Networking Fundamentals: OSI Model and TCP/IP Suite

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Assignment 1

Contents
Question 1 List the layers of the OSI model and the TCP/IP protocol suite (the Internet Model)...............3
Question 2 How do the layers of the OSI correlate to the layers of the TCP/IP protocol suite?..................3
Question 3 Which layers of the TCP/IP protocol suite are the network support layers and which layers are
the user support layers?...............................................................................................................................4
Question 4 what is data encapsulation (with respect to Questions 1-3)?......................................................4
Question 5 what are the responsibilities of the Data Link layer?.................................................................4
Question 6 what is the difference between Network layer and Transport layer delivery?...........................4
Question 7 If the Data link layer can detect errors between hops,why do you think weneed another
mechanism at the Transport layer?..............................................................................................................5
Question 8 what are the responsibilities of the Network layer?...................................................................5
Question 9 what are the responsibilities of the Transport layer?.................................................................5
Question 10 what is the difference between a port address, a logical address and a physical address?.......6
Question 11 Name some services provided by the Application layer..........................................................6
Question 12 what are the advantages of combining Session, Presentation and Application layers of the
OSI model to a single layer in the TCP/IP protocol suite?...........................................................................7
References...................................................................................................................................................9

Question 1 List the layers of the OSI model and the TCP/IP protocol suite (the Internet
Model)
OSI model consists of the following layers-
1. Layer 1- Physical Layer
2. Layer 2- Data link layer
3. Layer 3- Network layer
4. Layer 4- Transport Layer
5. Layer 5- Session layer
6. Layer 6- Presentation layer
7. Layer 7- Application layer (Mitchell, 2019)
Figure 1 OSI model
(Source: Mitchell, B. 2019)
On the other hand, the TCP/IP model consists of the following layer-
1. Layer 1- Network access layer
2. Layer 2-Internet layer
3. Layer 3-Transport Layer
4. Layer 4-Application layer (Edwards & Bramante, 2015)
Question 2 How do the layers of the OSI correlate to the layers of the TCP/IP protocol
suite?
The TCP/IP model consists of four layers which are application layer, transport layer, network
access layer and the internet layer. This model was prepared before the OSI model, therefore, the
layer present in the TCP/IP model has been broken into multiple layers which gives a total of
seven layers. The first layer which is the network access layer has been broken into data link
layer and Physical layer in the OSI model. Although the network layer of the OSI model is

similar to the Internet layer present in the TCP/IP model. Session layer present into the OSI
model is equivalent to the transport layer in the TCP/IP model. The session layer, presentation
layer, and application layer in the OSI model are replaced by a single application layer to
perform the operations (Goralski, 2017).
Question 3 Which layers of the TCP/IP protocol suite are the network support layers and
which layers are the user support layers?
The network support layer is responsible for physical data transfer in the TCP/IP protocol suite
and the layers responsible for the transfer are network access layer and the internet layer. These
layers perform similar functions as performed by the data link layer and physical layer for the
physical connection and network layer for connecting the systems. The user support layer has the
functions of translating the data, encoding the data and interacting with the application.
Therefore, the layers present in the OSI model which are an application, session, and
presentation layer in OSI model whose combination is application layer in TCP/IP suite (TCP/IP
Model Layers, 2019).
Question 4 what is data encapsulation (with respect to Questions 1-3)?
Encapsulation is done in the packet transmission of the data when a packet travels through each
layer, the data is combined with already present data such as the address of the host or the
receiver is added to the data for transfer, which is known as the encapsulation in TCP/IP
networking suite. In networking, a protocol takes the data from another protocol and translates it
in another form to send it over the network. Adding of header and trailer in a data packet is an
example of encapsulation in networking (Mahamuni & Barrett, 2016).
Question 5 what are the responsibilities of the Data Link layer?
The data link layer is the second layer present in the OSI model. It has functionalities such as:
 It receives the data from the network layer and converts it into frames which are more
manageable.
 It adds the information of headers and frames to the frames, which is the addressing
information of source and receiver machine.
 It controls the data of transmission rate so that it matches the speed which the receiver
can handle.
 It detects the errors present in the data such as the damaged, lost and duplicate frames and
functions to provide access control over the network. (Thakur, 2019)

