3G (Third generation of mobile telephony)

3G refers to the third generation of mobile telephony (that is, cellular) technology. The third generation, as the name suggests, follows two earlier generations.
The first generation (1G) began in the early 80's with commercial deployment of Advanced Mobile Phone Service (AMPS) cellular networks. Early AMPS networks used Frequency Division Multiplexing Access (FDMA) to carry analog voice over channels in the 800 MHz frequency band.
The second generation (2G) emerged in the 90's when mobile operators deployed two competing digital voice standards. In North America, some operators adopted IS-95, which used Code Division Multiple Access (CDMA) to multiplex up to 64 calls per channel in the 800 MHz band. Across the world, many operators adopted the Global System for Mobile communication (GSM) standard, which used Time Division Multiple Access (TDMA) to multiplex up to 8 calls per channel in the 900 and 1800 MHz bands.
The International Telecommunications Union (ITU) defined the third generation (3G) of mobile telephony standards IMT-2000 to facilitate growth, increase bandwidth, and support more diverse applications. For example, GSM could deliver not only voice, but also circuit-switched data at speeds up to 14.4 Kbps. But to support mobile multimedia applications, 3G had to deliver packet-switched data with better spectral efficiency, at far greater speeds.
However, to get from 2G to 3G, mobile operators had make "evolutionary" upgrades to existing networks while simultaneously planning their "revolutionary" new mobile broadband networks. This lead to the establishment of two distinct 3G families: 3GPP and 3GPP2.
The 3rd Generation Partnership Project (3GPP) was formed in 1998 to foster deployment of 3G networks that descended from GSM. 3GPP technologies evolved as follows.
• General Packet Radio Service (GPRS) offered speeds up to 114 Kbps.
• Enhanced Data Rates for Global Evolution (EDGE) reached up to 384 Kbps.
• UMTS Wideband CDMA (WCDMA) offered downlink speeds up to 1.92 Mbps.
• High Speed Downlink Packet Access (HSDPA) boosted the downlink to 14Mbps.
• LTE Evolved UMTS Terrestrial Radio Access (E-UTRA) is aiming for 100 Mbps.

GPRS deployments began in 2000, followed by EDGE in 2003. While these technologies are defined by IMT-2000, they are sometimes called "2.5G" because they did not offer multi-megabit data rates. EDGE has now been superceded by HSDPA (and its uplink partner HSUPA). According to the 3GPP, there were 166 HSDPA networks in 75 countries at the end of 2007. The next step for GSM operators: LTE E-UTRA, based on specifications completed in late 2008.
A second organization, the 3rd Generation Partnership Project 2 (3GPP2) -- was formed to help North American and Asian operators using CDMA2000 transition to 3G. 3GPP2 technologies evolved as follows.

• One Times Radio Transmission Technology (1xRTT) offered speeds up to 144 Kbps.
• Evolution Data Optimized (EV-DO) increased downlink speeds up to 2.4 Mbps.
• EV-DO Rev. A boosted downlink peak speed to 3.1 Mbps and reduced latency.
• EV-DO Rev. B can use 2 to 15 channels, with each downlink peaking at 4.9 Mbps.
• Ultra Mobile Broadband (UMB) was slated to reach 288 Mbps on the downlink.

1xRTT became available in 2002, followed by commercial EV-DO Rev. 0 in 2004. Here again, 1xRTT is referred to as "2.5G" because it served as a transitional step to EV-DO. EV-DO standards were extended twice . Revision A services emerged in 2006 and are now being succeeded by products that use Revision B to increase data rates by transmitting over multiple channels. The 3GPP2's next-generation technology, UMB, may not catch on, as many CDMA operators are now planning to evolve to LTE instead.
In fact, LTE and UMB are often called 4G (fourth generation) technologies because they increase downlink speeds an order of magnitude. This label is a bit premature because what constitutes "4G" has not yet been standardized. The ITU is currently considering candidate technologies for inclusion in the 4G IMT-Advanced standard, including LTE, UMB, and WiMAX II. Goals for 4G include data rates of least 100 Mbps, use of OFDMA transmission, and packet-switched delivery of IP-based voice, data, and streaming multimedia.

Based on the International Telecommunications Union standards, the 3G network is the third generation of mobile networking and telecommunications. It features a wider range of services and advances network capacity over the previous 2G network. The 3G network also increases the rate of information transfer known as spectral efficiency. Telephony has received a wider area and more range, while video and broadband wireless data transfers have also been positively affected. These criteria are identified as the IMT-2000 standard.
A 3G network provides for download speeds of 14.4 megabits per second and upload speeds of 5.8 megabits per second. The minimum speed for a stationary user is 2 megabits per second. A user in a moving vehicle can expect 348 kilobits per second.

U Mobile Ropes In China's ZTE To Extend Mobile Network
KUALA LUMPUR, March 15 (Bernama) -- U Mobile Sdn Bhd and ZTE Corporation of China today signed an agreement which will see the local 3G mobile service operator extending its 42 Mbps network in the Klang Valley, Negeri Sembilan and the northern region by the second half of 2011.

The three-year deal also provides for the installation of LTE (long term evolution) platforms in line with the plan to bring 100 Mbps wireless network across key cities in Malaysia.

Present at the signing ceremony here were Information Communication and Culture Minister Datuk Seri Utama Dr Rais Yatim and Chinese Ambassador to Malaysia Chai Xi.

"In view of this strategic partnership, U Mobile is seen to be taking the way forward in providing the latest wireless technology for the country.

"Within the next 12 months, one should see an upgrade of U Mobile's 42 Mbps to 84 Mbps capability. A user's internet experience is likely to be ten times faster than the current rate," the companies said in a joint statement on Tuesday.

It also said that LTE technology in Malaysia would utilise 2.6 Gigahertz band and at the moment, final award of spectrum was still pending.

"Commercial launch is largely depending on the spectrum award timing by the Malaysian Communications and Multimedia Commission, and the availability of devices," it said.

Meanwhile, U Mobile chief executive officer Dr Kaizad Heerjee said his company aimed to roll out additionally 2,000 to 3,000 mobile base stations across Malaysia in the next 12 to 18 months.

Currently, it has more than 1,000 mobile base stations installed covering the Klang Valley, Seremban, Ipoh, Penang and Johor Baharu.
 Chinese telecom equipment maker Huawei Technologies has announced that it has signed a USD100 million contract with the New Zealand-based mobile network 2degrees to help the company upgrade its network over the next two years.
Eric Hertz, chief executive officer of 2degrees, said that the investment will ensure the company's network is ready to handle the requirement of the fourth-generation smartphones. It is learned that 2degrees already provides its customers with nationwide 2G and 3G mobile services via its own network and commercial roaming.
Hertz said that they are conscious that they need to build networks that deliver on tomorrow's speed and capacity demands, so being able to upgrade to 4G via a software activation rather than a network rebuild is especially important.
Winning the deal following a competitive process, Huawei will provide a turn-key project solution to meet 2degrees' development requirement. Arthur Zhang, Huawei New Zealand CEO, said that the fact that 2degrees has chosen Huawei as its partner for the building of phase two of its network marks a vote of confidence in Huawei's technology and its ability to build a world-class network for 2degrees' customers.

An interview with Zeng Xuezhong, Senior Vice President of ZTE Corporation

P&T/EXPO COMM CHINA 2010, to be held in Beijing this October, will be the most influential ICT event this year. The theme of the EXPO is tri-network convergence, and topics such as TD/LTE/4G evolution, green telecom, and Internet of Things will be discussed. In the lead up to the event, journalist Zhao Lili interviewed Zeng Xuezhong, Senior Vice President of ZTE Corporation, to find out how ZTE is working with Chinese operators to develop a new industrial chain in a new industrial environment.

