Mobile Core Engineer (Remote)

Telnyx Inc.

Job Overview

Location

Dublin; Amsterdam; Krakow

Job Type

Full-time

Full Job Description

📋 Description

• 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.
• 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 involves subscriber & connectivity troubleshooting, EPC platform operations, roaming & interconnect, on-call & incident response, and automation & tooling.
• Subscriber & connectivity troubleshooting involves investigating end-to-end attachment failures across S6a (Diameter), MAP (SS7), GTP-C, and GTP-U, decoding pcap traces from DRA, STP, and GTP proxy capture points to isolate signalling failures, tracing individual IMSIs across protocols and partner networks to find where sessions break, diagnosing DNN/APN routing mismatches, IMSI-pinned APN gaps, and private wireless gateway configuration issues, and handling customer-reported SIM connectivity issues end-to-end — from initial report through root cause to fix.
• EPC platform operations involve managing and troubleshooting HSS/HLR, DRAs (freeDiameter with custom Python transforms), STPs, PGWs, SMFs, and GTP proxies (Go), working with etcd-based steering/blocking infrastructure (forbidden PLMNs, platform-level blocking, 3G blocking), operating the GTP proxy routing database (IMSI groups, IMSI-pinned APNs, cache invalidation), and participating in vendor management — escalating and driving resolution with platform vendors and roaming partner NOCs.
• Roaming & interconnect involves supporting sponsored roaming relationships and direct bilateral agreements, investigating roaming registration failures, NRTRDE gaps, and steering/blocking issues, and coordinating with partner NOCs on S6a/MAP/GTP incidents, including pcap exchange and joint root-cause analysis.
• On-call & incident response involves participating in the weekly on-call rotation (1 week on, 10 weeks off), responding to Opsgenie alerts — SMF overload, DRA peer down, HSS failures, GTP session rejects, charging errors, driving incident resolution end-to-end, coordinating across internal teams and external vendors, writing post-incident summaries, and feeding learnings back into tooling and runbooks.
• Automation & tooling involves using and extending our pcap analysis tooling and protocol decoders to speed up investigations, contributing configuration and automation for EPC infrastructure (Ansible, Kubernetes), improving observability — Grafana dashboards, alerting rules, protocol-level metrics, and where a fix or diagnostic needs a small code change, being comfortable making one — but this is an operations role, not a software-development one.

🎯 Requirements

• 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)

🏖️ Benefits

• Bonus points for ability to read code and scripts well enough to follow a signalling path through a system
• Bonus points for working knowledge of a scripting or programming language (Python, Elixir, Go, or similar) for tooling and diagnostics
• Bonus points for experience with freeDiameter and custom AVP transforms
• Bonus points for Kubernetes and containerised EPC workloads
• Bonus points for roaming agreement experience — NRTRDE, TAP, sponsored roaming models, ORS blacklists
• Bonus points for multi-IMSI SIM applet knowledge and OTA provisioning
• Bonus points for experience with etcd-based configuration distribution
• Bonus points for 3GPP standards familiarity (TS 29.272, 29.060, 29.244, 29.002) — enough to read specs when chasing a protocol-level issue

Skills & Technologies

Python

TypeScript

Kubernetes

Linux

Grafana

Mobile

Remote

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Telnyx Inc.

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About Telnyx Inc.

Telnyx Inc. is a Chicago-based communications platform that provides global carrier-grade voice, messaging, SIP trunking, wireless data, and programmable telecom APIs. Its private, multi-cloud network spans 25 regions, offering real-time call routing, number management, and elastic trunking to enterprises and software vendors. The company delivers self-service portals, SDKs, and REST APIs for embedding voice, SMS, fax, and IoT connectivity into applications, with pay-as-you-go pricing and 24/7 support.

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