X) Networks and Communication

Question 1

Serial Data Transmission

Answer 1

Serial data transmission is when data is transmitted one bit at a time, down one data line.
For two way communication, an extra data line is required.
They can transmit at a rate of 1Gps ( 1000 million bits per second).

Question 2

Parallel Data Transmission

Answer 2

Parallel data transmission is where data is transmitted several bits simultaneously along separate data lines.
The more wires there are the more data that can be sent simultaneously, this creates large network channels, (processor and memory).

Question 3

Serial Vs Parallel Data Transmission

Answer 3

Serial:

• Only one-way data transmission
• Slower than parallel
• Less number of cables required
• Data can be transmitted over longer distances

Parallel:

• Two-way data transmission
• Faster than serial
• More prone to developing connection problems (Skew).
• Can only transmit data over short distances

Question 4

Connection problems

Skew and Crosstalk

Answer 4

Skew is a problem caused when each wire has slightly different properties, leading to different data speeds along each wire.
Crosstalk is the electromagnetic interference between two adjacent wires. This issue can become pronounced as the frequency of transmission increases.

Question 5

Synchronous Transmission

Answer 5

Synchronous data transmission is when all data transfers are timed to coincide with an internal clock.
The data is sent as one long stream of data with no gaps in the transmission. The receiver counts the bits and reconstructs bytes.

Question 6

Asynchronous Transmission

Answer 6

Asynchronous data transmission is when each byte is sent separately instead of waiting for a clock signal.
Each byte is preceded by a start bit and a stop bit, with a short gap between each byte.
This transmission is relatively slow as to the short gap between each byte. But is a cheap, serial transmission suited to low transmission connections.

Question 7

The parity bit

Answer 7

The parity bit is added as the 8th bit, to form an error detection. Can either be a 0 or 1 and is placed at the end of the byte, before the stop bit.

Question 8

Latency

Answer 8

Latency is the time delay between the moment the first byte is sent to when it is received at its destination.

Causes for latency:

• the time it takes data to pass through a communication medium.
• the time it takes for data to pass through a network depending on how many devices it has to pass through.

Question 9

Protocols

Answer 9

Protocols are a set of rules for governing data transmission across devices and networks.

The protocol defines:

• Standards for physical connections and cables
• The rate of data transmission
• How data is formatted
• Whether the transmission is synchronous or asynchronous

Question 10

Bit Rate

Answer 10

Bit rate is the rate at which data is transmitted, measured in bits per second (bps). The bit rate is directly proportional to bandwidth.
Using baseband, at each signal change one bit is transmitted, the faster the signal change, the greater the bit rate.

Question 11

Baud Rate and Broadband

Answer 11

Baud rate is the rate at which the signal in a communications channel changes state. Measured in megabits per second (Mbs).
Broadband carries multiple signals on a fixed carrier wave, where bits are sent as variations on the wave.

Question 12

How to calculate bit rate?

Answer 12

Bit rate = baud rate x number of bits per signal

Question 13

Bandwidth

Answer 13

Bandwidth is a measure of the capacity of the channel down which the data is being sent, measured in hertz (Hz).

Question 14

Local Area Networks (LANs)

Answer 14

A LAN is two or more computers connected together within a small geographical area.

• Devices can be sent data over to each other faster over a LAN.
• Computers safer from threats as data is not sent directly from a client, sent through a server.

Question 15

Bus Topology

Answer 15

A Bus network topology is where all nodes are connected to a single backbone cable.
Each node is passive and data is sent in one direction at a time only.
Only one computer can transmit successfully at any one time.

+ives:
Cheaper as only one cable is needed.
Easier to add new clients.

-ives:
Less secure as all data is transmitted down one cable.
If the main cable fails then all clients are affected.

Question 16

Star Topology

Answer 16

A Star network topology is where computers are connected to a central hub or switch.

• A switch sends each communication to the specific computer it is intended for.
• A hub broadcasts the message to every computer on the LAN.

+ives:
Fast connection speed as each client has a dedicated cable.
If one cable fails then only that client affected.