Journalist: 2009 saw the birth of 3G in China, and the country’s three major operators have been involved in 3G network deployment and operation ever since. What role has ZTE played in China’s 3G deployment? And how will ZTE establish strategic partnerships with these operators to develop their networks to LTE?
Zeng: In 2009, China’s Ministry of Industry and Information Technology issued 3G licenses to China Mobile (TD-SCDMA), China Unicom (WCDMA), and China Telecom (CDMA). This marked the formal entry of China into the 3G era, and for the first time, placed Chinese telecom vendors on an even footing with foreign competitors. ZTE is not only a key participant in China’s 3G network construction, but also an advocate for 3G industry development and technological innovation.
According to a report released by iSuppli in January 2010, ZTE holds the largest share in China’s 3G market. In the TD-SCDMA sector, ZTE has been a strategic partner of China Mobile throughout its TD network construction—from the phase one and two network trials in 2007 and 2008 to the large-scale phase three commercialization in 2009. ZTE has played a key role in China Mobile’s technical innovation, industrialization, network deployment, and service delivery.
ZTE has also become the industry leader in CDMA, holding the largest market share in China since 2007.  Close cooperation was established with China Telecom after it was awarded a CDMA license, and ZTE infrastructure equipment has now been deployed in 27 provinces throughout the country. ZTE helped China Telecom build approximately 60% of its local CDMA networks at the prefecture level, and undertook most of its 3G network planning, construction, and maintenance.
ZTE has also been a key supplier to China Unicom since the company started WCDMA network deployment in 2009. ZTE’s market share increased during phase two, phase three, and phase four of China Unicom’s WCDMA project. The largest share was clinched in phase four of the project, which covered 20 provinces and 108 cities. Leveraging its implementation efficiency and service capability, ZTE became the leader in fast project completion. Moreover, network tests were passed with excellent results. All this demonstrates ZTE’s comprehensive strength in the WCDMA field.
Operators worldwide are closely monitoring the evolution of 3G to LTE, and some are even initiating the process. ZTE is devoted to LTE research and development, and is continually increasing its strategic funding in both FDD and TDD. We have applied for more than 1,700 LTE patents, and own basic patents of the LTE standard. With a quality product portfolio and a growth strategy that is prudent and sustainable, ZTE is ranked among the Top 3 players in terms of LTE strength by research firm Garnet.
ZTE offers sophisticated services for TD-SCDMA, CDMA2000, and WCDMA, working with operators to develop the whole industrial chain. We are highly recognized by operators for our innovation mechanism, long-term strategies, and enhanced brand image. Chinese telecom vendors are certainly capable of competing with global telecom giants. The 3G era is a turning point for China’s telecom industry and is of far-reaching significance.

J: The theme of P&T/EXPO COMM CHINA 2010 is tri-network convergence, and the Chinese government has put in place support policies to speed up this process. What changes will happen in China’s telecom industry, and what challenges and opportunities will this present to equipment vendors?
Zeng: In January 2010, the State Council passed a general proposal for speeding up the convergence of telecommunications, broadcast TV, and Internet networks. This proposal will alter the whole industry, not only driving the growth of telecommunications, broadcast TV, and Internet businesses in China, but also presenting opportunities and challenges to all parties in the industrial chain.
Tri-network convergence will change the competition pattern of China’s telecommunications industry.  For equipment vendors, it will lead to increasing demands for equipment because of network construction and upgrade requirements. More importantly, as telecom operators transform into service providers, equipment vendors will also transform from simple equipment suppliers to end-to-end full-service solution providers. The group of three major operators in China will expand to include CATV operators. These new operators will have diversified business models and will challenge traditional operators with their control over TV content and broadcasting rights. Both telecom and CATV operators will have to innovate and explore new areas of business to gain a competitive advantage, and this will create new market and cooperative opportunities. Demand for triple play services will grow, and emerging multimedia services such as position shift TV (PSTV), interactive TV, high definition video, mobile monitoring, and mobile TV, will be widely sought after. Moreover, with the current bandwidth restrictions for broadband services, telecom operators will be compelled to increase network access bandwidth and to widely deploy FTTH networks. Likewise, because cable networks are incapable of bidirectional transmission, CATV operators will be compelled to restructure their networks as digital two-way systems.
Changes brought about by tri-network convergence will present opportunities and challenges for equipment vendors, but the opportunities are greater than the challenges. The entire industrial chain will be reshuffled. Infrastructure equipment vendors, service equipment vendors, OSS providers, high-end integrated terminal suppliers, and content and service providers will become the market’s focus of attention. With the most complete range of infrastructure, service, OSS, and terminal equipment, ZTE has much experience in integrated broadcasting and control platforms, interactive and converged services, transmission, IP, fixed-line networks, and service software. Drawing on the advantages of our products and end-to-end network solutions, ZTE will continue to be a key player in tri-network convergence, and will further improve its ability to rapidly respond to operator needs.

J: Green technology, carbon reduction, and energy conservation are of paramount importance in today’s telecommunications industry. What requirements are implied by these issues and how will equipment vendors and operators adapt to such requirements? Specifically, what is ZTE doing to minimize negative environmental impact?
Zeng: Green products, carbon reduction, and energy conservation are now integrally linked to the sustainable development of telecom enterprises, and represent a revolution in values, concepts, production modes, and lifestyles. In a recent government work report, Premier Wen Jiabao stated that the global financial crisis was giving rise to a technological and industrial revolution, and that great efforts should be made in developing emerging strategic industries including new energies, new materials, information networks, and high-end manufacturing. The ICT industry is vitally important in promoting a low-carbon economy.
Telecom vendors and operators must play an active role in a new low-carbon economy, and are obliged to promote healthier, more sustainable telecom models. To create green, innovative networks, and to drive sustainable development across the industry, ZTE has incorporated energy conservation and environmental protection into its technological innovation, product R&D, and manufacturing.
We have been active in drafting international standards, and have established a complete green operation and evaluation system incorporating product research, implementation, supervision, and management. Environmental protection is at the forefront of our product design, testing, and manufacturing, and this helps reduce TCO while improving profitability. Green packing, transportation, installation, and operation and maintenance are implemented as part of our logistics and project delivery. Moreover, we provide unified all-IP platforms, IMS core networks, IP service engines, multi-mode BSCs, and renewable energy sources for network evolution and convergence. Power consumption of base stations can be reduced by 30% or more over a 24 hour period, which translates into savings of up to 6,300kWh per site each year. Reducing power consumption of base stations implies limiting the use of auxiliary devices associated with power supply, cooling, and maintenance. When combined with new energy resources such as solar or wind, power savings of around 50% are achievable. These efforts are examples of how ZTE is developing green, low-carbon, and energy-saving products.

J: Driven by new service demands, new business models and new technologies such as Cloud Computing, Internet of Things, and mobile Internet have emerged and are being enthusiastically promoted within the industry. How will vendors and operators change their supply and demand relationships to cope with new forms of competition?
Zeng: The emergence of Cloud Computing, Internet of Things, and mobile Internet has driven operator demands for new products, industrial convergence, and business innovation.
Increasingly, equipment vendors are being asked to not only provide upgrade solutions for products and platforms, but also to develop new products. They must meet network requirements in a new industrial environment.
Today, the telecom industry is converging with IT, entertainment, Internet, and even traditional logistics,  and this trend inevitably presents challenges and opportunities to all parties in the industrial chain.  Traditional telecom enterprises, however, may have little knowledge of other fields. Providing operators with new products and technologies is not the only role played by telecom vendors; they must also work with operators to explore future technological trends, network development, and business models. As well as helping operators increase efficiency and profitability, vendors will become long-term strategic partners in the joint exploration of new market opportunities.
With the widespread deployment of 3G networks throughout China, operators have transformed into full-service providers. 3G service operation has become a primary focus, and mobile Internet strategies have been put forth. Since the first half of 2009, ZTE has been helping China Telecom build its software stores and this year won a project to build China Unicom’s software store. ZTE is working hard to enhance its service innovation, and is partnering with operators to offer high quality feature-rich 3G services.

J: Finally, what are the future plans of ZTE in China?
Zeng: China is a very important market for ZTE. In the coming years, we intend to continue helping domestic operators explore opportunities and to maintain our own high speed growth. Drawing on our strength in integrated solutions, quality project delivery, and technological innovation, we will cooperate with our partners to satisfy requirements for mobile broadband, to thoroughly enhance service quality, and to contribute to the country’s industrialization and information building.
On the whole, ZTE will enhance its ability to deliver integrated solutions and resources, and will seek to improve its competitive strategies, product planning and deployment, and market behaviors to provide operators with a full range of products and services. Although rooted in China, ZTE is stepping forward to world-class excellence by further improving operational efficiency and developing its global strategy.

TeliaSonera and Ncell bring 3G high speed communication to Mount Everest area

TeliaSonera today announced that its subsidiary in Nepal, Ncell, has successfully launched 3G services in the Mount Everest area. By the end of 2011 Ncell will provide mobile coverage to over 90 percent of the people in Nepal.
"This is a great milestone for mobile communications, and strong evidence of TeliaSonera’s pioneering role in this industry that is truly changing the lives of billions of people”, said Lars Nyberg, President and CEO of TeliaSonera.
“We are very proud to announce the world’s highest mobile data service as we launch 3G services in the Mount Everest area in the Khumbu valley. From its perch on the world’s tallest mountain, 3G high speed internet will bring faster, more affordable telecommunication services to the people living in the Khumbu Valley, trekkers, and climbers alike”, he continued.
Located at an altitude of 5,200 meter the highest 3G base station enables locals, climbers and trekkers to surf the web, send video clips and e-mails, as well as to call friends and family back home – all at far cheaper rates than the average satellite phone. Everest base camp just came a little closer.
3G grows subscriber base
Through the expanding 3G network, Ncell will also provide affordable services to the entire population of Nepal. Mobile penetration is still low, but rapidly rising. This trend is being driven largely by investments TeliaSonera and others are making in modern telecom infrastructure. When TeliaSonera entered Nepal in 2008, mobile penetration was around 15 percent, and by the end of the third quarter this year it was already over 30% percent. Ncell already boasts 3.7 million subscribers and the advent of the 3G network is expected to boost this subscriber base.
At a press conference held today in Kathmandu, Lars Nyberg, President and CEO, Tero Kivisaari, President of Business Area Eurasia and Pasi Koistinen, CEO of Ncell, also unveiled plans for future TeliaSonera investments in Nepal. TeliaSonera has decided to increase the pace of investment for 2011 and spend over 100 M USD. This will ensure mobile coverage to over 90% of the population with affordable telecom services that contribute to the economic and social development of the country, as well as 3G coverage in all major cities and other densely populated areas.
Click here to see the Finn Veikka Gustafsson, one of the few in the world to have climbed all the world’s highest mountains without bottled oxygen, talk about the importance and possibilities of the new 3G services in the Mount Everest basecamp


