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Mobile Computing - Wireless Mobile Clustering, Study notes of Mobile Computing

Detail Summery about Adaptive Clustering For Mobile Wireless Networks, Conventional Cellular Network (Single Hop), The Multicluster Architecture, Consider the System Topology, The Multicluster Architecture, Cluster maintenance.

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Adaptive Clustering For Mobile Wireless Networks
Clustering It can be considered as the most important unsupervised learning problem. It
deals with finding a structure in a collection of unlabeled data.
Definition of clustering“The process of organizing objects into groups whose members are
similar in some way.
A cluster is therefore a collection of objects which are “similar” s/w them & are “dissimilar”
to the objects belonging to other clusters.
Clustering : Two approach used for clustering
Distance : Two or more objects belong to the same cluster if they are close’ according to a given
distance. This is called distance-based clustering.
Conceptual : Two or more objects belong to the same cluster if this one felines a concept “common”
to all that objects, called conceptual clustering.
Goal: To determine the intrinsic grouping in a set of unlabeled data.
Requirements: clustering algo. should satisfy
scalability
ability to deal with noise & outliers
high dimensionality
interpretability & usability
dealing with different types of attributes
discovering clusters with arbitrary shape
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Adaptive Clustering For Mobile Wireless Networks

  • (^) Clustering – It can be considered as the most important unsupervised learning problem. It deals with finding a structure in a collection of unlabeled data.
  • (^) Definition of clustering – “The process of organizing objects into groups whose members are similar in some way.”
  • (^) A cluster is therefore a collection of objects which are “similar” s/w them & are “dissimilar” to the objects belonging to other clusters.
  • (^) Clustering : Two approach used for clustering
    • (^) Distance : Two or more objects belong to the same cluster if they are close’ according to a given distance. This is called distance-based clustering.
    • (^) Conceptual : Two or more objects belong to the same cluster if this one felines a concept “common” to all that objects, called conceptual clustering.
  • (^) Goal: To determine the intrinsic grouping in a set of unlabeled data.
  • (^) Requirements: clustering algo. should satisfy
  • (^) scalability
  • (^) ability to deal with noise & outliers
  • (^) high dimensionality
  • (^) interpretability & usability
  • (^) dealing with different types of attributes
  • (^) discovering clusters with arbitrary shape

Adaptive Clustering For Mobile Wireless Networks

  • Applications: clustering algo. Can be applied in many field
    • (^) Marketing – group of customers with similar behaviour
    • (^) Biology – classification of plants & animals
    • Libraries – book ordering
    • Insurance – identifying groups of motor insurance policy holders
    • (^) Earth quake studies – cluster observed earthquake epicenters
    • (^) www – document classification
    • (^) City planning – identifying groups of houses acc. To their house type
  • (^) Clustering Algos. It may be classified as –
    • (^) k-means (Exclusive)
    • (^) Fuzzy C-means (Overlapping)
    • (^) Hierarchical clustering (Hierarchical)
    • (^) Mixture of Gaussians ( Probabilistic)
  • (^) Architecture:
  • (^) In cellular (single hop) n/ws, all stations learn of each other requirements, either directly or through a control station (eg. BS) making the resource allocation easier. This can be extended to multi hop n/ws by creating cluster of radio, in such a way that access can be controlled & bandwidth can be allocated in each cluster. Most clustering Architectures of mobile radio n/ws are based on the concept of cluster head. Clusterhead acts as a local coordinator of transmission within the cluster.
  • (^) Multihopping : It means the ability of the radios to relay packets from one to another without the base stations.

Adaptive Clustering For Mobile Wireless Networks

  • (^) Adaptive Clustering in Mobile Wireless Networks:-
  • (^) The clusters are independently controlled & are dynamically reconfigured as node move. This n/w architecture has 3 main advantage –
  • (^) It provide spatial reuse of bandwidth due to node clustering bandwidth can be shared or reserved in a controlled fashion in each cluster.
  • (^) Finally, the cluster algo. is robust in the face of topological changes caused by node motion, node failure & mode insertion/removal.
  • (^) Eg. Shows cellular ,model used in wireless networks –
  • (^) P,Q.R & S are fixed BSs connected by a wired backbone nodes 1 through 8 are mobile nodes.
  • (^) A mobile node is only one hop away from a BS.
  • (^) Communication b/w two mobile nodes must be through fixed BSs & the wired backbone.
  • (^) If a BS fails, a mobile node may not be able to access the wired n/w in a single hop.
  • (^) Thus the, multihop requirement may arise in cellular n/ws. If a BS fails, a mobile node may not be able to access the wired n/w in a single hop.
  • (^) If BS Q fails, node 4 must access BSs P or R through node 2 or node 5, much acts as a wireless multihop repeaters.

Conventional Cellular Network (Single Hop)

P Q R S 1 3 4 5 6 7 8 2

Multihop Situation When BS Q Fails

P Q R S 1 3 4 5 6 7 8 2

The Multicluster Architecture:

  • (^) Objective :- of the clustering also is to partition the n/w into several cluster .
  • (^) Within each cluster, node can communication with each other in atmost two hops.
  • (^) The cluster can be constructed based on node ID
  • (^) Assumptions underlying the construction of the algo in a radio n/w
  • (^) A1: Every node has a unique ID know the IDs of its 1 hop neighbors
  • (^) A2 : A msg sent by a node is received correctly within a finite time by all its 1-hop neighbors.
  • (^) A3: n/w topology does not change during the algorithm execution. In this algo each node only broadcasts one cluster msg before the algo. stops and the time complexity is O(|V|) where V is he set of nodes.
  • (^) The clustering algo converges very rapidly. In the worst case, the convergence is linear in the total number of nodes.

