Donald F. Towsley

Inferring TCP connection characteristics through passive measurements

We propose a passive measurement methodology to infer and keep track of the values of two important variables associated with a TCP connection: the senders congestion window (cwnd) and the connection round trip time (RTT). Together, these variables provide a valuable diagnostic of end-user-perceived network performance. Our methodology is validated via both simulation and concurrent active measurements, and is shown to be able to handle various flavors of TCP. Given our passive approach and measurement points within a Tier-1 network provider, we are able to analyze more than 10 million connections, with senders located in more than 45% of the autonomous systems in todays Internet. Our results indicate that sender throughput is frequently limited by a lack of data to send, that the TCP congestion control flavor often has minimal impact on throughput, and that the vast majority of connections do not experience significant variations in RTT during their lifetime

Topology discovery service for router-assisted multicast transport

Many existing proposals for introducing network support for multicast transport require the establishment of signaling paths among adjacent active routers in a session. We present a general-purpose, lightweight protocol to establish a signaling overlay among sparsely deployed active nodes. The resulting overlay is tied to the underlying multicast route and adapts to changes in its topology. In addition, we make this overlay available to other protocols by means of efficient communication primitives to provide reliable signaling between neighboring active routers. Our protocol and associated services can serve as a building block for a variety of active multicast services and greatly simplify their development. We describe its applicability for implementing several previously proposed services.