ISDN or Integrated Services
Digital Network which was developed by Consultative Committee on
International Telegraph and telephone on early 1980s was dealt by some North
American carriers but few were really in doubt to it due to faults and fails on
data network. ISDN sets protocols for data transmission such as voice, data and
video over our traditional circuits in public switch telephone network. With
ISDN, transmission for data, video, and voice can be performed at the same
time.
ISDN has three basic access interfaces:
Basic Rate Interface, Primary Rate Interface and Broadband ISDN.
Let’s discuss Basic Rate Interface.
BRI-ISDN uses 2 bearer channels
running at 64Kbps and a data channel of 16Kbps. This is a payload of 128kbps
service delivered over a four wire bus. This is the reason why it is sometimes
called 2B+D. BRI-ISDN specifies the bandwidth allocated to the user. With
64kbps for bearer channel and different bandwidth for signaling, it gives user
full-pledge bandwidth for users. BRI-ISDN is created by a Network Terminal Type
1 (NT1). An ISDN device is connected to the NT1 which provides the ISDN network
with Echo Cancellation which terminates echoes from different noise and
discontinuities. Echoes are noise that is disastrous to your network. With NT1,
it removes echoes by reading what has being sent and monitoring the
transmission. NT1 also provides timing for all devices. NT1 serves as switch or
a traffic controller to which bearer channel to connect. The ISDN only serves
the 1st three layers of the OSI model the physical, network, and
data-link layers. The higher layer of services could be video-conferencing,
internet and other services.
Physical Interface of BRI
a.)S-bus or S/T interface from the
ISDN terminal up to the NT
The S/T Interface (S0) uses four
wires; one pair for the uplink and another pair for the downlink. It offers a full-duplex mode of operation. It is
define in I.430 by the International Telecommunications Union(ITU).
b.) U reference point from NT to
central Office
The U Interface uses two wires. The U interface
uses one wire pair with echo cancellation for the long last mile cable between the telephone exchange and
the network terminator. The
maximum length of this BRI section is between 4 and 8 km.
Primary Rate
Interface
Primary Rate Interface provides 23B+D and all
of these channels provide 64Kbps. The PRI uses T1 as physical interface with
extended superframe framing. Since it is now a T1 line NT1 perform as Channel
Service Unit and NT2 as private branch exchange. A T1 Primary Rate Interface user would have access to a
1.472-Mbit/s data service. But PRI-ISDN isn’t
limited to one T1 line but it could also add multiple T1 lines and a D channel
could handle or control all the channels. That is the reason why PRI is used in
big companies who handles lots of calls and data transmission while BRI is used
in small offices.
Broadband ISDN
Any service that has a speed greater than 1.544Mbps
is considered as broadband. This was according to John T. Gorgone. Therefore
with that definition, Broadband ISDN is basically means a transmission channel
that caters a speed greater than those of the primary rate interface. It is
only an extension of the term ISDN by name and it all includes the protocols,
services, architectures and technologies that have been improved.
B-ISDN Services
Interactive Services
Two-way exchange of information
(other than controlsignaling information) between two subscribers or between a
subscriber and a service provider.
Distribution Services
Primarily one way transfer of
information, from service provider to B-ISDN subscriber.
Conclusion
ISDN was a great technology developed by CCITT. It covered some
solutions for business problems mainly by providing dynamic
bandwidth are guaranteed over non-shared lines with wide range at one standard
cost. But it can’t compete with other technologies in
terms of providing high speed internet and other specialized services. It also
requires specialized
digital devices just like Telephone Company.
