DTP

2.1 Types & Methods of Data Transmission

Understanding data packets, packet switching, transmission methods (serial, parallel, simplex, half-duplex, full-duplex), and USB.

Learning Objectives

By the end of this lesson, you will be able to:

  • Understand that data is broken down intopacketsto be transmitted
  • Describe thestructure of a packet(header, payload, trailer)
  • Describe the process ofpacket switching, including the role of routers and reordering of packets
  • Describe how data is transmitted usingserialandparalleltransmission
  • Describe how data is transmitted usingsimplex,half-duplex, andfull-duplex
  • Explain thesuitability of each methodof data transmission for a given scenario
  • Understand theUniversal Serial Bus (USB)interface and explain how it is used to transmit data
  • Understand thebenefits and drawbacksof USB

Key Terms

Packet

A small 'chunk' of data that makes up a larger piece of data that has been broken down for transmission.

Packet Header

Contains the destination IP address, sender's IP address, and packet number.

Payload

The actual data being transmitted (e.g. ~64KiB).

Trailer

Marks the end of the packet and contains error checking information (e.g. checksum, CRC).

Packet Switching

A method of data transmission where messages are broken into packets, each of which can take its own route to the destination.

Router

A device that examines a packet's header and decides on the best route (next hop) for the packet to take.

Hop Number

A value added to the packet header; decreased by 1 each time it passes through a router. If it reaches 0, the packet is deleted.

Simplex

Data transmission in one direction only (e.g. computer to printer).

Half-Duplex

Data transmission in both directions but not at the same time (e.g. walkie-talkie).

Full-Duplex

Data transmission in both directions simultaneously (e.g. telephone, broadband).

Serial Transmission

Data is sent one bit at a time over a single wire or channel.

Parallel Transmission

Several bits of data are sent simultaneously via a series of cables (one wire per bit).

Skew

When bits in parallel transmission arrive at slightly different times due to timing differences between wires.

Universal Serial Bus (USB)

A serial method of transmitting data that has become the industry standard for connecting devices. Supports half- and full-duplex.

Asynchronous

Data transmission where the sender and receiver are not synchronised by a shared clock signal (USB uses this).

1. Data Packets

When data is sent over long distances, it is normally broken down intopackets. Packets tend to be quite small — e.g., 64KiB.

Advantages of Packets

  • Smaller packets areeasier to controlthan a single long stream of data.
  • Each packet can take itsown routeto its destination.
  • This addsredundancyto data transmission if a route goes down or becomes busy.
  • Interference and corruption are minimal as individual packets can beresentif they are lost or damaged.
  • The whole file doesn't need to be resent if corruption occurs — this saves time and bandwidth.
  • Packet switching isquickerthan sending a large packet as each packet finds the quickest way around the network.
  • It'sharder to hackan individual's data as each packet contains minimal data and travels through the network separately.

Disadvantages of Packets

  • Packets requirecareful constructionand additional information so they can be reassembled correctly at the destination.
  • There is adelay at the destinationwhile packets are re-ordered.
  • Packets can becomelost en routeand need to be re-sent.
  • Real-time streaming is more prone to errors.

Structure of a Packet

Each data packet containsthree main parts:

Packet Header
Payload
Trailer

Packet Header

  • Destination IP address
  • Sender's IP address
  • Packet number— e.g., 1 of 5
  • Packet size (in bytes)
  • Source and destination MAC addresses

Payload

  • Theactual databeing transmitted
  • e.g., ~64KiB (1–54 KiB typical)

Trailer

  • Marks the endof the packet
  • Some form oferror checkingto ensure the packet arrives error-free (e.g. Checksum, CRC)

Real-Life Analogy: Sending a Letter

Think of a packet like a letter in an envelope. Theheaderis like the address on the envelope (where it's going and where it came from). Thepayloadis the letter inside. Thetraileris like the seal on the envelope — it confirms the letter is complete and hasn't been tampered with.

