SUBJECT CODE: SCSB1501 UNIT-IV ISDN & ATM
DATA COMMUNICATION & COMPUTER NETWORKS Page 1
,SUBJECT CODE: SCSB1501 UNIT-IV ISDN & ATM
1 History:
1.1 Voice Communication over analog n/ws:
Initially, telecommunication n/ws were entirely analog n/ws and were
used for the transmission of analog information in the form of voice.
Local loops connecting the subscriber’s handset to the
telephone company’s central office were also analog.
DATA COMMUNICATION & COMPUTER NETWORKS Page 2
,SUBJECT CODE: SCSB1501 UNIT-IV ISDN & ATM
1.2 Voice and data communication over Analog n/ws:
With the advent of digital processing, subscribers needed to exchange
data as well as voice.
Modems, developed to allow digital exchanges over existing analog
lines.
1.3 Analog and digital services to subscribers:
To reduce cost and improve performance, telephone companies began
to add digital technologies while continuing their analog services to
customers.
Three types of customers: Traditional Customers using their land loops
only for analog purposes, customers suing analog facilities to transmit
digital information via modem, customers using digital services to
transmit data i.e. digital information.
First group was prominent, so most services offered remained analog.
DATA COMMUNICATION & COMPUTER NETWORKS Page 3
, SUBJECT CODE: SCSB1501 UNIT-IV ISDN & ATM
2. ISDN
2.1 Integrated Digital N/w (1DN):
Customers needed access to variety of N/ws, such as packet switched
n/ws and circuit switched n/ws, so telephone companies created 1DNs.
An IDN is a combination of n/ws available for different purposes.
Access to these n/ws is by digital pipes, which are time-multiplexed
channels sharing very high speed paths.
DATA COMMUNICATION & COMPUTER NETWORKS Page 4
DATA COMMUNICATION & COMPUTER NETWORKS Page 1
,SUBJECT CODE: SCSB1501 UNIT-IV ISDN & ATM
1 History:
1.1 Voice Communication over analog n/ws:
Initially, telecommunication n/ws were entirely analog n/ws and were
used for the transmission of analog information in the form of voice.
Local loops connecting the subscriber’s handset to the
telephone company’s central office were also analog.
DATA COMMUNICATION & COMPUTER NETWORKS Page 2
,SUBJECT CODE: SCSB1501 UNIT-IV ISDN & ATM
1.2 Voice and data communication over Analog n/ws:
With the advent of digital processing, subscribers needed to exchange
data as well as voice.
Modems, developed to allow digital exchanges over existing analog
lines.
1.3 Analog and digital services to subscribers:
To reduce cost and improve performance, telephone companies began
to add digital technologies while continuing their analog services to
customers.
Three types of customers: Traditional Customers using their land loops
only for analog purposes, customers suing analog facilities to transmit
digital information via modem, customers using digital services to
transmit data i.e. digital information.
First group was prominent, so most services offered remained analog.
DATA COMMUNICATION & COMPUTER NETWORKS Page 3
, SUBJECT CODE: SCSB1501 UNIT-IV ISDN & ATM
2. ISDN
2.1 Integrated Digital N/w (1DN):
Customers needed access to variety of N/ws, such as packet switched
n/ws and circuit switched n/ws, so telephone companies created 1DNs.
An IDN is a combination of n/ws available for different purposes.
Access to these n/ws is by digital pipes, which are time-multiplexed
channels sharing very high speed paths.
DATA COMMUNICATION & COMPUTER NETWORKS Page 4
