Seminar 4: - - PowerPoint PPT Presentation
Topics in Computer Networks 2010 Seminar 4: Peer-to-Peer Systems o r t s a Marcel C. Castro C C l e c marccava@kau.se r a M Topics in
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Topics in Computer Networks 2010
Seminar 4: Peer-to-Peer Systems
Marcel C. Castro marccava@kau.se
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Motivation
Internet Study http://www.ipoque.com/resources/internet- studies/
Peer-to-Peer Systems:
It is the dominating traffic type in the internet Based on application overlay routing
Protocol Type Distribution, Germany 2007
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Client-Server concept Understanding P2P P2P and Wireless Networks
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Powerful central entity to host:
the whole resource index global management of resources (i.e. access rights etc)
Low cost in messages for discovery Increase of clients may degrade the quality of service
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Fast and guaranteed discovery (if resource exists) Easy to deploy and charge system-wide services Easy to retain resource consistency Facilitates configuration for maximum security of delivered services
Weaknesses:
Single point of failure High initial installation and maintenance cost Performance bottleneck – scalability issue
Preferable in small environments
Good in relatively predictable growth patterns.
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Client-Server concept Understanding P2P P2P and Wireless Networks
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Issues addressed by P2P Eliminate the control that can be imposed on clients Provide high availability Provide scalability Provide privacy
How to address them By distributing the logic and the resources
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network of entities which contribute their individual resources and collaborate in order to reach the goal for which the network was built.
P2P networks are those which exhibit 3 characteristics: self-organization distributed control / resources symmetric communication
Dan Pascu, “Overview of P2P SIP Principles & Technologies”. Int. SIP Conf. 2007.
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the whole resource index global resource management (i.e. access rights etc)
Direct communication between nodes
Each node acts as both resource requestor and provider
Application specific networks Increase of nodes may improve the quality of service
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Robust and fault-resilient architecture Low installation and maintenance cost Enables inexpensive resource redundancy
Weaknesses
Slower not always guaranteed discovery Frequent join/leave actions of nodes Heterogeneous node capabilities High discovery cost– scalability issue Distributed data storage is hard to do in a consistent way
Suitable for large systems
unpredictable growth patterns
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An overlay network is a virtual network of nodes and logical links that is built on top of an existing network with the purpose to implement a network service that is not available in the existing network. (by I. Stoica) A P2P network is an overlay itself (over TCP/IP) E.g. of services:
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! Level of Centralization
Hybrid: node grouping with central index Pure: no centralised entity – equal nodes
Resource Location
Unstructured: any node may host any resource Structured: resources are hosted by well-defined nodes
Scalable Service Access”. ICCGI’08.
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1. Choice of identifier space (IS)
2. Map resources and peers to IS
3. Management of the IS by peers (or Resource Location)
4. Routing strategy
(Chord)
5. Maintenance strategy
correction
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"#!
Local (Unstructured P2P)
Each peer only indexes its own content and flood queries widely Can perform complex searches (rich queries not just key lookups Blind techniques: random forwarding from node to node. e.g.: Gnutela
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Unstructured P2P
Advantages
Fast lookup Low join and leave overhead Popular files are replicated many times
Weaknesses
Not 100% success rate Very high communication overhead Uneven load distribution
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Distributed (Structured P2P)
Also known as Distributed Hash Table (DHT) Efficient key lookup / routing (no flooding) Can perform only exact key lookups Many recent academic systems –
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IDEA: Route a packet based on a key to the node in the network that is currently responsible for the packet's key.
This process is referred to as indirect or key-based
routing.
