AQA Computer Science A-Level: Communication and Networking

Serial Transmission

A method of transmitting data one bit at a time over a single channel.

Parallel Transmission

A method of transmitting multiple bits simultaneously over multiple channels.

Advantages of Serial over Parallel Transmission

Serial transmission is generally faster over longer distances and has less interference compared to parallel transmission.

Synchronous Data Transmission

Data transmission where data is sent in a continuous stream, synchronized with a clock signal.

Asynchronous Data Transmission

Data transmission where data is sent at irregular intervals, with start and stop bits to indicate the beginning and end of transmission.

Start Bits

Bits used in asynchronous transmission to indicate the start of a data packet.

Stop Bits

Bits used in asynchronous transmission to indicate the end of a data packet.

Baud Rate

The number of signal changes in the medium per second.

Bit Rate

The number of bits transmitted over the medium per second, often measured in bits per second (bps).

Bandwidth

The range of frequencies that a communication medium is capable of transmitting, expressed in Hertz.

Latency

The difference in time between an action being initiated and its effect being noticed, often measured in milliseconds.

Protocol

A set of rules relating to communication between devices.

Bit Rate Formula

Bit rate = Baud rate × Number of bits per signal.

Relationship between Bit Rate and Baud Rate

A communication medium's bit rate will be higher than its Baud rate if there is more than one bit sent per signal.

Direct Relationship between Bandwidth and Bit Rate

Higher bandwidth results in a higher bit rate.

Effect of Latency with Distance

Latency usually increases with distance.

Symbol

A particular pattern of bits represented by a signal, for example, a symbol of four bits might be 1101.

Example of Latency

If you press the 'R' key on your keyboard and the letter R appears on screen 26ms later, the latency is 26ms.

International Protocols

Protocols published by international organizations that allow devices from different manufacturers to communicate seamlessly.

Signal Change

1 Baud (or 1Bd) is equal to 1 symbol change per second.

Higher Bit Rate

A communication medium's bit rate will be higher than its Baud rate if there is more than one bit sent per signal.

Communication Basics

Key concepts that help in understanding different methods of communication.

Data Transmission Methods

Computers can transmit data between their different components in two ways: serially or in parallel.

Serial data transmission

Data is sent one bit at a time over one communication line.

Parallel data transmission

Uses numerous parallel communication lines to send multiple bits simultaneously.

Skew

The problem where bits sent together may not be received together due to different electrical properties of communication lines.

Crosstalk

Occurs when tightly packed communication lines cause signals from one line to leak into another.

Advantages of serial over parallel

Serial data transmission doesn't suffer from skew or crosstalk, making it more reliable, especially over long distances.

Synchronous transmission

Data is transmitted using a shared clock signal to time when signals are sent.

Asynchronous transmission

Uses start and stop bits to indicate the duration of a transmission without a shared clock signal.

Start bit

The bit that indicates the beginning of a transmission, which can be either a 0 or a 1.

Stop bit

The bit that indicates the end of a transmission, which is always the opposite of the start bit.

Baud rate

The rate at which information is transferred in a communication channel.

Medium to long distances

The typical range for serial data transmission, such as from wired peripherals to a computer.

Short distances

The typical range for parallel data transmission, such as between parts of the processor and within RAM.

Corruption of data

Occurs when bits from different pulses overlap, leading to errors in the transmitted information.

Regular intervals

The timing at which signals are sent in synchronous data transmission.

Real-time systems

Systems that require information to be transmitted in the same order it was sent.

Communication medium

The physical medium used to transmit data, such as metal wire, optical fibre, or wireless channels.

Electrical properties

Characteristics of communication lines that can affect the speed and integrity of data transmission.

Multiple lines

Refers to the use of several communication lines in parallel data transmission to increase data transfer rates.

Data transmission

The process of sending data from one point to another through a communication medium.

Wired peripherals

Devices like mice and keyboards that connect to a computer using physical cables.

Processor busses

The pathways used within a computer's processor for data transfer during the fetch-execute cycle.

Network topology

The structure of a network, which can be physical or logical.

Physical network topology

The actual architecture of a network, determining how components are interconnected.

Physical star network topology

A network topology where each client has its own direct connection to a central hub.

Central hub

The device in a star network that receives packets from clients and delivers them to the correct recipient.

Advantages of physical star topology

Easy to add and remove clients; eliminates collisions as each cable has one device communicating.

Disadvantages of physical star topology

If the central hub fails, all communication stops; expensive to install due to cable requirements.

