Integrated Services Digital Network (ISDN)

Integrated Services Digital Network (ISDN) comprises communication standards facilitating the concurrent digital transmission of voice, video, and data over traditional public switched telephone network circuits. Unlike its predecessor, which primarily transmitted voice, ISDN’s innovation lies in integrating speech and data on the same lines, a capability absent in traditional telephone systems. Operating as a circuit-switched telephone network, ISDN also provides access to packet-switched networks for digital transmission, potentially offering superior voice and data quality compared to analog phones.

What is Integrated Services Digital Network ?

A set of communication standards known as Integrated Services Digital Network (ISDN) enables the simultaneous digital transmission of voice, video, data, and other network services across the public switched telephone network’s digitalized circuits. The standard was first developed at Bell Labs in 1980 and was fully standardized in the CCITT “Red Book” in 1988. When the standard although ISDN had a few specialized uses and experienced modest wider adoption in some regions, the technology was mainly disregarded and was given the industry moniker ” innovation subscribers didn’t need.”

For a while, it served as a small-office digital link, using phone lines to transmit data at 64 kbit/s, sometimes “bonded” to 128 kbit/s. However, the advent of 56 kbit/s modems reduced its usefulness in many applications.

In video-conference systems, where a direct end-to-end connection was preferred, it was also used. Its 64 kbit/s data rate served as the foundation for the H.320 standard. As a substitute for the T1/E1 lines it was first meant to extend, the underlying ISDN concepts found wider application, almost tripling the performance of those lines first introduced, faster networking systems were already in use, and ISDN’s market adoption was comparatively low. According to one estimate, there were 25 million ISDN users globally at the height of its use, while there were 1.3 billion active analog lines. Digital subscriber line (DSL) systems, which offer substantially superior performance than ISDN, have largely supplanted it.

History

Twisted pair copper lines have been used for telephone use since they were first introduced in 1881, by 2000, well over one billion individual connections had been made. The joining of these lines to form calls became more automated throughout the first half of the 20th century, reaching a peak with the crossbar switches, that, by the 1950s, had fully supplanted older ideas.

Bell Labs employees Ralph Wyndrum, Barry Bossick, and Joe Lechleider started one such project to create a last-mile solution around 1978. They investigated various T1’s AMI versions and found that a customer-side line could dependably transport roughly 160 kbit/s of data across a range of 4 to 5 miles (6.4 to 8.0 km). That would be sufficient to transmit two 64 kbit/s voice-quality lines and a separate 16 kbit/s data line. Modems were typically 300 bps at the time, and the 1200 bit/s and 2400 bit/s standards would not be completed until the early 1980s and 1984, respectively.

The telecommunication industry felt confident that there would be a large level of customer demand for such systems in both the home and office because ISDN allows for digital-quality speech, two distinct lines, and constant data. This turned out to be untrue. New ideas emerged during the protracted standardization process and largely rendered the system unnecessary.

Telephone lines were replaced in the workplace by multi-line digital switches like the Meridian Norstar, and local area networks like Ethernet offered a performance of roughly 10 Mbit/s, which had grown to be the standard for connections between computers in offices. ISDN was not at all competitive in the data market and provided no clear advantages in the voice space.

How Does ISDN Work?

The conventional copper phone connection is divided into several digital channels using ISDN. The simultaneous operation of these channels on a single copper line enables many phones to place and receive calls on the same physical line.

BRI or PRI are the two basic varieties of ISDN :

• BRI :
  The ISDN configuration known as BRI, or Basic Rate Interface, is generally utilized for voice-grade telephone services. It consists of two bearer channels (B-channels) running at 64 kbit/s each and a delta channel (D-channel) running at 16 kbit/s.
• PRI :
  The term “PRI” stands for Primary Rate Interface, which is used to transmit data and other Digital Signal Zero (DS0) services between an ISDN user and the network. Many large businesses, offices, and corporations employ PRI.

