Bit rate

In computing and telecommunications, the term bit rate (in English: bitrate, pronounced [bit rejt]) defines the number of bits that are transmitted per unit of time through a digital transmission system or between two digital devices. So, it is the data transfer rate.

Factors

The following are some of the factors that determine the transfer rate:

• diet-working;
• network topology;
• number of users on the network;
• the user's computer;
• the server;
• conditions of energy;
• congestion.

Choice

Theoretical network bandwidth is an important consideration in network design, because the network throughput is never greater than that bandwidth, due to limitations placed by the medium and technologies of chosen network.

Theoretical network bandwidth is an important consideration in network design, because the network throughput is never greater than that bandwidth, due to limitations placed by the medium and technologies of chosen network.

The unit with which the International System of Units expresses the bit rate is the bit per second (bit/s, b/s, bps). The b should always be written in lowercase, to avoid confusion with byte per second (B/s). To convert from bytes/s to bits/s, simply multiply by "8", otherwise divide by "8".

The fact that the unit used is the bit/s does not imply that multiples of it cannot be used:

• kbit/s o kbps (kb/s, kilobit/s or thousand bits per second)
• Mbit/s or Mbps(Mb/s, Megabit/s or one million bits per second)
• Gbit/s or Gbps (Gb/s, Gigabit, billion bits)
• byte/s (B/s or 8 bits per second)
• kilobyte/s (kB/s, thousand bytes or eight thousand bits per second)
• megabyte/s (MB/s, one million bytes or 8 million bit per second)
• gigabyte/s (GB/s, billion bytes or 8 billion bits)

Clarification: The system on which it is built is binary (not decimal), so everything is based on powers of 2. Therefore, although to simplify we express that 1,000,000 bit = 1,000 kbit = 1 Mbit, strictly speaking the relationship is: 1,048,576 bit = 1024 kbit = 1 Mbits. Where 1024 is 2 raised to the 10th power and 1,048,576 is 2 raised to the 20th power.

Examples

• Typical Internet connection access speeds:
  • RTB modem: 128 kbit/s = 16 kB/s (16 kilobytes per second)
  • ADSL: 64 Mbit/s = 8 MB/s (8 megabytes per second)
  • Cable: 30 Mbit/s = 3.75 MB/s (3.75 megabytes per second)
  • VSAT: 6 Mbit/s = 750 kB/s (750 kilobytes per second)
  • 3G mobile phone: 3 Mbit/s = 375 kB/s (375 kilobytes per second)

• Compression bit rates to MP3:
  • 4 kbit/s — minimum to recognize speech
  • 8 kbit/s — Conventional telephone quality
  • 32 kbit/s — AM radio
  • 96 kbit/s — FM radio
  • 128 kbit/s — semi-CD sound, very common in MP3
  • 192 kbit/s — CD quality sound in MP3 format
  • 320 kbit/s — highest quality for MP3 format

Internet bit rate

Internet connection speeds are gross. In practice, the net speed available to the user is usually between 10% and 15% lower, due to the bandwidth consumed by the headers and tails of the protocols. Consumers are generally the losers when paying for one Internet speed and receiving a lower one, a minimum percentage of admissible loss should be established as quality control.

Bit per second vs. Baud

A common mistake is to use baud as a synonym for bit per second. Baud rate, or baud rate, should not be confused with bit rate. The baud rate of a signal represents the number of state changes, or signaling events, that the signal has in one second. Each transmitted signaling event may carry one or more bits. Only when each signaling event carries a single bit do the data rate in baud and in bits per second match.

Bitrate Types

The data transfer rate can be constant or variable.

Constant

CBR applies a uniform quantization, so it does not take into account if there are areas with more or less information density in the signal, and quantizes the entire signal equally.

Variable

VBR applies a non-uniform quantization that does differentiate between areas with higher or lower information density, and the quantization is more efficient.