Route architecture, FDH placement, splitter design, and fiber count planning — the engineering decisions that determine whether your network builds on schedule and on budget. Get HLD right the first time.
High level design (HLD) is the first engineering phase after field survey. It establishes the macro-level route, equipment placement, and system architecture before low-level design (LLD) detailed engineering begins. HLD is where the fundamental decisions get made — and where the most expensive mistakes happen when those decisions are wrong.
A complete HLD engagement covers route selection and corridor mapping, FDH (fiber distribution hub) and FDT placement, PON architecture and splitter ratios, fiber count planning for feeder and distribution cables, aerial vs. underground determination for each segment, duct system layout, major splice point locations, preliminary bill of materials estimation, and optical budget modeling to validate that the proposed architecture will meet performance requirements before construction.
Think of HLD as the blueprint phase — the equivalent of architectural drawings before a building's structural engineering begins. A contractor can't build from blueprints alone, but they absolutely cannot build correctly without them. The HLD output is what every downstream deliverable — LLD, permitting packages, construction BOM, BEAD reporting documents — is built from. Compromising on HLD quality is the single highest-risk decision on a fiber project.
Avoiding common FTTH HLD design mistakes starts with understanding what the phase is actually for and what quality looks like in a finished HLD deliverable. The most common failure mode isn't exotic — it's HLD produced too quickly, off desktop data only, by engineers who haven't seen the terrain and don't understand the downstream design consequences of their architecture decisions.
A Draftech HLD engagement produces a complete set of engineering deliverables that are immediately actionable for LLD, permitting, and procurement — not a slide deck, not a network diagram in a PowerPoint, but actual engineering documentation your team can build from.
Complete fiber corridor maps showing feeder and distribution routes, serving area boundaries, and infrastructure reference layers — delivered in AutoCAD DWG and GIS-compatible formats.
Feeder and distribution cable sizes for every segment, sized for full buildout coverage, scalability, and spare capacity. Not minimum viable counts — counts that hold up through project completion.
Cabinet siting with serving area assignments, address count per FDH, proposed cabinet type and size, and mounting method recommendations based on site conditions.
PON split ratio configuration, splitter cascade design, FDT placement, and NAP strategy optimized for your address density, drop length constraints, and optical budget.
Identification of aerial spans where attachment height, existing load, or pole condition indicates a potential make-ready issue — flagged at HLD so route decisions can account for remediation cost.
Maximum and average aerial span measurements per corridor used to validate optical budget, identify long-span outliers, and flag underground crossing requirements.
Underground segment corridor planning with bore route layouts, conduit sizing, handhole spacing, and depth specifications for areas requiring underground construction.
Complete inventory of all permit triggers along the proposed routes — DOT crossings, railroad crossings, USACE waterways, municipal ROW — with estimated permit lead times built into the project schedule.
A weak HLD doesn't just produce a bad HLD — it produces a bad everything downstream. Every phase that follows depends on HLD decisions being correct, and when they're not, the cost of correction compounds with each phase completed.
The most direct failure path is fiber counts. An HLD that sizes feeder cables for a 70% penetration buildout on an 8,000-address deployment may look conservative, but if the actual penetration plan or the correct address count wasn't validated, you discover the problem when the LLD engineer calculates the required fiber allocation and comes up short. At that point, re-routing or re-sizing feeder cables in LLD can add 2–6 weeks and $15,000–$80,000 in rework depending on project scale — and that's before construction costs for any infrastructure that was ordered against wrong counts.
Wrong FDH placement is the second major failure mode. Placing a cabinet at a location that looks logical on a map but has access issues — a drainage ditch, private property with no easement, a corner lot with no suitable mounting point — means the LLD engineer has to redesign the serving area around a new cabinet location. Serving area redesign isn't just a map change: it cascades into fiber count recalculations, drop length analysis revisions, and updated optical budgets.
Splice points in inaccessible locations are a maintenance problem that starts at HLD. Where you put major splice points determines where technicians have to go when a fiber event happens at 2am during a storm. A splice closure at the top of a 45-foot pole in a flooded right-of-way is technically functional but operationally problematic. HLD is the place to think about this — LLD engineers are focused on making the design buildable, not necessarily on 10-year maintenance access.
