Although announced in the early 1980s, it took more than a decade before ISDN became widely available. It enjoyed a surge of growth in the early days of the Internet, because it provided the only higher-speed alternative to analog modems in many areas. Still working in many behind-the-scenes applications, ISDN is rarely used for Internet access.
Channels
ISDN uses 64 Kbps "B" (bearer) channels to carry voice and data. A separate "D" (delta) channel is used for control. The D channel signals the carrier's voice switch to make calls, put them on hold and activate features such as conference calling and call forwarding. It also receives caller ID data. Because the D channel connects directly to the telephone system's SS7 signaling network, ISDN calls are dialed much faster than regular telephone calls.
Basic Service
ISDN BRI (Basic Rate Interface) uses one wire pair to carry two 64 Kbps B channels and one 16 Kbps D channel (2B+D). Both B channels are often "bonded" into one, providing a total data rate of 128 Kbps.
High-Speed Service
ISDN PRI (Primary Rate Interface) uses four wire pairs to provide 23 B channels and one 64 Kbps D channel (23B+D). A PRI line is equivalent to a 24-channel T1 line. Bonding channels is common; for example, six channels provide 384 Kbps for high-quality videoconferencing. In Europe, PRI includes 30 B channels and one D channel, equivalent to an E1 line. See SS7 and T1.
Connecting to ISDN
ISDN requires a network terminator (NT1) and terminal adapter (TA). The NT1 plugs into the two-wire line from the telephone company and provides four-wire output to the terminal adapter. In the U.S., the NT1 and TA are typically combined in one unit, but are separate in Europe and Japan.
The terminal adapter is called an "ISDN modem" if it has a built-in analog modem to hook up regular telephones and fax machines. If the ISP supports the Multilink PPP (MPPP) protocol, the TA can bond channels for faster Internet access.
The Terminal Adapter
TAs in the U.S. generally have a built-in NT1 and attach via a two-wire "U" interface. In Europe and Japan, the NT1 is installed by the telephone company and attaches to the TA via a four-wire "T" interface. The NT2 component, which is built into most devices, is a logical interface for multiple access and attaches via the "S" interface.
Typical SOHO Installation
An ISDN terminal adapter with phone support (ISDN modem) allows a telephone, fax machine and PC to communicate via the ISDN service.
Typical LAN Installation
LANs typically connect to ISDN via a router, which enables multiple users to share the available channels. For Internet access, the router supplies temporary IP addresses to each of the nodes. Routers may also provide analog phone support.
![]() | Reproduced with permission from Computer Desktop Encyclopedia. Copyright (c) 1981-2008 The Computer Language Company Inc. All rights reserved. |
Additional Resources
- Students (unaware/don't care) about music legalities
- I think the vast majority of people aren't too concerned about the inconsistencies, confusion and misunderstood legalities of sharing, trading and even possession of music tracks. But it does seem to be a growing problem, as a news reports suggest. Many university networks appear limited to some...
- Blog posts 2008-06-16
- T1 ISDN PRI Debugger Lite (zip)
- T1 ISDN PRI Debugger Lite is a network tool design to simplify PRI activity analysis and troubleshooting. The tool takes CiscoR debug logs from the router that has the PRI interface in it and extracts the ISDN information to present: Caller / Called numbers / Direction of Call / Status...
- Software downloads 2008-05-07
- ISDN Q-Interface Signaling Protocol Q.931 Tunneling Over the IP Network: Reduce the Cost of Private Telephony Networks
- Private Branch eXchanges PBXs are crucial communication components in any organization. As an organization grows and expands to multiple locations, it needs to establish multiple PBXs to keep the locations connected. The primary challenge in operating these multiple PBXs is to get them to work as a single entity so...
- White papers 2008-04-01
- Dr. Bott T3 USB 2.0 hub
- If you use a lot of USB devices (heck, two) with a MacBook Air, a hub is a necessity. The MBA has a single USB port which can give fits to people that need more. The problems with hubs is that they can be bulky and some require a separate...
- Blog posts 2008-03-21
- The cheapest way to do VoIP is still analog
- The cheapest way to do VoIP is still analogVery interesting!But these are probably more than I need at home. kiddingThanks George for a good topic!WiringThe problem with splitting out to analog is all the wiring punch down that has to be done. Being able to use an IP phone...
- Discussion threads 2008-03-20
- Friday Rant - More "Vista is doomed" nonesense
- Friday Rant - More "Vista is doomed" nonesenseUpgrade cycle is over, Win7 is DOOMED TOOApps are moving online, virtualization is increasing and we might be very close to the entire business market forcing MS to support XP indefinitely.This is definitely not like the other upgrade cycles. They are still...
- Discussion threads 2008-03-14
- Ninja Basic (exe)
- Ninja Basic offers the basic functions of the Ninja series. With some limitations to our Lite & Pro versions the Ninja Basic is thought as a first step into the Voice over IP world. Learn more about the possibilities of Ninja. The software phone Ninja offers the same features like...
- Software downloads 2008-02-21
- MultiNetwork Manager (exe)
- MultiNetwork Manager is a software solution, which makes laptop roaming easy and secure. It is targeted towards both home & business users and IT administrators & professionals. MultiNetwork Manager has an intuitive user interface that makes your connection quickly and easily regardless of the access method you use - WLAN/LAN/ISDN/DSL/GPRS....
- Software downloads 2008-01-21
- eMeeting Multi Video/Audio Conference (exe)
- eMeeting Conference 2.0 for workgroup conferencing in the organization through LAN, Intranet, VPN, ADSL, ISDN, Wire-less LAN and Internet. included Chat, Group Chat, File Transfer, Multi clients Video/Audio Conference, Multi clients On-line Presentation and Remote Desktop to VNC free edition server. It can use very easy and friendly for all...
