CS331 · Chapter 1 · Part 1 · Annotated SlidesIntroduction: Data Communications and Networking
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Overview

Introduction: Data Communications and Networking

What a data communication system is made of, how devices connect (point-to-point or multipoint, simplex to full-duplex), the four topologies and their link formulas, LAN / MAN / WAN, how ISPs build the Internet, and why standards exist. Tutorial 1 was written from this deck, so most of its questions are linked on the slides they come from.

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Every original slide is shown unchanged. Yellow marks on a slide point to a numbered note: hover or tap a mark to jump to its note, and hover a note to see its marks. Questions tagged Past exam appeared on a real paper; Prediction questions are likely angles, not confirmed. Pick an answer to each question: a wrong pick tells you why it is wrong, so you can try again.

All 32 slides
  1. 1 Introduction
  2. 2 Chapter 1-Part 1: Outline
  3. 3 Data Communications
  4. 4 Five components of data communication (Figure 1.1)
  5. 5 1.1.2 Message
  6. 6 1.2 Networks
  7. 7 Point-to-point connection (Figure 1.5)
  8. 8 Multipoint connection (shared) (Figure 1.6)
  9. 9 Data flow (direction of data flowing in the link) (Figure 1.2)
  10. 10 Categories of topology (Figure 1.7)
  11. 11 Fully connected mesh topology (for five devices) (Figure 1.8)
  12. 12 Star topology (Figure 1.9)
  13. 13 Bus topology (Figure 1.10)
  14. 14 Ring topology (Figure 1.11)
  15. 15 A hybrid topology: a star backbone with bus or ring networks
  16. 16 Categories of networks (Figure 1.12)
  17. 17 An isolated LAN in the past and today (Figure 1.8)
  18. 18 MAN (Figure 1.14)
  19. 19 LAN (two buildings) (Figure 1.13)
  20. 20 An internetwork made of two LANs and one WAN (Figure 1.11)
  21. 21 A heterogeneous network made of WANs and LANs
  22. 22 WAN (Figure 1.15)
  23. 23 1.3 The Internet
  24. 24 Internet Service Providers (ISPs)
  25. 25 Example: a tier-1 backbone (Lumen)
  26. 26 Internet structure: network of networks
  27. 27 The Internet today (Figure 1.13)
  28. 28 Methods of ISPs InterConnection
  29. 29 Internet Exchange Points (IXP)
  30. 30 1.4 Internet Standards
  31. 31 Internet Standards
  32. 32 Standards Organizations
Slide 1 / 32

Introduction

Slide 1: Introduction

Notes

  1. Data communication → networks (connections, topologies) → LAN / MAN / WAN → the Internet and ISPs → standards.

  2. Tutorial 1 covers this whole deck: scenarios, MCQs, true/false, fill-in and link counts.

Slide 2 / 32

Chapter 1-Part 1: Outline

Slide 2: Chapter 1-Part 1: Outline

Notes

  1. Three sections: 1.1 data communications, 1.2 networks, 1.3 network types (plus the Internet and standards at the end).

Slide 3 / 32

Data Communications

Slide 3: Data Communications

Notes

  1. Data communication = exchanging data between TWO devices over some transmission medium (wire, fiber, air).

  2. Seen again Ch 2 Part 2, slide 2: The transmission medium in detail

Slide 4 / 32

Five components of data communication (Figure 1.1)

Slide 4: Five components of data communication (Figure 1.1)

Notes

  1. The 5 components: message, sender, receiver, transmission medium, protocol.

  2. The protocol sits on BOTH sides: sender and receiver must follow the same rules.

  3. Memory trick “My Sister Reads The Paper”: Message, Sender, Receiver, Transmission medium, Protocol.

  4. Trap The medium is the physical path. The protocol is the set of rules. Don’t swap them.

Exam angle

Past exam · Tutorial 1

MCQ 1 · the physical path is the medium

Past exam · Tutorial 1

Fill-in 1 · fifth component = protocol

Past exam · Tutorial 1Q1

The __ is the physical path over which a message travels.

PredictionQ2

Which is NOT one of the five components of a data communication system?

PredictionQ3

List the five components of a data communication system.

Compare with the model answer

Message, sender, receiver, transmission medium and protocol.

Slide 5 / 32

1.1.2 Message

Slide 5: 1.1.2 Message

Notes

  1. Everything becomes bits: text (Unicode), numbers (binary), images (bit patterns), audio and video (continuous or a series of images).

