How speech is transmitted in a digital switching environment using PCM/TDM?

How speech is transmitted in a digital switching environment using PCM/TDM?
by

1 Answer

Answer :

A digital carrier system is a communications system that uses digital pulses rather than analogue signals to encode information. Fig shows the block diagram for a digital carrier system. This digital carrier system T1 uses PCM-encoded samples from 24 voice band channels for transmission over a single metallic wire pair or optical fibre transmission line. Each voice-band channel has a band width of approximately 300 Hz to 3000 Hz. Again, the multiplexer is simply a digital switch with 24 independent inputs and one time division multiplexed output. The PCM output signals from the 24 voice-band channels are sequentially selected and connected through the multiplexer to the transmission line. When a T1 carrier system, D-type (digital) channel banks perform the sampling, encoding and multiplexing of 24 voice-band channels, each channel contains an eight-bit PCM code and is sampled 8000 times a second. Each channel is sampled at the same rate. Fig. shows the channel sampling sequence for a 24-channel T1 digital carrier system. As the Fig. shows each channel is sampled once each frame but not at the same time. Each channel’s sample is offset from the previous channel’s sample by 1/24 of the total frame time. Therefore, one 64-kbps PCM-encoded sample is transmitted for each voice-band channel during each frame (a frame time of 1/8000 = 125 µs). Later, an additional bit (called the framing bit) is added to each frame. The framing bit occurs once per frame (8000-bps rate) and is recovered in the receiver, where it is used to maintain frame and sample synchronization between the TDM transmitter and receiver. 

image

by

Related questions

In a time multiplexed space switching system, one speech sample appears every (A) 125 micro sec (B) 20 msec (C) 125 msec (D) 1 sec

Description : In a time multiplexed space switching system, one speech sample appears every (A) 125 micro sec (B) 20 msec (C) 125 msec (D) 1 sec

Last Answer : (A) 125 micro sec

Explain the basic architecture of digital switching systems. Explain in detail companding.

Description : Explain the basic architecture of digital switching systems. Explain in detail companding.

Last Answer : A simple N X N time division space switch is shown in Fig. The switch can be represented in an equivalence form as a two-stage network with N X 1 and 1 X N switching matrices for the first and ... = Parameter used to define the amount of compression  Vout = Compressed output voltage. 

Name the switching schemes used in a digital exchange. How call processing takes place?

Description : Name the switching schemes used in a digital exchange. How call processing takes place?

Last Answer : The different switching systems used are: 1. Strowger Switching System 2. Cross bar Switching. 3. Electronic Switching System Basic Call Procedure: Fig. Shows a simplification ... machine detects an open circuit on that loop and then drops the connections through the switch.  

Example of circuit switching and S&F (Stored and Forward) switching is (A) Telephone and Post of Telegraph (B) Video Signal Post or Telegraph (C) Digital Signal Post or Telegraph (D) None of above

Description : Example of circuit switching and S&F (Stored and Forward) switching is (A) Telephone and Post of Telegraph (B) Video Signal Post or Telegraph (C) Digital Signal Post or Telegraph (D) None of above

Last Answer : (A) Telephone and Post of Telegraph

Using_________each connected device is assigned a time slot whether or not the device has any thing to send. (A) WDM (B) FDM (C) TDM (D) STDM

Description : Using_________each connected device is assigned a time slot whether or not the device has any thing to send. (A) WDM (B) FDM (C) TDM (D) STDM

Last Answer : (C) TDM

Time synchronization is necessary in (A) FDM. (B) TDM. (C) WDM. (D) Quadrature multiplexing

Description : Time synchronization is necessary in (A) FDM. (B) TDM. (C) WDM. (D) Quadrature multiplexing

Last Answer : (B) TDM.

Explain the CCITT hierarchical structure of switching and routing using block schematic.

Description : Explain the CCITT hierarchical structure of switching and routing using block schematic.

