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Networking Assignment: Wireless Systems & Networks


Answer the following questions through this networking assignment:

1. In CSMA, explain the operations and problems of 1-persistent CSMA.
2. Why is there no concept of acknowledgment (ACK) in the CSMA/CD protocol?
3. What is the hidden node problem? And explain how to resolve it with RTS and CTS.
4. In IEEE802.11 as shown below, we assume that MAC addresses of stations and APs are STA1, STA2, …, AP1, and AP2 instead of 48-bit addresses. The SSID for ESS is Univ_Net.

a. When STA3 tries to join BSS1, explain the process of (management) frame interactions between AP1 and STA3. (Describe and draw simplified frames focusing on frame control fields of 2-byte and 4 addresses.)
b. When STA3 leaves BSS1 and rejoin to BSS2, describe the process of between AP1 and AP2.

5. For a network to cover a region of 100×100 m2, we used 40 wireless nodes with the transmission range of 10m. What are the expected problems if we use:

a. More mobile nodes (for example, 80 wireless nodes in total)
b. More power in signal transmission (for example, transmission range of 20m)


Considering the research conducted on this networking assignment, CSMA stands for Carrier Sense Multiple Access under which 1-persistent CSMA is considered as an aggressive version of CSMA protocol. The operation of 1-persistent CSMA is done in Medium Access Control. Using this specific protocol, not only one user but two or more users can receive and send data by a single shared medium. The shared medium can be an optical fiber or single cable that connects to more than one node or it can be also connected to a part of the wireless spectrum (Islam et al. 2018). In this aggressive version called 1-persistent CSMA, a frame is owned by the transmitting station for the purpose of sending the data and the busy channel is also sensed by it, this CSMA also waits till the ending of transmission and then transmit without taking much time. 1-persistent CSMA sends the data with probability 1 and hence its name is given 1-persistent CSMA.

The problem of 1-persistent CSMA is having much probability of collision. In this method, there is a big chance of a particular situation that brings the chance of collision. The specific situation is when more than two or two stations find the channel in an idle position at the same time. The collision is also possible when the frames of more than two stations are transmitted at the same time. At the time of the collision, the stations have to spend some time and wait for the channels to be normal and idle before and the process is to restart again. Hence, the collision is one of the main problems of 1-persistent CSMA.

2. CSMA/CD stands for Carrier Sense Multiple Access/ Collision Detection. It is a network protocol that helps in transmitting the data frames. A medium access control layer is used to make this protocol work. The network protocol CSMA/CD senses the shared channel in the initial stage or process and then it broadcasts the frame. A frame is transmitted by this network protocol only if it senses the channel idle. The frame is transmitted by this protocol to check the transmission whether the process was successful or not. If the transmission of the frame is successful then another frame is being sent by the station. In the whole process, if any detection of collision is made or if it senses the collision then it sends a signal indicating stop or jam so that the shared channel can terminate the transmission of data (Kitindi et al. 2017). After a while when all the things become idle as before it sends the frame to the channel. In the whole process, there is no concept of acknowledgment because this network protocol does not use the ack concept to check whether the transmission was successful or not. Collision signals are used by this network to check the transmission was unsuccessful or successful.

3. The hidden node problem is also known as the hidden terminal problem can be often seen in wireless networking. This problem happens when a node is able to make communication with wireless AP (Wireless Access Point) but is not able to make its communication with several other nodes which are already making its communication with that access point. In short and simple language, hidden node problem in wireless local area network occurs when more than two or even two stations that are not in range with each other make its transmission simultaneously to the common recipient. Hidden node problem creates so many difficulties in MAC sublayers (medium access control) as so many data packets can be sent by multiple nodes at the same time due to which interference occurs at an access point that result in null packet getting through.

