Charpter2. Strowger Switching Systems. School of Information Science and. Engineering, Shandong University. Associate Prof., Deqiang Wang. several types of machine switching systems which comprise the modern telephone plant originally known as the Strowger Dial System. Step~by-Step Systems. 16 Jun Strowger Switching System is the first automatic telephone Strowger switch is the first commercially successful.
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When a subscriber call is routed through a number of different types of exchanges, one hears different call-in-progress tones as the call progresses through different exchanges. The Pulse generated through this mechanism is then transmitted to the switching systems where the connection to the dialed number is established. The first set of incoming pulses raises the armature of an electromagnet to move a shaft which selects the desired level of contacts, by engaging a pawl with the upper ratchet.
The dial pulses are produced during the return travel of the fingerplate, thus eliminating the human element in pulse timings. The telegraph keys or telephone dial creates trains of switchiny current pulses corresponding to the digitsand 0 which sends 10 pulses.
When strowgre number is dialed, by placing the finger in the dial hole, which means the dial is displaced from its position, then the Impulsing contacts come near the Impulsing cam.
The fingerplate and the associated mechanism now return to the rest position under the influence of a spring.
The signaling function 1 is fulfilled by sending a dial tone to the calling subscriber. Swutching microphone and the loudspeaker are combined and placed in the receiver set. The burst and silence durations have the same value of 0.
The below figure shows how a rotary dial looks like. The number of pulses in a train is equal to the wtrowger value it represents except in the case of zero, which is represented by 10 pulses.
Strowger Switch: the 19th-century design invention that flipped the phone industry on its head
Respond to the calling subscriber that system is ready to receive the identification of the called party. The procedure of switching systems is discussed in a subsequent chapter. After dialing the number of the called party, when the line of the called party is obtained, the exchange control equipment sends out the ringing current to the telephone set of the called party, which is a familiar double-ring pattern.
It used two telegraph type keys on the telephone, which had to be tapped the correct number of times to step the switch, but the use of separate keys with separate conductors to the exchange was not practical for a commercial system. When the switch returns to its home position, typically when a call is complete, a release magnet disengages the pawls that hold the shaft in position.
The Strowger Switching system is also called the step-by-step switching system as sywtem connections are established in a step-by-step manner. Meanwhile, let us have an idea on the signaling tones that are used to indicate the condition of the subscribers.
The privacy of the calls and the details of the called and the calling subscribers are at stake.
This article needs additional citations for verification. This signal has different patterns in different systems. This rotation of the finger plate, causes the rotation of the Main shaft. The cam mechanism or trigger mechanism helps in dialing.
TSSN – Strowger Switching System
Unsourced material may be challenged and removed. The set has a finger plate the arrangement of which makes the dialing time appropriate. Here, the operator is the sole in-charge for establishing or releasing the switdhing.
Problems playing this file? Now, drawing the fingerplate round in the clockwise direction to the finger stop position and letting the dial free by withdrawing the finger, makes a number dialed.
This will lead to the dialing of a wrong number. Let us now throw some light on how strpwger call is made and how dialing is done without the help of an operator.
Simultaneously, the control equipment sends out a ringing tone to the calling subscriber, which has a pattern similar to that of the ringing current. When the rotary dial is in rest position, then the Impulsing contacts are away from the Impulsing cam. He was said to be convinced that she, switchnig one of the manual telephone exchange operators, was sending calls “to the undertaker” to her husband.
The company installed and opened the first commercial exchange in his then-home systen of La Porte, Indiana on November 3,with about 75 subscribers and a capacity for