Fax and ISDNIntroduction Living in a rapidly changing environment, it is far too easy to take for granted new technologies and the speed with which they advance. Not so long ago, people were very excited about PCs with no hard drives, 64 KB of memory, 8-bit processors, and no external communications links. Today, users demand PCs equipped with hard drives capable of storing billions of bits of information, megabits of RAM, 32- and 64-bit processors running at hundreds of megahertz, and 56 Kb/s or even broadband modems to stay connected round the clock. Over the years, consumers have became accustomed to continuous improvements in computer systems: hard drives and RAM provide higher capacity at lower cost; processors double their performance every other year; and new generations of computer buses and computer networking systems dramatically increase their data throughput.Nonetheless, there is one area in the computer communications system that remains unchanged - the interface to the telephone network, the most dispersed and widely used form of worldwide communications. Surprisingly, basic telephone service has not changed in the last 100 years, and still has the same analog interface designed for voice rather than data transmission. That limitation was overcome in the early phases of the computer-communications evolution with the development of modems and fax devices with new modulation, compression, and error-correction techniques. With their implementation, data transmission rates over analog lines have increased from 300 to 1,200 to 2,400 to 9,600 to 14,400 to 28,800, 33,600 and finally to 56 Kb/s. The latter is close to the maximum physical throughput of analog lines. As a result, data speeds have reached their limits over existing analog lines. One way to overcome this limitation is to use services of a new type of network called Integrated Services Digital Network (ISDN).History In the '60s, '70s, and '80s, after the benefits and advantages of digital technology were realized, telephone companies experienced a major transformation in their networks. They installed various digital components, including digital loop carrier equipment, digital switches, digital multiplexers, and network monitoring and provisioning systems. To complete the transformation of analog networks, and to take advantage of all benefits of digital end-to-end connectivity, phone companies needed to digitize the local loop, which is the connection between the Central Office (CO) and subscriber. When standards for digital end-to-end networks were developed and digital interfaces and services to the end users were specified, the digital network was called ISDN.The initiative for development of ISDN standards was first voiced in the late '60s. However, it took more than a dozen years for the international telecommunications standardization body, ITU-I (formerly known as CCITT), to agree on details of ISDN implementation. This group published the first set of ISDN standards in 1984. Within a few years, manufacturers around the world were producing cost-effective ISDN equipment for end users and telephone companies. But only in the '90s, with the need for Internet access, telecommuting, video conferencing, and high-speed dial-up digital connections, did the ISDN industry experience growth.Why ISDN? ISDN was the first digital dial-up telecommunications service capable of carrying all types of traffic including voice, fax, high-speed data, video, and packet-switched data. It was designed to provide these services over an existing wiring infrastructure through a universal interface. In addition, ISDN provides advanced call management, reporting, and monitoring capabilities by using out-of-band signaling. Overall, the integration of voice and non-voice capabilities on a single transport system means the user does not need to maintain multiple lines for various services. This flexibility and universality produces a significant cost savings. Users maintain just one access line for all their needs. Some other capabilities of ISDN services and their end-user benefits are outlined in the following table.
ISDN Benefits SummaryISDN Features - End-User Benefits · Significantly higher speeds for data transmission: up to 128 Kb/s uncompressed, or 512 Kb/s compressed · Enables new services and applications such as video, LAN extensions, and telecommuting · Decreases delays and response time, increases productivity · Clarity of digital end-to-end connectivity · Improves service quality · Superior reliability of data transmission · Minimizes data loss · Compatibility with existing analog devices such as telephones, fax machines, and modems · Eliminates the need to replace existing analog devices to utilize new services · Ability to have multiple separate calls occur simultaneously · Saves on cost - no additional voice or data channels are needed · Advanced call management · Enables new services and improves service quality · Ability to plug up to eight into a single