Data Transmission(Bit Rate)

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Data Transmission


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Bit Rates

The number of bits that can be sent in one second isknown as the Bit Rate

Bit Rate, as the name implies, describes the rate at

which bits are transferred from one location to another In other words, it measures how much data is

transmitted in a given amount of time. Bit Rate iscommonly measured in bits per second (bps), kilobitsper second (Kbps), or megabits per second (Mbps)

The unit used to measure the bit rate are BAUD.

1 Baud = 1 Bit per second


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Bit Rates

Bitrate can also describe the quality of an audioor video file. For example, an MP3 audio file thatis compressed at 192 Kbps will have a greaterdynamic range and may sound slightly more clearthan the same audio file compressed at 128 Kbps.This is because more bits are used to representthe audio data for each second of playback.Similarly, a video file that is compressed at 3000

Kbps will look better than the same filecompressed at 1000 Kbps. Just like the quality ofan image is measured in resolution, the quality ofan audio or video file is measured by the bitrate.


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Bit Rates


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Bit Rates


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Error Checking and Correcting

error detection and correction or error control aretechniques that enable reliable delivery ofdigital dataover unreliable communication channels

Luckily there are only two possible mistakes that canoccur, either a 1 is received as a 0, or a 0 is received asa 1. Mistakes occur rarely, but when they occur theycan be very serious, as the information is no longercorrect.

This makes it very important that there should bemethods for checking the data when it has beentransmitted.


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Methods for Checking the data

Echoing Back

Parity

Check Sum


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Echoing Back

The simplest way of checking the transfer of

the data is to send it back again

If the data that is sent back is the same as thedata that was sent in the first place then the

original data must have reached its

destination correctly, if not then it needs to be

sent again. This is known as echoing back


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Advantages & Disadvantages

Echoing back is very effective

But suffers from having to send data twice,

thus taking longer than necessary, andneeding to be a duplex, or half duplex, system

allow data transfer in both directions.


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Parity


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Check Sum


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Switching

Packet switching

Circuit switching


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Difference b/w Packet switching &

Circuit switching

Packet switching sends message in equal sized

pieces in any order, while in circuit switching the

message is sent in order meaning that it does not

need to be reassembled at destination

Packet switching involves the individual packets

being sent onto the network before a route is

established, while circuit switching requires aroute to be established before transmission


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Packet switching & Circuit switching


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Packet switching

Packet switching. The message is split into a number of equal sizedpackets. Each packet has a label saying where it is meant to be going and

what number packet it is. These packets are sent along communication

lines towards the destination. Each time a packet reaches a node on the

network the node decides which direction to send it on. So, one packet in

the message from A reaches node D. The obvious route to take is the one

directly to C, but it is already in use for another message, so D decides tosend it to E instead. The next packet arrives at D and, this time, the line to

C is free, so the packet is sent direct to C. When the message has all

arrived at C it has to be reassembled in the correct order.


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Circuit switching

Circuit switching. Before the message is sent, the network reserves a route

from A to C. The message can then be sent directly from A to C and will

not need to be reassembled when it gets there. Packet switching allows

optimum use of the connections around the network because as many

routes are in use at one time as possible, whereas circuit switching meansthat the whole message is kept together so it does not need to be

reassembled at the destination


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Protocols

When data is being transferred from one place to another in a computer system there must be

rules set up as to how the transfer is going to be done. Typical rules would be

1. A rule about the wire connecting the two parts of the system. Errors would occur

if one device had a serial connection and the other was expecting a parallel

connection

2. If one device sent data at a particular bit rate and the other device read what it

received at a different rate, the message would never be received correctly.

3. If one device used even parity and the other device used odd then no correctly

sent byte of information would ever be accepted.

The set of rules that needs to be set up to allow the transfer of data to be carried out is

known as a protocol. There are a number of protocols that you may have heard of e.g.

http, tcp(ip)


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Data Transmission(Bit Rate)

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