Assume propagation delay is less than transmission delay on a link connecting host A to B. If host A starts transmission at t=0, at time equal to transmission delay, where is the first bit of the packet?

Assume propagation delay is less than transmission delay on a link connecting host A to B. If host A starts transmission at t=0, at time equal to transmission delay, where is the first bit of the packet?Top of FormAt host AIn the linkAt host BBottom of FormSuppose N packets arrive simultaneously at a router every T seconds. Suppose the packets are of size S bits and the transmission rate of the router is R bps.

What should the minimum value of T be such that the queuing delay does not grow without bound?Top of FormNR/S(N-1)S/R(N-2)S/RNS/RBottom of FormAnswer DescriptionFor the queuing delay to not increase without bound, its important that the queue is empty before the next batch of packets arrive. The time it takes to send out (transmit) N packets is NS/R. So T is NS/R.

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At this value of T, what is the average queuing delay experienced by a packet?Answer DescriptionThe delay experienced by the first packet in the batch is 0. By the second packet is S/R. The third is 2S/R and so on.

Averaging it yields [ 0 + S/R + 2S/R + ............ + (N-1)S/R ] / N = (N-1)S / (2R)Top of FormNS/RNS/2R(N-1)S/2R(N-2)S/2RBottom of Form Bit Length

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On a 1 Mbps link, where light travels at 2*10^8m/s, what would the bit length be in meters? Format to use X (no decimals, eg. 365)

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File transfer time: What is the time required in sec (from 1st bit sent to last bit received) to send 10 MB of data?

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Assume a 1 Gbps link with a propagation delay of 10 ms. Specify time in sec. Format X.xxx (3 decimal places. Eg. 99.999, 9.999)Top of Form

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Assume a 100 kbps link with a propagation delay of 10 ms. Specify time in sec. Format X.xxx (3 decimal places. Eg. 99.999, 9.999)HintTotal time = Tx time + Propagation time Bits

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Suppose two hosts A and B are connected by a 1 Mbps link of length 10 km. Suppose the speed of light over the link is 2 * 10^8 m/s. If a 5 MB file were to be transferred between the hosts as back-to-back packets, how many bits will be in the link at any given time? Format X (e.g. 100)

File fragmentationA-----R-----B

Hosts A and B are connected via a router R. Suppose the Bandwidth of the A to R link as well as R to B link is 10 Mbps. Assume propagation delay on each link is 10 us and processing speed at R is 30 us. Assume the router needs to retrieve the entire packet before processing. Calculate the time (in us) it takes to transmit 10k bits from A to B.

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Assume the 10k bits are sent as two 5k bit packets back-to back.Specify the time in us (microsec). Format X (e.g. 1000)Top of Form

Bottom of FormHintPipelining plays a role here

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Assume the 10k bits are sent as a single packet. Specify the time in us (microsec). Format X (e.g. 1000)See Figure. Suppose the I/O bus within a host has a speed of 100 Mbps, would it be possible to sustain a rate of 100 Mbps on the outgoing link? Why or why not. Justify your answer.See Figure. Suppose a workstation is configured as a router with an internal I/O bus speed of 10 Gbps. Assume DMA mode of memory access and that the CPU has to examine the headers (all at once) to determine the route of the packet. If the total headers size is 10% of the total packet size and the router has to output packets at a rate of 1 million packets per sec, what should be the packet size in bits such that the router can sustain this outgoing rate?Top of Formp < 5000p > 5000p < 4762p > 4762Bottom of Form10dB attenuation means the signal strengthTop of Formhalveddoubledreduced by factor of tenincreased by factor of tenBottom of FormIf a cable suffers 3dB attenuation per 100m and if the transmit power is 100mw. What is the received power if the cable length is 1km? Express the received power in mw. Format X.x (E.g. 1.1)

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Determine the distance between a transmitter and receiver of a wireless 900Mhz link if the transmit power is 1 watt, received power is 0.1 nano watt. Assume free space path loss model. Ignore antenna gains (not covered in class). Express the distance in km. Format X.xx (E.g. 3.45)

No choiceWhich among the following does NOT causes distortion of a signal?Top of Formreflectionmobilityattenuationlinear amplificationBottom of FormA noiseless 4 KHz channel can support which of the following data rates (in kbps) if binary pulses are employed?

Top of Form48 (wrong)16all of the above

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SNR Reuired --To achieve 50 kbps data rate on a 5 khz channel, what SNR (in dB) is needed? Format X (E.g. 13) 30Max data rate -- A transmission line has a bandwidth of 1 Mhz. When 10 dBm power is transmitted, the receiver receives -60 dBm. The noise level at the receiver is -100 dBm. What is the maximum theoretical rate (in Mbps) that can be achieved on this link? Format X.x (E.g 5.1)

Note dBm is nothing but power ratio in decibels (dB) of the observed power referenced to one milliwatt (mW). So it boil downs to 10log_10(P in mw). Eg. 0dBm = 10 log_10(1mw)

Packet error rate

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What is the Packet Error Rate (PER) in percentage at a bit error rate of 10^-7 if packet size is 10k bits.1-(1-10 power-7)1000Top of Form1%0.1%0.01%0.001%

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Signal bandwidth

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See figure. What is the bandwidth in Mhz occupied by the signal if T is 1us? Format X (e.g. 2) or answer "inf" for infinity. 1 inf Clock Synchronization

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Which of the following encodings do not provide proper clock synchronization?

