[You have downloaded this from: http://telecom.dyndns.biz near Fort Lauderdale, Florida US. Welcome and I'm glad you are interested in Voice Technologies. I have a business here where I do technology consulting ... mainly targeted these days at the Motor Yacht and Marine customers, but also working with small businesses and homes. Please see the bottom for my contact information. Thanks again!] Objectives There are four topics in this lesson. Place the cursor over each topic name below to view the objectives of that topic. The goal of this lesson is to explain the essential telecommunications technologies within the marketplace. (image: Signaling Mechanisms: Loop Start, Ground Start, Wink Start, E&M, Signaling Systems...) ------------------------------------------------------------------------------ Telecommunication Network Overview The current three technologies of a network utilized in a Public Switched Telephone Network (PSTN) - transmission, switching, and signaling -- are dependent upon one another. The transmission provides a path (physical or logical) between two points within a LAN or WAN. When more than one destination is desired, switching is required to achieve multiple destinations. Signaling is needed then to identify the destination on the network and to set up and tear down the transmission path. Upon completion of this topic, you will be able to: Explain the three key telecommunication network technologies. ------------------------------------------------------------------------------ Public Switched Telephone Network The standard Public Switched Telephone Network (PSTN) is basically a large, circuit-switched network that supports traditional voice systems. PSTN also refers to the collection of interconnected systems operated by the various telephone companies and administrations (telcos and PTTs) around the world. PSTN uses a specific numbering scheme that complies with the ITU-T E.164 recommendations. Telephone service carried by the PSTN is often called Plain Old Telephone Service (POTS). In a typical voice/analog telephone network, users make outside phone calls from the phone on their desk. The call connects to the company's internal phone system or directly to the PSTN, over either a basic telephone service analog trunk or a T1/E1 digital trunk. From the PSTN, the call is routed to the recipient, such as an individual at home. If a call connects to a company's internal phone system, the call may be routed internally to another phone without ever going through a PSTN. The PSTN utilizes the basic fundamentals of public or private telecommunication networks. What is PTT? PTT is an abbreviation for postal, telegraph, and telephone (organization). In countries having nationalized telephone and telegraph services, this organization, which is usually a governmental department, acts as its nation's common carrier. ITU-T E.164 ITU - T is an abbreviation for International Telecommunication Union--Telecommunication Standardization Bureau which is responsible for studying technical, operating, and tariff questions and issuing recommendations with the goal of standardizing telecommunications worldwide. E.164 is the International Public Telecommunication Numbering Plan. ------------------------------------------------------------------------------ Principles of Telecommunications Network Technologies The three technologies necessary for the provision of any telecommunications system or PBX network are: Transmission: The physical or logical paths that provide the transport of analog or digital signals between two points. Switching: The process that allows users to establish connections (associations) between end points of a system or network on either a permanent or temporary basis for the purpose of transferring information. Signaling: The mechanism that allows network entities (customer premises or network switches) to establish, maintain, and terminate sessions in a network. Signaling can be in-band (for example, single or multi-frequency) or out-of-band (such as common channel). PBX Private Branch Exchange (PBX) is a private telephone network used by most medium-sized and large companies. PBX users share a certain number of outside lines for external calls. A PBX is less expensive than connecting an external telephone line to every telephone in the organization. Also, it is easier to call within a PBX network because the number dialed is typically just three or four digits. ------------------------------------------------------------------------------ Transmission Transmission can be analog or digital. The physical or logical paths that provide the transport of signals between two points can be transported over various media: coaxial cable, copper wire, fiber-optic cable, and wireless media. Basic transmission consists of electrons being passed back and forth over a LAN or WAN. ------------------------------------------------------------------------------ Switches When more than one destination is desired, switching is required to achieve multiple destinations. The two basic types of switching are circuit and packet. As the demand for networking bandwidth grows, network exchange companies invest more heavily in the infrastructure and equipment necessary to carry a higher volume of traffic. Some companies design entirely new voice-and-data converged (integrated) internetworks into Local Exchanges and Trunk Exchanges. Circuit Switching Circuit switching is the process of dedicating a pair of wires to each phone call made over the Public Switched Telephone Network (PSTN). Circuit switching is ideal for communications