Networking Concepts and Applications

Week 5/6 iLab Report

Jainika Soni

DeVry University

MIS589: Networking Concepts and Applications

MIXED 11B/11G WLAN PERFORMANCE

Submitted to:

Professor: Nichelle Manuel

Date: 6/13/2014

Mixed 11b/11g WLAN Performance

1. In your opinion, what is the purpose of our dropping the transmit power to such a low level?

With dropping the power output will help increase stability if there is a lot of interference with outside noise. The node might not need the extra performance or the extra distance the higher transmit power would generate.

1. What do access point connectivity statistics collected for the roaming station show?

[pic 1]

By looking at the graph it looks that the Wireless LAN Access Point connectivity the first line stays connected for 10 seconds and then drop for  two second and then up for 8 seconds and then drop again for 2 seconds and up again for 8 seconds. So there is some interference but overall it looks staying connected.

1. 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.

1. How much did our roaming node reduce the total throughput in our heavily loaded WLAN?

[pic 2]
When simulation started throughput was at 25,000,000 bits/sec from 1 to 12 seconds. Then at 13 second it dropped to around 10,000,000 bits/sec and stayed same till 22secons. At 22 seconds it went back up to 25,000,000 bits/sec.

1. 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

1. 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?

The 802.11g LANs, operating in the same lower frequency band as 802.11b and being backwards compatible with 802.11b yet with the higher speed transmission rates of 802.11a. (Kurose 527). The speed of 802.11b is up to 11Mbps and the speed of 802.11g is up to 54Mbps just like 802.11a. 802.11g is by far most popular technology. (Kurose 526).

1. 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 are the optional mechanism used by the 802.11 wireless networking protocols to reduce frame collision introduced by the hidden node problem. Modern RTS/CTS includes ACKs and does not solve the exposed node problem. CTS-to-self mechanism the sending node avoids an RTS/CTS exchange and instead initiated transmission by directly sending a CTS-to-self. The primary reason for doing so is to prevent unnecessary overhead associated with RTS/CTS exchange. It reduces overhead associated with each transmission.
   
2. 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?
   The 802.11b signals are modulated using complementary code keying (CCK) to compress data using a series of compression keys broadcast during the preamble portion of each transmission. Enabling 802.11b and 802.11g network will cause a general performance drop. For purposes of backward compatibility, all initial 802.11g network transmissions are sending using CCK.
   
3. 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?
   Some network transport protocols such as TCP provide for reliable delivery of packets. In the event of packet loss, the receiver asks for retransmission or the sender automatically resends any segments that have not been acknowledged. Retransmitting missing packets causes the throughput to drop.
   
4. In situations where 802.11g and 802.11b are coexisting, what steps might you take to minimize the impact of the presence of the legacy nodes?

To minimize the impact of the presence of the legacy nodes where 802.11g and 802.11b are coexisting, make sure the frequencies are not overlapping.

[pic 3]

Conclusion: