High Level Design Engineering
for Fiber Networks
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.
What Is HLD in Fiber Network Design?
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.
What Draftech Delivers in HLD
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.
AutoCAD / GIS Route Maps
Complete fiber corridor maps showing feeder and distribution routes, serving area boundaries, and infrastructure reference layers, delivered in AutoCAD DWG and GIS-compatible formats.
Fiber Count Plan
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.
FDH Location Plan
Cabinet siting with serving area assignments, address count per FDH, proposed cabinet type and size, and mounting method recommendations based on site conditions.
Splitter Architecture Diagram
PON split ratio configuration, splitter cascade design, FDT placement, and NAP strategy optimized for your address density, drop length constraints, and optical budget.
Preliminary Pole Loading Flag List
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.
Span Length Analysis
Maximum and average aerial span measurements per corridor used to validate optical budget, identify long-span outliers, and flag underground crossing requirements.
Duct & Conduit Route Design
Underground segment corridor planning with bore route layouts, conduit sizing, handhole spacing, and depth specifications for areas requiring underground construction.
Permit Package Outline
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.
How HLD Sets Up LLD for Success
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 to 6 weeks and $15,000 to $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 for Different Network Types
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:
- FTTH Greenfield: Clean network architecture from scratch. No legacy plant conflicts, but address data quality and terrain validation are critical. HLD sets the serving area framework that everything downstream follows. The schedule pressure on greenfield ISP builds is usually the biggest challenge; we've turned around greenfield HLDs for 8,000-address deployments in under three weeks when the project demanded it.
- FTTH Overbuilds: Designing around an incumbent's existing plant on shared poles introduces make-ready complexity at HLD that doesn't exist on greenfield builds. We identify overbuild segments at HLD where incumbent attachment density will require extensive make-ready, and we flag those as schedule risk items before the LLD phase begins.
- BEAD Subgrantee HLD: BEAD projects have specific HLD documentation requirements driven by NTIA guidelines and individual state broadband office standards. Our BEAD HLD packages are structured to satisfy those documentation requirements directly, including the network maps, coverage area definitions, and design standards certifications that state reporting requires. See our overview of BEAD HLD requirements for subgrantees for a detailed breakdown of what state programs typically require.
- Electric Cooperative Network Expansions: Co-ops entering broadband use their existing power pole infrastructure, which simplifies some aspects of HLD (route is largely predetermined by the distribution system) and complicates others (joint-use agreement requirements, NESC clearance from power conductors, and the need to work with the co-op's GIS data format). We have extensive co-op HLD experience across the Southeast, Midwest, and Great Plains.
- Middle-Mile Fiber: Middle-mile HLD focuses on route economics over longer distances, often with DWDM or high-fiber-count dark fiber architecture. Splice point placement strategy differs from FTTH: fewer, more deliberately placed closures with higher-count cables between them.
- MDU/MTU Fiber Design: Multi-dwelling unit HLD addresses riser cable routing, IDF and MDF placement, in-unit wiring strategy, and the interaction between the OSP feeder design and the building's internal network. MDU HLD is a distinct engineering discipline that our team handles as part of larger FTTH engagements or as standalone MDU design projects.
Tools & Standards
Draftech HLD engineers work in the tools and to the standards that the industry builds on. Our toolset includes:
- AutoCAD: Primary drafting platform for route maps, serving area drawings, and HLD plan sheets. We deliver in native DWG and as PDFs formatted for client review and permit submission.
- ArcGIS: Spatial analysis, address layer management, route optimization, and GIS deliverable production. Most client-facing GIS deliverables come out of ArcGIS to ensure compatibility with industry-standard network inventory platforms.
- QGIS: Used internally for datasets that are cleaner in open formats and for clients whose workflows are built around open-source GIS infrastructure.
- IQGeo: For clients running IQGeo network management platforms, we can deliver HLD outputs directly into the network inventory system rather than as standalone files.
- MicroStation: For clients and permitting authorities whose workflows require MicroStation-format deliverables, particularly in transportation agency environments.
Our HLD work is designed to the standards that govern fiber OSP construction:
- GR-20: Generic requirements for optical fiber and fiber optic cable, used to specify cable types and performance characteristics in HLD BOM and architecture documents.
- ANSI/TIA-568: Telecommunications cabling standards applied to structured cabling elements within the network design.
- NESC (National Electrical Safety Code): Aerial clearance and loading requirements that inform our preliminary pole loading flag process during HLD.
- Utility Pole Owner Attachment Rules: Joint-use and attachment agreements vary by pole owner. We work within the specific attachment standards of investor-owned utility, telecom, co-op, and municipal pole owners depending on the project geography.
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.
HLD Engineering Services: FAQ
What is the difference between HLD and LLD in fiber design?
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.
What deliverables come out of an HLD engagement?
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.
How long does a fiber HLD typically take?
Timeline varies by project size and complexity. A focused HLD for a 5,000-address rural deployment can be completed in 3 to 5 weeks from field survey data receipt. A larger BEAD project covering 20,000+ addresses across multiple counties typically runs 6 to 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.
Does HLD include pole loading analysis?
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.
Can Draftech do both HLD and LLD on the same project?
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.
Start Your HLD with Draftech
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 50 U.S. states.
Contact Our Engineering TeamOr reach us directly at info@draftech.com or 305-306-7407; we reply within one business day.