Our FTTH design services integrate HLD and LLD under the same engineering team precisely to avoid these handoff failures. When the HLD engineers and LLD engineers are the same people, architecture decisions are made with LLD consequences in mind — and the institutional knowledge of why a route or placement was chosen is preserved through the full design lifecycle.
HLD methodology isn't uniform — the approach, assumptions, and deliverable emphasis vary significantly based on what kind of network is being designed. Draftech delivers HLD for the full range of fiber network types:
Draftech HLD engineers work in the tools and to the standards that the industry builds on. Our toolset includes:
Our HLD work is designed to the standards that govern fiber OSP construction:
HLD that's ready for LLD: Our HLD deliverables are structured so that the LLD engineer — whether our team or yours — can pick up the package and begin detailed engineering without a discovery phase. Route rationale, fiber count methodology, splitter architecture decisions, and permit trigger inventory are all documented in the HLD package, not held in an engineer's head.
When you're ready to move from HLD to construction documents, our LLD detailed design team takes the approved HLD and converts it into complete, permit-ready construction packages. The transition is seamless when both phases are handled by Draftech — and the combined HLD/LLD scope delivers the most accurate, lowest change-order-rate construction packages in the industry.
High level design (HLD) establishes the network architecture — serving area boundaries, route corridors, FDH and splitter placement, fiber count allocation, PON topology, and optical budget at a macro level. Low level design (LLD) is the construction document set — pole-by-pole span details, splice case placements, conduit schedules, reel cut assignments, and AutoCAD plan sheets that construction crews work from directly. HLD answers what will be built and where; LLD answers exactly how every section of the network will be built. You cannot produce a reliable LLD without a solid, approved HLD — projects that skip or abbreviate HLD consistently run into fiber count problems, wrong splitter placements, and costly redesigns mid-construction.
A complete Draftech HLD engagement delivers: AutoCAD and GIS route maps showing fiber corridors and serving area boundaries, a fiber count plan specifying feeder and distribution cable sizes, an FDH location plan with cabinet type and serving area assignments, a splitter architecture diagram showing split ratios and cascade configurations, a preliminary pole loading flag list identifying spans that may require make-ready, a span length analysis for optical budget validation, a duct and conduit route design for underground segments, and a permit package outline identifying all permit triggers with estimated timelines. All route deliverables are provided in both CAD and GIS formats.
Timeline varies by project size and complexity. A focused HLD for a 5,000-address rural deployment can be completed in 3–5 weeks from field survey data receipt. A larger BEAD project covering 20,000+ addresses across multiple counties typically runs 6–10 weeks for HLD. Complexity factors that extend timeline include MDU-heavy deployments, areas with limited GIS data quality requiring field verification, and projects with multiple hub-site options requiring comparative design analysis before a preferred architecture can be approved. We provide a project-specific schedule estimate at kickoff.
HLD includes a preliminary pole loading flag list — we identify spans where attachment height, existing load, or pole age indicate a potential loading issue that will need to be resolved before construction. Full NESC-compliant pole loading analysis with O-Calc or SPIDA calculations is performed during the LLD phase, once route finalization and exact attachment specifications are confirmed. Flagging loading issues at HLD is important because it affects route decisions — a section where many poles need replacement may warrant a route adjustment to a lower-cost corridor, and discovering that at HLD is far less expensive than discovering it during make-ready.
Yes — and most clients prefer it that way. When the same team does HLD and LLD, design knowledge transfers cleanly: the engineers who made the HLD architecture decisions produce the LLD construction documents, so decisions about why a splitter went at a particular location or why a corridor was chosen are preserved and reflected in the LLD. When HLD and LLD are split across two firms, there's almost always a translation gap that adds time and creates errors. We offer full-scope engagements covering HLD, LLD, pole loading, permitting, and as-built documentation as a single integrated engagement.
ARE YOU A FIBER HLD ENGINEERING FIRM?
This page describes the service we deliver to clients. If you provide HLD or LLD production for fiber networks and are looking for a consistent subcontract pipeline, we have ongoing capacity needs across all states.
Whether you're beginning a BEAD subgrantee deployment, designing a new greenfield FTTH network, or need an independent review of an existing HLD, our engineering team is ready to talk through your project. We serve ISPs, electric cooperatives, utilities, EPC contractors, and municipalities across all 48 continental states.
Contact Our Engineering TeamOr reach us directly at info@draftech.com or 305-306-7406 — we reply within one business day.