Test everything first in a closed scenario, and if everything works well, do the migration. Never migrate all the equipment at once. Never trust old cables. After a migration wait for 2 or 3 days before continue. And check for user feedback.

To avoid unexpected downtime and system failures when upgrading your network infrastructure, conduct thorough planning and risk management, which includes a comprehensive assessment of current systems and the identification of potential risks alongside mitigation strategies. Implement upgrades in stages, beginning with a pilot test, and ensure that critical systems have redundancy and regular backups. Schedule the upgrade during low-usage periods, maintain clear communication with stakeholders and vendors, and provide continuous monitoring and extensive post-upgrade testing. Additionally, train IT staff on new systems and ensure that technical support is available throughout the process.

To avoid unexpected downtime and system failures during a network upgrade, conduct thorough planning, perform risk assessments, schedule upgrades during low-traffic periods, implement redundancy, test changes in a controlled environment, and have a rollback plan ready.