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                   B O S T O N   U N I V E R S I T Y
                      Computer Science Department
                          C O L L O Q U I U M
                     Wednesday, November 21, 11:00 AM 
                       (Coffee served at 10:45PM)
                         Seminar Room / MCS 135


                Access-Level and POP-Level Traffic Dynamics 
                        at a Tier-1 Backbone POP


			Supratik Bhattacharyya
	 	      Sprint Labs, Burlingame, CA

ABSTRACT :

Network traffic measurements provide essential data for networking
research and operation.  Measurement data is used to study traffic
demands, develop models for network traffic, provision networks, and
evaluate network performance.  While there has been extensive work on
network measurement systems, much of it has focused on specialized
systems that collect a single type of data, and many of the
measurements have been performed on edge networks or in research
environments.  We have designed a passive measurement system which
collects header information from every packet on OC-3, OC-12, and
OC-48 network links, and uses GPS synchronized clocks to accurately
timestamp each packet. We have collected multiple full day traces
at a major POP in Sprint's Tier-1 IP backbone.

The first part of the talk will present the design of our monitoring
equipment, and briefly describe the ongoing projects at Sprint that
utilize this data. The second part of the talk will focus on a
particular project that studies traffic dynamics at a POP.  Spatial
and temporal information about traffic dynamics is central to the
design of effective traffic engineering practices for IP backbones.
We develop a methodology that combines packet-level traces from access
links in the POP and BGP routing information to build components of
POP-to-POP traffic matrices. Our analysis shows that there is wide
disparity in the geographic distribution of traffic across POPs in the
USA.  Also, time of day behaviors for different POPs and different
access links reveal a high degree of heterogeneity.  We study the
"elephants and mice" phenomenon at the granularity level of destination
address prefixes.  We demonstrate that these aggregates exhibit
stability throughout the day on per-hour time scales, and thus they
form a natural basis for splitting traffic over multiple paths to
improve load balancing.




Host: Mark Crovella
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