ATM Adaptation Layer 2
ATM Adaptation Layer 2 is an ATM adaptation layer for Asynchronous Transfer Mode, used in telecommunications. The standard specifications related to AAL2 are ITU standards I.363.2 and I366.1. AAL2 is a variable bitrate, connection-oriented, low latency service intended to adapt voice for transmission over ATM. Like other ATM adaptation layers, AAL2 defines segmentation and reassembly of higher-layer packets into ATM cells, in this case packets of data containing voice and control information. AAL2 is further separated into two sub-layers that help with the mapping from upper layer services to ATM cells; these are named Common Part Sub-layer. The AAL2 protocol improves on other ATM Adaptation Layers, by packing lots of small packets efficiently into one standard-sized ATM cell of 53 bytes. A one-byte packet thus no longer has an overhead ratio of 52 unused bytes out of 53. Total of 11 one-byte CPS packets could squeeze into a single cell. Of course, CPS packets can come in other sizes with other CIDs, too.
When the transmission is ready, the CPS packets are all multiplexed together into a single cell and transported over standard ATM network infrastructure. The transport networks for ATM are well standardized fiber optic or copper cable based synchronous networks with built-in redundancy and OAM-related network features which Ethernet networks never had but are sorely missed in metro Ethernet standard networks. Efforts to improve Ethernet networks are in a sense trying to reinvent the wheel à la ATM. AAL2 is one example of a useful benefit of ATM, as a general standard for Layer 2 protocols. ATM/AAL2's efficient handling of small packets contrasts with Ethernet's minimum payload of 46 bytes vs the 1-byte minimum size for an AAL2 CPS packet. AAL2 is the standard layer 2 protocol used in all Iu interfaces, i.e. the interfaces between UMTS base stations and UMTS Radio Network Controllers, inter-RNCs, UMTS RNCs and UMTS Serving GPRS Support Nodes, UMTS RNCs and media gateways. The basic component of AAL2 is the CPS packet.
A CPS packet is an unanchored unit of data that can cross ATM cells and can start from anywhere in the payload of the ATM cell, other than the start field. The STF is the first byte of the 48-byte ATM payload; the STF gives the byte index into the ATM cell. Byte 0 is the STF; the data from byte 1... would be the straddled remainder of the previous ATM cell's final CPS packet. If there is no remainder from the previous cell, the STF is 0, the first byte of the cell after the STF is the location of the start of the first CPS packet; the format for the 1 byte STF at the beginning of the ATM cell is: 6 bits - offset field 1 bit - sequence number 1 bit - parity The Offset Field carries the binary value of the offset, in octets, between the end of the P bit and the start of the CPCS-PDU Payload. Values of greater than 47 are not allowed; the Sequence Number numbers the stream of CPCS-PDUs. The Parity bit is used to detect error in the SN fields. If the ATM cell has fewer than 47 bytes, the remainder will be filled by padding.
One common adaptation of AAL2, AAL2u, doesn't use the STF field at all. In this case, one single CPS packet is aligned to the beginning of the cell. AAL2u is not used in standardized interfaces, but rather in proprietary equipment implementations where the multiplexing/demultiplexing, etc. that needs to be done for standard AAL2 either is too strenuous, is unsupported, or requires too much overhead from the internal system's point of view. Most computer chips do not support AAL2, so stripping this layer away makes it easier to interwork between the ATM interface and the rest of the network; the following is diagram of the AAL2 ATM cell: A CPS packet has a 3-byte header and a payload of between one and 45 octets. The standard defines a 64-octet mode, but this is not used in real 3G networks; the 3-byte CPS header has following fields: 8 bits - channel identifier 6 bits - length indicator 5 bits - user to user indication 5 bits - header error control The Channel Identifier identifies the user of the channel.
The AAL2 channel is a bi-directional channel and the same channel identification value is used for both directions. The maximum number of multiplexed user channels is 248; as some channels are reserved for other uses, such as peer-to-peer layer management. CE: Channel Element CID = CE -E + ID The Length Indicator indicates the length of the CPS information field, can have a value between 1 and 45 or sometimes between 1 and 64. For a given CID all channels must be of the same maximum length NB: the LI is one less than the actual length of the payload, so 0 corresponds to the minimum length of 1 octet, 0x3f to 64 octets. User to User Indication conveys specific information transparently between the users. For example, in SSSAR, UUI is used to indicate that this is the final CPS packet for the SSSAR PDU; this is checks for errors in the CID, LI and UUI fields. The generator polynomial for the CPS HEC is: G = x 5 + x 2 + 1 The following is a diagram of the CPS packet: Broadband Forum - ATM
Telecommunication is the transmission of signs, messages, writings and sounds or information of any nature by wire, optical or other electromagnetic systems. Telecommunication occurs when the exchange of information between communication participants includes the use of technology, it is transmitted either electrically over physical media, such as cables, or via electromagnetic radiation. Such transmission paths are divided into communication channels which afford the advantages of multiplexing. Since the Latin term communicatio is considered the social process of information exchange, the term telecommunications is used in its plural form because it involves many different technologies. Early means of communicating over a distance included visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, optical heliographs. Other examples of pre-modern long-distance communication included audio messages such as coded drumbeats, lung-blown horns, loud whistles. 20th- and 21st-century technologies for long-distance communication involve electrical and electromagnetic technologies, such as telegraph and teleprinter, radio, microwave transmission, fiber optics, communications satellites.
