Introduction to Telecommunications 11 Other interested parties include governmental officials who are keen on having national approaches adopted as international standards and academic experts who want to become inventors of new technological approaches.
Many international standards include alternatives and options from which a national authority selects those suitable for their own national standards. These options are included in cases for which a common global understand- ing could not be agreed on.
Sometimes some aspects are left open and they require a national standard. For example, national authorities determine the details of their national telephone numbering plan, for which international standards give only guidelines. Another example is frequency allocation. International standards define usage of frequency bands e. Some examples of national authorities are shown in the Figure 1. They take care of all areas of standardization, and they set up specialized organizations or working groups to work with the standardization of each specific technical area, such as telecommunications and information technol- ogy.
These example organizations are shown in Figure 1. Telecommunications network operators and manufacturers participate in standardization work. One example of standards made by ETSI is the digital cellular mobile system GSM, which became a major standard for second gen- eration digital mobile communications all around the world.
The deregulation of telecommunications forced national PTTs to become network operators equal to other new operators and they are not allowed to make standards alone any more.
Some of these organizations are shown in Figure 1. The Institute of Electrical and Electronics Engineers IEEE is one of the largest professional societies in the world and it has produced many impor- tant standards for telecommunications. For example, international standard ISO Many of its standards, such as those for connectors for personal computers, have achieved global acceptance. It is a government organization that regu- lates wire and radio communications. It has played an important role, for example, in the development of worldwide specifications for radiation and susceptibility of electromagnetic disturbances of telecommunications equipment.
Its task is to adapt the global standard to the American environment [4]. ITU-T works for the standards of public telecommunications networks e. Many parties participate in their work, but only national authorities may vote. ISO has done important work in the area of data communications and protocols, and IEC in the area of electro- mechanical for example, connectors , environmental, and safety aspects. The organizations shown in Figure 1. Some of these are active in ITU-T and ISO, and many international standards are based on or may even be copies of the initial work of these groups.
We introduce some of these as examples of standards organizations without official status see Figure 1. Unofficial forums are more flexible and can produce necessary standards on a shorter timescale than can official organizations. Their specifications are often used as a basis for later official standards. The Telemanagement Forum TMF is an organization of system manu- facturers that works to speed the development of network management stan- dards. With the help of these standards, telecommunications network operators will be able to control and supervise their multivendor networks efficiently from the same management center.
The organizations mentioned here are just examples; many other such organizations and cooperative units exist. New groups appear and some organizations disappear every year.
One important problem in standardization is the question of intellec- tual property rights IPRs. One company involved in development of a stan- dard may have a patent or copyright for a method or function that is essential for implementation of the standardized system.
In such a case, other manu- facturers may not be able to implement the standard in an economically fea- sible manner without interfering with a patent or copyright.
There are no fixed rules regarding how to solve this problem, but very often the patent or copyright owner agrees to license the patent or copyright for a standardized system under fair terms [5]. The national PTTs were once the only national telecommunications operators in most countries.
For political reasons domestic manufacturers were preferred as suppliers of the systems needed in the network. Competi- tion was not allowed, and the development of services and networks was slow in many countries.
During the latter part of the s the deregulation of the telecommu- nications business started in Europe and proceeded rapidly in many other areas of the world. Competitive telecommunications services are important for the development of an economy, and governments supported the devel- opment of free markets heavily.
In Europe the European Union has paid much attention to the deregu- lation of the telecommunications business. New operators have obtained licenses to provide local and long-distance telephone and data services and mobile telecommunications services. Previously many standards, such as ana- log mobile telephone standards, did not even support a multioperator envi- ronment. The initial requirement of the digital mobile telecommunications system GSM in Europe was the support of multiple networks in the same geographical area.
The deregulation of the telecommunications business has reduced tariffs on long-distance calls and mobile calls to a small fraction of the tariffs paid in the mids. The reduction of fees has further increased the demand for services, which has prompted reductions in the price of ter- minal equipment, such as mobile telephones, and the fees for calls.
These developments have demonstrated how dangerous it is for manu- facturers to be too dependent on a single domestic customer. Many telecom- munications manufacturers that were independent in the past do not exist as independent suppliers anymore. This process still continues. At the same time, new small manufacturers are appearing. Their window of opportunity is to produce special equipment, in which the largest vendors are not inter- ested, or systems for brand new rapidly growing services.
Plain old telephone service POTS will still be important in the future, but mobile and data communications grow most rapidly in volume. The two main directions of this development are in the areas of voice communica- tions, which will become mobile, and data communications, which will become wideband, high-data-rate communications.
