Week1Lctr

NETW 250

VOICE/VOIPWeek 1 Prof Reyes

VOIP• Telecommunications and VoIP If you walk into a major electronics store and

head into the cell phone department, what do you see? New electronic gadgets such as iPhones, iTouch, third-generation (3G) phones that have the capability to provide GPS, text, connect to Internet services, download and listen to our favorite music, take and edit pictures, play video games (even play with the person next to me), and watch television shows.

• Oh, by the way, you can make voice calls out of these gadget phones too! It is amazing what phone services can provide these days!

• This shows how telecommunications have evolved over time. This also illustrates the demand on telecommunications companies to provide the technology and bandwidth required to provide multimedia services.

• With the introduction of voice over IP, the telecommunications infrastructure has moved to a new model to carry voice, data, and video services.

• The object of this lecture is to describe the elements of PSTN and its history and define telecommunications. To truly understand and appreciate these advancements, we must look back into the evolution of telecommunications and this infrastructure called PSTN.

VOIP• Telecom Defined • To learn more about the PSTN, let us take a few steps back and define

telecommunications. • The word telecommunications is a combination of Greek (word tele, meaning "far

off") and Latin (communicare meaning "to share"). Telecommunications is the electronic transmission of data or information over a distance. It involves the use of technology to move information.

• The transfer of information over distance is important for our existence. This movement of information is provided by electronic means, at the fastest speeds possible.

• Telecommunications services are used for business, social life, and entertainment. These services are provided by telephone companies that have the technology to deploy transmission links and switching systems.

• Telecommunications involves many participants, such as the public telecommunications operators, service providers, manufacturers of equipment, the end users, financial investors, and, of course, the government, to provide regulations and standards.

VOIP• Telecommunications can be divided into the following forms of applications:

• Telephone calls • Computer data • Music • Video, and more

• In the telecommunications world, information is sent and received over distance. This means that information transfer may travel between buildings, across town, from city to city, from one country to another, or just several feet. When a call is made, it always follows a telecommunications model, where there is always the source or sender, channel or media to send information, and the destination or receiver.

• Telecommunications were invented to have the ability to communicate from a distance. Also, as time moved on, businesses have looked at telecommunications as a business tool that they can use for their business applications.

• The objectives of telecommunications provided the foundation to apply the proper technology for a business advantage. These four telecommunications objectives presented how it supports a company’s business goal.

VOIP• The four telecommunication objectives are: communicate, allow organizations or

individuals to share and distribute information, allow organizations to connect and operate with dispersed or distant functions, and share resources regardless of distance.

• We are in a time where information is considered an asset to a person or corporation. The ability to access information within a short time frame determines an individual's or company’s success in the business world. The advancements in telecommunications are a necessity for this generation and for generations to come

• A Brief Telecom History How did the telephone and telecommunications evolve over the years? The table below highlights the advancements in telecommunications. The major developments are a result of a number of scientific and technological inventions and discoveries over time. Some are major inventions, while others are modifications from previous inventions.

• These innovations came about from the need to communicate for business, personal, government, and military needs. In the history of telecommunications, some factors in the advancements are industrialization, the need to trade goods, and war. The following is a condensed version of telecom history:

VOIP• The Evolution of Telecommunications Through Deregulation Telecommunications

is considered a public utility in this country, and therefore the government provides rules on how the network will be utilized. Regulations and deregulations have introduced major turns in the history of telecommunications. There are a couple of regulation/deregulation points in history that I would like to discuss: AT&T divestiture of 1984, and Telecommunications Act of 1996.

• AT&T Divestiture of 1984• One of the most important movements toward deregulation was the antitrust

lawsuit filed by Microwave Communications Inc. (MCI) on the grounds that the AT&T Bell operating system was illegally preventing its competitor's access to their lines, thus inhibiting market share.

• The argument by the Bell System was that they provided "universal service," which meant that a single company can provide a better service to the customers; however, around 1980, a lot of new telecom applications were being developed by other companies, and they were not able to market them. AT&T had sought to delay the process in circuit courts, but by 1981, Judge Harold Greene divested AT&T.

VOIP• AT&T Divestiture of 1984• The process was completed in 1984, when AT&T was broken up into Regional Bell

Operating Companies (RBOCs), but it would retain its manufacturing, long-distance services, and research arm. This opened the market to new telecom firms that offered telecom services into a rapid and competitive entry into the market

• Telecommunications Act of 1996President Bill Clinton signed this legislation into law on February 8, 1996. This law promoted competition and deregulation in almost all aspects of the telecom industry. It provided cable TV regulation, where any company who has the capital can provide telephone, Internet, and/or TV service.

