Answer: a, open system interconnection

Solution: OSI is the abbreviation for Open Systems Interconnection model, a conceptual framework used to describe the functions of a networking system.

Answer: d, 7

Solution: The OSI model is defined with seven distinct layers, each performing a specific set of networking functions.

Answer: b, Physical ? Data Link ? Network ? Transport ? Session ? Presentation ? Application

Answer: b, Application Layer

Answer: c, Bit transmission over a medium

Solution: The Physical Layer deals with the mechanical, electrical, procedural, and functional characteristics to transmit raw bits over a communication medium.

Answer: b, Mechanical and electrical interface of the transmission channel

Solution: The Physical Layer defines the specifications for the physical components (cables, connectors, voltage levels, etc.) used to connect devices and transmit data.

Answer: d, Congestion control

Solution: Congestion control is a function of the Transport Layer (or sometimes Network Layer). The Physical Layer handles signal encoding (Modulation, Line coding) and accessing the shared medium.

Answer: a, TDM

Solution: Time Division Multiplexing (TDM), Frequency Division Multiplexing (FDM), and Wavelength Division Multiplexing (WDM) are common multiplexing techniques used to combine signals for transmission on the physical medium. Token Passing is a Data Link Layer function.

Answer: c, Encoding

Solution: Encoding (or signal conversion/digital-to-analog conversion) is the process used by the Physical Layer to transform digital bits into physical signals (electrical, light, or radio waves) suitable for the transmission medium.

Answer: a, Interface between data terminal equipment and transmission medium

Solution: The Physical Layer defines the rules for the interface between the Data Terminal Equipment (DTE) or Data Communications Equipment (DCE) and the actual physical transmission medium (e.g., specifying connectors and voltage levels).

Answer: b, Provide error detection and framing

Solution: The Data Link Layer is responsible for reliable point-to-point or point-to-multipoint data transfer, primarily through framing (dividing data into frames) and error detection/control.

Answer: d, Encryption of data

Solution: Encryption of data is typically performed at the Presentation Layer or Application Layer, although it can be implemented at other layers for specific purposes (like IPsec at Network Layer).

Answer: b, Bridge

Solution: A Bridge (or a Layer 2 Switch) uses MAC addresses to forward data frames and operates at the Data Link Layer. A Router operates at the Network Layer.

Answer: b, CRC

Solution: Cyclic Redundancy Check (CRC) is a common and powerful technique used to detect errors introduced during transmission at the Data Link Layer.

Answer: a, LLC and MAC

Solution: The Data Link Layer is typically split into the Logical Link Control (LLC) sublayer (for error and flow control) and the Media Access Control (MAC) sublayer (for addressing and channel access).

Answer: a, CSMA/CD

Solution: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) is a Media Access Control (MAC) protocol used in wired Ethernet networks to manage shared access to the physical transmission medium.

Answer: b, Error detection

Solution: The Frame Check Sequence (FCS) is a field added to the end of a Data Link Layer frame that contains the result of the CRC calculation, used by the receiver for Error detection.

Answer: b, Data Link Layer

Solution: The MAC (Media Access Control) address is a physical or hardware address unique to each network interface, used by the MAC sublayer of the Data Link Layer.

Answer: c, Performs framing

Solution: The Data Link Layer breaks the data stream from the Network Layer into fixed-size or variable-size data units called frames.

Answer: a, PPP

Solution: Point-to-Point Protocol (PPP) is a widely used protocol for establishing a direct connection between two nodes (e.g., dial-up or VPN connections).

Answer: c, MAC Address

Solution: The Data Link Layer uses the MAC Address (a local hardware address) to uniquely identify and deliver data frames to the correct device on the same local network.

Answer: c, Sender overwhelming receiver

Solution: Flow control manages the rate of data transmission to ensure a fast sender doesn't send data faster than the slow receiver can process it, preventing the receiver's buffer from overflowing.