1.1 Background
Mobile radio communications dates back to Marconi. For a time it was the principal application of radio. This was ship-to-shore and ship-to-ship communications. The pioneer in this was the Marconi Company of the United Kingdom. It spread to land vehicles and aircraft in the 1920s. Since 1980, mobile radio communication has taken on a more personal flavor.
Cellular radio systems have extended the telephone network to the car, to the pedestrian, and even into the home and office. A new and widely used term in our vocabulary is personal communications. It is becoming the universal tether. No matter where we go, on land, at sea, and in the air, we can have near instantaneous
two-way communications by voice, data, and facsimile. At some time it will encompass video.
Personal radio terminals are becoming smaller. There is the potential of becoming wristwatch size. However, the human interface requires input–output devices that have optimum usefulness. A wristwatch-size keyboard or keypad is rather difficult to operate. A hard-copy printer requires some minimum practical dimensions,
and so forth. A new name has entered our vocabulary, wireless. The British have been using the term since Marconi. It is relatively new in North America, and with a different flavor in meaning. I think we can define wireless as a telecommunication method that does not require wires to communicate. From our perspective, wireless and radio are synonymous.
Reference 28 states that there were 1 billion (1 × 109) by the end of 2002;
and Reference 27 expects there to be 3 billion (3 × 109) traditional telephone and wireless users in the world by the year 2010. It is our opinion that this latter estimate may be on the low side.
1.2 Scope and Objective
This chapter presents an overview of “personal communications” or what many call wireless. Much of the discussion deals with cellular radio and wireless LANs (WLANs), and it extends this thinking inside of buildings. The coverage most necessarily includes propagation for the several environments, propagation
impairments, and methods to mitigate these impairments, access techniques, bandwidth limitations, and ways around this problem. It will cover several mobile radio standards and compare a number of existing and planned systems. The chapter objective is to provide an appreciation of mobile/personal communications.
Space limitations force us to confine our discussion to what might be loosely called “land mobile systems.”
Cellular radio systems connect a mobile terminal to another user, usually through the PSTN. The “other user” most commonly is a telephone subscriber of the PSTN. However, the other user may be another mobile terminal. Most of the connectivity is extending POTS to mobile users. Data and facsimile services are
in various stages of implementation (see Chapter 13, Section 6). Some of the terms used in this section have a strictly North American flavor. The heart of the system for a specific serving area is the mobile telephone switching office (MTSO). The MTSO is connected by a trunk group to a nearby telephone exchange providing an interface to, and connectivity with, the PSTN. The area to be served by a cellular geographic serving area (CGSA) is divided into small geographic cells which ideally are hexagonal. Cells are initially laid out with centers spaced about 4 to 8 miles (6.4 to 12.8 km) apart. The basic system components are the cell sites, the MTSO, and mobile units. These mobile units may be hand-held or vehicle-mounted terminals.
Each cell has a radio facility housed in a building or shelter. The facility’s radio equipment can connect and control any mobile unit within the cell’s responsible geographic area. Radio transmitters located at the cell site have a maximum effective radiated power (ERP∗) of 100 watts. Combiners are used to connect multiple transmitters to a common antenna on a radio tower, usually between 50 and 300 ft (15 and 92 m) high. Companion receivers use a separate antenna system mounted on the same tower. The receive antennas are often arranged in a space-diversity configuration.
The MTSO provides switching and control functions for a group of cell sites.
A method of connectivity is required between the MTSO and the cell site facilities.
The MTSO is an electronic switch and carries out a fairly complex group of processing functions to control communications to and from mobile units as they move between cells as well as to make connections with the PSTN. Besides making connectivity with the public network, the MTSO controls cell site activities
and mobile actions through command and control data channels. The connectivity between cell sites and the MTSO is often via DS1 on wire pairs or on microwave facilities, the latter being the most common.
A typical cellular mobile unit consists of a control unit, a radio transceiver, and an antenna. The control unit has a telephone handset, a push button keypad to enter commands into the cellular/telephone network, and audio and visual indications for customer alerting and call progress. The transceiver permits full
duplex transmission and reception between a mobile and cell sites. Its ERP is nominally 6 watts. The unit is usually vehicle-mounted. Hand-held terminals combine all functions into one small package that can be easily held in one hand. The ERP of a hand-held is a nominal 0.6 watts. It seems that this package
is being made smaller and smaller.
In North America, cellular communication is assigned a 25-MHz band between 824 and 849 MHz for mobile unit-to-base transmission and a similar band between 869 and 894 MHz for transmission from base to mobile. The original North American cellular radio systems was called AMPS (advanced mobile telephone
system). The original system description was contained in an entire issue
Bell System Technical Journal (BSTJ) of January 1979. The present AMPS is based on 30-kHz channel spacing using frequency modulation. The peak deviation is 12 kHz. The cellular bands are each split into two to permit competition.
Thus only 12.5 MHz is allocated to one cellular operator for each direction of transmission. With 30-kHz spacing, this yields 416 channels. However, nominally 21 channels are used for control purposes, with the remaining 395 channel available for cellular end-users.
Common practice with AMPS is to assign 10 to 50 channel frequencies to each cell for mobile traffic. Of course, the number of frequencies used depends on the expected traffic load and the blocking probability. Radiated power from a cell site is kept at a relatively low level with just enough antenna height to
cover the cell area. This permits frequency reuse of these same channels in nonadjacent cells in the same CGSA with little or no co-channel interference. A well-coordinated frequency reuse plan enables tens of thousands of simultaneous calls over a CGSA. Here four channel frequency groups are assigned in a way that avoids the same frequency set used in adjacent cells. If there were uniform terrain contours, this plan could be applied directly.
However, real terrain conditions dictate further geographic separation of cells that use the same frequency set. Reuse plans with 7 or 12 sets of channel frequencies provide more physical separation and are often used depending on the shape of the antenna pattern employed.
With user growth in a particular CGSA, cells may become overloaded. This means that grade of service objectives are not being met due to higher than planned traffic levels during the busy hour (BH). In these cases, congested cells can be subdivided into small cells, each with its own base station,
 These smaller cells use lower transmitter power and antennas with less height, thus permitting greater frequency reuse.

    An important issue in wireless communication systems is multiple random access: communication links can be activated at any moment while several links can be active simultaneously. As multi-access and random-access are properties mainly determined by the chosen data-communication technique it is important to keep these requirements in mind from the very beginning. Three possible concepts to realize a multi-access communication system are in use:
  1. FDMA  
    Frequency Division Multiple Access, commonly used in conventional telephone systems: every user gets a certain frequency band assigned and can use this part of the spectrum to perform its communication. If only a small number of users is active, not the whole resource (frequency-spectrum) is used. Assignment of the channels can be done centrally or by carrier-sensing in a mobile. The latter possibility enables random-access.
  2. TDMA  
    Time Division Multiple Access, applied nowadays in mobile phone systems: every user is assigned a (set of) time-slots. Transmission of data is only possible during this time-slot, after that the transmitter has to wait until it gets another time-slot. Synchronization of all users is an important issue in this concept. Consequently, there must be a central unit (base-station) that controls the synchronization and the assignment of time-slots. This means that this technique is difficult to apply in random-access systems.
  3. CDMA  
    Code Division Multiple Access (Spread Spectrum). A unique code is assigned to each user. This code is used to ``code'' the data message. As codes are selected for low cross-correlation properties, all users can transmit simultaneously in the same frequency channel while a receiver is still capable of recovering the desired signal. Synchronization between links is not strictly required and so random-access is possible. A practical application at the moment is the cellular-cdma phone system IS-95   [Qua92].
Combinations are also possible, the popular European cellular phone systems dect   and gsm   for instance use a combination of tdmaand fdma. There a single transmission-cell is defined by a combination of a frequency channel and a time-slot.
From the above list it is clear that both fdmaand cdma are candidate transmission techniques to enable multiple random access. There are however a number of reasons for choosing cdma over fdma. The first alternative provides [Sch94, SOSL85a, Dix84]:
  •   Interference limited operation. In all situations the whole frequency-spectrum is used. As a result the more active users are present, the higher the interference level will be.
  • Privacy due to unknown codes. The applied codes are - in principle - unknown to a hostile user. This means that it is hardly possible to detect the message of another user.
  • Applying spread spectrum implies the reduction of multi-path effects. By using a wide frequency-band, the influence of narrow-band fades is reduced.
  • Random access possibilities. Users can start their transmission at any arbitrary time (no infrastructure required).
  • Good anti-jamming performance. Small-band interference is reduced as explained in the next section.
These were the reasons for selecting cdma as multi-access technique in the non-cellular target communication system. As this choice has a large impact on further design stages, the next section provides an introduction to cdma-techniques.



