Two routes. One shared risk? How to assess fibre diversity

Identify the shared resource

RFC 4202 describes a shared risk link group, or SRLG, as links that share a resource whose failure may affect them together. Its example is two fibres in the same conduit. A link can belong to more than one such group.

For a connectivity buyer, the practical implication is straightforward: compare physical dependencies as well as commercial suppliers. Two circuits can look independent in a contract while relying on a common section of infrastructure.

Look beyond the middle of the route

Illustrative failure scenario. This is not an ADNET network topology.

Begin at the customer premises. Separate long-haul paths may converge at one building entry, cable chamber, meet-me room or powered facility. Ask where the paths separate, where they rejoin and which resources they share along the way.

Use a dependency register

Build a route comparison that an engineering team can maintain. A simple register is more useful than a claim of diversity without supporting detail.

• Physical plant: cable sections, ducts, crossings and building entries.
• Sites: handoff facilities, shared rooms, power sources and access restrictions.
• Operations: maintenance coordination, escalation paths and field restoration responsibilities.
• Evidence: route documents, relevant test records, confirmation dates and unresolved questions.

Sensitive route information can be exchanged through the appropriate commercial process. What matters is that the assessment records which dependencies are known, which are shared and which remain unverified.

Separate diversity from protection

Diversity concerns the resources that paths use. Protection concerns how traffic is maintained or moved when a failure occurs. Specify both in the service design. A protected service still needs a clear explanation of its failure coverage and any shared dependencies.

Ask what happens during a fibre cut, an equipment failure and a planned maintenance event. Establish whether failover is automatic, which party controls it and how performance is tested. Use the agreed service specification for commitments, rather than assuming a recovery time from a product label.

Make resilience an acceptance condition

Document the agreed path separation and any exceptions before delivery. Define the evidence and test procedure required for acceptance, the person responsible for approving it and how later route changes will be communicated.

For an international corridor, repeat the review at every handoff. A diverse route inside Türkiye can still have a shared dependency in a neighbouring segment. ADNET assesses these questions for each proposed route; the corridor map does not certify physical diversity.