Answer: b, Layer 2 Switch

Solution: A Layer 2 Switch forwards data based on MAC addresses, which is the addressing scheme of the Data Link Layer.

Answer: b, Framing

Solution: Framing is the function of the Data Link Layer that encapsulates the network layer datagram into a frame for transmission over the physical medium.

Answer: c, Both A and B

Solution: Both Stop-and-Wait Automatic Repeat Request (ARQ) and Sliding Window ARQ are protocols used by the Data Link Layer to provide reliable data transfer by detecting and retransmitting lost or corrupted frames.

Answer: b, Routing of packets from source to destination

Solution: The Network Layer (Layer 3) is responsible for the source-to-destination delivery of packets across multiple networks (inter-networking), primarily through the function of routing.

Answer: b, IP

Solution: Internet Protocol (IP), along with ICMP and routing protocols like RIP/OSPF, are the most fundamental protocols operating at the Network Layer.

Answer: b, Network Layer

Solution: A Router is a Layer 3 device that uses IP addresses and routing tables to determine the best path for packets to travel across different networks.

Answer: b, Dijkstra’s Algorithm

Solution: Dijkstra’s Algorithm (and its derivatives like in OSPF) is a path-finding algorithm used by routing protocols to calculate the most efficient (shortest/least cost) route from one node to all other nodes.

Answer: c, IP addressing

Solution: The Network Layer uses IP (Internet Protocol) addressing for logical, global, and hierarchical identification of devices across the entire internetwork.

Answer: d, Flow control

Solution: Flow control is primarily a function of the Data Link Layer (node-to-node) and the Transport Layer (end-to-end) to manage the rate of data exchange.

Answer: c, Router

Solution: A Router may need to perform fragmentation—breaking a packet into smaller pieces—if the packet's size exceeds the Maximum Transmission Unit (MTU) of the next link/network it is traversing.

Answer: b, Fragmentation

Solution: Fragmentation is the specific process at the Network Layer of dividing a single large packet into smaller datagrams so they can pass through a link with a smaller MTU.

Answer: c, RIP

Solution: Routing Information Protocol (RIP), along with OSPF and BGP, is a routing protocol used by routers to dynamically share information about network reachability and path costs.

Answer: a, ICMP

Solution: Internet Control Message Protocol (ICMP) is used for diagnostic functions (like the ping utility) and to report errors or status information about delivery failures.

Answer: b, Which route a packet should follow

Solution: The core function of the Network Layer is to determine the most efficient path (route) for a packet to travel from the source network to the destination network.

Answer: b, Which route a packet should follow

Solution: This is a repeat of the previous question, emphasizing the core routing function.

Answer: b, IPv4/IPv6 Address

Solution: The Network Layer is responsible for the addition of the logical IP (IPv4 or IPv6) source and destination addresses to the packet header.

Answer: c, Network

Solution: While congestion can affect many layers, the most critical control and the place where global congestion becomes apparent is at the Network Layer, especially at busy routers that drop packets due to full queues.

Answer: b, End-to-end communication and reliability

Solution: The Transport Layer provides logical communication between application processes running on different hosts, ensuring host-to-host or end-to-end delivery of data.

Answer: b, TCP & UDP

Solution: TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are the two core protocols of this layer.

Answer: b, Error control and flow control

Solution: As a reliable protocol, TCP ensures data integrity and delivery by managing data transmission rate (flow control) and handling lost/corrupted segments (error control).

Answer: b, Low latency is more important than reliability

Solution: UDP's low overhead makes it faster, ideal for real-time applications where a slight delay is worse than losing a few packets.

Answer: b, Sequence Number

Solution: The Sequence Number in the TCP header is crucial for the receiver to reassemble the data in the correct order, especially if segments arrive out of sequence.

Answer: a, Process-to-process delivery

Solution: By using port numbers, the Transport Layer delivers data to the correct application process (or service) running on the destination host.

