Introduction to Data Communication Networks
Tip: press → / ← to jump between sections, F for present mode. The activities work on phones too. Your answers are recorded under your name so your lecturer can give feedback; they are not graded.
This week
Two online sessions. Keep this page open; we'll use it for every activity.
Tuesday 10:00–10:50 50 min
Thursday 14:00–15:50 110 min
Where this course picks up
From one signal on one link, to a whole network.
Signals & Systems
Signals, spectra, basics of modulation.
Principles of Communication
AM, FM, PM, PSK, and the point-to-point link.
Data Communication & Network
Many devices sharing links, and the rules that make it work.
Warm-up: where does your message go?
You send “Dah sampai?” on WhatsApp to a friend at UTM KL. Build the path you think it takes.
Tap the stops in order, from your phone to your friend's phone. Tap a stop in your path to remove it. Some stops are traps. We'll check your answer in Part 03.
Your path
Your path is saved automatically. When you're done, post how many stops you have in the meeting chat.
A communication model
What every exchange of data has in common
What is data communication?
It only works well if it gets four things right:
Delivery
Data reaches the right device, and only that device.
Accuracy
Data arrives unaltered, or the errors are caught.
Timeliness
Data arrives in time to be useful, e.g. live video.
Jitter
Packets should arrive at an even pace, not in bursts.
A simple communications model
Every system in this course, from a Bluetooth headset to the Internet, fits these five blocks.
Your laptop writing an email
Network card or modem
Cables, radio, switches, routers
Network card or modem
The mail server
Scrambled! Put the blocks back in order.
Tap one block, then tap another to swap them. Press Check when you're done.
From message to signal, and back
The same model, showing what the data looks like at each point.
Noise lab: can your letter survive the trip?
Type one letter. It becomes 8 bits, g(t), and is sent as a signal, s(t). Turn up the noise and attenuation, then watch what the receiver decodes. The receiver reads each bit at its midpoint: above the dashed line means 1, below means 0.
Challenge: find the lowest noise level that still corrupts your letter. Then explain why attenuation above 50% breaks every 1.
The five components
Protocols: the rules of the conversation
A human protocol
A network protocol
Think: what happens if someone replies to “Hi” with silence? Or answers before you ask? Next week: how protocols are stacked into layers (OSI, TCP/IP).
Read: Kurose §1.1.3Data flow: who talks, and when
Simplex
One direction only.
e.g. keyboard to computer, TV broadcast
Like a one-way street
Half-duplex
Both directions, one at a time.
e.g. walkie-talkie
Like a single-lane bridge
Full-duplex
Both directions at the same time.
e.g. phone call, video call
Like a two-way road
Quick check: simplex, half or full?
Tasks every network must handle
Getting data from source to destination involves many tasks. This course takes them one at a time.
| When | Tasks |
|---|---|
| Week 3 | Signal generation · Synchronization · Interfacing · Error detection & correction |
| Week 4 | Flow control · Exchange management |
| Week 5 | Message formatting (framing) |
| Weeks 6–9 | Transmission system utilization · Sharing a LAN · Switching |
| Weeks 10–14 | Addressing · Routing · Recovery, security & network management |
Before you leave today
In one sentence: why is the received signal r(t) not the same as the transmitted signal s(t)?
Hint: think back to the noise lab.
Types of networks
How networks are judged, shaped and sized
What makes a good network?
Performance
- Throughput: how much data gets through
- Delay: how long it takes
- Depends on the users, the medium, the hardware and the software
Reliability
- How often it fails
- How long it takes to recover
- How it survives a disaster
Security
- Protects data from unauthorised access
- Protects data from damage
- Has policies to recover from breaches and data loss
Two ways to connect devices
Point-to-point
A dedicated link between exactly two devices. The whole capacity belongs to that pair.
e.g. a TV remote and the TV; a leased line between two offices
Multipoint
More than two devices share one link, either at the same time or by taking turns.
e.g. devices on one Wi-Fi channel; an old shared Ethernet cable
Physical topologies
The shape of the links. Most real networks combine several of these into a hybrid.
Build it, then break it
Pick a topology and the number of devices. Then click a cable or a device to break it, and see who can still talk to whom. Click it again to repair it.
Choosing a topology
| Topology | Strength | Weakness | Where you'll see it |
|---|---|---|---|
| Star | Easy to add devices and to monitor traffic at the centre | If the centre fails, the whole network fails | Home Wi-Fi, office Ethernet |
| Bus | Cheap and simple: little cable | A cable fault takes the network down; every node hears every message | Early Ethernet |
| Ring | Little cable; orderly access | Adding a device means breaking the ring | Older token ring, some fibre metro rings |
| Tree | Layered stars; easy to expand | A fault high in the tree cuts off everything below it | Campus networks |
| Full mesh | Most reliable; no shared links | Many ports and cables; costly to grow | Backbone routers |
| Hybrid | Mixes the strengths above | Redundant devices and cables add cost | Most real networks |
How many links does a full mesh need?
n devices need
duplex links, and every device needs n − 1 ports.
Each device links to n − 1 others; dividing by 2 stops each link being counted twice.
5 devices → 5 × 4 / 2 = 10 links
Each device needs 4 ports.
A lab has 12 routers in a full mesh.
