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For other uses, see Modem (disambiguation).
Modem (from modulator-demodulator) 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. Modems can be used over any means of transmitting analog signals, from driven diodes to radio.
The most familiar example is a voiceband modem that turns the digital 1s and 0s of a personal computer into sounds that can be transmitted over the telephone lines of Plain Old Telephone Systems (POTS), and once received on the other side, converts those 1s and 0s back into a form used by a USB, Serial, or Network connection. Modems are generally classified by the amount of data they can send in a given time, normally measured in bits per second, or "bps". They can also be classified by Baud, the number of times the modem changes its signal state per second.
Baud is NOT the modem's speed. The baud rate varies, depending on the modulation technique used. Original Bell 103 modems used a modulation technique that saw a change in state 300 times per second. They transmitted 1 bit for every baud, and so a 300 bit/s modem was also a 300-baud modem. However, casual computerists confused the two. A 300 bit/s modem is the only modem whose bit rate matches the baud rate. A 2400 bit/s modem changes state 600 times per second, but due to the fact that it transmits 4 bits for each baud, 2400 bits are transmitted by 600 baud, or changes in states.
Faster modems are used by Internet users every day, notably cable modems and ADSL modems. In telecommunications, "radio modems" transmit repeating frames of data at very high data rates over microwave radio links. Some microwave modems transmit more than a hundred million bits per second. Optical modems transmit data over optical fibers. Most intercontinental data links now use optical modems transmitting over undersea optical fibers. Optical modems routinely have data rates in excess of a billion (1x109) bits per second. One kilobit per second (kbit/s or kb/s or kbps) as used in this article means 1000 bits per second and not 1024 bits per second. For example, a 56k modem can transfer data at up to 56,000 bits per second over the phone line.
News wire services in the 1920s used multiplex equipment that met the definition, but the modem function was incidental to the multiplexing function, so they are not commonly included in the history of modems. George Stibitz connected a New Hampshire teletype to a computer in New York City by phone lines in 1940. Modems in the United States were part of the SAGE air-defense system in the 1950s, connecting terminals at various airbases, radar sites, and command-and-control centers to the SAGE director centers scattered around the U.S. and Canada. SAGE ran on dedicated communications lines, but the devices at each end were otherwise similar in concept to today's modems.
A few years later, a chance meeting between the CEO of American Airlines and a regional manager of IBM led to development of a "mini-SAGE" as an automated airline ticketing system. The terminals were at ticketing offices, tied to a central computer that managed availability and scheduling. The system, known as SABRE, is the ancestor of today's Sabre system.
AT&T monopoly in the United States
For many years, AT&T maintained a monopoly in the United States on the use of its phone lines, allowing only AT&T-supplied devices to be attached to its network. For the growing group of computer users, AT&T introduced two digital sub-sets in 1958. One is the wideband device shown in the picture to the right. The other was a low-speed modem, which ran at 200 baud.

Legacy modem for leased line operation.
In the summer of 1960, the name Data-Phone was introduced to replace the earlier term digital subset. The 202 Data-Phone was a half-duplex asynchronous service that was marketed extensively in late 1960. In 1962, the 201A and 201B Data-Phones were introduced. They were synchronous modems using two-bit-per-baud phase-shift keying (PSK). The 201A operated half-duplex at 2000 bit/s over normal phone lines, while the 201B provided full duplex 2400 bit/s service on four-wire leased lines, the send and receive channels running on their own set of two wires each.
The famous 103A was also introduced in 1962. It provided full-duplex service at up to 300 baud over normal phone lines. Frequency-shift keying (FSK) was used with the call originator transmitting at 1070 or 1270 Hz and the answering modem transmitting at 2025 or 2225 Hz. The readily available 103A2 gave an important boost to the use of remote low-speed terminals such as the KSR33, the ASR33, and the IBM 2741. AT&T reduced modem costs by introducing the originate-only 113D and the answer-only 113B/C modems.
The Carterfone decision

The Novation CAT acoustically coupled modem
Before 1968, AT&T maintained a monopoly on what devices could be electrically connected to its phone lines. This led to a market for 103A-compatible modems that were mechanically connected to the phone, through the handset, known as acoustically coupled modems. Particularly common models from the 1970s were the Novation CAT (shown in the image) and the Anderson-Jacobson, spun off from an in-house project at the Lawrence Livermore National Laboratory.
Hush-a-Phone v. FCC was a seminal ruling in United States telecommunications law decided by the DC Circuit Court of Appeals on November 8, 1956. The District Court found that it was within the FCC's authority to regulate the terms of use of AT&T's equipment. Subsequently, the FCC examiner found that as long as the device was physically attached it would not threaten to degenerate the system. Later, in the Carterfone decision, the FCC passed a rule setting stringent AT&T-designed tests for electronically coupling a device to the phone lines. AT&T made these tests complex and expensive, so acoustically coupled modems remained common into the early 1980s.
In December 1972, Vadic introduced the VA3400. This device was remarkable because it provided full duplex operation at 1200 bit/s over the dial network, using methods similar to those of the 103A in that it used different frequency bands for transmit and receive. In November 1976, AT&T introduced the 212A modem to compete with Vadic. It was similar in design to Vadic's model, but used the lower frequency set for transmission. It was also possible to use the 212A with a 103A modem at 300 bit/s. According to Vadic, the change in frequency assignments made the 212 intentionally incompatible with acoustic coupling, thereby locking out many potential modem manufacturers. In 1977, Vadic responded with the VA3467 triple modem, an answer-only modem sold to computer center operators that supported Vadic's 1200-bit/s mode, AT&T's 212A mode, and 103A operation.
The Smartmodem and the rise of BBSes

US Robotics Sportster 14,400 Fax modem (1994)
The next major advance in modems was the Smartmodem, introduced in 1981 by Hayes Communications. The Smartmodem was an otherwise standard 103A 300-bit/s modem, but was attached to a small controller that let the computer send commands to it and enable it to operate the phone line. The command set included instructions for picking up and hanging up the phone, dialing numbers, and answering calls. The basic Hayes command set remains the basis for computer control of most modern modems.
Prior to the Hayes Smartmodem, modems almost universally required a two-step process to activate a connection: first, the user had to manually dial the remote number on a standard phone handset, and then secondly, plug the handset into an acoustic coupler. Hardware add-ons, known simply as dialers, were used in special circumstances, and generally operated by emulating someone dialing a handset.
With the Smartmodem, the computer could dial the phone directly by sending the modem a command, thus eliminating the need for an associated phone for dialing and the need for an acoustic coupler. The Smartmodem instead plugged directly into the phone line. This greatly simplified setup and operation. Terminal programs that maintained lists of phone numbers and sent the dialing commands became common.
The Smartmodem and its clones also aided the spread of bulletin-board systems (BBSs). Modems had previously been typically either the call-only, acoustically coupled models used on the client side, or the much more expensive, answer-only models used on the server side. The Smartmodem could operate in either mode depending on the commands sent from the computer. There was now a low-cost server-side modem on the market, and the BBSs flourished.
Softmodem (dumb modem)
Main article: Softmodem

A PCI Winmodem/Softmodem (on the left) next to a traditional ISA modem (on the right). Notice the less complex circuitry of the modem on the left.
A Winmodem or Softmodem is a stripped-down modem that replaces tasks traditionally handled in hardware with software. In this case the modem is a simple digital signal processor designed to create sounds, or voltage variations, on the telephone line. Softmodems are cheaper than traditional modems, since they have fewer hardware components. One downside is that the software generating the modem tones is not simple, and the performance of the computer as a whole often suffers when it is being used. For online gaming this can be a real concern. Another problem is lack of portability such that other OSes (such as Linux) may not have an equivalent driver to operate the modem. A Winmodem might not work with a later version of Microsoft Windows, if its driver turns out to be incompatible with that later version of the operating system.
Apple's GeoPort modems from the second half of the 1990s were similar. Although a clever idea in theory, enabling the creation of more-powerful telephony applications, in practice the only programs created were simple answering-machine and fax software, hardly more advanced than their physical-world counterparts, and certainly more error-prone and cumbersome. The software was finicky and ate up significant processor time, and no longer functions in current operating system versions.
Almost all modern modems also do double-duty as a fax machine as well. Digital faxes, introduced in the 1980s, are simply a particular image format sent over a high-speed (9600/1200 bit/s) modem. Software running on the host computer can convert any image into fax-format, which can then be sent using the modem. Such software was at one time an add-on, but since has become largely universal.
Narrowband/phone-line dialup modems

28.8 kbit/s serial-port modem from Motorola
A standard modem of today contains two functional parts: an analog section for generating the signals and operating the phone, and a digital section for setup and control. This functionality is actually incorporated into a single chip, but the division remains in theory. In operation the modem can be in one of two "modes", data mode in which data is sent to and from the computer over the phone lines, and command mode in which the modem listens to the data from the computer for commands, and carries them out. A typical session consists of powering up the modem (often inside the computer itself) which automatically assumes command mode, then sending it the command for dialing a number. After the connection is established to the remote modem, the modem automatically goes into data mode, and the user can send and receive data. When the user is finished, the escape sequence, "+++" followed by a pause of about a second, is sent to the modem to return it to command mode, and the command ATH to hang up the phone is sent.
The commands themselves are typically from the Hayes command set, although that term is somewhat misleading. The original Hayes commands were useful for 300 bit/s operation only, and then extended for their 1200 bit/s modems. Faster speeds required new commands, leading to a proliferation of command sets in the early 1990s. Things became considerably more standardized in the second half of the 1990s, when most modems were built from one of a very small number of "chip sets". We call this the Hayes command set even today, although it has three or four times the numbers of commands as the actual standard.
Increasing speeds (V.21 V.22 V.22bis)