Last Answer : Hierarchical network are capable of handing heavy traffic where required, and at the same time use minimal number of trunk groups. A 5-level switching hierarchy is recommended by CCITT as ... A strictly hierarchical network suffers from serious drawback i.e. its poor fault tolerance future.

ISDN handles data pertaining to (A) All digital services (B) Speech and Video (C) Computer data only (D) Speech only

Description : ISDN handles data pertaining to (A) All digital services (B) Speech and Video (C) Computer data only (D) Speech only

Last Answer : (A) All digital services

What are the advantages and disadvantages of packet switching over circuit switching?

Description : What are the advantages and disadvantages of packet switching over circuit switching?

Last Answer : The comparison of packet switching and circuit switching showing advantages and disadvantages of packet switching over circuit switching is given below:

Through two block diagrams explain the difference between Space division and time division switching.

Description : Through two block diagrams explain the difference between Space division and time division switching.

Last Answer :  Space and Time Switching: Space Switches: Connections can be made between incoming and outgoing PCM highways by means of a cross point matrix of the form shown in Fig. However, different channels of ... of the speech store, whose contents are read out and sent over the outgoing highway.  

Show how finite state machine model helps in designing a switching system and give a typical example.

Description : Show how finite state machine model helps in designing a switching system and give a typical example.

Last Answer : Switching system basically belongs to the class of finite state machines (FSM) which are asynchronous in nature and follows a sequential logic for their operation. They can be modeled by ... circuits and memory elements. Clocked synchronous operation shown in Fig. overcome such problems.  

Compare electromechanical switching system with electronic switching system.

Description : Compare electromechanical switching system with electronic switching system.

Last Answer : Ans:

What is time multiplexed space switching? With a neat diagram explain its operation.

Description : What is time multiplexed space switching? With a neat diagram explain its operation.

Last Answer : Time division switches where an inlet or an outlet corresponded to a single subscriber line with one speech sample appearing every 125 µs on the line. Such switches are used in local exchanges. We now ... / Mt , Where t is the switching time including memory access time per inlet-outlet pair.  

What is meant by common control? Explain all the categories that are served by Common Control switching.

Description : What is meant by common control? Explain all the categories that are served by Common Control switching.

Last Answer : In some switching systems, the control subsystem may be an integral part of the switching network itself. Such system is known as direct control switching systems. Those systems in which the control ... may be carried out at the level of the common control unit or the switching network.  

What is time division switching? With the help of block diagram explain basic time division time switching method.

Description : What is time division switching? With the help of block diagram explain basic time division time switching method.

Last Answer : Time Division Switching: A switching element can be shared by number of simultaneously active speech circuits. This is the principle of time division switching. Obviously, with the way the switching elements are shared in time ... to MDR. This is done by the in-gate and out-gate units.

What is store program control (SPC)? Give the organization of centralized SPC. Discuss the advantages of SPC automation in telephone switching.

Description : What is store program control (SPC)? Give the organization of centralized SPC. Discuss the advantages of SPC automation in telephone switching.

Last Answer :  In stored program control systems, a program or set of instructions to the computer is stored in its memory and the instructions are executed automatically one by one by the processor. Carrying out ... of services can be provided to customers.  (v) Increase level of automotive in switching 

With neat diagrams explain the configuration of a step-by-step switching system.

Description : With neat diagrams explain the configuration of a step-by-step switching system.

Last Answer : The schematic diagram for such an exchange is given in Fig. Each subscriber is connected to a single rotary pre-selector switch at the exchange, the outputs from this switch being ... two further digits, connection is established, providing the called subscriber's to answer his telephone.

