1. University of Diyala
College of Engineering
Communication Department
Private Branch
Exchange

2. contents
1. Introduction
2. BASIC PRINCIPLES
3. PBX Generations
4. FUNCTION OF A PBX
5. DATA TRANSMISSION WITH A PBX
6. PBX NETWORKING
7. Switched Services Networks
8. Electronic Tandem Networks
9. Advantages of using a PBX
10.Disadvantages
11.CONCLUSION

3. Introduction
The PBX a device for switching telephone
calls within a building such as office , block or
factory.
Before PBXs were computerized, the
attendant manually connected both the caller
and the person being called by physically
inserting a cord.
PABX is simply an automatic version of the
PBX. The PABX is also faster with data
communication, and can handle more
telephone calls at the same time.

6. PBX Generations
• First Generation:
 Analog switching and transmission .
 Electronic
 Stored program control
• Second Generation:
 Analog transmission
 Some digital switching
 Blocking architecture providing limited data
transmission capability

7. PBX Generations
• Third Generation:
• Fourth Generation:
Fully digital
switching and
transmission .
Fully digital
 Non blockingVoice and data
capability.
Distributed
architecture
LAN-based

8. PBX Generations
Fifth Generation:
Broadband digital switching and
transmission via fiber optics .
Fully integrated voice, data, and
full-motion video
Possibly integrated optical
switching

9. FUNCTION
OF A PBX
A PBX is a means of providing switched communications
to a number of different users, usually within one or a
group of buildings. The PBX also acts as the primary
interface to either public or leased networks via either
direct connection or a series of gateways
The present generation of PBXs are configured in a star
topology, meaning that the PBX is a central switching unit
to which all devices are directly attached
Transmission speed :
•
•
Digital PBX : 64 Kbps , Non-standard system :
higher data
ISDN PBX : 144 Kbps
rate

10. DATA TRANSMISSION WITH A PBX
The signal passes from the device connected
through the switch in a digitally encoded form, it
matters little whether the originating device is a
telephone, personal computer or a mainframe.
 In the majority of third-generation PBXs the data
transmission capability is provided by a modem
that interconnects the terminal device with the
PBX network .(modem pooling)
The high-bandwidth circuits in the office to
support applications such as improved graphics,
faster remote file access are used.

11. PBX NETWORKING
Networks can be managed and developed
independently of the local PTT or network
operator and can frequently offer a much higher
degree of sophistication than would be avail-able
directly through the public network.
There are two types of subsections
 Switched Services Networks (SSN)
 Electronic Tandem Networks (ETN)

12. Switched Services Networks
(SSN)
SSNs are communications packages designed by
public carriers for large customer networks. To
be classified as a SSN, a LEC switch, and private
circuits provided by an IC must interconnect with
multiple PBX systems.
 There are three basic SSNs:
 Tandem Tie Trunk Networks (TTTN)
Common Control Switching Arrangements
(CCSA)
 Enhanced Private Switched Communications
Services (EPSCS)

13. Electronic Tandem Networks
(ETN)
Electronic Tandem Networks (ETN) consist of privately
owned trunk and switching facilities. One important
aspect of an ETN is a uniform numbering plan. Each
switch has a specific location code
ETNs provide automatic routing of private network traffic
and can take advantage of least-cost routing schemes.
Additionally, ETN switches can define calling privileges
for specific terminals or groups of terminals.
Most ETN switches can also support Satellite PBX
systems. This is usually done through special switch
trunks that make certain attendant and station features
transparent to the network

14. Advantages of using a PBX
No rewiring necessary.
Standard interfaces for attaching to the network.
Not geographically limited.
Provides gateway access to public and private data
networks.
Any extension user can be equipped to transmit data
traffic.
No difficulty in moves and changes.
Main access point to ISDN.
Good network management and network utilization
information.

15. Disadvantages
Limited transmission bandwidth.
 Designed primarily for voice traffic.
 PBX failure could be catastrophic if a large
proportion of all voice and data traffic are
reliant on it.
 High cost per port for voice and data, especially
if only a limited number of data users.
 PBXs are at present most widely used to switch
voice, not data.
 PBX is perceived as a telecommunications and
not a data processing facility.

16. CONCLUSION
The conclusion that can be derived from
the overall studies is that it is very simple
in functioning. The PBX can act as main
gateway to long distance networks for a
variety of data communications
 As this private branch exchange is
experimental type, and dialing number is
limited to a single digit, so some are to be
made before put to actual use in large
public places/buildings

17. reference
•http://www.seminarslides.com