ISDN BRI connection via a passive bus · Saves on cost - reduces need for additional channels · Flexible data speeds · Enables various new services such as high-quality voice, video conferencing, and high-speed LAN-to-LAN connection · Unified interfaces for all devices worldwide · Allows rapid fall of ISDN access equipment prices worldwide. (e.g., telephones, high-speed modems, bridges, routers) · Significantly faster call setup · Saves time in connecting to services, improves productivity ISDN Configurations There are two types of services offered by ISDN. Basic Rate Interface (BRI) is intended for users with low voice/fax/data traffic requirements like residential, Small Office Home Office (SOHO), and small to medium business markets. Primary Rate Interface (PRI) is optimal for high volume voice/fax/data traffic environments such as medium to large business enterprises.BRI BRI consists of three channels: two Bearer channels (B1 and B2) and one Delta channel (D). Often BRI is represented by the formula: 2B+D. Each of the B channels is 64 Kb/s full-duplex and is used for all types of services - voice, fax, data, and video. The D channel, on the other hand, is used only for packet-switched data services and for out-of-band signaling; its bandwidth is 16 Kb/s for BRI and 64 Kb/s for PRI. Every 2B+D BRI line can handle up to three calls simultaneously, two of which may be voice or fax, and the third is a packed switched data service. BRI also can combine two 64 Kb/s B channels, B1 and B2, into one 128 Kb/s data pipe. The BRI service can be ordered in different configurations: D channel only, 1B+D, or 2B+D.PRI PRI supports higher capacity than BRI and was intended for business users with a PBX or Local Area Network. Because of differences in the digital transmission hierarchies used in North America and Europe, it was not possible to get agreement on a single data rate. Thus, the United States, Canada, and Japan use a transmission structure based on 1.544 Mb/s. This is known also as a T-1. In Europe, PRI is based on E-1 and is available with a 2.048 Mb/s data rate. The channel structure for the 1.544 Mb/s (T-1) rate is 23B+D (23 B channels plus one 64 Kb/s D channel). For the 2.048 Mb/s (E-1) rate, the channel structure is 30B+D (30 B channels plus one 64 Kb/s D channel). PRI, like BRI, has its own flexibility. It is possible for customers with lesser requirements to order PRI with fewer B channels, as long as the formula nB+D is maintained. But typically, PRI with less than 10 B channels is less cost effective than 5 BRI services with equal number of B channels.Out-of-Band Signaling Besides fully digital end-to-end connectivity, higher bandwidth, flexibility, and universality that separate ISDN from the existing services, the out-of-band signaling makes ISDN stand out. The out-of-band signaling employed in ISDN to manage its call control permits its many unique functions and capabilities.Signaling refers to information sent by the Central Office and subscriber to operate the communications channel. For example, when we go off hook, we tell the Central Office we are ready to dial. The CO sends a dial tone to indicate it is ready to receive dialed digits. The signaling information in the analog world is passed through the same channel that is handling the call. Such signaling begins at the original subscriber and follows the same path as the call itself. The advantage of this approach is that no additional transmission facilities are needed for signaling, because facilities for voice/fax/data transmission are shared with control signaling. The disadvantage of this method is that voice/fax/data transmission is interrupted every time signaling information is passed to and from Central Office.ISDN, on the other hand, relies on an out-of-band signaling system based on data messages sent over the separate D channel. These messages are directed by customer premises equipment to the switch, which may take action on part of a message and forward other parts to other switches in the network. There are many advantages to the out-of-band signaling. Mainly, it has much faster call setup, and it creates no interruptions during voice/fax/data transmission to support advanced features like call waiting, call transfer, and three-way conferencing.Fax and ISDN There are many benefits of ISDN services that fax systems and applications can use. These include:· More reliable connections · Lower line noise and interference, essential for high-speed fax transmission · Better call progress analysis · More sophisticated error reporting mechanisms But there are additional ISDN benefits such as streamlined fax routing, faster call setup and doubled wiring cable utilization that make it unique for fax applications.Streamlined Fax Routing To implement fax routing capabilities in low-density LAN servers, businesses are using a Direct Inward Dialing (DID) service that assigns virtual numbers to one or more lines used for inbound traffic only. Because