Editing Bit rate (section)

=== Information rate ===
{{See also|Code rate}}

The [[physical layer]] '''net bitrate''',<ref name="Rappaport">Theodory S. Rappaport, [https://books.google.com/books?id=TbgQAQAAMAAJ&q=%22net+bit+rate%22+ Wireless communications: principles and practice], Prentice Hall PTR, 2002</ref> '''information rate''',<ref name="Guimarães"/>  '''useful bit rate''',<ref>Lajos Hanzo, Peter J. Cherriman, Jürgen Streit, [https://books.google.com/books?id=UPi04XAlfWQC&dq=%22useful+bitrate%22&pg=PA510 Video compression and communications: from basics to H.261, H.263, H.264, MPEG4 for DVB and HSDPA-style adaptive turbo-transceivers], Wiley-IEEE, 2007.</ref> '''payload rate''',<ref name="Bagad">V.S. Bagad, I.A. Dhotre, [https://books.google.com/books?id=srkNoDo3mbwC&dq=%22payload+rate+is%22&pg=SA6-PA26 ''Data Communication Systems''], Technical Publications, 2009.</ref>  '''net data transfer rate''',<ref name="3G"/> '''coded transmission rate''',<ref name="Pahlavan"/> '''effective data rate'''<ref name="Pahlavan"/> or [[wire speed]] (informal language) of a digital [[communication channel]] is the capacity excluding the [[physical layer]] protocol overhead, for example [[time division multiplex]] (TDM) [[framing bits]], redundant [[forward error correction]] (FEC) codes, equalizer training symbols and other [[channel coding]]. Error-correcting codes are common especially in wireless communication systems, broadband modem standards and modern copper-based high-speed LANs. The physical layer net bitrate is the datarate measured at a reference point in the interface between the [[data link layer]] and physical layer, and may consequently include data link and higher layer overhead.

In modems and wireless systems, [[link adaptation]] (automatic adaptation of the data rate and the modulation and/or error coding scheme to the signal quality) is often applied. In that context, the term '''peak bitrate''' denotes the net bitrate of the fastest and least robust transmission mode, used for example when the distance is very short between sender and transmitter.<ref>Sudhir Dixit, Ramjee Prasad [https://books.google.com/books?id=L2tA56H9rC0C&q=peak+bit+rate+is&pg=PA145 ''Wireless IP and Building the Mobile Internet''], Artech House</ref> Some operating systems and network equipment may detect the "'''connection speed'''"<ref>Guy Hart-Davis,[https://books.google.com/books?id=oLU1XDaiZv8C&q=connection+speed&pg=PA704 Mastering Microsoft Windows Vista home: premium and basic], John Wiley and Sons, 2007</ref> (informal language) of a network access technology or communication device, implying the current net bit rate. The term '''line rate''' in some textbooks is defined as gross bit rate,<ref name="Bagad"/> in others as net bit rate.

The relationship between the gross bit rate and net bit rate is affected by the FEC [[code rate]] according to the following.
: net bit rate ≤ gross bit rate × [[code rate]]

The connection speed of a technology that involves forward error correction typically refers to the physical layer ''net bit rate'' in accordance with the above definition.

For example, the net bitrate (and thus the "connection speed") of an [[IEEE 802.11a]] wireless network is the net bit rate of between 6 and 54&nbsp;Mbit/s, while the gross bit rate is between 12 and 72&nbsp;Mbit/s inclusive of error-correcting codes.

The net bit rate of ISDN2 [[Basic Rate Interface]] (2&nbsp;B-channels + 1&nbsp;D-channel) of 64+64+16 = 144&nbsp;kbit/s also refers to the payload data rates, while the D channel signalling rate is 16&nbsp;kbit/s.

The net bit rate of the Ethernet 100BASE-TX physical layer standard is 100&nbsp;Mbit/s, while the gross bitrate is 125&nbsp;Mbit/s, due to the [[4B5B]] (four bit over five bit) encoding. In this case, the gross bit rate is equal to the symbol rate or pulse rate of 125&nbsp;megabaud, due to the [[NRZI]] [[line code]].

In communications technologies without forward error correction and other physical layer protocol overhead, there is no distinction between gross bit rate and physical layer net bit rate. For example, the net as well as gross bit rate of Ethernet 10BASE-T is 10&nbsp;Mbit/s. Due to the [[Manchester code|Manchester]] line code, each bit is represented by two pulses, resulting in a pulse rate of 20&nbsp;megabaud.

The "connection speed" of a [[ITU-T V.92|V.92]] [[voiceband]] [[modem]] typically refers to the gross bit rate, since there is no additional error-correction code. It can be up to 56,000&nbsp;bit/s [[downstream (computer science)|downstream]] and 48,000&nbsp;bit/s [[upstream (networking)|upstream]]. A lower bit rate may be chosen during the connection establishment phase due to [[adaptive modulation]]{{snd}}slower but more robust modulation schemes are chosen in case of poor [[signal-to-noise ratio]]. Due to data compression, the actual data transmission rate or throughput (see below) may be higher.

The [[channel capacity]], also known as the [[Shannon–Hartley theorem|Shannon]] capacity, is a theoretical upper bound for the maximum net bitrate, exclusive of forward error correction coding, that is possible without bit errors for a certain physical analog node-to-node [[communication link]].
: net bit rate ≤ channel capacity

The channel capacity is proportional to the [[analog bandwidth]] in hertz. This proportionality is called [[Hartley's law]]. Consequently, the net bit rate is sometimes called [[digital bandwidth]] capacity in bit/s.