DHT Optimizations for mobile devices. Seminar Mobile Systems Supervisor: Thomas Bocek Student: Dario Nakic

Transcription

1 DHT Optimizations for mobile devices Seminar Mobile Systems Supervisor: Thomas Bocek Student: Dario Nakic

2 Agenda 1. Peer to Peer systems 2. Lookup problems in P2P systems 3. Distributed Hash Tables 4. DHT optimitazion for mobile devices Energy and Battery consumption

3 1.Peer to peer systems No need for central coordination instances Decentralized system Peers are both, suppliers and consumers of resources The term Servent is used, composed of the first syllable of the term Server and the second of the term Client P2P systems suggest a way to aggregate and make use of the tremendous computation and storage resources Survey by ipoque GmbH 50% 90% of Intenet traffic

4 Types of peer to peer systems Unstructured peer to peer network Peers don t maintain information about other peers Centralized peer to peer network Central lookup server File sharing only between peers Pure peer to peer network Peers act as equals Hybrid peer to peer systems Distributing clients into to groups: Client nodes Overlay nodes Stay scalable clients per overlay node Structured peer to peer network Peers maintain information about other peers

5 2.The lookup problem If a node A wants to store a data X Where to store the data X How can node B find the data X

6 The lookup problem(2) One approach is to maintain a central database Peer submits all information and services Flooding search Broadcast message to all neighbors Time To Live of an request is restricted Hierarchical approach Nodes are organized into a hierarchy Symmetric distributed lookup Following references from node to node Each node maintains information of small number of other nodes Distributed indexing Distributed Hash Tables Nodes organized in a structured overlay and establish a small amount of routing information

7 3.Distributed Hash Tables (DHTs) Structured P2P system O(logN) references O(logN) hops Very robust against random failures and atacks DHT guarantees to find a stored data

8 Fundamentals of DHTs Distributed Management of Data Each node is responsible for a particular range of data items Adressing in DHT Data item is assigned an ID Large number of integers from 0 to Routing Core functionality of DHT Peer maintain a bounded number to other nodes Data Storage Direct storage Storing references of the data item

9 DHT Mechanism Node arrival 4 steps for a node to join DHT 1. Using a arbitrary node as entry point 2. Assigned partition in address space 3. Routing table update 4. Retrieving all (key,value) pairs Node failure DHT algorithms are designed to deal with all likely events that may happen Reactive recovery Proactive recovery Node departure Nodes need to notify the system

10 DHT Interfaces Routing interface send primitive accepting ID and delivering to the specific node recieve primitive passes IDs to the recieving node Storage interface put primitive stores (key, value) pair get primitive accepts identifier and returns the value associated with the identifier

11 4.DHT Optimization for Mobile Devices Little research is done in the mobile P2P network Problem is battery consumption Power consumption of a typicall P2P download Power consumption of P2P related to other activities Power consumption of a full peer and client only mode Batterry consumption by sending parallel requests

12 Energy consumption in Mobile P2P

13 Energy consumption in Mobile P2P(2) Figure 1 Source: Jukka K. Nurminen Energy Consumption in a Mobile Peer to Peer Quantitative Results from File Sharing

14 Energy consumption in Mobile P2P(3) Figure 2 Source: Jukka K. Nurminen Energy Consumption in a Mobile Peer to Peer Quantitative Results from File Sharing

15 Energy consumption in Mobile P2P(4) Figure 3 Source: Jukka K. Nurminen Energy Consumption in a Mobile Peer to Peer Quantitative Results from File Sharing

16 Batterie saving in DHT

17 T Mobile G1 Devices

18 Android Programm

19 Results (2)

20 Results(2.1) Div 1 25 sec, 5 req 12:26:45 10 sec, 2 req 10:07:23 5 sec, 1 req 11:12:10 Div 2 25 sec, 5 req 15:22:39 10 sec, 2 req 12:43:16 5 sec, 1 req 13:37:57 Div 3 25 sec, 5 req 11:37:46 10 sec, 2 req 10:53:35 5 sec, 1 req 11:27:38

21 Results (3)

22 Results(3.1) Request type Average time Standard deviation 25 sec, 5 req 13:09:03 01:57:19 10 sec, 2 req 11:09:32 01:20:21 5 sec, 1 req 12:05:55 01:10:22

23 Results (4)

24 Results(4.1) Request type Average time Standard deviation 25 sec, 5 req 12:02:15 01:21:32 10 sec, 2 req 10:30:29 00:59:49 5 sec, 1 req 11:19:54 00:20:36

25 Conclusion P2P systems are more and more used DHT is a provable system Downloading in a moderate amount is acceptable for Battery consumption Energy consumption of Bit Torrent is on the same level as Voice calls Sending 5 requests all 25 sec battery consumption is the lowest Sending 2 requests all 10 sec battery consumption is the highest