In a high availability over WAN deployment, the ASR or TTS servers cannot be across the WAN from the active Cisco Unified CCX site. This is because the ASR or TTS servers require a low latency connection to the Unified CCX engine, and the WAN link may introduce delays or packet loss that can affect the quality and performance of the speech recognition or text-to-speech services. Therefore, the ASR or TTS servers must be co-located with the active Unified CCX site, and they must fail over to the standby site if the active site goes down. References: Deploying Cisco Unified Contact Center Express (UCCXD) v6.0 - Module 1: Design a Cisco Unified Contact Center Express System Deployment - Lesson 4: High Availability and Network Design - Topic: Unified CCX High Availability over WAN1