471: CH1

Consider the circuit-switched network shown in the figure below, with circuit switches A, B, C, and D. Suppose there are 12 circuits between A and B, 20 circuits between B and C, 13 circuits between C and D, and 17 circuits between D and A.

62

Assume a constant transmission rate of R = 1700000 bps, a constant packet-length L = 3600 bits, and a is the average rate of packets/second. Traffic intensity I = La/R, and the queuing delay is calculated as I(L/R)(1 - I) for I < 1. Assuming that a = 33, what is the queuing delay?

I = (3600 * 33) / 1700000 = .0699 Queuing Delay = I(L/R)(1 - I) * 1000 = 0.0699*(3600/1700000)*(1-0.0699) * 1000 = 0.1377 ms.

Suppose that the packet length is L= 12000 bits, and that the link transmission rate along the link to router on the right is R = 100 Mbps. What is the transmission delay?

L/R = 12000 bits / 100000000 bps = 0.00012 seconds

link 1 Assume the length of a packet is 4000 bits. The speed of light propagation delay on each link is 3x10^8 m/sec transmission rate: 1000 mbps link length: 3 Km What is the transmission delay of link 1?

L/R = 4000 bits / 1000000000 bps = 4.00E-6 second

If the buffer has a maximum size of 998 packets, how many of the packets would be dropped upon arrival from the previous question? given 1683 packets arrive

Packets dropped = packets - buffer size = 1683 - 998 = 685 dropped packets.

Assuming the router's buffer is infinite, the queuing delay is 0.3182 ms, and 1683 packets arrive. How many packets will be in the buffer 1 second later?

Packets left in buffer = a - floor(1000/delay) = 1683 - floor(1000/0.3182) = 0 packets.

What layer in the IP stack best corresponds to the phrase: 'bits live on the wire'

Physical Layer

Suppose that the packet length is L= 12000 bits, and that the link transmission rate along the link to router on the right is R = 100 Mbps. What is the maximum number of packets per second that can be transmitted by this link?

R / L = 100000000 bps / 12000 bits = 8333 packets

What is the probability that more than 6 users are transmitting?

To find P(x = k), use binompdf(n,p,k) • To find P(x ≤ k), use binomcdf(n,p,k) • To find P(x < k), use binomcdf(n,p,k-1) • To find P(x > k), use 1-binomcdf(n,p,k) • To find P(x ≥ k), use 1-binomcdf(n,p,k-1)

What is the probability that one user (any one among the 11 users) is transmitting, and the remaining users are not transmitting?

To find P(x = k), use binompdf(n,p,k) • To find P(x ≤ k), use binomcdf(n,p,k) • To find P(x < k), use binomcdf(n,p,k-1) • To find P(x > k), use 1-binomcdf(n,p,k) • To find P(x ≥ k), use 1-binomcdf(n,p,k-1)

What is the probability that any 6 users (of the total 11 users) are transmitting and the remaining users are not transmitting?

cTo find P(x = k), use binompdf(n,p,k) • To find P(x ≤ k), use binomcdf(n,p,k) • To find P(x < k), use binomcdf(n,p,k-1) • To find P(x > k), use 1-binomcdf(n,p,k) • To find P(x ≥ k), use 1-binomcdf(n,p,k-1)

link 1 Assume the length of a packet is 4000 bits. The speed of light propagation delay on each link is 3x10^8 m/sec transmission rate: 1000 mbps link length: 3 Km What is the propogation delay of link 1?

d/s = 3 Km * 1000 / 3*10^8 m/sec = 1.00E-5 seconds

ADSL bandwidth is shared. True False

false

Before sending a packet into a datagram network, the source must determine all of the links that packet will traverse between source and destination. True False

false

Ethernet is a popular residential Internet access technology. True False

false

In the connection flooding attack, the attacker sends a deluge of packets to the targeted host, clogging the target's access link with packets. True False

false

Suppose 10 connections traverse the same link of rate 1 Gbps. Suppose that the client access links all have rate 5 Mbps. Then the maximum throughput for each connection is 100 Mbps. True False

false

The HTTP protocol was invented at Netscape in the early 1990s. True False

false

The Internet provides its applications two types of services, a TDM service and a FDM service. True False

false

The acronym API in this textbook stands for "Advanced Performance Internet". True False

false

Twisted-pair cooper wire is no longer present in computer networks. True False

false

Suppose that these maximum number of connections are all ongoing. What happens when another call connection request arrives to the network, will it be accepted? Answer Yes or No

no

What is the probability that a given (specific) user is transmitting, and the remaining users are not transmitting?

p*(1-p)^N-1

Suppose that every connection requires 2 consecutive hops, and calls are connected clockwise. For example, a connection can go from A to C, from B to D, from C to A, and from D to B. With these constraints, what is the is the maximum number of connections that can be ongoing in the network at any one time?

so to find the bottleneck link it's the min of the paths that the packet has to take for a packet to go a->c the bottle neck link is min(18, 16) which is 16 and from c->a its min(12, 11) = 11 so that value would be 11+16 = 27 you do the same for the b->d and d->b packet which gives you 12+11 = 23 then you do max(27, 23) so the answer is 27

Consider a queue preceding a transmission link of rate R. Suppose a packet arrives to the queue periodically every 1/a seconds. Also suppose all packets are of length L. Then the queuing delay is small and bounded as long as aL < R. True False

true

In a virtual-circuit packet-switched network, a packet switch maintains state information for each connection passing through the router. True False

true

Layers four and five of the Internet protocol stack are implemented in the end systems but not in the routers in the network core. True False

true

Network News was present in the Internet before the emergence of the World Wide Web? True False

true

With ADSL, each subscriber gets more downstream bandwidth than upstream bandwidth. True False

true

In practice, does the queuing delay tend to vary a lot? Answer with Yes or No

yes

Suppose that 13 connections are needed from A to C, and 11 connections are needed from B to D. Can we route these calls through the four links to accommodate all 24 connections? Answer Yes or No

yes