By Greg White, CableLabs and Richard Woundy, Yiu Lee, Carl Williams, Comcast
The sizing of the cable modem (CM) upstream buffer can significantly impact application performance and end-user quality of experience. Too little buffering will result in poor TCP throughput in the upstream direction. Too much buffering will have a negative impact on latency sensitive applications when the upstream link is heavily utilized. Studies have indicated that cable modems in the field today have perhaps an order of magnitude greater buffering than is needed to ensure TCP throughput, with the result being a sluggish user experience for web browsing, and outright failure of VoIP and real-time games at times when the upstream is being used simultaneously by TCP.
This paper provides a background on the network dynamics involved, describes a new feature in the DOCSIS® 3.0 specification that allows the operator to tune the upstream buffer, and provides some initial experimental work that seeks to pr