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Questions with Solutions

Chapter Two

The OSI Model and TCP/IP Model

2020/2021
Q1/ List the specific responsibilities of the Physical Layer?
Ans.
The specific responsibilities of the Physical Layer:
a) Convert the logical 1’s and 0’s coming from layer 2 into electrical signals.
b) Transmission of the electrical signals over a communication channel.

Q2/ List the specific responsibilities of the Data link Layer?

Ans.
a) Error control to compensate for the imperfections of the physical layer.
b) Flow control to keep a fast sender from swamping a slow receiver.

Q3/ List the specific responsibilities of the Network Layer?

Ans.
a) Chose the best path from Source-to-destination Packet delivery.
b) Routing packets from source to destination.
c) Logical addressing.
Q4/ List the specific responsibilities of the Session Layer?
Ans.
a) Managing dialogue control.
b) Graceful close.
c) Token management.
d) Synchronization.

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Q5/ List the specific responsibilities of the Presentation Layer?

Ans.
a) Data Representation, and Translation.
b) Compressing and decompressing data.
c) Data compression.
d) Data Encryption and decryption.
e) Security.

Q6/ List the specific responsibilities of the Application Layer?

Ans.
a) Allows user to interface with the network.
b) Provides protocols that are commonly needed.

Q7/ Compare between specific responsibilities of the Transport vs. network layer.
Ans.
Transport layer network layer
logical communication between processes logical communication between hosts
Sender: breaks application messages into Sender:, encapsulates the PDU that it
segments (Segment the PDU), and passes to receives from the Transport layer in the
network layer form of packet PDU and passes to data link
layer

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Q8/ What is the main differences between TCP and UDP Services?
Ans.
Transmission Control Protocol (TCP) User Datagram Protocol (UDP)
Service Service
1. Connection-oriented Connectionless
2. Reliable transfer of data. Unreliable Not guaranteed.
3. Segment retransmission and flow No windowing or retransmission
control through windowing
4. Segment sequencing No sequencing
5. Acknowledge sequencing No acknowledgment
6. Lost data retransmission Feasible Practically, not possible.
7. There is a delay in transfer of The transmission is faster. Due to the
information.
absence of connection establishment phase,

Q9/ Give the Definition of the Connection-Oriented and Connectionless.

Ans.
Connection-Oriented: – before data is sent, the service from the sending computer must
establish a connection with the receiving computer. (Email is connection-oriented).
Connectionless: – data can be sent at any time by the service from the sending computer.
(Downloading a music file from the Internet is connectionless).
Q10/ What does PDU abbreviation stands for in computer networking? Then draw
table showing the shape for the PDU for each layer?

Answer:

PDU stands for: Protocol Data Unit

The Layer Shape of data (PDU)

Top three layers (Application layer). Data

Transport layer Segment

Network layer Packets

Data Link layer Frames

Physical layer Bits

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Q11/ Explain the delivery of data with shapes of data and type of addressing in Layered
model? Or

Q11/ Fill the following table of the delivery data in layered model.

layer Type of delivery Shape of data Type of addressing

Ans.

layer Type of delivery Shape of data Type of addressing

Transport End to End Segment Port (socket)

Network Source To Destination Packet Logical (IP)

Data Link Node to Node Frame Physical (MAC)

Q12/ Define OSI protocol model Encapsulation and the PDU protocol.
OR Q20/ Explain with drawing the Encapsulation process and the PDU protocol.
Ans.

Encapsulation: As application data is passed down the protocol stack on its way to be
transmitted across the network media, various protocols add information to it at each level.
This is commonly known as the encapsulation process.
The form that a piece of data takes at any layer is called a Protocol Data Unit (PDU). PDU’s
are used for peer-to-peer contact between corresponding layers.

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Q13/ Describe the OSI model and explain each layers function and assign each protocol
in the layer.

