Welcome to our section on communication basics. There are many terms it pays to be familiar with when it comes to communication and data transfer over a network. Some of these can be seen below:
Bit rate measured as bits per second, kilobits per second or megabits per second is the speed at which data is being physically transferred one bit at a time over a digital network.
Baud rate, named after Emile Baudot, is used to express the number of changes per second to the signal. The change could be in voltage, frequency, or phase. NRZ (No return to zero) binary-only contains two symbols which are used to represent either a 1 or a 0. So the baud rate should match the bit rate. However, in other cases, symbols can represent multiple bits in which case the baud rate would not match the bit rate.
Baseband is the original frequency range of a signal before it has been converted for transmission. Most protocols can’t transmit information in its original baseband and so the signal has to be converted to a higher range that it can be transmitted in. Once it has been transmitted in this higher range the signal is then converted back to its original baseband. One of the few data transmission protocols that can actually transmit data in its original baseband is Ethernet. Baseband transmissions are usually sent via a single wire and while data can travel in both directions along that single wire it can’t do both at the same time. This means that data can be sent or received but not both simultaneously.
Broadband allows for much higher data transmission speeds as each cable is able to carry huge amounts of data and it is possible to have two cables for simultaneous sending and receiving of data. Thanks to this broadband is now started replacing baseband in networks.
Bandwidth and Throughput
In networking, bandwidth is the absolute maximum number of bits than can be transferred per second (bps) through a connection at any given time. We often see bandwidth capabilities advertised when looking for a new ISP for our homes or businesses. If an ISP offered you a connection of 1Mbps they would actually be offering you a connection that had the potential for 1048576 bits to be transferred every second.
However, bandwidth is only the maximum potential transfer rate of the connection and not necessarily the rate at which data will transfer along this connection every single time. There are many other factors that affect the rate data can be transferred and the actual speed it is being transferred is known as throughput.
Some of the things that can effect bandwidth and thus reduce the actual throughput are:
- Network congestion
- The number of users accessing a server simultaneously
- Network protocols being used
Asynchronous Data Transmission and Parity Bits
Asynchronous data transmission is a method of communication for transferring data either along a network or between internal computer components. Asynchronous communication is when data is transmitted without having to abide by the constraints of a clock or specific timings as opposed to synchronous communication where the transmission is controlled by a clock or timing.
As there are no timings or clock control with asynchronous data transmission, each device communicating via this method is free to do so at its own pace. Each device communicating asynchronously must wait for a signal from the device telling them it intends to communicate. Alternatively, instead of waiting for a signal from others, devices that communicate this way can also generate their own signal if it is they themselves that wish to communicate with other devices. The signal that indicates an upcoming asynchronous communication is referred to as a handshake.
The RS-232 protocol is widely acknowledged as one of the most successful protocols for this form of communication. In fact, it proved so successful at managing communication to external devices like modems that it has since been adapted and molded for use in ways that were not originally intended.
This RS-232 protocol is so successful largely thanks to its flexibility, made possible by the utilization of start and stop bits in the blocks of data being communicated. The start and stop bits in each block being communicated mean that if for some reason there is an interruption, communication can resume with the next block that comes along.
Parity bits are optional extra bits that can be used with the RS-232 protocol. In asynchronous transmission, the parity bits are intended for error checking, using odd or even parity to find any errors that sometimes occur with data transmission. With parity bits, an added single bit of either a 0 or a 1 indicates whether the information being transmitted contains an odd or even number of 0 and 1 bits.