A revolution in wireless communication began in the first decade of the 20th century with the pioneering developments in radio communications by Guglielmo Marconi, who won the Nobel Prize in Physics in 1909, other notable pioneering inventors and developers in the field of electrical and electronic telecommunications. These included Charles Wheatstone and Samuel Morse, Alexander Graham Bell, Edwin Armstrong and Lee de Forest, as well as Vladimir K. Zworykin, John Logie Baird and Philo Farnsworth; the word telecommunication is a compound of the Greek prefix tele, meaning distant, far off, or afar, the Latin communicare, meaning to share. Its modern use is adapted from the French, because its written use was recorded in 1904 by the French engineer and novelist Édouard Estaunié. Communication was first used as an English word in the late 14th century, it comes from Old French comunicacion, from Latin communicationem, noun of action from past participle stem of communicare "to share, divide out.
Homing pigeons have been used throughout history by different cultures. Pigeon post had Persian roots, was used by the Romans to aid their military. Frontinus said; the Greeks conveyed the names of the victors at the Olympic Games to various cities using homing pigeons. In the early 19th century, the Dutch government used the system in Sumatra, and in 1849, Paul Julius Reuter started a pigeon service to fly stock prices between Aachen and Brussels, a service that operated for a year until the gap in the telegraph link was closed. In the Middle Ages, chains of beacons were used on hilltops as a means of relaying a signal. Beacon chains suffered the drawback that they could only pass a single bit of information, so the meaning of the message such as "the enemy has been sighted" had to be agreed upon in advance. One notable instance of their use was during the Spanish Armada, when a beacon chain relayed a signal from Plymouth to London. In 1792, Claude Chappe, a French engineer, built the first fixed visual telegraphy system between Lille and Paris.
However semaphore suffered from the need for skilled operators and expensive towers at intervals of ten to thirty kilometres. As a result of competition from the electrical telegraph, the last commercial line was abandoned in 1880. On 25 July 1837 the first commercial electrical telegraph was demonstrated by English inventor Sir William Fothergill Cooke, English scientist Sir Charles Wheatstone. Both inventors viewed their device as "an improvement to the electromagnetic telegraph" not as a new device. Samuel Morse independently developed a version of the electrical telegraph that he unsuccessfully demonstrated on 2 September 1837, his code was an important advance over Wheatstone's signaling method. The first transatlantic telegraph cable was completed on 27 July 1866, allowing transatlantic telecommunication for the first time; the conventional telephone was invented independently by Alexander Bell and Elisha Gray in 1876. Antonio Meucci invented the first device that allowed the electrical transmission of voice over a line in 1849.
However Meucci's device was of little practical value because it relied upon the electrophonic effect and thus required users to place the receiver in their mouth to "hear" what was being said. The first commercial telephone services were set-up in 1878 and 1879 on both sides of the Atlantic in the cities of New Haven and London. Starting in 1894, Italian inventor Guglielmo Marconi began developing a wireless communication using the newly discovered phenomenon of radio waves, showing by 1901 that they could be transmitted across the Atlantic Ocean; this was the start of wireless telegraphy by radio. Voice and music had little early success. World War I accelerated the development of radio for military communications. After the war, commercial radio AM broadcasting began in the 1920s and became an important mass medium for entertainment and news. World War II again accelerated development of radio for the wartime purposes of aircraft and land communication, radio navigation and radar. Development of stereo FM broadcasting of radio
UMTS Terrestrial Radio Access Network
UTRAN is a collective term for the network and equipment that connects mobile handsets to the public telephone network or the Internet. It contains the base stations, which are called Node B's and Radio Network Controllers which make up the UMTS radio access network; this communications network referred to as 3G, can carry many traffic types from real-time Circuit Switched to IP based Packet Switched. The UTRAN allows connectivity between the core network; the RNC provides control functionalities for one or more Node Bs. A Node B and an RNC can be the same device, although typical implementations have a separate RNC located in a central office serving multiple Node Bs. Despite the fact that they do not have to be physically separated, there is a logical interface between them known as the Iub; the RNC and its corresponding Node Bs are called the Radio Network Subsystem. There can be more than one RNS present in a UTRAN. There are four interfaces connecting the UTRAN internally or externally to other functional entities: Iu, Uu, Iub and Iur.