Networks by size
Personal area
About 10 m
Your phone and earbuds
Bluetooth
Local area
A building or campus
Your faculty's network
Ethernet, Wi-Fi
Metropolitan area
A city
Offices linked across Johor Bahru
Metro Ethernet, fibre
Wide area
Countries and continents
UTM JB linked to UTM KL
Leased lines, MPLS, submarine cable
PAN, LAN, MAN or WAN?
Who owns it, and how networks join up
Public network
Run by a telecom company and open to anyone who pays. The Internet is the largest.
Private network
Built by one organisation for its own needs, e.g. power grid or railway control networks.
An internetwork: two LANs joined by a WAN
Routers connect networks to each other. The Internet is the global internetwork.
The Internet
The network of networks you use every day
Two ways to describe the Internet
Nuts and bolts
Billions of connected devices (hosts), joined by links and packet switches, organised into ISPs, all running protocols such as TCP and IP.
A service platform
An infrastructure that delivers data for applications such as WhatsApp, YouTube and e-learning. Apps run on end systems and ask the network to carry their data.
The building blocks
Hosts (end systems). Laptops, phones, servers, sensors. Like buildings.
Communication links. Fibre, copper, radio, rated in bits per second. Like roads.
Packet switches. Routers and link-layer switches forward packets. Like junctions.
ISPs. Each ISP is itself a network of links and switches.
The links and switches a packet crosses form its route, or path.
The edge and the core
Network edge
Where users and applications live
- End systems run the applications
- Access networks connect them to the first router:
- Home: fibre (FTTH), DSL, cable
- Campus/office: Ethernet, Wi-Fi
- Mobile: 4G, 5G
Network core
Where packets are moved
- A mesh of routers and the links between them
- Packets hop from router to router: store-and-forward
- Links are shared on demand (packet switching)
The devices that make it work
Switch
Connects devices inside a LAN, closest to the users. Forwards frames.
More in Week 7
Router
Connects different networks. Picks a path using the destination IP address.
More in Weeks 10–12
Firewall
Sits between networks with different trust levels and enforces a security policy.
More in Week 13
Access point
Connects wireless users to the wired network. Large sites manage many APs from a controller (AC).
More in Week 7
Who am I?
A network of networks
No single company runs the Internet. Customer ISPs pay provider ISPs; ISPs at the same level often peer at an IXP to save cost. Content providers such as Google run their own networks to get closer to users.
Read: Kurose §1.3.3Two ways to move data through a network
Circuit switching vs packet switching
Circuit switching
e.g. the phone network- A path is reserved end to end before talking starts
- Guaranteed rate for the whole call
- The reserved capacity sits idle during silence
Packet switching
e.g. the Internet- Data is cut into packets, each sent on its own
- Each router stores, then forwards, each packet
- Links are shared on demand; packets may queue
Warm-up, revisited: your message's journey
Here's the path a WhatsApp message really takes.
How close was your Tuesday guess?
Post your score in the chat. Who got 8/8? Which stop did most people miss?
Data communication network trends
Where networks are heading, and why
Three forces that keep networks changing
Traffic growth
More users, more devices, more video. Demand keeps rising.
New services
Streaming, cloud apps, online banking, IoT. Each one needs more capacity.
Better technology
Faster, cheaper links and chips: fibre, 5G, better Wi-Fi.
Trends shaping networks today
5G and beyond
Faster mobile links with lower delay; can rival fixed broadband. 6G is in research.
Internet of Things
Billions of sensors and devices; needs segmenting and monitoring to stay secure.
SDN and SD-WAN
Networks controlled centrally by software instead of box by box.
Cloud and edge
Apps live in data centres; edge computing moves processing closer to users.
Automation and AI
Scripted, repeatable configuration; AI analytics spot problems early.
Wi-Fi 6, 6E and 7
Faster, denser wireless LANs for crowded spaces like lecture halls.
Spot the trend
Closer to home: Malaysia
JENDELA
The national digital infrastructure plan, launched in 2020 to widen and speed up broadband coverage.
5G roll-out
5G service began in December 2021 through Digital Nasional Berhad, a single wholesale 5G network.
Which of today's trends do you already rely on? Which one would most improve your own internet connection right now?
Week 1 in one screen
A communication model
Source, transmitter, transmission system, receiver, destination. Protocols are the rules.
Types of networks
Judged by performance, reliability and security; shaped by topology; sized as PAN, LAN, MAN, WAN.
The Internet
A network of networks: hosts at the edge, routers in the core, ISPs tiered and peering at IXPs.
Trends
Traffic, services and technology push each other: 5G, IoT, SDN, cloud, automation, Wi-Fi 7.
Final check
Six questions on this week
Got fewer than 4? Re-read the part shown under each question before Week 2.
One last thing: what is still unclear after this week?
Before Week 2: Protocol architecture
Read one of these on OSI and TCP/IP
- Forouzan Ch. 2, Network Models
- Stallings Ch. 2, Protocol Architecture, TCP/IP
- Kurose & Ross §1.5, Protocol Layers
- Huawei §2.1, Overview of Protocols
Week 2 is a flipped class: come having read it.
- Post your weekly reflection on e-learning
- Install Wireshark (wireshark.org)
- Create a free NetAcad account for Cisco Packet Tracer