Consider the System Topology 1 2 4 3 19 11 12 10 13 18 20 6 16 14 17 15 5 7 8 9 After Clustering 1 2 4 3 19 11 12 10 13 18 20 6 16 14 17 15 5 7 8 9

C
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Cluster maintenance

  • (^) Cluster maintenance :- In the dynamic radio n/w
  • (^) nodes can change location
  • (^) nodes can be removed and
  • (^) nodes can be added
  • (^) A topological change occurs when a node discount connects , thus altering the cluster structure. System performance is affected by frequent cluster change therefore ,it is imp to design a cluster maintenance scheme to keep the cluster infrastructure as stable as possible the cluster maintenance scheme was designed to minimize the number of node transitions from, one cluster to another. Two step are required to maintain the cluster architecture
  • (^) Step 1 - check if there is any member of my cluster has moved out of my locality.
  • (^) Step 2 - If step 1 is successful , decide whether I should change cluster or remove the nodes no is my location from my cluster.

Cluster maintenance

  • (^) Fig (a) show there are 5 nodes in the cluster the hop distance is no more than 2 because of mobility, the topology changes to the configuration fig (b) in this nodes 4 is the highest {1,2,3} do not changes cluster however node 5 should either join another cluster or from a new cluster
  • (^) Reclustering:- we let the highest connectivity node its neighbors to stay in the original cluster remove the other nodes 2 5 1 4 3 2 5 1 4 3 Fig (a) Fig (b)
  • (^) Internal Node
  • (^) Cluster Head
  • (^) Gateway Node 2

QoS Routing

  • (^) Routing :- For a n/w to deliver QOs guarantees that it must reserve control resources. Routing is the first step in reservation the routing product first hinds a path with reservation along the path .The key resource for multimedia QoS support is bar width bandwidth can be defined as the no of real time connections than can pass through that node. A node can at most transmit one paket per frame
  • (^) QoS Routing scheme
  • (^) The goal of the bandwidth routing algo is to find the shortest path such that the free bandwidth is above the minimum requirement in shortest path computation the weight of each link is equal to 1 in addition to load balancing our routing scheme also supports the alternative paths. This is very important in a mobile environment where link will fail because of mobility in such an environment, routing optimality is of secondary importance the routing protocol must be capable of finding new routes quickly when a topological change destroys existing routes to this end we propose to maintain secondary path a which can be used immediately when the primary path fails.
  • (^) Each node uses the primary route its packets when the first link on the path (S,N) fails the secondary stand by path (S,N3 ) will be computed. The secondary (stand by) route is easily computed using the DSDV algorithm (Destination sequenced distance vector). Each neighbour of nodes s periodically inform s of its distance to destination d the neighbor with shortest dist yields the primary route the runner up yields the second rotue

File systems - consistency problems THE big problem of distributed, loosely coupled systems

  • (^) are all views on data the same?
  • (^) how and when should changes be propagated to what users? Weak consistency
  • (^) many algorithms offering strong consistency (e.g., via atomic updates) cannot be used in mobile environments
  • (^) invalidation of data located in caches through a server is very problematic if the mobile computer is currently not connected to the network
  • (^) occasional inconsistencies have to be tolerated, but conflict resolution strategies must be applied afterwards to reach consistency again Conflict detection
  • (^) content independent: version numbering, time-stamps
  • (^) content dependent: dependency graphs

File systems for limited connectivity Symmetry

  • (^) Client/Server or Peer-to-Peer relations
  • (^) support in the fixed network and/or mobile computers
  • (^) one file system or several file systems
  • (^) one namespace for files or several namespaces Transparency
  • (^) hide the mobility support, applications on mobile computers should not notice the mobility
  • (^) user should not notice additional mechanisms needed Consistency model
  • (^) optimistic or pessimistic Caching and Pre-fetching
  • (^) single files, directories, subtrees, partitions, ...
  • (^) permanent or only at certain points in time

CODA( Command Data Availability) file System

  • (^) Coda is a network file system developed as a research project at Carnegie Mellon University since 1987 under the direction of Mahadev Satyanarayanan. It descended directly from an older version of AFS (AFS-2) and offers many similar features. The InterMezzo file system was inspired by Coda. Coda is still under development, though the focus has shifted from research to creating a robust product for commercial use.
  • (^) Coda has many features that are desirable for network file systems, and several features not found elsewhere.
  • (^) disconnected operation for mobile computing
  • (^) is freely available under a liberal license
  • (^) high performance through client side persistent caching
  • (^) security model for authentication, encryption and access control
  • (^) continued operation during partial network failures in server network
  • (^) network bandwidth adaptation
  • (^) good scalability
  • (^) well defined semantics of sharing, even in the presence of network failures
  • (^) Offers two different types of replication
    1. Server replication 2) Caching on clients

Coda File System

  • (^) disconnected operation for mobile clients
    • (^) reintegration of data from disconnected clients
    • (^) bandwidth adaptation
  • (^) Failure Resilience
    • (^) read/write replication servers
    • (^) resolution of server/server conflicts
    • (^) handle of network failures which partition the servers
    • (^) handle disconnection of clients
  • (^) Performance and scalability
    • (^) client side persistent caching of files, directories and attributes for high performance
    • (^) write back caching
  • (^) Security
    • (^) kerberos like authentication
    • (^) access control lists (ACL's)
  • (^) Well defined semantics of sharing
  • (^) Freely available source code