1 GroCoca: Group-based Peer-to-Peer Cooperative Caching in Mobile Environment Authors: Chi-Yin Chow, Hong Va Leong, and Alvin T. S. Chan Present: I-Wei Ting IEEE Journal on Selected Areas in Communications, Vol. 25, NO. 1, January 2007 Department of Computer Science and Information Engineering National Cheng Kung University, Taiwan R.O.C.

2 Mobile P2P environments

3 Local Cache Hit

4 Mobile P2P environments Global Cache Hit

5 Mobile P2P environments Global Cache Miss

6 Related works Cooperative CAching scheme (COCA)

7 Similarity Measurement in Mobility Patterns mobile host i,jweight m0m0 m0m0 mjmj mimi Two-dimensional weighted average Distance matrix (WADM) Stored in MSS

8 Similarity Measurement in Data Access Patterns Two-dimensional access similarity matrix (ASM) Stored in MSS m0m0 m0m0 mjmj mimi

9 How to find Tightly-Coupled Group (TCG)? MSS A B C D Case 1: data request Case 2: update its location Check two tables

10

11

12

13 How to reduce the unnecessary search process? Data signature Cache signature Peer signature Search signature MSS BC D A ? ? ?

14 Bloom Filter bits h 1 ( ) h 2 ( ) h 3 ( ) h 4 ( ) … h k ( )

15 Data signature bits h 1 ( ) h 2 ( ) h 3 ( ) h 4 ( ) … h k ( ) URL, Keyword, Integral identifier Attribute value Data signature Data object:

16

17 Peer signature superimpose Cache sig. of peer A Cache sig. of peer BPeer signature

18 Search signature When an MH encounters a local cache miss, it generates a data signature for the required data item, called search signature. It also computes a peer signature by superimposing the peers’ cache signatures maintained in the local cache. The data signature is then compared with the peer signature by performing a bitwise AND operation on them.  If the result is zero, it indicates that no peer caches the required data item, so the MH bypasses the Peer Cache layer and requests the data item from the MSS.  If the result is the same as the search signature, the neighboring peers are likely to cache the data item, so the MH broadcasts the request to them.

19 Cache exchange protocol MSS A B Cache Sig. Request Cache Sig. Reply

20 Cooperative cache management Local cache miss  Search signature is true Send request to its peer (If global cache hit) From TCG member Not cache and update the TTL (Time-To-Live) From Non-TCG member Cache and update the TTL  Search signature is false Send request to MSS

21 Client Disconnection Handling Protocol Each MH maintains a list, OutstandSigList, to record members not yet turned in their cache signatures. MSS A B

22 Average latency under different cache size

23 Server request ratio under different cache size

24 Global cache ratio under different cache size

25 Power consumption under different cache size