Because of deregulation, subscribers can choose which network operator they want to use to get wide- band access to the Internet over ordinary telephone lines. Cable TV opera- tors are also providing similar services in competitive terms. The provision of developing multimedia services in the future will be especially interesting. The expansion of the Internet, with its improving capability to transmit voice in addition to data, presents a new challenge to the public telecommunications network operators.
This requires telecommunications network operators, including cellular net- work operators, to change their strategies from telephone and data transmis- sion to complete service and information content provision. These services will contain Internet portals and location-based services, such as information on the nearest fast-food restaurant, in cellular networks. For the future development of the telecommunications business, we must pay attention to customer services that technology can provide, not technology itself.
Many good technologies, which we explain in later chap- ters, have not been successful because ordinary subscribers have not viewed them as attractive. On the other hand, some services, such as the WWW, have grown very rapidly. We have to keep in mind that only attractive services make new technologies successful. Problem 1. Explain why you think so because this is a matter of opinion. Explain both political and business interests.
References [1] Carlson, A. Hanzo, Mobile Radio Communications, 2nd ed. The operation of a conventional telephone, which is easy to understand, is used to clarify how telephone con- nections are built up in the network.
We look at subscriber signaling over the subscriber loop of the telephone network. The same kind of signaling is needed in modern telecommunications networks, such as ISDN and cellular networks. We start with this simple service to lay a foundation for under- standing more complicated types of service in later chapters. In this chapter we divide the network into layers and briefly describe different network technologies that are needed to provide various kinds of service.
Some of these, such as mobile and data networks, are discussed in more detail later in this book. The last topic of this chapter is an introduction to the theory of traffic engineering; that is, how much capacity we should build into the network in order to provide a sufficient grade of service for the customers.
These users of public networks, for example, a telephone network, are called subscribers. We will see that the telecommunications net- work consists of many different networks providing different services, such as data, fixed, or cellular telephony service. These different networks are dis- cussed in later chapters. In the following section we introduce the basic func- tions that are needed in all networks no matter what services they provide.
The three technologies needed for communication through the net- work are 1 transmission, 2 , switching, and 3 signaling. Each of these technologies requires specialists for their engineering, operation, and maintenance.
Transmission systems use four basic media for information transfer from one point to another: 1. Copper cables, such as those used in LANs and telephone sub- scriber lines; 2. Optical fiber cables, such as high-data-rate transmission in telecom- munications networks; 3. Radio waves, such as cellular telephones and satellite transmission; 4. Free-space optics, such as infrared remote controllers.
In a telecommunications network, the transmission systems intercon- nect exchanges and, taken together, these transmission systems are called the transmission or transport network. Note that the number of speech channels which is one measure of transmission capacity needed between exchanges is much smaller than the number of subscribers because only a small fraction of them have calls connected at the same time.
We discuss transmission in more detail in Chapter 4. However, as the number of telephones grew, operators soon noticed that it was necessary to switch signals from one wire to another. Then only a few cable connections were needed between exchanges because the number of simultaneously ongo- ing calls is much smaller than the number of telephones Figure 2.
Strowger developed the first automatic switch exchange in At that time, switching had to be controlled by the telephone user with the help of pulses generated by a dial. For many decades exchanges were a complex series of electromechanical selectors, but during the last few decades they have developed into software-controlled digital exchanges.
Modern exchanges usually have quite a large capacity—tens of thousands subscrib- ers—and thousands of them may have calls ongoing at the same time. Signaling is carried out with the help of specific signals or messages that indicate to the other end what is requested of it by this connection. Signaling is naturally needed between exchanges as well because most calls have to be connected via more than just one exchange. Many different signaling systems are used for the interconnection of different exchanges.
Sig- naling is an extremely complex matter in a telecommunications network. In approximately 10 seconds he is able to receive calls directed to him. Information transferred for this function is carried in hun- dreds of signaling messages between exchanges in international and national networks.
Signaling in a subscriber loop is discussed in Section 2. This subscriber line, which carries speech signals as well, is a twisted pair called a local loop. The principle of the power supply coming from the exchange site makes basic tele- phone service independent of the local electric power network. Local exchanges have a large-capacity battery that keeps the exchange and subscriber sets operational for a few hours if the supply of electricity is cut off.
This is essential because the operation of the telephone network is especially impor- tant in emergency situations when the electric power supply may be down. Figure 2. Elements of the figure and operation of the subscriber loop are explained later in this chapter.
