Task 1: question 1
Calculation of CRC involves looking at the data or message as one binary number, and then it is divided by a particular value, where the remainder is the CRC.
M=10011101 is the input or the message in form of a binary number, while P=1001 is the particular divisor, and the calculation follows as below.
10011101
1001
00001101
1001
0100 = remainder = CRC checksum
The CRC is 0100, which if converted to decimal numbers it is 4.
Question 2
If the transmission is successfully sent, the cyclical redundancy check calculation for the receiver will appear as follows,
Message with CRC = 10011101
Polynomial = 1001
10011101 1000 = the input with a check value of 4 bits
1001 = remains as the divisor. The calculation follows as below,
10011101 1000
1001
00001101 1000
1001
0100 1000
100 1
000 0000 = remainder, hence there is no error that occurred during the transmission, meaning he received the right data as sent from the sender.
Question 3
When the third bit digit from left in the message that is zero is inverted, it will be interpreted as one, and an error will occur, calculated as follows.
10111101 = the message with the third bit from left inverted.
1001 remains the polynomial divisor, and the check is still to 4 bits as in the previous check.
10111101 1000
1001
00101101 1000
1001
001001 1000
1001
0000 1000
1001
0001 = remainder, which represents the error.
Task 2: question 1
Sliding window flow control is a mechanism used in TCP for transmission of data in way to ensure reliability of the information sent. The sliding window enhances matching the rate of transmission of data from the sender to that of the receiver with the networks transmission rate. This is to mean that the sender does not send too much data packets than the receiver can process. For instance, a new model computer may send bigger many packets of data at a time than an older model. The sliding window flow control will ensure to control the speed so that the receiver can process at its own pace. A diagram of the sliding window technique is s follows,
Source: The TCP/IP Guide (2005).
The window is the maximum number of packets or maximum information that can be sent without having to wait for an acknowledgement. Acknowledgement is used here to mean the message or indication that data has been sent to the receiver that is receive by the sender when the message is sent. If the time set by network for sending the message elapses, the message is resent again by the sender, hence, it is not lost in the way. In the diagram, the category 1 is already confirmed to the sender, the window carries a maximum of 20 bytes and from the diagram, the window is sending the data in a sliding way where it starts from the first byte, and slides to the rest taking 20 bytes at a time. Depending on the receiver, category 3 is not received yet, probably because the receiver cannot process more information beyond 14 bytes at a time. Category 4 is the data beyond the maximum that a window can hold; hence, the data is yet to be sent by the widow (The TCP/IP Guide, 2005).
Question 2
Due to the ability of the sliding window to vary the transmission rate, it is ideal for transmitting data in continuous flow; hence, there is no need to wait until data is sent to send more. In a stop and wait flow control, the sender cannot send more information until there an acknowledgement is received. The method is not efficient enough especially when the data is broken into several portions, unlike the sliding window that will continue to send until the message is fully sent. The sender can send several frames to be in the transmission at one time while the stop and wait cannot. These make the sliding window more efficient than the stop and wait method (The TCP/IP Guide, 2005).
Question 3
Sometimes the TCP reduces the size of the window temporarily for some various reasons such as how much the server is engaged in other connections. Other problems could include a faster sender sending data to a slow receiver. If the window size is 360 bytes, and a receiver has a buffer of just 260 bytes, the window size will automatically reduce to allow the receiver to take information at its pace. If the receiver is engaged in other connection on the TCP, the buffer or amount of data that it can receive reduces, hence the window is reduced. Another reason that could reduce the size of the window is if the receiver switches off or reboots in the process of transmitting data. An acknowledgement will not be sent, hence the sender will try to resend the data that has not been received, which could be lesser in size, and hence the window reduces to the size of the message being resent.
Task 3: question 1
The WIMAX wireless technology is used mostly in mobile internet connection, where people can access the internet from their mobile digital devices such as mobile phones and laptops. This is to mean that it one can access internet from anywhere without needing to connect to a cable. The current WIMAX has a capacity of 40Mbp/ s, which is lesser than the other internet connections through a cable. However, the current WIMAX that is under innovation is expected to handle higher quantity, meaning that one could access the internet with the same speed or more from a wireless connection. In addition, the WIMAX does not require one to have a SIM card for connection, since its chip can be put on mobile devices such as laptops and phones, and access to the internet can be easier since it is designed to optimize data access. In addition, the WIMAX operates on distances, and because unlike WI-FI, it is licensed, it can cover greater distances, allowing connection in further distances from the station, such as in radio frequencies. This means that one can still access connection to the network from outdoors when moving around, and stay connected to other sources. For this purpose, the WIMAX will be needed for meeting the demand for connection and sharing of information for daily purposes b y corporate users and people. Moreover, due to its ability for wider coverage, it will be more reliable and cheaper to the users than the services provided by cellular operators. The WIMAX has an advantage over the cellular services since it will allow voice to be transmitted as well as videos, which is not available with the cellular services.
