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University College Of Engineering,Kota
CONTENT ADDRESSABLE NETWORK
Presented by – ALKA
11/638(CP-1)
Submitted To –
C.P. Gupta
(Asso. Prof. & HOD of CP & IT Dept.)
Mrs. Iti Sharma
Contents1. Introduction to CAN
2. CAN Routing
3. CAN Construction
4. CAN Problems
5. Node departure
6. Architecture improvements
a. Path Latency Improvement
b. Hop Latency Improvement
c. Mixed approaches
7. CAN Cons
8.CAN Pros
9.CAN summary
10.CAN References
What is CAN?
The goal was to make a scalable peer-to-peer file distribution system
Napster problem: centralized File Index
Gnutella problem: File Index completely decentralized
• There is a single point of failure: Low data availability
• Non scalable : No way to decentralize it except to build a new
system
• Network flood: Low data availability
• Non scalable: No way to group data
CAN - Content Addressable Network
What is CAN?CAN - Distributed, Internet-Scale, Hash table.
CAN provides Insertion, Lookup and Deletion operations under Key, Value
pairs (K,V), e.g. file name, file address
• CAN is designed completely Distributed
(does not require any centralized control)
• CAN design is Scalable, every part of the system maintains only a small
amount of control state and independent of the no. of parts
• CAN is Fault-tolerance (It provides a rooting even some part of the system is
crashed)
CAN features
ABOUT CAN
• Usage: P2P file-sharing systems, large scale storage management systems, wide-area name resolution services.
• It was one of the original four distributed hash tables introduced concurrently. (Chord, Pastry and Tapestry)
Content-Addressable Networks (CAN)
• d-dimensional hyperspace with n zones
6
y
Peer
Keys
Zone
x
CAN Routing
• d-dimensional space with n zones
• Two zones are neighbors if d-1 dimensions overlap
7
y
x
[x,y]Peer
Keys
lookup([x,y])
Routing in a CAN
A routing message hops from node to node, Getting closer and closer to the Destination.
A node only knows about its immediate Neighbors
Routing Path Length is (d/4)(n1/d)
As d approaches log(n), the totalPath length goes to log(n).
8
CAN Construction
Joining CAN
1.Pick a new ID [x,y]
2.Contact a bootstrap node
3.Route a message to [x,y], discover the current owner
4.Split owners zone in half
5.Contact new neighbors
9
y
xNew Node
[x,y]
CAN Construction
CAN architecture: Access
How to get an access to CAN system
1. CAN has an associated DNS domain
2. CAN domain name is resolved by DNS domain to Bootstrap server’s IP addresses3. Bootstrap is special CAN Node which holds only a list of several Nodes are currently in the systemUser scenario
1. A user wants to join the system and sends the request using CAN
domain name
4. The user chooses one of them and establishes a connection.
2. DNS domain redirects it to one of Bootstraps
3. A Bootstrap sends a list of Nodes to the user
CAN problems
Main problems:
1. Routing Latency
a. Path Latency - avg. # of hops per path
b. Hop Latency - avg. real hop duration
2. Increasing fault tolerance
3. Increasing data availability
Basic CAN architecture archives:
1. Scalability, State of distribution
2. Increasing data availability (Napster, Gnutella)
CAN construction: Node departure
Node is crashed
1. Periodically every node sends a message to all its neighbors
2. If Node does not receive from one of its neighbors a message for period of time t
it starts a TAKEOVER mechanism
3. It sends a takeover message to each neighbor of the crashed Node, the neighbor
which did not send a periodical message
4. Neighbors receive a message and compare its own Zone with the Zone of the
sender. If it has a smaller Zone it sends a new takeover message to all crashed
Node neighbors.
5. The crashed Node’s Zone is handled by the Node which does not get an answer
on its message for period of time t
Data stored on the crashed Node are unavailable until source owner refreshes the CAN state.
