Mobile Core Engineer

About Telnyx Telnyx is an industry leader that's not just imagining the future of global connectivity—we're 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, we're shaping a new era of seamless interconnection between people, devices, and applications. We're driven by a desire to transform and modernize what's antiquated, automate the manual, and solve real-world problems through innovative connectivity solutions. As a testament to our success, we're 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. We're currently seeking passionate individuals who are excited about the opportunity to contribute to an industry-shaping company while growing their own skills and careers. About You You'll be part of the Core Wireless Squad — an 11-person team responsible for running and improving Telnyx's wireless EPC infrastructure. We operate a mobile core spread across multiple data centres with several roaming partners and a range of vendor platforms. The opportunity This is a hands-on operations role. You'll spend your time debugging real subscriber issues, working pcap traces, coordinating with roaming partners and vendors, and keeping the mobile core healthy. The work is deep protocol-level investigation combined with practical platform operations. The Role Subscriber & connectivity troubleshooting Investigate end-to-end attachment failures across S6a (Diameter), MAP (SS7), GTP-C, and GTP-UDecode pcap traces from DRA, STP, and GTP proxy capture points to isolate signalling failuresTrace individual IMSIs across protocols and partner networks to find where sessions breakDiagnose DNN/APN routing mismatches, IMSI-pinned APN gaps, and private wireless gateway configuration issuesHandle customer-reported SIM connectivity issues end-to-end — from initial report through root cause to fix EPC platform operations Manage and troubleshoot HSS/HLR, DRAs (freeDiameter with custom Python transforms), STPs, PGWs, SMFs, and GTP proxies (Go)Work with etcd-based steering/blocking infrastructure (forbidden PLMNs, platform-level blocking, 3G blocking)Operate the GTP proxy routing database (IMSI groups, IMSI-pinned APNs, cache invalidation)Participate in vendor management — escalating and driving resolution with platform vendors and roaming partner NOCs Roaming & interconnect Support sponsored roaming relationships and direct bilateral agreementsInvestigate roaming registration failures, NRTRDE gaps, and steering/blocking issuesCoordinate with partner NOCs on S6a/MAP/GTP incidents, including pcap exchange and joint root-cause analysis On-call & incident response Participate in the weekly on-call rotation (1 week on, 10 weeks off)Respond to Opsgenie alerts — SMF overload, DRA peer down, HSS failures, GTP session rejects, charging errorsDrive incident resolution end-to-end, coordinating across internal teams and external vendorsWrite post-incident summaries and feed learnings back into tooling and runbooks Automation & tooling Use and extend our pcap analysis tooling and protocol decoders to speed up investigationsContribute configuration and automation for EPC infrastructure (Ansible, Kubernetes)Improve observability — Grafana dashboards, alerting rules, protocol-level metricsWhere a fix or diagnostic needs a small code change, be comfortable making one — but this is an operations role, not a software-development one Who We’re Looking For 3+ years operating or engineering telecom infrastructure — EPC, HSS/HLR, DRA, STP, PGW, SMF, or equivalentStrong understanding of mobile core signalling: Diameter (S6a, S6d, Gx), SS7/MAP/TCAP, GTPv2-C, GTP-UComfort reading pcap traces — tshark/Wireshark protocol dissection, filtering by IMSI/AVP/transaction, protocol hierarchy analysisSolid Linux systems skills and comfort operating infrastructure via configuration/automation tooling (Ansible or equivalent)Comfort working in a vendor-managed environment — driving external partners and roaming NOCs to resolution without direct control Bonus points for Ability to read code and scripts well enough to follow a signalling path through a systemWorking knowledge of a scripting or programming language (Python, Elixir, Go, or similar) for tooling and diagnosticsExperience with freeDiameter and custom AVP transformsKubernetes and containerised EPC workloadsRoaming agreement experience — NRTRDE, TAP, sponsored roaming models, ORS blacklistsMulti-IMSI SIM applet knowledge and OTA provisioningExperience with etcd-based configuration distribution3GPP standards familiarity (TS 29.272, 29.060, 29.244, 29.002) — enough to read specs when chasing a protocol-level issue LI-REMOTE LI-KG1