Locating objects in mobile computings

Station BaseStation Base Fixed Host Mbps to Gbps Mobile Host Host Mobile Wireless LAN cell Mobile Host 1 Mbps Mobile Host Fixed Network 9 Kbps Base Host Fixed Station Fixed Host Fixed...

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Station Base

Station Base

Fixed Host

Mbps to Gbps

Mobile Host

Host Mobile

Wireless LAN cell

Mobile Host

1 Mbps

Mobile Host

Fixed Network

9 Kbps Base

Host Fixed Station

Fixed Host Fixed

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(+) Support for locality Increased number of operations (database operations and communication messages)

(-)

(-) Increased load and storage requirements at higher-levels

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Dynamic (adaptive) or static

Per object, group of objects, geographical region

Call Stability

Call Stability

When x is called by y, cache x’s location at y’s zone

Selectively replicate x’s address at the zones from which

it receives the most calls

When x moves, add a forwarding pointer from its old

to its new address

Cache update overhead occurs at moves Cache update overhead occurs at calls Additional constraints are set

on the number of replicas per site and on the number

of replicas per user

the replication sites are computed dynamically by each mobile host locally

Restrict the length of the chain of forwarding

Working Set:

Caching

Replication

Forwarding Pointers

Adaptive and distributed:

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Replication

Caching Method

Selectively replicate x’s location at internal and/or leaf databases.

When x at zone i is called by user y at zone j, cache at a node on the path from j to LCA(i, j)

a pointer to a node on the path from i to LCA(i, j)

to be used by any subsequent call to x from zone j.

Forwarding Pointers When and how to purge

Up to which tree level

to maintain cache entries

When to update cache entries

the forwarding pointers

Setting the level m

resides instead of its exact location Keep information about the partition in which the user crosses the boundary of a partition rarely

the user moves inside a partition frequently and Divide the locations into sets (partitions) so that Partitions

When x moves from cell i to cell j, instead of updating all databases on the path from i to LCA(i, j) and from LCA(i, j) to j, update all databases up to some level m and add a forwarding pointer at the level m ancestor

of i to point to the level m ancestor of j.

Issues/Variations

Large CMR Call Stability

Call Stability

Move Stability Small LCMR Large CMR

Appropriate when:

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to maintain cache entries

When to update cache entries

the forwarding pointers

Setting the level m

resides instead of its... computed dynamically by each mobile host locally

Restrict the length of the chain of forwarding

Working Set:

Caching

Replication... Keep information about the partition in which the user crosses the boundary of a partition rarely

the user moves inside a partition frequently and Divide the locations into sets