Link width

As you know, the final speed of the Internet depends on the bandwidth. Also on the speed of information transfer is affected:

What parameters affect application performance? Part 2. Bandwidth and link utilization

Very often when communicating with IT specialists, the network department or narrow links are blamed for slow performance of corporate applications. The simplest solution to all the problems is more bandwidth (wider channel) and fewer left-handed applications in the channel (less competitors for bandwidth) and then everything will fly. Of course you have to pay attention to pure channels and their usage, but that's not the only parameters. The easiest solution to evaluate channel health is Flow technologies and data correlation between key application performance and data from NetFlow (jFlow, Sflow, etc.).

In data networks, latency is a fact of life. By understanding their nature, you can reduce the negative effect, thereby improving the quality of communication. Network delays are defined by ITU standards and must be within certain limits:

Acceptable for most user applications.

Acceptable as long as administrators are aware of transmission time and its effect on transmission quality in user applications.

Not acceptable for general network planning purposes. However, it is recognized that this limit may be exceeded in some exceptional cases.

The sequential principle of transmitting packets over a communication link introduces latency. The delay in transmitting information from one user to another consists of several components and can be divided into two large classes – fixed and variable.

Variable delays are mainly queue delays at each of the network nodes: router, switch, network adapter. Fixed delays include packet delay, sequential delay, codec delay (for video or audio). The transmission medium can be copper pair, fiber optic cable or ether. The amount of delay depends on the clock frequency and, to a much lesser extent, on the speed of light in the transmission medium.

How to increase the speed of applications without changing the bandwidth of the communication channel?

Naturally, the easiest way out is to increase the bandwidth, but sometimes this is not possible or is very expensive for corporate clients. In this case, it is logical to reduce the amount of data transmitted on the communication channel. Reduce the volume can be done in several ways. Data compression, use of thin clients, caching, use of traffic optimization solutions – this sometimes allows to achieve traffic reduction from 2 to 5 times (different applications are compressed differently).

You can also understand the structure of traffic and how the channel is really used by using Flow technologies and further by prioritizing traffic to reduce possible packet losses and growth of queues in the active equipment.

What is the channel width in the Wi-Fi router settings

The channel width in the router settings is its bandwidth, it may differ on different models. Standard for household networks and, in particular, a modem, supports 20 or 40 MHz. Wireless Wi-Fi uses a frequency range of 2.4 GHz and 5 GHz.

In turn, channels or so-called frequency lines are identified in the range. Their presence makes it possible to place different electrical devices within one band, each of which will be able to work effectively and not affect the others. So, within 2.4 GHz there are 13 such channels allocated, but only three of them do not overlap; in 5 GHz their number is higher and the total width is an order of magnitude greater.

Visually, the channel width can be represented as arcs with lower and upper boundaries of 22 MHz thickness, some of them may have common points of intersection. In a practical sense this means that the wireless networks of other tenants in the house affect each other and can cause disruptions in Internet access.

That is why it is so important to choose a quality provider from the beginning and to be able to change the bandwidth. Then there will be no question, 20 or 40 MHz Wi-Fi, which is better.

Interesting! In upgraded modems that support 5 GHz, you can set not only the width of 20 and 40, but also 80 MHz.

What frequency to set the "bandwidth" to

At first glance, a Wi-Fi bandwidth of 40 MHz is preferable to 20 MHz, since the channel width determines the speed of the Internet connection. But not everything is unambiguous about their performance.

• With a 20 MHz bandwidth, there are three channels that do not overlap. Thanks to their free arrangement independently of each other, no interference enters the common band. In this case, you can easily connect up to three different devices without worrying that they will interact negatively.
• The 40 MHz band allows only one non-overlapping channel to be placed. Therefore, when you connect multiple devices to Wi-Fi, each will create an obstacle and limit the overall access speed. Wireless devices are particularly susceptible to interference.
• If obsolete hardware is used, pure modes (40 MHz and above) are not suitable for continuous operation by technical standards, as they can provoke incompatibility.

Throughput Measurement

Measuring throughput is a rather important operation. It is carried out in order to find out the exact speed of the Internet connection. The measurement can be done using the following steps:

• The easiest one is to download a voluminous file and send it to the other end. The disadvantage is that it is impossible to determine the accuracy of the measurement.
• In addition, you can use the resource speedtest.net. The service allows you to measure the width of the Internet channel "leading" to the server. However, this method is also not suitable for holistic measurement, the service gives data on the entire line to the server, not a specific communication channel. In addition, the object to be measured has no access to the global Internet.
• The optimal solution for measurement is the client-server utility Iperf. It allows you to measure the time, the amount of data transmitted. After the completion of the operation, the program provides the user with a report.

