IST 220: Networking and Telecommunications, Fall 2019                       Homework Assignment 2

Note:

          This is an individual assignment. Each student needs to work on and submit his/her own assignment independently. Be sure to explain your answers and/or show the steps.

          There are six questions in this assignment. Questions 1-5 are worth 100 points in total. Question 6 is for Midterm exam preparation purpose only and will not be graded.

          Submit a single .doc or .pdf file to the corresponding Dropbox on Canvas. The submission may be either typed or a scanned copy of your handwritten work.

          Due: Friday 10/25 at 11:59pm.

1.       Amplitude and Frequency Shift Keying (20 points). Consider the input signal with 3 levels shown below.

A.      Assume we want to use 2 sin⁡ (2 π 3 t) as the carrier, and use the following amplitude shift keying (ASK) scheme: 3V level ‘1’; 2V level ‘0’; 1V level ‘-1’. Please draw the resulting waveform after modulation.

B.      Assume we want to use 2 sin⁡ (2 π 3 t) as the carrier, and use the following frequency shift keying (FSK) scheme: 5Hz level ‘1’; 3Hz level ‘0’; 1Hz level ‘-1’. Please draw the resulting waveform after modulation.

 

2.       Phase Shift Keying (10 points). Assume we want to use sin⁡ (2 πt) as the carrier, and we want to use the 2-PSK (Constellation diagram shown below) to send four bits “0111” in one second. Please draw the resulting waveform after modulation.

 

 

 

3.       Code Division Multiplexing (20 points).

A.      For each of the following pair of vectors, determine whether they are orthogonal or not:

a)       (1, 1, 0) and (-1, 0, 1);

b)       (2, 2, 2) and (-1, -1, 2);

c)       (1, 1, 1, 1, 1, 1) and (1, -1, 1, -1, 1, -1)

 

B.      Suppose two senders want to use the CDM scheme to send data through a shared media. The chip sequence and data value of each sender are shown below. Compute the final signal that will be transmitted via the media. Please show the steps. (Note: For this question you need to first convert the binary values into vectors of bits that use -1 to represent 0.)

Sender

Chip Sequence

Data Value

A

(1, 0)

1 1 1 1

B

(1, 1)

1 1 1 0

 

 

4.       Number Systems (20 points).

  1. Convert (10010011) 2 to decimal
  2. Convert (DAD) 16 to decimal
  3. Convert (197) 10 to binary
  4. Convert (197) 10 to hexadecimal

 

 

5.       Bus Topology (30 points). Consider the following network where each computer is connected to the bus through a NIC. Assume the MAC address of computer 1 is E78D45C4BBFD, of computer 2 is 7E8D4C54BB4D, of computer 3 is 78DF4C84BBF2.  Assume computer 2 now wants to send the message “ER” to computer 3. The hexadecimal value for “E” is 45; for “R” is 52.

 

A.      To send out the message, computer 2 will first build the frame and forward it to computer 2’s NIC. The NIC will then compute the CRC for the frame and add it to the frame. Please draw the format of the final frame which will be sent out by NIC-2.  (When drawing the frame, please use hexadecimal values for the header and payload, and use “SOH”, “EOT”, and “CRC” to indicate the Start of Header, End of Transmission, and CRC codes, respectively).

 

B.      NIC-2 will use CSMA/CD to send out the frame. Before the frame is sent out, computer 2’s NIC will first sense the bus for carriers.

a)       If a carrier is sensed, what will NIC-2 do?

b)       If no carrier is sensed, NIC-2 will send out the frame.

b.1) Before the frame is sent out, will the frame be first modulated?

b.2) After the frame is sent out, will NIC-2 sense the bus continuously for a period of time? Why?

b.3) Please say TRUE or FALSE: “Since the frame is sent to computer 3, so after the frame arrives at computer 2’s connecting point, it will only turn right to computer 3.”

 

C.      When the NIC of computer 3 senses the signal (carrier) sent from computer 2, what will the NIC do (here we assume the minimum length of payload is 2)? Please explain step by step.

 

D.     After NIC-3 receives the frame successfully, the frame will be forwarded to computer 3’s processor. What is the format of the frame forwarded to the processor?

 

E.      Will computer 1 sense the carrier sent from computer 2? Will computer 1’s NIC forward the frame to computer 1’s processor? Why?

 

 

6.       LAN Extensions (For Midterm preparation only. No need to turn in). Consider the following campus network where 8 computers are connected.  Here B1 and B2 are two bridges and R is a repeater. Assume that the physical address of NIC-1 is 78DF4C84F2D3; the physical address of NIC-8 is 7E4C8D4C544C. Assume the minimum length for a frame can be 1. Assume that computer 1 wants to send the message "R" to computer 8, and the hexadecimal value of 'R' is 52.

test2-f03-1

A.      How many LAN segments are there?

 

B.      In order to send out the message, P-1 will compose the frame then forward it to NIC-1. NIC-1 will then compute the CRC and add it to the frame. Please draw the format of the final frame which will be sent out by NIC-1.  (When drawing the frame, please use hexadecimal values for the header and payload, and use “SOH”, “EOT”, and “CRC” to indicate the Start of Header, End of Transmission, and CRC codes, respectively).

 

C.      NIC-1 will use CSMA/CD to send out the frame.  Say TRUE or FALSE to the following statement: “NIC-1 will keep on sensing the bus (after the frame is sent out) until computer 8 receives the frame.”

 

D.     After a while, NIC-L of B1 will sense the frame, then what will NIC-L do? Please explain step by step.

 

E.      Then NIC-L will forward the frame to P-B1, and P-B1 will forward the frame to NIC-R of B1, then NIC-R of B1 will start to sense the bus.  Assume at this moment, a frame sent out by computer 4 is already on the bus. What will NIC-R do?

 

F.      If NIC-4 senses another carrier during the transmission (time) of the frame sent out by computer 4, then there is a collision. Give one situation that causes the collision.

 

G.     Say TRUE or FALSE to the following statement: “After a while, NIC-7 will sense the collision mentioned in the above question.”

 

H.     Assume NIC-R of B1 finally puts the frame on the bus.  After a while, repeater R will get the frame, what will R do?  Here we assume there are no collisions on this LAN.

 

I.        If there is nothing wrong, after a while NIC-L of B2 will get the frame and forward it to P-B2. When P-B2 receives the frame, what is the format of the frame?

 

J.       After NIC-R of B2 sends out the frame, the frame will be sensed and capture by NIC-7. What will NIC-7 do then?

 

K.     During the whole transmission process from P-1 to P-8, if we consider only the devices that are directly involved in the process, how many demodulation operations are done?

 

L.      During the whole transmission process from P-1 to P-8, if we consider only the devices that are directly involved in the process, how many times is a CRC computed?