that require data to be transmitted in real time. Packet Switching Packet switching is the process of sending packets (bundles of specially formatted data) over a network of interconnected equipment, such as hubs and routers. Packet switching is more efficient and robust for data that can withstand some delays in transmission, such as e-mails and Web pages. Local Exchanges Local exchanges are equivalent to the Central Office (CO). The CO is a building that houses all the switching equipment (circuit, packet, and cell switches). The local exchange consists of Local Exchange Carriers (LEC), local or regional telephone companies that own and operate telephone networks and the customer lines that connect to them. In the United States, there are an estimated 16,000 LECs. Because of the emerging technologies, such as DSL, 80% of customers are in a three-mile radius of a local loop. Trunk Exchanges Trunk exchanges are the physical and logical connections between two switches across a network. A number of trunks compose a telephone network backbone. The trunk exchanges are the focal point for areas of the country where inter-exchange carriers (IXC - regional carriers) provide connection to a T1 line. Note The priority given to voice or data traffic is a key consideration when designing a converged network. Companies that carry data traffic that exceeds voice traffic design their networks mainly for data transport and build the ability to carry voice traffic into their network design as a secondary requirement. However, other companies give preference to voice traffic. ------------------------------------------------------------------------------ The PSTN complies to the recommendations of: ITU-T E.164 ------------------------------------------------------------------------------ Signaling The purpose of signaling in a voice network is to manage the voice session. Signaling occurs at the ingress to the network. It seizes the line, establishes the path across the network, and -- at the remote peer -- acknowledges the call. In general, signaling is needed to identify the destination on the network and to establish, set up, and tear down the transmission path within a network connection. If the facilities are digital, one of two different methods of signaling can be employed: Channel Associated Signaling (CAS), also known as Robbed Bit Signaling, and Common Channel Signaling (CCS), used in ISDN. ISDN One of the first attempts by the telecommunications industry to create a combined voice/data network was Integrated Services Digital Network (ISDN). ISDN allows a service provider to multiplex voice and data traffic on the same physical wires using Time Division Multiplexing (TDM) techniques. ISDN supplies 64 Kbps channels for voice or data. ISDN has been deployed widely by some telecommunication companies in Europe and Japan. ------------------------------------------------------------------------------ Review The objective of this topic was to explain the three key telecommunication network technologies. A PBX is a component in a telecommunication network. Companies must manage private or public networks by utilizing the three basic technologies needed for a telecommunication network: transmission, switching, and signaling. However, for voice technology, the following still exist: Transmission - providing physical/logical paths for analog/digital signaling Switching - allowing users to establish connections on a network Signaling - the mechanism that allows network entities to establish, maintain, and terminate sessions in a network You should now have the knowledge to explain the three key telecommunication network technologies. ------------------------------------------------------------------------------ Subscriber to Network Connections Today, two communications networks -- the telephone network and the cable TV network -- enter most homes in North America. The subscriber-to-network connections exist between the customer premises and the Central Office (CO), utilizing the three key telecommunication technologies. These network connections support three applications: voice calls, data calls, and video entertainment. Consumers are interested in high-speed access to the Internet, business networks for home office use, and entertainment. Various interface types and service providers are used by U.S. and European consumers. Upon completion of this topic, you will be able to: Identify the telecommunication categories of the service providers. ------------------------------------------------------------------------------ Interface Types - US and Europe BRI - Basic Rate Interface PRI - Primary Rate Interface PBX - Private Branch Exchage ATM - Asynchronous Transfer Mode SDH - Synchronous Digital Hierarchy T1/E1 - U.S./Europe first level digital multiplex Key Point The U.S. and Canadian transmission paths contain connections between the customer premises and the Central Office (CO) that support analog and digital signals. The customer premises can consist of various types of connections: Standard analog phones PBX system with various connections of analog T1 lines Two-wire ISDN connection with basic rate interface LAN connections utilizing fiber optics and routers The U.S. and Canada CO has an analog voice switch with 24 timeslots for multiplexing onto a T1. The customer connection method for the European market and the rest of the world is consistent with North America (U.S. and Canada). The European connection options differ by having 32 timeslots for multiplexing (30 used for communication and two used for signaling) on an E1 providing higher