1. Zhen Feng, Mingwei Xu, Yu Wang and Qing Li Tsinghua University, Beijing, China, Globalcom2013 – NGN Symposium Katto Lab Hiroto Kisara AN ARCHITECTURE FOR CACHE CONSISTENCY SUPPORT IN INFORMATION CENTRIC NETWORKING

2. Outline Introduction Related Work Design of CUVS Why traditional approach in ICN The hash tree structure The strong consistency of metadata The process of CUVS Evaluation and Result Evaluation Setting Results Infinite Cache Size Scenario Finite Cache Size Scenario Summary Conclusion 1

3. Introduction ICN is an architectural redesign proposed to deal with the most prominent requirements. Many schemes have been proposed. => caching when the origin copy of content changes sometime, the cache consistency among all the copies needs to be taken into consideration. Contents will be never modified. Contents will be never modified. Contents will be updated in real time. Contents will be updated in real time. Contents May change occasionally Contents May change occasionally 2

4. Introduction (cont.) no academic efforts have been put on the cache consistency issue in the ICN field. In author’s opinion, the wide spread caching in ICN makes the issue more intractable. And the traditional approaches which mainly aim to operate in a small size or relatively self-managed environment cannot be efficiently applied in ICN. Content Update Validation System (CUVS) Content Update Validation System (CUVS) 3

5. Introduction (cont.) Content Update Validation System(CUVS) is an overlay system build upon the ICN network layer. provides the service of validating whether the version number in a content name is the latest. employs a hierarchical structure similar to DNS. Evaluation A testbed to evaluate their scheme is built and implemented the NDN design. The performance and overhead of four scheme: 1) Fixed TTL 2) Polling-Every-Time 3) Lease 4) CUVS 4

6. Related Work Traditional cache consistency schemes can be categorized into cache validation (Polling-Every-Time, TTL) and server invalidation (Lease). TTL approach When the TTL of a cached content is expired, the cache will send validation to the origin server. Polling-Every-Time Each time a request is received, the cache will send validation to the origin server. Lease approach The origin server will keep track of each cache which is called lease for a period of time. It will notify the caches whose lease is still valid. The caches have to update their lease to the server periodically. The authors optimize this approach to provide a strong consistency mechanism. 5

7. Design of CUVS - Why traditional approaches fail in ICN In the cache validation approach and the server invalidation approach, the origin server has two same roles: 1) serving contents 2) validating or invalidating caches All the network devices may cache contents, so the validation requests from widespread caches may impact the performance of the origin server or even overwhelm it. It is feasible in traditional network since the number of contents is limited and most importantly they behave in a controlled manner. In ICN, the situation has dramatically changed!! 6

8. Design of CUVS - Why traditional approaches fail in ICN Proposed idea originates from the separation of the two roles of the origin server. 1)The cache validation or invalidation function This function can be done by CUVS system which employs the wide spread servers located in every domain. 2)function of serving contents The origin server has only this function. This improves the scalability and robustness of the ICN network. 7

9. Design of CUVS - The hash tree structure The advantage of hash tree structure is that you do not need to validate every piece of content in a name space. If the root hash key of the name space is not changed, all of its contents remain unchanged. The hash tree is a metadata of a name space, and it is generated by the origin server. Whenever the content is updated, its hash tree should be recalculated. Fig.1. Hash tree structure 8

10. Design of CUVS - The strong consistency of metadata Whether the content is stale or not can be decided by the CUVS servers according to the metadata. Xin Chen proposed a strong consistency mechanism in DNS. In their design, the local DNS server will use dynamic Lease approach to keep its record the same as targeted DNS server. If there is an update, the targeted DNS server will notify every local DNS server to renew its cache The authors apply this design to their proposed scheme. Fig.2. Website hash tree update multicast 9

11. Design of CUVS - The process of CUVS Fig.3. The working process of CUVS 10

12. Evaluation and Results Fig.4. Experimental topology 11 Performance The average response time Performance The average response time Overhead The origin server load Bandwidth consumption Staleness ratio Overhead The origin server load Bandwidth consumption Staleness ratio

13. Evaluation Setting Two Scenarios: ・ Infinite cache size ・ Finite cache size Size: ・ Interest and Data (with no content) packet: 20B ・ Data(with content) packet: 1KB The request Interval: ・ Based on Poisson distribution ・ the mean value is 2s The popularity: Based on Zipf distribution Duration of experiment: 10minutes Content update interval: ・ infinite scenario: every 80s ・ finite scenario: divided into 3 grades 1) most popular 10 contents never change 2) following 50 contents every 40s 3) the other 40 contents every 80s 12

14. Results – Infinite Cache Size Scenario Fig5(a) Staleness RatioFig5(b) Average response time Fig5(c) Origin serever loadFig5(d) Bandwidth consumption 13

15. Results – Finite Cache Size Scenario Fig6(a) Average response time Fig6(c) Bandwidth consumption Fig6(b) Origin server load Fig6(d) Staleness ratio 14

16. Summary Polling-Every-Time Lease Fixed TTL and CUVS Advantage Strong cache consistency Advantage Strong cache consistency disadvantage Long response time Heavier load of origin server disadvantage Long response time Heavier load of origin server Advantage Strong cache consistency Shortest response time Advantage Strong cache consistency Shortest response time disadvantage More bandwidth consumption Heavier load of origin server disadvantage More bandwidth consumption Heavier load of origin server disadvantage Weak cache consistency disadvantage Weak cache consistency Performance TTL < CUVS Performance TTL < CUVS Advantage of CUVS The load of the origin server is very low. Advantage of CUVS The load of the origin server is very low. 15

17. Conclusion In this paper, a cache consistency architecture named Content Update Validation System (CUVS) is proposed. It aims to resolve the ubiquitous caching validation requirements in the ICN network. It is designed as a hierarchical overlay in ICN and provides the service of validating cached contents. The architecture has the following advantages. 1)it relieves the origin server from the work of cache validation. 2)its validation service can be invoked by any routers in the network 3)its overlay architecture makes its design independent from the preliminary ICN network layer designs and can be easily deployed. 4)the hierarchical structure of the system ensures good scalability. 16