P2P and Mobility Support

Transcription

1 Informatik III () Prof. Dr. P. Tran-Gia P2P and Mobility Support and Kurt Tutschku www3.informatik.uni-wuerzburg.de Workshop der FG und FG 5.2.4, Mobilitätsmodelle + (vertical) Handover, München, March 23th 2006

2 P2P and Mobility Mobility means moving subscribers in a geographical layout (vertical) handover required to offer connectivity system required to support (vertical) handover motion introduces spatial and temporal load changes ease installation and configuration of attachment points Next generation wireless networks consist of several access technologies, like GSM/GPRS, WLAN, UMTS, WiMAX,... Large-scale heterogeneous networks w.r.t. users and APs P2P mechanisms are candidates to handle these challenges overlay networks on top of lower layers (heterogeneity) scalable and self-organizing (large-scale) However, P2P networks are logical and do not consider layout 2

3 P2P and Mobility (cont d) P2P distributes load, e.g. requests to database, equally among peers Utilize information of a particular application to improve overlay (local searches for VHO) Might not be necessary for well planned wireless networks Modify P2P mechanism to cope with geographical layout overlay routing modified overlay 3

4 Carrier-Grade Peer-to-Peer (CaPi) Project from 10/ /2005 Siemens AG Com: Frank-Uwe Andersen, Department of : Prof. Dr. Phuoc Tran-Gia, Dr. Kurt Tutschku,, Simon Oechsner University of Genova, D.I.S.T., Department of Communications, Computer and Systems Science: Prof. Dr. F. Davoli, Luca Caviglione, Marco Perrando Does P2P offer carrier-grade and dependable solutions when supporting mobility? Compare P2P with traditional solutions and modify it 4

5 Applications to Support Mobility Supporting vertical handover Easy configuration of APs Carrier-grade requirement: efficiency ISC HDU Overlay Routing!?!?!? HDU N ISC Distributed o QueryResponse HIS d e B Carrier-grade requirement: robustness 5

6 Vertical Handover WLAN AP? Handover How to make decision a based handover on previously more obtained secure? coverage information!? coverage information at the location of the mobile is needed to conduct VHO??? Available measurements RSSI BLER RSCP NodeB Measurements are obtained by other mobile devices or APs 6

7 Problem Formulation Locality-bound measurement information has to be made available (e.g. signal strength) Different access technologies must be supported Information is time-dependent (changing network conditions) Large number of handover requests has to be served Fast response times are needed for viable handover VHO support system must be scalable and efficient 7

8 HIS: Querying a Database for Information WLAN AP Disadvantages: high load single point of failure HIS Intelligent Service Control (ISC)?!!?!? Response Query Centralized Handover Decision Unit NodeB Example: Network initiated handover 8

9 Our Approach: Distribution of Database WLAN AP ISC HDU Overlay Routing Scalability (ability to handle a large number of nodes, requests) Load distribution Fault tolerance (no single point of failure) Self-organization (heterogeneous networks) Network can be made up of inexpensive components!??!!? NodeB HDU Query ISC Distributed HIS Response 9

10 How to find the distributed coverage information? Coverage information stored at NodeB and WLAN Access Points which are peers in the overlay Each peer only stores a segment of the information Geographically close peers should be neighbors in the overlay Overlay metric has to be symmetric and location-aware Structured P2P used to locate and route data (scalability) Pastry can be enhanced to fulfill these requirements 10

11 Pastry and its Modifications Random ID: r 1 r 2 r 3 r 4 Location-aware ID: x 1 y 1 x 2 y 2 Pastry routing not changed

12 Hop distributions Connection to server modeled as one hop 1 Normal Pastry takes log(n) hops to route messages 0.8 server modified Pastry with shortcut Shortcut improvement cuts off the most ineffective part of the search probability modified Pastry w/o shortcut original Pastry Our modifications improve the routing by shortening the search path due to local searches number of hops 12

13 Search time distributions Standard Pastry performs not as good as classical client/server approach 1 When improved with locality and shortcuts, search is sped up Modified algorithm is faster than a central server Modifications are necessary to get dependable systems CDF with shortcut w/o shortcut original Pastry server Neglecting physical network hop processing times and time in waiting queues: current work search time [s] 13

14 Applications to Support Mobility Supporting vertical handover Easy configuration of APs Carrier-grade requirement: efficiency ISC HDU Overlay Routing!?!?!? HDU N ISC Distributed o QueryResponse HIS d e B Carrier-grade requirement: robustness coverage information is collected in a database on handover request coverage information has to be retrieved quickly Pastry P2P overlay used information distributed among APs application causes local searches modified to our needs (IDs are location aware) symmetric metric 14

15 Current Network Management First level of management hierarchy element manager Polling and distribution of information, e.g., SSID cryptographic key handover policies network IDs attachment points 15

16 Problem formulation Support heterogeneous large-scale networks with many cells System must be flexible to react on changes in the network topology, i.e. variable number of APs Avoid central management reliability (single point of failure, congestion) split of responsibility and interoperability Self-organization of access networks required Application of P2P technology Attachment point are peers Distribute configuration data to suited nodes (i.e. cells that overlap) Neighboring cells/nodes have to be identified 16

17 Distribution of Configuration Functions exchange of configuration information (e.g. network IDs) neighborhood relationship (overlay connection) 17

18 ecap Architecture ecap easy configuration of attachment points Basic algorithm is based on Kademlia To achieve adaptation in the required sense (automatic detection of close nodes), a spatial metric is used Coordinates (known e.g. via GPS) are used as node IDs Distance in the overlay is the Euclidean distance Symmetry of the metric is conserved 18

19 Spatial metric location of an attachment point Attachment point/peer p Y X bucket N bucket N-1 bucket N-2 bucket i of peer p consists of peers q with distance d( p, q) 2 ;2 N i N i+ 1 19

20 Results Network organizes itself High number of known nodes implies a high number of known neighbors After some time, the network stabilizes itself Time to stabilization depends on a number of parameters (e.g., network size) Different methods for neighborhood detection have been tested probability Immediately after join number of known nodes (in buckets) 20

21 Applications to Support Mobility Supporting vertical handover Easy configuration of APs Carrier-grade requirement: efficiency ISC HDU Overlay Routing!?!?!? HDU N ISC Distributed o QueryResponse HIS d e B Carrier-grade requirement: robustness coverage information is collected in a database on handover request coverage information has to be retrieved quickly knowledge of neighboring APs automatically collected and updated new APs can be easily inserted without human effort Pastry P2P overlay used information distributed among APs application causes local searches modified to our needs (IDs are location aware) symmetric metric Kademlia P2P overlay used information of close APs implicitly in routing table modified to our needs (proximity metric instead XOR) search traffic utilizes to stabilize overlay 21

22 Informatik III () Prof. Dr. P. Tran-Gia Thank you! Any questions? www3.informatik.uni-wuerzburg.de