A 2400 bit/s modem for a laptop.
The 300 bit/s modems used frequency-shift keying to send data. In this system the stream of 1s and 0s in computer data is translated into sounds which can be easily sent on the phone lines. In the Bell 103 system the originating modem sends 0s by playing a 1070 Hz tone, and 1s at 1270 Hz, with the answering modem putting its 0s on 2025 Hz and 1s on 2225 Hz. These frequencies were chosen carefully, they are in the range that suffer minimum distortion on the phone system, and also are not harmonics of each other.
In the 1200 bit/s and faster systems, phase-shift keying was used. In this system the two tones for any one side of the connection are sent at the similar frequencies as in the 300 bit/s systems, but slightly out of phase. By comparing the phase of the two signals, 1s and 0s could be pulled back out, for instance if the signals were 90 degrees out of phase, this represented two digits, "1,0", at 180 degrees it was "1,1". In this way each cycle of the signal represents two digits instead of one. 1200 bit/s modems were, in effect, 600 symbols per second modems (600 baud modems) with 2 bits per symbol.
Voiceband modems generally remained at 300 and 1200 bit/s (V.21 and V.22) into the mid 1980s. A V.22bis 2400-bit/s system similar in concept to the 1200-bit/s Bell 212 signalling was introduced in the U.S., and a slightly different one in Europe. By the late 1980s, most modems could support all of these standards and 2400-bit/s operation was becoming common.
For more information on baud rates versus bitrates, see the companion article List of device bandwidths.
Increasing speeds (one-way proprietary standards)
Many other standards were also introduced for special purposes, commonly using a high-speed channel for receiving, and a lower-speed channel for sending. One typical example was used in the French Minitel system, in which the user's terminals spent the majority of their time receiving information. The modem in the Minitel terminal thus operated at 1200 bit/s for reception, and 75 bit/s for sending commands back to the servers.
Three U.S. companies became famous for high-speed versions of the same concept. Telebit introduced its Trailblazer modem in 1984, which used a large number of 36 bit/s channels to send data one-way at rates up to 18,400 bit/s. A single additional channel in the reverse direction allowed the two modems to communicate how much data was waiting at either end of the link, and the modems could change direction on the fly. The Trailblazer modems also supported a feature that allowed them to "spoof" the UUCP "g" protocol, commonly used on Unix systems to send e-mail, and thereby speed UUCP up by a tremendous amount. Trailblazers thus became extremely common on Unix systems, and maintained their dominance in this market well into the 1990s.
U.S. Robotics (USR) introduced a similar system, known as HST, although this supplied only 9600 bit/s (in early versions at least) and provided for a larger backchannel. Rather than offer spoofing, USR instead created a large market among Fidonet users by offering its modems to BBS sysops at a much lower price, resulting in sales to end users who wanted faster file transfers. Hayes was forced to compete, and introduced its own 9600-bit/s standard, Express 96 (also known as "Ping-Pong"), which was generally similar to Telebit's PEP. Hayes, however, offered neither protocol spoofing nor sysop discounts, and its high-speed modems remained rare.
4800 and 9600 (V.27ter, V.32)
Echo cancellation was the next major advance in modem design. Local telephone lines use the same wires to send and receive, which results in a small amount of the outgoing signal bouncing back. This signal can confuse the modem. Is the signal it is "hearing" a data transmission from the remote modem, or its own transmission bouncing back? This was why earlier modems split the signal frequencies into answer and originate; each modem simply didn't listen to its own transmitting frequencies. Even with improvements to the phone system allowing higher speeds, this splitting of available phone signal bandwidth still imposed a half-speed limit on modems.
Echo cancellation got around this problem. Measuring the echo delays and magnitudes allowed the modem to tell if the received signal was from itself or the remote modem, and create an equal and opposite signal to cancel its own. Modems were then able to send at "full speed" in both directions at the same time, leading to the development of 4800 and 9600 bit/s modems.
Increases in speed have used increasingly complicated communications theory. 1200 and 2400 bit/s modems used the phase shift key (PSK) concept. This could transmit two or three bits per symbol. The next major advance encoded four bits into a combination of amplitude and phase, known as Quadrature Amplitude Modulation (QAM). Best visualized as a constellation diagram, the bits are mapped onto points on a graph with the x (real) and y (quadrature) coordinates transmitted over a single carrier.
The new V.27ter and V.32 standards were able to transmit 4 bits per symbol, at a rate of 1200 or 2400 baud, giving an effective bit rate of 4800 or 9600 bits per second. The carrier frequency was 1650 Hz. For many years, most engineers considered this rate to be the limit of data communications over telephone networks.
Error correction and compression
Operations at these speeds pushed the limits of the phone lines, resulting in high error rates. This led to the introduction of error-correction systems built into the modems, made most famous with Microcom's MNP systems. A string of MNP standards came out in the 1980s, each increasing the effective data rate by minimizing overhead, from about 75% theoretical maximum in MNP 1, to 95% in MNP 4. The new method called MNP 5 took this a step further, adding data compression to the system, thereby increasing the data rate above the modem's rating. Generally the user could expect an MNP5 modem to transfer at about 130% the normal data rate of the modem. MNP was later "opened" and became popular on a series of 2400-bit/s modems, and ultimately led to the development of V.42 and V.42bis ITU standards. V.42 and V.42bis were non-compatible with MNP but were similar in concept: Error correction and compression.
Another common feature of these high-speed modems was the concept of fallback, allowing them to talk to less-capable modems. During the call initiation the modem would play a series of signals into the line and wait for the remote modem to "answer" them. They would start at high speeds and progressively get slower and slower until they heard an answer. Thus, two USR modems would be able to connect at 9600 bit/s, but, when a user with a 2400-bit/s modem called in, the USR would "fall back" to the common 2400-bit/s speed. This would also happen if a V.32 modem and a HST modem were connected. Because they used a different standard at 9600 bit/s, they would fall back to their highest commonly supported standard at 2400 bit/s. The same applies to V.32bis and 14400 bit/s HST modem, which would still be able to communicate with each other at only 2400 bit/s.
Breaking the 9.6k barrier
In 1980 Gottfried Ungerboeck from IBM Zurich Research Laboratory applied powerful channel coding techniques to search for new ways to increase the speed of modems. His results were astonishing but only conveyed to a few colleagues[1]. Finally in 1982, he agreed to publish what is now a landmark paper in the theory of information coding.[citation needed] By applying powerful parity check coding to the bits in each symbol, and mapping the encoded bits into a two dimensional "diamond pattern", Ungerboeck showed that it was possible to increase the speed by a factor of two with the same error rate. The new technique was called "mapping by set partitions" (now known as trellis modulation). This new view was an extension of the "penny packing" problem[clarify] and the related and more general problem of how to pack points into an N-dimension sphere such that they are far away from their neighbors. The greater two bit sequences are from one another, the easier it is to correct minor errors.
The industry was galvanized into new research and development. More powerful coding techniques were developed, commercial firms rolled out new product lines, and the standards organizations rapidly adopted to new technology. The "tipping point" occurred with the introduction of the SupraFAXModem 14400 in 1991. Rockwell had introduced a new chipset supporting not only V.32 and MNP, but the newer 14,400 bit/s V.32bis and the higher-compression V.42bis as well, and even included 9600 bit/s fax capability. Supra, then known primarily for their hard drive systems, used this chip set to build a low-priced 14,400 bit/s modem which cost the same as a 2400 bit/s modem from a year or two earlier (about US$300). The product was a runaway best-seller, and it was months before the company could keep up with demand.
V.32bis was so successful that the older high-speed standards had little to recommend them. USR fought back with a 16,800 bit/s version of HST, while AT&T introduced a one-off 19,200 bit/s method they referred to as V.32ter (also known as V.32 terbo), but neither non-standard modem sold well.
V.34 / 28.8k and 33.8k

An ISA modem manufactured to conform to the V.34 protocol.
Any interest in these systems was destroyed during the lengthy introduction of the 28,800 bit/s V.34 standard. While waiting, several companies decided to "jump the gun" and introduced modems they referred to as "V.FAST". In order to guarantee compatibility with V.34 modems once the standard was ratified (1994), the manufacturers were forced to use more "flexible" parts, generally a DSP and microcontroller, as opposed to purpose-designed "modem chips".
Today the ITU standard V.34 represents the culmination of the joint efforts. It employs the most powerful coding techniques including channel encoding and shape encoding. From the mere 4 bits per symbol (9.6 kbit/s), the new standards used the functional equivalent of 6 to 10 bits per symbol, plus increasing baud rates from 2400 to 3429, to create 14.4, 28.8, and 33.8 kbit/s modems. (See Tables 8 and 10 of the specification; maximum speed listed as "33 800".) This rate is near the theoretical Shannon limit. When calculated, the Shannon capacity of a narrowband line is Bandwidth * log2(1 + Pu / Pn), with Pu / Pn the signal-to-noise ratio. Narrowband phone lines have a bandwidth from 300-3100 Hz, so using Pu / Pn = 100,000: capacity is approximately 35 kbit/s.
Without the discovery and eventual application of trellis modulation, maximum telephone rates would have been limited to 3429 baud * 4 bits/symbol == approximately 14 kilobits per second using traditional QAM.[citation needed]
Using digital lines and PCM (V.90/92)
In the late 1990s Rockwell and U.S. Robotics introduced new technology based upon the digital transmission used in modern telephony networks. The standard digital transmission in modern networks is 64 kbit/s but some networks use a part of the bandwidth for remote office signaling (eg to hang up the phone), limiting the effective rate to 56 kbit/s DS0. This new technology was adopted into ITU standards V.90 and is common in modern computers. The 56 kbit/s rate is only possible from the central office to the user site (downlink) and in the United States, government regulation limits the maximum power output to only 53.3 kbit/s. The uplink (from the user to the central office) still uses V.34 technology at 33.6k.
Later in V.92, the digital PCM technique was applied to increase the upload speed to a maximum of 48 kbit/s, 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 option 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 ) V.92 also adds two other features. The first is the ability for users who have call waiting to put their dial-up Internet connection on hold for extended periods of time while they answer a call. The second feature is the ability to "quick connect" to one's ISP. This is achieved by remembering the analog and digital characteristics of the telephone line, and using this saved information to reconnect at a fast pace.
Using compression to exceed 56k
Today's V.42, V.42bis and V.44 standards allow the modem to transmit data faster than its basic rate would imply. For instance, a 53.3 kbit/s connection with V.44 can transmit up to 53.3*6 == 320 kbit/s using pure text. However, the compression ratio tends to vary due to noise on the line, or due to the transfer of already-compressed files (ZIP files, JPEG images, MP3 audio, MPEG video). [2] At some points the modem will be sending compressed files at approximately 50 kbit/s, uncompressed files at 160 kbit/s, and pure text at 320 kbit/s, or any value in between. [3]
In such situations a small amount of memory in the modem, a buffer, is used to hold the data while it is being compressed and sent across the phone line, but in order to prevent overflow of the buffer, it sometimes becomes necessary to tell the computer to pause the datastream. This is accomplished through hardware flow control using extra lines on the modem–computer connection. The computer is then set to supply the modem at some higher rate, such as 320 kbit/s, and the modem will tell the computer when to start or stop sending data.
Compression by the ISP
As telephone-based 56k modems began losing popularity, some Internet Service Providers such as Netzero and Juno started using pre-compression to increase the throughput & maintain their customer base. As example, the Netscape ISP uses a compression program that squeezes images, text, and other objects at the server, just prior to sending them across the phone line. The server-side compression operates much more efficiently than the "on-the-fly" compression of V.44-enabled modems. Typically website text is compacted to 4% thus increasing effective throughput to approximately 1300 kbit/s. The accelerator also precompresses Flash executables and images to approximately 30% and 12%, respectively.
The drawback of this approach is a loss in quality, where the graphics become heavily compacted and smeared, but the speed is dramatically improved such that webpages load in less than 5 seconds, and the user can manually choose to view the uncompressed images at any time. The ISPs employing this approach advertise it as "DSL speeds over regular phone lines" or simply "high speed dialup".
List of dialup speeds
Note that the values given are maximum values, and actual values may be slower under certain conditions (for example, noisy phone lines).[4] For a complete list see the companion article List of device bandwidths.
Connection Bitrate