the DID channel cannot provide bi-directional communications, businesses must also purchase and maintain additional channels for outbound traffic. Although fax routing is very convenient, it is necessary to bear the cost of two sets of channels: DID and outbound. With ISDN, this problem is permanently solved. ISDN allows the assignment of 64 virtual numbers to each B channel for a total of 128 per BRI line; at the same time, any B channel can be used for outbound traffic when needed. Thus, with ISDN there is no need to maintain and bear the cost of two sets of channels to enable fax routing capabilities.Faster Call Setup Because BRI uses out-of-band signaling, it takes less than a second to set up a call. In contrast, with analog services, it might take up to 20 seconds. The benefit of ISDN's faster call setup capabilities is quickly realized on systems with high outbound traffic requirements or on fax broadcast systems.ISDN Plain Old Telephone Service (POTS)Average time saved with ISDNAverage time per dial· <1 sec · ~5 sec · ~4 sec Average time per 1,000 dials· 1,000 sec · ~5,000 sec · ~4,000 sec For example, when the system dials 1,000 times over an analog line and spends, on average, five seconds to set up a call, it uses 5,000 seconds. With ISDN, the system spends less than 1,000 seconds for every 1,000 dials. In total it saves more than 4,000 seconds or more than one hour. For the fax system, this time is enough to send at least 60 additional three-page faxes. As the result, with no additional expenses, the system gets a performance boost by using ISDN out-of-band signaling capabilities.Double Cable Utilization Another frequently overlooked advantage of ISDN is the ability to double the utilization of the building and loop wiring infrastructure. Because digital compression is used to multiplex two channels and transport them over a single pair of wires, the utilization of building and loop wiring is simply doubled. For expanding systems, in many cases, it saves expensive replacement of the existing cables or laying new ones.Intel® Dialogic® ISDN Voice and Fax Product Offerings Intel® Dialogic® voice and fax products provide an extensive and cost-effective OEM product solution for ISDN voice/fax environments. The products address both BRI and PRI market segments and include optional voice processing capabilities. All products are expandable and can be cost effectively used in expanding installations. Additional channels can be added at any time on an as-needed basis.BRI Intel® Dialogic® CPi/200 BRI provides two fax channels over a single BRI connection. It supports all standard fax protocols and is based on a fax cell architecture, which provides guaranteed compatibility with all fax devices anywhere in the world. The CPi/200 BRI is a scalable product. Up to 15 boards can be installed in the single chassis and can be integrated with applications that support Intel® Dialogic® products. The CPi/200 BRI is ideal for small to medium fax traffic environments and can be used for inbound, outbound, and DID-like applications. Moreover, CPi/200 BRI provides full compatibility with all existing fax devices connected either to analog lines or to the BRI lines through TAs (terminal adapters) and does not introduce any incompatibilities with existing fax devices.PRI Intel® Dialogic® digital interface boards provide PRI support for many popular protocols based on both T-1 and E-1 physical interfaces. They can be used with any combination of CP4/SC, CP6/SC, and CP12/SC fax boards, providing maximum flexibility and scalability while protecting the investment in hardware and application code.Supplementary Material What Does It Mean to Order an ISDN Line? ISDN services offer a variety of features. Many of them must be specified during the service order from a local telephone company. In addition to different features, there are different "flavors" of ISDN. ISDN can be proprietary or standard, and there are service differences in ISDN implementation in the US and in Europe. Prices for ISDN services still vary greatly from region to region. Here are the key ISDN service parameters:Number of Channels BRI and PRI services can provide various combinations of B channels for a total of 47 configurations. Default for BRI is 2B+D, and default for PRI is 23B+D. But it also may be 0B+D and 1B+D for BRI; or for PRI, 0B+D, 1B+D, 2B+D all the way through 23B+D.Bearer Services It is important to specify what service the B channels will be handling. Although it is totally transparent and the channel always handles 64 Kb/s data, the network handling that data channel not always is. For example, when the B channel carries voice, the network might apply echo cancellation to the channel. Or it may convert the PCM encoding from A law, which is used in North America, to Mu law, which is used in Europe. Because this conversion destroys data carried by the B channel, it must be avoided for data connections.Directory Number (DN) Each ISDN interface must