Example: Transmitting a Message

To transmit the message"This is a message :)"over the internet, TCP might break the message down into 4 packets:

Packet 1
Source IP: 197.34.213.4
Dest IP: 185.124.20.1
Data: "THIS"
Packet No: 1
Packet 2
Source IP: 197.34.213.4
Dest IP: 185.124.20.1
Data: "IS A"
Packet No: 2
Packet 3
Source IP: 197.34.213.4
Dest IP: 185.124.20.1
Data: "MESSAGE"
Packet No: 3
Packet 4
Source IP: 197.34.213.4
Dest IP: 185.124.20.1
Data: ":)"
Packet No: 4

Error Checking in Packets

  • Error checksmake sure that when a packet is received there is minimal or no corruption of the data.
  • Corruptionis where packet data is changed or lost in some way, or data is gained that originally was not in the packet.
  • Cyclic Redundancy Checks (CRCs)are used to check data packets: the sending computer adds up all 1-bits in the payload and stores this as a hex value in the trailer. The receiving computer recalculates the number of 1-bits and checks it against the value sent in the trailer. If the two values match, no transmission errors have occurred; otherwise the packet needs to be re-sent.

Activity 1: Packet Structure

A company has a website that is stored on a web server. The website data is broken down into packets to be transmitted to a user.

  1. Describe the structure of a data packet. [4]
  2. Explain why the packet number is important. [2]
  3. What is the purpose of the trailer in a data packet? [2]
Solution:
  1. Any four from: [4]
    • It has aheader
    • The header contains thedestination address
    • The header contains thepacket number
    • The header contains theoriginator's (source) address
    • It has apayload(the actual data)
    • It has atrailer(error checking / end of packet)
  2. The packet number allows the destination to [1]reassemble the packets in the correct orderto rebuild the original message / detect if any packets are missing [1].
  3. The trailer contains a method oferror checking(e.g. checksum) [1] to ensure the packet arrives error-free and data has not been corrupted during transmission [1].

Check Your Understanding: Data Packets

  • [1]Smaller packets are easier to control and route than a single large stream of data
  • [1]Each packet can take its own route, so if one route is busy or fails, other packets can still get through
  • [1]Packet header
  • [1]Payload
  • [1]Trailer
  • [1]Destination IP address
  • [1]Sender's (source) IP address
  • [1]Packet number (sequence number)
  • [1]It marks the end of the packet
  • [1]It contains a method of error checking (e.g. checksum, CRC) to ensure the packet arrives error-free
  • [1]Corruption is where packet data is changed or lost in some way during transmission
  • [1]Or data is gained that originally was not in the packet
  • [1]Advantage: Each packet can take its own route, so faulty/busy routes can be avoided
  • [1]Advantage: Individual packets can be resent if lost/damaged (no need to resend whole file)
  • [1]Disadvantage: Packets require careful construction and additional information so they can be reassembled correctly (delay at destination)

2. Packet Switching

Packet switchingis a method of sending and receiving data (packets) across a network. It is a connectionless network switching technique — there is no need to establish a dedicated circuit for communication.

The Five-Stage Process

1

Data is broken down into packets.

2

Each packet is assigned asequence numberbefore being sent.

3

Each packet can take itsown routeto the destination based on congestion.

4

Routersare responsible for controlling the route each packet takes.

5

Packets may arriveout of order. Once the final packet arrives, they arereorderedcorrectly.

How Packet Switching Works

The message comprises four packets (A, B, C, D) which may follow different routes from the sender to the receiver. Each packet has aheader(containing addressing information used by intermediate routers) and apayload(carrying the actual data).

Sender
Router
Receiver

Packets A, B, C, D may take different paths through the network. At the destination, it is the responsibility of the receiving device toreorderthe packets to retrieve the original message.

Advantages of Packet Switching

  • No need to tie up a single communication channel.
  • Easy to overcome busy or faulty lines byre-routing packets.
  • Relatively easy to expand package usage.
  • Possible to achieve ahigh data transmission rate.
  • Delay in delivery of packets is less, since packets are sent as soon as they are available.
  • Switching devices don't require massive storage, since they don't have to store the entire message before forwarding it to the next node.
  • Data delivery can continue even if some parts of the network face link failure — packets can be routed via other paths.
  • Allows simultaneous usage of the same channel by multiple users.
  • Ensures better bandwidth usage as packets from multiple sources can be transferred via the same link.