Modem 110 baud
0.1 kbit/s
Modem 300 (300 baud) (Bell 103 or V.21)
0.3 kbit/s
Modem 1200 (600 baud) (Bell 212A or V.22)
1.2 kbit/s
Modem 2400 (600 baud) (V.22bis)
2.4 kbit/s
Modem 2400 (1200 baud) (V.26bis)
2.4 kbit/s
Modem 4800 (1600 baud) (V.27ter)
4.8 kbit/s
Modem 9600 (2400 baud) (V.32)
9.6 kbit/s
Modem 14.4 (2400 baud) (V.32bis)
14.4 kbit/s
Modem 28.8 (3200 baud) (V.34)
28.8 kbit/s
Modem 33.6 (3429 baud) (V.34)
33.8 kbit/s
Modem 56k (8000/3429 baud) (V.90)
56.0/33.6 kbit/s
Modem 56k (8000/8000 baud) (V.92)
56.0/48.0 kbit/s
Bonding Modem (two 56k modems)) (V.92)
112.0/96.0 kbit/s [5]

Hardware compression (variable) (V.90/V.42bis)
56.0-220.0 kbit/s
Hardware compression (variable) (V.92/V.44)
56.0-320.0 kbit/s
Server-side web compression (variable) (Netscape ISP)
100.0-1000.0 kbit/s
Radio modems
Direct broadcast satellite, WiFi, and mobile phones all use modems to communicate, as do most other wireless services today. Modern telecommunications and data networks also make extensive use of radio modems where long distance data links are required. Such systems are an important part of the PSTN, and are also in common use for high-speed computer network links to outlying areas where fibre is not economical.
Even where a cable is installed, it is often possible to get better performance or make other parts of the system simpler by using radio frequencies and modulation techniques through a cable. Coaxial cable has a very large bandwidth, however signal attenuation becomes a major problem at high data rates if a digital signal is used. By using a modem, a much larger amount of digital data can be transmitted through a single piece of wire. Digital cable television and cable Internet services use radio frequency modems to provide the increasing bandwidth needs of modern households. Using a modem also allows for frequency-division multiple access to be used, making full-duplex digital communication with many users possible using a single wire.
Wireless modems come in a variety of types, bandwidths, and speeds. Wireless modems are often referred to as transparent or smart. They transmit information that is modulated onto a carrier frequency to allow many simultaneous wireless communication links to work simultaneously on different frequencies.
Transparent modems operate in a manner similar to their phone line modem cousins. Typically, they were half duplex, meaning that they could not send and receive data at the same time. Typically transparent modems are polled in a round robin manner to collect small amounts of data from scattered locations that do not have easy access to wired infrastructure. Transparent modems are most commonly used by utility companies for data collection.
Smart modems come with a media access controller inside which prevents random data from colliding and resends data that is not correctly received. Smart modems typically require more bandwidth than transparent modems, and typically achieve higher data rates. The IEEE 802.11 standard defines a short range modulation scheme that is used on a large scale throughout the world.
WiFi and WiMax
Wireless data modems are used in the WiFi and WiMax standards, operating at microwave frequencies.
WiFi is principally used in laptops for Internet connections (wireless access point) and wireless application protocol (WAP).
Mobile modems & routers
External modems for mobile phone lines (GPRS and UMTS), are also known as datacards and cellular routers. The datacard is a PC card, where a phone card is included, whereas a cellular router may or may not have an external datacard. Most cellular routers do, except for the WAAV CM3 mobile broadband cellular router.
Nowadays, there are USB modems with an integrated SIM cardholder (i.e, Huawei E220); that is, you only need a USB port and a modem to connect to the Internet.
See : flat rate.
[edit] Broadband

DSL modem
ADSL modems, a more recent development, are not limited to the telephone's "voiceband" audio frequencies. Some ADSL modems use coded orthogonal frequency division modulation (DMT).
Cable modems use a range of frequencies originally intended to carry RF television channels. Multiple cable modems attached to a single cable can use the same frequency band, using a low-level media access protocol to allow them to work together within the same channel. Typically, 'up' and 'down' signals are kept separate using frequency division multiple access.
New types of broadband modems are beginning to appear, such as doubleway satellite and powerline modems.
Broadband modems should still be classed as modems, since they use complex waveforms to carry digital data. They are more advanced devices than traditional dial-up modems as they are capable of modulating/demodulating hundreds of channels simultaneously.
Many broadband modems include the functions of a router (with Ethernet and WiFi ports) and other features such as DHCP, NAT and firewall features.
When broadband technology was introduced, networking and routers were unfamiliar to consumers. However, many people knew what a modem was as most internet access was through dialup. Due to this familiarity, companies started selling broadband modems using the familiar term "modem" rather than vaguer ones like "adapter" or "transceiver".
Most modems must be configured properly before they can use a router. This configuration is known as bridge mode.
Deep-space telecommunications
Many modern modems have their origin in deep-space telecommunications systems of the 1960s.
Differences with deep space telecom modems vs landline modems
• digital modulation formats that have high doppler immunity are typically used
• waveform complexity tends to be low, typically binary phase shift keying
• error correction varies mission to mission, but is typically much stronger than most landline modems
Voice modem
Voice modems are regular modems that are capable of recording or playing audio over the telephone line. They are used for telephony applications. See Voice modem command set for more details on voice modems. This type of modem can be used as FXO card for Private branch exchange systems (compare V.92).
A CEA study in 2006 found that dial-up Internet access is on a notable decline in the U.S. In 2000, dial-up Internet connections accounted for 74% of all U.S. residential Internet connections. The US demographic pattern for (dialup modem users per capita) has been more or less mirrored in Canada and Australia for the past 20 years.
Dialup modem use in the US had dropped to 60% by 2003, and currently (2006) stands at 36%. Voiceband modems were once the most popular means of Internet access in the U.S., but with the advent of new ways of accessing the Internet, the traditional 56K modem is losing popularity.
1. ^ IEEE History Center. "Gottfried Ungerboeck Oral History". Retrieved on 2008-02-10.
2. ^ Modem compression: V.44 against V.42bis
3. ^
4. ^ Data communication over the telephone network
5. ^ About bonding modems
External links

Wikimedia Commons has media related to:
Standards Organizations and modem protocols
• International Telecommunications Union ITU: Data communication over the telephone network
• 56k
• V.92
• Columbia University - Protocols Explained - no longer available, archived version
• Basic handshakes & modulations - V.22, V.22bis, V.32 and V.34 handshakes
General modem info (drivers, chipsets, etc.)
• A very good primer about modems
• Installing, testing, troubleshooting & tweaking modems
• Costmo Modem Site
• How Stuff Works - Modems
• ModemHelp.Net
• Modem Tutorial - what is a modem - How modems can be applied for machine telemetry applications
• - Site operated by Zoom and is mainly a sales pitch for v.92
• - Tutorial Asterisk and Analog Interface Cards, User Comments
• Modem initialisation string
Source :

Universal Mobile Telecommunications System

From Wikipedia, the free encyclopedia
Universal Mobile Telecommunications System (UMTS) is one of the third-generation (3G) cell phone technologies, which is also being developed into a 4G technology. Currently, the most common form of UMTS uses W-CDMA as the underlying air interface. It is standardized by the 3GPP, and is the European answer to the ITU IMT-2000 requirements for 3G cellular radio systems.
To differentiate UMTS from competing network technologies, UMTS is sometimes marketed as 3GSM, emphasizing the combination of the 3G nature of the technology and the GSM standard which it was designed to succeed.
This article discusses the technology, business, usage and other aspects encompassing and surrounding UMTS, the 3G successor to GSM which utilizes the W-CDMA air interface and GSM infrastructures. Any issues relating strictly to the W-CDMA interface itself may be better described in the W-CDMA page.
UMTS, using W-CDMA, supports up to 14.0 Mbit/s data transfer rates in theory (with HSDPA), although at the moment users in deployed networks can expect a transfer rate of up to 384 kbit/s for R99 handsets, and 7.2 Mbit/s for HSDPA handsets in the downlink connection. This is still much greater than the 9.6 kbit/s of a single GSM error-corrected circuit switched data channel or multiple 9.6 kbit/s channels in HSCSD (14.4 kbit/s for CDMAOne), and—in competition to other network technologies such as CDMA2000, PHS or WLAN—offers access to the World Wide Web and other data services on mobile devices.
Precursors to 3G are 2G mobile telephony systems, such as GSM, IS-95, PDC, PHS and other 2G technologies deployed in different countries. In the case of GSM, there is an evolution path from 2G, to GPRS, also known as 2.5G. GPRS supports a much better data rate (up to a theoretical maximum of 140.8 kbit/s, though typical rates are closer to 56 kbit/s) and is packet switched rather than connection orientated (circuit switched). It is deployed in many places where GSM is used. E-GPRS, or EDGE, is a further evolution of GPRS and is based on more modern coding schemes. With EDGE the actual packet data rates can reach around 180 kbit/s (effective). EDGE systems are often referred as "2.75G Systems".
Since 2006, UMTS networks in many countries have been or are in the process of being upgraded with High Speed Downlink Packet Access (HSDPA), sometimes known as 3.5G. Currently, HSDPA enables downlink transfer speeds of up to 7.2 Mbit/s. Work is also progressing on improving the uplink transfer speed with the High-Speed Uplink Packet Access (HSUPA). Longer term, the 3GPP Long Term Evolution project plans to move UMTS to 4G speeds of 100 Mbit/s down and 50 Mbit/s up, using a next generation air interface technology based upon OFDM.
UMTS supports mobile videoconferencing, although experience in Japan and elsewhere has shown that user demand for video calls is not very high.
Other possible uses for UMTS include the downloading of music and video content, as well as live TV.
See also: List of Deployed UMTS networks
UMTS combines the W-CDMA, TD-CDMA, or TD-SCDMA air interfaces, GSM's Mobile Application Part (MAP) core, and the GSM family of speech codecs. In the most popular cellular mobile telephone variant of UMTS, W-CDMA is currently used. Note that other wireless standards use W-CDMA as their air interface, including FOMA.
UMTS over W-CDMA uses a pair of 5 MHz channels. In contrast, the competing CDMA2000 system uses one or more arbitrary 1.25 MHz channels for each direction of communication. UMTS and other W-CDMA systems are widely criticized for their large spectrum usage, which has delayed deployment in countries that acted relatively slowly in allocating new frequencies specifically for 3G services (such as the United States).
The specific frequency bands originally defined by the UMTS standard are 1885–2025 MHz for the mobile-to-base (uplink) and 2110–2200 MHz for the base-to-mobile (downlink). In the US, 1710–1755 MHz and 2110–2155 MHz will be used instead, as the 1900 MHz band was already utilized.[1] Additionally, in some countries UMTS operators use the 850 MHz and/or 1900 MHz bands (independently, meaning uplink and downlink are within the same band), notably in the US by AT&T Mobility, and in Australia by Telstra (850 MHz only). A UMTS900 network has also opened in Finland, planned for more rural areas and other hard coverage areas over the GSM shared 900 MHz spectrum, supported currently by Elisa and Nokia (by model 6121 classic) and also encouraged by the local regulators.
For existing GSM operators, it is a simple but costly migration path to UMTS: much of the infrastructure is shared with GSM, but the cost of obtaining new spectrum licenses and overlaying UMTS at existing towers can be prohibitively expensive.
A major difference of UMTS compared to GSM is the air interface forming GSM/EDGE Radio Access Network (GeRAN). It can be connected to various backbone networks like the Internet, ISDN, GSM or to a UMTS network. GeRAN includes the three lowest layers of OSI model. The network layer (OSI 3) protocols form the Radio Resource Management protocol (RRM). They manage the bearer channels between the mobile terminals and the fixed network including the handovers.
The evolution of the system will move forward with so called releases. Each release will introduce new features. The following features are examples of many others in these new releases.
Release '99
• Bearer services
• 64 kbit/s circuit switched
• 384 kbit/s packet switched
• Location services
• Call services: compatible with Global System for Mobile Communications (GSM), based on Universal Subscriber Identity Module (USIM)
Release 4
• Edge radio
• Multimedia messaging
• MExE (Mobile Execution Environment)
• Improved location services
• IP Multimedia Services (IMS)
Release 5
• IP Multimedia Subsystem (IMS)
• IPv6, IP transport in UTRAN
• Improvements in GERAN, MExE, etc
Release 6
• WLAN integration
• Multimedia broadcast and multicast
• Improvements in IMS