Thanks to the above methods, it is possible to measure the real speed of the Internet connection without much trouble. If the readings do not meet your current needs, you may need to think about changing your provider.

Throughput Calculation

In order to find and calculate the bandwidth of a communication line, you need to use the Shannon-Hartley theorem. It states: you can find the bandwidth of a communication link (line) by calculating the reciprocal relationship between the potential bandwidth as well as the bandwidth of the communication link. The formula for calculating bandwidth is as follows:

In this formula, each element has its own value:

The Shannon-Hartley theorem suggests that it is best to use a wide data cable to reduce external noise or to increase signal strength.

Bitrate

The bandwidth of a real channel is calculated according to theory. A noise model, such as additive Gaussian, is constructed and an expression of the Shannon-Hartley theorem is derived:

B is the bandwidth (Hz); S/N is the signal-to-noise ratio. The logarithm on base 2 allows you to calculate the bitrate (bps). The values of signal, noise are written in squares of volts, or watts. Substituting decibels gives wrong results. The formula for peer-to-peer wireless networks is slightly different. They take the spectral noise density multiplied by the bandwidth. Separate expressions of channels with fast and slow fades are derived.

Multimedia files.

For entertainment applications, the bitrate indicates the amount of information stored, played back every second:

The golden mean is chosen to help minimize the bitrate, providing acceptable quality. Sometimes compression irreversibly distorts the source material with compression noise. The bit rate often shows the number of bits in a unit of playback time for audio, video (displayed by the player). Sometimes the value is calculated by dividing the file size by the total duration. Since the dimension is given bytes, a multiplier of 8 is introduced. Often the multimedia bitrate jumps. The entropy rate is the minimum rate that ensures complete preservation of the original material.

CDs

The audio CD standard prescribes a 44.1 kHz sampling rate (16-bit depth) stream. Typical stereo format music is composed of two channels (left speaker, right speaker). The bitrate is doubled to mono. The bandwidth of the pulse-code modulation channel is defined by an expression:

The audio CD standard gives a final figure of 1.4112 Mbps. A simple calculation shows: 80 minutes of recording takes up 847 MB, not including headers. The large file size determines the need to compress the content. Here are the figures for MP3 format:

Examples of channel bandwidth

Consider the evolution of digital transmission technologies.

Modems

1. Acoustic pair (1972) – 300 baud.
2. Vadik & Bell 212A modem (1977) – 1200 baud.
3. ISDN channel (1986) – 2 channels of 64 kbit/s (final speed – 144 kbit/s).
4. 32bis (1990) – up to 19.2 kbit/s.
5. 34 (1994) – 28.8 Kbps.
6. 90 (1995) – 56 kbit/s downstream, 33.6 kbit/s upstream.
7. 92 (1999) – 56/48 kbit/s downstream/upstream.
8. ADSL (1998) – up to 10 Mbps.
9. ADSL2 (2003) – up to 12 Mbit/s.
10. ADSL2+ (2005) – up to 26 Mbit/s.
11. VDSL2 (2005) – 200 Mbit/s.
12. fast (2014) – 1 Gbit/s.

Ethernet Local Area Network.

1. Experimental version (1975) – 2.94 Mbps.
2. 10BASES (1981, coaxial cable) – 10 Mbps.
3. 10BASE-T (1990, twisted pair) – 10 Mbps.
4. Fast Ethernet (1995) – 100 Mbit/s.
5. Gigabit Ethernet (1999) – 1 Gbit/s.
6. 10 Gigabit Ethernet (2003) – 10 Gbit/s.
7. 100 Gigabit Ethernet (2010) – 100 Gbps.

Wi-Fi

1. IEEE 802.11 (1997) – 2 Mbps.
2. IEEE 802.11b (1999) – 11 Mbps.
3. IEEE 802.11a (1999) – 54 Mbps.
4. IEEE 802.11g (2003) – 54 Mbps.
5. IEEE 802.11n (2007) – 600 Mbps.
6. IEEE 802.11ac (2012) – 1000 Mbps.

Cellular communications.

1. First generation:
   1. NMT (1981) – 1.2 kbps.
   1. GSM CSD, D-AMPS (1991) – 14.4 kbps.
   2. EDGE (2003) – 296/118.4 kbit/s.
   1. UMTS-FDD (2001) – 384 kbit/s.
   2. UMTS HSDPA (2007) – 14,4 Mbps.
   3. UMTS HSPA (2008) – 14.4/5.76 Mbps.
   4. HSPA+ (2009) – 28/22 Mbps.
   5. CDMA2000 EV-DO Rev. B (2010) – 14.7 Mbps.
   6. HSPA+ MIMO (2011) – 42 Mbit/s.

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