Mobile Core Engineer (Remote)

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-U
• Decode pcap traces from DRA, STP, and GTP proxy capture points to isolate signalling failures
• Trace individual IMSIs across protocols and partner networks to find where sessions break
• Diagnose DNN/APN routing mismatches, IMSI-pinned APN gaps, and private wireless gateway configuration issues
• Handle 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 agreements
• Investigate roaming registration failures, NRTRDE gaps, and steering/blocking issues
• Coordinate 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 errors
• Drive incident resolution end-to-end, coordinating across internal teams and external vendors
• Write 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 investigations
• Contribute configuration and automation for EPC infrastructure (Ansible, Kubernetes)
• Improve observability — Grafana dashboards, alerting rules, protocol-level metrics
• Where 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 equivalent
• Strong understanding of mobile core signalling: Diameter (S6a, S6d, Gx), SS7/MAP/TCAP, GTPv2-C, GTP-U
• Comfort reading pcap traces — tshark/Wireshark protocol dissection, filtering by IMSI/AVP/transaction, protocol hierarchy analysis
• Solid 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 system
• Working knowledge of a scripting or programming language (Python, Elixir, Go, or similar) for tooling and diagnostics
• Experience with freeDiameter and custom AVP transforms
• Kubernetes and containerised EPC workloads
• Roaming agreement experience — NRTRDE, TAP, sponsored roaming models, ORS blacklists
• Multi-IMSI SIM applet knowledge and OTA provisioning
• Experience with etcd-based configuration distribution
• 3GPP standards familiarity (TS 29.272, 29.060, 29.244, 29.002) — enough to read specs when chasing a protocol-level issue

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