Parity Checking (1 Viewer)

[goan_crazy]

Can someone please help me 2 understand what parity checking is and what it involves
i know its a method of error checking
the other 2 methods are checksum? and cyclic redundancy checking
but can some1 explain parity?
thanks

 

[melsc]

I get so lost when i comes 2 parity coz isnt there 2 kinds or something

 

[goan_crazy]

odd and even yes
its like 101010101 ODD


100101100 EVEN

i dont get it
*sigh*

 

[melsc]

Neither...when the tyeacher explained it i just nodded my head like i knew wat she was going on abt...

 

[Lazarus]

I can give you the general idea.

Let's say you want to transmit to someone the following stream of bits: 1010101

The parity of a number refers to whether the number is odd or even.

The parity of that bit stream is the parity of the sum of the bits:

1 + 0 + 1 + 0 + 1 + 0 + 1 = 4 = EVEN. (Because four is an even number.)

The sender encodes the parity of the stream into the bit sequence itself by designating a specific bit (usually the eighth) to be the parity bit. If the parity is even, the parity bit is set to 1. If the parity is odd, the parity bit is set to 0.

So, the stream might be sent as follows: 11010101

The parity bit has been bolded.

This allows the recipient of the data to check for minor transmission errors. If a single bit becomes garbled or messed up during the transfer (i.e. switching from 1 to 0 or vice versa), the parity of the stream will be different to the parity indicated by the parity bit.

Note that it's only a very simple check - if TWO bits switched (or any even number of bits), the parity wouldn't change, and the error(s) might go unnoticed.

 

[melsc]

Oh i get it now...thnx

 

[_muse_]

parity is easy

 

[lourai*87]

1 + 0 + 1 + 0 + 1 + 0 + 1 = 4 = EVEN. (Because four is an even number.)

The sender encodes the parity of the stream into the bit sequence itself by designating a specific bit (usually the eighth) to be the parity bit. If the parity is even, the parity bit is set to 1. If the parity is odd, the parity bit is set to 0

I thought if if the parity is even, the parity bit had to be 0 to keep it even But if the parity was odd then it had to be 1 to keep it odd?

 

[Lazarus]

It could be the other way around. I don't know. I was only describing the general idea.

I don't know whether the parity bit itself is included in the count - wouldn't that mean it would always have to be set to 0? A value of 1 is always going to change the sum from odd to even or vice versa.

Try asking Google.

 

[Huratio]

I can give you the general idea.

Let's say you want to transmit to someone the following stream of bits: 1010101

The parity of a number refers to whether the number is odd or even.

The parity of that bit stream is the parity of the sum of the bits:

1 + 0 + 1 + 0 + 1 + 0 + 1 = 4 = EVEN. (Because four is an even number.)

The sender encodes the parity of the stream into the bit sequence itself by designating a specific bit (usually the eighth) to be the parity bit. If the parity is even, the parity bit is set to 1. If the parity is odd, the parity bit is set to 0.

So, the stream might be sent as follows: 11010101

The parity bit has been bolded.

This allows the recipient of the data to check for minor transmission errors. If a single bit becomes garbled or messed up during the transfer (i.e. switching from 1 to 0 or vice versa), the parity of the stream will be different to the parity indicated by the parity bit.

Note that it's only a very simple check - if TWO bits switched (or any even number of bits), the parity wouldn't change, and the error(s) might go unnoticed.

i think in IPT the parity bit goes at the end so: 10101011

 

[melsc]

Yep thats wat i thought....the parity is @ the end...I THINK

 

[Trev]

Yes, I also had the thought that parity was the 'end bit'.

 

[melsc]

parity just sucks...lol simple as that....maybe if we ignore it, it wont be in the HSC

 

[lourai*87]

parity just sucks...lol simple as that....maybe if we ignore it, it wont be in the HSC

I like that theory...quick everyone, start ignoring parity

One could be so hopeful!

 

[_muse_]

alright, in my effort to be nice.. ill write whats in my textbook about parity..and whats in the excel book about parity.. then u get 2 general ideas which SHOULD help you guys to understand.. if it doesnt, then shoot me.

TEXT BOOK:
Parity checking is a method of checking for errors in data transmission using an additional bit called a parity bit. This bit is used only for the purpose of identifying whether the bits being moved have arrived successfully. When data is represented using an 8-bit ASCII, then a ninth bit is used that holds a 0 or a 1. When an odd parity is chosen, the number of 1s in the 9 bits must be odd. This means that

. The sender and receiver can also decide to send an even parity, in which case the number of 1s in the 9 bits must be even. If an error has occured in a single bit, then the parity will be different and an error in transmission has occured.

EXCEL BOOK:
Seven bits represent the normal ASCII character set when an 8-bit byte is used in a computer. The 8th bit can be used to check whether that byte has been received correctly by using the ideas of parity.
It works as follows:

- the originating computer counts the number of 1s and determines whether there is an odd or even number.
- the 8th bit in the byte is then used to create a byte with an even number of 1s if even parity is set, or an off number of 1s if odd parity is set in the protocol governing the particular communication session.

The transmission of the ASCII character 'R' demonstrated this process.

0 1 0 1 0 0 1 0 (Parity = bold)

Because the number of 1s is three, which is odd, we add 0 as the parity bit to maintain odd parity checking.



Problems with parity checking

- it can detect 1 error but is stumped if there are two.
- if two bits flip value, then the parity bit will not alert the receiver.
- Any byte with an even numbers of errors will slip through undetected.


make sense?

 

[melsc]

thnx 4 that

 

[Huratio]

why can't the IPT course just omit the parity and checksum methods.. its not like many things use it anymore seeing those many disadvantages. Cyclic redundancy check is widely used now and should be the only on on the IPT syllabus.

 

[Lwaxana]

That's what I have been saying about System flowcharts

they are rarely used in Industry anymore
so why include them in the syllabus

 

[_muse_]

system flowcharts are evil. ive never been able to do them...

maybe they jus put parity and everything in there to fill in space on the syllabus - we dont need it, but they do to fill up the missing spots

 

[melsc]

system flowcharts are evil. ive never been able to do them...

maybe they jus put parity and everything in there to fill in space on the syllabus - we dont need it, but they do to fill up the missing spots

They are evil i can never remember the symbols