• 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.

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.

NLANR Caching Hierarchy

NLANR Caching Hierarchy

Provided by NLANR

Hierarchical Caching Provides an Infrastructure for Asynchronous Reliable Multicasting

National Network National Network

Regional Network Regional Network

LocalISP

LocalISP

LocalISP

LocalISP

clients

InternationalPath

National Network

Regional Network

InstitutionalNetwork

Receivers

International PathNational Cache

Regional Cache

InstitutionalCache

Origin Server

Access link

Asynchronous Reliable Multicast

National Network

Regional Network

InstitutionalNetwork

Receivers

International PathNational Cache

Regional Cache

InstitutionalCache

Origin Server

Access link

Latency in Cache Hierarchy

Multicast Latency

Receivers

National Network

Regional Network

InstitutionalNetwork

International Path

Origin Server

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.

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.