GATE IT 2008 | Question: 18

Question

How many bytes of data can be sent in $15$ seconds over a serial link with baud rate of $9600$ in asynchronous mode with odd parity and two stop bits in the frame?

• A. $10,000$ bytes
• B. $12,000$ bytes
• C. $15,000$ bytes
• D. $27,000$ bytes

Comments

A_i_$_h

baud rate = 2 * bit rate

This is very incorrect.

Baud rate = Number of symbols sent per unit time.

When by "symbol" we mean a "bit", then we say Bit rate = Number of bits sent per unit time.

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Baud Rate = 2 * Bit Rate,

Only in the case where we are using manchestor and differential manchestor encoding.

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For those confused between bit rate and baud rate for serial communications see:
https://gateoverflow.in/1019/gate-cse-2004-question-22?show=10129#a10129

Answer 1

Answer: B

Given that it is asynchronous mode of transmission, then along with per byte, you have to send some extra bit like start, stop bit and parity bits,etc (start and stop bit are compulsory).

$1\text{ bit}$ for start bit,$8\text{ bits}$ for data, $1\text{ bit}$ for parity, $2\text{ bits}$ for stop bits.

$\dfrac{9600\times 15}{(1+8+1+2)}\text{ Byte} = 12000\text{ Byte}.$

Comments

 @heena singh

in the case of asynchronous transmission data is transmitted as a group of 8 data bits(it contains stop and start bits as compulsory bits) remaining bits like parity etc are for error handling....

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as it is said that communication is asynchronous so we need to some how synchronize the things sofor that reason we have to add the given additional information as 1 startbit, 8databit 1 paritybit and 2 stop bit = 12 bit.

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how are u getting the unit as byte?

Answer 2

Answer: B

Assumption bit rate = baud rate
Also, Trasmission Time (T_t) = Data / Bandwidth

Data(sent in 15 second) = T_t * B.W = 15 sec * 9600 bps = 144000 bits

Now to convert bits into bytes, we divide by 8 but here as we are sending extra information 1 bit as start bit, 8 bits of data, 1 bit for parity, 2 bits for stop bits. So Effective bits for sending a byte will be 12 bits.

Data = 144000 bits / 12 bits = 12000 Byte

Comments

Here 1byte = 8+1+1+2=12bit

So 15*9600/12= 12000 byte

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actually we need to send 12 bits for each byte(8 bits) of data...here 4 bits are extra bits and 8 bits are actual data bits....hopefully question is asking about actual data bytes so

12 bits are sent for = 1 byte data

9600*15 bits are sent for = 1200 bytes of data

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where is one start bit given?

Answer 3

The biggest confusion out here would regarding that of baud rate or bit rate. Baud rate is supposed be no. of Signal elements per second and still we use for the calculations regarding bits. 

One can say that bitrate is not given. But they have mentioned the communication to be of Serial link type, and for any serial link communication ( be it asynchronous or synchronous)  the baud rate and data rate are both same  i.e. in serial links, one bit is transmitted in one signal.

So, if it says that baud rate is 9600, it must be clear that 9600 signal elements will be transmitted per second, all carrying 1 bit each, making the bit rate as 9600 bits per second.

That being done, since its asynchronous, all bytes will be accompanied with some extra bits. 

So, to transmit one byte, we will have to put in 12 bits (8 bits of data + 1 start bit + 1 parity bits + 2 stop bits) and not just 8 bits.

 

$\frac{9600*15}{(1+8+1+2)}$ Bytes=12000 Bytes.

 

So, whenever if Serial Link is given, it is assumed that the student has the knowledge that baud rate and bit rate are supposed to be the same. 

And also most of the times, as Serial communication is used for short distance purposes,  these used in asynchronous only.

For example, those 9 pin male connectors in old computers to connect printers and monitors used this type of commination mode.

 

Answer 4

For simple communication systems, the baud rate is the number of bits per second.

Source: https://www.electro-tech-online.com/threads/understanding-baud-rate.130720/

Baud rate basically tells you the number of symbols transferred per second. These "symbols" can be anything — bit, byte, character.

Unless otherwise stated, it's best to assume (especially for GATE) that baud rate = bit rate.

 

Given, baud rate = bit rate = 9600.
=> 9600 bits per second.

So in 15 seconds, bits sent = $9600 * 15=144000$

To obtain bytes, we divide by 8. But we need to obtain "bytes of data" here.
It is given that each "byte of data" is accompanied by "odd parity and two stop bits"
Parity bit size = 1 bit (just 1 bit extra is enough to make the number of 1's even or odd)
Two stop bits = 2 bits
One start bit = 1 bit. (Not mentioned in the question, but without start bit, there's no significance of stop bits. This is implicit information)

Hence, total "packet" size = $8 + 1 + 2 +1=12$ bits — each such "packet" has 1 "byte of data"

So, $144000/12=12000$

Option B

Answer 5

As given 9600 baud rate .

Generally relation between baud rate and bit rate , baud rate = N*bit rate

But here Nothing given , so baud rate = bit rate . 9600 bits / sec

and now we send 1 bytes with others bits parity bit , synchronize bit  etc

For 1 byte send  we will send 12 bits =1 bit for start bit, 8 bits for data, 1 bit for parity, 2 bits for stop bits.

As Here to send 1 byte takes 12 bits . Let replace byte will character word .

So total character sent 9600 bits/sec * 12 bit/character =800 character/sec

In 15 sec it will send 800 character/sec*15 sec = 12000 character .

Now again replace character with byte = 12000 byte .

Answer 6

for 8 bit of data → 12 bit is transmitted

means, for 8 bit → 4 extra bits transmitted

for x bits of data → x/2 extra bits will be transmitted

so, (x+x/2) bits = 15*9600 bits

=> 3x/2= 15*9600

=> x= 96000 bits

=> x= 9600/8 bytes

=> x=12000 bytes