A two stage non-blocking network requires twice the number of switching elements as the single stage non-blocking network. (A) TRUE (B) FALSE

Description : A two stage non-blocking network requires twice the number of switching elements as the single stage non-blocking network. (A) TRUE (B) FALSE

Last Answer : Ans: (A)

The Signalling connection control part (SCCP) and message transfer part (MTP) together are referred to as (A) Signal Switching Points (SSPs) (B) Signal Transfer Points (STPs) (C) Signal Control Points (SCPs) (D) Network service part (NSP)

Description : The Signalling connection control part (SCCP) and message transfer part (MTP) together are referred to as (A) Signal Switching Points (SSPs) (B) Signal Transfer Points (STPs) (C) Signal Control Points (SCPs) (D) Network service part (NSP)

Last Answer : (D) Network service part (NSP)

Packet switching is used for (A) Credit card verification (B) Automated Teller Machine (C) The internet and the World Wide Web (D) All of the above

Description : Packet switching is used for (A) Credit card verification (B) Automated Teller Machine (C) The internet and the World Wide Web (D) All of the above

Last Answer : (D) All of the above

Trunks are the lines that run between (A) Subscribers and exchange (B) Switching system and power plant (C) Local area network (D) Switching stations

Description : Trunks are the lines that run between (A) Subscribers and exchange (B) Switching system and power plant (C) Local area network (D) Switching stations

Last Answer : (D) Switching stations

Traffic Handling Capacity is given by (A) Switching capacity ×Theoretical maximum load (B) Switching capacity / Theoretical maximum load (C) Theoretical maximum load / Switching capacity (D) Theoretical maximum load + Switching capacity

Description : Traffic Handling Capacity is given by (A) Switching capacity ×Theoretical maximum load (B) Switching capacity / Theoretical maximum load (C) Theoretical maximum load / Switching capacity (D) Theoretical maximum load + Switching capacity

Last Answer : (B) Switching capacity / Theoretical maximum load

In step by step switching line finders are connected to the (A) Calling subscriber. (B) Switching network. (C) Called subscriber. (D) Between exchanges.

Description : In step by step switching line finders are connected to the (A) Calling subscriber. (B) Switching network. (C) Called subscriber. (D) Between exchanges.

Last Answer : (A) Calling subscriber.

Trunks are the lines that run between (A) subscribers and exchange (B) switching system and power plant (C) Local Area Network (D) switching systems

Description : Trunks are the lines that run between (A) subscribers and exchange (B) switching system and power plant (C) Local Area Network (D) switching systems

Last Answer : (B) switching system and power plant

For two stage network the switching elements for M inlets with r blocks and N outlets with s blocks is given by (A) Ms + Nr (B) Mr + Ns (C) (M + N) (r + s) (D) (M + N)rs

Description : For two stage network the switching elements for M inlets with r blocks and N outlets with s blocks is given by (A) Ms + Nr (B) Mr + Ns (C) (M + N) (r + s) (D) (M + N)rs

Last Answer : (A) Ms + Nr

SPC stands (A) Standard Protocol Control (B) Stored Program Control (C) Signaling and switching Centre (D) Signaling Process Center

Description : SPC stands (A) Standard Protocol Control (B) Stored Program Control (C) Signaling and switching Centre (D) Signaling Process Center

Last Answer : (B) Stored Program Control

The final selector is connected to the (A) calling subscriber. (B) switching network. (C) called subscriber. (D) line finder.

Description : The final selector is connected to the (A) calling subscriber. (B) switching network. (C) called subscriber. (D) line finder.

Last Answer : (C) called subscriber

Traffic Capacity is given by (A) Switching capacity × Theoretical maximum load (B) Switching capacity / Theoretical maximum load (C) Theoretical maximum load / switching capacity (D) Theoretical maximum load × Switching capacity

Description : Traffic Capacity is given by (A) Switching capacity × Theoretical maximum load (B) Switching capacity / Theoretical maximum load (C) Theoretical maximum load / switching capacity (D) Theoretical maximum load × Switching capacity

Last Answer : (A) Switching capacity × Theoretical maximum load

Trunks are the lines that run between (A) Subscribers and exchange (B) switching system and power plant (C) Local area network. (D) Switching stations.

