Network Infrastructure Engineer

📋 Job Overview

Design, build and keep evolving the physical networks that connect the clusters in the Scaling Inference Lab (SIL). The SIL, backed by ARIA, is a neutral, UK-based testbed where new AI technologies (accelerators, memory systems and interconnects) are tested at rack scale against real workloads for the very first time. The results help UK startups, investors and public compute programmes decide what to build, fund and buy, and they build lasting UK capability in the infrastructure that AI depends on.

🏢 About CommonAI C.I.C.

CommonAI C.I.C. is an equal opportunity employer and is committed to creating an inclusive and diverse workplace.

🎯 The Role

The network is critical to every experiment and this role will own the cabling, switch layouts and topologies for the out-of-band, frontend and accelerator fabrics in our lab at Kao Data in Harlow, and in any further facilities we establish in the UK. The SIL is an R&D facility and its requirements evolve rapidly. You will gather requirements from members, CommonAI staff and other key stakeholders to create flexible and resilient network designs.

✅ Key Responsibilities

• Design the physical network for each new cluster across out-of-band, frontend/storage and accelerator fabrics: topology, switch placement, port maps, cable schedules and bills of materials.
• Specify fibre and copper infrastructure in detail, including fibre grade, connectors, polarity, pinning, trunk and cassette layouts, patch-panel arrangements and end-to-end loss budgets, and select matching transceivers, DACs and AOCs.
• Plan changes to existing clusters so equipment can be re-cabled and reused with minimal disruption to running work.
• Act as the technical authority for suppliers and installers: produce drawings and specifications, review quotations, and inspect and test completed work.
• Maintain accurate, well-labelled as-built documentation of every rack, cable, port and link.
• Work with project managers on sequencing and lead times, and with operators and software colleagues on bring-up and fault-finding.

📌 Required Qualifications

• Experience designing networks for HPC or AI cluster deployments, with examples of designs you have owned from specification to installation.
• A thorough understanding of the differences between out-of-band, frontend and accelerator (GPU) fabric networking.
• Practical knowledge of InfiniBand, RoCE or similar lossless fabrics, including fat-tree and rail-optimised topologies.
• A very clear understanding of data centre fibre optics: OS2 versus OM4/OM5, MTP/MPO versus LC, APC versus UPC, Type A/B/C polarity, pinned and unpinned connectors, and the losses introduced by patch panels, cassettes and connectors.
• The ability to communicate a design clearly to installers, suppliers, project managers and engineers.

⭐ Desirable Experience

• Experience with 400G/800G Ethernet and OSFP/QSFP-DD optics, optical circuit switching or other novel interconnects, high-density liquid- or air-cooled racks, documentation tools such as NetBox, and colocation facilities.

🎁 Benefits

• A collaborative and supportive work environment
• The opportunity to have a high impact in a growing organisation
• Competitive salary package, including pension and benefits
• Professional development opportunities
• Networking opportunities with influential figures from across the tech sector and academia
• A vibrant office environment located a few minutes' walk away from Cambridge train station

🛂 Visa & Eligibility

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