Computer Network Assignment: Techniques & Protocols used in TCP/IP Model

Question

Task: Question: Requirements
Prepare a detailed computer network assignment report addressing the following questions:
1. Fig. 1 illustrates how a message is transmitted from the application layer to the physical layer in the Internet model of a data communication network.
a. With the aid of the diagrams of header formats, explain the main purpose of all fields of the header formats of the transport, network, and data link layers protocols. For example, the main purpose of the source address and destination address of an IP Header is to provide the sender and receiver IP addresses, respectively. Note, for IP header, include IPv4 packet header format only i.e., you do not need to consider IPv6 packet header format.

b. Use your web browser to connect to one of the following websites whose number in the number list is equal to the first non-zero digit of your student ID. Let your student ID be 32684567. Since the first digit of your student ID is 3, you need to select https://www.harvard.edu/ (3rd item) of the following list:

1. https://web.mit.edu/
2. https://www.stanford.edu/
3. https://www.harvard.edu/
4. http://www.ox.ac.uk/
5. https://www.imperial.ac.uk/
6. https://www.berkeley.edu/
7. https://www.southwales.ac.uk/
8. https://www.wisc.edu/
9. http://umanitoba.ca/

Using the Wireshark protocol analyser, capture all packets generated in response to your request for the above web page. For a selected pair of the first HTTP request response lines, write the hex/decimal values of all fields of the header formats of the transport, network and data link layers protocols whatever available in your file captured by Wireshark.

2. Draw how the bit pattern 1 0 1 1 0 0 1 1 would be sent using
a. Unipolar signalling
b. Return to zero (RZ) signalling
c. Non return to zero (NRZ) signalling
d. Manchester encoding
e. Amplitude Modulation (AM)
f. Frequency Modulation (FM)
g. Phase Modulation (PM)
N.B. You can draw the bit pattern on papers and insert them as pictures into your document.

3. Answer the following questions on media access control:
a. What is media access control and why is it important
b. List two examples of controlled access and contention-based media access protocols and their application areas.
4. Briefly describe the Web of Things (WoT). List four examples of WoT applications.

Answer

Computer Network Assignment Answer 1
Part a
TCP Header

Source Port

Sending port
Destination Port
Receiving port
Sequence number
If SYN flag is set, then this is initial sequence number else it is accumulated sequence number

Acknowledgement number
If ACK flag is set, then it next sequence number that sender is expecting
Data offset
It denotes size of TCP header in units of 32-bit words

Reserved
It is for future use and must be set to 0

Flags
NS:- concealment protection
CWR:- It indicates that it received TCP segment with ECE flag set and sent response in congestion control mechanism
ECE:- If SYN flag is set, TCP sender is ECN capable else it indicates network congestion to TCP sender
URG:- indicates if urgent pointer field is significant
ACK:- indicates if acknowledgement field is significant
PSH:- Asks to push buffered data to receiving application
RST:- Resets connection
SYN:- Synchronise sequence numbers
FIN:- Last packet from sender

Window size
Number of window size units that the sender of this segment can receive

Checksum
checksum used for error checking of TCP header, payload and IP
pseudo header
Urgent pointer
Offset from sequence number indicating last urgent byte
Options
Extra TCP options
IPv4 Header

Version
IP protocol version. For IPv4 it’s 4
Internet Header Length (IHL)
Size of IPv4 header in units of 32-bit words
Total length
Entire packet size including header and data
Identification
Used for identifying fragment from group of fragments of single datagram

Flags
Bit 0:- Reserved; is zero
Bit 1:- Don’t fragment
Bit 2:- More Fragments

Fragment offset
It denotes offset of this fragment in the original unfragmented datagram
Time to Live (TTL)
It specifies maximum number of hops the datagram can take before reaching destination
Protocol

Protocol used in data portion of IP datagram
Header Checksum
It is used for error checking of header
Source Address
Address of sender of packet
Destination Address
Address of receiver of packet
Options
Extra IPv4 options. Usually not used
Ethernet Header

Preamble
It is special bit pattern which allows devices on network to synchronise their receiver clocks
Start frame delimiter (SFD)
It denotes end of preamble and start of Ethernet packet MAC destination
Receiver’s MAC address
MAC source
Sender’s MAC address
802.1Q tag
If present, it indicates virtual LAN membership.
Length
Size of payload in octets
Payload
The data payload for higher layers
Frame check Sequence (FCS)
It is a CRC checksum for handling corrupt frames which is computed as function of MAC source and destination addresses, length field, MAC client data and padding.