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K6 K46 K36 N1 N8 N14 N21 N32 N38 N42 N48 N51
Large id space
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root node for key
id space
nodeId key
64 |0 (6 bits)
NodeIds picked randomly from space Hash[192.168.1.1] = N1 Keys picked randomly from space Hash[picture.jpg] = K46 Key is managed by its root node: Live node with id closest to the key location of object or
actual object
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K46 N1 N8 N14 N21 N32 N38 N42 N48 N51
nodeId key
query
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for maintaining the network
lookup a node for a given key
node itself and its predecessor
known as the finger table, which is used to improve lookup performance and increase fault tolerance
table which has the closest hash value preceding the hash of the queried resource
Lookup Service for Internet Applications”, SIGCOMM’01
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Full Mesh Ring Chord
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Structured P2P
Advantages
Scalability: O(log N) routing Load-balancing Overlay robustness
Weaknesses
No control where data is stored Complex queries are not possible Join and leave overhead
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Client-Server concept Understanding P2P P2P and Wireless Networks
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Differences between the Internet and a Mobile Wireless Networks:
Bandwidth limitation Multi-access interference Node mobility
Limited energy State-efficiency trade-off
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Physical, to all nodes in transmission range area Virtual, multiple unicasts Broadcast Mobile Fixed Peer Mobility Proactive, reactive, hybrid Proactive, reactive, hybrid Routing Physical structure corresponding to logical structure Physical apart from logical structure Structure Restricted area Any Internet point Peer location Low ( wireless connections) High ( physical connections) Connection confidence Wireless and indirect Fixed medium and direct Connection Between two nodes A physical infrastructure to provide connectivity Logical infrastructure to Provide a service Motivation for Creating the network MANET P2P Networks Physical, to all nodes in transmission range area Virtual, multiple unicasts Broadcast Mobile Fixed Peer Mobility Proactive, reactive, hybrid Proactive, reactive, hybrid Routing Physical structure corresponding to logical structure Physical apart from logical structure Structure Restricted area Any Internet point Peer location Low ( wireless connections) High ( physical connections) Connection confidence Wireless and indirect Fixed medium and direct Connection Between two nodes A physical infrastructure to provide connectivity Logical infrastructure to Provide a service Motivation for Creating the network MANET P2P Networks
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%./,& Key-based routing MANET (DHT routing) Broadcast,
routing (AODV) MANET Routing Structured, DHT Unstructured, Flooding P2P techniques
1
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Query Phase Response Phase
sharing system for mobile ad hoc networks”.VTC 2003
Broadcast-based P2P lookup protocol over MANET on- demand routing protocols.
Strict layering of unstructured overlay approached on top of wireless routing protocols is unlikely to work in MANETs.
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%./,& Key-based routing MANET (DHT routing) Broadcast,
routing (AODV) MANET Routing Structured, DHT Unstructured, Flooding P2P techniques
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DHT-based P2P protocol
P2P lookup can be scalable Underlying network routing protocol is based on broadcast Complexity of routing algorithm
200 400 600 800 1000 1200 4 9 16 25 36 49 Number of Nodes Total Overlay Traffic (Kbytes)
NO management CUSTOM management STANDARD management 0,00 10,00 20,00 30,00 40,00 50,00 60,00 70,00 80,00 90,00 100,00 4 9 16 25 36 49 Number of Nodes Success Ratio (%) NO management CUSTOM management STANDARD management
maintain the DHT.
P2P over Wireless Multi-hop Networks”. MESH 2008
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!,-#2! Oracle provided by an ISP
Information is provided, like link delay, bandwidth estimations, etc. As input to the Oracle, a list of P2P nodes sharing a known content is given and the list ranked according to different performance metrics is returned from Oracle
Results
P2P applications won’t have to perform such measurements by themselves The Oracle gives ISPs a way to control overlay routing Underlay to overlay information exchange improves overlay operations and underlay network usage
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!,-#2! Oracle provided by an ISP
Information is provided, like link delay, bandwidth estimations, etc. As input to the Oracle, a list of P2P nodes sharing a known content is given and the list ranked according to different performance metrics is returned from Oracle
Results
P2P applications won’t have to perform such measurements by themselves The Oracle gives ISPs a way to control overlay routing Underlay to overlay information exchange improves overlay operations and underlay network usage
.4&",&5 6(# .##!4&! #* Standardize information exchange between applications and ISPs in order to help in peer selection .4&",&5 6(# .##!4&! #* Standardize information exchange between applications and ISPs in order to help in peer selection
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!,-#2! Caching key-lookups to reduce routing stretch:
How much information can be used by a node to reduce the routing stretch?
information in the hello messages together with cache information;
information ?