In a switched telephone network, signaling conveys the intelligence needed for one subscriber to interconnect with any other in that network. Signaling tells the switch that a subscriber desires service and then gives the local switch the data necessary to identify the required distant subscriber and hence to route the call
properly. It also provides supervision of the call along its path. Signaling also gives the subscriber certain status information, such as dial tone, busy tone (busy
back), and ringing. Metering pulses for call charging may also be considered a form of signaling.
There are several classifications of signaling:
1. General.
a. Subscriber signaling.
b. Interswitch signaling.
2. Functional.
a. Audible–visual (call progress and alerting).
b. Supervisory.
c. Address signaling.
 It should he appreciated that on many telephone calls, more than one switch is involved in call routing. Therefore switches must interchange information among switches in fully automatic service. Address information is provided between modern switching machines by  interregnum signaling, and the supervisory function is provided by line signaling. The audible–visual category of signaling
functions inform the calling . The alerting function informs the called subscriber of a call waiting or an extended “off-hook” condition of his or her handset. Signaling information can be conveyed by a number of means from subscriber to switch or between (and among) switches. Signaling information can be transmitted by means such as
• Duration of pulses (pulse duration bears a specific meaning)
• Combination of pulses
• Frequency of signal
• Combination of frequencies
• Presence or absence of a signal
• Binary code
• For dc systems, the direction or level of transmitted current
Supervisory signaling provides information on line or circuit condition and indicates whether a circuit is in use or idle. It informs the switch and interconnecting trunk circuits whether a calling party is “off hook” or “on hook” or whether a called party is “off hook” or “on hook.” The meaning and importance of the terms
“on hook” and “off hook” were detailed in Chapter 1, Section 2. The assumption is that a telephone in the network can have one of two states: busy or idle. Idle, of course, is represented by the “on-hook” condition.
The reader must appreciate that supervisory information–status must be maintained end to end on every telephone call. It is necessary to know when a calling subscriber lifts his/her telephone off hook, thereby requesting service. It is equally important that we know when the called subscriber answers (i.e.,
lifts her telephone off hook), because that is when we may start metering the call to establish charges. It is also important to know when the called and calling subscribers return their telephones to the on-hook condition. Charges stop, and the intervening trunks comprising the talk path as well as the switching points
are then rendered idle for use by another pair of subscribers. During the period of occupancy of a talk path end to end, we must know that this particular path is busy (is occupied) so that no other call attempt can seize it. Dialing of a subscriber line is merely interruption of the subscriber loop’s off-hook condition, often called “make and break.” The “make” is a current flow condition (or off hook), and the “break” is the no-current condition (or on hook). How do we know the difference between supervisory and dialing? Primarily by duration—the on-hook interval of a dial pulse is relatively short and is distinguishable from an on-hook disconnect signal (subscriber hangs up), which is transmitted in the same direction for a longer duration. Thus the switch is sensitized to duration to distinguish between supervisory and dialing of a subscriber loop.
2.1 E and M Signaling
Probably the most common form of trunk supervision is E and M signaling, particularly with multiplex equipment (Chapters 5 and 8). Yet it only becomes true E and M signaling where the trunk interfaces with the switch (see Figure 4.3). E-lead and M-lead signaling systems are semantically derived from historical designation of signaling leads on circuit drawings covering these systems. Historically, the E and M signaling interface provides two leads between the switch and what we may call trunk-signaling equipment (signaling interface). One lead is called the “E-lead,” which carries signals to the switching equipment.
3.1 General
Up to this point we have reviewed the most employed means of supervisory trunk signaling (or line signaling). Direct-current signaling, such as reverse-battery signaling, has notable limits on distance because it cannot be applied directly to multiplex systems (Chapters 5 and 8) and is limited on metallic pairs due to the IR drop of the lines involved. Direct-current trunk signaling is addressed in Section 10.
There are many ways to extend these limits, but from a cost-effectiveness standpoint there is a limit that we cannot afford to exceed. On trunks exceeding dc capabilities, some form of ac signaling will be used. Traditionally, ac signaling systems are divided into three categories: low-frequency, in-band, and out-band
(out-of-band) systems. Each of these can derive the four E and M signaling states.
3.2 Low-Frequency AC Signaling Systems
An ac signaling system operating below the limits of the conventional voice channel (i.e., <300 Hz) are termed low frequency. Low-frequency signaling systems are one-frequency systems, typically 50 Hz, 80 Hz, 135 Hz, or 200 Hz. It is impossible to operate such systems over carrier-derived channels because of the excessive distortion and band limitation introduced. Thus low frequency signaling is limited to metallic-pair transmission systems. Even on these systems, cumulative distortion limits circuit length. A maximum of two
repeaters may be used, and, depending on the type of circuit (open wire, aerial cable, or buried cable) and wire gauge, a rough rule of thumb is a distance limit of 80–100 km.
3.3 In-Band Signaling In-band signaling refers to signaling systems using an audio tone, or tones inside
the conventional voice channel, to convey signaling information. In-band signaling is broken down into three categories: (1) one frequency (SF or single frequency), (2) two frequency (2VF), and (3) multi frequency (MF). As the term implies, in-band signaling is where signaling is carried out directly in the voice
channel. As the reader is aware, the conventional voice channel as defined by the CCITT occupies the band of frequencies from 300 Hz to 3400 Hz. Single frequency and two-frequency signaling systems utilize the 2000- to 3000-Hz portion, where less speech energy is concentrated.
3.3.1 Single-Frequency Signaling. Single-frequency signaling is used almost exclusively for supervision. In some locations it is used still for interregister signaling, but the practice is diminishing in favor of more versatile
methods such as MF signaling. The most commonly used frequency is 2600 Hz, particularly in North America. On two-wire trunks, 2600 Hz is used in one direction and 2400 Hz is used in the other.
3.3.2 Two-Frequency Signaling. Two-frequency signaling is used for both supervision (line signaling) and address signaling. We often associate SF and 2VF supervisory signaling systems with carrier (FDM) operation. Of course, when we discuss such types of line signaling (supervision), we know that the term “idle”
refers to the on-hook condition while “busy” refers to the off-hook condition.
Thus, for such types of line signaling that are governed by audio tones of which SF and 2VF are typical, we have the conditions of “tone on when idle” and “tone on when busy.” The discussion holds equally well for in-band and out-of-band signaling methods. However, for in-band signaling, supervision is by necessity
tone-on idle; otherwise subscribers would have an annoying 2600-Hz tone on throughout the call.
A major problem with in-band signaling is the possibility of “talk-down,” which refers to the premature activation or deactivation of supervisory equipment by an inadvertent sequence of voice tones through the normal use of the channel. Such tones could simulate the SF tone, forcing a channel dropout (i.e.,
the supervisory equipment would return the channel to the idle state). Chances of simulating a 2VF tone set are much less likely. To avoid the possibility of talk down on SF circuits, a time-delay circuit or slot filters to bypass signaling tones may be used. Such filters do offer some degradation to speech unless they are
switched out during conversation. The tones must be switched out if the circuit is going to be used for data transmission [7].
It becomes apparent why some administrations and telephone companies have turned to the use of 2VF supervision, or out-of-band signaling for that matter. For example, a typical 2VF line signaling arrangement is the CCITT No. 5 code, where f1 (one of the two VF frequencies) is 2400 Hz and f2 is 2600 Hz. 2VF signaling is also used widely for address signaling (see Section 4.1 of this chapter) .
3.4 Out-of-Band Signaling
With out-of-band signaling, supervisory information is transmitted out of band (i.e., above 3400 Hz). In all cases it is a single-frequency system. Some out-of band systems use “tone on when idle,” indicating the on-hook condition, whereas others use “tone off.” The advantage of out-of-band signaling is that either system, tone on or tone off, may be used when idle. Talk-down cannot occur because all supervisory information is passed out of band, away from the speech-information portion of the channel.
The preferred CCITT out-of-band frequency is 3825 Hz, whereas 3700 Hz is commonly used in the United States. It also must be kept in mind that out-of band signaling is used exclusively on carrier systems, not on wire trunks. On the wire side, inside an exchange, its application is E and M signaling. In other
words, out-of-band signaling is one method of extending E and M signaling over a carrier system.
In the short run, out-of-band signaling is attractive in terms of both economy and design. One drawback is that when channel patching is required, signaling leads have to be patched as well. In the long run, the signaling equipment required may indeed make out-of-band signaling even more costly because of the extra
supervisory signaling equipment and signaling lead extensions required at each end and at each time that the carrier (FDM) equipment demodulates to voice.
The major advantage of out-of-band signaling is that continuous supervision is provided, whether tone on or tone off, during the entire telephone conversation.
Address signaling originates as dialed digits (or activated push buttons) from a calling subscriber, whose local switch accepts these digits and, using that information, directs the telephone call to the desired distant subscriber.