RTS/CTS that stands for Request to Send/ Clear to Send is considered as the practical solution to mitigate the difficulties of hidden node problems. The nodes in this mechanism send small packets in order to request and get permission to access points so that they can send larger data packets. As all the responses from the access point are seen by these nodes, synchronization of nodes can be done to avoid interference while the transmission is made. The process of solving the problem undergoes in this way. Ready To Send signal is firstly sent by the node while sending the data. If the AP is receiving the data without any interferences it will send the Clear To Send signal back (Lee and Hong 2017). After that, the node gets the Clear To Send signal from the AP without the Ready To Send signal, it will be clear that the Clear To Signal is for the hidden terminal and it will stop transferring any data. In this way, the hidden node problem can be resolved by RTS and CTS.

4. a) When STA3 will try to join the BSS1 as per the given scenario, the access point will help the frames to transmit it to the STA3. The servers are responsible for creating the frames and this is the reason that the source address of any of the frames is the MAC address. Here, in the given case, the frames are totally relayed in the AP1 and this AP1 will use its transmitter address in the form of a wireless interface. Then after that, the frames will be sent to the STA3 which is now the client for the AP1. In this way, the frames will be managed and the frame interaction is done in between the AP1 and STA3.

b) When STA3 leaves BSS1, then it will automatically disconnect to the AP1. As we know, the stations and devices are not directly communicating with each other and that is the reason for the access point requirement for the purpose of communication and sending and receiving of data. The access point is acting as a medium. As per this theory, all the communications will be cut off from the station STA3 and the devices that are connected to the AP1.

Now, when the STA3 will connect to the AP2 then communication can be possible between STA3 and the connected devices with the AP2. Now there is no link between the AP2 and STA3 and a new link will be formed between the STA3 and AP2 as STA3 is now under the surroundings of AP2.

5. a) If there is an increase of a greater number of mobile nodes then it will create high consumption of energy as every node is equipped with the help of a battery. In the given case scenario, we were having 40 nodes and now we are just increasing the number of nodes in that particular given area. Every node will require energy for the charging of its battery. In this situation, we are increasing the power demands in that area. As power is not increased and only, we are increasing the node numbers so, this will increase the demand for power on that network (Raschella et al. 2017). This is the reason that will create the power failure of the network system as the number of nodes are doubled in the given scenario.

b) As we know, that the power is calculated with the help of a formula. For a defined area having a fixed number of nodes, power is also fixed. We are just calculating the power as per the number of nodes and the area in which the power is required. This fixes the requirement of power in any particular area for any particular number of nodes.If we increase more power in signal transmission in the given area then it can lead to the overpower supply to the number of nodes in that network system (Han et al. 2018). This will lead to a negative effect on the nodes and the increase in power will break down the overall network system. This can create an issue for the overall network system and there can be dis-functionalities in the nodes connected to that network.

Kitindi, E.J., Fu, S., Jia, Y., Kabir, A. and Wang, Y., 2017. Wireless network virtualization with SDN and C-RAN for 5G networks: Requirements, opportunities, and challenges. IEEE Access, 5, pp.19099-19115.
Han, K., Li, S., Tang, S., Huang, H., Zhao, S., Fu, G. and Zhu, Z., 2018. Application-driven end-to-end slicing: When wireless network virtualization orchestrates with NFV-based mobile edge computing. IEEE Access, 6, pp.26567-26577. Lee, D. and Hong, C.S., 2017, September. Access point selection algorithm for providing optimal AP in SDN-based wireless network. Networking assignment In 2017 19th Asia-Pacific Network Operations and Management Symposium (APNOMS) (pp. 362-365). IEEE.
Islam, M.M., Funabiki, N., Kuribayashi, M., Debnath, S.K., Munene, K.I., Lwin, K.S., Sudibyo, R.W. and Al Mamun, M.S., 2018. Dynamic access-point configuration approach for elastic wireless local-area network system and its implementation using Raspberry Pi. International Journal of Networking and Computing, 8(2), pp.254-281.
Raschella, A., Bouhafs, F., Seyedebrahimi, M., Mackay, M. and Shi, Q., 2017. Quality of service oriented access point selection framework for large Wi-Fi networks. IEEE Transactions on Network and Service Management, 14(2), pp.441-455.


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