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2G (or 2-G) is short for second-generation wireless telephone technology. Second generation 2G cellular telecom networks were commercially launched on the GSM standard in Finland by Radiolinja (now part of Elisa Oyj) in 1991.^[1] Three primary benefits of 2G networks over their predecessors were that phone conversations were digitally encrypted; 2G systems were significantly more efficient on the spectrum allowing for far greater mobile phone penetration levels; and 2G introduced data services for mobile, starting with SMS text messages.

After 2G was launched, the previous mobile telephone systems were retrospectively dubbed 1G. While radio signals on 1G networks are analog, radio signals on 2G networks are digital. Both systems use digital signaling to connect the radio towers (which listen to the handsets) to the rest of the telephone system.

2G has been superseded by newer technologies such as 2.5G, 2.75G, 3G, and 4G; however, 2G networks are still used in many parts of the world.

2G technologies[link]

2G technologies can be divided into TDMA-based and CDMA-based standards depending on the type of multiplexing used. The main 2G standards are:

• GSM (TDMA-based), originally from Europe but used in almost all countries on all six inhabited continents. Today accounts for over 80% of all subscribers around the world. Over 60 GSM operators are also using CDMA2000 in the 450 MHz frequency band (CDMA450).^[2]
• IS-95 aka cdmaOne (CDMA-based, commonly referred as simply CDMA in the US), used in the Americas and parts of Asia. Today accounts for about 17% of all subscribers globally. Over a dozen CDMA operators have migrated to GSM including operators in Mexico, India, Australia and South Korea.
• PDC (TDMA-based), used exclusively in Japan
• iDEN (TDMA-based), proprietary network used by Nextel in the United States and Telus Mobility in Canada
• IS-136 a.k.a. D-AMPS (TDMA-based, commonly referred as simply 'TDMA' in the US), was once prevalent in the Americas but most have migrated to GSM.

2G services are frequently referred as Personal Communications Service, or PCS, in the United States.

Capacities, advantages, and disadvantages[link]

Capacity[link]

Using digital signals between the handsets and the towers increases system capacity in two key ways:

• Digital voice data can be compressed and multiplexed much more effectively than analog voice encodings through the use of various codecs, allowing more calls to be packed into the same amount of radio bandwidth.
• The digital systems were designed to emit less radio power from the handsets. This meant that cells had to be smaller, so more cells had to be placed in the same amount of space. This was made possible by cell towers and related equipment getting less expensive.

Disadvantages[link]

• In less populous areas, the weaker digital signal may not be sufficient to reach a cell tower. This tends to be a particular problem on 2G systems deployed on higher frequencies, but is mostly not a problem on 2G systems deployed on lower frequencies. National regulations differ greatly among countries which dictate where 2G can be deployed.
• Analog has a smooth decay curve, digital a jagged steppy one. This can be both an advantage and a disadvantage. Under good conditions, digital will sound better. Under slightly worse conditions, analog will experience static, while digital has occasional dropouts. As conditions worsen, though, digital will start to completely fail, by dropping calls or being unintelligible, while analog slowly gets worse, generally holding a call longer and allowing at least a few words to get through.
• While digital calls tend to be free of static and background noise, the lossy compression used by the codecs takes a toll; the range of sound that they convey is reduced. You will hear less of the tonality of someone's voice talking on a digital cellphone, but you will hear it more clearly.

Evolution[link]

2G networks were built mainly for voice services and slow data transmission.

Some protocols, such as EDGE for GSM and 1x-RTT for CDMA2000, are defined as "3G" services (because they are defined in IMT-2000 specification documents), but are considered by the general public to be 2.5G or 2.75G services because they are several times slower than present-day 3G service.

2.5G (GPRS)[link]

2.5G ("second and a half generation") is used to describe 2G-systems that have implemented a packet-switched domain in addition to the circuit-switched domain. It does not necessarily provide faster services because bundling of timeslots is used for circuit-switched data services (HSCSD) as well.