Top of FormNRZNRZIManchester4B/5B

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102Which of the following encodings have problem with long sequence of 1's

Top of FormNRZNRZIManchester4B/5

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Manchester encoding can be thought of as XB/YB encoding. What are X,Y? Format X,Y (E.g. 1,3 )4,5No choice

Assume a bit duration of 1ms. Suppose the sender clock is r`unning 5% slower than the receiver clock and the receiver samples the bit in what it believes to be the middle of the bit. If NRZ encoding is used, at what bit position starting from 1, can the receiver possibly make an error. This means the sender sends first bit from 0 to 1.05ms, second bit from 1.05 to 2.1ms and so on. The receiver samples first bit at 0.5, second bit at 1.5 and so on.

Express answer as a bit position (starting from 1). Format X (e.g. 7)

4B/5B

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When employing 4B/5B encoding, what would the below bit sequence translate to?

0011 1000 1111101011001011101

Format: bit sequence without spaces (E.g. 001100011011010)

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Can you design an encoding scheme with an even stronger requirement of no more than 2 consecutive 0's in the encoded bit stream?

What would be the efficiency of such a scheme?4B/5B NCCCCCDLL FRAME Can errors in one frame affect the next frame?

Top of Formyesno

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Byte Stuffing

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Suppose the last two bytes of the BiSYNC protocol are DLE ETX, what sequence of bytes precede CRC?

Top of FormDLE DLE DLE ETX ETX

DLE DLE ETXDLE DLE ETX ETXDLE DLE DLE ETXBottom of Form

Bit Stuffing

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If the following bit pattern is received as part of HDLC data, what does the HDLC decoder output after removing stuffed bits?

1101111101001

Express the answer as a sequence of bits with no spaces (e.g. 1100110011)

Escape characters

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Can this sequence 'A DLE DLE ETX' appear in the data portion of the transmission when using the Bisync protocol, where A is the ASCII character 'A'.

Top of FormyesnoBottom of FormError Control

Hamming distance

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If a code has a hamming distance of 7, how many errors can it detect? Format X (e.g. 2)6

Top of Form6Bottom of Form 0 / 1 points

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If a code has a hamming distance of 7, how many errors can it correct? Format X (e.g. 1)3If a code contains the following code words:

c1 = 0101010, c2 = 1111111, c3 = 1010101, c4 = 0000000 and c5 = 1100001

What is the hamming distance of this code? Mr. Error Prone wants to decide on whether to use error correction or detection on a link with packet error rate of 10^-5. Suppose the packet size is 923 bits and he is considering BCH ( Bose-Chaudhuri-Hocquenghem) code for error correction, where 1023 code bits are sent for 923 data bits and CRC for error detection ,where 32 bits are added to 923 data bits.

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What is the transmission overhead of the error correction in %? Transmission overhead is the percentage of 'additional' bits transmitted per data bit. Format X.x (e.g. 15.3)Top of Form

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What is the transmission overhead of the error detection in %? Transmission overhead is the percentage of 'additional' bits transmitted per data bit. Format X.x (e.g. 15.3)

Puzzle

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A bit challenging but fun nonetheless...

An absent minded professor's glasses are inside one of three rooms. He wants to send five of his students in groups to the three rooms to check for his glasses. One of his students may lie, while others always tell the truth about whether they found the glasses in the room or not.

How should the professor divide the students into groups so that he can determine where his glasses are?

Also, how can he determine in which room his glasses are?

Could the professor determine where his glasses are if there were only four students, and onlyone of them might lie?

Map this problem to error correcting codes and solve. Detection Single bit parity

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Smarty Pants wants to enhance single bit party scheme and decided to use two redundant bits. One bit represents the parity of all odd-numbered bits and second bit the parity of all even-numbered bits.Example: 0111 is encoded as 011110 (assuming 'even-parity').

Whats the hamming distance of this code? Note message bits can be any number, redundant bits are 2. Answer Format X (e.g. 5)

Has he done better than single bit parity in terms of hamming distance? Do not answer this in the box, just for your thinking.

NCCCCCCCCCCCCCCCcc

Two dimensional parity

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What is the general set of circumstances under which a 4-bit error cannot be detected by a two dimensional parity?HintRectangle

NCCCCCCCCCCCCCc

Internet Checksum

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The IP protocol implements Internet checksum over just the IP header. As the packet passes through the routers, one field called TimeToLive (TTL) (8-bits long) in the IP header is decremented at each router. So, each router needs to decrement this field and then update the checksum in the header. Is there a way to update the checksum without having to recalculate the checksum over the entire header?

Hint16-bit word in checksum calculation is made up of two bytes. Consider two cases, where TTL field falls in low byte order (least significant byte) and another where it falls in higher byte order (most significant byte).

NCCCCCCCCCCCCCc

CRC

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For a generator polynomial of x^3+x^2+1, what is the CRC value if the message is 10011010? Express answer as a bit sequence with no spaces (Eg. 011)

CRC Burst Errors

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Show that any bursts of length