Modernising a multi-site network estate involves more than choosing the right technology. These ten considerations cover the planning, commercial, and operational factors that most commonly affect timescales and costs.
Modernising a network estate is rarely straightforward. The technology choices matter, but they are often not where projects run into difficulty. Timescales slip, costs increase, and programmes stall for reasons that were foreseeable at the outset: incomplete estate mapping, underestimated security clearance requirements, incumbents who do not cooperate, or a gap between the aspirational design and what the current estate can support during transition.
These ten considerations will not remove that complexity, but working through them before the programme starts will help manage it.
A detailed profile of every site in scope is the foundation of any accurate plan. Location, access restrictions, wayleave requirements, and criticality all affect timescales and cost, and they vary significantly across a typical multi-site estate. Sites that are geographically remote, or that require specific security arrangements for access, need to be identified early. Your provider will need to understand which sites are operationally critical and which have more flexibility, both for prioritisation and for accurate commercial modelling.
The number of sites matters independently of their individual size. A hundred small sites creates a different programme shape from ten large ones, even if the total scope is similar.
For organisations in regulated or security-conscious sectors, including policing, health, and government, engineering teams working on site may need to be cleared to a minimum of Security Check (SC) level. Gaining clearance requires sponsorship to the project and carries administrative lead time that cannot be compressed significantly.
The more sites in scope, the more people need clearance, across both the lead provider and any supply chain partners involved in last-mile delivery. This needs to be factored into the programme timeline from the start. It is not an afterthought, and it cannot be accelerated once it is running late.
Third-party providers such as Openreach also need advance notice. Decisions about the network architecture and last-mile approach should be made early enough for all supply chain participants to plan their resource requirements.
Specialist networking equipment continues to carry meaningful lead times depending on the kit. Where a particular solution requires hardware that is not in standard supply, this needs to be planned for explicitly rather than assumed. The right choice of solution should drive the hardware decision, not the other way around. Compromising on architecture to accommodate availability is a decision that tends to cost more over the life of the network than the time saved at procurement.
Your organisation will need to allocate people to the programme alongside the supplier. The more geographically dispersed the estate, and the faster the required pace, the earlier recruitment and resource planning needs to begin. Going to market for skilled engineers, getting each person cleared, and scheduling them across the estate takes time that is easy to underestimate when the programme is being scoped.
The same applies to supplier-side resourcing. Give your provider as much forward notice as possible. Availability of cleared, experienced engineers is a genuine constraint on delivery pace.
Transitioning from an existing supplier to a new one introduces a dependency that is not always within your control. Contract exit obligations vary, and the pace at which an incumbent cooperates with handover activities is not guaranteed. Read exit obligations carefully before the programme begins, and be prepared to hold the incumbent to account if transitions slow. The commercial leverage you have is strongest at the point of contract expiry, not after.
Decide early how you want to structure the procurement: as a single contract covering the full estate, or as separate tranches covering core deliverables. A single contract is simpler to manage commercially, but if the programme runs over multiple years, it may approach renewal before all sites are live. Splitting the programme into discrete tranches gives more control over delivery milestones and reduces the risk of contractual dependencies complicating the later stages.
For public sector organisations, framework choice also matters here. The procurement vehicle needs to be compatible with the commercial model and the delivery timeline.
Not all sites have the same resilience requirements, and assuming they do leads to over-specification and unnecessary cost. A single circuit may be entirely appropriate for some sites. Dual-homed or fully resilient configurations are warranted for sites where an outage has operational consequences. Work through the criticality of each site before specifying resilience, rather than applying a single standard across the estate.
Bandwidth requirements need to be assessed against current and anticipated workloads. Cloud-first working, video conferencing, and AI-enabled applications all change the traffic profile of a site relative to what the existing network was designed for.
During a phased migration, the estate will run in a split state for an extended period. Some services and workloads will move to the new network while others remain on the legacy infrastructure. A bridging mechanism that maintains secure connectivity between the two environments is essential throughout this period, ensuring consistent security posture across both and no disruption to live users.
This is often underplanned. The transition state can last months or longer on a complex estate, and the security architecture needs to be designed to operate during it, not just at the point when migration is complete.
The most reliable way to estimate time and cost accurately is to complete three pieces of work in sequence: a Current Mode of Operations (CMO) assessment, a Future Mode of Operations (FMO) design, and a gap analysis between them.
The CMO is a thorough architectural review of the existing estate: all sites, data centres, third-party connections, integrations, and how they interoperate. The FMO captures what the network needs to do, covering required capabilities, performance, security, visibility, and integration requirements. The gap analysis plots the journey from one to the other.
In practice, organisations frequently start with the FMO and skip the CMO. The result is a plan built on assumptions about the current state that turn out to be incorrect, with the consequences surfacing at the point of delivery rather than at planning.
One practical approach to WAN transformation is to migrate core infrastructure first, before tail sites are moved in priority order. This is not necessarily faster than other approaches, but it is more controlled: core workloads are stabilised on the new platform before the wider estate is migrated, and the dependency on incumbent providers is reduced earlier in the programme.
Cloud Gateway designs and operates managed network estates for regulated organisations across the UK, working across police forces, NHS trusts, central government, and multi-site commercial organisations. For more on how we approach network modernisation, see our Modernise your network page or Business Everywhere: SD-WAN.