The first major step in the evolution of GSM networks to 3G occurred with the introduction of General Packet Radio Service (GPRS). CDMA2000 networks similarly evolved through the introduction of 1xRTT. The combination of these capabilities came to be known as 2.5G.

GPRS could provide data rates from 56 kbit/s up to 115 kbit/s. It can be used for services such as Wireless Application Protocol (WAP) access, Multimedia Messaging Service (MMS), and for Internet communication services such as email and World Wide Web access. GPRS data transfer is typically charged per megabyte of traffic transferred, while data communication via traditional circuit switching is billed per minute of connection time, independent of whether the user actually is utilizing the capacity or is in an idle state.

1xRTT supports bi-directional (up and downlink) peak data rates up to 153.6 kbit/s, delivering an average user data throughput of 80-100 kbit/s in commercial networks.^[3] It can also be used for WAP, SMS & MMS services, as well as Internet access.

2.75G (EDGE)[link]

GPRS1 networks evolved to EDGE networks with the introduction of 8PSK encoding. Enhanced Data rates for GSM Evolution (EDGE), Enhanced GPRS (EGPRS), or IMT Single Carrier (IMT-SC) is a backward-compatible digital mobile phone technology that allows improved data transmission rates, as an extension on top of standard GSM. EDGE was deployed on GSM networks beginning in 2003—initially by Cingular (now AT&T) in the United States.

EDGE is standardized by 3GPP as part of the GSM family and it is an upgrade that provides a potential three-fold increase in capacity of GSM/GPRS networks. The specification achieves higher data-rates (up to 236.8 kbit/s) by switching to more sophisticated methods of coding (8PSK), within existing GSM timeslots.

See also[link]

• Mobile radio telephone, also known as 0G
• 1G
• 3G
• 4G
• 2G spectrum scam, India

References[link]

3-2-1 Contact is an American science educational television show that aired on PBS from 1980 to 1988, and an adjoining children's magazine. The show, a production of the Children's Television Workshop, teaches scientific principles and their applications. Dr. Edward G. Atkins, who was responsible for much of the scientific content of the show, felt that the TV program wouldn't replace a classroom but would open the viewers to ask questions about the scientific purpose of things.^[1]

History[link]

3-2-1 Contact was the brainchild of Samuel Y. Gibbon, Jr., who had been the executive producer of The Electric Company for CTW from 1971 to 1977. (Gibbon actually left CTW before Contact's production began, though he was still credited as "Senior Consultant.")

The first season of 65 programs began airing January 14, 1980 on select PBS member stations; it featured a cast of three college students who discussed science in an on-campus room known as the Workshop. The first season came to an end on April 11, 1980, but funds for more episodes were not sufficient until 1982.

When production resumed for the second season, which premiered on October 17, 1983, the show presented a more realistic appearance, as the new cast convened in a suburban basement (these segments were shot at Reeves Teletape, which also housed Sesame Street at the time). This cast continued until October 18, 1985. Ozzie Alfonso was Contact's new director and Al Hyslop its executive producer.

When the fifth season began on September 22, 1986, a third cast was introduced. However, unlike the previous casts, they did not meet in any specific setting; instead, they appeared in various taped and filmed segments. Episodes continued to be produced through November 1988.

For a time in the mid-1980s, the program was co-produced with the French television network FR3 and featured several new French cast members in addition to the American cast. From 1982 to 1983 the program was aired in Spain with dubbed-over versions of the American original broadcasts, and some local add-ons with four Spanish cast members: Sonia Martínez, Luis Bollain, Fernando Rueda and Marifé Rodríguez.^[2] Another Spanish version of the broadcast was aired from 1990 to 1992.

From September 1, 1991 until May 1, 1992, an edited version of the series titled 3-2-1 Classroom Contact was produced, specifically for in-school viewing.

