Page 40 - Intelligent Communication Systems

24 INTELLIGENT COMMUNICATION SYSTEMS
Prior to ISDN, each service was provided separately through its own network.
With ISDN all services can be transmitted via a single digital network. Using
ISDN, the following new service can be achieved. When the phone rings we don't
know who is calling. We know who is calling after we hang up. This is a source-
oriented communication service. Thanks to the introduction of the digital network,
we can now have 2B + D channels in a subscriber line. By 2B we mean two base-
band channels; D means one data channel. By using the D channel we can trans-
mit information to identify the ID of the source phone number. So when the phone
rings, the source ID can be shown on the display of the telephone before we answer
the call. This gives us a choice of whether or not to answer the call. We call this a
destination-oriented communication service. Through the introduction of ISDN, a
more human-friendly telephone service is achieved.

4.1 INTEGRATED SERVICES DIGITAL NETWORK

In this chapter, ISDN is described. To provide the wide area network service, it is
necessary to provide network architectures for wide area. There are N-ISDN, B-
ISDN, and ATM switching systems for this purpose.
As multimedia services evolved, it became necessary to transmit not only
voice signals but also video, image, and text information through the network con-
currently. For this purpose, ISDN architecture was proposed and implemented.
ISDN provides the transmission of all kinds of data through a single channel in
time-division mode. Depending on the transmission speed, ISDN is classified as
N-ISDN or B-ISDN.

4.2 N-ISDN

N-ISDN has been standardized as I series recommendations by ITU-T. I series con-
sist of 1.100,1.200,1.300,1.400,1.500, and 1.600.1.100 defines the basic concepts
of ISDN. 1.200 defines the service specifications of ISDN. 1.300 specifies the net-
work functions of ISDN. 1.400 specifies the interface of user and network. 1.500
specifies the internetworking interface. 1.600 specifies the maintenance and man-
agement functions of ISDN.
As user-network interface (UNI) reference points, points T, S, and R are spec-
ified, as shown in Figure 4.1. Point T is the terminal point of the network as well as
the interface point of network terminal equipment NT 1. When NT2, such as a PBX
or an LAN, is connected to point T, the terminal point of NT2 is called point S.
TE1, such as a digital telephone, a G4 fax, or digital equipment, is connected to
point S. In the case of analog equipment TE2, such as an analog telephone, or an
analog fax, the interface equipment TA acts as the interface between TE2 and NT2.
The interface point between TA and TE2 is point R. In N-ISDN, the B-channel,
D-channel, and H-channel are provided. The B-channel is a user's communication