This paper deals with the problem of summarization and visualization of communication patterns in a large scale corporate social network. The solution to the problem can have significant impact in understanding large scale social network dynamics. There are three key aspects to our approach. First we propose a ring based network representation scheme - the insight is that visual displays of temporal dynamics of large scale social networks can be accomplished without using graph based layout mechanisms. Second, we detect three specific network activity patterns - periodicity, isolated and widespread patterns at multiple time scales. For each pattern we develop specific visualizations within the overall ring based framework. Finally we develop an activity pattern ranking scheme and a visualization that enables us to summarize key social network activities in a single snapshot. We have validated our approach by using the large Enron corpus - we have excellent activity detection results, and very good preliminary user study results for the visualization.