OSI 3

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Questions and Answers

What is the primary purpose of the OSI model?

To minimize the layers in data transmission

To standardize the functions of a communication system (correct)

To eliminate the need for communication protocols

To enhance hardware performance in networks

In the OSI model, what is the primary role of the transport layer?

To manage application-level data formats

To handle end-to-end communication and error recovery (correct)

To provide user interface interactions

To define the electrical and physical specifications of the connection

What is the primary function of networking?

To connect computers and share information. (correct)

To limit communication to devices in the same area.

To enhance the graphical capabilities of computers.

To replace physical card catalogs with electronic formats.

Which OSI model layers are primarily implemented in hardware?

Physical and Data Link layers Signup and view all the answers

In which type of network are devices connected within the same building?

Local Area Network (LAN) Signup and view all the answers

How does the layered architecture of the OSI model benefit network management?

It allows for easy debugging and management Signup and view all the answers

What is the significance of protocols in the OSI model?

They define the format, control, and timing of data exchange Signup and view all the answers

What technological advancement has improved both LAN and WAN speed and reliability?

Fiber optic cables Signup and view all the answers

What was the original data rate of the Ethernet developed in the 1970s?

3 Mbps Signup and view all the answers

Which layer of the OSI model is closest to the end user?

Application layer Signup and view all the answers

Which protocol was used in the original Ethernet for managing network traffic?

Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Signup and view all the answers

What type of issues does the upper layer of the OSI model primarily deal with?

Application issues Signup and view all the answers

Which IEEE standard corresponds to the 10-Mbps Ethernet specification developed in 1985?

IEEE 802.3 Signup and view all the answers

What network communication protocols are based on the OSI model?

All modern communication protocols Signup and view all the answers

Which statement correctly describes the relationship between LANs and WANs?

WANs typically use dedicated leased lines for data transmission. Signup and view all the answers

Which of the following best describes Ethernet's popularity?

It is the most widely deployed network technology in the world. Signup and view all the answers

What is one primary purpose of twisted pair cables?

To cancel out electromagnetic interference Signup and view all the answers

Which of the following correctly describes unshielded twisted pair (UTP) cables?

They have no protective sheathing around the copper wires. Signup and view all the answers

What is a distinguishing feature of shielded twisted pair (STP) cables compared to unshielded twisted pair (UTP) cables?

STP cables are more expensive due to their protective sheathing. Signup and view all the answers

What is the role of transmission media in networking?

To provide physical pathways for data to travel. Signup and view all the answers

Which type of modulation is used in Digital Modulation techniques mentioned?

Frequency Shift Keying Signup and view all the answers

What advantage do twisted pair cables offer compared to coaxial cables?

Twisted pair cables are less expensive. Signup and view all the answers

What does the term 'unbound media' in transmission mediums generally refer to?

Wireless connections like infrared and satellite. Signup and view all the answers

What is the primary characteristic of bound media in transmission mediums?

They require physical cables to transmit data. Signup and view all the answers

What is the maximum distance for installation using twisted pair cables?

500 meters Signup and view all the answers

What is a common characteristic of coaxial cables?

High noise immunity Signup and view all the answers

Which of the following is NOT typically associated with fibre optic cables?

Sensitive to weather Signup and view all the answers

What is true about the inner conductor of coaxial cables?

It is encased in insulation. Signup and view all the answers

In which application did coaxial cables first see extensive use?

Submarine cables in the 1950s Signup and view all the answers

What is a disadvantage of twisted pair cables?

Limited distance coverage Signup and view all the answers

Which of the following features pertains to fibre optic systems?

Carries information through a guided fibre cable Signup and view all the answers

Which of the following statements is incorrect regarding coaxial cables?

They have very low noise immunity. Signup and view all the answers

What is one main advantage of using fibre optic cables over conventional microwave radio systems?

Fibre optic cables can transmit at higher frequencies. Signup and view all the answers

What is the function of the cladding in fibre optic cables?

To surround the core and enable total internal reflection Signup and view all the answers

Which type of fibre optic mode is characterized by using multiple light paths?

Multimode Signup and view all the answers

What material is considered the best for constructing fibre optic cables?

Glass or Silica Signup and view all the answers

What is the typical diameter range for the core of fibre optic cables?

50 to 500 nanometers Signup and view all the answers

What is a disadvantage of fibre optic cables?

