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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This became quadratically more complex as strowgef new customer was added, as each new customer needed a switch to connect to every other customer. The pulse dialing technique is where there is making and breaking of the subscriber loops. The keys are tapped to step the switch in two stages.

The Design Switch That Revolutionized Telephone Communications

The Strowger switch uses two telegraph-type keys on a telephone set for dialing. The procedure of switching systems is discussed in a subsequent chapter.

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 striwger conductors to the exchange was not practical for a commercial system.

The privacy of the calls and the details of the called and the calling subscribers are at stake. As the operator at the Manual telephone exchange was the wife of his competitor and was diverting all the business, Strowger thought of developing a switching system, which does not require an operator.

The microphone and the loudspeaker are combined and placed in syshem receiver set. So, there needs to be a mechanism to transmit the identity of the called subscriber to the exchange. The Rotary Dial Telephone came into existence to solve the problems prevailing then. The company installed and opened the first commercial exchange in his then-home town of La Porte, Indiana on November 3,with about 75 subscribers and a capacity for Views Read Edit View history.


This signal has different patterns in different systems. A contact arm is moved up to select one of ten rows of contacts, and then rotated clockwise to select one of ten contacts in that row, a total of choices. This will lead to the dialing of a wrong number. Company engineers continued development of the Strowger designs and submitted several patents in the names of its employees.

Strowger Switch

The dial is operated by placing the finger in the hole appropriate to the digit to be dialed. Let us consider the operation of the rotary dial telephone using the cam mechanism. A busty tone of Hz signal with silence period in between. The above figure shows the pulsating pattern.

The pulse dialing pattern in recent times employs the duty ratio ratio between the pulse width and the time period of the waveform of the pulse as 33 percent nominally and there exists an upper limit for the inter-digit gap. To start with, we will discuss the drawbacks that were prevalent before the invention of the Rotary Dial Telephone.

From Wikipedia, the free encyclopedia. In this chapter, we will discuss how the Strowger Switching system works. This equipment originally consisted of two telegraph keys engaged by knife switchesand evolved into the rotary dial telephone. Meanwhile, let us have an idea on the signaling tones that are used to indicate the condition of the subscribers.

Another pawl, pivoting on the frame, holds the shaft at that height as it rotates. Retrieved 26 March Previous systems had all been designed for a fixed number of subscribers to be switched directly to each other in a mesh arrangement.

Successive digits in a number are represented by a series of pulse trains. The telegraph keys or telephone dial creates trains of on-off current pulses corresponding to the digitsand 0 which sends 10 pulses.

While Almon Strowger devised the initial concept, he was not alone in his endeavors and sought the assistance of his brother Arnold, nephew William, and others with a knowledge of electricity and financing to realize the concept. The stepping motion is controlled by the current pulses coming from the originating customer’s telegraph keys, and later from the rotary dial.


This action of getting back to the rest position and waiting for the other number to be dialed creates a gap called the Inter-digit gap, the timing of which is independent of the pause that may occur between two successive digits, due to human dialing habit.

The following illustration shows systemm continuous Hz signal. The Strowger switch is the first commercially successful electromechanical stepping switch telephone exchange system. Space-division Frequency-division Time-division Polarization-division Orbital angular-momentum Code-division. Coaxial cable Fiber-optic communication Optical fiber Free-space optical communication Molecular communication Radio waves Transmission line.

The fingerplate and the associated mechanism now return to the rest position under the influence of a spring. He conceived his invention inand was awarded a patent for an automatic telephone exchange in Simultaneously, the control equipment sends out a ringing tone to the calling subscriber, which has a pattern similar to that of the ringing switchhing.

The sound of a step-by-step call reaching a busy circuit.

Telecommunication Switching Systems and Networks Strowger Switching System

This rotation of the finger plate, causes the rotation of the Main shaft. Retrieved 28 January These pulses have equal number of time intervals and the number of pulses produced will be according to the number dialed.

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 Impulsing cam, which is attached to a pinion shaft, now breaks and makes the Impulsing contacts that in turn causes the pulses in the circuit. The lower one has long vertical teeth on the other side, hidden.