DCIM: Distributed Cache Invalidation Method for Maintaining Cache Consistency In Wireless Mobile Networks
This paper proposes distributed cache invalidation mechanism (DCIM), a client-based cache consistency scheme that is implemented on top of a previously proposed architecture for caching data items in mobile ad hoc networks (MANETs), namely COACS, where special nodes cache the queries and the addresses of the nodes that store the responses to these queries. We have also previously proposed a server-based consistency scheme, named SSUM, whereas in this paper, we introduce DCIM that is totally client-based. DCIM is a pull-based algorithm that implements adaptive time to live (TTL), piggybacking, and prefetching, and provides near strong consistency capabilities. Cached data items are assigned adaptive TTL values that correspond to their update rates at the data source, where items with expired TTL values are grouped in validation requests to the data source to refresh them, whereas unexpired ones but with high request rates are prefetched from the server. In this paper, DCIM is analyzed to assess the delay and bandwidth gains (or costs) when compared to polling every time and push-based schemes. DCIM was also implemented using ns2, and compared against client-based and server-based schemes to assess its performance experimentally. The consistency ratio, delay, and overhead traffic are reported versus several variables, where DCIM showed to be superior when compared to the other systems.
The cache consistency mechanisms in the literature can be grouped into three main categories: push based, pull based, and hybrid approaches. Push-based mechanisms are mostly server-based, where the server informs the caches about updates, whereas Pull-based approaches are client-based, where the client asks the server to update or validate its cached data. Finally, in hybrid mechanisms the server pushes the updates or the clients pull them
DISADVANTAGES OF EXISTING SYSTEM:
- The major issue that faces client cache management concerns the maintenance of data consistency between the cache client and the data source. All cache consistency algorithms seek to increase the probability of serving from the cache data items that are identical to those on the server.
- However, achieving strong consistency, where cached items are identical to those on the server, requires costly communications with the server to validate (renew) cached items, considering the resource limited mobile devices and the wireless environments they operate in.
In this paper, we propose a pull-based algorithm that implements adaptive TTL, piggybacking, and prefetching, and provides near strong consistency guarantees. Cached data items are assigned adaptive TTL values that correspond to their update rates at the data source. Expired items as well as nonexpired ones but meet certain criteria are grouped in validation requests to the data source, which in turn sends the cache devices the actual items that have changed, or invalidates them, based on their request rates. This approach, which we call distributed cache invalidation mechanism (DCIM), works on top of the COACS cooperative caching architecture.
ADVANTAGES OF PROPOSED SYSTEM:
- Ø TTL algorithms are popular due to their simplicity, sufficiently good performance, and flexibility to assign TTL values to individual data items.
- Ø Also, they are attractive in mobile environments because of limited device energy and network bandwidth and frequent device disconnections.
- Ø TTL algorithms are also completely client based and require minimal server functionality. From this perspective, TTL-based algorithms are more practical to deploy and are more scalable.
- Ø This is the first complete client side approach employing adaptive TTL and achieving superior availability, delay, and traffic performance.
Overview of DCIM basic design.
Interactions between nodes in a DCIM system.
ü Algorithm 1- Decision flow at the server.
ü Algorithm 2- Inner loop and outer loop (shaded part) functions.
Decision flow at the server.
Inner loop and outer loop (shaded part) functions.
ü Processor – Pentium –IV
ü Speed – 1.1 Ghz
ü RAM – 256 MB(min)
ü Hard Disk – 20 GB
ü Key Board – Standard Windows Keyboard
ü Mouse – Two or Three Button Mouse
ü Monitor – SVGA
v Operating System : LINUX
v Tool : Network Simulator-2
v Front End : OTCL (Object Oriented Tool Command Language)
Kassem Fawaz, Student Member, IEEE, and Hassan Artail, Senior Member, IEEE-“DCIM: Distributed Cache Invalidation Method for Maintaining Cache Consistency in Wireless Mobile Networks”- IEEE TRANSACTIONS ON MOBILE COMPUTING VOL. 12, NO. 4, APRIL 2013.