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Details about this E-Book:
The objective of this e-book is to ensure that CISA candidate get adequate knowledge on concept of ‘OSI Layers ’. Concepts have been simplified for easy reference of CISA candidates.
Questions, Answers and Explanation (QAE) on concept are designed in accordance with CISA exam pattern.
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Physical Layer (1^st^ layer):
-Physical layer is concerned with electrical and physical specifications for hardware.
-This layer defines the cable, connector, cards and physical aspects of hardware required for physical connection of device to the network.
Data Link Layer (2^nd^ layer):
-Data link layer connects to another device on the same network using a MAC address.
-Bit stream (received from physical layer) is converted into data packets and sent to network layer.
-Data packets (received from network layer) is converted into bit stream and sent to physical layer.
-Frames of data link layer consist of original data and control fields for synchronization, error detection and flow control.
Network Layer (3^rd^ layer):
-Responsibilities of network layer is to insert information into packet header for proper addressing and routing.
-Network layer understands the IP addresses and is responsible for routing.
-Network layer provides confidentiality, authentication, and data integrity services.
Transport Layer (4^th^ layer):
-Transport layer is concerned with reliability of data transfer between two systems.
-Transport layer ensure that data reaches its destination.
-Transport layer also make sure that packets on the receiving system are delivered in proper sequence.
-Transport layer uses connection-oriented protocols.
-Transport layer implements a flow control mechanism that can detect congestion, reduce data
transmission rates during congestion and increase transmission rates when the network appears to
no longer be congested.
Session Layer (5^th^ layer):
-Session layer is used to control connections that are established between systems.
-It establishes, manages and terminates the connection between the application layers.
-It is like telephone call in which first we established the connection, then exchange a message and then finally terminate the session.
Presentation Layer (6^th^ layer):
-Presentation layer coverts data into presentable format that is acceptable by all.
-Presentation layer provides services such as encryption, text compression and re-formatting.
Application Layer (7^th^ layer):
-Application layer contains programs that communicate directly with the end user.
-Application Layer works closed to the user.
-Application layer provides interface for applicants to communicate.
(1)Data link layer works on MAC address whereas Network layer works on IP address.
(2)Network layer inserts IP address and routing whereas transport layer ensure proper delivery.
(3)When CISA question is about electric signal or hardware devices, our answer should be physical layer.
(4)When CISA question is about MAC address, our answer should be data link layer.
(5)When CISA question is about routing or IP address, our answer should be network layer.
(6)When CISA question is about reliable delivery or connection oriented or congestion control or order of sequence, our answer should be transport layer.
(7)When CISA question is about establishing connection, our answer should be session layer.
(8)When CISA question is about acceptable format, our answer should be presentation layer.
(9)When CISA question is about end user, our answer should be application layer.
Below QAE are solely on the concept of OSI layers. Candidates are advised to attempt below questions multiple times. More emphasis to be given on explanation part for better understanding.
Which of the ISO/OSI model layers provides service for how to route packets between nodes?
A. Application layer
B. Physical layer
C. Network layer
D. Data link layer
Answer: C. Network
Explanation:
Responsibility of network layer is to insert information into packet header for proper addressing and routing. Network layer understands the IP addresses and is responsible for routing.
Which OSI layer tracks the order in which packets are delivered to address the out-of-sequence message?
A. Physical layer
B. Transport layer
C. Application layer
D. Network layer
Answer: B. Transport layer
Explanation:
Transport layer is concerned with reliability of data transfer between systems. Transport layer ensure that data reaches its destination. Transport layer includes the protocols that are able to tract the orders in which packets are delivered. Typically each transported packet will have a serialized number that the receiving system will use to make sure that packets are delivered in order. Transport layer also make sure that packets on the receiving system are delivered in proper order.Neither the network, physical or application layers address re-sequencing.
Which of the following OSI layer contains programs that communicate directly with the end user?
A. Physical layer
B. Transport layer
C. Application layer
D. Network layer
Answer: C. Application layer
Explanation:
Application layer contains programs that communicate directly with the end user. Application layer provides interface for applicants to communicate.
Which of the following OSI layer controls the connection established between the systems?
A. Session layer
B. Transport layer
C. Application layer
D. Network layer
Answer: A. Session layer
Explanation:
The session layer in OSI module is used to control the connection established between the systems.
It establishes, manages and terminates the connection between the application layers. It is like telephone call in which first we established the connection, then exchange a message and then finally terminate the session.
Which of the following OSI layer is primarily concerned with reliability of data transfer between the systems?
A. Session layer
B. Transport layer
C. Application layer
D. Network layer
Answer: B. Transport layer
Explanation:
Transport layer is concerned with reliability of data transfer between systems. Transport layer ensure that data reaches its destination. Transport layer also make sure that packets on the receiving system are delivered in proper order.
Which of the OSI model is concerned with electrical and physical specifications for the devices?
A. Data link
B. Physical
C. Transport
D. Session
Answer: B. Physical
Explanation:
Physical layer is concerned with electrical and physical specifications for devices. It provides hardware that transmits and receives the bit. Physical layer defines the cable, connector, cards and physical aspects of hardware required for physical connection of device to the network.
Which of the following OSI layers handles congestion control?
A. Session layer
B. Transport layer
C. Application layer
D. Network layer
Answer: B. Transport layer
Explanation:
The transport layer is responsible for reliable data delivery. This layer implements a flow control
mechanism that can detect congestion, reduce data transmission rates and increase transmission
rates when the network appears to no longer be congested.
Which of the OSI model layers provides for routing services?
A. Data link
B. Network
C. Transport
D. Session
Answer: B. Network
Explanation:
Responsibility of network layer is to insert information into packet header for proper addressing and routing. Network layer understands the IP addresses and is responsible for routing.
What kind of protocols does the Transport Layer provide to ensure reliable communication?
A. Non-connection-oriented protocols
B. Connection-oriented protocols
C. Application-oriented protocols
D. Non-application-oriented protocols
Answer: B. Connection-oriented protocols
Explanation:
The transport layer of the TCP/IP protocol suite provides for connection-oriented protocols to ensure reliable communication.
Which of the following protocols is the FIRST to establish security for the user application?
A. Data link
B. Network
C. Transport
D. Session
Answer: D. Session
Explanation:
The session layer provides functions that allow two applications to communicate across the
network. The functions include security, recognition of names, logons and so on. The session
layer is the first layer where security is established for user applications.
Which of the following OSI layers provides confidentiality, authentication, and data integrity services?
A. Network layer
B. Presentation layer
C. Session layer
D. Physical layer
Answer: A. Network layer
The network layer is responsible for transmitting a message from source to destination. It provides routing (path control) services to establish connections across communications networks. Achieving this goal requires confidentiality, authentication, and data integrity services.
[* Other CISA Exam- Study Material *]
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Point to remember for CISA Exam: (1)Data link layer works on MAC address whereas Network layer works on IP address. (2)Network layer inserts IP address and routing whereas transport layer ensure proper delivery. (3)When CISA question is about electric signal or hardware devices, our answer should be physical layer. (4)When CISA question is about MAC address, our answer should be data link layer. (5)When CISA question is about routing or IP address, our answer should be network layer. (6)When CISA question is about reliable delivery or connection oriented or congestion control or order of sequence, our answer should be transport layer. (7)When CISA question is about establishing connection, our answer should be session layer. (8)When CISA question is about acceptable format, our answer should be presentation layer. (9)When CISA question is about end user, our answer should be application layer.