data rates. ------------------------------------------------------------------------------ Customer Premises The North American premise consists of the United States and Canada. U.S. telecommunication customers make up 35% of the world's telecommunication market. This large percentage is due to the United States consisting of 50 states with a common standard, language, regulation, and currency. The European market does not have this common luxury. However, the European Telecommunication Standard Institute for Standardization (ETSIS) will assist in maintaining a standard. Regardless of different currencies, consumers of various geographical areas have a significant number of service providers available. However, there are key players within different arenas. ------------------------------------------------------------------------------ Service Options Service providers are called on to play a larger role in enterprise network infrastructures as the needs of customers become more complex. This means providing services for intranet and extranet applications, integrated data, voice, and video, and flexible access options ranging from dial to broadband. Consumers have several different provider options available with each of the telecommunication categories. Providers of telecommunication service include Public Telephone Operators, Inter-exchange Carriers, and Local Exchange Carriers ------------------------------------------------------------------------------ Public Telephone Operators (PTO) The Public Telephone Operators (PTOs) provide an end-to-end service that includes the telephone on the desk, the local loop, and the total service. Since the breakup of the Bell System, the PTO equivalent in the United States consists of the Incumbent Local Exchange Carriers (ILEC). PTOs have typically enjoyed a monopoly in Mexico and Europe through the provision of terminal equipment and network services. While terminal equipment has been largely liberalized, network services are still primarily noncompetitive. Thanks to a more competitive view by the European Commission (and to a lesser extent the PTOs), legal competition in network services for most European Union (EU) member countries began in 1998. ------------------------------------------------------------------------------ Interexchange Carriers The Inter-Exchange Carriers (IXC) are growing rapidly due to the advancement of technology. These IXC companies compete for inter-Local Access and Transport Area (inter-LATA) services. They provide telecommunications services between LATAs or between exchanges within the same LATA. LATA is a U.S. term that refers to a geographic region assigned to one or more telephone companies for providing communication services. The IXC group began in 1977 in the United States with MCI and Sprint and in the U.K. in 1984. AT&T, MCI, Sprint, and other cable and wireless companies have been the dominant market players. The Local Exchange Carriers are concerned with providing services within their LATAs as well as interfacing with IXCs for inter-LATA traffic. ------------------------------------------------------------------------------ Local Exchange Carriers Inter-exchange carriers usually have relied on Local Exchange Carriers (LEC) for the local origination and termination of their traffic. LECs are identified by two categories: Incumbent Local Exchange Carriers (ILEC) and Competitive Local Exchange Carriers (CLEC), both competing for switch connectivity and local loop customers. The LEC group began in the United Kingdom in 1990, competing with British Telecom (BT) for local loop connections within cities. In the U.K., cable television companies are the dominant providers to local loops, but others will emerge as market competition increases. In the European cable market, the LECs are built on their own infrastructure. This consists of installing their own wire pairs and wireless connections. This creates a dominant cable market, since coaxial installation for data and cable television will also serve as transmission for voice services over circuit switches. North America's competitive LECs are getting their facilities from the phone companies instead. This requires the phone companies to unbundle the local loops from the switching circuits and then co-locate their switching and multiplexing equipment in the local central office. This rental from the operator of the local central office is the direct distinction between the North American and European competition. ------------------------------------------------------------------------------ Competitive Market Factors Today's network service providers are in a fiercely competitive market. Service providers range from government-supported monopolies to small startups. Service providers continue to face the market challenges of service definition and delivery, traffic measurement, and billing. Competitors are offering the same services at more attractive prices. Service providers need to differentiate themselves from their competitors by offering value-added services in addition to transport of circuit-switched voice and traditional data applications. ------------------------------------------------------------------------------ Review The objective of this topic was to identify the telecommunication categories of the service providers. The three categories of service providers are: The Public Telephone Operators (PTOs) groups have typically enjoyed monopolies in Europe and Mexico. They provide an end-to-end service that includes the telephone on the desk, the local loop, and the total service. The Inter-exchange