Disadvantages of Packet Switching

  • Packets can becomelost en routeand need to be re-sent.
  • Real-time streamingis more prone to errors.
  • There aredelays at the destinationwhile packets are re-ordered.
  • Unsuitable for applications that cannot afford delays in communication (e.g. high-quality voice calls).
  • High installation costs.
  • Requirescomplex protocolsfor delivery.
  • Network problems may introduce errors in packets, delay delivery, or cause packet loss. If not properly handled, this may lead to loss of critical information.
  • Protocols for packet switching can be more complex than those for circuit switching.

Hopping

Sometimes packets get lost and keep 'bouncing' around from router to router and never get to their destination. Eventually, the network could grind to a halt as the number of lost packets mounts up and clogs up the system.

To overcome this, a method calledhoppingis used. Ahop numberis added to the header of each packet. Each packet is only allowed to hop a finite number of times. Each time a packet passes through a router, the hop number is decreased by 1. If the packet has not reached its destination and the hop number = 0, then it will be deleted when it reaches the next router.

Worked Example: Downloading a Web Page

Question:How would packet switching be used to download a page from a website?

Answer:

  • The web page is divided up into data packets.
  • Each packet has a header, which includes the IP address of the destination.
  • The router checks the header against values stored in the routing table to determine which router the packet needs to be sent to next (hopped).
  • The MAC address of the next router is added to the package header.
  • The hop value is checked to see if it equals zero.
  • Each packet may go by a different route.
  • The destination computer reassembles the packets, building up the final web page.

Worked Example: Video Conferencing

Question:Suppose we are carrying out video conferencing using packet switching as the method of routing data. The performance of the communication is not very good. Describe some of the poor performance you might expect and give a reason.

Answer:

  • Picture and sound may not be in synchronisation (packets arriving at different times).
  • Video not continuous — pauses (time delay in reassembling the packets of data).
  • Degraded quality of sound and video (possibly caused by competing traffic in communication lines).
  • Possible drop out (packets take different routes, so it is possible for packets to be lost).

Activity 2: Packet Switching & Routers

  1. Explain how packet switching is used to transfer messages across the internet. [5]
  2. Outline the function of a router in packet switching. [3]
Solution:
  1. Any five from: [5]
    • A large message is divided up into a group of smaller chunks of the same size calledpackets.
    • The packet has aheaderand apayload.
    • The header contains asource IP address,destination IP address(and sequence number).
    • Each packet is dispatched independently and may travel alongdifferent routes/paths.
    • The packets may arriveout of orderand are reassembled into the original message at the destination.
    • If packets are missing/corrupted, are-transmission requestis sent.
  2. Any three from: [3]
    • The router examines the packet'sheader.
    • It reads theIP address of the destinationfrom the packet header.
    • A router has access to arouting tablecontaining information about available hops / netmask / gateway used and the status of the routes.
    • The router decides on thenext hop / best route.
    • And sends the packet on its next hop.

Check Your Understanding: Packet Switching

  • [1]A method of data transmission where a message is broken up into a number of packets
  • [1]Each packet can be sent independently and may take a different route to the destination
  • [1]A router examines the packet's header and reads the destination IP address
  • [1]It uses a routing table to determine the best route/next hop and forwards the packet accordingly
  • [1]Each packet can take its own route based on network congestion
  • [1]Some routes may be longer or have more traffic, so packets arrive at different times and need to be reordered
  • [1]A hop number is added to the header of each packet and is decreased by 1 each time the packet passes through a router
  • [1]It prevents packets from being lost and bouncing around the network forever — if the hop number reaches 0, the packet is deleted
  • [1]No need to tie up a single communication channel
  • [1]Easy to overcome busy or faulty lines by re-routing packets
  • [1]Packets may take different routes and arrive at different times, causing picture and sound to be out of synchronisation
  • [1]There may be pauses while the destination waits for missing packets and reassembles them in order
  • [1]Packets can be lost entirely, causing drop-outs in the video/audio stream

3. Data Transmission Methods

When data is sent from one device to another, three factors need to be considered (each factor has to be agreed by both sender and receiver for this to work without error):

  • Thedirectionof the data transmission (i.e. in one direction only or in both directions)
  • Themethod of transmission(how many bits are sent at the same time)
  • Themethod of synchronization(activity) between the two devices

Direction of Transmission

Simplex

A
B

Data travels inone direction onlyvia a single cable.

