Transmission versus Propagation Delay Applet (Chapter 1)
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 (Chapter 1)
As we learned in Chapter 1, 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!
Message Segmentation (Chapter 1)
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.
HTTP Delay Estimation (Chapter 2)
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 (Chapter 2)
In Section 2.5 of the text the authors gave examples of recursive and
iterative DNS queries. 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.
Go-Back-N Protocol (Chapter 3)
This applet animates Go Back N, covered in Section 3.4 of the text. Go
Back N provides reliable data transfer using 'cumulative'
acknowledgments, a sending window size > 1, and a receiving window size
Selective Repeat Protocol (Chapter 3)
This applet animates Selective Repeat, also covered in Section
3.4 of the text. Selective Repeat provides reliable data transfer using
'selective' acknowledgments, and both sending and receiving windows
sizes > 1. Compare and contrast this applet with the previous Go Back N
Flow Control (Chapter 3)
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.
IP Fragmentation (Chapter 4)
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 datagram. Compare the results from this applet to that
of Table 4.2 in the text. You will see a discrepancy, as there is an
error in how the applet calculates the offset. If you would like to
create a new version of this applet that corrects this problem, please
contact the authors.
CSMA/CD (Chapter 5)
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!
802.11 CSMA/CA WITHOUT Hidden Terminals (Chapter 6)
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.
802.11 CSMA/CA WITH Hidden Terminals (Chapter 6)
This applet is similar to the previous applet, but now none of the
mobile stations can hear the transmission of any other mobile station.