Week 3 iLab Report
David M. Fontanez
DeVry University
NETW360: Wireless Technologies and Services
MIXED 11B/11G WLAN PERFORMANCE
Submitted to: Professor Adnan Turkey Date: Jan 22, 2014
Mixed 11b/11g WLAN Performance
Specific questions from iLab
Guidelines
Answer each of the following questions using the sequence and data from the iLab instructions. Answer all questions in full college-level sentences.
1. In your opinion, what is the purpose of our dropping the transmit power to such a low level?
I think the purpose is to create a small scale test network.
2. What do access point connectivity statistics collected for the roaming station show?
The Access Point Connectivity statistics collected show that the data remains the same. AP Connectivity remained constant throughout the 30 seconds of the simulation.
3. What do you think the Wireless LAN control traffic received by the roaming 11b node when it is in the engineering building is composed of?
According to the lab help files it contains random outcomes for the size of generated packets (specified in bytes).
4. How much did our roaming node reduce the total throughput in our heavily loaded WLAN?
When the simulation started, throughput was at 25,500,000 bits/sec. At 13 seconds which is when the roaming node entered the engineering building, throughput dropped to about 21,600,000 bits/sec at a loss of 3,900,000 bits/sec. At it left (at around 18 seconds), throughput went up to 25,500,000 bits/sec.
5. What caused this reduction in “goodput” on the 11g WLAN?
The interference of the roaming node most likely caused it as we see the throughput drop when it enters the range of the 11g WLAN.
General Questions Concerning Mixing 11b and 11g Clients
Guidelines: Answer each of the following questions using knowledge gained from the iLab, readings from the textbook, and individual research on the Web. Answer all questions in full college-level sentences and paragraphs.
6. Supposedly, 802.11b is backwards compatible with 802.11g, yet this lab demonstrates there are significant problems with allowing the two to coexist. What is the primary incompatibility between b and g?
Appliances may interfere on the unregulated signal frequency.
7. There is another mechanism besides RTS/CTS that helps the incompatibility. Explain briefly the difference between RTS/CTS and CTS-to-self and when each is used.
RTS/CTS exchange is a way for the client to tell the AP, "hey I'm going to transmit, please let everyone know" and the CTS is then sent by the AP to tell everyone else, "hey, be silent while this other node transmits." The difference is that CTS-to-self is a way for the AP to protect its own transmissions from disruption.
8. What is the protection scheme talked about in the standard? In short, how do 11g nodes know that an 11b node is associating and how is CCK involved?
RTS/CTS and CTS-to-self are called protection mechanisms. They protect one transmission from being broken up by someone else. The original purpose of RTS/CTS was basically a way for 802.11g stations to tell 802.11b stations to be silent.
802.11b specifies Complementary Code Keying (CCK), which consists of a set of 64 eight-bit code words. As a set, these code words have unique mathematical properties that allow them to be correctly distinguished from one another by a receiver even in the presence of substantial noise.
9. In addition to the added overhead of the RTS/CTS scheme, what else causes the drop in throughput you see? Are there other factors that can affect the throughput?
If you don't have any hidden nodes, then the use of RTS/CTS will only increase the amount of overhead, which reduces throughput. A slight hidden node