It was reported in 1984 that 3-2-1 Contact had an audience of over 7 million viewers and was broadcast in 26 countries including West Germany, France, Italy and Spain making their own dubbed-over versions.^[1]

Broadcasters wanted the children to record the episodes without being afraid of infringement of copyright violations.^[1]

Hosts[link]

The Bloodhound Gang[link]

A frequent segment of the show was The Bloodhound Gang, a series about a group of young detectives who used science to solve crimes. Episodes of the series needed to be run in regular sequence for understandable viewing, as many Bloodhound Gang mysteries were cut among two or three Contact episodes.

The magazine[link]

Three months before the show premiered, a print magazine of the same name that also focused on science was released. In 1985, the magazine absorbed some of the content of sibling publication Enter (which went out of print that same year), including reader submissions of computer programs written in the BASIC computer language as well as reviews of popular computer programs. A new feature called "The Slipped Disk Show" appeared in mid-1985, starring a fictional disc jockey who answered computer-related questions submitted by readers.

Beginning in 1987, the magazine also featured content from another CTW production, Square One Television. Such content frequently took the form of a two-page comic strip, often parodying a popular show or movie of the time, with a math-related question at the end.

The Bloodhound Gang mysteries also made the leap to the magazine, but they were subsequently replaced with a series entitled The Time Team in September 1990. These stories found teenage characters Sean Nolan and Jenny Lopez traveling to different time periods in the past and future. Their surroundings and personal encounters were described with great detail, educating readers as to the customs of various cultures throughout history, and – on trips to the future – often pushing present day hot-button issues. For example, a 1993 story saw the duo traveling to what appeared to be a prehistoric forest, but near the end, they found a Brazil flag, a newspaper clipping from 1995, and a bulldozer at work: this was in fact a Brazilian rainforest being levelled.

In 1996, The Time Team was replaced by a comic serial, Cosmic Crew, which focused on the adventures of a group of teenagers and their robot butler in space. Their first story arc (which ran for more than a year) had them trying to figure out a series of riddles relating to places in the solar system in order to claim a treasure (which turned out to be a scholarship fund). Another story arc had a delinquent (who had been a villain in the first arc) join them in order to chase down a gang of other delinquents. Despite being effectively replaced, a few Time Team stories were run whenever there were gaps between installments of Cosmic Crew.

Many of the magazine's cover stories involved current events, such as 1990s oil fires in the Middle East. In addition, the magazine offered a games section in which most of the games were related to the stories in the issue.

In 1996, CTW presumably concluded that faithful readers from the late 1980s and early 1990s had long since moved on, and the magazine began to reprint non-time-sensitive stories from years past. For example, a 1991 article on the geography of the Galápagos Islands – a relatively unchanging subject – could very well re-appear in an identical format a half a decade later.

Under Sesame Workshop the magazine later became Contact Kids, removing the original reference to the television show. Production of the magazine was suspended indefinitely in 2001.

After production[link]

Though the show went off the air in 1988, it appeared in reruns from 1999 to 2003 on the cable television network Noggin, then a joint venture of CTW and Nickelodeon. Occasionally, shows were also rerun on Nickelodeon's Cable in the Classroom time period. For all these Nickelodeon and Noggin airings, the series was rated TV-Y7 (possibly due to the target audience). It also still aired on some PBS stations as reruns from 1989 to 1998 before it was switched to Noggin in 1999. As of 2003, Noggin no longer airs any shows produced by Sesame Workshop. The shows were modified for the shorter running time on these networks to allow for their interstitials.

Sources of funding[link]

Funding for 3-2-1 Contact was provided by the following:^[3]

• National Science Foundation (January 14, 1980–November 18, 1988)
• United States Department of Education (January 14, 1980–November 18, 1988)
• Corporation for Public Broadcasting (January 14, 1980–November 18, 1988)
• Andrew W. Mellon Foundation (January 14, 1980–November 18, 1988)
• IBM Corporation (January 14, 1980–November 18, 1988)
• Carnegie Corporation of New York (October 31, 1983-November 18, 1988)

Five sponsors funded the show for its entire run. They were originally supposed to fund for 20 new episodes until 1989.^[1]

References[link]

External links[link]

• 3-2-1 Contact at the Internet Movie Database
• 3-2-1 Contact at TV.com