1. Suppose you have a satellite access link that provides 3Mbps downloads; the l

Question

1.       Suppose you have a satellite access link that provides 3Mbps downloads; the link is 36000Km (geosynchronous), the average download packet is 5x 10^6 bytes, and the average upload packet is 400 bytes, further the Internet response time to the satellite portal (the other end of the link) is 2 seconds. What is the typical round trip time (RTT) for your users offsite requests?

Suppose 30% of the information requested over the link is redundant (that is 30% of the downloads are duplicates). Show the effective access time that would result if a proxy server were installed. [if you need further information state any assumptions to satisfy that need].

Explanation / Answer

Answer

The standard OS and server platform hardware have not been optimized for applications that transfer large multimedia files, resulting in poor server I/O performance. One source of the problem is that several redundant copies are introduces when the data is transferred from disks to a Network Interface Card. To solve the problem of redundant copies, we propose a Contents Delivery Accelerator that accelerates large file transfers by eliminating the redundant copies from disks to the NIC. To eliminate the redundant copies, the CDA introduces a new function, called a logical direct link, which provides the shortest path from the disks to the NIC. By using the shortest path, we can completely eliminate the redundant copies, thereby improving the I/O performance of server. The CDA architecture is a combined hardware-software approach. Thus, it comprises CDA hardware and a modified Linux kernel. We implemented the current version of the CDA on a Linux 2.4.18 kernel and an IXP1200 evaluation board. In the experiment, we compared the logical-direct path with a redundant path. For the transfer of data from disks to the NIC, our experimental results show that the average transfer latency of a direct path is as much as 30 percent less than a redundant path.

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