Description : Trunks are the lines that run between (A) Subscribers and exchange (B) switching system and power plant (C) Local area network. (D) Switching stations.

Last Answer : (D) Switching stations.

ARQ is transmitted in the event of: (A) Loss of signal (B) Error in received data (C) Improve reliability (D) During time out

Description : ARQ is transmitted in the event of: (A) Loss of signal (B) Error in received data (C) Improve reliability (D) During time out

Last Answer : (B) Error in received data

The CCITT standard bandwidth for speech is: (A) 20000 Hz (B) 15000 Hz (C) 7000 Hz (D) 3400 Hz

Description : The CCITT standard bandwidth for speech is: (A) 20000 Hz (B) 15000 Hz (C) 7000 Hz (D) 3400 Hz

Last Answer : (D) 3400 Hz

SS7 Protocol uses: (A) Out of band signalling. (B) Associated signalling. (C) Speech control signalling. (D) No signalling.

Description : SS7 Protocol uses: (A) Out of band signalling. (B) Associated signalling. (C) Speech control signalling. (D) No signalling.

Last Answer : (A) Out of band signalling.

Common channel signalling in SS7 is (A) out band control channel. (B) in band control channel. (C) speech control channel. (D) none of the above.

Description : Common channel signalling in SS7 is (A) out band control channel. (B) in band control channel. (C) speech control channel. (D) none of the above.

Last Answer : (B) in band control channel.

Side tone is the speech heard by (A) the receiving subscriber (B) both the receiving and calling subscriber (C) by on looker (D) by calling subscriber

Description : Side tone is the speech heard by (A) the receiving subscriber (B) both the receiving and calling subscriber (C) by on looker (D) by calling subscriber

Last Answer : (D) by calling subscriber

Common channel signalling______________ (A) Uses the speech or data path for signaling. (B) Does not use the speech or data path for signaling. (C) Needs no additional transmission facilities. (D) Finds it difficult to handle signaling during speech.

Description : Common channel signalling______________ (A) Uses the speech or data path for signaling. (B) Does not use the speech or data path for signaling. (C) Needs no additional transmission facilities. (D) Finds it difficult to handle signaling during speech.

Last Answer : (C) Needs no additional transmission facilities.

What are the different ways of designing 100 line exchange using uni selector and two motion selectors? Show at least three variations. Which is the best option?

Description : What are the different ways of designing 100 line exchange using uni selector and two motion selectors? Show at least three variations. Which is the best option?

Last Answer : Here three different designing methods for 100 line exchange are discussed: Design 1: Here, Strowger switching system is designed using one two-motion selector for each subscriber. A ... only under certain specific traffic conditions and generally lead to higher blocking probabilities.  

Using a combination of uniselectors and two motion selectors, draw a schematic of thousand line exchange and explain its working.

Description : Using a combination of uniselectors and two motion selectors, draw a schematic of thousand line exchange and explain its working.

Last Answer : The schematic diagram for such an exchange is given in Fig. Each subscriber is connected to a single rotary pre-selector switch at the exchange, the outputs from  this switch being ... further digits, connection is established, providing the called subscriber's to answer his telephone.  

Using ______ARQ, a sending modem must wait for a return ACK for each sent block before sending the next block. (A) discrete (B) efficient (C) continuous (D) delivered

Description : Using ______ARQ, a sending modem must wait for a return ACK for each sent block before sending the next block. (A) discrete (B) efficient (C) continuous (D) delivered

Last Answer : (A) discrete

A large numbers of computers in a wide geographical area can be efficiently connected using (A) twisted pair lines (B) coaxial cables (C) Communication satellites (D) all of the above

Description : A large numbers of computers in a wide geographical area can be efficiently connected using (A) twisted pair lines (B) coaxial cables (C) Communication satellites (D) all of the above

Last Answer : (D) all of the above

What do you mean by numbering and addressing? Draw the ISDN address structure and explain how the addressing works?

