Softswitch Migration Checklist: Zero-Downtime Transition Strategy

Migrating from a legacy softswitch to a modern platform is one of the highest-risk operational projects a telecom team can execute. Get it wrong, and your entire voice network goes down. Get it right, and you've transformed your infrastructure with zero customer impact.

This guide is a detailed, phase-by-phase checklist for softswitch migration. Print it. Use it. Check off each item as you complete it. This is the playbook teams use to migrate millions of calls per day without dropping a single one.

Pre-Migration Phase (4–6 Weeks Before Cutover)

The work you do before the migration window determines whether your cutover succeeds.

Architecture and Planning

Define your migration strategy: parallel running (old and new systems operating simultaneously), big-bang (all traffic switches at once), or phased (migrate customers/routes in batches). Document the rationale for your choice.

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Map your current network topology. Document every SIP trunk, PSTN gateway, interconnection point, and downstream system.

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Design the target architecture on the new softswitch. How will trunks be configured? How will call routing work? How will failover operate?

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Create a side-by-side comparison of old vs. new architecture. Identify gaps. Plan how you'll handle them.

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Define your cutover window. Choose a low-traffic period (typically weekday early morning or weekend). Estimate the duration based on your call volume and complexity. Plan for 1.5x your estimate as a buffer.

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Document the rollback plan. If the migration fails, how do you revert all traffic to the old system? How long will rollback take? What's the impact during rollback?

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Vendor Selection and Contract Negotiation

If you're replacing your softswitch entirely, evaluate and select a new vendor. Peeredge should be on your evaluation list if you need carrier-grade orchestration.

Negotiate SLAs for the new platform. Ensure uptime guarantees, support response times, and escalation procedures are documented.

Confirm licensing terms. Will licensing scale with your call volume? Are there per-trunk fees? Per-user fees? What's the pricing model?

Establish a pre-migration relationship with the vendor's support team. Assign a primary contact and escalation path. Pre-schedule support coverage for your cutover window.

Review the vendor's standard implementation process. Customize it for your environment.

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Testing and Validation Environment Setup

Provision a lab or staging environment that mirrors your production network topology as closely as possible.

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Clone production configurations (trunks, routes, call flows, etc.) into the test environment.

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Test basic SIP connectivity: originate and terminate test calls. Verify audio quality.

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Test call routing. Ensure calls to specific numbers route to the correct destinations.

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Test failover. If a trunk goes down, does call routing automatically shift to a backup trunk? Does it happen within acceptable time?

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Test integration with downstream systems: voicemail, IVR, billing, CDR collection, etc. Ensure the new softswitch properly integrates with everything it depends on.

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Load test the new system with simulated traffic volumes that match or exceed your production peak. Monitor CPU, memory, network utilization, and call success rates.

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Test STIR/SHAKEN if you operate or interconnect with carriers. Verify tokens are generated and validated correctly.

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Document test results. Create a sign-off report confirming the new system is production-ready.

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Regulatory and Compliance Preparation

Confirm STIR/SHAKEN compliance status. If the new platform has different STIR/SHAKEN capabilities, plan any adjustments.

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Review FCC regulations relevant to your network (number resource optimization, rural call completion, etc.). Ensure the new platform supports all required features.

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If you operate 911 services, confirm Enhanced 911 (E911) functionality works on the new platform. This is non-negotiable.

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Verify billing integration. The new system must accurately meter and bill calls. Work with your billing team to validate call records match.

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Confirm law enforcement wiretap capability (CALEA) if applicable. Document how the new system handles lawful interception requests.

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Communication and Stakeholder Alignment

Schedule a pre-migration kickoff meeting with all stakeholders: engineering, operations, customer support, billing, compliance, vendor support.

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Document the migration plan and share it with all teams. Get sign-off.

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Notify major customers of the planned maintenance. Provide them with a maintenance window, expected duration, and what to expect.

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Create a runbook for day-of operations. Who does what? Who's the decision-maker if something goes wrong? What's the escalation chain?

