ISDN

Chapter 10: Integrated Services Digital Network (ISDN)


Origins of ISDN


The ISDN was a concept developed by the Consultative Committee on International Telegraph and the Telephone(CCITT). The CCITT has changed its name to ITU-T, though the name had changed its still all the same. The world's Government were the handlers and monopolized the carriers except for Canada and United States for most of the Telco's there were private. Although there were also same Telco's in U.S that owned the bulk of important Telco's that covers the Large population centers.


Origins of the Standards


The ITU-T is a UN treaty organization and has permitted each country to send its representative to attend in any committee meeting. The representative that will be sent are mostly coming from the government that runs the PTT monopoly. The world's Telco's has permitted the competition when it become privatized. The competition cause an interesting struggle within each country to find the person that will be the representing the interest of the country at ITU-T. ITU-T came out due to the privatization trend separating telephone business from the post office.


 The CCITT comprises to a study groups(SG).

• SG VII on public data networks (X.25) X- series standards 
• SG VIII terminal equipment for telematic services 
• SG XI ISDN and telephone network switching and signaling 
• SG XII transmission performance of the telephone networks and terminals
• SG XV transmission systems
• SG XVII data transmission over public telephone networks 
• SG XVIII digital networks, including ISDN

 Integrated Services Digital Network(ISDN)
   
A ISDN is an international set of standard for transporting voice, video and data simultaneously through a digital telephone line or in a normal telephone wires with a transfer rate of 64 Kbps. As the CCITT back in 1988 the ISDN was defined. The ISDN has a features that integrates the speech and data at the same lines which were the classic telephone system cant provide. The ISDN has several level of services the Basic Rate Interface, and the Primary Rate Interface.

• Basic Rate Interface(BRI) has two telephone circuit that switches the digital 64 kbps across the Bearer-channels and 16 kbps for D-channel. A Basic Rate Interface user can have up to 128 Kbps service. A B- channels are used in voice or user data, and the D channel are used for any combinations, control/signaling and the X.25 packet networking. The Basic Rate Interface are usually installed in the residential or in small business in may country.
•  Primary Rate Interface(PRI) is the level of ISDN service that is based on T-carrier(T1)line in Canada , U.S. and Japan, and E-carrier(E1) for the other country. PRI can provide 23-30 B-channels that can be used flexibly and could be reassigned when it is necessary to meet the special need such as videoconfernces.                                                                                                                                       

As we know, the standard telephone connection did not die, and in fact increasing demand for extra phone lines (and fax lines) has made the telco business very profitable. However, ISDN has grown into a premium service, which the telcos like to target towards high-end or highvolume telephony users, typically businesses rather than home users. Let's look at some of the advantages that have given ISDN its unique niche:

• Dialup is fast. ISDN calls typically dial and connect in 1 to 3 seconds. 
• It's digital. 64kbps bandwidth for each "B" channel is guaranteed. 
• It's multi-mode. A "B" channel can carry data, voice, fax or video. 
• It concentrates calls: a PRI connection can deliver 30 concurrent calls through one cable. A BRI delivers 2 calls through one cable. 
• Through MSN you can associate many telephone numbers to the same line (at a fraction of the cost of separate, multiple telephone lines).

The ISDN Primary Rate connection is well suited for server-end or central-site tasks, where many concurrent connections or calls will be handled in one place. As well as acting as a central point for incoming connections, a server-based connection to ISDN can (at the same time) act as a Gateway offering telephony services to users on the local area network (LAN) in the office. For example, a server connected to ISDN can accept incoming faxes, and route them to individual users on the LAN: this is a growing application today, since it is convenient for users to receive fax and voicemail messages in the same way that they receive email. 

Most of the whitepaper discusses the central site, but it's worth focusing briefly on ISDN Basic Rate, and the user-side of the equation. ISDN BRI can be used for many purposes from a standard desktop or laptop PC. Applications are comparable to a modem, although there are some key advantages for ISDN, for example:

• 64kbps or 128kbps Internet connection, with 1-3 second dialup 
• Send/Receive fax: Group 3 and Group 4 (64kbps digital) 
• Concurrent Internet access and phone/fax use 
• Telephony with multiple phone numbers 
• Point-to-point video conferencing 

ISDN BRI is ideal for remote working (teleworking), since it gives access to most of the services available in an office including: telephony; fax; email; Internet. The fast dialup speed and high throughput (when compared to a conventional modem) offers a more effective remote working environment. 

Another important aspect of ISDN is that it solves the problem of the local Loops. The Local Loops was just designed for voice and ISDN solves that. ISDN is a circuit-switched Telephone network system, that are providing  an access to packet switched networks and are designed to allow digital transmission for voice and data. Since the ISDN are in digital it lessen noise in lines and has a potentially better voice quality than an alalog phone can provide. ISDN sometimes mistaken for its use with a specific protocol, such as Q.931 wherby the ISDN serve as the network. Though ISDN were said to be good at voice transmission, it is limited in providing Q.931 and related protocols.

Sources:


en.wikipedia.org/.../Integrated_Services_Digit..

www.ralphb.net/ISDN/


hea-www.harvard.edu/~fine/ISDN/index.html