Scenario: news caches at an ISP Data Center and POPs

About this scenario

This section provides an example of an ISP that provides both Web service and news service to its customers. The ISP has a number of POPs. The news server is at the Data Center.

Reasons for deploying news caches

The ISP decided to deploy a news cache at the Data Center to gain the following benefits:

Reduce the number of Reader servers that are necessary to handle the volume of news traffic. Often, one news cache can handle the load of multiple Reader servers.
Decrease the "expense" of the news server handling multiple requests for the same article. Currently, with the news servers deployed in this ISP example, each time a client requests a particular article, the Reader server must search through the directory structure for the article. NetCache can handle such requests more efficiently than the Reader servers at this ISP.

The ISP decided to deploy a news cache at each POP to gain the following benefits:

Reduce the amount of bandwidth required for news service. Currently, the POP must send all news requests to the Data Center.
Save bandwidth and improve quality of service by fulfilling client requests faster.
The administrator of the POP is concerned with quality of service and bandwidth usage. Sending every news request to the ISP Data Center uses considerable bandwidth and increases the response time. Deploying a news cache at the POP reduces bandwidth usage and response time because multiple requests for news can be resolved by the POP news cache. Additionally, any connectivity problems that might occur between the POP and Data Center will have less impact on news service.

Deployment illustrated

The following illustration shows the news caching deployment for the ISP. For simplicity, only two POPs are shown in the illustration.

Types of NetCache appliances that were deployed

The ISP deployed NetCache appliances as follows:

Deployment at the POPs
The NetCache appliance at POP 1 handles only news traffic, whereas the NetCache appliance at POP 2 handles both Web traffic and news traffic. The deployments shown at the POPs are intentionally different to illustrate that each type of deployment is possible. The ISP could also have dedicated news caches and dedicated Web caches at the POPs.
Deployment at the Data Center
All NetCache appliances are dedicated to either news caching or Web caching. The reason is that the Data Center NetCache appliances must handle higher volumes of each type of traffic than the NetCache appliances at the POPs handle. The Data Center appliances must handle cache misses from many POPs. Additionally, the ISP wanted the maximum level of performance and reliability possible.

Why POP caches are not sending cache misses directly to the news server

This scenario describes news caches at the POPs sending cache misses to a news cache at the ISP Data Center, rather than the POPs sending cache misses to the news server directly. The ISP took this approach because the Reader server could not handle the number of connections that would result from many POPs sending cache misses to it.