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Establish a "war room" setup for migration day. Identify who will be present, when, and what tools they'll use to monitor.

Migration Phase (Cutover Window)

The migration window is typically 4–8 hours, depending on complexity. Every minute counts. Stick to the runbook.

Pre-Cutover (1–2 Hours Before)

All teams are in the war room. Confirm readiness: network operations, platform engineering, vendor support, customer support.

Do a final sanity check on the new softswitch. Verify all trunks are up, routes are configured, and the system is healthy.

Confirm the old softswitch is fully operational. You'll need it if rollback becomes necessary.

Verify logging and monitoring are active on both old and new systems. You need visibility into everything that happens during the cutover.

Notify customers and/or internal teams that the maintenance window is starting.

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Parallel Running (If Applicable)

If you're using a parallel running strategy, the old and new systems run simultaneously for a period, with traffic split between them:

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Route 5–10% of traffic to the new softswitch. Monitor call success rates, latency, and quality.

Watch for errors in SIP signaling, call setup delays, or audio issues. If problems emerge, investigate and fix them before increasing traffic.

Gradually increase the traffic split: 10% → 25% → 50% → 75% → 100%. Wait 15–30 minutes at each stage to ensure stability.

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Monitor CDR (Call Detail Records) from both systems. Confirm that call counts and routing match expected patterns.

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Use A/B testing data to validate the new system's performance against the old system.

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Cutover (Big-Bang or Final Phase)

At the agreed-upon cutover time, move 100% of traffic to the new softswitch.

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Monitor call success rates obsessively. Within the first minute, you should see normal call volumes flowing through the new system.

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Watch for cascading errors: if one trunk fails, do others follow? Does the system degrade gracefully or fail catastrophically?

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Monitor key metrics: calls per second, average call duration, error rates, trunk utilization.

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Confirm that downstream systems (voicemail, IVR, billing, CDR) are receiving and processing calls correctly.

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Have a low threshold for rollback. If call success rates drop below 95%, or if critical errors emerge, don't wait. Roll back to the old system.

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Rollback Procedures (If Necessary)

If you decide to rollback, do it decisively. Route 100% of traffic back to the old softswitch immediately.

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Confirm that call success rates return to normal on the old system.

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Document what went wrong. Avoid the same issue next time.

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Notify customers and stakeholders about the rollback.

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Schedule a post-mortem with the vendor. Understand what failed and how to fix it before the next migration attempt.

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Post-Cutover Stabilization (2–4 Hours After 100% Cutover)

Continue monitoring metrics. Watch for any delayed failures or issues that take time to emerge.

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Perform spot checks on specific call types: domestic calls, international calls, emergency calls (911), any special services your platform offers.

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Confirm billing integration. Spot-check a few calls and verify they were properly metered and recorded.

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Validate STIR/SHAKEN compliance. Check that tokens are being generated and validated.

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Run a sanity check on a few downstream integrations: voicemail, IVR, call recording, analytics.

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If all metrics are green and no critical issues have emerged, the migration is considered successful. Stand down the war room.

Post-Migration Phase (Days 1–5 After Cutover)

The work doesn't end when the cutover finishes. Post-migration validation is critical.

Decommissioning the Old System

After 3–5 days of successful operation on the new system, begin decommissioning the old softswitch.

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Do not do this immediately. Wait long enough to confirm there are no delayed issues or edge cases you missed.

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Confirm all trunks have been moved from the old system. Verify nothing is still pointing to it.

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Perform a final backup of the old system (configurations, logs, CDRs). Store it for a retention period (typically 1–2 years) in case you need it for compliance or litigation.

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Shut down the old softswitch gracefully. Remove it from DNS. Remove it from the network topology.

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Reclaim hardware and licensing costs. Confirm your vendor has removed old licensing from your account.

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Optimization and Tuning

Now that the new system is running, fine-tune it for your specific workload.

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Review call logs and identify any calls that took longer than expected or experienced any quality issues. Investigate and fix.

