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 Computer Networks 2010 • Seminar 4 1
Motivation � Peer-to-Peer Systems: � It is the dominating traffic type in the internet � Based on application overlay routing Protocol Type Distribution, Germany 2007 ������������������������������� o r t s Internet Study a C C http://www.ipoque.com/resources/internet- l e c studies/ r a M Topics in Computer Networks 2010 • Seminar 4 2
������� �� ������������ ������� � Client-Server concept � Understanding P2P � P2P and Wireless Networks ������������������������������� o r t s a C C l e c r a M Topics in Computer Networks 2010 • Seminar 4 3
������������������� ������������������������������� � Simple Architecture � Powerful central entity to host: � the whole resource index � global management of resources (i.e. access rights etc) o � Low cost in messages for discovery r t s a C � Increase of clients may degrade the quality of service C l e c r a M Topics in Computer Networks 2010 • Seminar 4 4
����������������������������� � Advantages: � 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 o � Good in relatively predictable growth patterns. r t s a C C l e c r a M Topics in Computer Networks 2010 • Seminar 4 5
������� �� ������������ ������� � Client-Server concept � Understanding P2P � P2P and Wireless Networks ������������������������������� o r t s a C C l e c r a M Topics in Computer Networks 2010 • Seminar 4 6
������������� ��� � 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 By expanding horizontally not vertically (collaboration) � By adapting to network changes on the fly � o r t By using direct client-to-client communication s � a C C l e c r a M Topics in Computer Networks 2010 • Seminar 4 7
�������������� � A self-organizing, distributed 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 o r t � symmetric communication s Dan Pascu, “Overview of P2P SIP a C C Principles & Technologies”. Int. SIP Conf. l e 2007. c r a M Topics in Computer Networks 2010 • Seminar 4 8
������������ ������������������������������� � No central entity: distribution among all nodes of � 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 o r t s � Application specific networks a C C � Increase of nodes may improve the quality of service l e c r a M Topics in Computer Networks 2010 • Seminar 4 9
���������������������� � Advantages � 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 o r t � unpredictable growth patterns s a C C l e c r a M Topics in Computer Networks 2010 • Seminar 4 10
������� ���������� � 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: • Routing (Resilient Overlay Networks, BGP routing, MPLS) • Security (VPN) o • Application-level Multicast r t s a C C l e c r a M Topics in Computer Networks 2010 • Seminar 4 11
�������������� � ������� ������������������������������� �� o r t s a C C l e c r a M Topics in Computer Networks 2010 • Seminar 4 12
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��������������������!����� ������������������������������� � Level of Centralization G. Exarchakos , “P2P Overlays for Scalable Service Access”. ICCGI’08. � Hybrid: node grouping with central index � Pure: no centralised entity – equal nodes � Resource Location o � Unstructured: any node may host any resource r t s a C C � Structured: resources are hosted by well-defined nodes l e c r a M Topics in Computer Networks 2010 • Seminar 4 14
����������� ������ 1. Choice of identifier space (IS) - 128 bits overlay identifier 2. Map resources and peers to IS - HASH(MAC, IP, or Locality) 3. Management of the IS by peers (or Resource Location) - Unstructured, structured 4. Routing strategy ������������������������������� - Flooding, random walk, Finger table (Chord) 5. Maintenance strategy - Proactive (probe), or reactive o r t s a correction C C l e c r a M Topics in Computer Networks 2010 • Seminar 4 15
������������������"�����������#�!� � 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. ������������������������������� o r t s a C C l e e.g.: Gnutela c r a M Topics in Computer Networks 2010 • Seminar 4 16
������������������"�����������#�!� � 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 o r t s a C � Uneven load distribution C l e c r a M Topics in Computer Networks 2010 • Seminar 4 17
������������������"�����������#�!� � 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 – • CAN, Chord , Kademlia, Pastry, Tapestry, Viceroy, Bamboo. o r t s a C C l e c r a M Topics in Computer Networks 2010 • Seminar 4 18
$%&�� $�����'(����%����&�'�� 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 . o r t s a C C l e c r a M Topics in Computer Networks 2010 • Seminar 4 19
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