Layer layers function Protocols

7th Application To allow access to network DNS TELNET
6th Presentation To translate, encrypt, and compress data FTP HTTP SMTP
5th Session To establish, manage, and terminate DHCP
sessions
4th Transport To provide reliable process-to-process TCP UDP
message and error recovery
3rd Network layer To move packet from source to destination IP ICMP ARP
to provide internetworking
2nd Data link To organize bits into frames to provide hop
to hop delivery ETHERNET
1st Physical To transmit bits over a medium to provide Bluetooth
mechanical and electrical specifications

Q14/ Match of the following responsibilities with the corresponding OSI layer?

1- To allow access to network resource. Ans. (Application laver)

2- Data compression. Ans. (Presentation layer)

3- Token management. Ans. (session laver)

4- Connection-oriented and connectionless services. Ans. (Transport layer)

5-Internet Protocol (IP) addressing (Logical addressing). Ans. (Network Layer)

6-Bridges & Switches (multi-port bridges). Ans. (data link laver)

7-Transmission mediums (transmit bits over medium). Ans. (physical laver)

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Q15/ Match of the following responsibilities with the corresponding OSI model.

1- Provides protocols that are commonly needed. Ans. (Application laver)

2- Data encryption. Ans. (Presentation laver)

3- Managing dialogue control. Ans. (session laver)

4- Provide reliable process to process message delivery & error recovery. Ans. (Transport
Laver)

5- Controls the operation of the subnet. Ans. (Network Laver)

6- Error detection and correction methods. Ans. (data link laver)

7- Provide mechanical and electrical specification. Ans. (physical laver)

Q16/ Match of the following responsibilities with the corresponding OSI model?

1- (FTP), (HTTP). (SMTP). (DNS), (DHCP), (Telnet). Ans. (Application laver)

2- Concerned with the syntax and semantics of the information. Ans. (Presentation laver)

3-Allows users on different machines to establish sessions (dialogue) Ans. (Session laver)

4-End-to-end flow control. Ans. (Transport laver)

5-Routing algorithms (Routing packets from source to destination). Ans. (Network Laver)

6-Hop to hop delivery. Ans. (data link laver)

7-Hubs (multi-port repeater). Ans. (physical laver)

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Q17/ which of the OSI layers handles each of the following functions:
1. Sequencing and reassembling?
Ans.- The transport layer
2. Proving best path to reach destination?
Ans.- The network layer
3. Dividing the transmitted bit stream into frames?
Ans.- Data link layer
4. Responsible for error detection?
Ans.- Data link layer
5. Determining which route through the subnet to use?
Ans.- the network layer
6. The layer is closest to the transmission media?
Ans.- The physical layer.
7. Reliable process to process data transportation?
Ans.- The transport layer.
8.Provides access to the network for end user?
Ans.- The application layer.
9.Flow control?
Ans.- Data link layer.

Q18/ Which OSI layers is the network support layers?

Answer: (Physical, Data link, network layers)

Q19/ Which OSI layers is the user support layers?

Answer: (Session, Presentation, Application)

Q20/ Which OSI layer functions as a liaison between user support layers and network
support layers?
a) Network
b) Physical
c) Transport
d) Application
Answer: c) Transport

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Q21/ What are the main protocols used in application layer and mention the job of each
one.
Ans.
protocols Job Description
DNS (Domain Name System) Matches domain names with IP addresses.
HTTP (Hyper Text Transfer to transfer data between clients/servers.
Protocol)
SMTP (Simple Mail Transfer Used to send email messages from clients to servers over
Protocol) & POP3 (Post the internet.
Office Protocol version 3)
FTP (File Transfer Protocol) Allows the download/upload of files between a
client/server

Telnet Allows users to login to a host from a remote location and

take control as if they were sitting at the machine (virtual
connection).
DHCP (Dynamic Host Assigns IP addresses, subnet masks, default gateways,
Configuration Protocol) DNS servers, etc. to users as they login the network.