• This resulted in infrastructure sharing, convergence via integration of telephone, computer, or cable industries. This act gave birth to competitive local exchange carriers (CLECs). With this law in place, the CLECs could now compete with the major telephone companies called incumbent local exchange carriers (ILECs) and provide telecom services to consumers.

VOIP• Telecommunications Act of 1996 • This led to a very competitive market, which drove the prices down on both

services and equipment. It also led to a number of telecom mergers and acquisitions.

• If you were working in the telecommunications industry at that time, chances are you were a part of a merger, or a colleague of yours joined a newly formed CLEC; however, like most industries, the telecom market subsided after a few years. Stock prices fell on most technology-based industries. This affected the CLECs and had a lot to do with their demise.

• Nowadays, only a few have survived, but they brought a major change in the overall evolution of telecommunications.

• For more insight into this subject, here is an FCC page discussing the Act: Telecommunications Act of 1996.

VOIP• The Public Switched Telephone Network (PSTN)

The diagram above illustrates a PSTN and its basic components. The PSTN is composed of these major parts:Central offices Transmission facilitiesIntelligent networks (signaling)Station equipment and Customer premises equipment

VOIP• Central office contains telecommunications equipment, such as telephone

switches (Class 5), digital cross-connect equipment, and routing equipment. • Transmission facilities are mostly interoffice trunks that carry information

between COs and nodes in the network. Lines (aka local loops) carry information from COs to the customers. Circuits can also be established in these transmission facilities, which provides a dedicated, end-to-end, temporary path from start-up to the termination of a call.

• Intelligent network provides signaling that determines the best way to route a call across a network.

• Station equipment is customer equipment, such as telephones, fax machines, and modems.Customer premises equipment is equipment that is stationed inside a customer’s property or building, such as a PBX.

• These components follow the standards established by the International Telecommunications Union (ITU-T). Many of its provisions have been unchanged for decades because they are reliable. With the introduction of VoIP, we will see if any changes will be made to accommodate these changes.

VOIP• The Public Switched Telephone Network (PSTN)• The telecommunications industry needs a network to run its applications. Since

Alexander Graham Bell sent the first voice transmission over a wire in 1876, the public switched telephone network (PSTN) has evolved with the advancements in telecommunications.

• It has evolved from a one-way voice transmission to a collection of interconnected network elements designed to carry complex telecommunications services. Its evolution was initially intended to support the needs of a voice infrastructure.

• It was analog, mostly had electromechanical telecom equipment, and was not well suited to serve the emerging needs of packet and video services. Over the last two decades, digital transmission has transformed the network and provided an economical advantage to move information.

• The service providers justified the need to switch to digital transmission, which gave them a lower operating cost due to emerging nonvoice services. Equipment manufacturers also provided better equipment that can move information at a higher rate.

VOIP?• PSTN in the Early Days (Predivestiture) • Around the 1960s, the PSTN was implemented by the Bell System using

hierarchical setup. With this network, there are five levels of switching. Basically, the number of levels in this PSTN depends on the costs of transmission and facility.

• Calls would be routed through the lowest available level. If all of the facilities are used, the call is blocked. It is then routed to an alternate route. The diagram below illustrates the early days of PSTN:

• PSTN After Divestiture In the 1980s, the PSTN took a different form after the divestiture. Since the market opened up for other companies (aside from AT&T) to provide telecom services (long distance and local), interexchange carriers (IXC), local exchange carriers (LEC), and local access transport areas (LATA) were introduced.

• AT&T is now one of the IXCs that provide long-distance services. The LATA networks provide local exchange telecom services to telephone customers, as well as access to the networks of IXCs for intercity and long-distance services. The LECs must use the IXC to connect calls across an LATA. The LECs, however, are not allowed to provide long-distance services.

VOIP? Around the 1960s, the PSTN was implemented by the Bell System using hierarchical setupThere are five levels of switching. The number of levels in this PSTN depends on the costs of transmission and facility. Calls would be routed through the lowest available level. If all of the facilities are used, the call is blocked. It is then routed to an alternate route. The diagram llustrates the early days of PSTNPublic Switched Telephone Network

VOIP?• Each IXC interfaces with an LATA at a single point known as point-of-presence (POP).

End offices may now connect to a POP or route through a Tandem switch. The tandem switch replaced the Class 4 switch in the previous hierarchical setup. The diagram below illustrates the PSTN after the divestiture:

VOIP?• Anatomy of a Phone Call (POTS)

Now that we have a background of the PSTN and its components, let us put it all together by going through a simple phone call over the network.. Over the years, as voice equipment has evolved, the concepts to transmit a phone call and move voice from one end to another have remained the same. These concepts are encoding, transmitting, and receiving.

