In a public switched telephone network, real time monitors on SS7 links will collect interoffice signaling messages. A site processor compiles data from the signaling messages relating to individual calls, to form call detail records (CDRs) for all interoffice call attempts. The site servers upload the CDRs to a central server. Automatic Message Accounting (AMA) records also are accumulated for at least selected central office switching systems and uploaded to a server. Programs running on the servers enable network operations personal to analyze a variety of network traffic patterns, for example to study the number of calls to particular numbers during various times periods and the hold time of the calls in order to identify the numbers of Internet Service Providers (ISPs). As another example, the traffic analysis may indicate the amount of traffic between two end offices and the percentage thereof routed through a tandem office, to allow network planners to design trunk upgrades between the various offices and/or to plan the addition of new offices.