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Communication Basics Learning Objectives • What serial and parallel data transmission are. • What bandwidth, bit rate and baud rate are and the differences between them. • How latency affects the actual speed of transmission. • What synchronous and asynchronous data transmission are. • How devices establish communication through handshaking. • Which protocols areused to establish rules and standards by which transmissions can take place. Communication Basics Data Transmission The best ways that computers can transmit data is to reduce it to its binary form, although some medium is analogue – whether it is text, images or video. Moving data from one place to another is called DATA TRANSMISSION Transmission Medium Transmitter Receiver Communication Channel Tranmission Media Guided – cabling, twisted pairs, coaxial, optic Unguided – wireless, radio, microwaves Communication Basics Data Transmission Data transmission can happen between communication applications, networks and on the motherboard itself between the CPU and various other components and peripheral devices via the buses Two types of data transmission 1) Serial 2) Parallel Communication Basics Serial Communication Serial transmission sends and received data one bit at a time in sequence 101001 101111 100001 111001 Speed of transmission will depend on the cabling. Not necessarily slow. Universal Serial Bus (USB) uses a high speed serial connection – capable of transmission rates of 1Gbps Serial data transmission is used for long-distance communication. The main reason for using serial data transmission is that it needs only one signal pathway each way. This makes it easier to regenerate the signal. Signal strength can fall significantly over long distances. Communication Basics Parallel Transmission This uses a number of wires to send a number of bits simultaneously. The more wires, the more data can be sent. This method is used inside the computer on the buses. Depending on the word length a computer can send 8,16,32 or 64 bits of data at a time. Used for short distances – for instance buses or printers nearby. Faster than serial data tranmisssion. Different properties on each line can lead to skew. Communication Basics Parallel Transmission 010101 110101 001111 101001 111101 101010 110101 111001 Communication Basics Advantages of serial over parallel Transmission • The significant reduction in soze and complexity of connectors in serial transmission results in lower costs. Better for smaller devices as well • “Crosstalk” can occur over parallel lines leading to corrupted data – therefore need to be resent. • Serial links are more reliable over greater distances • Lack of interference at higher frequencies means frequencies can be higher Communication Basics Bandwidth • Amount of data that can be transmitted along the medium at any one time. Measured in Hz but closely associated with BIT RATE (bps) Bit Rate • The speed at which a particular transmission is taking place. Measured in (bps) Bits per second. Bandwidth is the range of frequencies that can be transmitted and bit rate is the number of bits that can be transmitted per unit of time. Bit Rate is therefore directly proportional to Bandwidth. Communication Basics Baud Rate • Another term to describe the speed at which data can be transmitted. • Baud rate is the electronic state change per second. • Usually equivalent to 1 bit of information but sometimes a electronic state change can represent a number of bits – so you are effectively sending symbols rather than bits. Communication Basics Latency • This is the time delay between the moment the first byte or data packet of a communication starts and when it is received at its destination. • Communication sometimes has to travel via satellites, via cable, through busses and logic gates. • Latencies from using peripheral devices might be unnoticeable but using the internet or playing online games – distances are greater therefore it might be more noticeable. • Three types • Propagation Latency – Amount of time it takes for a logic gate within a circuit to transmit the data. • Transmission Latency – Amount of time it takes to pass through a particular communication medium, e.g. cable • Processing latency – The amount of time it takes data to pass around a network depending on how many servers or devices it has to pass through. Communication Basics Study tasks 1) Explain why you rarely achieve the connection speed that is theoretically possible from your internet connection. 2) What are the highest bit rates that are theoretically possible between two devices using a) Serial communication b) Parallel communication 3) Which country has the highest average internet speeds? Where does the UK come in the world rankings and why? Communication Basics Synchronous Data Transmission • Data is transmitted by having the sending device and receiving device synchronising their transmission signals. • Sending device uses the system clock to control the transmission rate to be in time with the device or computer receiving the signal. • If the devices are not synchronised then data can be lost. • Devices are kept in time permanently. Sender Data Receiver Communication Basics Asynchronous Data Transmission • Does not require the permanent synchronisation of the sender and receiver’s clocks. • Synchronises for the duration of the communication only. • Uses start and stop bits to synchronise. • May also include a parity bit for validation of data. Sender STOP Data Start STOP Data Start Receiver Communication Basics Asynchronous Data Transmission • Start bit causes receiver to synchronise its clock to the same rate as the sender • Both devices agree on how many bits will follow, whether a parity bit is used and how many stop bits • Stop bits arrive so receiver processor can handle those bits. Can now also identify when the next start bit will arrive. • If more data – another start bit will be sent and the process repeated. • Sender just keeps sending data and does not have to wait for synchronisation signal from receiver. Sender STOP Data Start STOP Data Start Receiver Communication Basics Protocols 1) A set of rules relating to communication between devices. 2) So many different devices involved in communication all around the world from so many different manufacturers - that ways of them communicating to each other needs to be standardised. 3) This is why standardised protocols are established. 