56K modem
Encyclopedia
Voiceband
In electronics, voiceband means the typical human hearing frequency range that is from 20 Hz to 20 kHz. In telephony, it means the frequency range normally transmitted by a telephone line, generally about 200–3600 Hz. Frequency-division multiplexing in telephony normally uses...
modems nominally capable of download speeds up to 56 kbit/s (56,000 bits per second). In the late 1990s
1990s
File:1990s decade montage.png|From left, clockwise: The Hubble Space Telescope floats in space after it was taken up in 1990; American F-16s and F-15s fly over burning oil fields and the USA Lexie in Operation Desert Storm, also known as the 1991 Gulf War; The signing of the Oslo Accords on...
, they were the most popular access method for personal Internet usage, but their use had declined as broadband technologies such as DSL gained wider availability.
Speed
The 56 kbit/s theoretical speed is only possible when the system being dialled into has a digital connection to the telephone system, such as DS0 service. By the time 56k modems came into use, most of the telephone system beyond the local loopLocal loop
In telephony, the local loop is the physical link or circuit that connects from the demarcation point of the customer premises to the edge of the carrier or telecommunications service provider's network...
was already digital, so the new 56k protocols took advantage of this.
If both calling party
Calling party
The calling party is a person who initiates a telephone call over the public switched telephone network, usually by dialing a telephone number....
and called party
Called party
The called party is a person who answers a telephone call. The person who initiates a telephone call is the calling party....
have an analog connection, the voiceband signal will be converted from analog to digital and then back to analog. Each conversion adds noise, and there will be too much noise from the second conversion for 56k to work. The modem's negotiation processes will fall back
Fall back and forward
Fall back is a feature of a modem protocol in data communication whereby two communicating modems which experience data corruption can renegotiate with each other to use a lower-speed connection...
to the less demanding 33.6 kbit/s mode. Other local loop conditions, such as certain antiquated pair gain
Pair gain
In telephony, pair gain is a method of transmitting multiple POTS signals over the twisted pairs traditionally used for a single traditional subscriber line in telephone systems. Pair gain has the effect of creating additional subscriber lines...
systems, may have similar results.
In 8-N-1
8-N-1
8-N-1 is a common shorthand notation for a serial port parameter setting or configuration in asynchronous mode, in which there are eight data bits, no parity bit, and one stop bit....
connections (1 start bit, 8 data bits, No parity bit, 1 stop bit), which were typical before LAPM became widespread, the actual throughput is a maximum of 5.6 kilobytes per second, since ten bits are transmitted for every 8-bit byte
Byte
The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...
, although effective throughput can be increased as high as 32 kbytes/s using internal compression, or 100 kbytes/s using ISP-side compression.
Effective throughput
Measuring network throughput
Throughput of a network can be measured using various tools available on different platforms. This page explains the theory behind what these tools set out to measure and the issues regarding these measurements.-Reasons for measuring throughput in networks:...
will vary, depending on framing protocols, noise, data compression
Data compression
In computer science and information theory, data compression, source coding or bit-rate reduction is the process of encoding information using fewer bits than the original representation would use....
, and other factors. See V.42 and Comparison of synchronous and asynchronous signalling
Comparison of synchronous and asynchronous signalling
Synchronous and asynchronous transmissions are two different methods of transmission synchronization. Synchronous transmissions are synchronized by an external clock, while asynchronous transmissions are synchronized by special signals along the transmission medium.-The need for...
article for more detail.
The upload speed is 33.6 kbit/s if an analog voiceband modem is used (V.90), or 48.0 kbit/s using a digital modem (V.92
V.92
V.92 is an ITU-T recommendation, titled Enhancements to Recommendation V.90, that establishes a modem standard allowing near 56 kb/s download and 48 kb/s upload rates. With V.92 PCM is used for both the upstream and downstream connections; previously 56K modems only used PCM for downstream...
). Due to the design of public telecommunications networks, higher speed dialup modems are unlikely to ever appear. Also, depending on the quality of the line conditions, the user may not be able to reach this maximum speed. While faster communications such as DSL and cable modem
Cable modem
A cable modem is a type of network bridge and modem that provides bi-directional data communication via radio frequency channels on a HFC and RFoG infrastructure. Cable modems are primarily used to deliver broadband Internet access in the form of cable Internet, taking advantage of the high...
s became widely available to urban consumers in the early 2000s in the United States, dial-up Internet access remains common, since high speed rural Internet
Rural Internet
Rural Internet is the access to the Internet from rural areas , which are settled places outside towns and cities. Inhabitants live in villages, hamlets, on farms and in other isolated houses...
connections are often scarce and because people may still use it to send fax
Fax
Fax , sometimes called telecopying, is the telephonic transmission of scanned printed material , normally to a telephone number connected to a printer or other output device...
es.
History
Initially there were two rival 56k modem systems. One was K56flex from RockwellRockwell International
Rockwell International was a major American manufacturing conglomerate in the latter half of the 20th century, involved in aircraft, the space industry, both defense-oriented and commercial electronics, automotive and truck components, printing presses, valves and meters, and industrial automation....
and Lucent. The other was X2 from US Robotics. In February 1998 the International Telecommunication Union
International Telecommunication Union
The International Telecommunication Union is the specialized agency of the United Nations which is responsible for information and communication technologies...