ISDN Features

ISDN Interfaces

The ISDN standard specifies the number of different interface types, including the Basic Rate Interface (BRI), Primary Rate Interface (PRI), and Broadband (B-ISDN).

• Basic Rate Interface (BRI) :
  Two 64-B channels and one D channel are included in the ISDN Basic Rate Interface for broadcast control information. In certain cases, it’s written as 2B+D. The following network interface is designated by ISDN BRI (Basic Rate Interface). In North America, Basic Rate Interface (BRI) is far less frequent than it is in Europe. It is called INS64 in Japan.
• ISDN-U connection :
  Two wires connect the exchange and network terminating unit via the ISDN-U interface. ISDN-U interfaces are typically the deciding factor in networks outside of North America.
• ISDN-T connection :
  An ISDN-T interface is a modem’s digital counterpart. Among computers and terminal adapters, a serial device is an ISDN-T interface.
• ISDN-S connection :
  Devices used by ISDN customers plug into a four-wire bus. The indication points for the ISDN-T and ISDN-S interfaces are often used as a single interface.
• ISDN-R connection :
  A terminal adapter and non-ISDN devices are connected using an ISDN-R interface, which provides conversion to and from such a device.
• ISDN’s Primary Rate Interface (PRI) :
  In the US, the ISDN Primary Rate Interface (PRI) has 23 B channels and 1 D channel, while in Europe it has 30 B channels and 1 D channel. Worldwide, Primary Rate Interface is widely used, especially for PSTN lines to PBXs. ISDN is a word used by numerous networks throughout the world to describe low bandwidth lines.
• Broadband (B-ISDN) :
  B-ISDN (Broadband ISDN) is a different variant of ISDN that takes advantage of broadband communications. Broadband may send data at a 1.5 Mbps broadcast rate. Fiber optic lines are generally required for B-ISDN (Broadband ISDN). It is necessary to subscribe to an ISDN phone line to receive access, and customers will need particular equipment for it, such as a terminal adapter used to connect to the phone company switch or other ISDN devices. Most broadband channels transmit signals at 64 kbit/s.

ISDN Services

Users receive a completely integrated digital service from ISDN. The bearer services, teleservices, and supplemental services are subcategories of these services.

• Bearer Services :
  The bearer network enables the transfer of information (voice, data, and video) between users without the network changing the information’s content. The network does not need to handle the data and does not alter the information’s content as a result. The first three layers of the OSI model include bearer services. The ISDN standard gives them clear definitions. They can be delivered over networks that are circuit-, packet-, frame-, or cell-switched.
• Teleservices :
  In this case, the network can modify or process the data’s contents. Layers 4 through 7 of the OSI model relate to these services. Teleservices are built to handle complicated user needs and rely on the bearer services’ infrastructure. The user is not required to understand every step of the procedure. Telephony, teletex, telefax, videotex, telex, and teleconferencing are all examples of teleservices. Even though these services are specifically defined by the ISDN, they have not yet become standards.
• Supplemental Service :
  Supplemental services offer more features in addition to bearer services and teleservices. Call waiting, message handling, and reverse charging are a few examples of supplemental services that are common in today’s telephone company offerings.

ISDN Channels

A central ISDN office is part of the ISDN architecture. An electronic conduit connects each user to this office. This digital pipe could have a range of capacity and data transfer rates. These digital conduits, which connect the central office and the clients, are divided into a variety of channels of varying widths.