Their termination is complex and requires special tools. Signup and view all the answers

What causes attenuation in fibre optic cables?

Absorption of light due to impurities and material properties Signup and view all the answers

How does the carrying capacity of fibre optic cables generally compare to that of microwave radio systems?

Fibre optic cables have a much greater carrying capacity. Signup and view all the answers

What is a significant characteristic of fibre optic transmission?

Needs repeaters for long distances Signup and view all the answers

Which of the following is NOT a typical use of fibre optic transmission?

Microwave Point-to-Point Signup and view all the answers

How does the frequency of transmission affect data throughput?

Higher frequencies allow more data to be transmitted per second Signup and view all the answers

Which of the following statements about microwave point-to-point transmission is true?

Microwave links are affected by obstacles like hills and buildings Signup and view all the answers

What was demonstrated by Daniel Colladon and Jacques Babinet in the early 1840s?

The ‘Light Fountain’ or ‘Light Pipe’ Signup and view all the answers

Which mediums are classified as unbound mediums?

All forms of electromagnetic transmission Signup and view all the answers

What is a common limitation of infrared (IR) point-to-point transmission?

Limited penetration through obstacles Signup and view all the answers

What kind of transmission does microwave point-to-point use?

Wireless and requires direct line of sight Signup and view all the answers

Study Notes

International & Access Foundation Programmes

Computer Science Module, Semester 2, Part 4
Focuses on networks: OSI Model and Ethernet

The OSI Model

Developed by the International Organization for Standardization (ISO)
Aims to standardize communication functions using abstraction layers.
Groups similar communication functions into logical layers.
Each layer serves the layer above it and is served by the layer below.
It is crucial to network communication, especially today's protocols.

OSI Model Layers

Layer 7: Application: Application issues, typically software-based. Handles communication between end-users.
Layer 6: Presentation: Data conversion, encryption, and decryption.
Layer 5: Session: Interhost communication. Maintains session order (starts and stops).
Layer 4: Transport: Ensures delivery of entire messages. Handles end-to-end connections and reliability of communication.
Layer 3: Network: Path determination and logical addressing.
Layer 2: Data Link: MAC and LLC for physical addressing.
Layer 1: Physical: Media, Signal, and binary transmission.

Layers of the OSI

Simplify network design.
Allow easy debugging of applications.
Support easier network management.
Layers follow rules called protocols (controls data format and timing of interactions).

The Upper Layers

Handle application issues and typically implemented in software.
Closest to the end user.
Communication between users starts here.

The Lower Layers

Handles data transport
Physical layer and Data Link layer are implemented in hardware and software.

OSI in Networks

Modern network communication protocols largely follow the OSI model.
Ethernet and IP protocols are part of the OSI model.
Included examples of Modern GSM Mobile Networks.

Networking

Networking enables computers to exchange information.
The Internet is a prominent networking example that interconnects millions of computers globally.
Numerous smaller networks also play vital roles in daily life (e.g., libraries).
Networking allows multiple devices to communicate and access information.

LAN's (Local Area Networks) & WAN's (Wide Area Networks)

Local Area Networks (LANs) connect devices in a confined area, such as a building.
Wide Area Networks (WANs) connect devices over large geographical areas, often using leased lines from telephone companies.
Fiber optic connections have improved speeds and reliability in LANs and WANs.

Ethernet (IEEE 802.x)

Original Ethernet was developed in the 1970s using coaxial cables.
Initial data rate was 3 Mbps, with a CSMA/CD protocol.
10 Mbps Ethernet specification (IEEE 802.3) followed, significantly expanding the ability to share information from different nodes.

Ethernet (Advantages)

Most popular and widely deployed network technology.
New technologies are integrated with mechanics of operation from the original design.
Devices communicate with each other over a shared cable.

Ethernet (Disadvantages)

Practical network size limits due to physical cable limitations.
Signal attenuation (weakening as it travels).
Electrical interference from surrounding devices.

Terminology

Protocols in networking are sets of rules controlling communication.
Protocols act like languages, enabling different devices to communicate effectively.
Medium (cable): Path for electrical signals.
Segment: Shared medium within a network.
Node: Device connected to the network segment.
Frame: Short message used for network data communication.

Motivation for Local Area Networking

Private ownership and limited coverage, and free selection of technology and services.
Technical, economic, and organizational drivers drive demand: cost savings, sharable resources, and interaction between departments.

