1. Web caches are being rapidly deployed in the Internet. Hierarchical Web caching provides an infrastructure for asynchronous reliable multicast. There isn’t a need for reliable multicast at the network/transport layers.

2. Web Caches are Being Rapidly Deployed NLANR Backbone caches: 6 caches: 5 supercomputer sites and one NAP. Sites communicate over vBNS. Each cache is a parent to 125-200 client caches.

3. NLANR Caching Hierarchy

4. Provided by NLANR

5. Hierarchical Caching Provides an Infrastructure for Asynchronous Reliable Multicasting

6. National Network Regional Network Institutional Network Receivers International Path National Cache Regional Cache Institutional Cache Origin Server Access link Asynchronous Reliable Multicast

7. National Network Regional Network Institutional Network Receivers International Path National Cache Regional Cache Institutional Cache Origin Server Access link Latency in Cache Hierarchy

8. Multicast Latency Receivers National Network Regional Network Institutional Network International Path Origin Server

9. Comparison of Continuous Multicast Push & Caching Caching latency is typically less than multicast. For multicast, transmission rate is bottleneck rate between server and receiver. For caching, transmission rate is bottleneck rate between nearest cache with object and receiver.

10. Do we need reliable multicast infrastructure at network/transport layers? Unreliable multicast targets live information. Reliable multicast targets stored information. Stored information can be distributed through a cache hierarchy. Cache hierarchy is easier to deploy than reliable multicast. Cache hierarchy typically provides lower latency than continuous multicast push.