Example:Computer to printer; computer to monitor; microphone to computer; sensor to computer.

Half-Duplex

A
B

Data can travel inboth directionsvia a single cable — butnot at the same time.

Example:Two-way radio (walkie-talkie); printer cable that responds with "Ink low" after receiving a file.

Full-Duplex

A
B

Data can travel inboth directions at the same timeusing two communication channels.

Example:Telephone; broadband connection; instant messaging; video conferencing; network cables.

TransmissionAdvantagesDisadvantages
SimplexSimple and low-cost for one-way communicationCannot support two-way communication
Half-DuplexCheaper than full-duplex for two-way communicationSlower due to one-direction-at-a-time
Full-DuplexFast, supports simultaneous two-way data transferMore expensive to implement

Serial vs Parallel Transmission

Serial Transmission

Data is sentone bit at a timeover asingle wire or channel.

Sender
Receiver
  • Works well overlong distances.
  • Data is transmitted at aslower ratethan parallel.
  • No problem of data arriving out of synchronisation (bits arrive in order).
  • Applications:USB, Wi-Fi, computer to modem, mouse, telephone line system.

Parallel Transmission

Several bits of data (usually 1 byte) are sent downseveral wires or channelsat the same time.

Sender



Receiver
  • Works well overshort distances.
  • Fastermethod of data transmission than serial.
  • Over longer distances, bits can becomeskewed— they arrive at slightly different times, so they are no longer synchronised.
  • Applications:Integrated circuits, buses, internal computer components, sending data to a printer using a ribbon connector.
Serial TransmissionParallel Transmission
Less risk of external interference than parallel (fewer wires)Faster rate of data transmission than serial
More reliable transmission over longer distancesWorks well over shorter distances
Transmitted bits won't have the risk of being skewedParallel ports require more hardware, making them more expensive to implement
Used if the amount of data being sent is relatively small (slower transmission rate)If data is time-sensitive, parallel is the most appropriate transmission method
Less expensive than parallel due to fewer hardware requirementsSince several wires are used, bits can arrive out of synchronisation (skewed)

Combinations of Transmission Methods

Wires can be combinations of serial, parallel, simplex, half-duplex, and full-duplex:

Serial-Simplex
Serial-Half-duplex
Serial-Full-duplex
Parallel-Simplex
Parallel-Half-duplex
Parallel-Full-duplex
  • Serial-Simplex:Data transmitted one bit at a time in one direction only on a single wire.
  • Serial-Half-duplex:Data transmitted one bit at a time, can flow in both directions but not at the same time (uses a single shared wire).
  • Serial-Full-duplex:Data transmitted one bit at a time in both directions simultaneously (requires two wires).
  • Parallel-Simplex:Multiple bits transmitted simultaneously in one direction only using multiple wires.
  • Parallel-Half-duplex:Multiple wires send multiple bits in both directions, but only one direction at a time.
  • Parallel-Full-duplex:Multiple wires send multiple bits in both directions simultaneously.

Worked Example: Parallel Half-Duplex Suitability

Question:A company has a website stored on a web server. The company uses parallel half-duplex data transmission to transmit the data for new videos to the web server. Explain why parallel half-duplex data transmission is the most appropriate method. [6]

Answer:

  • Parallel would allow for thefastest transmission[1]
  • As large amounts of data [1]
  • Can be uploaded and downloaded [1]
  • But this does not have to be at the same time [1]
  • Data is not required to travel a long distance [1]
  • Therefore, skewing is not a problem [1]

Exam tip: Any four of these points qualifies as a full answer, however make sure your answer is cohesive.

