Asynchronous_Synchronous - Copy

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Asynchronous_Synchronous - Copy

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DIGITAL  DATA  COMMUNICATIONS TECHNIQUES : 

DIGITAL  DATA  COMMUNICATIONS TECHNIQUES

Introduction : 

2 A message to be transmitted from one computer to another is composed of textual and non-textual characters. Characters, in turn, are composed of bits. These bits are sent across electrical wires, and are indicated by signal levels. Introduction

Introduction : 

3 For the sender and the receiver to successfully transmit bits, a rhythm must be agreed upon by the two so that the receiver can determine the correct end of one bit and the start of another bit. Introduction

Slide 4: 

4

ASYNCHRONOUS    AND    SYNCHRONOUS COMMUNICATIONS : 

5 ASYNCHRONOUS    AND    SYNCHRONOUS COMMUNICATIONS

ASYNCHRONOUS : 

6 ASYNCHRONOUS The ASYNCHRONOUS (ASYNC) format for data transmission is a procedure or protocol in which each information CHARACTER or BYTE is individually synchronized or FRAMED by the use of Start and Stop Elements, also referred to as START BITS and STOP BITS.

ASYNCHRONOUS : 

7 ASYNCHRONOUS The Asynchronous Transmission Format is also known as START-STOP mode or CHARACTER mode. Each character or byte is framed as a separate and independent unit of DATA that may be transmitted and received at irregular and independent time intervals.

ASYNCHRONOUS : 

8 ASYNCHRONOUS The characters or bytes may also be transmitted as a contiguous stream or series of characters.

ASYNCHRONOUS : 

9 ASYNCHRONOUS

ASYNCHRONOUS : 

10 ASYNCHRONOUS A character is often composed of seven or eight bits. So, when transmitting one character, the START bit is sent, and then the bits of the character are sent one after another. After which the PARITY bit is sent and finally the STOP bit is sent.

ASYNCHRONOUS : 

11 ASYNCHRONOUS A seven or eight bit character requires three bits as overhead to be properly sent from the sending device to the receiving device. This overhead in asynchronous transmission can limit the amount of useful information that could be sent.

SYNCHRONOUS : 

12 SYNCHRONOUS The term synchronous is used to describe a continuous and consistent timed transfer of data blocks.

SYNCHRONOUS : 

13 SYNCHRONOUS These types of communications are used when large amounts of data must be transferred very quickly from one location to the other. The speed of the synchronous connection is attained by transferring data in large blocks instead of individual characters.

SYNCHRONOUS : 

14 SYNCHRONOUS

SYNCHRONOUS : 

15 SYNCHRONOUS The following is a list of characteristics specific to synchronous communication: There are no gaps between characters being transmitted. Timing is supplied by modems or other devices at each end of the connection. Special syn characters precede the data being transmitted. The syn characters are used between blocks of data for timing purposes.

Duplex Communication : 

16 Duplex Communication Duplex communication system is a system composed of two connected parties or devices that can communicate with one another in both directions.

Half-duplex : 

17 Half-duplex A half-duplex system provides communication in both directions, but only one direction at a time (not simultaneously). Typically, once a party begins receiving a signal, it must wait for the transmitter to stop transmitting, before replying.

Half-duplex : 

18 Half-duplex A good analogy for a half-duplex system would be a one-lane road with traffic controllers at each end. Traffic can flow in both directions, but only one direction at a time, regulated by the traffic controllers.

Half-duplex : 

19 Half-duplex

Full-duplex : 

20 Full-duplex A full-duplex, allows communication in both directions, and, unlike half-duplex, allows this to happen simultaneously. Land-line telephone networks are full- duplex, since they allow both callers to speak and be heard at the same time.

Full-duplex : 

21 Full-duplex A good analogy for a full-duplex system would be a two-lane road with one lane for each direction.

Full-duplex : 

22 Full-duplex

ADSL : 

23 ADSL Asymmetric Digital Subscriber Line (ADSL) is one form of the Digital Subscriber Line technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide.

ADSL : 

24 ADSL It does this by utilizing frequencies that are not used by a voice telephone call. A splitter allows a single telephone connection to be used for both ADSL service and voice calls at the same time.

ADSL : 

25 ADSL

ADSL : 

26 ADSL

ADSL – Frequency Range : 

27 ADSL – Frequency Range

Trunks : 

28 Trunks

Trunks : 

29 Trunks A trunk is a line or link designed to handle many signals simultaneously, and that connects major switching centers or nodes in a communications system. The transmitted data can be voice (as in the conventional telephone system) data, computer programs, images, video or control signals.

Trunks : 

30 Trunks Telephone system is organized into three classes: local, tandem, and toll. A local office (or end office) was a switching centre that connected directly to the customers’ telephone instruments. A tandem office was one that served a cluster of local offices. Atoll office was involved in switching traffic over long-distance (or toll) circuits.

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