Ad Hoc Mobility Management with Uniform Quorum Systems

UQS –Distributed mobility-management scheme –For ad hoc –Size of quorum intersection is a design parameter that can be tuned to adapt to the traffic and mobility patterns of the network nodes –Tradeoff system reliability and cost of location update (more intersection ， more quorum size ， then increase traffic of location update) –One possible solution ： partitioning of the network

Conventional HLR Conventional scheme HLR –fixed association (node-HLR) ： For specific node ， it has specific HLR UQS –dynamic association (node-HLR)

Virtual backbone Location databases which form a virtual backbone Routing does not necessarily go through the databases The node location provided by the databases can provide vital information to the routing protocol Define the location of a mobile host as the ID number of its nearest location database

Virtual backbone Need to maintain connectivity Due to backbone nodes are few compared with the whole network ， the extra overhead causes by routing is less

node-DB association Nodes containing the location databases can dynamically detach and reattach to the network at any time due to mobiles’ movements or changes in the communication environment

node-DB association Fail –whenever the node containing the database detaches from the network for a long time Fixed association between nodes and databases (node-DB association)

node-DB association Avoid fail problem ： multiple HLRs (but still has fixed association problem) Solution ： virtual HLR or adaptive HLR (Randomly choose a node as a new HLR ， and the database name of this HLR is still the same)

Dynamics of UQS UQS ： dynamic association (node-HLR) between any particular quorum to any mobile host May choose the quorum contains the nearest database ， and this kind of quorum may be several ones and randomly choose one of them as HLR ）

Dynamics of UQS Difference with multiple HLR ： If all multiple HLRs of the node are fail ， then fail to the node As long as at least one complete quorum is survival ， then the system is not fail Each quorum may (can) be the HLR of the node

Dynamics of UQS Because the intersection property of quorum ， UQS is dynamic (no fixed association between any particular quorum to any mobile host) (node- HLR)

Others of quorum Quorum is more flexible than adaptive HLR ， for example ： fixed node-HLR association 、 others need to know your HLR Quorum has high reliability ， because “at least one quorum survives…” Other advantage ： location and service provider independent numbering 、 load balancing…

Others of quorum BIB (Balanced Incomplete Block) design problem is the same as UQS construction Cost ： cost to accessing databases 、 call loss due to database failure But large intersection size require larger size of quorums, which increase the cost of location updates and location queries

Fail & Inaccessible When a backbone node detached from the network ， a nearby non-backbone node is recruited to take its place in the virtual backbone When detach exceeds the threshold (time) then replacement But the original database in the node is lost ， we call this database fail Inaccessible ： detach doesn’t not exceed the threshold

Fail & Inaccessible Need a mechanism to check accessibility of nodes ， and the frequency of checking is much higher than that of location update and query (and because the number of virtual nodes is few ， the cost is low) Number of intersections will affect backup and reliability Fail and inaccessible should be solved

Update location Situation of update location ： –(1) When using the quorum (read) ， update the quorum –(2) change of quorum (due to change of location or other reasons) –(3) periodic

Call loss Call loss ： –(1)database fail (may have erroneous information) –(2)database inaccessible (low probability ， due to the time of inaccessible is low) The probability of call loss depends on the stability of network 、 the frequency of update (but more overhead)

Construction of UQS Five parameters for UQS construction –N ： number of database –Q ： number of quorum –K ： size of quorum –Mi ： number of quorum contain database i –R ： number of intersection Represented by a N*Q matrix ， entry will be 0 or 1 On purpose of uniform ， each (database or quorum) R 、 K 、 M is the same

Construction of UQS Some properties of UQS ： –Parameter is dependent –For a given set of parameters ， its UQS may not exist UQS is the same as BIB ， so solution to BIB is solution to UQS

Construction of UQS Due to no sufficient condition of BIB ， there is no way to decide whether UQS exists or not 。 And there is no formula can represent the relation among N 、 K 、 R ， so it can only be studied some UQS parameter sets under certain situation

Construction of UQS Five series…(skip now) Given N ， show the allowable variation of r in Fig3 (the five series) But the five series can’t contain all situations In fact ， the choice of N will be affected by routing and load Even given R ， the relation of N-K is not one-to- one

Construction of UQS