– Key’s request that passes through a node; – Key’s request that nodes can hear in its transmission range (cross-layer information).
1000 Nodes: Stretch versus Node Density 1 1,5 2 2,5 3 3,5 4 ~10 ~13 ~22 ~40 Node Density Stretch default NoN NoN+Cache256 NoN+Cache-1
MANETs”. Adhoc'09, Sweden.
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6,-#2!
Georoy: a location-aware DHT for WMNs
It combines an unit ring topology and a butterfly network topology
Two-tier architecture
distributed resource catalog.
request resources by querying their associated super peers.
managing the point to the LP’s physical location.
Leaf Peer Super Peer
s * square region side R=[0,s)2 (x,y) * coordinate of peer in R 3 – constant with 0 < 3 < s
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Simulations: ns-2
Comparison:
exploiting leafset information and routing tables -> fast ring traversal
logical and physical hops
network size due to routing table information
nodes increase -> logical and physical topologies tightly coupled
physical path.
performance of DHT-based protocols for opportunistic networks”. FUNEMS, Italy, 2010.
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Interaction between Overlay networks and Underlay required!
To enable ISPs to perform efficient traffic engineering by enabling traffic control To enable overlays to create better overlay structure/topology To reduce overhead as overlay probe network for bandwidth availability/delay
Example: Wireless Mesh Networks as Underlay
Increases the problem due to interference and control traffic overhead Multi-Channel operation required to allow higher capacity Internet Gateways are a strong topology element could optimize the
Need to engineer channel assignment to match with traffic demands and topology Cross-layer approach can create an information exchange between Overlay and Mesh Underlay
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Issues”. Perspectives Workshop: Peer-to-Peer Mobile Ad Hoc Networks - New Research Issues, 2005. 2. Thomas C. Zahn, “Structured Peer-to-Peer Services for Mobile Ad Hoc Networks”, PhD Thesis FU Berlin, 2006. 3. Jorg Eberspacher et al., “Structured P2P Networks in Mobile and Fixed Environments”HET-NETs04. 4.
and H. Balakrishnan. “Chord: A scalable peer-to-peer lookup protocol for internet applications”. IEEE/ACM Transaction Network, 11(1):17–32, 2003. 5.
Ring Routing: Network routing inspired by DHTs”. In ACM SIGCOMM’06, pages 351-362, 2006. 6.
Underlay: Scalable Routing for Hybrid MANETs”, Technical Report, Universität Karlsruhe (TH) 2006-12, June 2006.
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comparison of peer-to-peer overlay network schemes”. IEEE Communications Surveys, 7(2):72–93, 2005. 8.
mobile ad hoc networks”.VTC 2003. 9.
Sep 2005, Konstanz, Germany. 10.
Abstractions in MANETs“. Book Chapter in Theoretical and Algorithmic Aspects of Sensor, Ad Hoc Wireless, and Peer-to-Peer Networks,CRC Press, 2005. 11.
In Wireless on Demand Network Systems and Services (WONS), 2007. 12.
Georoy: A location-aware enhancement to viceroy peer-to-peer algorithm. Computer Networks, 2007.
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Mobile Ad-hoc Networks (MANET) consist of mobile nodes communicating with each other using multi-hop wireless links. Self-organization for communication. Self-healing to cope with network failures. Without (necessarily) using a pre-existing infrastructure.
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"A survey and comparison of peer-to-peer overlay network schemes” E. Keong Lua, J. Crowcroft, M. Pias,
Tutorials, Second Quarter 2005, Volume: 7, Issue: 2 pp 72-93. "Theoretical and Algorithmic Aspects of Sensor, Ad Hoc Wireless, and Peer-to-Peer Networks”. Y. C. Hu, S. M. Das, and H. Pucha, CRC Press, 2005, ch. Peer-to-Peer Overlay Abstractions in MANETs, pp. 858–871.