Carriers (IXCs) are rapidly growing due to the advancement of technology. These companies compete for inter-Local Access and Transport Areas (inter-LATA) by providing services between LATAs or between exchanges within the same LATA. Inter-exchange carriers have usually relied on Local Exchange Carriers (LECs) for the local origination and termination of their traffic. LECs are identified by two categories: Incumbent Local Exchange Carriers (ILEC) and Competitive Local Exchange Carriers (CLEC), both competing for switch connectivity and local loop customers. LECs have a dominant presence in the U.S. and European markets. Successful service providers will be the ones who move away from commodity services into value-added services that provide a much higher return on investment. This topic covered information about network connection options and providers. You should now have the knowledge to identify the various network connections. ------------------------------------------------------------------------------ Analog to Digital Conversion Although humans are well-equipped for analog communications, analog transmission is not particularly efficient. When analog signals become weak because of transmission loss, it is hard to separate the complex analog structure from the structure of random transmission noise. Digital signals, having only one-bit and zero-bit states, are more easily separated from noise and can be amplified without corruption. Over time, it has become obvious that digital coding is more immune to noise corruption on long-distance connections, and the world's communications systems have converted to a digital transmission format. Upon completion of this topic, you will be able to: Describe digital voice and how it is transmitted. ------------------------------------------------------------------------------ Digitizing Voice Analog voice signals can be sampled at rates of 8 kHz because, as stated before, the frequency range for voice is under 4 kHz. This calculation uses what is called the Nyquist Theorem. If an 8-bit sample is used, the data bandwidth requirement is 64 Kbps. This rate is termed DS-0. The technique is called Pulse Code Modulation (PCM). Nyquist Theorem Sample at twice the highest frequency. Bit rate of digital voice: = 2 x 4 kHz x 8 bits per sample = 64,000 bits per second ------------------------------------------------------------------------------ DS-1 Signal Format It generally is not economical to send just one 64 Kbps voice channel over a transmission channel, so multiple digital voice channels are byte-interleaved into a frame which is transmitted at the sampling rate of a DS-0 channel. In the DS-1 frame there are 193 bits, because one bit is added for framing. Receiving DS-1 frames at 8 kHz requires a bandwidth of 1.544 Mbps. The 193rd bit also can be used to synchronize larger sequences. A sequence of 12 DS-1 frames is called a D4 superframe and contains 288 voice channels. The 12-bit pattern of framing bits, which repeats every superframe, is 100011011100. Extended superframes use 24 DS-1 frames, containing 576 voice channels, and a 4-bit signaling scheme. In extended superframes, the 193rd bit is used not only for synchronization, but for a data link control channel and error detection using a Cyclic Redundancy Check (CRC). ------------------------------------------------------------------------------ Where Does Voice Become Digital? Digital channel banks combine many voice inputs into one wide-band digital channel. The Bell System channel banks are called D-type (for digital) and form the foundation of a whole series of multiplexers. The output of a D-type channel bank is a DS-1 (1.544 Mbps) signal typically transmitted on a T1 or E1 line. A D1 channel bank encodes/decodes 24 analog channels in a T1 line (32 in an E1), adds signaling information, and multiplexes the digital stream onto the transmission medium. The success of D1 banks since 1962 has led to modifications and improvements. There are five kinds of D-channel banks (D1, D2, D3, D4 and DCT). Packing densities were improved in D2, providing 96 channels to every 72 in D1. D3 and D4 banks further improved channel capacity to 144 channels. Finally, the Digital Carrier Trunk (DCT) was developed by the Bell System to be smaller, lower-cost, and easier to maintain than the D4 channel bank. ------------------------------------------------------------------------------ Robbed Bit Signaling in DS-1 Robbed Bit signaling typically uses bits known as the A and B bits. These bits are sent by both the near and far side of a T-1 termination and are buried in the voice data. Since the bits are not stolen very frequently, there is no noticeable compromise in voice quality. The available signaling combinations are limited to ringing, hang up, wink, and pulse digit dialing. this is a rather limited scheme, especially for sending information such as DTMF tones. ------------------------------------------------------------------------------ Common Channel Signaling A network architecture that uses Signaling System 7 (SS7) protocol for the exchange of information between telecommunication nodes and networks on an out-of-band basis is said to perform common channel signaling. In off-hook signaling, one channel is devoted to signaling, so a frame carries only 23 voice channels instead of 24. This is a component of ISDN because it allows the exchange of signaling for interoffice circuit connections. It also allows the exchange of additional information services and features (for instance, class, database queries, and so forth). It provides improved