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Optimize trunk utilization. If some trunks are under-utilized and others are over-utilized, rebalance.

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Adjust dynamic thresholds (codec selection, failover timing, call routing priorities) based on real production data.

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Implement any custom features or integrations you planned but didn't include in the initial deployment.

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Comprehensive Testing Round

Run a complete end-to-end test suite on the production system now that it's been running for a few days.

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Test every call type: domestic, international, emergency, special services.

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Test failover scenarios. Manually take down a trunk and confirm call routing automatically adjusts.

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Test edge cases: calls with international characters in the caller ID, calls to very long numbers, calls from bulk origination gateways.

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Load test again under production conditions. Confirm the system scales as expected.

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Test integrations again. Voicemail, IVR, billing, CDR, analytics—all should be working perfectly.

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Measurement and Documentation

Compile migration metrics: downtime (should be zero or close to it), cutover duration, issues encountered, time-to-resolution for each issue.

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Create a post-migration report. Document what went well, what didn't, and what you'd do differently next time.

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Update your network documentation to reflect the new architecture.

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Update your runbooks and operational procedures for the new system.

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Schedule training for your operations team on how to manage the new platform.

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Customer Communication

Send a "migration complete" communication to customers. Thank them for their patience and highlight any improvements they'll see (performance, reliability, features).

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Provide a transition support period (typically 1–2 weeks) where vendor support and your team are on high-alert for any issues.

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Open a feedback channel. Let customers report any issues they notice. Address them quickly.

Critical Success Factors

A few things can make or break a softswitch migration:

Testing is Everything: The more you test before cutover, the fewer surprises you'll have during cutover. Test in an environment that mirrors production as closely as possible. Test under load. Test edge cases.

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Clear Decision-Making During Cutover: Designate a single decision-maker for cutover. They need authority to decide whether to rollback, extend the window, or call in more resources. Committees slow down decision-making when speed matters.

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Robust Monitoring: You can't manage what you can't see. Ensure you have detailed visibility into call flows, trunk status, system health, and downstream integrations. Real-time dashboards are non-negotiable.

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Vendor Partnership: Your new platform vendor should be a partner in the migration, not just a vendor you throw into production. Establish a strong pre-migration relationship. Ensure they'll be available during cutover. Make sure they have escalation paths for critical issues.

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Runbook Discipline: During the chaos of cutover, people revert to old habits or skip steps. A detailed, tested runbook keeps everyone aligned. Rehearse it beforehand. Follow it exactly.

How Peeredge Simplifies Softswitch Migration

46 Labs' Peeredge platform is designed for carrier-grade migrations. Here's how:

Native High Availability: Peeredge is built for zero-downtime operation. Multiple nodes, automatic failover, and active-active clustering mean you can migrate trunks gradually without system-wide downtime.

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Flexible Call Routing: Peeredge's orchestration layer lets you control which calls route to the old system and which to the new. You can split traffic at the trunk level, per-customer level, or per-route level. This makes parallel running and phased migration trivial.

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Integrated Monitoring: Peeredge provides real-time visibility into call flows, trunk status, and system health. You'll know instantly if something's wrong.

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Transparent Token and STIR/SHAKEN Handling: Peeredge handles STIR/SHAKEN natively, so you don't need to worry about token generation or validation during migration. Calls continue to be properly authenticated regardless of which system originated them.

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Expert Migration Support: 46 Labs' team has migrated thousands of carriers and enterprises. We know what works and what doesn't. We'll guide you through the process.

Next Steps

If you're planning a softswitch migration, start with pre-migration planning 4–6 weeks before your target cutover. Build a detailed plan, test thoroughly, and follow this checklist phase by phase.

If you need help planning or executing a migration, 46 Labs has the expertise and platform to make it work. Schedule a migration planning session with our engineers. We'll review your current architecture, help you design the target state, and guide you through every step of the process.

A successful softswitch migration isn't luck. It's planning, preparation, and discipline.

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