3G Handsets and Modems
All of the major 2G phone manufacturers are now developers of 3G phones. The early 3G handsets and modems were specific to the frequencies required in their country, which meant they could only roam to other countries on the same 3G frequency (though they can fall back to the older GSM standard). Canada and USA have a common share of frequencies, as do most European countries. Look at UMTS frequency bands to see the similarities between each country's network frequency. Canada phones could be used in BAND II and/or V as an example.
There are almost no 3G phones/modems available supporting all 3G frequencies (850/900/1700/1900/2100, UMTS, not GSM). Some modems like the Huawei E270 meet this specification [2], however many phones are offering more than one band which still enables extensive roaming. For example, a tri-band chipset with 850/1900/2100 allows usage in most countries.
Newer phone models have 3G built-in but are usually designed for a specific provider's network as per UMTS frequency bands. These phones may be used for the Internet directly on the phone or, via tether mode, can be attached via Wifi, Bluetooth, Infrared or USB to a computer to access the Internet. [3]
PDA and Smartphones
• Symbian Based: with 65% of the market. Nokia and Sony Ericsson are the major SymbianOS users. There is a lot of SymbianOS software available but often only applicable to specific phones. Tethering is available using USB, bluetooth or Wifi (with JoikuSpot: Convert your Symbian Phone into a router).[4]
• Windows Mobile Based: with 12% of the current market. Windows Mobile 6.1 offers a range of features for UMTS. Tethering is available using USB, bluetooth, or Wifi (with WMWifiRouter: convert your Windows Mobile unit into a router)[5] Windows Mobile is used by many manufacturers including Sony, Samsung, Palm, Motorola, and several manufacturers familiar with the PC market.
• RIM OS Based: with 11% of the market. Most BlackBerry smartphones are not currently 3G capable, with the exception of certain models such as model 8707v, EVDO capable models and the upcoming BlackBerry 9000 series. One reason is that BlackBerry, typically known for long battery life, would have shorter battery life with 3G. The emergence of greatly improved multimedia and tethering capabilities on recent BlackBerry models, is currently pressuring RIM to include 3G in future BlackBerry models.
• Mac OS X-like iPhone OS Based: with 7% of the market. Apple's first generation iPhone did not support 3G and is restricted to using the EDGE standard. Apple claimed this was to maintain a reasonable battery life on the telephone. Power usage of 3G is improving, and Apple released a 3G/UMTS iPhone on July 11, 2008.
• Palm OS (also known as "Garnet OS") was initially developed by Palm Computing, Inc. for personal digital assistants (PDAs) in 1996 and was later also used on some mobile phones. It is provided with a suite of basic applications for personal information management. Palm OS has been used in Sony Clié handsets (Sony now uses Windows Mobile & Symbian) and by Samsung (which now use Windows Mobile).
• Android is a software platform and operating system for mobile devices based on the Linux operating system and developed by Google and the Open Handset Alliance.[6] It allows developers to write managed code in a Java-like language that utilizes Google-developed Java libraries,[7] but does not support programs developed in native code. When released in 2008, most of the Android platform will be made available under the Apache free-software and open-source license.[8]
External Modems
Using a cellular router, PCMCIA or USB card, customers are able to access 3G broadband services, regardless of their choice of computer (such as a tablet PC or a PDA). Some software installs itself from the modem, so that in some cases absolutely no knowledge of technology is required to get online in moments.
Using a phone that supports 3G and Bluetooth 2.0, multiple Bluetooth-capable laptops can be connected to the Internet. The phone acts as a router, but via Bluetooth rather than wireless networking (802.11) or a USB connection.
Interoperability and global roaming
UMTS phones (and data cards) are highly portable—they have been designed to roam easily onto other UMTS networks (assuming your provider has a roaming agreement). In addition, almost all UMTS phones (except in Japan) are UMTS/GSM dual-mode devices, so if a UMTS phone travels outside of UMTS coverage during a call the call may be transparently handed off to available GSM coverage. Roaming charges are usually significantly higher than regular usage charges.
Most UMTS licensees consider ubiquitous, transparent global roaming an important issue. To enable a high degree of interoperability, UMTS phones usually support several different frequencies in addition to their GSM fallback. Different countries support different UMTS frequency bands – Europe initially used 2100 MHz while the USA used 1700 MHz, and a UMTS phone and network must support a common frequency to work together. Because of the frequencies used, early models of UMTS phones designated for the US will likely not be operable elsewhere and vice versa. There are now 11 different frequency combinations used around the world—including frequencies formerly used solely for 2G services.
UMTS phones use a USIM (Universal Subscriber Identity Module) (based on GSM's SIM) and also accept GSM SIM cards. This is a global standard of identification, and enables a network to identify the phone user to authenticate both local and roaming customers. Roaming agreements between networks allow for calls to a customer to be redirected to them while roaming and determine the services (and prices) available to the user. In addition to user subscriber information and authentication information, the USIM provides storage space for phone book contacts—phones can store their data on their own memory or on the USIM card (which is usually more limited in its phone book contact information). A USIM can be moved to another UMTS or GSM phone, and the phone will take on the user details of the USIM—meaning it is the USIM (not the phone) which determines the phone number of the phone and the billing for calls made from the phone.
Japan was the first country to adopt 3G technologies, and since they had not used GSM previously they had no need to build GSM compatibility into their handsets and their 3G handsets were smaller than those available elsewhere. In 2002, NTT DoCoMo's FOMA 3G network was the first commercial W-CDMA network—it was initially incompatible with the UMTS standard at the radio level but used standard USIM cards, meaning USIM card based roaming was possible (moving the USIM card into a UMTS or GSM phone when travelling). Both NTT and SoftBank Mobile (which launched 3G in December 2002) now use the standard UMTS, and their PDC 2G networks run in parallel.
Spectrum allocation
Main article: UMTS frequency bands
Over 120 licenses have already been awarded to operators worldwide (as of December 2004), specifying W-CDMA radio access technology that builds on GSM. In Europe, the license process occurred at the end of the technology bubble, and the auction mechanisms for allocation set up in some countries resulted in some extremely high prices being paid for the original 2100 MHz licenses, notably in the UK and Germany. In Germany, bidders paid a total 50.8 billion euros for six licenses, two of which were subsequently abandoned and written off by their purchasers (Mobilcom and the Sonera/Telefonica consortium). It has been suggested that these huge license fees have the character of a very large tax paid on income expected 10 years down the road—in any event they put some European telecom operators close to bankruptcy (most notably KPN). Over the last few years some operators have written off some or all of the license costs. More recently, a carrier in Finland has begun using 900 MHz UMTS in a shared arrangement with its surrounding 2G GSM base stations, a trend that is expected to expand over Europe in the next 1–3 years.
The 2100 MHz UMTS spectrum allocated in Europe is already used in North America. The 1900 MHz range is used for 2G (PCS) services, and 2100 MHz range is used for satellite communications. Regulators have, however, freed up some of the 2100 MHz range for 3G services, together with the 1700 MHz for the uplink. UMTS operators in North America who want to implement a European style 2100/1900 MHz system will have to share spectrum with existing 2G services in the 1900 MHz band.
AT&T Wireless launched UMTS services in the United States by the end of 2004 strictly using the existing 1900 MHz spectrum allocated for 2G PCS services. Cingular acquired AT&T Wireless in 2004 and has since then launched UMTS in select US cities. After AT&T's acquisition of Cingular, it was renamed AT&T Mobility and is rolling out some cities with a UMTS network at 850 MHz to enhance its existing UMTS network at 1900 MHz and now offers subscribers a number of UMTS 850/1900 phones.
T-Mobile's roll-out of UMTS in the US will focus on the 2100/1700 MHz bands just auctioned.
Initial rollout of UMTS in Canada will also be undertaken using the 850 and 1900 MHz bands due to the large areas that will be needed to cover.
In Australia, Telstra rolled out a national 3G network, branded as NextG, operating in the 850 MHz band to replace the existing CDMA network (April 2008) and enhance its existing 2100 MHz UMTS network. Optus is currently rolling out a 3G network with the same coverage as its GSM network, using the 2100 MHz band in cities and most large towns, and the 900 MHz band for regional areas. Vodafone is also building a 3G network using the 900 MHz band. The 850 MHz and 900 MHz bands provide greater coverage compared to equivalent 1700/1900/2100 MHz networks, and are best suited to regional areas where greater distances separate subscriber and base station.
Carriers in South America are now also rolling out 850 MHz networks.
Other competing standards
There are other competing 3G standards, such as CDMA2000 and TD-SCDMA, though UMTS can use the latter's air interface standard.
On the Internet access side, competing systems include WiMAX and Flash-OFDM. Different variants of UMTS compete with different standards. While this article has largely discussed UMTS-FDD, a form oriented for use in conventional cellular-type spectrum, UMTS-TDD, a system based upon a TD-CDMA air interface, is used to provide UMTS service where the uplink and downlink share the same spectrum, and is very efficient at providing asymmetric access. It provides more direct competition with WiMAX and similar Internet-access oriented systems than conventional UMTS.
Both the CDMA2000 and W-CDMA air interface systems are accepted by ITU as part of the IMT-2000 family of 3G standards, in addition to UMTS-TDD's TD-CDMA, Enhanced Data Rates for GSM Evolution (EDGE) and China's own 3G standard, TD-SCDMA.
CDMA2000's narrower bandwidth requirements make it easier than UMTS to deploy in existing spectrum along with legacy standards. In some, but not all, cases, existing GSM operators only have enough spectrum to implement either UMTS or GSM, not both. For example, in the US D, E, and F PCS spectrum blocks, the amount of spectrum available is 5 MHz in each direction. A standard UMTS system would saturate that spectrum.
In many markets however, the co-existence issue is of little relevance, as legislative hurdles exist to co-deploying two standards in the same licensed slice of spectrum.
Most GSM operators in North America as well as others around the world have accepted EDGE as a temporary 3G solution. AT&T Wireless launched EDGE nationwide in 2003, AT&T launched EDGE in most markets and T-Mobile USA has launched EDGE nationwide as of October 2005. Rogers Wireless launched nation-wide EDGE service in late 2003 for the Canadian market. Bitė Lietuva (Lithuania) was one of the first operators in Europe to launch EDGE in December 2003. TIM (Italy) launched EDGE in 2004. The benefit of EDGE is that it leverages existing GSM spectrums and is compatible with existing GSM handsets. It is also much easier, quicker, and considerably cheaper for wireless carriers to "bolt-on" EDGE functionality by upgrading their existing GSM transmission hardware to support EDGE than having to install almost all brand-new equipment to deliver UMTS. EDGE provides a short-term upgrade path for GSM operators and directly competes with CDMA2000.
Problems and issues
Some countries, including the United States and Japan, have allocated spectrum differently from the ITU recommendations, so that the standard bands most commonly used for UMTS (UMTS-2100) have not been available. In those countries, alternative bands are used, preventing the interoperability of existing UMTS-2100 equipment, and requiring the design and manufacture of different equipment for the use in these markets. As is the case with GSM-900 today, standard UMTS 2100 MHz equipment will not work in those markets. However, it appears as though UMTS is not suffering as much from handset band compatibility issues as GSM did, as many UMTS handsets are multi-band in both UMTS and GSM modes. Quad-band GSM (850, 900, 1800, and 1900 MHz bands) and tri-band UMTS (850, 1900, and 2100 MHz bands) handsets are becoming more commonplace.
In the early days of UMTS there were issues with rollout:
• overweight handsets with poor battery life;
• problems with handover from UMTS to GSM, connections being dropped or handovers only possible in one direction (UMTS → GSM) with the handset only changing back to UMTS after hanging up, even if UMTS coverage returns—in most networks around the world this is no longer an issue;
• for fully fledged UMTS incorporating video on demand features, one base station needed to be set up every 1–1.5 km (0.62–0.93 mi). This was the case when only the 2100 MHz band was being used, however with the growing use of lower-frequency bands (such as 850 and 900 MHz) this is no longer so. This has led to an increase in the interest in the lower-band networks by operators since 2006.
Some of these issues may still be ongoing; for instance, Apple, Inc. cited[9] UMTS power consumption as the reason that the first generation iPhone only supported EDGE. Their release of the iPhone 3G quotes talk time in 3G mode as half that of the 2G mode.
Other, non-UMTS, 3G and 4G standards:
• CDMA2000: evolved from the cmdaOne (also known as IS-95, or "CDMA") standard, managed by the 3GPP2
• WiMAX: a newly emerging wide area wireless technology.
UMTS is an evolution of the GSM mobile phone standard.
Other useful information
• Mobile modem
• Spectral efficiency comparison table
• Code Division Multiple Access (CDMA)
• Common pilot channel or CPICH, a simple synchronisation channel in WCDMA.
• Multiple-input multiple-output (MIMO) is the major issue of multiple antenna research.
• Wi-Fi: a local area wireless technology that is complementary to UMTS.
• Mobile Internet access worldwide lists mobile (mainly UMTS/HSDPA) Internet access solutions worldwide.
• List of device bandwidths
• Martin Sauter: Communication Systems for the Mobile Information Society, John Wiley, September 2006, ISBN 0-470-02676-6
1. ^ The FCC's Advanced Wireless Services bandplan
2. ^ "Huawei E270 GSM/UMTS modem specifications". Retrieved on 2008-06-08.
3. ^ ^ For an example of tether mode,
4. ^ ^
5. ^ ^
6. ^ "Industry Leaders Announce Open Platform for Mobile Devices" (HTML) (in English). Open Handset Alliance (2007-11-05). Retrieved on 2007-11-05.
7. ^ "Google's Android parts ways with Java industry group".
8. ^ "Open Handset Alliance Releases Android SDK" (HTML) (in English). Open Handset Alliance (2007-11-12). Retrieved on 2007-11-12.
9. ^ ^
External links
• GSM/UMTS market statistics from the 'Global mobile suppliers association'
• 3GPP Specifications Numbering Scheme
• 3GPP document listing all UMTS Technical Standards for Release 6 and earlier
• Vocabulary for 3GPP Specifications, up to Release 8
• UMTS FAQ on UMTS World d
• Worldwide W-CDMA frequency allocations on UMTS World
• UMTS TDD Alliance The Global UMTS TDD Alliance
• 3GSM World Congress