Exam angle

PredictionQ1

Text is represented in data communication as:

Slide 6 / 32

1.2 Networks

Slide 6: 1.2 Networks

Notes

  1. Trap More throughput and less delay pull against each other: pushing more data in raises the delay.

  2. Memory trick Criteria = “PRS”: Performance, Reliability, Security.

Exam angle

Past exam · Tutorial 1

MCQ 5 · failure frequency and recovery time = reliability

Past exam · Tutorial 1

Written Q3 · the three criteria

Past exam · Tutorial 1

Related question: Fill-in 3 · distributed processing

Past exam · Tutorial 1Q1

Frequency of failure and recovery time after a failure measure a network’s:

PredictionQ2

Network performance is evaluated by:

PredictionQ3

Increasing throughput usually also increases delay.

PredictionQ4

List and explain the three criteria of an effective network.

Compare with the model answer

Performance: throughput (data a user can send) and delay (transit and response time). Reliability: how often it fails and how long a link takes to recover. Security: protecting data from unauthorized access and damage, with policies for recovering from breaches.

Slide 7 / 32

Point-to-point connection (Figure 1.5)

Slide 7: Point-to-point connection (Figure 1.5)

Notes

  1. Point-to-point: a DEDICATED link between exactly two devices. Wired or wireless both count.

Exam angle

PredictionQ1

A point-to-point connection can be wireless.

Slide 8 / 32

Multipoint connection (shared) (Figure 1.6)

Slide 8: Multipoint connection (shared) (Figure 1.6)

Notes

  1. Multipoint = the link’s capacity is SHARED, in space (all at once) or in time (taking turns).

  2. Seen again Ch 3 Part 2, slide 2: Sharing a broadcast link needs multiple access

Exam angle

Past exam · Tutorial 1

MCQ 2 · more than two devices share a link

Past exam · Tutorial 1Q1

In a __ connection, more than two devices can share a single link.

Slide 9 / 32

Data flow (direction of data flowing in the link) (Figure 1.2)

Slide 9: Data flow (direction of data flowing in the link) (Figure 1.2)

Notes

  1. Simplex: one direction only, always (keyboard → computer, TV, radio).

  2. Half-duplex: both directions, but one at a time; each side gets the whole channel while sending (walkie-talkie).

  3. Full-duplex: both directions at the same time; the channel capacity is shared by the two directions (telephone).

  4. Memory trick Half-duplex = “over” on a walkie-talkie. Full-duplex = talking over each other on the phone.

Exam angle

Past exam · Tutorial 1

T/F 1 · full-duplex sends and receives at once

Past exam · Tutorial 1

Fill-in 2 · capacity shared at all times = full-duplex

Past exam · Tutorial 1

Written Q2 · half- vs. full-duplex with examples

Past exam · Tutorial 1Q1

In full-duplex transmission, both stations can transmit and receive simultaneously.

PredictionQ2

A walkie-talkie is an example of:

Past exam · Tutorial 1Q3

In which mode is the channel capacity shared by both directions at all times?

PredictionQ4

Explain the difference between half-duplex and full-duplex, with a real example of each.

Compare with the model answer

Half-duplex: both sides can send but not at the same time, so they take turns and the sender uses the whole channel (walkie-talkie). Full-duplex: both send and receive at the same time and the capacity is split between the two directions (telephone call).

Slide 10 / 32

Categories of topology (Figure 1.7)

Slide 10: Categories of topology (Figure 1.7)

Notes

  1. Four basic ones: mesh, star, bus, ring (plus hybrids).

  2. Memory trick Four topologies: “My Star Bus Rings” (Mesh, Star, Bus, Ring).

Slide 11 / 32

Fully connected mesh topology (for five devices) (Figure 1.8)

Slide 11: Fully connected mesh topology (for five devices) (Figure 1.8)

Notes

  1. Every device has a dedicated link to every other one. Links = N(N-1)/2; each device needs N-1 ports (NICs).

  2. Expensive because of all the cabling and ports: that is the answer to “why?”.

  3. Memory trick N = 8 → 8 × 7 / 2 = 28 links, 7 ports per device.

  4. Trap Ports per device is N-1, not N(N-1)/2.

Exam angle

Past exam · Tutorial 1

Fill-in 4 · mesh links = n(n-1)/2

Past exam · Tutorial 1

Written Q1 · links for 8 devices

Past exam · Tutorial 1

Related question: Scenario 1 · offices across the world

PredictionQ1

How many links are needed for a fully connected mesh of 6 devices?