The following three channel types are defined by the ISDN standard :

• B Channel :At a speed of 64 kbps, a bearer channel (B Channel) is defined. It is the fundamental user channel and can transmit any kind of digital data in a full duplex mode so long as the needed bit rate is no greater than 64 kbps.Digital data, digital audio, and any other low data rate information can all be transmitted using it.Over a B channel, four different connections can be established :
  • Circuit-switched :
    A current switched connection is formed with another network user once the user places a call.
  • Packet switched : Data is transmitted between the user and other users via X.25 while they are linked to a packet switching mode.
  • Frame mode :
    Users can share data via LAPF while linked to a frame relay mode.
  • Semi-permanent :
    A call establishment protocol is not necessary because this connection to another user was established already. It functions similarly to a leased line.
• D Channel :
  • A data channel (D channel) carries the bearer channels’ control signal.
  • Depending on the user’s needs, this channel can be either 16 or 64 kbps and does not transmit any data.
  • The same wire carries data and control signals if we are using in-band signaling.
  • If out-of-band signaling is being used, as in ISDN, then data and control information is carried across two distinct cables.
• H-Channel :
  • User information is provided across a hybrid channel (H-channel) at higher bit rates.
  • Depending on the data rates, there are four different types of H-Channels :
    1. H0 = 384 kbit/s(6 B channels)
    2. H10 = 1472 kbit/s(23 B channels)
    3. H11 = 1536 kbit/s(24 B channels)
    4. H12 = 1920 kbit/s(30 B channels) – International (E-carrier) only.
  • High data rate applications like video and teleconferencing employ hybrid channels.

ISDN Devices

The equipment needed to connect the end node to the network is referred to as the ISDN standard. Even though some suppliers offer devices with several purposes, each function is defined by a different device in the standard. Each device has a defined set of protocols, each of which is assigned a particular letter. These letters are R, S, T, and U, which are also known as reference points. The device kinds are also described by ISDN standards. NT1, NT2, TE1, TE2, and TA are their names.

Identifiers

• A telephone number, also known as a ten-digit identification code used by standard telephone lines, is given permanently. Similar IDs are used by ISDN, but they are not as universally recognized as phone numbers. An ISDN connection is made using five different identifiers. The service profile identifier (SPID) and the directory number are two of these that the provider assigns when the connection is first established (DN). The other three are dynamically configured each time a connection is created, therefore these are the ones that are utilized the most frequently. The bearer code, service address point identifier, and terminal endpoint identifier are the three dynamic identifiers (BC).
• The ten-digit phone number that the telephone company assigns to every analog line is known as the directory number (DN).
• The most crucial number required while utilizing ISDN is the service profile identifier (SPID). The SPID must be configured correctly because it is distinct throughout the entire switch. If it is erroneous, it will have the same effect as dialing the incorrect phone number : you won’t be able to get in touch with the person you’re attempting to reach.
• The specific ISDN device is identified to the switch via a terminal endpoint identification (TEI). Each time a device is connected to the ISDN, its identifier is different. The TEI is dynamically assigned by the central switch, unlike the SPID or the DN.
• An identification made up of the TEI and SAPI combination is known as the bearer code (BC). It serves as the call reference and, like the two IDs included within it, is dynamic. Every time a connection is made, it changes.

Reference Points for ISDN

Logical interfaces are defined using reference points. In actuality, they are a form of communication protocol.

The points of reference are listed below :

• A TE2 device and a TA device’s reference point is defined by R.
• Between TE1 devices and NT1 or NT2 devices, S defines the reference point.
• The reference point between NT1 and NT2 devices is defined by T.
• Between NT1 devices and line termination equipment, U defines the reference point. Typically, this is the main switch.

Tips for Troubleshooting ISDN

Uses of ISDN

Some of the uses of ISDN are as follows :

• ISDN circuits have shown to be quite beneficial for video conferencing. With a single ISDN line (128 Kbps) and a set-top video conferencing Codec, a video conference can be started (at both ends). Because ISDN is a circuit-switched network with no packet losses and equal throughput for both upstream and downstream transmissions, it can perform video conferencing at a much lower bandwidth than a packet-switched network (like Internet leased lines or high-speed broadband) (which is so critical for sending and receiving real-time video in both the ends). In addition to the rental, only usage is covered by the payment (duration in minutes). To enable a meeting at higher bandwidth (thus higher quality) or conduct a multi-party video conference, multiple ISDNs (up to four, in most video conferencing systems) can be terminated concurrently.

