Exam

Question 1

What are the 5 layers?

Answer 1

Application, Transport, Network, Link, Physical

Question 2

What is c/s architecture?

Answer 2

Client/Server. Always on central server that requests and receives services from client devices

Question 3

what is p2p archetecture.

Answer 3

Peer-to-peer. No central server, just peers pooling resources

Question 4

Formula for dtrans

Answer 4

dtrans = L/R (packet size[bits]/ link bandwidth[bits/sec])

Question 5

Formula non-persistant HTTP response time

Answer 5

2RTT + dtrans for file and each object

Question 6

Throughput formula

Answer 6

min rate along the path

Question 7

Formula dnodal

Answer 7

dnodal = dproc + dqueue + dtrans + dprop

Question 8

Formula dprop

Answer 8

dprop = m/s (length[m]/prop speed[m/s])

Question 9

Formula de2e

Answer 9

de2e = total packet size/e2e throughput

Question 10

How many bits is IPv4

Answer 10

32

Question 11

How many bits is port number

Answer 11

16

Question 12

What are the reserved port numbers

Answer 12

0-1023

Question 13

What is UDP and how many bytes is the header

Answer 13

connectionless transport protocol, 8 byte header

Question 14

How to do checksum

Answer 14

1’s complement sum. Add numbers and wrap around extra bit. Flip each bit. Add together and should be all 1’s

Question 15

Formula utilization with no window size

Answer 15

U = L/R / (L/R) +RTT

Question 16

Formula utilization with window size N

Answer 16

U = N(L/R) / (L/R) +RTT

Question 17

What is TCP and how many bytes is the header

Answer 17

connection-oriented, needs handshake

Question 18

Formula Estimated RTT

Answer 18

EstRTT = (1-a)estRTT + asampleRTT

Question 19

Formula Dev RTT

Answer 19

DevRTT = (1-B)DevRTT + B|sampleRTT-estimatedRTT|

Question 20

What is average TCP throughput

Answer 20

Avg TCP throughput ≈ 3/4 * W/RTT segments/sec

Question 21

How many bits is IPv6

Answer 21

128

Question 22

How big is IPv4 datagram

Answer 22

20B fixed, 40B optional

Question 23

How big is IPv6 datagram

Answer 23

fixed 40 B

Question 24

What does DHCP stand for

Answer 24

Dynamic Host Configuration Protocol

Question 25

What are the 5 DHCP messages

Answer 25

Discover, Offer, Request, Ack, Release

Question 26

RSA key generation process

Answer 26

Large primes p, q n = p*q z = (p-1)*(q-1) choose e such that 1 < e < z and is coprime to z choose key d such that 1 < d < z and e*d mod z = 1

Question 27

RSA encryption formula

Answer 27

c = m^e mod n

Question 28

RSA decryption formula

Answer 28

m = c^d mod n

Question 29

Diffie-Hellman key exchange

Answer 29

Each person has private key a, public key A = r^a mod p and secret key k = B^a mod p

Question 30

Number of attempts to find a collision for a hash of length n

Answer 30

1.25 sqrt(2^n)

Question 31

Formula dc/s

Answer 31

max { NF/us, F/di }

Question 32

Formula dp2p

Answer 32

max { F/us , NF/(us + Nui) , F/di }