Activity 3: Transmission Methods

  1. Describe serial data transmission. [2]
  2. Describe parallel data transmission. [2]
  3. Give one benefit and one drawback of parallel data transmission compared to serial over short distances. [2]
  4. Give one example where parallel data transmission is used. [1]
  5. Describe half-duplex data transmission. [2]
Solution:
  1. Data is transmitted one bit at a time [1] using a single wire [1].
  2. Data is transmitted multiple bits at a time/simultaneously [1] using multiple wires [1].
  3. Benefit:Quicker/faster data transfer [1].Drawback:More chance of data being skewed due to bits being sent simultaneously/out of order, or more expensive as requires more wires, or more chance of interference as more wires are used [1].
  4. Used in integrated circuits, RAM, or connections to peripheral devices (e.g. printer) [1].
  5. Data is transferred in two directions [1] but data is sent in only one direction at a time [1].

Check Your Understanding: Transmission Methods

  • [1]Simplex transmission is in one direction only
  • [1]Half-duplex transmission is in both directions but not at the same time
  • [1]Over longer distances, bits can become skewed (arrive at slightly different times)
  • [1]This means the data is no longer synchronised and errors occur
  • [1]Telephone / broadband connection / video conferencing / instant messaging
  • [1]Skew is when bits in parallel transmission arrive at slightly different times
  • [1]This happens because separate bits travel on different wires and may experience different delays
  • [1]Serial (single wire)
  • [1]Half-duplex (both directions, but not at the same time)
  • [1]Serial uses a single wire, so there is less chance of interference/data corruption
  • [1]Bits will still be synchronised after transmission (no skew)
  • [1]It is cheaper to set up and more reliable over greater distances

4. Universal Serial Bus (USB)

TheUniversal Serial Bus (USB)is a serial method of transmitting data. It has become the most common type of input/output used in computing and an industry-standard method of transferring data between devices.

Key Facts about USB

  • USB is aserialdata transmission method.
  • USB allows for bothhalf-duplexandfull-duplexdata transmission.
  • It is anasynchronousserial data transmission method.
  • The USB cable consists of afour-wire shielded cable:
    • Two wires are used forpower and earth(red = +5V, black = ground)
    • Two wires are used fordata transmission(green = Data+, white = Data−)
Red
Power +5V
Black
Ground
Green
Data +
White
Data −

What Happens When a Device is Plugged In?

  • The computerautomatically detectsthat a device has been connected.
  • It looks for the correctdriver:
    • If the driver is already installed, the appropriate device driver is loaded so that the device can communicate with the computer.
    • If the device is new, the computer will look for a compatible device driver.
    • If one cannot be found, the user must download and install an appropriate driver manually.

USB Connector Types

USB-A

Commonly used for flash drives, mice, keyboards, external HDD

USB-B

Found in printers, scanners, and older external storage devices

USB-C

Latest standard — small size, fast transfer speeds, carries power

Micro

Smaller connectors used in mobile devices

USB Generations & Speeds

  • USB 1.1— 12 Mbps (very slow)
  • USB 2.0— 480 Mbps (very common but slower compared to modern versions)
  • USB 3.0 / 3.1 / 3.2— 5 Gbps to 20 Gbps (much faster, used for external HDDs and gaming devices)
  • USB 4 / USB 4.2.0— Up to 80 Gbps (the latest and fastest, used for high-speed data transfer)

USB-C advances:Smaller and thinner than previous versions. Offers 100 watts (20 volts) of power — full-sized devices can now be charged via USB. Supports data transfer of up to 10 gigabits per second — enough for 4K video streaming. Backwards-compatible with USB 2.0 and 3.0.

Benefits of USB

  • Industry-standard — and therefore very well-supported.
  • Devices connected via USB areautomatically detectedand appropriate device drivers loaded.
  • Supplies+5V of power, so most USB-connected devices do not need an additional power source.
  • Designed to bebackwards-compatible(newer USB standards work with older USB standards).
  • AUSB hubcan be used to easily add extra ports to an existing device.
  • USB protocol can notify the transmitting device tore-transmit dataif it detects errors.
  • The connector can only fit one way — this prevents incorrect connections being made.
  • Several different data transmission rates are supported.