operations procedures network management and administration of the telecommunications network. Example DPNSS is a standard in British ISDN that enables PBXs from different manufacturers to be tied together with E-1 lines as if the phones were extensions of the same PBX. The international standards are called QSIG, Q.931 or Euro-ISDN. Key Point In systems that use CCS, data rates are limited to 56K, because the system is periodically stealing one bit from the bit stream (referred to as CCS). In order for the Central Office (CO) to communicate with the coder/decoder, the boxes steal the eighth bit from each frame. This leaves seven bits in each frame, and 7 x 8,000 = 56K. ------------------------------------------------------------------------------ Voice Compression After the signaling process, voice compression is utilized. The purpose of voice compression is to reduce bandwidth consumption by using compression algorithms optimized for voice. Standard telephone PCM uses eight bits for the code and thus consumes 64 Kbps per call. Another telephone voice standard, called Adaptive Differential PCM (ADPCM), codes voice into 4-bit values and so consumes only 32 Kbps. ADPCM is often used on long-distance connections. ADPCM can be taken to 16 Kbps by using only two bits (four values), but each time the number of different voice amplitude values is reduced, the block representation of voice created is more unlike the original signal, and voice quality is degraded. A second group of standards provides better voice compression and, at the same time, better quality. In these standards, the voice coding uses a special algorithm called linear predictive code (LPC) that models the way human speech actually works. Because LPC can take advantage of an understanding of the speech process, it can be much more efficient without sacrificing voice quality. Why is compression not the best option? Why is Compression Not the Best Option? Compression can only approximate the analog waveform. Quality may suffer, delays may be introduced, and unnecessary extra expense could be incurred for local connections. ------------------------------------------------------------------------------ Voice Compression - ADPCM The differential in Adaptive Differential PCM (ADPCM) means that using eight bits for a sample allows 256 different levels of amplitude to be recognized. To reduce bandwidth to 32 Kbps, only four bits (64 values) are used, and the bit value represents the change from the prior value. This means that the changes between samples are encoded. The adaptive in Adaptive Differential PCM (ADPCM) refers to maintaining a high Signal-to-Quantizing-Noise Ratio (SQR); that is, the quantization granularity also is adjusted automatically. What this means is that companding occurs automatically, depending upon the signal. G.726 describes ADPCM coding at 40, 32, 24, and 16 Kbps. ADPCM voice may also be interchanged between packet voice and public phone or PBX networks, providing the latter has ADPCM capability. ------------------------------------------------------------------------------ Voice Compression - CELP Code Excited Linear Predictive (CELP) voice compression reflects additional knowledge of speech and codebook. The speech is analyzed and compressed with a vector quantizer. The excitation is transmitted as an index into a large vector quantizer codebook, with a gain term to control its power. Typically, the codebook index is represented with about 10 bits (to give a codebook size of 1024 entries) and the gain is coded with about five bits. This technique has produced relatively good speech as low as 2.4 Kbps. The CELP standard is 4.8 Kbps, but some drawbacks were computational power and an introduced delay. 728 describes low-delay CELP; voice compression requires only 16 Kbps of bandwidth. CELP voice coding must be transcoded to a public telephony format for delivery to or through telephone networks. G.729 describes further improvements known as Conjugate Structure Algebraic CELP compression. This enables voice to be coded into 8 Kbps streams. There are two forms of this standard, and both provide speech quality as good as that of 32 Kbps ADPCM. G.729 and G.729a are designed for voice, not DTMF. G.729 vs. G.729a vs. G.729b vs. G.723.1 DTMF The Dual Tone Multi-Frequency (DTMF) system is used by touch-tone telephones. DTMF assigns a specific frequency, or tone, to each key so that it can easily be identified. G.729 vs. G.729a vs. G.729b vs. G.723.1 G.729 - requires 20 MIPS G.729a - requires 11 MIPS G.729b - G.729a with built-in VAD G.723.1 - Video and audio requires up to 30 MIPS used in H.323 (37.5 msec) Can compress to 6.5 kbps ------------------------------------------------------------------------------ Companding: u-Law, A-Law One of the problems with using only eight bits to encode the audio signal is that the volume or amplitude is reduced, which reduces the resolution. One important measure of the resolution, or quality, is the Signal-to-Quantizing-Noise Ratio (SQR). For a linear system, the large amplitude signals tend to mask any noise because they have a higher SQR, and the small amplitude signals will be hard to distinguish. But, since small amplitude signals are more likely to occur, something must be done. More intelligent quantization schemes adjust the encoding scheme to use finer quantization for small-amplitude signals and courser quantization for large-amplitude signals. This is called compressing the signal. On the receiving end, the inverse operation is called expanding -- hence, the term companding. U-law (sometimes called micro-law) is