An important factor to be considered in switching system design that directly affects both signaling and customer satisfaction is post dialing delay. This is the amount of time it takes after the calling subscriber completes dialing until ring back is received. Ring-back is a backward signal to the calling subscriber telling
her that her dialed number is ringing. Postdialing delay must be made as short as possible.
Another important consideration is register occupancy time for call setup as the setup proceeds from originating exchange to terminating exchange. Call-setup equipment, that equipment used to establish a speech path through a switch and to select the proper outgoing trunk, is expensive. By reducing register occupancy
per call, we may be able to reduce the number of registers (and markers) per switch, thus saving money.
Link-by-link and end-to-end signaling each affect register occupancy and post dialing delay, each differently. Of course, we are considering calls involving one or more tandem exchanges in a call setup, because this situation usually occurs on long-distance or toll calls. Link-by-link signaling may be defined as a signaling
system where all interregister address information must be transferred to the subsequent exchange in the call-setup routing. Once this information is received at this exchange, the preceding exchange control unit (register) releases. This same operation is carried on from the originating exchange through each tandem
(transit) exchange to the terminating exchange of the call. The R-1 system is an
example of link-by-link signaling.
End-to-end signaling abbreviates the process such that tandem (transit) exchanges receive only the minimum information necessary to route the call. For instance, the last four digits of a seven-digit telephone number need be exchanged only between the originating exchange (e.g., the calling subscriber’s local exchange or the first toll exchange in the call setup) and the terminating exchange in the call setup. With this type of signaling, fewer digits are required to be sent (and acknowledged) for the overall call-setup sequence. Thus the
signaling process may be carried out much more rapidly, decreasing post dialing delay. Intervening exchanges on the call route work much less, handling only the digits necessary to pass the call to the next exchange in the sequence

Wide Area Network

A wide area network (WAN) is a computer network that covers a broad area (i.e., any network whose communications links cross metropolitan, regional, or national boundaries).[1] This is in contrast with personal area networks (PANs), local area networks (LANs), campus area networks (CANs), or metropolitan area networks (MANs) which are usually limited to a room, building, campus or specific metropolitan area (e.g., a city) respectively.

Design options

WANs are used to connect LANs and other types of networks together, so that users and computers in one location can communicate with users and computers in other locations. Many WANs are built for one particular organization and are private. Others, built by Internet service providers, provide connections from an organization's LAN to the Internet. WANs are often built using leased lines. At each end of the leased line, a router connects to the LAN on one side and a hub within the WAN on the other. Leased lines can be very expensive. Instead of using leased lines, WANs can also be built using less costly circuit switching or packet switching methods. Network protocols including TCP/IP deliver transport and addressing functions. Protocols including Packet over SONET/SDH, MPLS, ATM and Frame relay are often used by service providers to deliver the links that are used in WANs. X.25 was an important early WAN protocol, and is often considered to be the "grandfather" of Frame Relay as many of the underlying protocols and functions of X.25 are still in use today (with upgrades) by Frame Relay.
Academic research into wide area networks can be broken down into three areas: Mathematical models, network emulation and network simulation.
Performance improvements are sometimes delivered via WAFS or WAN optimization.

Connection technology options

There are also several ways to connect NonStop S-series servers to WANs, including via the ServerNet Wide Area Network (SWAN) or SWAN 2, 3, 4, 5, 6, 7, 8, 9, 10 concentrators, which provides WAN client connectivity to servers that have Ethernet ports and appropriate communications software. You can also use the Asynchronous Wide Area Network (AWAN) access server, which offers economical asynchronous-only WAN access. Several options are available for WAN connectivity:

Transmission rates usually range from 1200 bit/s to 24 Mbit/s, although some connections such as ATM and Leased lines can reach speeds greater than 156 Mbit/s. Typical communication links used in WANs are telephone lines, microwave links & satellite channels.
Recently with the proliferation of low cost of Internet connectivity many companies and organizations have turned to VPN to interconnect their networks, creating a WAN in that way. Companies such as Cisco, New Edge Networks and Check Point offer solutions to create VPN networks.

Telecom terminologies

Telecom Words

Telecom, short for Telecommunications, includes anything and everything that is transmitted over wire, fiber or microwaves owned by a telephone company or other common carrier. Leased Line - a dedicated telephone line leased from the telephone company on a monthly basis for a flat fee. It is always connected whether or no there is traffic. Commonly a 56kbs line, but 128kbs, T1 and higher speeds are available.
Multiplex - combining several voice and/or data streams into a single signal at one end, and sorting them out into separate signals at the other end. By this means a single wire, fiber or microwave signal can carry many simultaneous conversations or data transmissions. The signal must be very high in frequency (high bandwidth) compared to the voice / data streams it carries, or transmission speed of each stream will be negatively impacted.
There are many multiplexing schemes, but the simplest is to timeslice the carrier signal, giving each stream a slice when its turn comes. More sophisticated systems are demand sensitive, allowing no slice to an idle stream - and from there it starts getting rather complex.
  • TDMA - Time Division Multiple Access (same as TDM).
  • TDM - Time Division Multiplexing (same as TDMA).
  • DWDM - Dense Wavelength Division Multiplexing.
Dial-up Line - a plain switched telephone line or an ISDN line. Charged by the minute only when actually connected (dialed).
WAN - Wide Area Network - is grouped here under telecom because the most easily understood definition is that a WAN is the part of a company's data network that passes over a connection not owned by the company - generally a link owned by a telephone company or other common carrier. A seldom used subset of WAN is MAN - Metropolitan Area Network.
Local Loop - The telephone wire from your demarc, phone, KSU or PBX equipment to the local Central Office Often called a CO line.
Loop Start - A method of initiating a telephone connection (getting a dialtone) used for single line and ksu phones. PBXs generally prefer Ground Start. Loop start shorts tip to ring through a resistance.
Ground Start - A method of initiating a telephone connection (getting a dialtone) used for PBXs. Single line phones prefer Loop Start. Ground start shorts tip to ground through a maximum of 550 ohms of resistance.
Tip & Ring - the two wires of a standard dialup telephone line. Derived from the plugs used in manual switches (see pictures of old telephone offices). The plug shaft ended in a ball (the tip). Right behind the ball was a ring, insulated from the ball on one side and the shaft on the other. Tip is the wire that goes to the tip, Ring is the wire that goes to the ring.
VAN - Value-Added Network - A privately operated network originally devoted to EDI transactions. VANs now provide other services as well, including translation of EDI transactions for Internet tranmission (EDI-INT).
PDN - Public Data Network - switched or leased lines maintained by a telephone company or other carrier and available for a fee to organizations needing Wide Area (WAN) or Metropolitan Area (MAN) networking.
PSDN - Public Switched Data Network - a switched (connection based) data network similar to a telephone company, but offering data services instead of voice services. Some PSDN carriers are: Compuserve, SprintNet and Tymnet.
PSTN - Public Switched Telephone Network - your local and long distance telephone service.
PTT - Postal, Telephone & Telegraph - International - generally designating a state owned monopoly.
QOS - Quality of Service - a promised or contracted level of speed and reliablility for data and voice communications services, generally from a common carier. QOS is largely mythical at this time.
CO, Central Office - The telephone company switching equipment to which your telephone system is wired by the Local Loop.
Demarc - Demarcation point between the telephone company's equipment and your equipment. Today, the demarc is as close to the edge of your facility as possible. You are responsible for all wiring and equipment on your side of the demarc.
Hunt Group - A group of telephone numbers that looks like a single number to the outside world. If the main number is dialed, but buisy, the ring will be routed to an available number in the hunt group. Numbers in the hunt group can also be individually dialed, where only the dialed number will ring, and outgoing calls can be placed on any of them.

Telecom Business Units

BOC, RBOC - Regional Bell Operating Company - USA - "Local" phone companies created by the court mandated breakup of the AT&T monoply. Notworthy for defining the concept of "monopoly" on a regional basis. Now they are all merging to form a new national monopoly. The Telecommunications Reform Act at work.
LEC, ILEC, CLEC - Local Exchange Carier, Incumbent Local Exchange Carrier, Competetive Local Exchange Carrier - Created by deregulation. The ILEC is your old telephone company before deregulation, the CLEC is a new carrier selling you services over the ILEC's lines. CLECs generally specialize in a particular type of service.
LATA - Local Access Transport Area - The Bell divestiture divided the U.S. into 161 local exchanges. Calls with both ends within the LATA are the provence of the LEC (Local Exchange Carier), and InterLATA calls, where the two ends are in different LATAs) are fair game for long distance carriers.