The Iu interface is an external interface. The Uu is external, connecting the Node B with the User Equipment; the Iub is an internal interface connecting the RNC with the Node B. And at last there is the Iur interface, an internal interface most of the time, but can, exceptionally be an external interface too for some network architectures; the Iur connects two RNCs with each other. UMTS - Universal Mobile Telecommunications System GERAN - GSM EDGE Radio Access Network
The Universal Mobile Telecommunications System is a third generation mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP, UMTS is a component of the International Telecommunications Union IMT-2000 standard set and compares with the CDMA2000 standard set for networks based on the competing cdmaOne technology. UMTS uses wideband code division multiple access radio access technology to offer greater spectral efficiency and bandwidth to mobile network operators. UMTS specifies a complete network system, which includes the radio access network, the core network and the authentication of users via SIM cards; the technology described in UMTS is sometimes referred to as Freedom of Mobile Multimedia Access or 3GSM. Unlike EDGE and CDMA2000, UMTS requires new base stations and new frequency allocations. UMTS supports maximum theoretical data transfer rates of 42 Mbit/s when Evolved HSPA is implemented in the network. Users in deployed networks can expect a transfer rate of up to 384 kbit/s for Release'99 handsets, 7.2 Mbit/s for High-Speed Downlink Packet Access handsets in the downlink connection.
These speeds are faster than the 9.6 kbit/s of a single GSM error-corrected circuit switched data channel, multiple 9.6 kbit/s channels in High-Speed Circuit-Switched Data and 14.4 kbit/s for CDMAOne channels. Since 2006, UMTS networks in many countries have been or are in the process of being upgraded with High-Speed Downlink Packet Access, sometimes known as 3.5G. HSDPA enables downlink transfer speeds of up to 21 Mbit/s. Work is progressing on improving the uplink transfer speed with the High-Speed Uplink Packet Access. 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 orthogonal frequency-division multiplexing; the first national consumer UMTS networks launched in 2002 with a heavy emphasis on telco-provided mobile applications such as mobile TV and video calling. The high data speeds of UMTS are now most utilised for Internet access: experience in Japan and elsewhere has shown that user demand for video calls is not high, telco-provided audio/video content has declined in popularity in favour of high-speed access to the World Wide Web—either directly on a handset or connected to a computer via Wi-Fi, Bluetooth or USB.
UMTS combines three different terrestrial air interfaces, GSM's Mobile Application Part core, the GSM family of speech codecs. The air interfaces are called UMTS Terrestrial Radio Access. All air interface options are part of ITU's IMT-2000. In the most popular variant for cellular mobile telephones, W-CDMA is used, it is called "Uu interface", as it links User Equipment to the UMTS Terrestrial Radio Access Network Please note that the terms W-CDMA, TD-CDMA and TD-SCDMA are misleading. While they suggest covering just a channel access method, they are the common names for the whole air interface standards. W-CDMA or WCDMA, along with UMTS-FDD, UTRA-FDD, or IMT-2000 CDMA Direct Spread is an air interface standard found in 3G mobile telecommunications networks, it supports conventional cellular voice, text and MMS services, but can carry data at high speeds, allowing mobile operators to deliver higher bandwidth applications including streaming and broadband Internet access. W-CDMA uses the DS-CDMA channel access method with a pair of 5 MHz wide channels.
In contrast, the competing CDMA2000 system uses one or more available 1.25 MHz channels for each direction of communication. W-CDMA systems are criticized for their large spectrum usage, which delayed deployment in countries that acted slowly in allocating new frequencies for 3G services; the specific frequency bands defined by the UMTS standard are 1885–2025 MHz for the mobile-to-base and 2110–2200 MHz for the base-to-mobile. In the US, 1710–1755 MHz and 2110–2155 MHz are used instead, as the 1900 MHz band was used. While UMTS2100 is the most deployed UMTS band, some countries' UMTS operators use the 850 MHz and/or 1900 MHz bands, notably in the US by AT&T Mobility, New Zealand by Telecom New Zealand on the XT Mobile Network and in Australia by Telstra on the Next G network; some carriers such as T-Mobile use band numbers to identify the UMTS frequencies. For example, Band I, Band IV, Band V. UMTS-FDD is an acronym for Universal Mobile Telecommunications System - frequency-division duplexing and a 3GPP standardized version of UMTS networks that makes use of frequency-division duplexing for duplexing over an UMTS Terrestrial Radio Access air interface.
W-CDMA is the basis of Japan's NTT DoCoMo's FOMA service and the most-commonly used member of the Universal Mobile Telecommunications System family and sometimes used as a synonym for UMTS. It uses the DS-CDMA channel access method and the FDD duplexing method to achieve higher speeds and support more users compared to most used time division multiple access and time division duplex schemes. While not an evolutionary upgrade on the airside, it uses the same core network as the 2G GSM networks deployed worldwide, allowing dual mode mobile operation al