(ITU) drafted a 56 kbit/s standard called V.90 which was carefully designed to allow both types of modem to be converted to it by a firmware upgrade. This was formally approved during September 1998.
K56flex
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
chipset
Chipset
A chipset, PC chipset, or chip set refers to a group of integrated circuits, or chips, that are designed to work together. They are usually marketed as a single product.- Computers :...
from Rockwell and Lucent that gave users the possibility of receiving data on ordinary phone lines at 56 kbit/s as opposed to the previous maximum of 33.6 kbit/s.
K56flex is a combination of two competitors' efforts at 56k technology. Lucent developed the K56 protocol, while Rockwell developed the 56flex protocol. This occasionally led to incompatibilities between Lucent and Rockwell chipsets as their implementation of K56flex differed.
X2
U.S. Robotics
USRobotics Corporation is a company that makes computer modems and related products. It sold high-speed modems in the 1980s, and had a reputation for high quality and compatibility. With the reduced usage of voiceband modems in North America in the early 21st century, USR is now one of the few...
. The protocol used V.34+ to upload at 33.6 kbit/s, and downloaded under PCM at 56 kbit/s. X2 was found to consistently have a lower top end speed, yet overall performance was faster than K56flex. The incompatibilities experienced between variant Lucent and Rockwell chipsets in K56flex were also avoided as there was only one X2 standard.
V.90
V.90 is an ITU-T recommendation for a modemModem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
, allowing 56 kbit/s PCM
Pulse-code modulation
Pulse-code modulation is a method used to digitally represent sampled analog signals. It is the standard form for digital audio in computers and various Blu-ray, Compact Disc and DVD formats, as well as other uses such as digital telephone systems...
download and 33.6 kbit/s analog-modulated upload. It replaced two vendor standards (K56flex and X2) and was designed to allow modems from both prior standards to be flash upgraded to support it. It was developed between March 1998 and February 1999. It is also known as V.Last as it was anticipated to be the last standard for modems operating near the channel capacity of POTS
Plain old telephone service
Plain old telephone service is the voice-grade telephone service that remains the basic form of residential and small business service connection to the telephone network in many parts of the world....
lines to be developed. A follow-on standard, V.92
V.92
V.92 is an ITU-T recommendation, titled Enhancements to Recommendation V.90, that establishes a modem standard allowing near 56 kb/s download and 48 kb/s upload rates. With V.92 PCM is used for both the upstream and downstream connections; previously 56K modems only used PCM for downstream...
, was developed later in 1999 to replace V.90.
V.92
V.92 is an ITU-TITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
recommendation, titled Enhancements to Recommendation V.90, that establishes a modem
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
standard allowing 48 kbit/s PCM upload, but at the expense of download rates. For example a 48 kbit/s upstream rate would reduce the downstream as low as 40 kbit/s, due to echo on the telephone line. To avoid this problem, V.92 modems offer the +PIG=1 command to turn off the digital upstream and instead use a 33.6 kbit/s analog connection, in order to maintain a high digital downstream of 50 kbit/s or higher. (See November and October 2000 update at http://modemsite.com/56k/v92s.asp )
V.92 was first presented in August 1999. It was intended to succeed the V.90 standards. Like earlier protocol improvements, V.92 was ineffective unless implemented at both ends of the connection. Unlike those, this enhancement was introduced at a time when, due to the spread of broadband Internet access
Broadband Internet access
Broadband Internet access, often shortened to just "broadband", is a high data rate, low-latency connection to the Internet— typically contrasted with dial-up access using a 56 kbit/s modem or satellite Internet with inherently high latency....
, dial-up service was declining rather than growing, so Internet service providers
Internet service provider
An Internet service provider is a company that provides access to the Internet. Access ISPs directly connect customers to the Internet using copper wires, wireless or fiber-optic connections. Hosting ISPs lease server space for smaller businesses and host other people servers...
were buying few new modems, and uptake was low. Some providers such as Netzero
NetZero
NetZero is an Internet service provider based in Woodland Hills, Los Angeles, California. It is a subsidiary of United Online, owner of Juno Online Services and BlueLight Internet Services. The current chairman, president, and CEO of United Online is Mark Goldston.- History :NetZero launched in...
offer V.92 lines, but with features like "Modem on Hold" turned off.
Quick Connect
This reduces negotiation times to around 10 seconds instead of over 20 seconds. Quick connect works by training the client modem on the first call; analog and digital characteristics are stored in a local profile, and then retrieved for future connections.
"Modem on Hold" (MOH)
This allows the connection to be temporarily severed and then reconnected, reducing the possibility of dropped connections. This is particularly useful for lines that have call waiting so the user can take voice calls.
V.44 compression
V.44 compression replaces the existing V.42bis compression standards. It generally allows for between 10% and 50% better compression. In most situations the improvement is around 15%.
See also
- ITU-T V-Series Recommendations
- Dial Up
- List of device bandwidths