What is Telephone System and voip phone?

Principles of Exchanges

The Prime purpose of an exchange is to provide a temporary path for simultaneous bidirectional transmission of speech between.

i. Subscriber lines connected to some exchange.

ii. Subscriber lines and trunks to other exchange.

iii. Subscriber lines and trunks some other exchange.

iv. Pair of trunks towards different exchange.

An Exchange which can set up just the first three types of connection is called a Subscriber or Local exchange. If an Exchange can set up only the fourth types of connection it is called a Transit or Tandem Exchange.

SPC(Stored Program Controlled)

SPC exchange consists of five main sub-system.

1. Terminal equipment,provides on individual basis for each subscriber line and for inter 

    Exchange trunk.

2. Switching network may be space-division or time division unidirectional or bidirectional .

3. Switching process consisting mainly of  processors and memories.

4. Switching peripherals.

5. Signalling interfaces depending on type of signalling used.

6.data processing peripherals.

There are two types of electronics switching :-

1. Space division.

2. Time division.

Space division:-

In a space division switching system a continuous physical path is set up between input and output terminating.

Time division:-

In time division switching a number of calls share the same path on time division sharing basis .the path is same for each connection.

Switching Processor:-

The Switching processor is a special purpose real time computer designed and optimized for dedicated applications of processing telephone calls.

Line interface circuits:-

To enable an electronics exchange to function with the existing outdoor telephone network certain interfaces are required between the network and the exchange.

Analogue subscriber line interafce:-

The functions of a subscriber line interface for each two wire line are often known by the acronym:- BORSHT

B-Battery feed.
O-Overload protection.
R- Ringing.
S- Supervision of loop status.
H- Hybrid.
T- Connection to test equipment.

Transmission interface:-

Transmission interface between analogue trunks and digital trunks such as A/D and D/A converters are known as CODEC.

SS7 is a layered protocol used in telecommunication system based  on OSI reference model. The function of the TCAP and ISUP layer correspond to the Application layer of the OSI reference model.

CCS Network is comprised of four major components.

1. Service Switching Point (SSP).
2. Signalling Transfer Point (STP).
3. Service Control Point (SCP).
4. Data Signalling Trunks (SLK).

SSP:-

SSPs are referred to as an "End office switch" central office switch  to "tandem". The lowest class office in a network will be the one providing dial tone to subscriber .SSP is typically found in Tandem or class 5 offices.

Basic Concept of Telephone Traffic:-

The hour in which maximum traffic usually occurs in an exchange is known as Busy Hour. Busy Hour Traffic in the average value of maximum traffic in the  busy hour.sometimes it is convenient to busy  refer to Busy hour calling rate(BHCR). Busy  Hour calling rate is the number of calls originated per subscriber in the busy hour.
Traffic Intensity is the average number of call  simultaneously in progress. The unit of traffic intensity is measured in Erlang.

Call Completion Rate :-

The call completion rate(CCR) measures the percentage of originated calls successfully completed.CCR further categorized into:-
1. Answer Bid Ratio(ABR).
2. Answer Seizure Ratio(ASR).
3. Congestion(CONG).
ABS:-The ABS is the ratio of successful calls to total originating international calls.
ASR:- The ASR is the ratio of successful calls to total incoming international calls.
CONG:- The CONG is the percentage of calls  lost due to congestion in the international network.

Switching Network Configuration of some modern Switches:-

1. E10B           T-S-T
2. EWSD         T-S-S-S-T
3. AXE10         T-S-T
4. CDOT(MBM) T-S-T
5. 5ESS             T-S-T
6. OCB283        T

OCB 283/CSN

The OCB 283 /CSN exchange is a multi service switching System which serves as local ,Tax,Tandem ,International gateway exchange and service switching point (SSP) from Mobile radio and Intelligent network(IN).OCB 283 is the controller part of the exchange which  has a distributed architecture with control station like main control station (SMC) consisting of call processing,data base,charging,message distribution management of connection etc.

CSN is digital subscriber concentrated to interface subscriber.CSN could be co-located(CSNL) or remoted(CSND). The switch also incorporates second level remoting(CNE) at distant subscriber equipment(CSND).

The main servces are Plain Old Telephone Services (POST) ISDN services Intelligent network services ,digital circular radio telephone services etc.

SALIENT FEATURES

i. OCB Stands for Organ Control Binarie.
ii. Digital Switching system with signal T stage.
iii. It supports different types of signalling systems 
       (a) Decadic.
       (b) CAS.
       (c) CCS7
iv. Varieties of services provided are
       (a) Basic Telephony.
       (b) ISDN.
       (c) Mobile.
       (d) Videotext
v. Traffic handling capacity is 8000000 BHCA.
vi. Automatic fault recovery feature and remote monitoring.
vii. Operating system used is RTOS(Real Time Operating System)

About Digital Switching:-

Switching of digital signals can be achieved using Two differents modes of operation.
1. Space Switching.
2. Time Switching.
Usually a combination of both the modes is used.

Space Switching:-

Space Switching mode corresponding time slots of I/C and O/G PCM highway are interconnected.

Time Switching:-

Time Switching on the other hand involves the interconnection of different times slots on the I/C and O/G highway by re-assigning the channel sequence.

What is Signalling?

A Signalling devices uses a language which enables two switching equipment devices to converse for the purpose of setting up calls.

Types of Signalling:-

1. Subscriber Line Signalling.
2. Inter Exchange Signalling.
3. Digital Signalling

Digital Signalling:-

Inter Exchange Signalling can be transmitted over a channel directly associated with the Speech Channel.

Subscriber line Signalling:-

1. Calling line signalling

     i.call request.
    ii. address signal.
    iii. End of selection signal
    iv. answer back signal.
    v. release signal.
   vi. Permanent line signal.

2. Called subscriber line signal.

    i. ring signal.
    ii. answer signal.
    iii. Release signal.
    iv. register recall signal.

Inter-Exchange signalling

1. Line Signals

   i. DC Signalling

  ii. In-band and Out-band signals.

 iii. E & M Signals.

2. Resister Signals

3. R2 Signalling

R2 signalling system to be used on National and International routes.

CCS#7 Common Channel Signaling System

In analog communication networks channel associated signalling systems have so far been used to carry the control information .fault free operation is guaranteed with the channel-associated signaling systems in analog communication network