Description : What do you mean by numbering and addressing? Draw the ISDN address structure and explain how the addressing works?

Last Answer :  Numbering and Addressing: In telephone and data networks, the end equipments are more often single units than multiple devices units like PABX or LAN. Historically, a telephone, a computer, or a ... as reference point may also be addressed by using direct inward dialing (DID) feature.  

Explain the process of inter-register signalling.

Description : Explain the process of inter-register signalling.

Last Answer : Registers are used in common control exchanges to store and analyze routing data. They are provided on a common basis is a single register provides routing data for a number of speech circuits. Once a call ... it is released and the originating register signals to the next register.

Draw a centralized SPC organization and explain how it works under load sharing operation.

Description : Draw a centralized SPC organization and explain how it works under load sharing operation.

Last Answer : In centralized control, all the control equipment is replaced by a single processor which must be quite powerful. It must be capable of processing 10 to 100 calls per second, depending on the ... both the processors are active simultaneously and share the load and the resources dynamically.  

Explain FDM and show how CCITT standards help in building the base band?

Description : Explain FDM and show how CCITT standards help in building the base band?

Last Answer : Frequency Division Multiplexing: It is the process of combining several information channels by shifting their signals to different frequency groups within the spectrum so that they can be transmitted simultaneously ... of 24 channels were assembled together in one stage of modulation.     

What are transmission bridges? How do they help in satisfying the connectivity?

Description : What are transmission bridges? How do they help in satisfying the connectivity?

Last Answer : A typical transmission bridge is shown in Fig. The series capacitance and the shunt inductances of the two relays provide a high-pass filter to transmit the AC speech signals, while the relays respond independently to the DC loop/disconnect signals from the calling and called customer.  

How numbering plan is achieved in modern telephony? Give the structure with example.

Description : How numbering plan is achieved in modern telephony? Give the structure with example.

Last Answer :  The objective of numbering plan is to uniquely identify every subscriber connected to a telecommunication network. A numbering plan may be open, semiopen or closed. An open-numbering plan permits wide ... known as the subscriber number which is the number listed in the telephone directory.   

How does a touch tone receiver differs from pulsed dial receiver? Explain with schematic.

Description : How does a touch tone receiver differs from pulsed dial receiver? Explain with schematic.

Last Answer : Pulse dialing: 1. Generated through make and break contact. 2. DC Current pulse is generated. 3. Each number is separated by a short pause to prevent overlapping. 4. Codes ... dialing pulse is not misinterpreted as the phone being returned to its on-hook (idle) condition.   

Discuss different Routing plan adopted in a Telephone network.

Description : Discuss different Routing plan adopted in a Telephone network.

Last Answer : Hierarchical networks are capable of handing heavy traffic where required, and at the same time use minimal number of trunk groups. Three methods are used for deciding on the route for a ... selection methods can be implemented. Computer based routing is a standard feature in data networks.  

Discuss briefly subscriber loop system. Give some technical specification for subscriber lines.

Description : Discuss briefly subscriber loop system. Give some technical specification for subscriber lines.

Last Answer : Subscriber Loop System: Every subscriber in a telephone network is connected generally to the nearest switching office by means of a dedicated pair of wires. Subscriber loop refers to this pair of wires. It is un ... 1. Diameter of wire 2. D.C. resistance per Km 3. Attenuation per Km 

What is Traffic Engineering? Define the term busy hour, traffic intensity and grade of service.

Description : What is Traffic Engineering? Define the term busy hour, traffic intensity and grade of service.

Last Answer : Traffic engineering provides the basis for analysis and design of telecommunication network to carry a given traffic at a particular loss probability. It provides a means to determine the quantum of common equipments ... A0  Where  A= offered traffic  A0 = carried traffic  A-A0= lost traffic