-ives:
Expensive to set up and increase capacity.
The central server can get congested as all communications go past it.

Question 17

Carrier Sense Multiple Access (CSMA)

Answer 17

CSMA with Collision Detection (CSMA/CD) detects two nodes attempting to transmit simultaneously.
Both nodes cease transmission and then wait a random amount of time before reattempting.

Question 18

Media Access Control Addressing (MAC addressing)

Answer 18

Each networked device has a Network Interface Card (NIC), a NIC enables a device to connect to a network.
The type of NIC determines the speed at which data can be transmitted between the device and the network.

Question 19

Physical and Logical Topology

Answer 19

The physical topology of a network is how the devices are physically connected.
The logical topology of a network is how the devices communicate across the physical topology.

Question 20

Client-server network

Answer 20

A client is a computer that requests the services or resources provided by a server.
The client sends requests to the server and waits for a reply.
A server is a powerful computer that provides services or resources required by any of the clients.
The server waits for requests from clients, then it may pass the request to another server, which in effect becomes a client.

Question 21

Features of a client-server network

Answer 21

• A central server is used to manage security.
• Some processing tasks are performed by the server.
  -Suitable for both small and large types of organisations.
• Can require specialist IT staff to administer the network.
  -Many specialised servers, each with a dedicated task:
  Web Server
  File Server
  Database Server
  Print Server

Question 22

Peer-to-peer network

Answer 22

A peer-to-peer network is a network where all devices share resources between them rather than having a central server.

Question 23

Features of a peer-to-peer network

Answer 23

• Suitable for small organisations with few computers.
• All computers share the same files.
• No central server to control files and security.
• All computers can communicate with each other without going through a central server.

Question 24

Peer-to-peer on a WAN

Answer 24

Peer-to-peer (P2P) can be used for file-sharing websites.
This means with people downloading, data can be passed between computers rather than through a central server.
P2P is used for the illegal distribution of copyright material such as films and music.

Question 25

Cloud Computing

Answer 25

Cloud computing is the storing and accessing of data through the internet.
Whereby using remote servers run by organisations, data can be held or accessed on different networks.

Question 26

Advantages of Cloud Computing

Answer 26

• Software and data is accessible from any computer around the world.
• Data is automatically backed up, so no danger of losing data.
• Software and data doesn’t occupy space on the users hard drive.

Question 27

Wi-Fi

Answer 27

Wi-Fi is a wireless networking technology providing high-speed Internet and network connections.
Devices connect to the Internet via a Wireless network Access Point (WAP).

Question 28

Connecting to a wireless network

Answer 28

Each device that wants to connect to the internet must require a NIC (Network Interface Card) which then enables the device to communicate to a WAP.

WAP requires a connection to a router, the router requires a connection to a modem, the modern converts digital signals from a computer to analogue signals which are then sent down a network line.

Question 29

Service Set Identifier (SSID)

Answer 29

SSIDs identify each network by a unique name. SSIDs are used by all devices on that network.
SSIDs can be set to broadcast to wireless devices in range of an access point.

Question 30

Securing a wireless network

Answer 30

Wireless networks can be less secure than wired networks. Unauthorised users can be hard to spot and transmitted data can easily be intercepted.

Security measures used are WPA and WPA2

Question 31

Collisions and avoidance

Answer 31

When several devices are transmitting via a single WAP, a protocol is needed to prevent two devices from transmitting simultaneously.

Question 32

CSMA/CA

CSMA/CA using RTS/CTS

Answer 32

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol.
Collisions are avoided by each station transmitting only when the channel is idle.

CSMA/CA

1. Assemble a frame
2. Is channel Idle?
3. No- wait a random time until data can be transmitted.
4. Yes- transmit data

Using RTS/CTS

1. Assemble a frame
2. Is channel Idle?
3. No- wait a random time until data can be transmitted.
4. Transmit RTS (Request To Send)
5. CTS (Clear To Send) received?
6. No- wait a random time
7. Yes- transmit data