Physical bus topology

A network topology that connects clients to a single cable called a backbone.

Backbone

The single cable in a bus topology that connects all clients.

Terminator

A device placed at either end of the backbone in a bus topology.

Advantages of physical bus topology

No central hub reduces chances of network failure and decreases installation costs.

Disadvantages of physical bus topology

Packets are visible to all clients on the network, which can lead to security issues.

Peer-to-peer networking

A type of networking where each device can act as both a client and a server.

Client-server networking

A type of networking where clients request services and resources from a centralized server.

WiFi

A wireless networking technology that allows devices to connect to a network without physical cables.

Components required for wireless networking

Devices such as routers, access points, and network adapters that facilitate wireless communication.

Wireless network security

Measures taken to protect a wireless network from unauthorized access and attacks.

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)

A wireless protocol that helps manage how data packets are transmitted over a network to avoid collisions.

Request to Send/Clear to Send (RTS/CTS)

A mechanism used in wireless networking to prevent collisions by signaling when a device is ready to send data.

Service Set Identifier (SSID)

A unique identifier for a wireless network that allows devices to connect to it.

Logical bus network topology

A representation of how data flows through a network, regardless of its physical layout.

Differentiation between physical and logical topologies

Physical topology refers to the actual layout of the network, while logical topology refers to how data flows within that layout.

Operation of physical star topology

In a star topology, data packets are sent directly to the intended recipient through the central hub.

Operation of physical bus topology

In a bus topology, all devices share a single communication line, and packets are sent through the backbone.

Backbone

The backbone is used for communication by multiple clients, introducing the risk of collisions.

Network Failure

Should the backbone fail, the entire network becomes unusable.

Logical Topology

A network's logical topology refers to the flow of data packets within a network.

Logical Bus Network

A logical bus network delivers packets to all clients on the network.

Logical Star Network

A logical star network delivers packets only to their recipient.

Mixing Topologies

If a network is set up as a physical star, it can still behave as a logical bus.

Host

A host is a device on a network that provides services.

Server

A server can provide services such as file storage, printer sharing and internet access.

Client

Clients on a network can also provide services themselves.

Client-Server Networking

In a client-server network, one or more central servers provide services to the clients on the network.

Central Management

Most schools, colleges and businesses use client-server networks to allow for central management of clients on the network.

Peer-to-Peer Networking

Peer-to-peer networks do away with a shared server, with services provided by the clients themselves.

Equal Status in Peer-to-Peer

In peer-to-peer networking, every client has equal status.

Disadvantage of Peer-to-Peer

The primary disadvantage of peer-to-peer networking is that all of the clients which provide services must be running.

Cost Effectiveness of Peer-to-Peer

Peer-to-peer networking is more cost effective than client-server networking as there is no need for a powerful server.

Ease of Setup

Peer-to-peer networks are easier to set up and maintain than their client-server counterparts.

Large File-Sharing Networks

Large file-sharing networks and multimedia providers use peer-to-peer networking to provide high-performance services without the requirement for a server.

Packet Delivery

A logical bus network delivers packets to all clients while a logical star network delivers packets only to their recipient.

Physical Star Topology

If the physical connections between clients and the central hub follow that of the physical star topology, running a bus protocol on the hub allows it to distribute packets to all of the connected clients.

Client Requests

The clients on the network request services from the servers, which then respond to the client with the requested service.

Services Provided by Servers

Services provided by servers in a client-server network could include file storage as well as management of emails, user accounts and print queues.

Wireless networks

Allow clients to communicate within a network without being physically connected to it.

Wireless access point

Connects to a wired network just like any other client would.

Wireless network adapter

The device that connects to the wireless network.

WiFi

Refers to a wireless local area network that is based on international standards.

WPA

Stands for WiFi protected access and requires that a new wireless client enters a password to connect to the network.

WPA2

An enhanced version of WPA that also secures wireless networks.

SSID

Stands for service set identifier and is the name that identifies a wireless network.

Disabling SSID broadcast

Stops wireless devices within range from displaying that the network is available.

MAC address filter

Allows only specific devices to connect to a network by creating whitelists or blacklists.

MAC address

Assigned to every wireless device by their manufacturer and is unique to that device.

CSMA/CA

A protocol used in wireless networks to avoid data collisions caused by multiple devices communicating simultaneously.

Exponential backoff algorithm

Increases the time period for which the device waits with each check of the channel.