CAN construction: Node departure Node departure
b. Otherwise one of the neighbors handles two different zones
a. If Zone of one of the neighbors can be merged with departing Node’s Zone to produce a valid Zone. This neighbors handles merged Zone
CAN construction: Node departure 2. Node departure
b. Otherwise one of the neighbors handles two different zones
a. If Zone of one of the neighbors can be merged with departing Node’s Zone to produce a valid Zone. This neighbors handles merged Zone
CAN construction: Node departure 1. Node departure
b. Otherwise one of the neighbors handles two different zones
a. If Zone of one of the neighbors can be merged with departing Node’s Zone to produce a valid Zone. This neighbors handles merged Zone
In both cases (a and b):
1. Data from departing Node is moved to the
receiving Node
2. The receiving Node should update its
neighbor list
3. All their neighbors are notified about changes
and should update their neighbor lists
Path latency Improvements 1
Realities: multiple coordinate spaces
• Maintain multiple (R) coordinate spaces with
each Node
• Every Node contains different Zones in different
Realities, all zones are chosen randomly
• Contents of hash table replicated on every reality
• Each coordinate Space is called Reality
• All Realities have
The same no. of Zones
The same data
The same hash function
Path latency Improvements 2
The extended routing Algorithm for Realities
b. The request is forwarded in the best Reality
a. Every Node on the path checks in which of its realities a distance to the destination is the closest one
1. The destination Zone are the same for all realities
2. Each Zone can be own by many Nodes
3. For routing is applied a basic algorithm withfollowing extensions:
Path latency Improvements 2
The extended routing Algorithm for Realities
b. The request is forwarded in the best Reality
a. Every Node on the path checks in which of its realities a distance to the destination is the closest one
1. The destination Zone are the same for all realities
2. Each Zone can be own by many Nodes
3. For routing is applied a basic algorithm withfollowing extensions:
Path latency Improvements 2
The extended routing Algorithm for Realities
b. The request is forwarded in the best Reality
a. Every Node on the path checks in which of its realities a distance to the destination is the closest one
1. The destination Zone are the same for all realities
2. Each Zone can be own by many Nodes
3. For routing is applied a basic algorithm withfollowing extensions:
Path latency Improvements 3
n = 1000, equal zones
d Avg. path length
2 15
3 7.5
5 5
10 4.95
Multi-dimensioned Coordinates Spaces
• Average path length is
• the no. of dimensions d increases
• the average path Length decreases
)n*O(d 1/d
Hop latency improvement
RTT CAN Routing Metrics
2. New Metrics: Cartesian Distance + RTT
1. RTT is Round Trip Time (ping)
• Expanded Node is the closest to the destination by Cartesian Distance
• RRT between current Node and expanded Node is minimal for all optimal Nodes
number of dimensions
routing without RTT (ms) per hop
routing with RTT (ms) per hop
2 116.8 88.3
3 116.7 76.1
4 115.8 71.2
5 115.4 70.9
Mixed Improvement: Overloading Zones 1Overloading coordinate zones
• One Zone – many Nodes
• MAXPEERS – max no. of Nodes per Zone
• Every Node keeps list of its Peers
• The number of neighbors stays the same(O(1) in each direction)
•The general routing algorithm is used(from neighbor to neighbor)
Mixed Improvement: Overloading Zones 2Extended construction algorithm
New node A joins the system:
1. It discovers a Zone (owner Node B)
2. B checks: how many peers does it have
3. If less than MAXPEERS1. A is added as a new Peer
2. A gets a list of Peers and Neighbors from B
4. Otherwise
1. Zone is split in half
2. Peer list is split in half too
3. Refresh the peer and neighbor lists
Mixed Improvement: Overloading Zones 2Extended construction algorithm
New node A joins the system:
1. It discovers a Zone (owner Node B)
2. B checks: how many peers does it have
3. If less than MAXPEERS1. A is added as a new Peer
2. A gets a list of Peers and Neighbors from B
4. Otherwise
1. Zone is split in half
2. Peer list is split in half too
3. Refresh the peer and neighbor lists
Mixed Improvement: Overloading Zones 2Extended construction algorithm
New node A joins the system:
1. It discovers a Zone (owner Node B)
2. B checks: how many peers does it have
3. If less than MAXPEERS
1. A is added as a new Peer
2. A gets a list of Peers and Neighbors from B
4. Otherwise1. Zone is split in half
2. Peer list is split in half too
3. Refresh the peer and neighbor lists
Mixed Improvement: Overloading Zones 2Extended construction algorithm
New node A joins the system:
1. It discovers a Zone (owner Node B)
2. B checks: how many peers does it have
3. If less than MAXPEERS
1. A is added as a new Peer
2. A gets a list of Peers and Neighbors from B
4. Otherwise1. Zone is split in half
2. Peer list is split in half too
3. Refresh the peer and neighbor lists
Mixed Improvement: Overloading Zones 2Periodical self updating
1. Periodically, Node gets a peer list ofeach its neighbors
2. Node estimates a RRT to every node in peer list
3. Node chooses the closest peer Node as a New Neighbor Node in this direction
CAN construction improvements
Uniform Partitioning
1. The Node to be split compares the
volume of its Zone with Zones of its
Neighbors
2. The Zone with the largest volume
should be split
30
ISSUES
- Security (DoS attacks)
- Parameter tuning needed to achieve scalability (Cannot vary d as nincreases - n not known by any node)
- CAN maintenance protocol overhead? (Cost of update operation)
- Accommodation of administrative boundaries? (handling of key value pairs?)