High-Speed Downlink Packet Access

From Wikipedia, the free encyclopedia
High-Speed Downlink Packet Access (HSDPA) is a 3G (third generation) mobile telephony communications protocol in the High-Speed Packet Access (HSPA) family, which allows networks based on Universal Mobile Telecommunications System (UMTS) to have higher data transfer speeds and capacity. Current HSDPA deployments support down-link speeds of 1.8, 3.6, 7.2 and 14.4 Mbit/s. Further speed increases are available with HSPA+, which provides speeds of up to 42 Mbit/s downlink.[1]
The High-Speed Downlink Shared Channel (HS-DSCH) lacks two basic features of other W-CDMA channels — variable spreading factor and fast power control. Instead, it delivers the improved downlink performance using adaptive modulation and coding (AMC), fast packet scheduling at the base station, and fast retransmissions from the base station, known as hybrid automatic repeat-request (HARQ).
Hybrid automatic repeat-request (HARQ)
HARQ uses incremental redundancy, where user data is transmitted multiple times using different codings. When a corrupted packet is received, the user device saves it and later combines it with the retransmissions, to recover the error-free packet as efficiently as possible. Even if the retransmitted packets are corrupted, their combination can yield an error-free packet.
Fast packet scheduling
The HS-DSCH downlink channel is shared between users using channel-dependent scheduling to make the best use of available radio conditions. Each user device periodically transmits an indication of the downlink signal quality, as often as 500 times per second. Using this information from all devices, the base station decides which users will be sent data on the next 2 ms frame and how much data should be sent for each user. More data can be sent to users which report high downlink signal quality.
The amount of the channelisation code tree, and thus network bandwidth, allocated to HSDPA users is determined by the network. The allocation is "semi-static" in that it can be modified while the network is operating, but not on a frame-by-frame basis. This allocation represents a trade-off between bandwidth allocated for HSDPA users, versus that for voice and non-HSDPA data users. The allocation is in units of channelisation codes for Spreading Factor 16, of which 16 exist and up to 15 can be allocated to HSDPA. When the base station decides which users will receive data on the next frame, it also decides which channelisation codes will be used for each user. This information is sent to the user devices over one or more HSDPA "scheduling channels"; these channels are not part of the HSDPA allocation previously mentioned, but are allocated separately. Thus, for a given 2 ms frame, data may be sent to a number of users simultaneously, using different channelisation codes. The maximum number of users to receive data on a given 2 ms frame is determined by the number of allocated channelisation codes. By contrast, in CDMA2000 1xEV-DO, data is sent to only one user at a time.
Adaptive modulation and coding
The modulation scheme and coding is changed on a per-user basis depending on signal quality and cell usage. The initial scheme is Quadrature phase-shift keying (QPSK), but in good radio conditions 16QAM modulation almost doubles data throughput rates. With 5 Code allocation, QPSK typically offers up to 1.8 Mbit/s peak data rates, while 16QAM up to 3.6. Additional codes (e.g. 10, 15) can also be used to improve these data rates or extend the network capacity throughput significantly. Theoretically, HSDPA can give throughput up to 14.4 Mbit/s.
Other improvements
HSDPA is part of the UMTS standards since release 5, which also accompanies an improvement on the uplink providing a new bearer of 384 kbit/s. The previous maximum bearer was 128 kbit/s.
As well as improving data rates, HSDPA also reduces latency and so the round trip time for applications.
Along with the HS-DSCH channel, three new physical channels are also introduced: HS-SCCH, HS-DPCCH and HS-PDSCH. The High Speed-Shared Control Channel (HS-SCCH) informs the user that data will be sent on the HS-DSCH 2 slots ahead. The Uplink High Speed-Dedicated Physical Control Channel (HS-DPCCH) carries acknowledgment information and current channel quality indicator (CQI) of the user. This value is then used by the base station to calculate how much data to send to the user devices on the next transmission. The High Speed-Physical Downlink Shared Channel (HS-PDSCH) is the channel mapped to the above HS-DSCH transport channel that carries actual user data.
HSDPA UE categories
HSDPA comprises various versions with different data speeds.
Category Max. number of
HS-DSCH codes Modulation Max. data rate
1 5 QPSK and 16-QAM
2 5 QPSK and 16-QAM 1.2
3 5 QPSK and 16-QAM 1.8
4 5 QPSK and 16-QAM 1.8
5 5 QPSK and 16-QAM 3.6
6 5 QPSK and 16-QAM 3.6
7 10 QPSK and 16-QAM 7.3
8 10 QPSK and 16-QAM 7.3
9 15 QPSK and 16-QAM 10.2
10 15 QPSK and 16-QAM 14.4
11 5 QPSK only 0.9
12 5 QPSK only 1.8
The first phase of HSDPA has been specified in the 3rd Generation Partnership Project (3GPP) release 5. Phase one introduces new basic functions and is aimed to achieve peak data rates of 14.4 Mbit/s (see above). Newly introduced are the High Speed Downlink Shared Channels (HS-DSCH), the adaptive modulation QPSK and 16QAM and the High Speed Medium Access protocol (MAC-hs) in base station.
The second phase of HSDPA is specified in the upcoming 3GPP release 7 and has been named HSPA Evolved. It can achieve data rates of up to 42 Mbit/s.[1] It will introduce antenna array technologies such as beamforming and Multiple-input multiple-output communications (MIMO). Beam forming focuses the transmitted power of an antenna in a beam towards the user’s direction. MIMO uses multiple antennas at the sending and receiving side. Deployments are scheduled to begin in the second half of 2008.
After HSDPA the roadmap leads to HSOPA, a technology under development for specification in 3GPP Release 8. This project is called the Long Term Evolution initiative. The first release of LTE offers data rates of over 320 Mbit/s for downlink and over 170 Mbit/s for uplink using OFDMA modulation.
For details, see [1]
See also: List of Deployed HSDPA networks
As of May 25, 2007, 102 HSDPA networks have commercially launched mobile broadband services in 55 countries. Nearly 40 HSDPA networks support 3.6 Mbit/s peak downlink data throughput. A growing number are delivering 7.2 Mbit/s peak data downlink, leveraging new higher-speed devices coming into the market. One network has been declared as “14.4 Mbit/s (peak) ready” and several others will have this capability by end 2007. The first commercial HSUPA uplink network is launched, with several more set to follow in 2007.
This protocol is a relatively simple upgrade where UMTS is already deployed.[1]
CDMA-EVDO networks had the early lead on performance, and Japanese providers were highly successful benchmarks for it. But lately this seems to be changing in favour of HSDPA as an increasing number of providers worldwide are adopting it. In Australia, Telstra announced that its CDMA-EVDO network would be replaced with a HSDPA network (since named NextG), offering high speed internet, mobile television and traditional telephony and video calling. Rogers Wireless deployed HSDPA system 850/1900 in Canada on April 1, 2007. Singapore is currently the only country boasting nationwide HSDPA.[2]
So far, 171 device models from 47 suppliers have been launched, comprising: 53 handsets, 35 notebooks, 30 datacards, 19 wireless routers, 15 modems, 11 embedded module, 2 wireless modules, 1 wireless residential gateway, 1 media player, 1 camera, 1 GPS handset, 1 convergence platform & 1 baseband processor. [3]
Marketing as mobile broadband
During 2007, an increasing number of telcos worldwide began selling HSDPA USB modems as mobile broadband connections. In addition, the popularity of HSDPA landline replacement boxes grew — providing HSDPA for data via Ethernet and WiFi, and ports for connecting traditional landline telephones. Marketed with connection speeds of "up to 7.2 Mbit/s",[4] which is only attained under ideal conditions. As a result these services can be slower than expected, especially when in fringe coverage indoors. However, signal strength can be greatly improved by using commercial solutions that can attach 3G external antennas.[5]
See also
• 3GPP Long Term Evolution
• Cellular router
• High-Speed Uplink Packet Access
• High-Speed OFDM Packet Access
• List of device bandwidths
• List of HSPA mobile phones
• Mobile Internet access worldwide
• Quad band
• Tri band
• UMTS frequency bands
1. ^ a b c d HSPA mobile broadband today
2. ^ "MobileOne (M1) HSDPA Network, Singapore". Retrieved on 2008-05-24.
3. ^
4. ^ Vodafone UK 7.2MBs service
5. ^ and
• Martin Sauter: Communication Systems for the Mobile Information Society, John Wiley, September 2006, ISBN 0-470-02676-6
External links
• Official HSPA Website
• Understand HSDPA's implementation challenges

