Dissertation/Thesis Abstract

Peer selection algorithm in stochastic content delivery networks to reduce file download time
by Lehrfeld, Michael, Ph.D., Nova Southeastern University, 2010, 118; 3389939
Abstract (Summary)

The download duration of peer-to-peer overlay networks is highly dependent upon the client's selection of candidate node-servers and the algorithms used in that process. Recent findings suggest that as node-server network capacity increases the deviation from the average total download time can vary as much as 300 percent between selection algorithms. This work investigated the current selection algorithms based upon chunk size, parallel connections, permanent connection, and time based switching.

The time based switching algorithm is a variation of the chunk based algorithm. Time based switching enables a client to randomly select a new node-server regardless of connection speed at predetermined time slots. Using time base switching, a client is better able to mitigate the negative effects of poor performing node-server; i.e. reduce the probability of selecting and staying with a poor performing node-server. Simulations indicate a 41% percent decrease in download time when compared to chunk based switching.

The effects of inserting chokepoints in the time based switching algorithm were investigated. With each of the current selection algorithms, a client is still bound to an extended relationship with a poor performing node-server for either an entire chunk or time slot. This work investigated improving a client's download performance by preemptively releasing a client from a poor performing node-server. To achieve this, the client will gather a peer-to-peer network overlay capacity from a global catalog. This information will be used to seed a client choke algorithm. Clients will then be able to continually update a local capacity average based upon past download sessions. This local average will be used to make a comparison between the current download session and the previously calculated average. A margin has been introduced to allow the client to vary from the average calculated capacity. The client will perform comparisons against chokepoints and make performance decisions to depart a node-server that does not meet minimum capacity standards.

Experimental results in this research demonstrated the effectiveness of applying a choking algorithm to improve upon client download duration as well as increasing the accuracy of download duration estimates. In the single downloader scenario, the choke based algorithm improved performance up to 44% in extreme congestion and a more modest 13% under normal conditions. The multiple client scenarios yielded on average a 1% decrease in client download duration along with a 44% increase download homogeneity. Furthermore, the results indicate that a client based choking algorithm can decrease overall peer-to-peer network congestion buy improving upon client selection of node-servers.

Indexing (document details)
Advisor: Simco, Gregory
Commitee: Mitropoulos, Francisco, Mukherjee, Sumitra
School: Nova Southeastern University
Department: Computer Information Systems (MCIS, DCIS)
School Location: United States -- Florida
Source: DAI-B 71/02, Dissertation Abstracts International
Source Type: DISSERTATION
Subjects: Computer science
Keywords: Content delivery networks, Download time, Network performance, Peer selection strategy, Peer-to-peer networks
Publication Number: 3389939
ISBN: 9781109572964
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