KEYWORDS: Algorithms, Prototyping, Internet, Data modeling, Information operations, Computer simulations, Control systems, Reflectors, Associative arrays, Computing systems
The Internet consists of about 13,000 Autonomous Systems (AS's) that
exchange routing information using the Border Gateway Protocol (BGP).
The operators of each AS must have control over the flow of traffic
through their network and between neighboring AS's. However, BGP is a
complicated, policy-based protocol that does not include any direct
support for traffic engineering. In previous work, we have
demonstrated that network operators can adapt the flow of traffic in
an efficient and predictable fashion through careful adjustments to
the BGP policies running on their edge routers.
Nevertheless, many details of the BGP protocol and decision process
make predicting the effects of these policy changes difficult. In
this paper, we describe a tool that predicts traffic flow at network
exit points based on the network topology, the import policy
associated with each BGP session, and the routing advertisements
received from neighboring AS's. We present a linear-time algorithm
that computes a network-wide view of the best BGP routes for each
destination prefix given a static snapshot of the network state,
without simulating the complex details of BGP message passing. We
describe how to construct this snapshot using the BGP routing tables
and router configuration files available from operational routers. We
verify the accuracy of our algorithm by applying our tool to routing
and configuration data from AT&T's commercial IP network. Our route
prediction techniques help support the operation of large IP backbone
networks, where interdomain routing is an important aspect of traffic
engineering.
The burstiness of compressed video complicates the provisioning of network resources for emerging multimedia services. For stored video applications, the server can smooth the variable-bit-rate stream by prefetching frames into the client playback buffer in advanced of each burst. Drawing on a priori knowledge of the frame lengths and client buffer size, such bandwidth smoothing techniques can minimize the peak and variability of the rate requirements while avoiding underflow and overflow of the playback buffer. However, in an internetworking environment, a single service provider typically does not control the entire path from the stored-video server to the client buffer. To develop efficient techniques for transmitting variable-bit- rate video across a portion of the route, we investigate bandwidth smoothing across a tandem of nodes, which may or may not include the server and client sites. We show that it is possible to compute an optimal transmission schedule for the tandem system by solving a collection of independent single-link problems. To develop efficient techniques for minimizing the network bandwidth requirements, we characterize how the peak rate varies as a function of the buffer allocation and the playback delay. Simulation experiments illustrate the subtle interplay between buffer space, playback delay, and bandwidth requirements for a collection of full-length video traces. These analytic and empirical results suggest effective guidelines for provisioning network services for the transmission of compressed video.
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