MW / Cutover Guide

A cutover is the controlled process of transferring live network traffic from an existing (legacy) fiber infrastructure to a new one. Unlike a fresh installation where no services are running, a cutover happens on a live network — customers are actively using the circuits being moved. This makes it a high-stakes operation where every minute of downtime matters.

Cutovers are required in several scenarios:

• Migrating subscribers from an old fiber route to a newly built route
• Replacing damaged or degraded cable segments with new cable
• Upgrading network architecture (e.g., moving from a point-to-point to a PON design)
• Relocating infrastructure due to construction, road work, or utility conflicts
• Consolidating multiple fiber paths into a single optimized route

Old and new PLP side by side during a cutover migration

The goal of every cutover is zero or minimal service interruption. In practice, this means the actual downtime window — the time between disconnecting the old fiber and lighting up the new fiber — should be measured in minutes, not hours.

A successful cutover is 90% preparation. The following steps must be completed before any live traffic is moved.

2.1 Scope Definition

• Identify every circuit, customer, and service affected by the cutover
• Document the exact fiber pairs being moved (old route → new route)
• Determine the number of splices, connectors, and enclosures involved
• Confirm whether the cutover is a full cable swap or individual fiber migration

2.2 New Infrastructure Validation

Before scheduling the cutover, the new fiber path must pass these tests:

1. OTDR testing — End-to-end trace on every fiber in the new cable. Verify splice losses are within spec (typically ≤ 0.1 dB for fusion splices). Document all events.
2. Insertion loss testing — Measure total link loss with a calibrated light source and power meter. Compare against the calculated loss budget.
3. Connector inspection — Every connector in the new path must be cleaned and verified. Clean and re-test until pass criteria are met.
4. Continuity verification — Use a VFL (Visual Fault Locator) to confirm fiber routing and polarity on every fiber pair.
5. Label verification — Confirm all splice trays, enclosures, patch panels, and fiber assignments match the design documentation.

OTDR verification at NDP

Label verification — IN/OUT tags

2.3 Cutover Runbook

Create a detailed runbook document that includes:

• Step-by-step sequence of operations (numbered, no ambiguity)
• Assigned roles: who performs each step, who verifies
• Communication plan: who is notified at each stage (NOC, customer, PM)
• Timing: estimated duration per step, total cutover window
• Rollback trigger criteria: specific conditions under which you abort
• Contact list: every person involved with phone numbers

2.4 Pre-Cutover Checklist

On cutover day, follow the runbook exactly. No improvisation. Every step is performed, verified, and acknowledged before moving to the next.

After all services are confirmed up, perform these verification steps before leaving the site:

4.1 Testing

1. Power meter check at NIU — Measure receive power at the NIU with VeEX. Must be above LL threshold for the technology (GPON: -22.0 dBm, XGS-PON: -22.0 dBm, Go-Long: -28.0 dBm).
2. OTDR trace on the completed cutover path — Run OTDR to verify all splice losses are within spec. Compare to pre-cutover traces if available.
3. Service-level verification — Confirm with NOC that all circuits are passing traffic normally, bandwidth is nominal, and no alarms are present.

4.2 Physical Inspection

• All splice enclosures properly sealed (IP68 rating maintained)
• All patch panel connections seated fully, dust caps on unused ports
• Cable routing is clean — no kinks, no tight bends, proper radius maintained
• All cable ties and supports installed, no hanging or unsupported cable
• Old (decommissioned) fibers properly capped, labeled as inactive, or removed

PLP — organized splice tray

Vault — PLP secured inside

Vault lid closed and bolted

4.3 Soak Period

After the cutover, NOC monitors the new path for 10–15 minutes. If all circuits come back up clean — no alarms, no loss, levels are good — it's hands off. You're done.

• Stay on-site during the soak — NOC may need you to re-check a port or clean a connector
• If something doesn't come up, troubleshoot immediately while the MW is still active
• Once NOC confirms all clear, pack up and close the ticket

5.1 When to Rollback

Trigger a rollback if any of these conditions are met during or after cutover:

• Light levels on the new path are outside acceptable range and cannot be remediated on-site
• Services do not come up within the defined maintenance window
• Multiple circuits fail simultaneously on the new path
• Physical damage is discovered on the new route during cutover
• Project manager or NOC explicitly calls for rollback

5.2 Rollback Steps

1. Announce to all crew and NOC: "Initiating rollback."
2. Disconnect the new path connections.
3. Clean the old fiber connectors (they should still have dust caps from Step 4).
4. Re-connect the old fiber pairs in the original configuration.
5. Verify light levels on the restored old path.
6. Confirm with NOC that services are back to normal on the old path.
7. Log all rollback times and reasons.
8. Conduct a debrief to determine root cause and plan re-attempt.

Every cutover must produce a complete documentation package. This is not optional — it is how future crews maintain the network.

6.1 Required Documentation

• Cutover completion report — Summary of what was done, when, by whom
• OTDR traces — Pre-cutover (baseline) and post-cutover for every fiber
• Insertion loss test results — Per-fiber actual vs. budgeted loss
• Splice records — Splice tray diagrams showing old-to-new fiber mapping
• Photos — Before and after at every work location
• As-built drawings — Updated route maps reflecting the new configuration
• Time log — Start/end of each step, total downtime per circuit
• Issues log — Any problems encountered and how they were resolved

6.2 Handoff

Deliver the documentation package to the project manager and network operations team. Confirm that all as-built records in the GIS/mapping system have been updated. The cutover is not complete until documentation is accepted.