Transmission versus Propagation Delay
This simple applet illustrates one of the most fundamental concepts in computer networking: transmission delay versus propagation delay. Although this concept is discussed in detail in Chapter 1, an "interactive animation speaks a thousand words". You set the length of the link, the packet size, and the transmission speed; the applet shows the packet being sent from sender to receiver.
Queuing and Loss Applet
As we learned, the most complicated and interesting component of end-to-end delay is queuing delay. In this applet, you specify the packet arrival rate and the link transmission speed. You'll then see packets arrive and queue for service. When the queue becomes full, you'll see the queue overflow--that is, packet loss. Enjoy!
With this interactive applet, you will see the effect of pipelining when a large message is chopped up into many small packets. There are four nodes: a source, a destination and two intermediate store-and-forward switches. Each packet sent from the source must be transmitted over three links before it reaches the destination.
This applet provides "back-of-the-envelope" visualizations and calculations for Web response times. You define the number of objects in the Web page, the round-trip time (RTT), whether persistent connections are used or not, and the number of parallel connections. The applet then does all the work!
Recursive/Iterative Queries in DNS
This DNS applet animates additional combinations of iterative and recursive queries among four name servers: a local name server, a root name server, an intermediate name server, and an authoritative name server.
Multithreaded Web Server
This Web server that is capable of serving multiple requests in parallel based on HTTP1.0,as defined in RFC 1945.
Mail Sender (User agent)
This Mail Sender provides a graphical interface for the sender ,with fields for sender's e-mail address, recipient's e-mail address, subject of the message, and the message itself. It can set the SMTP server's IP address.
This insightful applet animates the Go-Back-N theory, covered in Section 3.4 of the text. In this applet, the window limits the sender to a maximum of five unacknowledged packets. Try repeatedly clicking on "Send New" six or more times. What happens?
This applet animates the interaction between the sending application, the TCP send buffer, the TCP receive buffer, and the receiving application. The receiving application reads chunks of bytes at random times. When the receive buffer becomes full, the TCP receiver advertises a receive window of 0. As described in the text, the sender then continues to send segments with one byte of data. There is a small bug in this applet for a certain combination of file and buffer sizes. Can you find it?
In this simple "calculator applet," you provide the datagram size and the MTU, and the applet returns information about the fragments that are derived from the
It provides important insights into random access protocols, animating the interaction between propagation delay and transmission time. Notice that at 10 Mbps, a single packet can monopolize the entire link for almost an eternity. Also notice that after a collision, the link can idle for an exceedingly long time before a node retransmits. You can learn a lot about CSMA by playing with the different parameters. Enjoy!
CSMA/CA WITHOUT Hidden Terminals
In this applet there is one access point and three mobile stations. By clicking on a station button, you instruct the station to emit a frame. Each station uses the CSMA/CA protocol. You'll be able to visualize the RTS/CTS sequence, the NAV, collisions, and the countdowns. In this version, all of the stations can hear each other's transmissions. The applet provides great insights into a complex protocol.
CSMA/CA WITH Hidden Terminals
This applet is similar to the previous applet, but now none of the mobile stations can hear the transmission of any other mobile station.