Midterm #1 Study Question Answers
- Name one networking function that is implemented only at the application layer, one the is implemented only at the transport layer and one that is implemented only at the network layer of the Internet stack.
Caching of HTML responses is implemented only at application layer, congestion control is implemented only at the transport layer, and routing based on topology is implemented only at the network layer.
- Explain the fundamental differences between the FTP file transfer protocol and HTTP, the fundamental protocol of the Web.
FTP works using TCP connections between client and server in a very simple way: one connection to allow a user to log in and control browsing and another connection for each file transfer. FTP does not make assumptions about the type of files transfered based on file name or any other metadata (with the possible exception of files named README). HTTP browsers interpret file types, and in particular recognize the .html (and .htm) file name extensions as containing HTML. Files named in an HTML page, such as images, are automatically fetched, and HTTP makes additional TCP connections and/or pipelines multiple file transfers on each TCP connection.
- Explain the Slashdot Effect. Explain how Content Distribution Newtork and Parallel Server Cluters provide different ways to address this issue.
The Slashdot Effect occurs when a high volume of traffic is directed simultaneously directed at a single internet server, as occurs when a URL is posted on the Slashdot tech news feed. The result is the congestion of the networks to which the server is attached and/or the overwhelming of the server itself, resulting in the unavailability of the advertised service and/or a server crash.
- Explain how the problem of freeriding is dealt with in BitTorrent
Freeriding in peer-to-peer systems occurs when a participant receives service from peers but does not provide any services to others. In BitTorrent the ability of a participant to recieve downloads of file chunks from peers is limited until it provides service to others (this is called Tit-for-Tat).