Rose Stencil Valentine's Day Mug

by Twila Lenoir

Here's an inexpensive Valentine's Day gift that you can make yourself for that special someone. We provide the free, full-sized rose stencil pattern (at right) - or you could use your own romantic theme. Either way, a mug that you paint yourself is sure to please!
Rose Stencil Valentine's Day Mug
Materials List:
• white coffee mug
• printed rose stencil pattern (shown above, right)
• Perm enamel surface conditioner • Perm enamel paints (your choice of colors)
• Perm enamel gloss
• sharp nail scissors or Exacto knife

Stencil a Valentine's Day Coffee Mug

Purchase an inexpensive glass coffee mug or use a solid white one that you may already have around. Clean the mug well with dishwashing liquid and water, then rinse and dry thoroughly.

With a paint brush, brush on the surface conditioner. You must let this dry, but you can usually paint on your design within an hour.

You can purchace stencil paper that is specifically manufactured for making your own stencils, but why not save the money and use plain paper and tape? Print out the pattern, put wide tape on both sides of the paper pattern, then cut out using sharp cuticle scissors or an exacto craft knife.

Put the stencil in position on the mug (not too close to the top) and keep it in place with spray stencil glue, or tape it firmly in place.

Use a makeup sponge to sponge the paint colors on the stencil. You will need two coats of paint. Make another stencil on the other side of the mug handle so that you have a picture on both sides of the mug. If you wish, try painting some small hearts at the bottom as a border, as well as down the stem of the handle.

Let dry overnight.

Paint on the perm enamel gloss with a brush, and let cure for ten days before washing. (Hint, I set mine in the oven at 225 degrees, when it was dry, for a couple of hours. The paint was fine and I was able to skip the 10 day waiting period.)


Check the manufacturers instructions when applying paint, particularly if you are using paint on an object that will be used for serving food or drinks. Most paints should not be applied close to the lip of a cup, for instance - so please make sure you read the bottle label carefully.

Happy Valentine's Day!


How to Make Screen-Printed T-shirts

By eHow Hobbies, Games & Toys Editor
Rate: (9 Ratings)
At-home T-shirt making can save you money and time, and garner praise for your creative craftiness. It will take some patience, but making screen-printed T-shirts will be worth your while when you receive your first compliment: Where did you find that great shirt? Oh, I made it.
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Difficulty: Moderately Challenging
Things You’ll Need:
• T-shirt
• Black or color ink
• Squeegee or wiper
• Cardboard
• Workstation table (optional)
• Screen with frames
• 150 watt light bulb
• Hanging light bulb socket
• Photo-emulsion kit
• Lukewarm water
• Duct tape or masking tape (optional)
• Transparency paper
• Hanger
• Iron
• Piece of white paper
• Ironing board (optional)
• Watering can (optional)
Pre-Screening Prep
Create a design—the simpler, the better. Try to come up with something with big lines and a small amount of detail. Your design should ideally be around 9 inches wide and 15 inches tall.
Pick an area to be your workstation. A small or medium-sized table will work well.
Gather your tools. The list of supplies you need will vary greatly depending on the method of screen-printing you choose to follow (see Ingredients above).
Making the Print
Copy your design onto transparency paper. You can purchase this yourself or go to your local copy or supply store and ask them to make you a copy on the darkest piece of transparency possible. Check your transparency copy carefully—this is what your print will look like on the T-shirt.
Build a screen so that you can screen-print your design. Art stores will have premade screens, or you can purchase a frame and some silk screen (based on the size of your design) and make the screen yourself. The cheaper option is to create the screen from scratch, as art stores will sell the items cheaper a la carte.
Stretch your screen across the frame and secure it using staples or nails. This step is only necessary if you chose to make the screen yourself. If you bought a premade screen, skip to the next step. Don't try to keep your screen in place with tape—it will not be tight enough. The method you use to secure the screen is up to you, but make sure it is as tight as possible.
Transfer your design onto the screen. This is the trickiest and costliest part of making screen-printed T-shirts, as you will probably need to buy a photo-emulsion kit from an art supply or craft store. (If you would rather not use photo-emulsion, try using a screen filler and drawing fluid. See Resources below.) Follow the directions in the photo-emulsion kit to burn your image on to the screen. You will have to use the heat from a hanging socket holding a light bulb of at least 150 watts to transfer your design from the transparency to the screen.
Wash the image out of the screen. This sounds counterintuitive, but you are only washing away the parts you don't need. The chemicals creating the design have been scorched into the screen. Use lukewarm water with low pressure: If you have a sprayer at your kitchen sink, this works well, otherwise a watering will work.
Place a piece of hard cardboard inside your T-shirt and arrange the screen on top of the shirt. Make sure to smooth everything out and work on a hard surface. Pour black or colored ink onto your screen on top of your T-shirt. Only pour ink on the screen! Using a wiper or squeegee (homemade or store bought), pull the ink from top to bottom over the screen, then from bottom to top. Lift the screen and you should see your image transferred on to your T-shirt.
Check to make sure the image has transferred, then hang the screen-printed T-shirt to dry. Allow the ink to fully dry. When dry, lay the T-shirt on an ironing board, place a clean piece of white paper over the screen print and iron for 4 to 5 minutes. This should set the ink in place on the T-shirt.


How to make Primitive Hang Tags

How to make Primitive Hang Tags
This is one of the easiest Primitive Crafts to make. All you need is some clip art, modge podge, manilla tags or cardstock and some items you probably have in your own kitchen right now.
When it comes to prim tags, the grungier the better! First step is to find some clip art you like. Primitive icons such as Raggedy Annie, Crows, Saltbox houses, Gingerbreads are very popular for prim tags. Victorian images are also very hot. There are lots of free sites on the internet that where you can get these images from. Do a google search and I am sure you will have several sites come up. Just be sure that the clipart you are using is royalty free, if you intend to sell these tags. If you dont have a printer or prefer some simpler tags, you can just hand print prim words, such as "Primitive", "Homespun", "Simple", "Annies", etc.
Now, go look in your kitchen, because all you need to make these tags is waiting right there. You will need, some instant coffee, some vanilla extract and some cinnamon.
To mix your primitive solution take 1 cup of very hot water. 4 heaping TBS of instant coffee and 4 TBS of vanilla extract. I always like to put a couple of sprinkles of cinnamon in the mix just for good measure, but it is optional. Now, with a spoon, mix up the ingredients well. I find this mix a dark enough mixture for my tastes, but do a test. Dip a piece of card stock or manilla tag into the mix and see if its dark enough for you. If its not, just add some more instant coffee.
Dip your manilla tags into the solution ( if you cant find manilla tags, simply cut some cardstock into tag shapes, generally they are 4 by 2 1/2. Just use a ruler to measure). I usually leave my tags in about 30 min. Then fish them out and lay them on some paper towels to drain and dry.
While your tags are drying, print off your clip art if that is what you are plaining to use and cut out your clip art pictures.
Once your tags are dry, squeeze some modge podge into a foam plate and with a brush ( I use those little black foam brushes, they are inexpensive and you can throw them away when you are through), brush some of the modge podge glue on the wrong side ( the side without the picture) of your clip art. Center in on your tag, and glue in place. Modge Podge dries fairly quickly, so just let it sit for two or three minutes. Take your foam brush and brush a coat of modge podge over the entire front of the tag. This will hold your clip art in place and also help the front of your tags from getting scratched up while in use.
And thats've made some primitive hang tags!

