Characteristics of transmission

Cards (9)

  • The number of bits that are transmitted over a channel each second (bits per second, or bps) is called the bit rate (also known as data rate). The higher the bit rate, the faster the data arrives. In the early days of the internet, bit rates were in the thousands (kilo-) of bits per second (kbps). Now, common bit rates are in the millions (mega-) or billions (giga-) of bits per second (Mbps or Gbps).
  • The baud rate is the number of times that the signal changes per second. A symbol corresponds to a set of bits that are transmitted with every signal change. Therefore, baud rate represents the symbol rate of a channel, i.e. how many symbols are transmitted per second.
  • Baseband transmission

    Supports two different signal levels (a high and a low frequency or voltage level), which means that every signal change represents one bit: either a 1 or a 0
  • Broadband transmission

    Supports more than two different signal levels (there are multiple frequency bands or voltage levels), so every signal change can represent more than one bit
  • Bit rate calculation
    Bit rate = baud rate × number of bits per signal change (symbol)
  • Every second, the number of bits that are transmitted is equal to the number of times that the signal changes per second multiplied by the number of bits encoded per signal change
  • Bandwidth is the maximum rate of data transfer of a communication channel. The relationship between bandwidth and bit rate is directly proportional: the greater the amount of data that can be transmitted over a channel, the more bits can be transmitted per second. 
  • The delay from the time that a signal is sent, to the time that it is received, is called the latency, and it is usually a few milliseconds.
  • A protocol is a set of rules that determine the communication between devices. Protocols are useful for connecting devices from different manufacturers into the same network, and for setting the standards of the communication. They specify all the details of the communication, including:
    • The type of transmission (synchronous or asynchronous)
    • The types of interfaces (serial or parallel)
    • The transmission channel (wired or wireless)
    • The speed of transmission (bit rate or baud rate)
    • The error checking techniques
    • The format of the transmitted data