On the Dynamics and Significance of Low Frequency Components of Internet Load

Dynamics of Internet load are investigated using statistics of round-trip delays, packet losses and out-of-order sequence of acknowledgments. Several segments of the Internet are studied. They include a regional network (the Jon von Neumann Center Network), a segment of the NSFNet backbone and a cross-country network consisting of regional and backbone segments. Issues addressed include: (a) dominant time scales in network workload; (b) the relationship between packet loss and different statistics of round-trip delay (average, minimum, maximum and standard-deviation); (c) the relationship between out of sequence acknowledgments and different statistics of delay; (d) the distribution of delay; (e) a comparison of results across different network segments (regional, backbone and cross-country); and (f) a comparison of results across time for a specific network segment. This study attempts to characterize the dynamics of Internet workload from an end-point perspective. A key conclusion from the data is that efficient congestion control is still a very difficult problem in large internetworks. Nevertheless, there are interesting signals of congestion that may be inferred from the data. Examples include (a) presence of slow oscillation components in smoothed network delay, (b) increase in conditional expected loss and conditional out-of-sequence acknowledgments as a function of various statistics of delay, (c) change in delay distribution parameters as a function of load, while the distribution itself remains the same, etc. The results have potential application in heuristic algorithms and analytical approximations for congestion control

Minimal TCP/IP implementation with proxy support

Over the last years, interest for connecting small devices such as sensors to an existing network infrastructure such as the global Internet has steadily increased. Such devices often has very limited CPU and memory resources and may not be able to run an instance of the TCP/IP protocol suite. In this thesis, techniques for reducing the resource usage in a TCP/IP implementation is presented. A generic mechanism for offloading the TCP/IP stack in a small device is described. The principle the mechanism is to move much of the resource demanding tasks from the client to an intermediate agent known as a proxy. In particular, this pertains to the buffering needed by TCP. The proxy does not require any modifications to TCP and may be used with any TCP/IP implementation. The proxy works at the transport level and keeps some of the end to end semantics of TCP. Apart from the proxy mechanism, a TCP/IP stack that is small enough in terms of dynamic memory usage and code footprint to be used in a minimal system has been developed. The TCP/IP stack does not require help from a proxy, but may be configured to take advantage of a supporting proxy

Network locality at the scale of processes

research relevant to the design and application of high performance scientific computers. We test our ideas by designing, building, and using real systems. The systems we build are research prototypes; they are not intended to become products. There is a second research laboratory located in Palo Alto, the Systems Research Center (SRC). Other Digital research groups are located in Paris (PRL) and in Cambridge