4) Internet Protocols: a) TCP/IP (Transmission Control Protocol/Internet Protocol)Relates to a set of rules that govern the transmission of data around the internet. Data sent around the internet are split into packets and this protocol handles the routing and re-assembly of these data packets. b) HTTP (Hypertext Transfer Protocol) Set of rules governing the exchange of the different types fo files that make up displayable web pages c) FTP (File Transfer Protocol) – Provides rule for transfer of files on the internet. Communication Basics Study tasks 1) Investigate how the TCP/IP Protocol actually works. What are the different layers that it uses. Create a visual presentation of your findings. Networks Learning Objectives • What components are needed to construct a network, including servers, clients, routers, switches and network cards. • How networks can be constructed using different topologies • The benefits of using different topologies • How networks can be client-server or peer to peer • How wireless networks work • How data is transmitted in frames and packets • How data is being transmitted using protocols to prevent collisions of data and keep data safe. Networks LAN 1) A number of computers and peripherals connected over a small geographical area. 2) Common in businesses, hospitals and educational establishments. 3) Usually made up of a number of servers and clients. Components of a LAN – LINK Networks Wide Area Networks • Were invented to solve the problem of connecting a LAN to a distant workstation or another remote LAN. • WAN are used to share information over a large geographical area. Connections used could be : The public switched telephone network High-speed, high bandwidth dedicated leased lines High-speed fibre optic cable Microwave transmission links Satellite links Radio Waves The Internet Carried out through either Circuit switching or packet switching. Communicating over a WAN – Connection oriented networks: Circuit Switching: A circuit is established between two nodes and all data follows this path. Communicating over a WAN – Connectionless oriented networks: Packet Switching: The data is split into a number of smaller packets that may take different routes to reach the destination. Networks TOPOLOGIES – STAR Network Star network topology: Hub or switch Networks TOPOLOGIES – STAR Network Star network client connection hardware: Hub Networks Star Networks • All clients are connected to a central server via an individual connection • Usually this is done through a switch or a hub • Server is a high specification machine. • Different servers used – Data, Software, Printer, Web, Email etc. • In reality the network will not look like a star – but this is a conceptual interpretation of it. Networks TOPOLOGIES – Bus Network Terminator ‘Workstation’ Backbone ‘Client’ ‘Terminal’ ‘Node’ Computer Terminator Server (optional) Networks TOPOLOGIES – Bus Network Network interface card (NIC) Terminator Workstation Backbone Client Terminator Server (optional) Terminator T connector – plugs into NIC Networks TOPOLOGIES – Bus Network Bus network operation: •All components are connected via a backbone. •At each end of the backbone is a terminator which stops signals ‘bouncing back’ down the network. •Each network interface card is passive: they all listen to the backbone for signals addressed for them. •Signals are sent in both directions of the backbone at the same time. •Only one computer can transmit successfully at any one time, however this is not regulated so collisions and data corruption do occur. •A protocol called CSMA-CD (carrier sense multiple access collision detection) is used to handle this problem. Networks TOPOLOGIES – Bus Network Networks CSMA/CD Summary 1 - A collision is detected. 2 - Devices involved in the collision keep transmitting for a short period of time, to make sure all devices on the network see the collision (also referred to as the jamming signal) 3 - Each device sees the jamming signal, and invokes the back-off algorithm. Each device will have a random timer that determines when it can transmit again. 4 - When the back-off timer expires, devices are free to transmit data again. Devices involved in the collision earlier do not have priority to transmit data. Networks Client Server Networks • In a client server networks, one or more computers known as Clients are connected to a powerful central computer known as the server. • How much the client holds with regards to data and software depends on whether they are fat or thin clients. Fat – most of the software, thin – server contains all the software. • Several type of servers might be connected to a network, File Web Mail Printer Networks Client Server Networks - Advantages • Security is better, since all files are stored in a a central location and access rights are managed by the server • Backups are done centrally so there is no need for individual users to back up their data. If there is a breakdown and some data is lost, recovery procedures will enable it to be restored. • Data and other resources can be shared. Networks Client Server Networks - Disadvantages • It is expensive to install and manage • Professional IT Staff are needed to maintain the servers and run the network. Networks Peer to peer networks • No central server. • Individual computers are connected together either locally or over a WAN. • Cheap to set up (especially a home one) • Enables resources to be shared • Not difficult to maintain. • Used in video on demand. Hundreds of computers are used to hold parts of the video to share the load. Networks Peer to peer networks - Disadvantages • Used for piracy for downloading films and other copyrighted material. Networks Wireless Networks • • • • Does not use cables Data sent using radio waves Can be used over LANs and WANs (WLANS and WWANs) Every device attached to a WiFi (WLAN) has a unique MAC Address (Media Access Control) This is coded onto the network interface card (NIC) of the device and is used in the addressing of packets and routing data) WiFi • • • • • A standard for connecting computers together wirelessly. IEEE 802.11 Different devices in a WLAN have different ranges – 802.11n and 802.11g WiFi hotspots are used by ISP providers (e.g. BT) WWANs make use of mobile phone networks and satellites (3G,4G,5G) Networks WiFi • Each Wireless Network Access Point (WAP) has a Service Set Identification (SSID) name – which is an informal name for the network. Networks WiFi • Most networks will be protected by a password (WiFi Protected Access (WPA)) or WPA2 • WPA2 is a 128-bit key encryption for data transmission. • Having the password allows you to send data from or to that WAP. Networks WiFi • To ensure the reliability of WiFi transmission certain protocols are in effect for instance the CSMA/CA to avoid data collisions. Start End Assemble a frame Transmit Data Channel idle? Yes Transmit RTS (Request to Send) No WAIT No Yes CTS (Clear to Send) received? Communication Basics Study tasks 1) “No more wires”. How likely is it that wireless networks will completely replace networks with cables. Build up a case that this my be true. Include the following in your presentation – a) The history of the growth of the use of WiFi b) c) d) e) WiFi Technologies – new and current, Advantages and disadvantages of Wireless Networking. The growing trend of the use of WiFi in society. The growing trend of the use of WiFi in businesses