSCF functions at a global scale with an accent on VoLTE expertise and the ability to modify Kamailio's C codebase. Focus on microservices architecture, solving complex concurrency challenges, and ensuring system reliability under heavy traffic.

Location: Remote from Dublin, Ireland; Amsterdam, Netherlands; or Krakow, Poland

Company

hirify.global is an industry leader building and modernizing global connectivity solutions with a focus on private, global, multi-cloud IP networks and hyperlocal edge technology.

What you will do

• Design and build P-/I-/S-CSCF call flows, configure Kamailio modules, and integrate HSS/UDM/UDR.
• Productize prototypes into supportable services with versioned configs, CI/CD, and observability.
• Tune performance for throughput, dialog/state handling, NAT traversal, DNS/SRV, and TLS/mTLS.
• Architect high availability/disaster recovery, lead load tests, game days, and incident reviews.
• Implement abuse/DoS controls, authentication, encryption, and audit-grade logging for security.
• Contribute fixes/patches and collaborate with the Kamailio community; participate in shared on-call duties.

Requirements

• VoLTE expertise with hands-on experience in IR.92 (voice/SMS), registration/attach flows, SIP/SDP, QoS/bearers via PCRF/PCF, emergency calling, and multi-vendor interop.
• 5+ years experience with SIP/IMS and a strong grasp of 3GPP standards (TS 23.228, 24.229, 29.xx), CSCF roles, registration, and service routing.
• Kamailio mastery, including confident authoring of kamailio.cfg routing logic, registrar/dialog/topology hiding, and IMS modules in production.
• Proficiency in C for high-performance network services, with experience building and changing Kamailio core/modules, adding/adjusting AVPs/headers, and writing new module logic.
• Experience with Linux networking, DNS (NAPTR/SRV), TLS/mTLS, and observability tools (Prometheus/Grafana, ELK/Loki/OpenTelemetry).
• Strong automation skills using Git workflows, CI/CD, Docker/Kubernetes, IaC (Terraform/Helm), and scripting (Python/Bash/Lua).

Nice to have

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

Culture & Benefits

• Work for a financially stable and profitable company.
• Opportunities for continuous learning and career growth.
• Contribute to an industry-shaping company building borderless connectivity.
• Be part of a team envisioning a world where borderless connectivity fuels limitless innovation.