a compander which is the standard for North American and Japanese telephone networks. A-law is the standard compander used in European networks. A-law produces slightly better signal-to-noise ratio for small-amplitude signals, but u-law has lower idle channel noise. A-law and u-law coding use more bits for smaller-amplitude signals, resulting in uniform SQR across the input range. ------------------------------------------------------------------------------ Review The objective of this topic was to describe digital voice and how it is transmitted. Digital voice is analog voice converted through channel banks called D-type. The output of a D-type channel bank is a digital signal, or DS-0. With DS-0, the transmission channel is divided into 12 DS-1 frames called a D4 superframe. The extended superframe uses a 24 DS-1 frame format. In the DS-1 format, one bit is robbed for signaling purposes. Another method used in digitizing voice is Common Channel Signaling (CCS). CCS has 24 voice channels in a frame, with one bit devoted to signaling, leaving 23 channels to carry voice. Voice compression is used in digitizing voice. There are three types of compression: ADPCM, CELP, and companding. ADPCM is used to encode changes in amplitude between PCM samples, rather than the actual amplitude. Representing the change requires fewer bits than does measuring the actual sample. With CELP, speech is analyzed and compressed with a vector quantizer, then transmitted as an index into a large vector quantizer codebook. A gain term is used to control its power. This technique produces relatively good speech at levels as low as 2.4 Kbps. With companding, linear coding to digital results in small amplitude signals that have poorer resolution than larger-amplitude signals. This is called compressing the signal. On the receiving end, the inverse operation is called expanding. A-law and u-law coding use more bits for smaller amplitude signals, which results in uniform SQR across the input range. ------------------------------------------------------------------------------ ISDN Protocol The Integrated Services Digital Network (ISDN) Protocol is really just the visible part of a larger telco network. The specifications simply define the network architecture and how to access it. The two basic ISDN standards are Basic Rate Interface (BRI) at 144 Kbps (2B+D) and Primary Rate Interface (PRI) at 1.544 Mbps (T1=23B+D, E1=30B+D). The services from a single connection can vary quite a lot. Email can be delivered to an unattended ISDN device. Call waiting, calling line ID, closed user groups, simultaneous data calls, and video conferencing can all be accessed via multiple devices on the same connection. The ISDN network interface is (more or less) an international standard through ITU-T recommendations. It is at least as standardized as the telephone system, so equipment might not work in another country, but services should be more standardized ------------------------------------------------------------------------------ D Channel ISDN defines a suite of protocols for accessing the network. Those protocols are carried out-of-band in the D channel. Protocols do not compete with data for bandwidth. The Layer 2 protocols, as defined in Q.291 or Q.290, specify framing and addressing within the OSI/ISDN model. Q.290/291 supports the communications for Layer 2 and maintains the connections between devices. Layer 3 protocols, as defined in Q.931 or Q.930, contain a rich set of parameters and possible values for setup, transfer mode, rate, privacy, authentication indicators, etc. Q.930/931 uses a standard set of messages to communicate in the network. The Layer 2 and Layer 3 protocol specifications are identical for BRI and PRI. What are the characteristics of the D Channel? What are the Characteristics of the D Channel? D Channel "signaling channel" characteristics include: 16 Kbps or 64 Kbps Carries instructions between customer equipment and network Carries information Can also carry packet-switch data (X.25) for the public packet-switched network ------------------------------------------------------------------------------ D Channel Encapsulation The D channel is a normal 64 Kbps voice channel for PRI and a 16 Kbps channel for BRI. The signaling encapsulation is what would be expected for a network architecture, with network and link layer information. The architecture is capable of carrying data packets. A flexible signaling channel such as this can provide a wide variety of services and capabilities. ------------------------------------------------------------------------------ Bearer Capability A significant capability is Bearer Capablity, where calls can be setup in a variety of transfer modes, rates, characteristics, and capabilities. The request is made and can be accepted or rejected on an item-by-item basis, depending on the service capabilities of the bearer at the time. The bearer can also propose an alternative. Reliability issues focus on: Parallel loading Lifeline 911 networks and regulations Existing call service warm restart Power failures Regulatory restrictions What are the characteristics of the B Channel? What are the Characteristics of the B Channel? B Channel bearer channel characteristics include: 64 Kbps (DS-0) Carries information (voice, data, video, etc.) ------------------------------------------------------------------------------ Network Access Whereas in the past, one could install separate lines for new services (such as foreign exchanges (FX) or a network connection), the ISDN connection is the network. All the services, including