Originally telephone microphones were so-called carbon microphones that had diaphragms with small containers of carbon grains and they operated as variable resistors supplied with battery voltage from an exchange site see the subscriber loop on the left-hand side of Figure 2. When sound waves pressed the carbon grains more tightly, loop resistance decreased and current slightly increased.
The variable air pressure generated a variable, alternating current to the subscriber loop. This variable current con- tained voice information. The basic operating principle of the subscriber loop is still the same today, although modern telephones include more sophisticated and better quality microphones. The earphone has a diaphragm with a piece of magnet inside a coil.
The coil is supplied by alternating current produced by the microphone at the remote end of the connection.
The cur- rent generates a variable magnetic field that moves the diaphragm that pro- duces sound waves close to the original sound at the transmitting end see the subscriber loop on the right-hand side of Figure 2.
The telephone network provides a dialed-up or circuit-switched serv- ice that enables the subscriber to initiate and terminate calls. The subscriber dials the number to which she wants to be connected. This requires addi- tional information transfer over the subscriber loop and from the exchange to other exchanges on the connection, and this transfer of additional informa- tion is called signaling.
The basic subscriber signaling phases are described in the following section. Modern electronic tele- phones would not necessarily need this if they could take their power from a power socket at home. However, getting the power supply from the exchange is still an important feature because it ensures that the telephone network operates even in emergency situations when the power network may be down.
When the hook is raised, the switch is closed and an approximately 50 mA of current starts flowing. This is detected by a relay giving information to the control unit in the exchange Figure 2. The control unit is an efficient and reliable computer or a set of computers in the telephone exchange.
It acti- vates signaling circuits, which then receive dialed digits from subscriber A. We call a subscriber who initiates a call subscriber A and a subscriber who receives a call subscriber B. The control unit in the telephone exchange con- trols the switching matrix that connects the speech circuit through to the called subscriber B.
Connection is made according to the numbers dialed by subscriber A. The ringing voltage is often about 70V ac with a Hz frequency, which is high enough to activate the bell on any telephone. When the exchange detects the off-hook condition of a subscriber loop, it informs us with a dial tone that we hear when we raise the hook that it is ready to receive digits.
After dialing it keeps us informed about whether the circuit establish- ment is successful by sending us a ringing tone when the telephone at the other end rings. When subscriber B answers, the exchange switches off both the ringing signal and the ringing tone and connects the circuit. At the end of the conversation, an on-hook condition is detected by the exchange and the speech circuit is released.
This indicates to the telephone exchange when a call is to be initiated and when it has to prepare to receive dialed digits. We call this principle rotary or pulse dialing. In rotary dialing a local loop is closed and opened according to the dialed digits, and the number of current pulses is detected by the exchange. This signaling method is also known as loop disconnect signaling. The main disadvantages of this method are that it is slow and expensive due to high- resolution mechanics and it does not support supplementary services such as call forwarding.
The local-loop interfaces in telephone exchanges have to support this old technology though it has been gradually replaced by tone dialing. When a digit is to be dialed, the dialing plate with finger holes is rotated clockwise to the end and released. While homing, the switch is break- ing the line current periodically and the number of these periods indicates the dialed digit.
For example, digit 1 has one period, 2 has two periods, and 0 has 10 periods or cycles. Mechanics make the homing speed approxi- mately constant and each period is about ms long with a ms break Figure 2. This method for the transmission of digits has also been used for signaling between exchanges and then it is known as loop disconnect signaling.
The value of the loop current differs slightly from country to country and it is also dependent on line length and supply voltage, for example. Typi- cally it is from 20 to 50 mA, high enough to control old generation electro- mechanical switches that used pulses to control directly the rotating switches of the switching matrix of an exchange. Digital exchanges do not require high-power pulses to drive the selectors as old electromechanical switches did.
However, subscriber lines are still, and will be, supplied by a — or —V battery so that telephones continue to operate independent of the electric power supply.
Modern telephones usually have 12 push buttons keys A to D of Figure 2. One of the frequencies is from the upper frequency band and the other from the lower band.
All frequencies are inside the voice frequency band —3, Hz and can thus be transmitted through the network from end to end, when the speech connection is estab- lished. This signaling principle is known as dual-tone multifrequency DTMF signaling. Tones are detected at the subscriber interface of the telephone exchange and, if necessary, signaled further to the other exchanges through which the connection is to be established.
