My company have 500+ employees, and I added all staffs to everyone's contact list using a third party software separate by Group "Country". One week before, everythings was fine. Suddenly, users in other countries reported that the status of the contacts shows "Presence Unknown", but still can chat. However, I checked that all users in my country and some other countries have no problem. After investigated, one country changed their traffic to another ISP and everything resume normal. But I would like to know what can it cause like this, and how can I solve if there have only one ISP? is it related to ISP problem or any thing I can trace? Very appreciate if any expert can help me. Thank you !!!!