- Initial knowledge of the deterministic hash function? Ways to be changed dynamically? Implications? (totalreconstruction of the CAN?)
- Specification of inter-update times, caching TTL values, etc.
Discussion - Pros
• Using some of the improvement made CAN a very robust routing and storage protocol.
• Using geographic location in the overlay creation would create smarter hops between close nodes.
31
Discussion - Cons
• Not much work on Load-Balancing the Keys
• When all of the Extra Features are running at once, CAN becomes quite complicated.
• Tough to guarantee uniform distribution of keys with hash functions on a large scale.
• Query Correctness
32
CAN - Weaknesses
• Impossible to perform a fuzzy search
• Susceptible to malicious activity
• Maintain coherence of all the indexed data (Network
overhead, Efficient distribution)
• Still relatively higher routing latency
• Poor performance w/o improvement
Discussion
• Addresses two key problems in the design of Content-Addressable Networks: scalable routing and indexing.
• Simulation results validate the scalability of our overall design – for a CAN with over 260,000 nodes, we can route with a latency that is less than twice the IP path latency.
• Future works– Secure CAN
– Key word searching
34
CAN: Summary CAN is scalable, distributed Hash Table
CAN provides:
• Dynamical Zone allocation
• Fault Tolerance Access Algorithm
• Stable Fault Tolerance Routing Algorithm
There are many improve techniques which
• Increase Routing Latency
• Increase Data availability
• Increase Fault Tolerance
The scalable, distributed, efficient P2P system was
designed and developed
REFERENCES
• [1] S. Ratnasamy, P. Francis, M. Handley, R. Karp, and S. Shenker. A Scalable Content-
Addressable Network. In ICSI Technical Report, Jan. 2001.
• [2] Balasubramanian, R.; Injong Rhee; Jaewoo Kang, "A scalable architecture for SIP
infrastructure using content addressable networks," Communications, 2005. ICC 2005. 2005
IEEE International Conference on , vol.2, no., pp.1314,1318 Vol. 2, 16-20 May 2005
• [3] Shidong Zhang; Bai Wang; Gengyu Wei; Chao Xin, "Web QoS Management Model
Based on CAN," Computational Intelligence and Design (ISCID), 2011 Fourth International
Symposium on , vol.1, no., pp.143,146, 28-30 Oct. 2011
• [4] Zhongtao Li; Weis, T., "Using zone code to manage a Content-Addressable Network for
Distributed Simulations," Communication Technology (ICCT), 2012 IEEE 14th International
Conference on , vol., no., pp.1350,1357, 9-11 Nov. 2012
• [5] Al-Omari, D.K.; Gurbani, V.K.; Anjali, T., "A novel architecture for a computer network
defense (CND) system using Content Addressable Networks (CAN)," Globecom Workshops
(GC Wkshps), 2012 IEEE , vol., no., pp.758,762, 3-7 Dec. 2012
THANK YOU