21-11-2012, 01:43 PM
Performance Analysis of a Parallel Downloading Scheme from Mirror Sites Throughout the Internet
Para2.ppt (Size: 541 KB / Downloads: 22)
Advantages of Paraloading
Performance is proportional to the realized aggregate bandwidth of the parallel connections
Less prone to complete download failures compared to the single connection download
Facilitates dynamic load balancing among parallel connections
Facilitates reliable, out-of-order delivery (similar to Netscape)
Disadvantages of Paraloading
Can be overly aggressive
Consumes more server resources
Overhead costs for scheduling, maintaining buffers, and sending block request messages
Only effective when mirror servers are available
Goals of Experiment
Main goal: To compare the performance of serial and parallel downloading
To verify the results of Rodriguez et al.
To examine whether varying the degree of parallelism, the number of mirror servers used, affects performance
To gain experience with paraloading and to find out what issues are involved in designing efficient paraloading systems
Experiment Setup
Implemented a paraloader application in Java, using HTTP1.1 (range-requests and persistent connections)
Files are downloaded at MIT from 3 different sets (kernel, mars, tucows) of 7 mirror servers
Degree of parallelism examined: M = 1, 3, 5, 7
Downloaded a 1MB and a 300KB file (S = 1MB, 300KB) in 1 hour intervals for 7 days
Block Size = 32KB
Results
Paraloading decreases download time over the average single connection case
Speedup is far from optimal case (aggregate bandwidth)
Block request gaps result in wasted bandwidth
Gaps are proportional to RTT
Congestion at client? Possible but unlikely.