Drawbacks of USB

  • Limited distance— only supports cable lengths of around5 metres. Can be extended but only with additional hardware (USB hubs).
  • Limitations of backwards-compatibility— support for older standards is becoming increasingly rare. Very old USB standards (e.g. USB 1.1) may not be supported in the near future.
  • Data transfer limitations— even newer versions like USB 3.0 and USB-C have slower data transfer speeds compared to Ethernet.

Worked Example: Benefits of USB for a Printer

Question:Leonard has a new laser printer to print letters for his business. He connects his printer to his computer using the USB port. Give three benefits of using the USB port to connect the printer to the computer. [3]

Answer (any three from):

  • It is a universal standard
  • It can't be inserted the wrong way around
  • Supports different transmission speeds
  • Automatically detects the device and installs the driver

Activity 4: USB Interface

  1. Julia uses a USB connection to transfer data onto her USB flash memory drive. (i) One benefit of using a USB connection is that it is a universal connection. State two other benefits. [2] (ii) Identify the type of data transmission used in a USB connection. [1]
  2. Nikita wishes to print out some documents and connects her printer to the computer using one of the USB ports. (i) Identify what type of data transmission is being used. [1] (ii) Give three reasons for using a USB port. [3]
Solution:
  1. (i) Any two from: It cannot be inserted incorrectly; supports different transmission speeds; high speed transmission; automatically detected; powers the device for data transfer [2]
    (ii)Serial[1]
  2. (i)Serial[1]
    (ii) Any three from: Automatically detects the hardware/installs drivers; plug only goes in one way/can't connect incorrectly; supports different data transmission speeds; has become the industry standard/universally used; backwards compatible with earlier versions of USB ports [3]

Check Your Understanding: USB

  • [1]Serial
  • [1]Approximately 5 metres
  • [1]Devices are automatically detected and drivers loaded
  • [1]Most USB-connected devices do not need an additional power source (USB supplies +5V)
  • [1]Newer USB standards can still be used with older USB devices/ports
  • [1]For example, a USB 3.0 device can be plugged into a USB 2.0 port (though it will run at the slower speed)
  • [1]Four wires in a shielded cable
  • [1]Two wires used for power and earth (red = +5V, black = ground)
  • [1]Two wires used for data transmission (green = Data+, white = Data−)
  • [1]Smaller and thinner than previous versions
  • [1]Offers 100 watts (20 volts) of power — full-sized devices can be charged via USB
  • [1]Supports data transfer of up to 10 gigabits per second (enough for 4K video streaming) and is backwards-compatible with USB 2.0 and 3.0

Key Takeaways

  • Data packetsare small chunks of data that make up a larger piece of data broken down by TCP.
  • A packet has three parts:header(destination IP, source IP, packet number),payload(actual data), andtrailer(error checking, end of packet).
  • Packet switchingis a five-stage process: break data into packets → assign sequence numbers → packets take own routes → routers control routes → packets reordered at destination.
  • Advantages of packet switching:no single channel tied up, easy to overcome faulty lines, high data transmission rate possible.
  • Disadvantages:packets can be lost, real-time streaming prone to errors, delays at destination while reordering.
  • Hoppingprevents packets from being lost forever — hop number decreases by 1 at each router; if it reaches 0, the packet is deleted.
  • Simplex:one direction only (computer to printer).Half-duplex:both directions but not at the same time (walkie-talkie).Full-duplex:both directions simultaneously (telephone).
  • Serial transmission:one bit at a time on a single wire. Reliable over long distances, cheaper, less interference.
  • Parallel transmission:multiple bits simultaneously on multiple wires. Faster but prone to skew and only suitable for short distances.
  • USBis a serial, asynchronous transmission method supporting half- and full-duplex.
  • USB cable hasfour wires: two for power (+5V and ground), two for data (Data+ and Data−).
  • Benefits of USB:industry standard, automatic detection and driver loading, powers devices, backwards-compatible, USB hub expands ports, error re-transmission.
  • Drawbacks of USB:limited to ~5m cable length, older standards may not be supported, slower than Ethernet.
  • USB-Cis the latest standard: symmetrical 24-pin connector, reversible, offers 100W power, supports up to 10 Gbps data transfer.