All digital local exchanges have a capability to use either pulse or tone dialing on a subscriber loop. The subscriber is able to select with a switch on his telephone which type of dialing is to be used. Tone dialing should always be selected if the local exchange is a modern digi- tal one. These services, for example, call transfer, are not avail- able with telephones that use pulse dialing.
We use tone dialing also to control value-added services. Value-added services are services that we can use via the telephone network but that are usually provided by another service provider, not the telecommunications network operator.
One example of value added services is telebanking. Tones are transmitted on the same frequency band as voice, and during a call we are able to dial digits to transmit, for example, our discount number and security codes to the telebanking machine.
The worst disadvantage of a fixed subscriber telephone is still the poor man—machine interface that makes new services difficult to use. Some tele- phones that have displays are more user friendly, but subscribers still have to memorize command sequences to use the new services offered by a modern telephone network.
The local loop, which connects a tele- phone to a local exchange is a two-wire 2W circuit that carries the signals in both transmission directions Figure 2. The Telecommunications Network: An Overview 29 loop. Subscriber loops are and will remain two-wire circuits, because they are one of the biggest investments of the fixed telephone network. By reading this book, you will gain a thorough understanding of converged voice and data networks and also the challenges you will face implementing various network technologies.
The book gives you the information needed to implement and support data and voice integration solutions at the network-access level. Whether you are preparing for CCVP certification or simply want to gain a better understanding of VoIP fundamentals, you will benefit from the foundation information presented in this book.
With 19 years of Cisco networking experience, Kevin has been a network design specialist for the Walt Disney World Resort and a network manager for Eastern Kentucky University. Watch the author perform fundamental CVoice configuration tasks in a series of six video-on-demand labs. Books in this series provide officially developed self-study solutions to help networking professionals understand technology implementations and prepare for the Cisco Career Certifications examinations.
It is easier to expand, upgrade and maintain than its traditional telephony counterparts. VoIP can compress more voice calls into available bandwidth than legacy telephony.. While there are many aspects of VoIP which provide considerable benefits, the technology is still very young and problems remain. The following section looks at some of the weaknesses of this technology and their consequences.
Individual packets can take different routes and varying delays can be encountered and packets lost in transit. Waiting for delayed packets or retransmission of lost packets can result in considerable degradation of quality. Long delays in transit can affect quality so much that the technology can become unusable, though many vendors do have solutions which aim to negate the degradation suffered due to transit delays. CME-3 dial-peer configuration dial-peer voice 1 voip destination-pattern CME dial-peer configuration dial-peer voice 2 voip destination-pattern To place a call enter the recipient's line number first using the keypad and then click on the handset to dial out.
To answer a phone call on the analog phone, click on the handset when the phone is ringing. While the line is connected, you can send Do, Re, or Mi to the recipient by pressing the respective buttons.
In order to hear the sounds, be sure Sound is enabled in Preferences. To end a call, click on the handset. The software will receive it's phone line number from the Cisco Call Manager Express server. To place a phone call, enter the number of the recipient phone using the keypad and then click the Dial button.
Once the recipient has answered the call, the status message will indicate that the Cisco IP Communicator is connected and a green light will show. Cloud computing allows consumers and business to use applications without installation and access their personal files at any computer with internet access. The same concept is going to be used in multi -core technology where the user tries to access his private account form a global content provider through cloud computing.
The measurement of traffic is a basic control activity in order to provide Quality of Service. Quality of service also involves controlling and managing network resources by setting priorities for specific types of data video, audio, files on the network. The primary goal of quality of service is to provide priority to networks, including dedicated bandwidth, controlled jitter, low latency and improved loss characteristics.
Its technologies supply the elemental building blocks that will be used for future business applications in campus, wide area networks and service provider networks. WHY 5G? Very High speed, high capacity, and low cost per bit.
It supports interactive multimedia, voice, video, Internet, and other broadband services, more effective and more attractive, and have Bi- directional, accurate traffic statistics. It offers the high quality services due to high error tolerance. It is providing large broadcasting capacity up to Gigabit which supporting almost 65, connections at a time. More applications combined with artificial intelligent AI as human life will be surrounded by artificial sensors which could be communicating with mobile phones.
Mobile terminals are obtaining each year more processing power, more memory on board, and longer battery life for the same applications. It is expected that the initial Internet philosophy of keeping the network simple as possible, and giving more functionalities to the end nodes, will become reality in the future generation of mobile networks, here referred to as 5G.
Evans and K.
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