How do you design integration between multiple DCS systems across different sites?

Multi-site DCS integration: architecture (centralized vs federated control, define data exchange requirements), communication (WAN infrastructure, latency tolerance, reliability requirements), data exchange (what data shared - process values, alarms, historian), security (DMZ architecture, VPN, firewall rules, authentication), and visualization (central monitoring center, remote operations). Technologies: OPC DA/UA over WAN, historian replication, web-based dashboards, and SCADA for supervisory level. Considerations: bandwidth limitations (prioritize critical data), latency impact on control (keep time-critical control local), cybersecurity (treat WAN as untrusted), and failure modes (site autonomy when WAN unavailable). Governance: change management coordination, alarm management consistency, and configuration standards. Document interfaces and data flow.