VOIP?EncodingEncoding is the process of changing the information into a format required for transmission. It is where voice is transformed from one form to another (analog to digital). Sound waves will not travel well through physical media; therefore, it must be encoded. As Mrs. Smith picks up the phone, she will hear a dial tone, provided from the Central Office (CO). She dials the desired digits, and Mrs. Jones's phone will ring. When Mrs. Jones answers the phone, the call is established. As Mrs. Smith starts to talk, her voice (analog) will be encoded into a digital format (0s and 1s).

TransmissionOnce Mrs. Smith's voice is encoded, it can now be moved from one location to another. It is moved though various physical media (for example, copper wires) from the calling party to the called party (Mrs. Jones).

ReceivingThe transmitted voice must be accepted and reorganized at the receiving end (Mrs. Jones). Decoding can happen at this point where the digital signals are converted back to analog ¡n a form that Mrs. Smith can understand, where she can hear Mrs. Jones's voice.

VOIP• Time Division Multiplexing (TDM)• The anatomy of the phone call is made possible by two major technologies – TDM

and PCM. These technologies are also the basis of digital transmission in the PSTN.• Time division multiplexing (TDM) is the basis of multiple-channel digital

communications. It is a process where a number of channels are grouped and "combined" into a single digital signal. As its name implies, it uses time as a reference for multiplexing data. Each channel input is periodically sampled and assigned to a certain time slot.

• The TDM sender has a multiplexer that scans each input line. At the first scan, the multiplexer accepts data from each line and builds a frame that represents data from each line. Each of these frames will also contain synchronization and signaling bits. At the receiving end, the demultiplexer looks at the position of data in the TDM frame to ensure that the information is parsed correctly into the output lines. Also, the synch bits are removed at the receiving end, and the pure data is sent into their corresponding lines or ports.

VOIP

• Time division multiplexing (TDM) is the basis of multiple-channel digital communications

VOIP• Pulse Code Modulation (PCM) • The basis of voice transmission was made possible by Pulse Code Modulation

(PCM). It is based on the Nyquist Theorem, and sampling method, which states that, to reconstruct an analog signal or waveform, the number of sample points must be equal to twice the maximum frequency of the signal. Each voice signal is about four Khz; thus, the sampling rate is 8,000 samples per second. The process of PCM includes three stages:

• Sampling: Each part of an analog voice waveform is sampled and would represent an infinite number of voltages. The voltages represent an amplitude of pulses and are organized to represent analog information. This method is called pulse amplitude modulation (PAM). The group of bits representing a sample is represented in an 8-bit, or a byte. Sampling is carried out at a rate of eight kHz, where an 8-bit encoding is used. Quantization: It is the process of reducing the PAM signal to a limited number of discrete signals. It converts a continuous signal into discrete values in amplitude. This is basically done to reduce noise during the PAM process.Encoding: This reduces the number of unique values from the PAM signal so that they can be coded in bits and grouped in bytes for transmission.

VOIP• From POTS call to VoIP• Understanding the PSTN and telecommunications gives a basic understanding on

the main PSTN components and what services it offered in the past; however, the PSTN does not fit all the needs of its users and providers.

• The PSTN is very reliable and was able to provide voice services over the years, but there are factors endeavoring to change it to a new network. The need for data transmission has equaled, or sometimes overtaken, voice as main traffic on many voice networks.

• There is also a need for a higher bandwidth to provide data services with voice. For new technologies, such as fast Ethernet, optical networks are required to send data at a higher rate.

• Efficiency was also an issue on PSTN. The circuit-switched calls required a permanent connection (while a call is in place), while data transmission has the capability to use the bandwidth only when it is required. New services such as DSL and high-speed cable modems were offered by service providers as well.

VOIP• From POTS call to VoIP• The popularity of the Internet and growth of data networks changed the PSTN

circuit-switched model into a new model where the Internet can carry voice, data, and video services. Now the idea of carrying voice over IP is in full swing.

• There are major investments made on the data network by private corporations and traditional carriers. VoIP service providers are rising. The economic advantages to customers are becoming more obvious. The advantages are also seen by providers as they save on transmission costs and network management costs.

• The need to optimize the usage of the PSTN and the Internet becomes more important as they create a competitive environment for providers, driving down the cost of services. This is a winning situation for everyone.

• As we turn our lectures and topics toward VoIP, the importance of PSTN becomes more visible. We will get more into these types of topics as we go through the next weeks of the term.