Q22/ Classify the following protocol with their uses in each layer in the TCP/IP
reference model.
TCP, IP, HTTP, UDP, ETHERNET, ICMP, FTP, TELNET, SMTP, DHCP
Ans.
Layer Protocols
Application HTTP TELNET FTP SMTP DHCP
Transport TCP UDP
Internet IP ICMP
Network access (Host-to-network) ETHERNET

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Q23/ What are the main differences between TCP/IP and OSI 7-layers model?
Ans.
The main differences between TCP/IP and OSI 7-layers model?
OSI Model TCP/IP Model
1. OSI refers to Open Systems TCP refers to Transmission Control
Interconnection. Protocol.
2. OSI uses the network layer to define TCP/IP uses only the Internet layer.
routing standards and protocols.
3. OSI layers have seven layers. TCP/IP has four layers.
4. In the OSI model, the data link layer and In TCP, physical and data link are both
physical are separate layers. combined as a single host-to-network layer.
5. Session and presentation layers are a part In TCP/IP application layer equal to
of the OSI model. application, presentation and session
Layers in OSI

TCP/IP OSI Reference Model

Application
Application

Presentation

Session

Transport Transport

Internetwork Network

Data Link
Network
Interface Physical

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Q24/ Show the encapsulation process at the network and Data link layer at each node in
the following cases:

a- If A send a message to Q
b- If P send a message to Q

A / 50 P / 77 Q / 60

R /75 T / 44 K / 66 F / 99
LAN 1 LAN 2 LAN 3

a- Answer.
Through LAN1 (from A/50 to R/75)

Through LAN2 (from T/44 to K/66)

Through LAN3 (from F/99 to Q/60)

b- Answer.
Through LAN2 (from P/77 to K/66)

Through LAN3 (from F/99 to Q/60)

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Q25: What are the types of connecting devices are used to connect a network or
multiple networks together and cite each device in which layer are used.
Ans.

There are two types of connecting devices:

a. Networking Devices:

1) Repeater: - Repeaters is a Layer 1 device.

2) Hub: - is a Layer 1 device.
3) Bridge: - A bridge is a Layer 2 device
4) Switch: - A switch is a Layer 2 device
b. Internetworking Devices.

5) Router: - Router is a Layer 3 device. choose the best path for them through the
network.
6) Gateway: Gateway is a Layer 7 device.
‫الشكل للتوضيح‬

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Q26: What is the addresses are used in an internet employing the TCP/IP
protocols, and cite each address in which layer are used.
Ans.
Four levels of addresses are used in an internet employing the TCP/IP protocols:

1-Physical Addresses: The physical address, also known as the link address or mac
address ,it is the address used in physical layer.

2-Logical Addresses (IP): Logical addresses are necessary for network to network
communication A logical address in the Internet is currently a 32-bit, and it is used in the
network layer.

3- Port Addresses: It is implemented in transport layer as process to process delivering,

and it is used in the transport layer.

4- Specific Addresses: it is used in the application layer.

‫الرسم للتوضيح‬

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Q27/ Choose the correct answer from the following:

1. The ___________ is responsible for delivering data units from one station to the next
without errors.
a. Network Layer b. Transport Layer c. Data link Layer e. Physically layer
Answer: (c). Data link Layer

2. Web and Mail services are provided by __________.

a. Session Layer b. Presentation Layer c. Application Layer e. Physically layer
Answer: (c). c. Application Layer

3. The TCP/IP __________ layer is equivalent to the combined session, presentation, and
application layers of the OSI model.
a. application b. network c. data link d. physical
Answer: (a).application

4. ____________ is responsible for process to process delivery.

a. network layer b. transport layer c. session layer d. data link layer
Answer: (b). transport layer

5. _________ provides the services to user.

a. application layer b. session layer c. presentation layer d. none of the mentioned
Answer: (a).application layer

6. The functionalities of presentation layer includes _________.

a. Data compression b. Data encryption. c. Data description. d. All of the mentioned
Answer: (d).All of the mentioned

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7. In the OSI model, as a data packet moves from the lower to the upper layers, headers
are _______.
a. Added b. Removed c. Rearranged d. None of the mentioned
Answer: (b).Removed

8. The ______ layer is responsible for the source-to-destination delivery of a packet across
multiple network links.
a. transport b. Network c. data link d. physical
Answer: (b).network

9. In OSI model dialogue control and token management are responsibilities of _______.
a. Session Layer b. Network layer c. Transport layer d. Data link layer
Answer: (a).Session Layer

