Some Networked Devices Improve The Channel By Compressing The Data They Send. Most Modems Use This Feature. 

Network Throughput, If The Size Of A File, For Example, 64 KB Can Reduce By Compression, The Time Required For Transfer Is Reduced.

This can hide from the user, so a compressed file can be transferred significantly faster than expected. Because this ‘hidden’ compression cannot be easily disabled, a file that cannot compress must be used to measure throughput by transferring files and scheduling transfer time.

Pre-compressed files, such as zip files, are often used for this purpose.

Assuming that it is not possible to compress the data, to transfer a 64 KB file over a 64 kbps transfer channel, the theoretical time it takes is 8.192 seconds, which is the minimum transfer time and, in practice, takes longer. . This is due to the overhead effect that is used to format the data in the agreed state.

Therefore, both sides of the relationship have a consistent view of the data.

There are at least two issues with compressing files that are not immediately apparent.

1. The throughput of the network that performs the compression does not improve with compression. From a bottom-up perspective (server to client), compression improves throughput. This is because the content of the information increases with compression for the same amount of information that is transmitted.

2. Compressing files in client and server systems requires more processor resources in both systems. The server uses its own processor to compress the files, which is not currently the case. The client also decompresses the files after receiving them. This can be considered one of the necessary costs (for server and client systems) to increase end-to-end throughput (although throughput for the same network does not change).

What is operational capacity?

The throughput of a network can be measured using different tools available on different operating systems. This page explains how these instruments are set up for measurement and the issues associated with these measurements.

Measuring network throughput is that people often want to know the maximum throughput of data in a communication link or network access in bits per second.

A common way to measure this quantity is to transfer a large file from one system to another and calculate the time required to complete the transfer or copy the file.

Operating power is then obtained by dividing the file size into megabits per second, kilobits per second, or bits per second.

Unfortunately, the results of such an experiment are in the range of good throughput, which is usually less than the maximum throughput given in theory, leading people to think that their communication link is not working properly.

 In fact, in addition to transmission overheads, including downtime, TCP receiving window size, and system constraints, there are many overheads in goodput, which means that the calculated goodput does not represent the maximum available throughput.

Typically, people use abbreviations that are often used interchangeably. For file sizes, they usually use ’64k ‘instead of ’64kilobytes’ or ‘100meg’ instead of ‘100megabytes’.

 When it comes to the bit rate, use the terms throughput, bandwidth, and speed to indicate the speed of the circuit as ’64k’ or ‘2meg’, meaning a circuit at 64 kbps or 2 megabits per second. they give. However, a 64k circuit cannot transfer a 64k file in one second.

 This may not be obvious to people unfamiliar with telecommunications and computing, as they sometimes make mistakes.

Overheads and data formats

The communication link used by most people is the serial link, which is also called the ‘asynchronous start-stop or ‘asynchronous’ link. If you use a modem externally connected to your home or office computer, your communication link may establish through an asynchronous serial connection.

The advantage of this link is that it is simple and can be implemented using only three wires: send, receive and ground signal (or common signal).

 In the RS-232 protocol, bit ‘0’ has a negative voltage relative to ground voltage, and bit ‘1’ has a positive voltage relative to ground voltage. An inactive RS232 signal has a negative voltage.

So any of the above descriptions about bits ‘0’ and ‘1’ are upside down here.

The starting bit of each byte has an upward voltage and indicates that the next bit is the first bit of serial data.

Asynchronous serial data at the TTL level is equal to ‘0’ at high voltage and ‘1’. A TTL / RS232 converter handles TTL level data, usually a maxim chip, such as the MAX232, which also inverts and changes the data level.

All signals inside a device are equipped with an RS232 connection and usually have an internal TTL level (0 and 5 volts or 0 and 3.3 volts or 0 and 3 volts), and converting to either RS232 is the last step in output data or first, which input data does.

In fact, more items such as one-bit transfer rate, number of bits per character, parity bit, and number of stop bits (meaning the end of a character) are agreed upon to advance the transfer.

For example, the agreed feature 9600-8-E-2 means that the channel has a transfer rate of 9600 bits per second, with 8 bits per character, even balance bits, and two stop bits.

These specifications in serial connections are usually set to 9600-8-N-1 (9600 bits per second, 8 bits per character, no balance bit, and 1 stop bit).

A total of 10 bits are transmitted to send each 8-bit character. (One start bit, 8 data bits, and one-stop bit). This means 25% overhead.

Therefore, an asynchronous serial link at 9600 bits per second (1200 bytes per second) does not transmit data at the same speed.

This situation can get worse. If a balanced bit and two stop bits are used, the overhead of each 8-bit character will be 4 bits (one start bit, balance bit, and 2 stop bits), which is equivalent to a 50% overhead.

In this case, a channel with a speed of 9600 bits per second can actually transmit 12,600 bytes per second (equivalent to 800 bytes per second).

Transfer speeds in asynchronous serial relationships are typically supported up to 230.4 kbps.

In this case, if the balance bit is not specified in the channel settings and a stop bit is used, the transfer rate will be 23.04 KB per second.

The advantage of the asynchronous serial connection is its simplicity. One of its disadvantages is its low efficiency in transportation. We can overcome this by using a simultaneous interface.

A clock signal is added via a separate wire in this type of interface, and the bits are transmitted according to the clock.

The interface no longer pays attention to each character’s start and stop bits; however, a mechanism is needed to ensure that the sending and receiving clocks are synchronous.

For this purpose, the data, with the help of known separators, into frames of different characters.