The symptoms you describe, based on the code you included in your first e-mail, seems to point to a simple and straightforward problem - you're running into TCP flow control blockage. This is a traditional TCP problem and is not directly related to Asio. Anytime you're sending data as fast as possible, and the receiving side is just slightly slower at receiving the data, send buffers in the OS will fill up. Eventually this will result in the send being blocked for a short period of time while the receiving side processes the data. If you're using blocking writes, the send will block for a period of time. If you're using async writes, the write completion handler will take longer before it is called (which is why I greatly prefer async operations all around). That the problem is transitory and takes a while to manifest is another clue - it depends totally on how fast the sending and receiving applications are running, and if there's a short period on the receiving side where the app can't run as fast (e.g. another app takes up some processing time), the blockage will be transitory. Cliff