phone, fax, etc., run on it. There are no separate lines to various customer equipment. All of the customer's equipment can be connected to a single ISDN switch with an ISDN interface ------------------------------------------------------------------------------ Review The objective of this topic was to explain ISDN. The Integrated Services Digital Network (ISDN) involves the digitization of the telephone network, which permits voice, data, text, graphics, music, video, and other source materials to be transmitted over the existing telephone network. With ISDN, separate lines are not required for various customer equipment. All customer equipment can be connected to a single ISDN switch with an ISDN interface. The ISDN protocols define the network architecture and how to access it. The D channel has Layer 2 and Layer 3 protocol specifications (protocol specifications are identical to BRI and PRI). The D channel is a normal 64 Kbps voice channel for PRI and 16 Kbps for BRI. The B channel (bearer channel) is used for call setup in a numerous variety of transfer modes, rates, characteristics, and capabilities. ------------------------------------------------------------------------------ Summary This lesson contained information and instruction about Voice Technology Fundamentals. By completing this lesson, you should have the knowledge to discuss the following topics. Take a moment to see if you can do the following: Explain the three key telecommunication network technologies Identify the telecommunication categories of the service providers Describe digital voice and how it is transmitted Explain ISDN For a synopsis of the topic, click the blue text. To go back to the beginning of a topic, click the TOPIC button. ------------------------------------------------------------------------------ Explain the Three Key Telecommunication Network Technologies The three key telecommunication network technologies are transmission, switching, and signaling. The transmission provides a path (physical or logical) between two points within a LAN or WAN. When more than one destination is desired, switching is required to achieve multiple destinations. Then, signaling is needed to identify the destination on the network and set up and tear down the transmission path among network communication. ------------------------------------------------------------------------------ Identify the Telecommunication Categories of the Service Providers The categories of the providers for telecommunication service are Public Telephone Operators, Inter-Exchange Carriers, and Local Exchange Carriers. The Public Telephone Operators (PTOs) provide an end-to-end service that includes the telephone on the desk, the local loop, and the total service. The Inter-exchange Carriers (IXCs) compete for inter-Local Access and Transport Areas by providing services between LATAs or between exchanges within the same LATA. Inter-exchange carriers usually have relied on Local Exchange Carriers (LECs) for the local origination and termination of their traffic. LECs are identified by two categories: Incumbent Local Exchange Carriers (ILEC) and Competitive Local Exchange Carriers (CLEC), both competing for switch connectivity and local loop customers. ------------------------------------------------------------------------------ Describe Digital Voice and How It Is Transmitted Digital voice is analog voice that has been converted. The different components of digital voice include: DS-0: Voice is digitized through a channel bank called the D-type. The transmission channel is divided in 12 DS-1 frames (called a D4 superframe), and the extended superframe uses 24 DS-1 frame format. CCS: Digital voice is signaled through a system called Common Channel Signaling (CCS). CCS uses a 24-frame format, where 23 channels are used for voice and one channel is used for signaling. Voice Compression: Digital voice is compressed in order to reduce bandwidth consumption. Three forms of voice compression -- ADPCM, CELP, and companding – are used to compress voice in order to use more of the channel trunk. ------------------------------------------------------------------------------ Explain ISDN The Integrated Services Digital Network (ISDN) involves the digitization of the telephone network, which permits voice, data, text, graphics, music, video, and other source materials to be transmitted over the existing telephone network. ISDN has two channels: the D (digital) channel and the B (bearer) channel. The D channel is a normal 64 Kbps voice channel for PRI and 16 Kbps for BRI. The B channel is used for call setup in a numerous variety of transfer modes, rates, characteristics, and capabilities. ------------------------------------------------------------------------------ The PRI and the BRI are two basic components available with ISDN. The PRI (Primary Rate Interface) at 1.544 Mbps (T1=23B+D, E1=30B+D) and BRI (Basic Rate Interface) at 144 Kbps (2B+D) are specifications that simply define the network architecture and how to access it. ------------------------------------------------------------------------------ [My contact information: Alan Spicer Telecom - http://telcom.dyndns.biz Motor Yacht Computers, Computer Networking, and High Speed Communications HIGH SPEED INTERNET ACCESS ON YOUR VESSEL! Broadband Wireless, Coastal Marine Internet, and Blue Water Satellite High Speed Internet near Fort Lauderdale, Florida USA Email Any Questions Here or Telephone +1 954-683-3426 a_spicer at bellsouth.net (take out the spaces and change "at" to "@") Tamarac, Florida, USA - Near Fort Lauderdale, Florida]