The Cisco SRND discusses network considerations for deploying CUCM/IM&P, however, any high latency connections are considered as best effort, and cannot guarantee the user experience will be good.
The influence of latency on design varies, based on the type of Unified Communications service considered for remote deployment. If a voice service is hosted across a WAN where the one-way latency is 200 ms, for example, users might experience issues such as delay-to-dialtone or increased media cut-through delays. For other services such as presence, there might be no problem with a 200 ms latency.
It might not be that big of a problem for IM, but it might be for voice/video depending on your scenario, depending on how big the RTT/delay is.
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