Communication study guide

Build the distinctions

Start by identifying what is being compared. Serial and parallel describe how many bits are transmitted at once: serial sends bits sequentially, while parallel sends multiple bits simultaneously. Synchronous and asynchronous describe how the timing and boundaries of transmission are managed. These are different distinctions, so a response should not treat serial as automatically meaning asynchronous or parallel as automatically meaning synchronous.

For a comparison question, explain both the mechanism and its consequence. Serial transmission uses fewer communication paths than parallel transmission. This can make the connection less complex and avoids the receiver having to interpret several separately transmitted bits that may not remain aligned. Parallel transmission can transmit multiple bits at the same time, but the separate bits may not arrive together. A strong answer therefore gives a reasoned advantage rather than merely stating that serial is 'better'.

Explain timing accurately

Synchronous transmission uses shared timing so that the receiver can interpret a continuing stream of data at the expected times. Asynchronous transmission sends separate units with start and stop information. The start bit tells the receiver that the unit is beginning; the stop bit or bits tell it that the unit has ended. In an exam answer, link each bit to its function rather than simply listing the terms. A useful structure is: definition, mechanism, then consequence.

Work with rates

When given a signal-change rate, first decide whether the question is asking for baud rate or bit rate. Baud rate counts signal changes per second. Bit rate counts bits per second. If one signal change encodes one bit, the two rates are equal. If one signal change encodes several bits, calculate:

bit rate = baud rate × bits encoded by each signal change

For example, a baud rate of 1500 with two bits represented by each signal change gives a bit rate of 3000 bits per second. This reasoning directly demonstrates why bit rate can be higher than baud rate.

Link bit rate and bandwidth

Bandwidth describes the capacity of the channel, while bit rate describes how many bits are transmitted per second. The specification requires the relationship that bit rate is directly proportional to bandwidth. Therefore, if bandwidth increases, the possible bit rate increases in direct proportion; if bandwidth decreases, the possible bit rate decreases in direct proportion. Do not replace this relationship with latency: a channel can be discussed in terms of its capacity and also in terms of communication delay, but these are different properties.

Exam application and self-check

For a definition question, give the precise term first and then its meaning. For a comparison question, define both methods and state a consequence of the difference. For a calculation, label the given baud rate, identify the number of bits per signal change, apply the multiplication, and include bits per second in the answer. Before finishing, check that you can explain protocol as a set of communication rules, distinguish latency from bandwidth, describe both start and stop bits, and state when bit rate is greater than baud rate.