Telecom Equipment

DSLAM - DSL Access Multiplexor - This is the device that must be within a certain distance from your site to provide DSL services at a particular speed (or at all). The DSLAM multiplexes a number of DSL feeds into a single high speed line connecting to the server operated by your ISP. The high speed side is usually an ATM line.
PBX - Private Branch Exchange - a customer owned telephone switching system used by larger companies and organizations. It is similiar in function to the switching systems at the telco's central office, but on a much smaller scale. A PBX is much more complex and capable than a KSU.
PABX - (Private Automatic Branch Exchange) - but since all PBX's are automatic now the A has been dropped.
CBX - (Computerized Branch Exchange) - a term for PABX used by Rholm and IBM.
EPABX - (Electronic Private Automatic Branch Exchange) - (give me a break!).
KSU - Key Service Unit - Telephone equipment for small offices. A typical KSU is served by 6 regular dial-up phone lines and fans them out to 24 desk phones (though thay do get larger). It also usually provides paging, intercom, music on hold and other local services. Next up from the KSU is the PBX.
Terminal Equipment - Device that terminates a transmition line. For instance an ISDN "modem" includes the terminal equipment for an ISDN line.
MDF - Main Distribution Frame - the wiring termination frames where incoming cables are punched down, and from where they are patched to telecom equipment.
CPE - Customer Premise Equipment - the equipment that terminates a transmission line at the customer demarc. Often, but not always, the CPE will be owned by the carrier. Notable exceptions are ISDN and DSL termination equipment (modems, bridges and routers) which are generally installed by the carrier but owned by the customer.
OLT / ONU - Optical Line Terminator / Optical Network Unit. The OLT is the device handling a fiber optic line at the CO (Central Office) end. The ONU is at the subscriber end and converts the optical signal to whatever the "last mile" format is (DSL, Ethernet, etc.).

Telecommunications Services & Protocols

POTS - Plain Old Telephone Service - the regular 2-line voice telephone service.
  • DS-0 - Digital Services, International name for 64-kbs digital data service.
  • DS-1 - Digital Services-1, T-1, 24 DS-0, 1.544-mbps
  • DS-3 - Digital Services-3, T-3, 24 DS-1, 44.736-mbps.
  • E-1 - European version of T-1, 2.048-mbs
  • ISDN - Integrated Service Digital Network
  • T-1 - DS-1, 24 DS-0, 1.544-mbps
  • T-3 - DS-3, 24 DS-1, 45-mbps
ATM - Asynchronous Transfer Mode - a former "latest and greatest" high speed network transport and protocol. "ATM to the desktop" was the battle cry. Unfortunately ATM is very complex to implement and quite costly, and incompatible with common LANs, so it never got as far as the desktop. It is used for campus backbones, Internet backbones and WANs.
When setting up a router to talk to an ATM circuit, you must set VPI (Virtual Packet Identifier), VCI (Virtual Circuit Identifier), and DLCI(Data Link Connection Identifier), which will be included in your packet headers. These numbers are provided by your service provider.
DSL, xDSL, ADSL, CDSL, IDSL, SDSL, G.Lite, G.SHDSL, HDSL-2, VDSL, RADSL, - Digital Subscriber Line - a high data rate digital voice data service over copper telephone lines. DSL is an "always-on" service like a dedicated line. There are two (incompatible) DSL protocols in use, called DMT (Discrete MultiTone) and CAP (carrierless Amplitude Phase). DMT is expected to predominate.
Alas, poor Germany. They did such a Teutonically efficient job of ripping out their obsolete telephone wiring and replacing it with fiber. Now everyone wants DSL, which only goes over copper wire.
  • ADSL - Asymmetric DSL. Downstream (to you) speed is considerably higher than upload speed. This is the variety of DSL being deployed to homes and small offices. Usually 345-kbps to 1500-kbps downstream (depending on provider) and about 64-kbps to 800-kbps upstream. Maximum distance from your site to telephone company's central office is 18,000 feet (3.5 miles). Sites closer than 12,000 feet can sometimes get speeds exceeding 1.6-mbps. 1-pair, can share a line with voice.
  • ADSL-Lite - Asymmetric DSL - 64-kbps to 384-kbps upstream, 1-mbps to 1.5-mbps downstream. To 25,000 feet. 1-pair, can share a line with voice.
  • CDSL - Consumer DSL. A version of ADSL that supports regular 56K V.90 modems if ADSL is not available. 128-kbps upstream, 1-mbps downstream. To 18,000 feet. 1-pair, can share a line with voice.
  • G.Lite - a variety of ADSL which requires no splitter at the subscriber end to separate voice and data. Phones may, however, need a low pass filter on their line.
  • G.SHDSL - Global Symmmetric High-bit-rate Digital Subscriber Line - a newer global standard expected to replace SDSL
  • HDSL - High Bit Rate DSL. At under 12,000 feet 768-kbps to 2.048-mbps. 2-pair except 2.048-mbps requires 3-pair, cannot share a line with voice.
  • HDSL-2 - High-speed DSL-2 1.5-mbps, and 2.408-mbps. 1-pair, to 12,000 feet, cannot share a line with voice.
  • IDSL - ISDN speed DSL, 128-kbps to 144-kbps. Slower than ADSL but with a range of up to 40,000 feet (7 miles) from the central office. 1-pair. Unlike standard ISDN, it is an "always on" connection rather than dial-up and does not support voice.
  • RADSL - Rate Adaptive DSL - adjusts speeds based on signal quality. 128-kbs to 1024-kbps upstream, 600-kbps to 700-kbps downstream. To 25,000 feet, can share a line with voice.
  • SDSL - Symmetric DSL. Has the same speed in both directions. About 184-kbps at 15,000 feet. At less than 10,000 feet 384-kbps to 768-kbps. 1-pair, cannot share with voice.
  • VDSL - Very High Bit Rate DSL - expected to be used for short drops from fiber to facilities requiring above T1 bandwidth. 1.6-mbps to 6.4-mbps upstream, 13-mbps to 52-mbps downstream. 1 pair, to 4,500 feet. can share a line with voice.
    A symetrical version of VDSL does 26-mbps both directions. 1-pair, to 4,500 feet.
  • xDSL - DSL, not specific as to type. Any of the above.
DWDM - Dense Wavelength Division Multiplexing - describes transmission by the use of multiple laser transmitters and receivers simultaneously on the same fiber. Each transmitter / receiver pair uses a different color (wavelength). Multiplexing allows several carrier streams to simultaneously use the same fiber. In most cases each of these streams will be multiplexed to carry a number of simultaneous voice or data streams.
Frame Relay - A telecomunications protocol for economical transport of digital material. It is used for transmission between two sites on a LAN, or from a LAN into the Internet. Frame can run over various transmission media. Most common are 64-kilobit/sec and 128-kilobit/sec leased lines. Over high speed media, Frame Relay can simultaneously carry both voice and data communications.
PON - Passive Optical Networking - a transmission scheme where a fiber transmission line uses splitters to fan out to multiple end points. Passive means the system has no active components such as amplifiers, repeaters, hubs or switches. This transmission method is limited to about 12 miles. The fiber can have up to 32 splits (64 end points).
Transmission speed is 155-Megabits/sec both ways, or 622-Megabits/sec downstream and 155-Megabits/sec upstream. PON is a shared line, so actual subscriber performance depends on how many subscribers are on the line and how heavy their traffic is.
PON is a relatively simple method of getting high speed connections out to more end users. The last link to the user is usually DSL, but instead of fanning out from a CO (Central Office), the fan out is from a number of "neighborhood gateways" or "mini-COs". This means subscribers need only be within 18,000 feet of a local mini-CO rather than within 18,000 feet of a full Central Office. SBC (Southern Bell Companies - including Pacific Bell) is the most agressive deployer of PON at this time (Project Pronto).
PVC / SVC - Permanent Virtual Circuit / Switched Virtual Circuit. A PVC looks like a permanent "Leased Line" to the subscribers at both ends of what is actually a packet switched, multiplexed network. A SVC looks to the subscriber as if it were a regular dial-up line even though it is actually a packet switched, multiplexed network.
Async - Asynchronous Communications - a protocol for transmission of binary data in which framing information defines the beginning and ending of each character transmitted. This makes it possible to transmit such data over long links or between differing systems where it is not possible to synchronize the two participants with timing signals.
BSC, BISYNC - Binary Synchronous Communications - an IBM protocol for transmission of binary data. There is no framing information as with Asynchronous (standard modem and serial) communications, nor is it needed as the sending and receiving machines are synchronized by timing signals.
ISDN - Integrated Services Digital Network - consists of one D-channel (Data channel) for signalling and low speed non-voice telemetry, and 2 or more B-channels (Bearer channels) for voice and data transmission.
  • Basic Rate ISDN consists of 1 D-channel (16-kbs) and 2 B-channels (64-kbs each, or 128-kbs combined)
  • Primary Rate ISDN consists of 1 D-channel (64-kbs) and 23 B-channels (16-kbs each, or 1.544-mbs combined).