We can perform several tasks at once using an ISDN line :

• We can place two calls on the phone (by connecting two analog phones to the adapter)
• When we receive a call while online, the call will be connected in one channel (64 Kbps), and we can continue using the Internet in the other channel at a slower speed (64 Kbps)
• We can chat on one channel while concurrently sending a fax on another channel (while the fax is being transmitted)
• Similar to how analog trunks are used, a lot of ISDN connections are used in some nations (like Germany) for basic voice communications (phone calls).
• Digital PBX/ IP PBX :
  There are ISDN interface cards that enable ISDN connections to be terminated on a business PBX (both for Digital – Mixed PBX as well as IP PBX). Therefore, the Digital ISDN lines can be terminated on the PBX and used for both incoming and outgoing calls from any phone within the company. Since the ISDN lines may be utilized for regular voice communications (via PBX) when they are not being used for video conferencing, this can be especially helpful for businesses who want to use ISDN for video conferencing.
• Back-up Internet Connectivity :
  Certain enterprise routers that offer an automatic fail-over to the ISDN network for Internet access when the principal Internet Line (Internet Leased Lines, Broadband, etc.) is down can directly terminate ISDN networks. In some cases, ISDN can serve as a small business’ main Internet connection in outlying areas where ADSL broadband networks are not supported.
• Bank ATM/ Point of Sale Locations :
  For linking vital but low bandwidth-consuming applications, such as many bank ATMs, Points of Sale like an exhibition that needs a network connection to collect credit card payments, etc., ISDN networks are an excellent option.

Difference between ISDN and DSL

Services, integrated Digital Subscriber Line, or DSL, is an always-on connection that does not require dialing over the lines it utilizes, whereas Digital Network, or ISDN, is a dial-up connection carried over specially established lines. The fundamental distinction between ISDN and DSL is that with ISDN, a connection must be established by dialing out before data can flow through. DSL eliminates the need for dial-out, allowing the user to place calls while online.

Both systems’ telephone cables use copper-based wires to transmit signals. Because an adaptor must be put at both ends of the line, ISDN lines must be installed. This means that the adapter must be owned by the service provider and installed in the building where the service is being used.

DSL often employs a modem and pre-existing telephone lines. As long as there is already a phone line in the house, installing additional wires is not necessary for a DSL connection. In reality, the majority of DSL connections use ADSL, where “A” stands for asymmetric. A home or business that downloads data more frequently than it uploads is better suited for ADSL.

ISDN and DSL differ from one another in a few significant ways. To begin with, DSL delivers data much more quickly than an ISDN line can.

This is so because ISDN uses a single line for dial-up service. DSL connections don’t require any dialing. Sometimes, they are referred to as “always-on connections”.

As a result, ISDN has a speed cap of about 128 Kbps while DSL has a speed cap of up to 100 Mbps.

Advantages of ISDN

• More rapid transmissions :
  ISDN transmits data at a rate that is substantially faster than its forerunners. Normal phone transmission rates of only 2.4 kbps were left in the dust by ISDN’s digital phone lines, which could carry 128 kbps over the same phone circuits.
• Better Signal Quality :
  Furthermore, compared to its predecessors, the lines that carry ISDN signals also convey signals of higher quality. The internet connection itself is also much more steady with fewer disruptions, and voice calls are of a higher quality with less static during the call.
• Cables With Multiple Uses :
  You can browse the internet and make a call at the same time because of ISDN lines’ ability to simultaneously transfer voice, video, fax, and data over the same cable. Because ISDN is more effective, the workplace can be more productive.
• Different Call Management Operations :
  Numerous helpful call features, like call forwarding, directed call pickup, message waiting for indicator, and more, are available with ISDN.

