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Today, with the rapid advance in broadband technology, streaming technology is applied to many applications, such as content delivery systems and web conference systems. On the other hand, we must implement digital rights management (DRM) to control content spreading and to avoid unintended content use. Traitor tracing is one of the key technologies that constructs DRM systems, and enables content distributors to observe and control content reception. General methods make use of watermarking to provide users' individual information unique to each user. However, these methods need to produce many individual contents. Especially, this is not realistic for real-time streaming systems. Furthermore, watermarking, which is a key technology adopted by contemporary methods, has known limitations and attacks against it. This is why the authors have proposed a method to monitor the content stream using traffic patterns constructed from only traffic volume information obtained from routers. The proposed method can determine who is watching the streaming content and whether or not a secondary content delivery exists. This information can be also used with general methods to construct a more practical traitor-tracing system. A method to cope with random errors and burst errors has also been investigated. Finally, the results of simulation and practical experiment are provided demonstrating the effectiveness of the proposed approach.