X modem, Y modem, Z modem

- Protocols to assure error free data transfer ovr unreliable connections, particularly modems. These protocols include CRC (Cyclical Redundancy Checking) and retransmission features.
  • X modem - One of the earliest protocols to assure error free transfer of data over telephone lines. Simple with CRC checking. Slow.
  • Y modem - Faster and more sophisticated than X modem, Y modem is particularly designed to handle batches of files.
  • Z modem - Faster and more sophisticated than Z modem.

CTI - Computer Telephone Integration

Computer Telephone Integration referrs to the equipment on your premises. At the telco, this integration was done long ago. Telephone switches are now just big computers. The most familiar uses of CTI are IVR (Interactive Voice Response - also the most annoying) and Voice Mail. IVR - Interactive Voice Response - "For cotton doilies, please press 5, for polyester doilies, please press 6, for paper doilies, please press 7".
Voice Mail - A system by which a computer answers the telephone and stores your message in a voice mailbox (on its hard disk) for later retrieval by the person who is pretending not to be there. The advantage of voice mail over an answering machine is that many individuals can have their own private mailboxes and not have to hear each other's messages.
Network providers commonly implement Frame Relay for voice (VoFR) and data as an encapsulation technique, used between local area networks (LANs) over a wide area network (WAN). Each end-user gets a private line (or leased line) to a frame-relay node. The frame-relay network handles the transmission over a frequently-changing path transparent to all end-users.
Frame Relay has become one of the most extensively-used WAN protocols. Its cheapness (compared to leased lines) provided one reason for its popularity. The extreme simplicity of configuring user equipment in a Frame Relay network offers another reason for Frame Relay's popularity.
With the advent of Ethernet over fiber optics, MPLS, VPN and dedicated broadband services such as cable modem and DSL, the end may loom for the Frame Relay protocol and encapsulation.[citation needed] However many rural areas remain lacking DSL and cable modem services. In such cases the least expensive type of non-dial-up connection remains a 64-kbit/s frame-relay line. Thus a retail chain, for instance, may use Frame Relay for connecting rural stores into their corporate WAN.
Network providers commonly implement Frame Relay for voice (VoFR) and data as an encapsulation technique, used between local area networks (LANs) over a wide area network (WAN). Each end-user gets a private line (or leased line) to a frame-relay node. The frame-relay network handles the transmission over a frequently-changing path transparent to all end-users.
Frame Relay has become one of the most extensively-used WAN protocols. Its cheapness (compared to leased lines) provided one reason for its popularity. The extreme simplicity of configuring user equipment in a Frame Relay network offers another reason for Frame Relay's popularity.
With the advent of Ethernet over fiber optics, MPLS, VPN and dedicated broadband services such as cable modem and DSL, the end may loom for the Frame Relay protocol and encapsulation.[citation needed] However many rural areas remain lacking DSL and cable modem services. In such cases the least expensive type of non-dial-up connection remains a 64-kbit/s frame-relay line. Thus a retail chain, for instance, may use Frame Relay for connecting rural stores into their corporate WAN.
Network providers commonly implement Frame Relay for voice (VoFR) and data as an encapsulation technique, used between local area networks (LANs) over a wide area network (WAN). Each end-user gets a private line (or leased line) to a frame-relay node. The frame-relay network handles the transmission over a frequently-changing path transparent to all end-users.
Frame Relay has become one of the most extensively-used WAN protocols. Its cheapness (compared to leased lines) provided one reason for its popularity. The extreme simplicity of configuring user equipment in a Frame Relay network offers another reason for Frame Relay's popularity.
With the advent of Ethernet over fiber optics, MPLS, VPN and dedicated broadband services such as cable modem and DSL, the end may loom for the Frame Relay protocol and encapsulation.[citation needed] However many rural areas remain lacking DSL and cable modem services. In such cases the least expensive type of non-dial-up connection remains a 64-kbit/s frame-relay line. Thus a retail chain, for instance, may use Frame Relay for connecting rural stores into their corporate WAN.


Local area networks (LANs) use a common transmission medium to interconnect workstations, servers, computers, and/or other related assets over a limited geographical area. Several LAN standards specify capability to serve up to a thousand or more devices on a single LAN. The geographical extension or “local area” may extend no more than several hundred feet (<100 m) to over 6 miles (>10 km) or more in other cases. The transmission media providing this connectivity may be wire pair, coaxial cable, or fiber-optic cable. Local area radio (wireless) schemes based on IEEE 802.11 standards are gaining wide acceptance.
Certain LAN schemes accommodate other devices as well such as digital telephones, facsimile, and video equipment. A basic rule on LANs was that only one user at a time may have access to the medium. Switching hubs and LAN routers have now changed this rule.
Data rates on current LANs vary from 1 Mbit/s to 10,000 Mbits/s. LAN data rates, the number of devices connected to a LAN, the spacing of those devices, and the network extension depend on:
The transmission medium employed
Transmission technique (i.e., baseband or broadband)
Network access protocol
Many LANs operate without error correction with bit error rates (BERs) specified in the range of 1 × 108 to 1 × 1012 or better.
The most common application of a LAN is to interconnect data terminals (workstations) with processing resources, where all the devices reside in a single building or complex of buildings, and usually these resources have a common owner. Cost containment is a driving force toward the implementation of LANs.
A LAN permits effective cost sharing of high-value data processing equipment, such as mass storage, mainframe or minicomputers, and high-speed printers.
There are other benefits as well. One, of course, is resource sharing. Another is e-mail and similar messaging services leading to a “paperless” environment. A
LAN may also be considered an aggregator of data for eventual transport of this data over a WAN.
LANs can be extended, up to a certain point, with repeaters or bridges. They can be segmented by means of switches, switching hubs, smart bridges, or routers.
Segmenting of a LANs can notably improve performance, especially on a LAN with many users.
The interconnection of LANs in the local area with a high-speed backbone is current practice. LAN interconnection with the outside world such as with distant
LANs via a wide area network is becoming prevalent. This is frame relay’s principal application. The interface is carried out with a router or gateway.
There are two generic transmission techniques utilized by LANs: baseband and broadband. Baseband transmission can be defined as the direct application of the baseband signal to the transmission medium. Broadband transmission, in this context, is where the baseband signal from the data device is translated in frequency to a particular frequency slot in the RF spectrum. Broadband transmission requires a modem to carry out the translation. Baseband transmission may require some sort of signal conditioning device. With broadband LAN transmission, we usually think of simultaneous multiple RF carriers that are separated in the frequency domain. Present broadband technology comes from the cable television (CATV) industry.
Use of the asynchronous transfer mode (ATM) is beginning to find favor in the LAN community and could radically change many of the concepts introduced in this chapter.
There are three types of LAN topology: bus, ring, and star. These are shown in
Figure 13.1 along with the tree network, which is a subset of the conventional bus topology. All three topology configurations have been shown previously in. They are repeated here for convenience of the reader.
A bus is a stretch of transmission medium. Originally, the medium was coaxial cable. Today it can also be
UTP or STP (unshielded twisted pair or shielded twisted pair). For high data rate
(e.g., 100 Mbits/s) LANs, fiber-optic cable is now widely used.
A ring is simply a bus that is folded back onto itself.                                                                                                                             
 User traffic flows in one direction around the ring. In one approach, which we discuss in this chapter, a second ring is added where the traffic flow is in the opposite direction. Such a dual counter rotating ring concept improves reliability in case of a failed station or a cut of the ring. At the center of the star is a switching device. This could be a switching hub. Users can be paired, two at a time, three at a time, or all at a time, segmented into temporary families of users depending on the configuration of the switch at that moment in time. Such a concept lends itself particularly well to ATM. In this case each user is connected to the switch on a point-to-point basis for the period of connectivity.