Question 6 what is the difference between the Network layer and Transport layer delivery?
S. No. Network layer Transport layer
1 The function of the network layer is
to deliver packets in the network
from source to destination.
The function of the transport layer is to
deliver entire data from one source to
another.
2 It translates the logical address into
a physical address.
Whereas it checks the data packet to
ensure they are error free.
3 It provides connection services for
the network.
It assembles and reassembles the
messages into packets.
4 It converts the data into packets and
delivers to the transport layer.
Whereas the transport layer sends the
packet further for transmission (Nastase,
2017).
Question 7 If the Data link layer can detect errors between hops, why do you think we
need another mechanism at the Transport layer?
The reason behind the error check mechanism present at the transport layer is that data link layer
can detect the error present between the nodes but if fails to detect the errors present at each node
hence the mechanism allows additional security. In the data link layer the communication takes
place through a physical channel but in transport layer entire subnet is used in place of a channel.
Also, the data link layer doesn’t specify the router which will communicate with the host which
is provided by the transport layer (Mula, Ravid, Wertheim, Sela & Kriss, 2017).
Question 8 what are the responsibilities of the Network layer?
The functionality of the network layer is as follow:
 It converts the logical address specified in the packet to its physical address.
 Performs packet switching
 The network layer provides the router and gateway functionality for transfer.
 It routes the packet to the final destination.
 It provides and controls network flow, packet sequencing and error detection.
 Break down larger packets into smaller ones (Mitchell, B. 2019).
Question 9 what are the responsibilities of the Transport layer?
The functionality of the transport layer is described below as:

 It adds the port address to the packet and checks that the packet should be delivered to the
correct process on the correct computer.
 It divides the message into segments and assigns them a sequence number so that the
message can be assembled at the transport layer present on destination.
 It replaces the packets which have been lost in the transmission of data.
 It is either connectionless or connection-oriented where it transmits the data without
establishing a connection and vice-versa.
 It has the functionality of controlling flow from end to end.
 It provides error control so that the message is delivered to the destination’s transport
layer without errors (Transport Layer Functions (Data Communications and Networking,
2019).
Question 10 what is the difference between a port address, a logical address and a physical
address?
Port address- the application running into the system run with a logical number which is known
as the port number. The port number is used to divide the ports in an operating system with the
help of kernels, that pot number is known as the port address (Port Addressing, 2019).
The logical address-logical address is the IP address of a system. It consists of a net ID and the
host ID which helps to identify a particular network from the group of networks present. By
changing the host address, the logical address can also be changed.
Physical address- it is defined as the address of network interface card present in the system
which makes it able to connect with cables. The address of a network interface card is known as
Mac address or physical address. Data link layer uses the physical address.
Question 11 Name some services provided by the Application layer
The services provided by the application layer are:
 Email services such as forwarding and storing emails.
 It creates a virtual terminal on the network so that the user can communicate like it is one
of its own terminals and the host responds to the user.
 It uses services to provide global information across the network.
 It has services like file transfer, management and access facilities (Service Application
Layer - an overview | ScienceDirect Topics, 2019).

Question 12 what are the advantages of combining Session, Presentation and Application
layers of the OSI model to a single layer in the TCP/IP protocol suite?
 Reduces the overall bandwidth.
 Increases the transmission
 Decreases the rigidity of the TCP/IP model (Mitchell, B. 2019).

References
Mitchell, B. (2019). The OSI Model Explained in Easy Steps. Retrieved from
https://www.lifewire.com/layers-of-the-osi-model-illustrated-818017
Edwards, J., & Bramante, R. (2015). Networking self-teaching guide: OSI, TCP/IP, LANs,
MANs, WANs, implementation, management, and maintenance. John Wiley & Sons.
Goralski, W. (2017). The illustrated network: how TCP/IP works in a modern network. Morgan
Kaufmann.
TCP/IP Model Layers. (2019). Retrieved from
https://www.sqa.org.uk/e-learning/HardOSEss04CD/page_06.htm
Mahamuni, A. B., & Barrett, C. (2016). U.S. Patent No. 9,294,584. Washington, DC: U.S. Patent
and Trademark Office.
Thakur, D. (2019). Data Link Layer. Retrieved from
http://ecomputernotes.com/computernetworkingnotes/communication-networks/which-are-the-
sub-layers-in-data-link-layer
Nastase, R. (2017). Computer Networking: Beginners guide for Mastering Computer Networking
and the OSI Model. Independently published.
Mula, L., Ravid, R., Wertheim, O., Sela, R., & Kriss, R. (2017). U.S. Patent Application No.
15/470,928.
Transport Layer Functions (Data Communications and Networking). (2019). Retrieved from
http://what-when-how.com/data-communications-and-networking/transport-layer-functions-data-
communications-and-networking/
Port Addressing. (2019). Retrieved from http://docs.testplant.com/ePN/3.0.0/epn-port-
addressing.htm
Service Application Layer - an overview | ScienceDirect Topics. (2019). Retrieved from
https://www.sciencedirect.com/topics/computer-science/service-application-layer