Interpacket Gap (IG)
It is idle time between two packets
Part b
Transport layer

Network Layer

Data Link Layer

Answer 2

a. Unipolar Signalling

b. Return to zero (RZ) signalling

c. Non return to zero (NRZ) signalling

d. Manchester encoding

e. Amplitude Modulation (AM)

f. Frequency Modulation (FM)

g. Phase Modulation (PM)

Answer 3
Part a
Media Access Control (MAC) is the sub layer that is responsible for controlling the hardware for interaction with wired medium, optical medium and wireless transmission medium. The data link layer in the OSI model is comprised of MAC sublayer and the LLC sublayer together. The function of MAC layer is to provide the flow control and multiplexing for the transmission medium. This sublayer corresponds to layer 2 of the OSI model which is the data link layer.

When sending data frames to other devices on the network, the MAC sublayer is responsible for encapsulating the frames provided by higher levels into frames which can be transmitted over the transmission medium. This sublayer adds a frame check sequence which is used to identify errors and then transfers the frame to the physical layer as soon as it is available to transmit data. When receiving data frames from a physical layer, it then verifies data integrity by using the frame check sequence of sender and then strips the ethernet header and sends the frame to a higher layer. This sublayer has protocols that determine how nodes share channels and prevents collision.

Part b
Token Passing
Token passing is controlled access MAC sublayer protocol. If many nodes are connected on a shared medium, token passing determines which node has the right to send a message in order to avoid collision on the physical layer. In this method, nodes on a shared medium logically form a ring. The token is a special bit pattern which is passed from node to node. Whoever has a token has permission to send frames on the physical layer. Once done, a token is passed to the next node.

This protocol can be used in scenarios where access delay for the physical medium needs to be bounded. Given N nodes, this protocol guarantees to give access to the physical medium with some upper bound in terms of N. On the light load, it’s performance is not very good. But when most of the users on the shared medium have large amounts of data to be transmitted , then network load becomes very high. In this scenario, token passing proves to be a very efficient scheme.

Pure Aloha
Pure Aloha is a contention based MAC sublayer protocol. This protocol allows the stations / nodes to transmit data over the physical medium at any time they want. After transmission, stations wait for sometime for the acknowledgement from the receiving medium. If acknowledgment is not received. Then it uses Back Off strategy and waits for a random amount of time. After this it resends the data packet again. It keeps on retrying until the Back Off limit is reached on which the transmission is cancelled.

Aloha is used in modern wireless communication systems. When the call is set up on a cellular telephone system which can be either analog or digital, Aloha random access is used for communication in the wireless medium. The random nature of aloha protocol reduces collision in the medium. It can be used in small scale networks as the load will be low hence less collisions. On large networks, the collisions increase a lot so that Aloha cannot be used.

Answer 4
The Web of things is a modern programming paradigm which will allow objects in this world to be able to come online and become part of the internet. WoT is analogous to the application layer of OSI stack and IoT is analogous to network layer of OSI stack. WoT provides the application layer interface to the IoT applications which are spread over a lot of devices running on different platforms and different application domains. IoT takes care of connectivity of the devices with the internet. So WoT does not focus on the connectivity of devices. It just assumes connectivity and pays attention to the development of applications.

Applications
Xively
It is a commercial website which is used for WoT data aggregation and data mining.

ThinkSpeak
This platform is used for collecting, analysing and acting ton the data generated by sensors and actuators.

Everything
This is a platform which is responsible for making connected devices and unconnected products as part of the Internet on WoT architecture.

Smart Factory
Factory equipments can be automated based on industrial protocols. This makes it very easy for remote access to the equipments.

References
Guinard, Dominique; Trifa, Vlad; Mattern, Friedemann; Wilde, Erik (2011). From the Internet of Things to the Web of Things: Resource Oriented Architecture and Best Practices (PDF). Springer. pp. 97–129

Trifa, Vlad (2011). Building Blocks for a Participatory Web of Things: Devices, Infrastructures, and Programming Frameworks (PDF) (Ph.D.). Computer network assignment ETH Zurich

Web of Things (WoT) Architecture (2020) https://www.w3.org/TR/wot-architecture/#example-smart-factory

Media Access Control - an overview | ScienceDirect Topics (2019). https://www.sciencedirect.com/topics/computer-science/media-access-control

Controlled Access Protocols in Computer Network (n.a.).https://www.geeksforgeeks.org/controlled-access-protocols-in-computer-network/

Local Area Networks (n.a.) https://nptel.ac.in/content/storage2/courses/117105076/pdf/5.4%20Lesson%2018%20.pdf

Access Control in Networking (n.a.) https://www.gatevidyalay.com/aloha-pure-aloha-slotted-aloha/

The ALOHA Protocol (n.a.) http://www.wirelesscommunication.nl/reference/chaptr06/aloha/aloha.htm