have at least one directory number. But the service can have more than one number. In fact, there is no limit on how many may be assigned. It is also possible to assign "hunt group" with a single directory number.Your Calling Party Number (CPN) When many users call out on the same interface, it is important to identify the individual user to the network for billing purposes. The default for equipment to supply a calling party number with each call request is NO. A separate choice is whether your CPN presented to the called device. Default is "yes," to permit AIN function, but the selection can be changed with an information element in the call request.Subaddress Information Each user may have another identification, called subaddress information, in addition to a DN. Subaddress information may be used at the termination end of a call to route the connection over a private network or to a specific station. During the call setup, the network needs to know if you plan to send or will accept subaddresses, either your own or the called party's.Calling Number Delivery You can specify if you want to receive the DN of the calling party.Reference Points ISDN reference points specify communications parameters between devices installed in an ISDN network. There are four protocol reference points on the customer side: R, S, T, and U. On the Central Office side, the ISDN reference point is called V.R The R reference point is located between TE2 and a terminal adapter. It is an analog interface used for the existing analog telephone networks and is tied to the standards of the specific country. It typically complies with an X series and V series of ITU-T recommendations.S/T The S reference point is located between ISDN user equipment TE1 or TE2 and the NT1 device. It is a four-wire digital connection that separates individual ISDN terminals from network-related communications functions. The S and T reference points are electrically identical, but the T point corresponds to the ISDN network termination at the customer's premises; this separates the network provider's equipment from the user's equipment.U The U reference point is a demarcation point between the public network and customer premises equipment. In many cases, it is a connection of NT1 or NT2 devices to the network at the local loop. It is a two-wire full-duplex digital connection.VThe V reference point is a counterpart of a U reference point. It is located on the other end of the local loop in the Central Office and is not available to end users.C. User Equipment ISDN BRI service is provided as three multiplexed channels over existing wire. To gain access to these channels, user premise equipment must be used. There are several types of user premise equipment NT1, NT1 Plus, and NT2 as well as devices connected to them TE1, TE2, and TA.Network Termination Devices Network termination devices serve as a demarcation point between telephone company and customer premises equipment.NT1 The NT1 is a two- to four-wire interface. It provides termination for the ISDN connection and supplies power to the ISDN line and non-powered ISDN devices. It has a U interface (RJ-45 or RJ-11 jack) to connect to the local loop side and S/T (RJ-45 jack) for the terminal equipment. Only one NT1 is needed to terminate the ISDN line. NT1 performs maintenance functions such as loopback testing and performance monitoring. It supports multiple devices in a multidrop arrangement in which different devices (up to eight in total) can be attached to a single NT1 interface via a multidrop line. In this configuration, NT1 uses a contention resolution algorithm to control access to the D channel.NT1 Plus NT1 Plus provides all the functionality of NT1. In addition, it supplies a TA interface for non-ISDN ready terminal equipment such as all existing analog devices. Neither device includes any capacity for managing a BRI connection.NT2 The NT2 device is an intelligent device that supports higher-level functionality. It can perform switching and concentration functions. Examples of NT2 are a digital PBX, a terminal controller, and a LAN.Terminal Equipment Any end-user equipment connected to an ISDN line through an NT device is called terminal equipment. There are two classes of terminal equipment in the ISDN world. They are ISDN-ready (or digital devices) and non-ISDN ready (or existing analog devices such as telephones, fax machines, and data modems).TA TA, Terminal Adapter, allows analog voice and data devices to work through an ISDN connection. TA can be standalone equipment, but more often it is a port of an NT1 or TE1.TE1 TE1 refers to the ISDN device that supports the standard ISDN interface. It can be a digital phone, digital fax, or any other device that connects without an adapter.TE2 TE2 includes any device that is non-ISDN ready, such as all existing analog equipment. It cannot be connected to the ISDN line directly and requires a terminal adapter.
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