9 IGCSE Computer Science Data Transmission PDF

Grade: 9 IGCSE Subject: Computer Science Topic – Data Transmission (2.1) Data Transmission Types and Methods  What is Network? A network consists of two or more computers that are linked in order to share resources exchange files,or allow electronic communications....

Grade: 9 IGCSE Subject: Computer Science Topic – Data Transmission (2.1) Data Transmission Types and Methods  What is Network? A network consists of two or more computers that are linked in order to share resources exchange files,or allow electronic communications. The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams.  Types of Network Local Area Network (LAN) Wide Area Network (WAN)  Connection  This might be practical for a small local area network with only a few nodes.  But it wouldn't work for a large network such as a WAN where millions of computers want to communicate randomly with each other. Circuit Switching  Circuit Switching Connection establishement - Dedicated path is created Data transfer Disconnect  Packet Format Data is broken up into DATA PACKETS Header Payload Trailer IP IP Address Squence Size The Method of Error Address of number of the actual identifying checking of Destination of packet packet data the end of the Source packet Packet Switching  Packet Switching each packet follow its own path routers will determine the route of each packet routing selection depends on the number of packets waiting to be processed at each node the shortest path available is selected- but not always packets can reach the destination in a different order Benefits: there is no need to tie up a single communication line it is possible to overcome failed, busy or faulty lines by simply re-routing packets easy to expand the package usage high data transmission Drawbacks: packets can be lost and need to be re-sent more prone to errors with real-time streaming delay at the destination to re-order packets.  Factors to be considered  Direction of transmission (i.e. one direction or both) – Simplex, Half Duplex or Full Duplex  Method of transmission (how many bits are sent at the same time) – Serial or Parallel  Synchronisation method between the two devices – Asynchronous and Synchronous  sending data from the keyboard to the CPU e lki s a ie W lk Ta Internet cables  Simplex: data transmission in one direction only. Two directional transmission is not possible. Half Duplex: data transmission in both directions is possible, but not at the same time. Full Duplex: data transmission is possible in both directions at the same time (simultaneously).  Sample Question State a use for the following data transmission methods. The use must be different for each data transmission methods : Simplex & duplex Sample answer: Simplex Duplex Microphone to computer Telephone call Voice over IP Sensor to computer, Computer to printer (only award once) Computer to printer Instant messaging Computer to speaker Broadband connections Computer to monitor Video conferencing Webcam to computer Sending data to and from devices e.g wireless technology Computer to modem  Serial Transmission  In serial data transmission, bits are sent sequentially (one after the other) down the same wire (channel).  Using a single wire reduces costs but slows down the speed of transmission.  Sending data sequentially is perfect for transmitting over longer distances as there are no synchronisation issues.  Parallel Transmission In parallel data transmission, multiple bits are sent simultaneously down different wires (channels) within the same cable. Data is synchronised by a clock, however this becomes problematic over longer distances where synchronisation errors may start to occur. Using parallel wires is more expensive but transmission is faster.  Parallel Transmission Parallel transmission is used when:  a large amount of data is being sent;  the data being sent is time-sensitive;  and the data needs to be sent quickly.  Fast transmission within a computer system  Short distances  Integrated Circuits (IC), Busses  UNIVERSAL SERIAL BUS The UNIVERSAL SERIAL BUS (USB) is an serial data transmission method, allows both half-duplex and full-duplex transmission. a four-wire shielded cable two of the wires are used for power and the earth two of the wires are used in the data transmission. When a device is plugged into a computer using one of the USB ports: the computer automatically detects that a device is present (this is due to a small change in the voltage level on the data signal wires in the cable) the device is automatically recognised, and the appropriate DEVICE DRIVER is loaded up so that computer and device can communicate effectively. if a new device is detected, the computer will look for the device driver which matches the device; if this is not available, the user is prompted to download the appropriate software.  USB - Benefits and drawbacks Devices plugged into the computer are standard USB supports a mximum cable length automatically detected; device drivers are of 5M. USB hubs are needed to extend the cable automatically uploaded length. The connectors can only fit one way; this prevents incorrect connections being made This has become the industry standard; this even though USB is backward compatible, very means that considerable support is available to early USB standards may not always be users supported by the latest computers. Several different data transmission rates are supported No need for external power source since cable even the latest version 3 and version 4 USB -C supplies +5V systems have a data transfer rate which is slow comapred to, for example, Ethernet connections. USB protocol notifies the transmitter to re- transmit data if any errors are detected. it is relatively easy to add more USB ports by using USB hubs. Newer USB standards are backward compatible with older USB standards