Question Bank

  • [1]It has a header containing the destination address
  • [1]The header contains the packet number
  • [1]The header contains the originator's (source) address
  • [1]It has a payload (actual data) and a trailer (error checking / end of packet)
  • [1]A large message is divided up into smaller chunks of the same size called packets
  • [1]Each packet has a header and a payload; the header contains source IP, destination IP, and sequence number
  • [1]Each packet is dispatched independently and may travel along different routes
  • [1]The packets may arrive out of order and are reassembled into the original message at the destination
  • [1]If packets are missing or corrupted, a re-transmission request is sent
  • [1]The router examines the packet's header and reads the IP address of the destination
  • [1]A router has access to a routing table containing information about available hops / netmask / gateway used
  • [1]The router decides on the next hop / best route and sends the packet on its next hop
  • [1]Uses several/multiple wires
  • [1]Transmits multiple bits at a time/simultaneously
  • Benefit [1]:Quicker/faster data transfer
  • Drawback [1]:More chance of data being skewed due to bits being sent simultaneously/out of order, or more expensive as requires more wires, or more chance of interference as more wires are used
  • (i)Data is transmitted one bit at a time [1]; data is transmitted using a single wire; bits arrive in order/sequence [1]
  • (ii)Data is transmitted multiple bits at a time/simultaneously [1]; data is transmitted using multiple wires; bits may arrive out of sequence/skewed [1]
  • (iii)Data is transmitted in both directions [1]; at the same time/simultaneously [1]
  • (a)Bits sent one at a time [1]; uses a single wire [1]
  • (b)USB / SATA / Wi-Fi / PCI Express / any appropriate serial device [1]
  • (c)Data is transferred in two directions [1]; data is sent in only one direction at a time [2]
  • Data is transmitted in one direction only, one bit at a time. →False
  • Data is transmitted in both directions, multiple bits at a time. →False
  • Data is transmitted in one direction only, multiple bits at a time. →False
  • Data is transmitted in both directions, but only one direction at a time. Data is transmitted one bit at a time. →True
  • Data is transmitted in both directions, but only one direction at a time. Data is transmitted multiple bits at a time. →False
  • [1]Parallel would allow for the fastest transmission
  • [1]As large amounts of data
  • [1]Can be uploaded and downloaded
  • [1]But this does not have to be at the same time
  • [1]Data is not required to travel a long distance
  • [1]Therefore, skewing is not a problem
  • (i)Any two from: It cannot be inserted incorrectly; supports different transmission speeds; high speed transmission; automatically detected; powers the device for data transfer [2]
  • (ii)Serial [1]
  • [1]It is a universal standard
  • [1]It can't be inserted the wrong way around
  • [1]Supports different transmission speeds / automatically detects the device and installs the driver
  • [1]Single wire means there is less chance of interference/data corruption
  • [1]Single wire reduces costs / more reliable over greater distances / bits will still be synchronised after transmission
  • Description 1:Data is transmitted several bits at a time down several wires in both directions simultaneously. →ParallelandFull-duplex
  • Description 2:Data is transmitted in one direction only, one bit at a time, down a single wire. →SerialandSimplex
  • Description 3:Data is transmitted one bit at a time down a single wire; the data is transmitted in both directions but not at the same time. →SerialandHalf-duplex
  • [1]The computer automatically detects that a device is present
  • [1]The device is automatically recognized and the appropriate device driver is loaded up so that the computer and device can communicate effectively
  • [1]If a new device is detected, the computer will look for a device driver which matches the device; if this is not available, the user is prompted to download appropriate software
  • [1]Parallel transmission is only suitable for short distances
  • [1]Over longer distances, bits can become skewed (arrive at different times), causing data corruption
  • [1]Serial transmission is more reliable over long distances, cheaper (single wire), and less prone to interference