Answer: d, Packet forwarding

Solution: Packet forwarding (or routing) is the primary function of the Network Layer.

Answer: c, Video streaming and VoIP

Solution: Real-time services like VoIP and video streaming prioritize speed and low delay over guaranteed delivery, favoring the connectionless UDP.

Answer: c, Connection-oriented – TCP

Solution: TCP is a connection-oriented protocol because it must establish a connection (3-way handshake) before data transfer begins.

Answer: b, Slow Start & Congestion Avoidance

Solution: Slow Start and Congestion Avoidance are algorithms used by TCP to dynamically adjust the transmission rate based on network congestion.

Answer: b, To identify the process/application

Solution: The port number specifies the particular application or service running on the host that should receive the data.

Answer: a, SYN ? SYN-ACK ? ACK

Solution: The process establishes a connection: Sender sends SYN, Receiver replies with SYN-ACK, Sender confirms with ACK.

Answer: b, UDP

Solution: UDP sends data packets without establishing a formal connection, which is why it is called connectionless.

Answer: b, Breaking application data into segments

Solution: The Transport Layer breaks large messages from the Application Layer into smaller, manageable units called segments (for TCP) or datagrams (for UDP).

Answer: c, ARQ (Automatic Repeat reQuest)

Solution: ARQ, which relies on acknowledgments and timeouts, is the fundamental mechanism TCP uses for error control to ensure reliability by retransmitting lost segments.

Answer: b, Dialog control and synchronization

Solution: The Session Layer manages the interaction between communicating systems, controlling the dialog (who sends, when) and inserting synchronization points for recovery.

Answer: c, Session Layer

Solution: Dialog control is the function of the Session Layer that determines whether the communication is simplex (one-way), half-duplex (two-way, but one at a time), or full-duplex (two-way simultaneously).

Answer: b, Layer 5

Solution: The Session Layer (Layer 5) is responsible for the setup and teardown of the connection, or session, between end-user application processes.

Answer: b, Session Layer

Solution: The Session Layer inserts checkpoints (synchronization points) into the data stream, which allows communication to resume from the last known good point if a failure occurs, ensuring orderly recovery.

Answer: a, RPC

Solution: Remote Procedure Call (RPC) is a protocol often described as operating at the Session and Presentation layers, enabling a program to request a service from a program located on another computer.

Answer: c, Dialog management

Solution: Dialog management encompasses controlling the flow and direction of communication between two applications.

Answer: c, Token management

Solution: Token management is a mechanism used by the Session Layer to control which device has the right to perform a specific operation at any given moment, often used for dialog control in half-duplex.

Answer: b, Session Layer

Solution: Synchronization allows the two communicating systems to agree on a point in the data exchange, which is essential for fault tolerance and recovery.

Answer: b, Session

Solution: Session Layer synchronization and checkpointing ensures that if a connection is broken, only data after the last successful checkpoint needs to be resent.

Answer: a, Simplex, Half duplex, Full duplex

Solution: These are the three fundamental modes of communication, and the Session Layer is responsible for managing the communication dialog according to one of these modes.

Answer: c, Establishing sessions between applications

Solution: This is the core function: the Layer 5 connection, or session, provides the structure for inter-application communication.

Answer: b, Session

Solution: By managing the establishment, maintenance, and synchronization of the data exchange, the Session Layer acts as the coordinator for application-to-application communication.

Answer: b, Dialog control

Solution: The primary focus of Layer 5 is the structured exchange of data, defined as dialog control.

Answer: d, Routing

Solution: Routing is the function of the Network Layer (Layer 3), which determines the best path for data across multiple networks.

Answer: b, Data encryption, compression, and translation

Solution: The Presentation Layer (Layer 6) deals with the syntax and semantics of the information, providing services like translation between different data formats, compression, and encryption.

Answer: d, Segmentation

Solution: Segmentation (breaking data into smaller units) is a function of the Transport Layer (segments) or sometimes the Data Link Layer (frames).

