1.1 A Day in the Life of an Application

• Connectivity: connect to one another and exchange data

Network Application

• Read and write data over network

• Dominant network: bidirectional, reliable byte stream connection

  • One side reads what the other writes

  • Operates in both directions

  • Reliable (unless connection breaks)

Byte Stream Model

• Either side can close the connection

World Wide Web (HTTP)

• Hypertext transfer protocol

• HTTP: document centric

  • Human readable

  • Request

    • "Get / HTTP / 1.1"

  • Response

    • "HTTP/1.1 200 OK"

BitTorrent

• Share and exchange large files

• Client request documents from other clients

• Swarms

• When the client wants to download a file, it first has to find something called a torrent file

  • Find it using the www

  • Download it using HTTP

• torrent file describes some information about:

  • data file you want to download

  • tracker: keeps track of what clients are members of the swarm

• Dense graphs of connections between clients, dynamically exchanging data

Skype

• NAT: network address translator

  • Behind a NAT: can open connections out to the Internet, but other nodes in the Internet can't easily open the connections to you

  • Red-green area

• Reverse connection (from B to A)

• This happens in Skype

  • Skype client: personal machine (behind NAT, for security)