PredictionQ2

In a mesh of 10 devices, how many I/O ports does each device need?

PredictionQ3

A mesh topology has no traffic (congestion) problems because each link is dedicated.

PredictionQ4

A network has 8 devices. How many cable links does a mesh, ring, bus and star need?

Compare with the model answer

Mesh: 8 × 7 / 2 = 28. Ring: 8. Bus: 1 main cable + 8 drop lines. Star: 8 (one per device to the hub).

Slide 12 / 32

Star topology (Figure 1.9)

Slide 12: Star topology (Figure 1.9)

Notes

  1. Each device links only to the central hub/switch, so devices never talk directly.

  2. Single point of failure: the hub. One cable failing only cuts off one device.

  3. Trap Robust ≠ fault-proof: one bad link only takes out its device, but the hub failing takes out everything.

Exam angle

Past exam · Tutorial 1

MCQ 3 · needs a central controller

Past exam · Tutorial 1

Scenario 2 · 20-employee office

Past exam · Tutorial 1Q1

Which topology requires a central controller or hub?

PredictionQ2

A 20-employee office wants every computer connected to one central device, easy to manage and to grow. Which topology, and why?

Compare with the model answer

Star. Every PC has its own link to a central switch, so adding or removing a PC is easy, a broken cable only affects one PC, faults are easy to find, and it needs less cabling than a mesh. The switch is the single point of failure.

Slide 13 / 32

Bus topology (Figure 1.10)

Slide 13: Bus topology (Figure 1.10)

Notes

  1. One long backbone cable; each device hangs off it on a drop line through a tap.

  2. Tip Formulas for N devices: mesh N(N-1)/2 links and N-1 ports each · star N links · ring N links · bus 1 main cable + N drop lines.

Exam angle

Past exam · Tutorial 1

T/F 4 · one break stops the bus

Past exam · Tutorial 1Q1

In a bus topology, one break in the cable can stop all transmissions on the segment.

PredictionQ2

A main cable plus N drop lines describes:

Slide 14 / 32

Ring topology (Figure 1.11)

Slide 14: Ring topology (Figure 1.11)

Notes

  1. Each device links to its two neighbours; the signal goes round the ring through each device’s repeater.

  2. Not robust: one broken link or device can break the ring (unless it is a dual ring).

Exam angle

PredictionQ1

A ring of 12 devices needs how many links?

PredictionQ2

Fault isolation is easy in a ring topology.

Slide 15 / 32

A hybrid topology: a star backbone with bus or ring networks

Slide 15: A hybrid topology: a star backbone with bus or ring networks

Notes

  1. Hybrid = a mix, e.g. a star backbone with buses or rings hanging off it.

Exam angle

Past exam · Tutorial 1

Related question: Scenario 1 · connecting offices worldwide

Slide 16 / 32

Categories of networks (Figure 1.12)

Slide 16: Categories of networks (Figure 1.12)

Notes

  1. A LAN does NOT cover more than about 2 miles: that is the Tutorial 1 trap.

Exam angle

Past exam · Tutorial 1

T/F 2 · LAN larger than 2 miles (false)

Past exam · Tutorial 1Q1

A LAN typically covers an area larger than 2 miles in diameter.

PredictionQ2

A network spanning a city is a:

Slide 17 / 32

An isolated LAN in the past and today (Figure 1.8)

Slide 17: An isolated LAN in the past and today (Figure 1.8)

Notes

  1. Past LANs: all hosts on a shared cable (bus). Today: every host has its own link to a switch (star).

  2. Seen again Ch 4, slide 24: Switched Ethernet replaced the shared bus

Slide 18 / 32

MAN (Figure 1.14)

Slide 18: MAN (Figure 1.14)

Notes

  1. MAN: covers a town or city, often run by a telecom company (the slide’s example: STC).

Slide 19 / 32

LAN (two buildings) (Figure 1.13)

Slide 19: LAN (two buildings) (Figure 1.13)

Notes

  1. LANs are built in layers: switches per building, a faster backbone switch, one router out to the Internet.

Slide 20 / 32

An internetwork made of two LANs and one WAN (Figure 1.11)

Slide 20: An internetwork made of two LANs and one WAN (Figure 1.11)

Notes

  1. Internetwork (an internet, small i) = two or more networks joined by routers.

  2. The Internet (capital I) is one specific, worldwide internet.

Exam angle

Past exam · Tutorial 1

T/F 5 · internet vs. Internet

Past exam · Tutorial 1Q1

An internet (lowercase i) is the same as the Internet (uppercase I).