Baseband and broadband are the two basic transmission techniques employed by LANS, which were introduced above.
With both these types of LANs (i.e., baseband and broadband), we are dealing with multipoint operation. Two transmission problems arise as a result. The first deals with signal level and signal-to-noise ratio, and the second deals with standing waves. Each access on a common medium must have sufficient signal level and S/N such that copied signals have a BER in the range of 1 × 108 to 1 × 1012. If the medium is fairly long in extension and there are many accesses, the signal level must be sufficiently high for a transmitting access to reach its most distant destination. The medium is flossy, particularly affecting the higher bit rates, and each access tap has an insertion loss. This leads to very high signal levels which may be rich in harmonics and spurious emissions, degrading bit error rate. On the other hand, with insufficient signal, the S/N degrades, which will degrade error performance. A good level balance must be achieved for all users. Each and every multipoint connectivity must be examined. The number of multipoint connectivities can be expressed by n(n 1), where n is the number of accesses. If, on a particular LAN, 100 accesses are planned, there are
9900 possible connectivities to be analyzed to carry out signal level balance.
One way to simplify the job is to segment the network, placing a regenerative repeater or bridge at each boundary. This reduces the signal balance job to reasonable proportions and ensures that a clean signal of proper level is available at reach access tap. For baseband LANs, 50-_ coaxial cable is favored over the more common 75-_ cable. The lower impedance cable is less prone to signal reflections from access taps and provides better protection against low-frequency interference.
The effects of standing waves can be reduced by controlling the spacing between access taps. For example, the Ethernet technical summary [1] recommends spacing no less than 2.5 m, for the 10-Mbit/s standard Ethernet LAN.
The technical summary says that by following this placement rule, the chance the objectionable standing waves will result is reduced to a very low (but not zero) probability. Again for Ethernet, up to 100 devices may be placed on a cable segment and the maximum segment length is 500 m. The segments can be connected through regenerative repeaters, with a maximum total end-to-end length of 2.5 km [1, 4, 21].
The baseband technique incorporates single signal transmission of a digital waveform on a transmission medium. Broadband transmission has the capability of transmitting multiple signals simultaneously on a medium, typically coaxial cable. Each signal is assigned a frequency slot in a frequency division multiplex plan. Broadband technology derives from the CATV (cable television) industry.
Baseband lends itself to bus and ring topologies, and broadband to bus and tree topologies. Broadband systems require a modem at each access; baseband systems do not. One extremely important consideration for baseband transmission is that only a single thread (transmission line) exists. It can accommodate only one user at a time; otherwise there is a high probability of data message collision. Collision is where the electrical signals bearing the traffic of two or more users interfere one with the other, corrupting the traffic of each. To help avoid collisions, segmenting has become an excellent alternative using bridges, hubs, or switches. These devices are discussed at the end of this chapter.
3.1 Broadband Transmission Considerations
Broadband transmission permits multiple users to access the medium without collision. Broadband means that we take advantage of the medium’s wide bandwidth.
This wide bandwidth is broken down into smaller bandwidth segments in an analogous fashion to FDM. Each of these segments is assigned to a family of users. The statement regarding collision is correct if there are no more than two accesses per frequency segment connected on a point-to-point basis, where one access receives while the other transmits. If, in this case, we assume contention as the access protocol, then as the family increases in number, the chances of collision start to increase. With a little imagination, we can see that, with the proper switching scheme implemented, a user can join any family by simply switching to the proper frequency band of that family. All that is required is a change in modem frequency and possibly modulation waveform. There may also be certain protocol considerations as well.
Unlike their baseband counterparts, broadband systems can be designed to accommodate digital or analog voice, data from kilobit to multimegabit rates, video, and facsimile. Thus broadband systems are versatile. They are also much more expensive than their baseband counterparts and require a higher level of design engineering effort.
As mentioned, much of our present broadband technology derives from cable television technology. Total system bandwidths are on the order of 300–500 MHz.
Each access requires a modem to modulate and demodulate the data or other user signal and to translate the modulated frequency to the assigned frequency slot on the cable.
This, then, is RF transmission and, by its very nature, must be one way or unidirectional. Thus a user can only access another user “downstream” from it.
If we assume a single medium, usually a 75-_ coaxial cable, then how does one access another user “upstream”? This is done using a similar approach to that of a two-way or interactive CATV (cable television) system, where two paths are provided on a single coaxial cable. This is accomplished by splitting the cable spectrum into two frequency segments, one segment for one direction and the other for the opposite direction. At a cable terminating point, which some even call a head end from CATV terminology, a frequency translator converts and amplifies signals from one direction (frequency segment) into signals for transmission in the opposite direction (frequency segment). Another term for “head end” for broadband LANs is central retransmission facility (CRF).
There are two choices of topology for broadband LANs: bus and tree. The head end or CRF is located at some termination point on the bus, and in the case of tree topology the CRF is located at its root, so to speak.
Another approach to achieve dual path operation is to use two cables; one provides the “go” path and the other the “return” path. For single-cable split-band operation, a rather large guard band is left in the center of the cable spectrum to ensure isolation between the two paths. Then we can see that with the provision of two-cable operation the usable bandwidth can be more than doubled. Modem operation is also simpler because, to access a particular net, only one frequency operation is required (i.e., the send and receive frequencies can be the same).With single-cable split-band operation, send and receive frequencies must necessarily be different [2].
Broadband services make up about 5% of the total LAN market. Baseband predominates.
Table 13.2 gives broadband channel allocations for CSMA/CD services and
Table 13.3 provides channel allocations for a broadband token bus configuration.
Recommended channelization for both single and dual cable operation is given.
3.2 Fiber-Optic LANs
Fiber-optic LANs may be considered broadbandin that a class of modem is required to place the digital signal on the fiber. The modem, of course, consists of a light source, detector, and the necessary driver and signal conditioning circuitry.
With wavelength-division multiplexing (WDM) we have a true broadband system.
At this time, single-wavelength operation prevails.
The type of fiber-optic cable selected for a LAN is a cost trade-off. The extension of a LAN is generally short such that multimode fiber can be used, and the mature short-wavelength technology permits other cost savings. Even plastic fiber may be considered. The losses of the fiber itself will generally be low due to the short-distance operation even at 820-nm operation. A LAN that is
1 km long might display a fiber loss from 2 dB to 5 dB. The major contributor to loss is the taps if a fully passive network is to be implemented.
Fiber lends itself to all three LAN topologies: bus, ring, and star. The use of passive couplers leads to a more reliable system, but the insertion loss of passive couplers is a consideration. With active coupling, the loss of one source or detector can cause the entire network to crash unless bypass switches are used.


4.1 General
Many of the widely used LAN protocols have been developed in North America through the offices of the Institute of Electrical and Electronic Engineers (IEEE)
The American National Standards Institute (ANSI) has subsequently accepted and incorporated these standards, and they now bear the ANSI imprimatur.
The IEEE develops LAN standards in the IEEE 802 committee, which is currently organized into the following subcommittees:
802.1Bridging & Management
802.2Logical Link Control
802.3CSMA/CD Access Method
802.4Token Passing Bus Access Method
802.5Token Ring Networks
802.6Metropolitan Area Networks (MANs)
802.7Broadband Technical Advisory Group
802.10LAN Security
802.11Wireless LAN
802.12Demand Priority Access Working Group
802.15Wireless Personal Area Networks
802.16Broadband Wireless Metropolitan Area Networks
802.17 Resilient Packet Ring
802.18 The Radio Regulatory TAG (Technical Advisory Group)
802.19 Coexistence Advisory Group
802.20 Mobile Broadband Wireless Access (Working Group)
The fiber distributed data interface (FDDI) standard, which is discussed in
Section 5.6, has been developed directly by ANSI.
4.2 How LAN Protocols Relate to OSI
LAN protocols utilize only OSI layers 1 and 2, the physical and data-link layers, respectively. The data-link layer is split into two sublayers: medium access control
(MAC) and logical link control. These relationships are shown in Figure 13.3.
Stallings [3] presents an interesting and rational argument on the reasoning for limiting the layering to the first two OSI layers. There is no question that the functions of OSI layers 1 and 2 must be incorporated in a LAN architecture. We now ask, Why not layer 3? Layer 3, the network layer, is concerned with routing.
There is no routing involved with LANs. There is a direct link involved between any two points. The other functions carried out by OSI layer 3—addressing, sequencing, and flow control—are carried out by layer 2 in LANs. The difference is that layer 2 performs these functions across a single link. OSI layer 3 carries out these functions across a sequence of links required to traverse a network. Of course, there is only one link required to traverse a LAN.
It would seem that layer 3 is required when viewed through an attached device.
The reason is that the device sees itself attached to a network connecting multiple devices. One would think that ensuring delivery of a message to one or more accesses would be a layer 3 function. the characteristics of the network allow these functions to be performed in the first two layers.
As shown in Figure 13.3, the OSI data-link layer is divided into two sub layers: logical link control (LLC) and medium access control (MAC). These sub layers carry out four functions:
1. Provide one or more service access points (SAPs). A SAP is a logical interface between two adjacent layers.
2. Before transmission, assemble data into a frame with address and error detection fields.
3. On reception, disassemble the frame and perform address recognition and error detection.
4. Manage communications over the link.
The first function and those related to it are performed by the LLC sub layer. The last three functions are handled by the MAC sub layer.
In the following subsections we will describe four common IEEE and ANSI standardized protocols. Logical link control (LLC) is common to all four. They differ in the medium access control (MAC) protocol.
A station on a LAN may have multiple users; oftentimes these are just processes, such as processes on a host computer. These processes may wish to pass traffic to another LAN station which may have more than one “user” in residence. We will find that LLC produces a PDU with its own source and destination address. The source address, in this case, is the address of the originating user. The destination address is the address of a user in residence at a LAN station. Such a user is connected through a service access point (SAP) at the upper boundary of the LLC layer. The resulting LLC PDU is then embedded in the information field of a MAC frame