- Software downloads 2008-01-21
- Aspects of Network Migration From ATM to MPLS
- Many telecoms operators which provide voice services as a significant part of their business have installed in the last decades ATM network to carry the traffic. Choosing ATM as backbone technologies was an obvious choice at that time: ATM can carries voice and data, mostly Frame Relay, providing a good...
- White papers 2008-01-01
- SkDNS ActiveX Control (exe)
- SkDNS ActiveX Control is a DNS Domain Name Service ActiveX control that can be used for network diagnosing, troubleshooting, and monitoring. The Magneto Software DNS Domain Name Service ActiveX control (SkDNS.OCX) allows developers to integrate the DNS protocol message sending capability into their applications. It can request any of 41...
- Software downloads 2007-12-29
- CC Proxy Server (exe)
- CC Proxy Server is easy-to-use Internet connection sharing software. Supporting dial-up, ISDN, DSL, and DDN connections, it helps you build your own proxy server and share Internet access within a LAN efficiently and easily. CC Proxy Server can act as HTTP/FTP/SOCKS/mail/news/telnet proxy servers. And it features powerful account management functions,...
- Software downloads 2007-12-27
- Verizon and telco revolutions
- Verizon and telco revolutionsFeeding the goose that lays golden eggsThe devil's in the details, of course, but it does look like Verizon is moving in the right direction; if so and it turns out to be profitable, then look for other providers to follow suit.The irony of all of this...
- Discussion threads 2007-11-28
- Internet Cyclone (zip)
- Internet Cyclone is a powerful, easy-to-use, Internet Optimizer for Windows 95, 98, ME, NT, 2000, and XP designed to automatically optimize your Windows settings which will boost your Internet connection up to 200%. Internet Cyclone is compatible with all modems and high-speed LAN, ISDN, CABLE, DSL, T1 or other connections....
- Software downloads 2007-11-22
- cFosSpeed (exe)
- cFosSpeed - Internet Acceleration with Traffic Shaping. Ping optimizer + packet prioritization. Maximum Download & Minimum Ping. For DSL, Cable, Modem, ISDN, Mobile, Filesharing (P2P), Online Games, VoIP, Streaming Media and Tuning More features: Free configurable Prioritization - self-calibrating - Layer-7 Analysis - Firewall - automatic router detection - optimal...
- Software downloads 2007-11-05
- New VoIP services dev platform seeks to accelerate carrier time to market
- A lot of what I've seen at Fall Von is best described as under-the-hood stuff. But let us not dismiss under-the-hood. In many cases, these are tools that help keep the VoIP services engines calibrated. For instance, I was briefed...
- Blog posts 2007-11-01
- Microsoft Unified Communications shuns G.722 wideband interoperability
- Microsoft launched its UC Unified Communications products this month with the intention of replacing the traditional PBX. But before it can get to a dominant market share position if it ever gets there at all, it's going to have to interoperate with existing telephony systems on the existing standards that...
- Blog posts 2007-10-31
- System Analyser (zip)
- System Analyser gives comprehensive information about your system: Bios, Network, Dos, CPU/FPU, Cache, Memory, SPD, Video, AGP, Monitor, Drives, partitions, IDE, ATAPI, SATA, CD-Rom, DVD, Blue-ray Disk, RPC2, Lpt, Rs232, Mouse, Keyboard, IEEE 1284, Modem, Fax, ISDN, Sound, ASPI/CAM, SCSI, DMI, PCI, PCI Express, PCMCIA, Plug and Play, APM, ESCD,...
- Software downloads 2007-10-11
- PC -- Telephone (exe)
- PC-Telephone is a powerful communications software application that enables you to exploit the full communications potential of the Internet and public telephone networks ISDN/PSTN. PC-Telephone turns your computer into Internet telephone, ISDN telephone, fax machine, answer phone, voicemail, file transfer.
- Software downloads 2007-10-02
- Okoker Internet Accelerator (exe)
- Okoker Internet Accelerator is a Internet toolkit, which accelerates your connection speed. You can easily optimize your windows settings and can get a very fast Internet or TCP/IP connection. Only you need to do is to go to Settings Dialog and select your connection type. Then it will optimize your...
- Software downloads 2007-08-16
Neighboring Terms
Premier Vendor Content Whitepapers, webcasts & resources from our Power Center Sponsors
- The Cisco Mobility Resource Center is your source for FREE mobility solutions
-
The Cisco Mobility Resource Center offers FREE videos, downloads, podcasts and more, all designed to help small and medium businesses get mobile connectivity solutions, improve productivity and drive sales and revenue.
- New mobility solutions at the Cisco Mobility Resource Center
- Marc Canter: The master of multimedia speaks
-
In this Super Techies interview, larger-than-life techie Marc Canter talks with ZDNet's Editor in Chief Dan Farber about his career as a multimedia pioneer.
- Watch the video >>
- New entries posted to Know Issues, Best Practices and Workarounds Wiki
-
Latest Topics: Running virtual machines and DHCP can cause Intel® AMT to be inaccessible; Wildcard certificates are currently not supported for remote; Dell 755 returns a duplicate UUID during activation configuration.
- See the latest entries on the Intel Wiki >>
-
-
Tasty Baking’s new LEED factory
0:57
Tasty Baking CIO: Brendan O’Malley
-
Balancing act: innovation vs. reliability
1:28
Facebook VP of technical operations: Jonathan Heiliger
-
Securing data at E-Loan
1:47
E-Loan CIO: Jay Shah
-
When crops are scarce
1:47
Del Monte Foods CIO: Marc Brown
- View all CIO Vision Series Videos »