Question 2
WI-FI and WIMAX are technologies used for wireless connection; however, they differ in terms of their technical use by the Media Access Controller (MAC) layer. In WI-FI, the MAC uses disputing access, where the subscribers that sending information through the wireless aces point, AP, have to compete for it, on a randomly interruptible basis. This means that users further away can be interrupted by users closer to the server, since it depends on distance and services among many users at the same time is hard to maintain. In contrast to the WI-FI, MAC uses a scheduling algorithm that reduces completion for the AP after initial entry for WIMAX 802.16. After entry each subscriber is given an access slot by the server station that can at times vary in size, but cannot be used by any other user, hence, interruption is unlikely. It is more efficient in overload subscription and allows the base station to control the quantity of service where it balances the time slots for the subscribers.
Question 3
WIMAX has several applications that allow it to be used by customers without needing to connect through a cable. One of the applications is dedicated point-to-point services where antennas are used for data transmission of up to 100 Mbps. This type of application has been used in networks of 10-66 GHz, and they use a line-of-sight where they are mostly used for corporate data networks (Asia-Pacific Broadcasting, 2009). The other application of this technology is the point-to-multi-point that is based on 802.16a or 802.16d that uses frequencies of 2-11 GHz in a non-line-of-sight application. The application is used to deliver wireless Digital Subscriber Line, DSL, at speeds comparable to fixed cable of 512kbps to 2-3 Mbps. With this application, the non-line-of-sight application makes availability of cheap customer premise equipment that can be self installed (Asia-Pacific Broadcasting, 2009). The third application of WIMAX is the mobile/nomadic applications that use the 802.16e standards at below frequencies of 6GHz that competes with 2G and 3G network services provided by cellular network operators. The WIMAX network is designed to optimize IP connectivity, which allows better internet connection services at cheaper costs than the cellular operators do (Asia-Pacific Broadcasting, 2009). This application allows the WIMAX to provide better services in connections to many stations over larger distances at cheaper costs.
Task 4: question 1
In this diagram, there are 17 collision domains. Switches are used to decide which message is sent first in case of collisions by several senders; hence, it breaks collision domains. In this regard, at every port of a switch, there is a collision domain. In this diagram, each port it the switch is considered a collision domain. In switch 0, the collision domain exists between stations A to D, and the one between router 0. If there were no switch, the collision domains would be one in the switch 0 connections since they would all be connected to one port, hence there are 5 collision domains at switch 0, 2 at switch 1, 2 at switch 2, 4 at switch 3, and 4 at switch 4. In this diagram, the switches have broken the collision domains into several of them, so that sending of message can be decided by the switch during a collision since it will send one message at a time and the rest after (Taiey, 2010).
Question 2
In the diagram, there are seven broadcast domains. Routers are considered to break broadcast domains between LANs; hence, each connection to LN from a router is considered a broadcast domain. In addition, Hubs will create a one-collision domain, and at the same time, one broadcast domain. Hence, at switch 2 and 3, there are broadcast domains between the switches and the Hubs, and at the same time, considering the connection between router 0 connecting to LAN 3 is another broadcast domain, as well as router 2 and LAN 2. More over, bridges break up collision domains but make one large broadcast domain, hence, switches are considered bridges with many ports to break up the collision domains, but form one broadcast domain. In the diagram, the LANS are considered broadcast domains, which add up to five, and are separated by the routers. The other two broadcast domains are in the LAN where there are Hubs, which are two (Taiey, 2010).
Question 3
Switching table
| Input | Output | ||
| port | Address | Virtual path indicator | Virtual channel indicator |
| 1 | A | 0 | 60 |
| 2 | B | 55 | 0 |
| 3 | C | 0 | 85 |
| 5 | D | 0 | 95 |
Source: (McQuerry, Jansen, & Hucaby, 2009)
References
Asia-Pacific Broadcasting. (2009). WiMAX Wars – Differences and similarities between Wi-Fi and WiMAX. Retrieved from http://www.apb-news.com/news/154-wimax-wars.html?start=5
McQuerry, S., Jansen, D., & Hucaby, D. (2009). Cisco LAN Switching Configuration Handbook. Boulevard Cisco, TX: Cisco Press
Taiey, T. (2010). The Complete One-Week Preparation for the CISCO CCENT/CCNA ICND1 Exam 640-822: A Certification Guide Based Over 2000 Sample Questions and Answers with Explanations. Bloomington, IN: iUniverse.
The TCP/IP Guide. (2005). TCP Sliding Window Acknowledgment System For Data Transport, Reliability and Flow Control. Retrieved from http://www.tcpipguide.com/free/t_TCPSlidingWindowAcknowledgmentSystemForDataTranspo-6.htm
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