Lecture 10

• what is addressing?


  a process that allows an application on one machine to send a message to an application on another machine. The idea is that the sending application must be able to identify the receiving application.
• How does addressing work?

  to identify the receiving application, one must specify the name or address of the host machine. As well as the identity of the receiving process (receiving application) on the receiving side.
• In the case of the internet, what is the destination host's address specified by?

  IP address
• can hardware ip address change? what about network ip address?

  hardware ip address cannot change. Network ip address can change if it is moved from one network to another.
• how many bits is an IP address?

  32
• how many bits is a port number

  16
• what is an analogy for ip addresses and port numbers?

  ip addresses are like the street address of an apartment building. port numbers are like the number of a particular apartment within the building. In order for a data packet, or letter, to be delivered properly, both numbers must be known.
• what is a software port?

  a virtual data connection that can be used by programs to exchange data directly, rather than through a file or other temp storage. The two most common are TCP and UDP ports, used to exchange data between computers on the internet.
• what is the structure of a network application?

  • the user interface; allows user to control application functionality.
  • application logic; software code, processing instructions that provide functionality
  • application-level protocol; the format and order of messages exchanged between processes, as well as actions taken on a transmission or receipt of message
• what data is being sent over the internet?

  packets: data, broken into smaller pieces for easier sending
• How can you use the internet in Processing?

  the Network library. It allows you to communicate with another processing application, download data from the internet, send data to be stored or processed remotely.
• how do you implement the use of the Network library in Processing

  Use the Client class. it is used to create a client object that connects to a server to exchange data.

  import processing.net.*;

  Client networkClient = new Client(this, "www.oreilly.com", 80);

  // connects to the server on port 80
• what are the characteristics of a client

  • sends the request
  • initiates requests
  • waits for and receives replies
  • usually connects to a small number of servers at one time
  • typically interacts directly with end-users using a GUI
• what is the Server class from the Network library used for?

  to create server objects that can send and receive data to and from any client connected to it.

  you can create a new server object by passing the port number that the server should be available on:

  Server srv = new Server(this, 5204);
• what are the characteristics of a Server?

  • it is the receiver of a request which is sent by a client
  • passive
  • waits for requests from clients
  • upon receipt of requests, processes them and then serves replies
  • usually accepts connections from a large number of clients
  • typically does not interact directly with end-users
• what is the transport layer?

  the layer of the network responsible for making sure packets get to their destination. Two protocols used to handle transport of packets on the internet: Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)
• what are the characteristics of the UDP model?

  • lightweight transport protocol with minimalist service model
  • connectionless, no handshaking before two processes start to communicate
  • provides unreliable data transfer service; no guarantee that message will reach receiver
  • messages may arrive out of order
  • no flow control; data may be sent at any rate.
  • good option for real-time data transfer, as lack of acknowledgements or retransmissions prevents transmission being slowed
  • no guarantee on delay
• TCP model characteristics


  • Connection-oriented service
  • Reliable data transfer
• TCP connection establishment


  1. Client and server exchange control information

  2. Prepare for transfer of packets (handshaking procedure)
• TCP connection


  Full-duplex connection between sockets of two processes, where both can send messages/data at the same time
• After TCP data transfer, the connection must be

  Torn down. The connection is a "connection-oriented "or "virtual circuit" service. the two processed are connected end-to-end in a loose manner without support from intermediate nodes
• TCP


  • Reliably delivers all messages without error, in order
  • Includes end-to-end flow control, regulating sender transmission based on availability of receiving buffer
  • Includes congestion control
• How does the user understand what an application is doing, how user actions have been interpreted, and How to get the application to do what the user wants?

  Feedback and Output
• What are some benefits of communicating over networks?

  • Enables applications to work remotely
  • gather data from internet
  • ability to network multiple devices and machines
• does all the communication in an interactive application have to be between the user and the app?

  No, in most interactive applications, a great part of the communication goes on between the application and other devices or applications
• what is the simplest network


  one-to-one connection between two objects
• Before communication between two objects takes place, what has to be established?

  Rules for communication must be established
• what are the layers of agreement (rules) for the communication between to objects?

  • physical: physical ports,pins
  • electrical: voltage levels
  • logical: what does an increase in voltage represent?
  • data: bit transfer (timing, size, packages or not)
  • application: how are groups of bits arranged into messages?
• In a simple network like Arduino to computer you only have two points: sender and receiver. What is used/needed In a more complex network, like the internet?

  A map to keep track of objects: addressing scheme.
• what are the different types of networks?

  • Directly connected Network; every system connected to each other
  • Star network; one hub and every system connected to the hub
  • Ring network; systems connected to only one system in a circle.