Answer: c, Presentation

Solution: The Presentation Layer handles the conversion of data formats (like character encoding schemes) so that data generated by one system can be understood by another.

Answer: a, JPEG

Solution: JPEG (Joint Photographic Experts Group), MPEG, and other image/video encoding standards define how data is presented, which is the role of the Presentation Layer.

Answer: a, Translation Layer

Solution: Due to its primary function of converting data from the format used by the application into a format suitable for transmission (and vice versa), it is often referred to as the Translation Layer.

Answer: b, Presentation

Solution: The Presentation Layer handles the encryption of data before transmission and the decryption upon reception, ensuring data privacy across the network.

Answer: b, Format translation

Solution: Format translation (or data representation) is the core service, ensuring the data's structure and representation are mutually intelligible to the communicating applications.

Answer: b, Data is presented in a format the receiving system can understand

Solution: Its key goal is to resolve differences in data representation, allowing systems with different architectures to communicate.

Answer: b, Presentation Layer

Solution: Data compression is used to reduce the number of bits to be transmitted, which increases transmission speed and is handled by the Presentation Layer.

Answer: c, JPEG image format

Solution: JPEG is a specific standard/syntax for representing image data, which falls under the Presentation Layer's domain of data representation.

Answer: b, Presentation

Solution: Since encryption secures the content's representation, algorithms like AES (Advanced Encryption Standard) are functionally performed at the Presentation Layer.

Answer: b, Compression

Solution: Compression is the process used to encode the data to reduce its size, minimizing bandwidth usage.

Answer: b, Ensures syntax and semantics of data

Solution: It ensures that the meaning (semantics) and format (syntax) of the data are preserved and understood by the communicating devices.

Answer: c, HTTP

Solution: HTTP (Hypertext Transfer Protocol) is used for accessing web pages and is a core Application Layer protocol. IP (Network), TCP (Transport), and ICMP (Network) are lower layer protocols.

Answer: b, Offer services directly to end-user applications

Solution: The Application Layer is the layer closest to the end user. It provides the interface and protocols that allow applications (like web browsers or email clients) to access network services.

Answer: a, SMTP

Solution: SMTP (Simple Mail Transfer Protocol) is the standard protocol for sending, or forwarding, electronic mail across networks.

Answer: c, File transfer

Solution: Services like File Transfer (using FTP), web access (using HTTP), and email (using SMTP) are handled by the Application Layer.

Answer: c, Application

Solution: DNS (Domain Name System) is an Application Layer protocol that resolves domain names into IP addresses.

Answer: a, DNS

Solution: The DNS protocol translates human-readable names (e.g., google.com) into machine-readable IP addresses.

Answer: b, Presentation Layer

Solution: The Application Layer (Layer 7) sits right above the Presentation Layer (Layer 6) in the OSI model.

Answer: b, HTTP

Solution: HTTP is the foundation of data communication for the World Wide Web, used by web browsers to request resources.

Answer: d, TCP

Solution: TCP (Transmission Control Protocol) is a Transport Layer protocol; the others are Application Layer protocols.

Answer: a, POP3

Solution: POP3 (Post Office Protocol version 3) is a common protocol used by clients to download emails from a server.

Answer: c, Network management and resource sharing

Solution: The layer provides services for applications, including network file access, messaging, and protocols like SNMP for network management.

Answer: b, SNMP

Solution: SNMP (Simple Network Management Protocol) allows network administrators to manage and monitor network devices.

Answer: a, FTP

Solution: FTP uses port 21 for its control channel (commands), while port 20 is typically used for the data channel.

Answer: a, NTP

Solution: NTP (Network Time Protocol) is used to synchronize the clocks of computer systems over data networks.

Answer: c, Application

Solution: TELNET is an application protocol used to provide a bidirectional interactive text-oriented communication facility using a virtual terminal connection.