17-11-2012, 12:08 PM
An Industrial Training Report On Digital Switching System OCB-283 At BSNL KANPUR
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HISTORY OF TELEPHONE EXCHANGE
The Telephone was invented by Mr. Graham Bell. During early stage of development of telephone exchange, the connections are established with help of human operator. Those type of exchange were called manual Telephone Exchange. The technology of telephony was going on progress with the introduction of automatic exchange. Manual telephone is replaced & automatic exchange became in use there were lot of advantage of automatic of automatic exchange over manual.
In manual telephony, the type of exchange used is Central Battery (C.B.). In certain case local battery exchange (L.B.) is also used. The local battery exchange is also called magnet exchange because the set has a magneto generator which the subscriber is required to rotate, to generate the A.C. necessary to operate the indicator at the exchange.
In the central battery exchange, the battery is located at the central place which is the exchange. This arrangement has many advantages over L.B. exchange & can be used for even for large & medium capacity exchange.In automatic telephony connections between two subscriber are established with the help of human operator. Obviously the junction of human operator is carried out by the machine known as switching or selector stages. After the development of automatic telephone exchange technology as a subscriber directly & it has many advantages over manual telephone exchange. Now a day electronic Automatic exchange is widely used due to their advantages.
ELEPHONE LINES
Telephone lines are very important in telephone exchange. By the cable the subscriber is connected with each other. In the whole process, we use two types of cable:
1. Switching Board Cable(S.B. cable)
2. Under Ground cable(U.G. cable)
SWITCH BOARD CABLE: S.B. cable is used for the indoor process. By this cable we connect exchange to the M.D.F. room. This cable has pairs. One S.B. cable has eight gaps & each gap has eight pair. One gap is connected with a L.C.C.(Line Circuit Card) & One module. The Cable is Connected to left switch of module.
COLOUR CODING OF S.B. CABLE: There are two colours wire in one pair. One colour is called prime colour & other one is called made colour.
INTRODUCTION
OCB-283 is digital switching system which supports a variety of communication needs like basic telephony, ISDN, interface to mobile communication ,data communication etc .This system has been developed by CIT ALCATEL of France and therefore has many similarities to its predecessors E-10B also known as OCB-181 in France.
The first OCB-283 exchange if R-11 version was commissioned in Brest, France and Beijing, china in 1911, the first OCB_283 exchange came to India in 1993 subsequently the system has been upgraded and current version R-20 was fully validated in January 1994. The exchanges, which are being supplied to India, belong to R-20 version. Thereafter time up gradation to this OCB-283 system was upgraded toR-25 version.
SALIENT FEATURE OF OCB-283
1. It is a digital switching system with an angle “T” stage switch a maximum of 2048 PCM can be connected.
2. It supports both analog & digital subscribers.
3.The system supports all the existing signaling system like decadic,M1(R2),CAS & also CCITT#7 signaling system.
4. It provides telephony,ISDN data communication,cellular radio & oother value added services.
5. The system has automatic recovery feature. When a serious fault occurs in control unit,it gives the message to SMM. The SMM pulls this unit out of service, loads software of this unit in a backup unit & brings it in to service diagnostic programme are runned on the faulty unit & a diagnosis is printed on terminal.
6.OCB-283 has a double remoting facility. Subscriber access unit CSNL can be placed at a remote place & connected to main exchange through PCM links. Further line connectors can also be placed at remote location & connected to CSNL or CSND through PCM this special feature can meet entire range of necessity viz urban,semi-urban & rural.
7.Various units of OCB-283 system are connected over Token ring. This enables fast exchange of information & avoid complicated links & wiring between various units.
8. The charge account of subscriber are automatically saved in a disk once in a day. This avoid loss of revenue in case of total power supply failure.