Describe the ISDN? Explain the types of ISDN Service.

ISDN stands for (Integrated Services Digital Network) is a system of digital phone connections. This system allows voice and data to be transmitted simultaneously across the world using End-to-End digital connectivity. The ISDN is a method used to bridge b/w the central office and the premise connection home.
ISDN uses the existing wiring so no new cabling is required with ISDN voice and data are carried by bearer channel. Occupying a bandwidth of (64Kb/s).  Some switches limit B channels to the capacity 56Kb/s. A data D channel handles signaling at 16Kb/s or 64Kb/s depending the service type.
There are Two types of ISDN service:
1. Basic Rate Interface (BRI)
2. Primary Rate Interface (PRI)

Basic Rate Interface:

BRI consists of 2B+D channels, which stands for 2 bearer channel of 64Kb/s each for data and 1D channel of 16Kb/s for handshaking and control. Having separate channels for handshaking and control is called Out of “band signaling”. The 2B channel can be bonded together for single data with a 128Kb/s transfer rate.

Primary Rate Interface:

PRI consists of 23B+d channels, which stands for 23 bearer channel of 64Kb/s each for data and 1D channel of 64Kb/s for handshaking and control. The bearer channel can be bonded in any combination as required PRI consists of two 64Kb/s B channels and one 16Kb/s for a total of one 44Kb/s. This basic service is intended to meet the needs of most individual user.
PRI intended for user with greater capacity requirement typically the channels structure 23B channels plus one 64Kb/s D channels for a total of 1536Kb/s.
In Europe PRI consists of 30B channels plus one 64Kb/s D channels for total of 1984Kb/s. it is also possible to supports multiple lines with one 64Kb/s D channel using (Non Facility Associated Signaling) NFAS.
ISDN lines can be dedicated lines that always up and connected or they can be dial on demand (DOD) lines. When the line is required the connection is dialed up and made. The connection for an ISDN line is very quick in the order 0.5second or so, this can result in a substations cost saving if used over long distance or paying by the minutes.
The lines charges are only for when data is being transferred and not when it is sitting idle.

Describes the ATM?

ATM is a high-speed networking standard designed to support both voice and data communications. ATM is normally utilized by Internet service providers on their private long-distance networks. ATM operates at the data link layer (Layer 2 in the OSI model) over either fiber or twisted-pair cable.
Asynchronous Transfer Mode, a network technology based on transferring data in cells or packets of a fixed size. The cell used with ATM is relatively small compared to units used with older technologies. The small, constant cell size allows ATM equipment to transmit video, audio, and computer data over the same network, and assure that no single type of data hogs the line.