Transmission Modes, Ch. 9
Mississippi College
Computer Science
Dr. Bennet
  1. Number of Lines.

    1. Parallel transmission: Multiple, independent connections.
      1. Multiple connections in use simultaneously.
      2. Several bits sent simultaneously, one per line.
      3. Usually a few extra lines for timing control.
      4. High throughput.
      5. Frequently used inside computers; matches the hardware.
    2. Serial transmission: Bits sent on one line, one after another.
      1. Specialized hardware.
        1. Converts between a parallel hardware signal and serial line.
        2. Sender receives bits in parallel on one side, doles them out serially on the other. Receiver the reverse.
        3. UART or USART, depending on the timing of the serial connection.
      2. Transmission order. A collection of bits sent serially must be sent in some order.
        1. Endpoints must agree on order.
        2. Usually sent in ascending or descending place value.
        3. Least-significant first: little-endian.
        4. Most-significant first: big-endian.
        5. Order of bytes within words may be specified differently than bits within bytes.
        6. Ethernet sends bytes big-endian, and bits little-endian.
          1. 32-bit number:
            b31b30b29b28b27b26b25b24 b23b22b21b20b19b18b17b16 b15b14b13b12b11b10b9b8 b7b6b5b4b3b2b1b0
          2. Bytes little-endian; bits in bytes, big-endian:
            b7b6b5b4b3b2b1b0 b15b14b13b12b11b10b9b8 b23b22b21b20b19b18b17b16 b31b30b29b28b27b26b25b24
          3. Bytes big-endian; bits in bytes, little-endian (Ethernet):
            b24b25b26b27b28b29b30b31 b16b17b18b19b20b21b22b23 b8b9b10b11b12b13b14b15 b0b1b2b3b4b5b6b7
          4. Both little:
            b0b1b2b3b4b5b6b7 b8b9b10b11b12b13b14b15 b16b17b18b19b20b21b22b23 b24b25b26b27b28b29b30b31
      3. Timing
        1. Asynchronous.
          1. The medium may be idle for an arbitrary time between transmissions.
          2. Each transmission must be synchronized.
          3. RS-232 is a common serial standard.
          4. Extra bits warn the receiver to start recording bits, and mark the end of the byte.
        2. Synchronous.
          1. The medium is always transmitting, and stays synchronized.
          2. Transmission divided into blocks, called frames.
            1. Marked by some starting and ending pattern.
            2. Marks usually designed to have a level change which can be used to keep the receiver's clock in sync.
          3. There is an idle frame which, indicates the contents is to be discarded. Used when sender has nothing to say.
        3. Isochronous.
          1. Type of synchronous transport designed to accept and deliver data at a fixed rate.
          2. Avoids any jitter in a multimedia recording.
          3. Traditional in phone networks.
  2. Plex
    1. Simplex. Transmission in one direction (broadcast TV).
    2. Duplex. Simultaneous transmission in both directions (telephone).
    3. Half-Duplex. Transmission in both directions, but only one at a time. (Walkie-talkie).
  3. DCE and DTE
    1. Old phone company terms.
      1. DCE Data Communications Equipment.
      2. DTE Data Terminal equipment.
    2. The DCE is the start of the phone company network.
    3. The DTE is the last part of the subscriber network.
    4. They are connected, carrying data from one to the other. Interface between the subscriber and phone company.
    5. The importance notion is that a standard interface can be defined between two different networking technologies.