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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?

  1. $10,000$ bytes
  2. $12,000$ bytes
  3. $15,000$ bytes
  4. $27,000$ bytes
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41 votes
41 votes

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.

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

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33 votes

Answer: B

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

Data(sent in 15 second) = Tt * 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

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7 votes

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.

 

7 votes
7 votes

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:

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