Scenario: telco movie delivery to home subscribers

About this scenario

In this scenario, a company named Webmovie.com wants to provide movies to home subscribers in the United States and Canada. Webmovie.com has contacted Edgeserve.com, a telco, to provide the bandwidth and CDN services that it needs for its movie subscription business.

In this scenario, assume that clients in each country use a local DNS nameserver that is close to the clients; that is, clients in the United States use a local DNS nameserver in the United States and clients in Canada use a local DNS nameserver in Canada. Therefore, a simple way of deploying GRM is to use just GRM DNS servers for redirection.

Organization's requirements

Webmovie.com's requirements are as follows:

Support both RTSP and MMS video streams
Provide the highest quality video possible
Support multiple bit-rate video
Webmovie.com customers will be connecting over a variety of types of connections, from slow-speed modems to DSL and cable modems.
Provide fast and reliable service

Deployment illustrated

The following illustration shows the deployment for Edgeserve.com and the path of a request from a client to a GRM agent cache that serves content to the client.

As the previous illustration shows, multiple GRM DNS servers are deployed in the data center so that content delivery service is not interrupted if one GRM DNS server becomes unavailable. Each GRM DNS server has been assigned the IP address that was previously assigned to an authoritative DNS nameserver in the data center.

Edgeservice.com deployed a GRM agent cache in the data center to provide failover in case all edge caches in an edge group become unavailable at the same time.

Edgeservice.com deployed edge caches configured for MMS and RTSP service in each of the two POPs (edge groups). The edge caches service only the clients in the edge group in which they are located. When a client in the POP makes a request, the GRM DNS server that receives the query from the local DNS nameserver returns the IP addresses of all eligible edge caches in the edge group with which the client is associated.

The center cache could be used to service content requests from the edge groups (instead of deploying edge caches in the POPs). However, this deployment was not chosen because Edgeservice.com requires high-quality video. If all clients are serviced from the center cache, the greater is the distance that content travels, the greater is the latency and the greater is the possibility of degradation of content quality due to problems such as network congestion. Streaming media is especially vulnerable to network congestion, which can cause jagged video and unsynchronized audio and video. Additionally, serving content from edge caches rather than center caches significantly reduces bandwidth consumption over the WAN. The bulk of bandwidth savings results from eliminating the need for each client to individually fetch a media stream from the content server at the other end of the WAN.