Synchronous optical networking

Synchronous optical networking
From Wikipedia, the free encyclopedia
(Redirected from SONET)
Synchronous optical networking (SONET) and Synchronous Digital Hierarchy (SDH), are two closely related multiplexing protocols for transferring multiple digital bit streams using lasers or light-emitting diodes (LEDs) over the same optical fiber. The method was developed to replace the Plesiochronous Digital Hierarchy (PDH) system for transporting larger amounts of telephone calls and data traffic over the same fiber wire without synchronization problems.
SONET and SDH are based on circuit mode communication, meaning that each connection achieves a constant bit rate and delay. For example, SDH or SONET may be utilized to allow several Internet Service Providers to share the same optical fiber, without being affected by each other's traffic load, and without being able to temporarily borrow free capacity from each other. Only certain integer multiples of 64 kbit/s are possible bit rates.
Since SONET and SDH are characterized as pure time division multiplexing (TDM) protocols (not to be confused with Time Division Multiple Access, TDMA), offering permanent connections, and do not involve packet mode communication, they are considered as physical layer protocols.
Both SDH and SONET are widely used today: SONET in the U.S. and Canada and SDH in the rest of the world. Although the SONET standards were developed before SDH, their relative penetrations in the worldwide market dictate that SONET now is considered the variation.
The two protocols are standardized according to the following:
• SDH or Synchronous Digital Hierarchy standard developed by the International Telecommunication Union (ITU), documented in standard G.707 and its extension G.708
• SONET or Synchronous Optical Networking standard as defined by GR-253-CORE from Telcordia and T1.105 from American National Standards Institute
Difference from PDH
Synchronous networking differs from PDH in that the exact rates that are used to transport the data are tightly synchronized across the entire network, made possible by atomic clocks. This synchronization system allows entire inter-country networks to operate synchronously, greatly reducing the amount of buffering required between elements in the network.
Both SONET and SDH can be used to encapsulate earlier digital transmission standards, such as the PDH standard, or used directly to support either Asynchronous Transfer Mode (ATM) or so-called Packet over SONET/SDH (POS) networking. As such, it is inaccurate to think of SDH or SONET as communications protocols in and of themselves, but rather as generic and all-purpose transport containers for moving both voice and data. The basic format of an SDH signal allows it to carry many different services in its Virtual Container (VC) because it is bandwidth-flexible.
Structure of SONET/SDH signals
SONET and SDH often use different terms to describe identical features or functions, sometimes leading to confusion that exaggerates their differences. With a few exceptions, SDH can be thought of as a superset of SONET. The two main differences between the two:
• SONET can use either of two basic units for framing while SDH has one
• SDH has additional mapping options which are not available in SONET.
Protocol overview
The protocol is an extremely heavily multiplexed structure, with the header interleaved between the data in a complex way. This is intended to permit the encapsulated data to have its own frame rate and to be able to float around relative to the SDH/SONET frame structure and rate. This interleaving permits a very low latency for the encapsulated data- data passing through equipment can be delayed by at most 32 microseconds, compared to a frame rate of 125 microseconds; many competing protocols buffer the data for at least one frame or packet before sending it on. Extra padding is allowed for the multiplexed data to move within the overall framing due to it being on a different clock to the frame rate, and the decision to allow this at most of the levels of the multiplexing structure makes the protocol complex, but gives high all-round performance.
The basic unit of transmission
The basic unit of framing in SDH is an STM-1 (Synchronous Transport Module level - 1), which operates at 155.52 Mbit/s. SONET refers to this basic unit as an STS-3c (Synchronous Transport Signal - 3, concatenated), but its high-level functionality, frame size, and bit-rate are the same as STM-1.
SONET offers an additional basic unit of transmission, the STS-1 (Synchronous Transport Signal - 1), operating at 51.84 Mbit/s - exactly one third of an STM-1/STS-3c. Some manufacturers also support the SDH equivalent STM-0, but this is not part of the standard.

In packet oriented data transmission such as Ethernet, a packet frame usually consists of a header and a payload, with the header of the frame being transmitted first, followed by the payload (and possibly a trailer, such as a CRC). In synchronous optical networking, this is modified slightly. The header is termed the overhead and the payload still exists, but instead of the overhead being transmitted before the payload, it is interleaved, with part of the overhead being transmitted, then part of the payload, then the next part of the overhead, then the next part of the payload, until the entire frame has been transmitted. In the case of an STS-1, the frame is 810 octets in size while the STM-1/STS-3c frame is 2430 octets in size. For STS-1, the frame is transmitted as 3 octets of overhead, followed by 87 octets of payload. This is repeated nine times over until 810 octets have been transmitted, taking 125 microseconds. In the case of an STS-3c/STM-1 which operates three times faster than STS-1, 9 octets of overhead are transmitted, followed by 261 octets of payload. This is also nine times over until 2,430 octets have been transmitted, also taking 125 microseconds. For both SONET and SDH, this is normally represented by the frame being displayed graphically as a block: of 90 columns and 9 rows for STS-1; and 270 columns and 9 rows for SDH/STS-3c. This representation aligns all the overhead columns, so the overhead appears as a contiguous block, as does the payload.
The internal structure of the overhead and payload within the frame differs slightly between SONET and SDH, and different terms are used in the standards to describe these structures. However, the standards are extremely similar in implementation, such that it is easy to interoperate between SDH and SONET at particular bandwidths.
It is worth noting that the choice of a 125 microsecond interval is not an arbitrary one. What it means is that the same octet position in each frame comes past every 125 microseconds. If one octet is extracted from the bitstream every 125 microseconds, this gives a data rate of 8 bits per 125 microseconds - or 64 kbit/s, the basic DS0 telecommunications rate. This relation allows an extremely useful behaviour of synchronous optical networking, which is that low data rate channels or streams of data can be extracted from high data rate streams by simply extracting octets at regular time intervals - there is no need to understand or decode the entire frame. This is not possible in PDH networking. Furthermore, it shows that a relatively simple device is all that is needed to extract a datastream from an SDH framed connection and insert it into a SONET framed connection and vice versa.
In practice, the terms STS-1 and OC-1 are sometimes used interchangeably, though the OC-N format refers to the signal in its optical form. It is therefore incorrect to say that an OC-3 contains 3 OC-1s: an OC-3 can be said to contain 3 STS-1s.

SDH Frame

A STM-1 Frame. The first 9 columns contain the overhead and the pointers. For the sake of simplicity, the frame is shown as a rectangular structure of 270 columns and 9 rows, but the protocol does not transmit the bytes in this order in practice