Slide 21 / 32

A heterogeneous network made of WANs and LANs

Slide 21: A heterogeneous network made of WANs and LANs

Notes

  1. Real networks mix LANs and point-to-point WANs; routers sit at every boundary.

Slide 22 / 32

WAN (Figure 1.15)

Slide 22: WAN (Figure 1.15)

Notes

  1. WAN: countries and continents. Usually a mesh or hybrid of point-to-point links.

Exam angle

Past exam · Tutorial 1

Scenario 1 · New York, London, Tokyo, Sydney

PredictionQ1

A company links its New York headquarters with offices in London, Tokyo and Sydney, needing high-speed, reliable and secure links. What kind of network and topology fit?

Compare with the model answer

A WAN. A mesh (or hybrid mesh) of dedicated point-to-point links between the sites gives redundancy if one link fails, dedicated capacity, and better security for the financial data.

Slide 23 / 32

1.3 The Internet

Slide 23: 1.3 The Internet

Notes

  1. Seen again Ch 1 Part 2, slide 14: The TCP/IP layers

Exam angle

Past exam · Tutorial 1

MCQ 4 · TCP/IP is the Internet’s protocol suite

Past exam · Tutorial 1Q1

__ is the protocol suite of the current Internet.

Slide 24 / 32

Internet Service Providers (ISPs)

Slide 24: Internet Service Providers (ISPs)

Notes

  1. Memory trick Tier number goes UP as you get closer to the customer: 1 = global, 2 = national, 3 = local.

Exam angle

PredictionQ1

STC and Mobily are examples of:

PredictionQ2

Tier-1 ISPs connect directly to other tier-1 ISPs.

Slide 25 / 32

Example: a tier-1 backbone (Lumen)

Slide 25: Example: a tier-1 backbone (Lumen)

Notes

  1. A tier-1 network owns links on every continent.

Slide 26 / 32

Internet structure: network of networks

Slide 26: Internet structure: network of networks
Slide 27 / 32

The Internet today (Figure 1.13)

Slide 27: The Internet today (Figure 1.13)

Notes

  1. Backbones in the middle, joined at peering points; provider networks hang off them; customers at the edge.

Slide 28 / 32

Methods of ISPs InterConnection

Slide 28: Methods of ISPs InterConnection

Notes

  1. Today: international ISPs use private peering; national ISPs meet at IXPs.

  2. Trap Private peering points are run by the ISPs; an IXP is run by a THIRD party.

Exam angle

PredictionQ1

An Internet Exchange Point (IXP) is managed by:

PredictionQ2

National ISPs usually interconnect using IXPs.

Slide 29 / 32

Internet Exchange Points (IXP)

Slide 29: Internet Exchange Points (IXP)

Notes

  1. Customers of each ISP reach each other through the IXP instead of going abroad. Example: the Saudi Arabian Internet Exchange.

Slide 30 / 32

1.4 Internet Standards

Slide 30: 1.4 Internet Standards

Notes

  1. Trap “A protocol is the structure or format of the data” ✗. That is only syntax, one element of a protocol.

  2. Seen again Ch 1 Part 2, slide 2: Protocol layering

Exam angle

Past exam · Tutorial 1

T/F 3 · protocol = format of data (false)

Past exam · Tutorial 1Q1

A protocol is defined as the structure or format of data.

PredictionQ2

A protocol is best defined as:

Slide 31 / 32

Internet Standards

Slide 31: Internet Standards

Notes

  1. Agreements are needed at many levels: voltages for 0/1, message boundaries, lost messages, addressing, routing, applications. Each turns into a layer later.

  2. Seen again Ch 1 Part 2, slide 2: Layers split these agreements up

Exam angle

Past exam · Tutorial 1

Written Q4 · why standards matter

PredictionQ1

Why are standards important in data communications? Give examples.

Compare with the model answer

They guarantee interoperability between equipment from different vendors, create a large market for hardware and software, and guide manufacturers and agencies. Examples: Ethernet (IEEE 802.3) lets any NIC talk to any switch; TCP/IP lets any computer join the Internet.

Slide 32 / 32

Standards Organizations

Slide 32: Standards Organizations

Notes

  1. ISO (international), ITU-T (UN telecom agency), ANSI (US), IEEE (LAN/MAN, e.g. 802.3 Ethernet), W3C (the web).

  2. Seen again Ch 4, slide 3: IEEE 802 LAN standards

Exam angle

PredictionQ1

Which organization specializes in LAN/MAN standards?