IGCSE Computer Science 0478 — 2.1 Data Transmission Types and Methods Hangman

The 36 key terms

1bit

A bit is a single binary digit that is either 0 or 1, like a switch that is off (0) or on (1). A group of 8 bits is called a byte.

2data transmission

The sending of data, such as text, images, audio or video, from a sender device to a receiver device.

3wired transmission

Sending data as signals along a physical cable, such as a USB, Ethernet or fibre optic cable. Wired links are usually fast and reliable.

4IP address

A unique number that identifies a device on a network, like a postal address, so data knows where to go. IPv4 looks like 192.168.1.5.

5packet

A small chunk of data with the sender, destination and order number attached. Packets travel a network by different routes and are put back in order at the destination.

7header, payload, trailer

The three parts of a packet, in order: the header (start) holds addresses and packet number, the payload (middle) holds the data, the trailer (end) marks the packet's end.

8packet header

The first part of a packet. It holds control information: the destination address, the originator's address and the packet number, used to deliver and reassemble the packet.

9destination address

The address in a packet header of the device the packet must be delivered to. Routers read it to choose where to send the packet. It is usually an IP address.

10originator's address

The IP address of the device that sent the packet, held in the header so the receiver knows who sent it and can reply or ask for a resend. It differs from the destination address.

11packet number

A number in the packet header showing the packet's position in the whole message (e.g. packet 3 of 10), so packets that arrive out of order can be put back in the right order.

12payload

The part of a packet that carries the actual data being sent, such as a piece of a file or message. The header and trailer are not payload.

13packet trailer

The last part of a packet. It marks where the packet ends and can hold error checking information, so the receiving device can check the data arrived correctly.

15router

A device that directs data between networks, such as joining a home LAN to the internet and choosing the path data packets take. A home Wi-Fi router also shares the connection wirelessly.

16packet switching

Data is split into packets that are sent separately, each routed on its own from router to router, then joined back together in the right order at the destination.

17routing

A router reads each packet's destination address in its header and picks the next router to send it to, so every packet's route is decided one step at a time.

18different routes

Packets from one message can take different routes because each router picks the best available path at that moment, avoiding busy or broken links. Routes may take different lengths of time.

19packets arrive out of order

Packets take different routes, so they may reach the destination in a different order from the one sent, e.g. packet 5 before packet 4. Order is not guaranteed.

20reordering packets

After the last packet arrives, the receiving device uses the packet numbers in the headers to put the packets in the right order and joins the payloads to rebuild the message.

21packet switching steps

Data is split into numbered packets, routers pick each packet's route, packets may arrive out of order, then they are reordered to rebuild the data once the last packet arrives.

22serial transmission

Sending data one bit at a time, one after another, down a single wire or channel. The bits arrive in the same order they were sent.

24parallel transmission

Sends several bits at the same time, each down its own wire in the same cable, e.g. 8 bits down 8 wires at once.

26skew

Bits sent together down parallel wires arrive at slightly different times, so data can be received incorrectly. It gets worse as the cable gets longer.

27serial vs parallel

Serial sends 1 bit at a time down one wire: cheaper, reliable, better over long distance. Parallel sends many bits at once down several wires: faster over short distances only.

28simplex

Data transmission in one direction only, from sender to receiver, with no reply possible. Example: a keyboard sending key presses to a computer.

29half-duplex

Data can travel in both directions, but only one direction at a time, so devices take turns, like a walkie-talkie.

30full-duplex

Data is sent in both directions at the same time, so both devices can send and receive at once, for example during a telephone call or over a broadband connection.

31direction trade-off

Simplex is one-way only but simple and has no collisions. Half-duplex is two-way by turns, so slower. Full-duplex is two-way at once and fastest, but needs more capacity and costs more.

32transmission method

Pick the direction (simplex, half-duplex or full-duplex) and the bit arrangement (serial or parallel), then justify both using the scenario's distance, speed and two-way needs.

33peripheral

An external device, wired or wireless, that connects to a digital system to add input, output or storage, such as a mouse, printer or USB drive.

34USB

Universal Serial Bus: a standard interface for connecting devices like keyboards, drives and phones to a computer and transferring data between them.

35USB serial transmission

USB sends data serially, one bit at a time, down a single cable. It works in both directions: half-duplex in older versions, full-duplex in later ones. The cable can also carry power.

36plug and play

When a USB device is plugged in, the computer automatically detects it and loads the driver it needs, so the device works straight away with no need to restart.

37USB standard connector

A USB port and plug of a set shape and wiring, so one cable type connects many different devices to a computer, such as a keyboard, a printer or a phone.

38USB benefits

One standard connector fits many devices, devices are detected automatically, older devices work in newer ports, power comes through the cable, and fast serial transfer is used.

39USB drawbacks

Limits of USB: short maximum cable length (unreliable over distance), slower speed than some interfaces (old ports slow new devices), and a limited number of ports.

40Evaluate USB

Judge if USB suits a use by weighing benefits (universal, plug and play) against drawbacks (short cable length, limited speed) for the scenario, such as a printer or drive.