CS188 Final

8/3/2019 CS188 Final

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CS 188

P2P Systems

Winter 2010

FINAL EXAM

Professor Giovanni Pau

Wednesday, March 10, 2010

This test is closed book

Estimated time: 1h and 50 minutes.

Name _____________________________

Student ID _______________________

Do NOT turn to the next page until told to do so.

Exercise Value Score

1 30

2 30

3 30

4 30TOTAL 120

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Intentionally empty.

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1) Answer the following True/False

1. Kademlia is not DHT protocol because of its tree topology

2. Napster is not fully distributed.

3. On a DHT. There are no restrictions about the algorithm to use to

map a content into a specific key

4. DHTs provide an efficient structured way of routing messages

5. Gnutella networks do not use a flooding algorithm to perform content

searching.

6. Skype does not have central servers to guarantee an high QoS

7. In Napster peers were not able to handle the data exchange without

the server sharing its bandwidth

8. Gnutella use flooding algorithms for massive exchange of data

9. In livestreaming the player must not have a buffer if the

underlaying network layer has already one

10.Chord’s routing system picks the node that has the closest id to the

destination from those ones present in the routing table

11.Mesh networks are way more efficient than tree based networks

12.The choice of the buffer dimension in a p2p livestream application

is not related with the bitstream of the content

13.Multimedia streams need a stream based protocol like TCP to have

good performance and no interruptions

14.In livestreaming a peer can recover packets lost using other peers’

buffers

15.Peers connected directly to the source are advantaged by the fact of

being able to download the stream with higher bandwidths than those

peers in the deeper levels

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2) Multiple choice (correct answer can be 1, 2, all or none)

1. Consider a Kadmelia network in the address space 0..65536, the

routing table will contain up to:

2 K-Buckets __ 8 K-Buckets __ 16 K-Buckets __ 511 K-Buckets __

None of the Above ___

2. The BitTorrent tracker:

Keeps track of which peer has which chunk ___

Shares all its information with every peer bootstrapping ___

Forces a node to connect to a specific peer __


3. In a tree based P2P streaming system:

Leafs do not collaborate with their resources___ The overlay performs better if the first level has a big fan out ___

Every level has different delays ___

None of the above___

4. Consider a live-streaming application. Peer-1 connects to peer-2

that has 2MBytes of stream cached. Knowing only this, which will be

the minimum delay from the source if the average bit rate is 1Mbps?

1 sec __ 2 sec __ 8 sec __ 16 sec __


5. Pastry Routing:

Uses XOR metrics for its routing table ___

Uses the neighborhood to forward the packets___

None of the above ___

6. Kadmelia Buckets:

Its content is sorted from the least recently seen to the most__

Contain a number of records proportional to the network size ____

Contain a pre-defined number of records__

None of the above ___

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1. CHORD Routing

Consider the following ring space 0..512 in Cord. :

The following nodes are in the ring: 0, 2, 4, 8, 12, 16, 20, 22,28,

32, 64, 127, 128, 224, 255,512

The routing table for NODE. 0 is:

a) [2 4 8 16 32 64 128 512]

b) [2 4 8 12 16 64 128 512]

b) [2 4 8 16 32 64 128 255]

To route a packet to the node 512 in the first hop the packet will

be sent to (from node 0):

a) 128

b) 255

c) 512

d) 2

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5. Pastry Routing

Consider the following ring space 0..255 in Pastry. :

The following nodes are in the ring: 0, 2, 4, 8, 14, 16, 20, 21,

22,23, 24, 32, 33, 34, 127, 128, 224, 255

d

For node 127 write down the pastry leafset assuming there are a

total of 16 entries. Point out which nodes are part of the lower

leafset and which one are part of the higher leafset.

a) L [128 224 255 0 2 4 8 14] H [20 21 22,23 24 32 33 34]

b) L [20 21 22,23 24 32 33 34] H [128 224 255 0 2 4 8 14]

In which row of the node 16 can the node 20 be placed ?

a) 0

b) 1

c) 2

In which column ?

a) 0

b) 2

c) 4

d) 8

e) 16!! !

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6. Consider a Kademlia network with 2^3 nodes please write down thefollwoing:

A) Considering node 001, draw the k-bucket on the picture

B) Considering node 100 which is the correct table for the K

buckets?

a)

Distance K-Bucket

[0,1] 101

[2,3] 110, 111

[4-7] 001, 011

b)

Distance K-Bucket

[0,1] 1

[2,3] 010, 011

[4-7] 100, 101

C) For which node this set of k buckets would be correct referring

to the picture?

Distance K-Bucket

[0,1] 1

[2,3] 010, 011

[4-7] 100, 101

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4. Suppose to have 4 nodes in a tree topology, respectively they haveNode 1: 10Mbit Download/1 Mbit Upload

Node 2: 10Mbit Download/0.5 Mbit Upload

Node 3: 100Mbit Download/0.5 Mbit Upload

Node 4: 1Mbit Download/10 Mbit Upload

A) How would you dispose them to optimize the distribution of a 512

Kb/s stream if the source has fan out 2 and your goal is to

reduce the height of the tree for future arrivals?

/-1-4

a) S

\-2-3

/-1-2

b) S

\-4-3

3

/

/-4-2

c) S \

1

B) If the stream is 300Kbit/sec what is the minimum buffer size

needed at each level to avoid interruption in a static ideal

condition? (i.e. the network does not change performance)

a) 1.2 MB

b) 1.2 KB

c) 120 KB

d) 0 KB

D) If node2 with both 10 Mbits/sec in download and upload connects

to node1 with the same resources that has a 2MB buffer completely

full. Supposing it gets the entire content of the buffer. How

bigger will be its delay compared with the one of the peer 2.

a) it won’t add any delay from what node 1 is receiving

b) ~1.6 secs

c) 0.0000...01 (Something really small, out of scale)

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CS188 Final