10. The layer of OSI model which is responsible about data compression and encryption is
________.
a) Session layer b) Presentation layer c) Application layer d) None of above

Answer: a) Presentation layer

11. Which type of address is used in an internet layer of TCP/IP model?

a) Physical address b) Port address c) Specific address d) Logical address

Answer: d) Logical address

12. The process to process delivery is the responsibility of________.

a) Network layer b) Transport layer c) Session layer d) Data link layer

Answer: b) Transport layer

13. Layer that is used to deal with Transmission mediums is________.

a) Data Link Layer b) Network Layer c) Physical Layer d) Transport Layer

Answer: c) Physical layer

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14. The layer which is responsible about node to node communication is ________.
a) Application layer b) Session layer c) Physical layer d) None of above

Answer: d) None of above

15. The operation of switch is depends on ________.

a) Port address b) Physical address c) Logical address d) None of above

Answer: b) Physical address

16. The frame trailer include information about ________.

a) Flow control b) Frame size c) Frame type d) Error control

Answer: d) Error control

17. The layer which allows access to network resource is ________.

a) Physical layer b) Transport layer c) Application layer d) Data link layer

Answer: c) Application layer

18. The main function of transport layer ________.

a) Find the best route to destination.

b) Receives data from upper layers and segments it into packets.

c) Give logical address to the segment

d) None of all

Answer: b) Receives data from upper layers and segments it into packets.
19. Which one of the following is a transport layer protocol used in internet?
a) TCP b) UDP c) Both (A) and (B) d) None of the mentioned

Answer: c) Both (A) and (B)

20. In transport layer, a message is normally divided into transmittable ________.

a) Segments b) Signals c) Networks d) Frames

Answer: a) Segments

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21. The encapsulation process at the network and Data link layer Through LAN2 If (R)
send a message to (Y) are

R / 30 W / 80 Y / 50

Q /75 V / 45 E / 65 K / 99
LAN 1 LAN 2 LAN 3

a-
Upper layer Data
Network layer R Y Data
Data link layer 65 45 RY Data T
b-
Upper layer Data
Network layer V E Data
Data link layer 65 45 VE Data T
c-
Upper layer Data
Network layer RY Data
Data link layer 30 50 RY Data T

d-
Upper layer Data
Network layer VE Data
Data link layer 30 50 RY Data T

Answer: a
Upper layer Data
Network layer R Y Data
Data link layer 65 45 RY Data T

22. UDP is considered as a connectionless protocol because ________.

a) There is no connection establishment and no connection termination is performed.

b) No flow control is needed. c) Segments Delivered out-of-order.

d) All of the mentioned

Answer: d) All of the mentioned

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23. The Layer which Convert the logical 1's and O's coming from layer 2 into electrical
signals is:
a. Physical layer b. Network layer c. Transport layer d. TCP layer

Answer: a. Physical layer

24. Downloading a music file from the Internet is:

a. connection- less b. Connection-oriented c. forwarding d. routing

Answer: a. connection- less

25 In no handshaking between sender and receiver.
a. UDP b. TCP c. both TCP and UDP d. DNS

Answer: a. UDP

26. Which protocol is used to transfer web page from server to client;
a. DNS b. SMTP c. FTP d. HTTP

Answer: d. HTTP

27. Which protocol is used to send email messages from clients to servers over the internet.
a. DNS b. SMTP c. FTP d. HTTP

Answer: b. SMTP

28. Which protocol allows the download/upload of files between a client/server.

a. DNS b. SMTP c. FTP d. HTTP

Answer: c. FTP

29. Which protocol allows users to login to a host from a remote location and take control
as if they were sitting at the machine (virtual connection).
a. DNS b. SMTP c. Telnet d. HTTP
Answer: c. Telnet

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30. Which protocol Assigns IP addresses, subnet masks, default gateways, DNS servers,
etc. to users as they login the network.
a. DHCP b. DNS c. SMTP d. Telnet
Answer: a. DHCP

31. Which protocol Matches domain names with IP addresses.

a. DHCP b. DNS c. SMTP d. Telnet
Answer: b. DNS

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