Is your specific area's coverage provided by AT&T equipment installed at your employer, or is your employer using other means to relay cell coverage? The article I linked explains how different things in the game are sent via different protocols which are affected differently by packets being out of order and retransmitted.
Opening ports etc isn't necessary - if the traffic wasn't allowed it wouldn't work at all, not intermittently. If something in the game (like another person's hit text, or auction chat, etc) was causing an issue it would crash the client, not cause a disconnect.
-Mcoy
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