For the sake of simplicity, the frame is shown as a rectangular structure of 270 columns and 9 rows. The first 3 rows and 9 columns contain Regenerator Section Overhead (RSOH) and the last 5 rows and 9 columns contain Multiplex Section Overhead (MSOH. The 4th row from the top contains pointers
The STM-1 (Synchronous Transport Module level - 1) frame is the basic transmission format for SDH or the fundamental frame or the first level of the synchronous digital hierarchy. The STS-1 frame is transmitted in exactly 125 microseconds, therefore there are 8000 frames per second on a fiber-optic circuit designated OC-1 (optical carrier one). The STM-1 frame consists of overhead plus a virtual container capacity. The first 9 columns of each frame make up the Section Overhead, and the last 261 columns make up the Virtual Container (VC) capacity. The VC plus the pointers (H1, H2, H3 bytes) is called the AU (Administrative Unit).
Carried within the VC capacity, which has its own frame structure of nine rows and 261 columns, is the Path Overhead and the Container . The first column is for Path Overhead; it’s followed by the payload container, which can itself carry other containers. Virtual Containers can have any phase alignment within the Administrative Unit, and this alignment is indicated by the Pointer in row four,
The Section overhead of an STM-1 signal (SOH) is divided into two parts: the Regenerator Section Overhead (RSOH) and the Multiplex Section Overhead (MSOH). The overheads contain information from the system itself, which is used for a wide range of management functions, such as monitoring transmission quality, detecting failures, managing alarms, data communication channels, service channels, etc.
The STM frame is continuous and is transmitted in a serial fashion, byte-by-byte, row-by-row.
STM–1 frame contains
• Total content : 9 x 270 bytes = 2430 bytes
• overhead : 9 rows x 9 bytes
• payload : 9 rows x 261 bytes
• Period : 125 μsec
• Bitrate : 155.520 Mbit/s (2430 x 8 bits x 8000 frame/s )
• payload capacity : 150.336 Mbit/s (2349 x 8 bits x 8000 frame/s)
The transmission of the frame is done row by row, from the top left corner
Framing Structure
The frame consists of two parts, the transport overhead and the path virtual envelope.
Transport overhead
The transport overhead is used for signaling and measuring transmission error rates, and is composed as follows:
• Section overhead - called RSOH (Regenerator Section Overhead) in SDH terminology: 27 octets containing information about the frame structure required by the terminal equipment.
• Line overhead - called MSOH (Multiplex Section Overhead) in SDH: 45 octets containing information about alarms, maintenance and error correction as may be required within the network.
• Pointer – It points to the location of the J1 byte in the payload.
Path virtual envelope
Data transmitted from end to end is referred to as path data. It is composed of two components:
• Payload overhead (POH): 9 bytes used for end to end signaling and error measurement.
• Payload: user data (774 bytes for STS-1, or 2349 bytes for STM-1/STS-3c)
For STS-1, the payload is referred to as the synchronous payload envelope (SPE), which in turn has 18 stuffing bytes, leading to the STS-1 payload capacity of 756 bytes.[1]
The STS-1 payload is designed to carry a full PDH DS3 frame. When the DS3 enters a SONET network, path overhead is added, and that SONET network element (NE) is said to be a path generator and terminator. The SONET NE is said to be line terminating if it processes the line overhead. Note that wherever the line or path is terminated, the section is terminated also. SONET Regenerators terminate the section but not the paths or line.
An STS-1 payload can also be subdivided into 7 VTGs, or Virtual Tributary Groups. Each VTG can then be subdivided into 4 VT1.5 signals, each of which can carry a PDH DS1 signal. A VTG may instead be subdivided into 3 VT2 signals, each of which can carry a PDH E1 signal. The SDH equivalent of a VTG is a TUG2; VT1.5 is equivalent to VC11, and VT2 is equivalent to VC12.
Three STS-1 signals may be multiplexed by time-division multiplexing to form the next level of the SONET hierarchy, the OC-3 (STS-3), running at 155.52 Mbit/s. The multiplexing is performed by interleaving the bytes of the three STS-1 frames to form the STS-3 frame, containing 2,430 bytes and transmitted in 125 microseconds.
Higher speed circuits are formed by successively aggregating multiples of slower circuits, their speed always being immediately apparent from their designation. For example, four STS-3 or AU4 signals can be aggregated to form a 622.08 Mbit/s signal designated as OC-12 or STM-4.
The highest rate that is commonly deployed is the OC-192 or STM-64 circuit, which operates at rate of just under 10 Gbit/s. Speeds beyond 10 Gbit/s are technically viable and are under evaluation. [Few vendors are offering STM-256 rates now, with speeds of nearly 40Gbit/s]. Where fiber exhaust is a concern, multiple SONET signals can be transported over multiple wavelengths over a single fiber pair by means of Wavelength division multiplexing, including Dense Wave Division Multiplexing (DWDM) and Coarse Wave Division Multiplexing (CWDM). DWDM circuits are the basis for all modern transatlantic cable systems and other long-haul circuits.
SONET/SDH and relationship to 10 Gigabit Ethernet
Another circuit type amongst data networking equipment is 10 Gigabit Ethernet (10GbE). This is similar to the line rate of OC-192/STM-64 (9.953 Gbit/s). The Gigabit Ethernet Alliance created two 10 Gigabit Ethernet variants: a local area variant (LAN PHY), with a line rate of exactly 10,000,000 kbit/s and a wide area variant (WAN PHY), with the same line rate as OC-192/STM-64 (9,953,280 kbit/s). The Ethernet wide area variant encapsulates its data using a light-weight SDH/SONET frame so as to be compatible at low level with equipment designed to carry those signals.
However, 10 Gigabit Ethernet does not explicitly provide any interoperability at the bitstream level with other SDH/SONET systems. This differs from WDM System Transponders, including both Coarse- and Dense-WDM systems (CWDM, DWDM) that currently support OC-192 SONET Signals, which can normally support thin-SONET framed 10 Gigabit Ethernet.
[edit] SONET/SDH data rates
SONET/SDH Designations and bandwidths
SONET Optical Carrier Level SONET Frame Format SDH level and Frame Format Payload bandwidth (kbit/s) Line Rate (kbit/s)
STS-1 STM-0 48,960 51,840
150,336 155,520
STS-12 STM-4 601,344 622,080
STS-24 STM-8 1,202,688 1,244,160
STS-48 STM-16 2,405,376 2,488,320
STS-96 STM-32 4,810,752 4,976,640
STS-192 STM-64 9,621,504 9,953,280
STS-768 STM-256 38,486,016 39,813,120
STS-1536 STM-512 76,972,032 79,626,120
STS-3072 STM-1024 153,944,064 159,252,240
In the above table, Payload bandwidth is the line rate less the bandwidth of the line and section overheads. User throughput must also deduct path overhead from this, but path overhead bandwidth is variable based on the types of cross-connects built across the optical system.
Note that the typical data rate progression starts at OC-3 and increases by multiples of 4. As such, while OC-24 and OC-1536, along with other rates such as OC-9, OC-18, OC-36, and OC-96 may be defined in some standards documents, they are not available on a wide-range of equipment.
As of 2007, OC-3072 is still a work in progress.
Physical layer
The physical layer actually comprises a large number of layers within it, only one of which is the optical/transmission layer (which includes bitrates, jitter specifications, optical signal specifications and so on). The SONET and SDH standards come with a host of features for isolating and identifying signal defects and their origins.
SONET/SDH Network Management Protocols
SONET equipment is often managed with the TL1 protocol. TL1 is a traditional telecom language for managing and reconfiguring SONET network elements. TL1 (or whatever command language a SONET Network Element utilizes) must be carried by other management protocols, including SNMP, CORBA and XML.
There are some features that are fairly universal in SONET Network Management. First of all, most SONET NEs have a limited number of management interfaces defined. These are:
• Electrical Interface. The electrical interface (often 50 Ω) sends SONET TL1 commands from a local management network physically housed in the Central Office where the SONET NE is located. This is for "local management" of that NE and, possibly, remote management of other SONET NEs.
• Craft Interface. Local "craftspersons" can access a SONET NE on a "craft port" and issue commands through a dumb terminal or terminal emulation program running on a laptop. This interface can also be hooked-up to a console server, allowing for remote out-of-band management and logging.
• SONET and SDH have dedicated Data Communication Channels (DCC)s within the section and line overhead for management traffic. Generally, section overhead (regenerator section in SDH) is used. According to ITU-T G.7712, there are three modes used for management:
• IP-only stack, using PPP as data-link
• OSI-only stack, using LAP-D as data-link
• Dual (IP+OSI) stack using PPP or LAP-D with tunneling functions to communicate between stacks.
An interesting fact about modern NEs is that, to handle all of the possible management channels and signals, most NEs actually contain a router for routing the network commands and underlying (data) protocols.
The main functions of Network Management include:
• Network and NE Provisioning. In order to allocate bandwidth throughout a network, each NE must be configured. Although this can be done locally, through a craft interface, it is normally done through a Network Management System (sitting at a higher layer) that in turn operates through the SONET/SDH Network Management Network.
• Software Upgrade. NE Software Upgrade is in modern NEs done mostly through the SONET/SDH Management network.
• Performance Management. NEs have a very large set of standards for Performance Management. The PM criteria allow for monitoring not only the health of individual NEs, but for the isolation and identification of most network defects or outages. Higher-layer Network monitoring and management software allows for the proper filtering and troubleshooting of network-wide PM so that defects and outages can be quickly identified and responded to.
With recent advances in SONET and SDH chipsets, the traditional categories of NEs are breaking down. Nevertheless, as Network architectures have remained relatively constant, even newer equipment (including "Multiservice Provisioning Platforms") can be examined in light of the architectures they will support. Thus, there is value in viewing new (as well as traditional) equipment in terms of the older categories.
Traditional regenerators terminate the section overhead, but not the line or path. Regens extend long haul routes in a way similar to most regenerators, by converting an optical signal that has already traveled a long distance into electrical format and then retransmitting a regenerated high-power signal.
Since the late 1990s, regenerators have been largely replaced by Optical Amplifiers. Also, some of the functionality of regens has been absorbed by the Transponders of Wavelength Division Multiplexing systems.
add-drop multiplexer (ADM)
ADMs are the most common type of NEs. Traditional ADMs were designed to support one of the Network Architectures, though new generation systems can often support several architectures, sometimes simultaneously. ADMs traditionally have a "high speed side" (where the full line rate signal is supported), and a "low speed side", which can consist of electrical as well as optical interfaces. The low speed side takes in low speed signals which are multiplexed by the NE and sent out from the high speed side, or vice versa.
Digital Cross Connect system
Recent Digital Cross Connect systems (DCSs or DXCs) support numerous high-speed signals, and allow for cross connection of DS1s, DS3s and even STS-3s/12c and so on, from any input to any output. Advanced DCSs can support numerous subtending rings simultaneously.
Network Architectures
Currently, SONET (and SDH) have a limited number of architectures defined. These architectures allow for efficient bandwidth usage as well as protection (i.e. the ability to transmit traffic even when part of the network has failed), and are key in understanding the almost worldwide usage of SONET and SDH for moving digital traffic. The three main architectures are:
• Linear APS (Automatic Protection Switching), also known as 1+1: This involves 4 fibers: 2 working fibers in each direction, and two protection fibers. Switching is based on the line state, and may be unidirectional, with each direction switching independently, or bidirectional, where the NEs at each end negotiate so that both directions are generally carried on the same pair of fibers.
• UPSR (Unidirectional Path Switched Ring): In a UPSR, two redundant (path-level) copies of protected traffic are sent in either direction around a ring. A selector at the egress node determines the higher-quality copy and decides to use the best copy, thus coping if deterioration in one copy occurs due to a broken fiber or other failure. UPSRs tend to sit nearer to the edge of a network and, as such, are sometimes called "collector rings". Because the same data is sent around the ring in both directions, the total capacity of a UPSR is equal to the line rate N of the OC-N ring. For example if we had an OC-3 ring with 3 STS-1s used to transport 3 DS-3s from ingress node A to the egress node D, then 100% of the ring bandwidth (N=3) would be consumed by nodes A and D. Any other nodes on the ring, say B and C could only act as pass through nodes. The SDH analog of UPSR is Subnetwork Connection Protection (SNCP); however, SNCP does not impose a ring topology, but may also be used in mesh topologies.
• BLSR (Bidirectional Line Switched Ring): BLSR comes in two varieties, 2-fiber BLSR and 4-fiber BLSR. BLSRs switch at the line layer. Unlike UPSR, BLSR does not send redundant copies from ingress to egress. Rather, the ring nodes adjacent to the failure reroute the traffic "the long way" around the ring. BLSRs trade cost and complexity for bandwdith efficiency as well as the ability to support "extra traffic", which can be pre-empted when a protection switching event occurs. BLSRs can operate within a metropolitan region or, often, will move traffic between municipalities. Because a BLSR does not send redundant copies from ingress to egress the total bandwidth that a BLSR can support is not limited to the line rate N of the OC-N ring and can actually be larger than N depending upon the traffic pattern on the ring. The best case of this is that all traffic is between adjacent nodes. The worst case is when all traffic on the ring egresses from a single node, i.e. the BLSR is serving as a collector ring. In this case the bandwidth that the ring can support is equal to the line rate N of the OC-N ring. This is why BLSRs are seldom if ever deployed in collector rings but often deployed in inter-office rings. The SDH equivalent of BLSR is called Multiplex Section-Shared Protection Ring (MS-SPRING).
Clock sources used by Synchronization in telecommunications networks are rated by quality, commonly called a 'stratum' level. Typically, a network element uses the highest quality stratum available to it, which can be determined this by monitoring the Synchronization Status Messages(SSM) of selected clock sources.
As for Synchronization sources available to an NE, these are:
• Local External Timing. This is generated by an atomic Caesium clock or a satellite-derived clock by a device located in the same central office as the NE. The interface is often a DS1, with Sync Status Messages supplied by the clock and placed into the DS1 overhead.
• Line-derived timing. An NE can choose (or be configured) to derive its timing from the line-level, by monitoring the S1 sync status bytes to ensure quality.
• Holdover. As a last resort, in the absence of higher quality timing, an NE can go into "holdover" until higher quality external timing becomes available again. In this mode, an NE uses its own timing circuits as a reference.
Timing loops
A timing loop occurs when NEs in a network are each deriving their timing from other NEs, without any of them being a "master" timing source. This network loop will eventually see its own timing "float away" from any external networks, causing mysterious bit errors and ultimately, in the worst cases, massive loss of traffic. The source of these kinds of errors can be hard to diagnose. In general, a network that has been properly configured should never find itself in a timing loop, but some classes of silent failures could nevertheless cause this issue.
Next-generation SONET/SDH
SONET/SDH development was originally driven by the need to transport multiple PDH signals like DS1, E1, DS3 and E3 along with other groups of multiplexed 64 kbit/s pulse-code modulated voice traffic. The ability to transport ATM traffic was another early application. In order to support large ATM bandwidths, the technique of concatenation was developed, whereby smaller multiplexing containers (eg, STS-1) are inversely multiplexed to build up a larger container (eg, STS-3c) to support large data-oriented pipes.
One problem with traditional concatenation, however, is inflexibility. Depending on the data and voice traffic mix that must be carried, there can be a large amount of unused bandwidth left over, due to the fixed sizes of concatenated containers. For example, fitting a 100 Mbit/s Fast Ethernet connection inside a 155 Mbit/s STS-3c container leads to considerable waste.
Virtual Concatenation (VCAT) allows for a more arbitrary assembly of lower order multiplexing containers, building larger containers of fairly arbitrary size (e.g. 100 Mbit/s) without the need for intermediate NEs to support this particular form of concatenation. Virtual Concatenation increasingly leverages X.86 or Generic Framing Procedure (GFP) protocols in order to map payloads of arbitrary bandwidth into the virtually concatenated container.
Link Capacity Adjustment Scheme (LCAS) allows for dynamically changing the bandwidth via dynamic virtual concatenation, multiplexing containers based on the short-term bandwidth needs in the network.
The set of next generation SONET/SDH protocols to enable Ethernet transport is referred to as Ethernet over SONET/SDH (EoS).
1. ^ International Engineering Consortium SONET Tutorial, undated, URL retrieved on 21 April 2007
External links
• Understanding SONET/SDH
• The Queen's University of Belfast SDH/SONET Primer
• SDH Pocket Handbook from Acterna/JDSU
• SONET Pocket Handbook from Acterna/JDSU
• The Sonet Homepage
• SONET Interoperability Form (SIF)
• Network Connection Speeds Reference
• Next-generation SDH and MSPP
• The Future of SONET/SDH (pdf)
• Telcordia GR 253 CORE: SONET Transport Systems: Common Generic Criteria
• ANSI T1.105: SONET - Basic Description including Multiplex Structure, Rates and Formats
• ANSI T1.119/ATIS PP 0900119.01.2006: SONET - Operations, Administration, Maintenance, and Provisioning (OAM&P) - Communications
• ITU-T recommendation G.707: Network Node Interface for the Synchronous Digital Hierarchy (SDH)
• ITU-T recommendation G.783: Characteristics of synchronous digital hierarchy (SDH) equipment functional blocks
• ITU-T recommendation G.803: Architecture of Transport Networks Based on the Synchronous Digital Hierarchy (SDH)
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Categories: SONET | Fiber-optic communications | Network protocols