LAN Designs

Peer-to-Peer: Simple way to share resources among connected devices.
Client/Server: Centralized server controls access to resources and handles tasks such as backup and security management.

Servers

HP Superdome 2: High-performance, mission-critical server platform.

Traditional Ethernet (Topology)

Uses a topology that connects devices along a common cable.
Potential for collisions if multiple devices request transmission at once.

Ethernet (CSMA/CD)

Device listening for transmission before sending data to avoid collisions.
If collision happens, a device resends data later.

Ethernet Disadvantages

Practical size limitations due to cable length and signal weakening/attenuation over long distances.
Susceptible to electrical interference from surrounding equipment.

Ring Topology

Stations are connected in a cycle.
Data moves sequentially around the ring.
Token controls access to the ring.

Star Topology

A central switch connects devices.
A switched Ethernet employs digital switches.

Mesh Topology

Each node serves as a relay for other nodes.
Provides redundancy and reliable data propagation.
Common in wireless settings.

Wireless Network Topology

Allows replacing fixed-wire connections.
Includes ad-hoc and portable to fixed networks (e.g., using Wi-Fi)

Linking Networks (Bridges)

Bridges connect separate Ethernet segments (increasing network spans, without increasing total collision domain).
They help regulate network traffic.

Repeaters

Improve signal integrity and extend the transmission distance.
Important for wired and wireless Ethernet (or, Wi-Fi) connections.

Switched Ethernet

Modern implementation using dedicated segments.
Eliminates shared-medium collisions and supports high data rates (especially in full-duplex implementations).
Allows creating dedicated paths between stations.

Ethernet Switches

Hardware devices facilitating connections for multiple devices.

Transmission Mediums

Physical pathways for signal transmission in a network.
Examples: twisted pair, coaxial cable, fiber optic cable, microwave, infrared, and satellite.

Bound Media

Physical mediums involving physical cable connections. Examples include twisted pair, coaxial, and fiber optics.

Unbound Media

Transmission via electromagnetic waves (e.g., radio, microwave, infrared, satellite).

The Electromagnetic Spectrum

Unbound mediums utilize portions of the electromagnetic spectrum.
Different frequencies are suited for various purposes.

Microwave Point-to-Point

High-frequency transmission.
Primarily line-of-sight transmission.

Infrared (IR) Point-to-Point

High-frequency, short-range communication.
Line-of-sight. Often used for short range (e.g., remote controls).

Satellite

Geosynchronous orbit for long-distance communication.
Used for communication between countries and continents.

Comparisons of Transmission Mediums

Comprehensive factors for choosing transmission mediums (cost, bandwidth, performance, and attenuation characteristics).

Evaluation Factors

Costs, bandwidth needs, latency requirements (real-time data), ease of installation, maintenance requirements, and projected lifespan.

Modulation

Converting data to a signal suitable for transmission. Includes techniques such as amplitude modulation (AM) and frequency modulation (FM) methods for efficient transmission of data.

Digital Modulation

Converting digital data (binary) into a modulation signal format (analog) for transmission.

Radio Frequencies

Frequencies used for wireless communication, spanning a broad range.
Example types include radio (AM/FM), TV broadcasts, shortwave radio, short-range networks.

Twisted Pair

Two copper wiring, twisted around each other, used for cabling systems
Offers advantages in both cost and ease of installation.

Co-axial Cable

Copper wire with insulation and a protective copper mesh, which can handle higher data rates compared to twisted pair cable
Typical applications are cable television and other data transmission needs between two or more locations.

Fibre Optic Cables

Light pulses transmitted through glass fiber.
High-bandwidth, long-distance transmission. High data rates.
Components include the core, cladding, and buffer to facilitate greater signal carrying capacity (and, minimizing signal attenuation).

Fibre Optic Modes

Multimode: multiple light paths, modal dispersion common
Single mode: single light path, less modal dispersion, greater bandwidth

Fibre Optic Cable Design

Core and cladding act as an optical waveguide.
Core diameter and material properties affect performance.

Fibre Optic Transmission

Light rays travel through the fibre core by total internal reflection.

Fibre Optic Construction

Use of glass (silica) for high bandwidth and signal propagation.
Attenuation is minimized for long-distance networking.

Disadvantages of Fiber Optics

Termination is more complex than other mediums (potentially demanding special tools).
Repeaters needed for longer distances.
Can be more fragile than other mediums.

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