Disadvantages of ISDN

• Minimal adaptability :
  Because old ISDN is less flexible and requires actual wires to connect, organizations find it challenging to integrate remote working and corporate expansions. In reality, a growing number of companies are switching to cloud-based solutions because they offer greater scalability and flexibility.
• Actual Cables :
  Because ISDN requires a physical connection through telephone lines, businesses may find the installation and setup of this to be laborious and irritating. In comparison to more recent technology, the system also has a higher failure rate.
• Regional restrictions :
  Since ISDN connections are tied to a particular area code, changing it may take several weeks to take effect. Because phone numbers are related to a specific place, businesses have a limited number of options.
• Cost inefficient :
  Even without including the cost of the service or the cost of leasing the lines, installing and setting up ISDN wires can be costly. Additionally, using bearer channels for calls is expensive.
• Generally Outdated :
  Given that VoIP (Voice Over Internet Protocol) is a more recent technology, ISDN may appear a little archaic in comparison. Despite being speedier and more dependable than its predecessors, ISDN just cannot compete with the speeds of a broadband internet connection.

Alternatives of ISDN

SIP Lines

SIP (Session Initiation Protocol) lines (or trunks), which are very quickly replacing conventional ISDN lines as the preferred option, are well-liked for their significantly cheaper cost and the ability to use telephones without relying on a circuit that is quickly depleting. SIP trunks work through virtual phone lines rather than actual wires, therefore their applications are essentially endless.

SIP lines’ key advantages are ease of installation, lower operating costs, and more flexibility as compared to phone numbers. The only major drawback of SIP trunk phone lines is that total data security may not always be possible.

Dual-Mode Phone System

Because it combines several forms of communication technologies to produce a versatile phone system, a hybrid phone system earns its name. Businesses that want to preserve their present phone system but also incorporate the benefits of other types of technology frequently employ a hybrid system.

A hybrid phone system’s key advantages include simple and seamless migration, high security, adaptability, and the chance to save money by forgoing a monthly fee. Hybrid phone systems can be expensive and challenging to set up, but they provide flexibility and can be customized to meet your unique needs.

Hosted Phone System

Because hosted phone systems are situated in the cloud, connecting to them online is simple. With this communication option, you can effortlessly extend your phone system and handle every aspect of the technology thanks to the highly sophisticated cloud technology.

A monthly subscription is required to use a hosted phone system, and this usually includes maintenance and security fees. The system is simple to manage as a result, and installation is inexpensive. The fact that you never truly own the entire system is the one major drawback of hosted phone systems. As an alternative, you are merely renting it from a supplier.

IP Phone System

Internet Protocol (IP) technology is used by IP phone systems, and phones can be connected to them over ethernet on either a local area network or a wide area network. You buy the phone system for your personal use, and you get to decide where to host it.

An IP phone system’s key benefit is that you own the whole thing, giving you total control over how it is utilized. The upfront payments can be significant, but you will also be able to access a range of services, avoid long-term obligations, and secure security.

Keep Your ISDN Lines

You can still use your ISDN connections up until BT decides to turn them off. If you are currently satisfied with the service you get over the phone, you might buy any extras you require and then switch to a choice later. Although this solution carries some risk, it might currently be simpler for your business.

Do not hesitate to contact our staff right away if you need a communications supplier you can trust.

Conclusion

• Voice, video, and data traffic can all be carried simultaneously over a single circuit connection thanks to the network access architecture known as ISDN.
• N-ISDN is mostly connected to the B channel and D channel types of channels. Data, voice, and video bearer services are all sent across the B channels. The D channel is employed as a means of moving the signaling traffic.
• Since the 1980s, ISDN has been a dependable technology for organizations, but as more cutting-edge technology has been produced, it just isn’t as durable as it once was.
• Given that new technologies may more effectively meet societal demands, ISDN will officially cease to exist in 2025.
• If you can access ISDN, it’s a wonderful WAN technology. DSL or cable modems, on the other hand, are quicker and more affordable options. If you required phone, video, data, and special application services—which DSL and cable modems do not offer—you would still utilize ISDN.