Nalanda

Paxson, V. 1997. End-to-end Internet packet dynamics. SIGCOMM Comput. Commun. Rev. 27, 4 (Oct. 1997), 139-152. DOI=http://doi.acm.org/10.1145/263109.263155

Paxson measures TCP transfers between 35 Internet sites to gather his data, with particular attention to dynamics of both sender and receiver, unlike many prior studies which only study sender behaviour. In doing so, he is able to study the end-to-end asymmetry in paths for individual transfers, and also deduce interesting characteristics of routers and links along these paths.

He also importantly draws our attention to several ways in which the effects of TCP may be disentangled from those of the network. One of the most interesting to me, for instance, was a reminder to consider that loss rate measurement for ACKs is very different from that for data packets; TCP adjusts data packet rates in response to loss, which illustrates how we could end up measuring an effect of TCP, rather than of the underlying network path.

Another interesting consideration was in the use of packet pairs for measurement. As the network evolves, packets may not traverse the same end-to-end link: they may be switched along different paths at a router. To deal with this problem, Paxson introduces the notion of “packet bunch modes”, where packets are sent in bunches of varying sizes to account for the different paths that they may traverse.

This was really deep and interesting paper that will take several more reads before I manage to absorb it completely.

R. Fonseca, G. Porter, R. H. Katz, S. Shenker, and I. Stoica. 2007. X-trace: A pervasive network tracing framework. In 4th USENIX Symposium on Networked Systems Design & Implementation, pp. 271-284. [Online]. Available: http://www.usenix.org/events/nsdi07/tech/fonseca.html

X-Trace provides the means to trace network requests across different services and layers of a network, by associating each request with a unique identifier. Protocols need to be modified, if required, to handle the extra X-Trace metadata.

Network elements need to support only two simple primitives - pushDown() and pushNext() - which are used to update request metadata to indicate it being pushed down a layer (e.g., HTTP to TCP), or across a layer (e.g., web browser to web server). Network elements also need to log reports based on this metadata to a persistent store.

Using the stored metadata, a tree may be reconstructed to show the sequence of requests, across, as well as up and down, network layers. I could imagine that this could potentially be extended to also capture logs within an application.

I like this approach for its simplicity, as it requires very little for instrumentation, and is easy to support in protocols that already allow for extension (e.g., HTTP headers). The challenge, of course, as the authors point out, would be to drive adoption to the point where it is sufficiently widespread that X-Trace reports could become useful across multiple administrative domains.