Content Distribution Architecture

Content Distribution Architecture

Taxonomy

Network

There are a number of different networking technologies; these share different fundamental capabilities. These include:

1. Broadcast only - it may be broadcast only (e.g. video channels, or vertical retrace based data traffic)
2. Multicast - does the technology support multicast traffic (traffic can be grouped as to interest)
3. Unicast - does the technology support unicast connection.

Latency

1. Low - what is experienced in most of the developed world, using broadband technologies.
2. High - Some wireless technologies impose high latencies, often since data has been an afterthought in either the wireless technology or in the wireless deployment. In addition, one or more satellite links are common in some countries.

Regulatory

In some countries, there may be additional issues that ensue due to regulatory constraints. For example, there are countries which signed extremely poor wide area peering agreements in the past, such that bandwidth out of the country is hideously expensive, putting an extremely high premium on in-country mirroring of content.

An other example is where there is no in-country peering between ISP's, sometimes resulting in international back-haul being the norm for interoperation between ISP's operating in country, rather than the exception. Longer term solutions are up to the local governments involved; organizations like the Packet Clearing House may be very useful to tap the expertise required to restore sanity to such network situations, though the country involved will also need to *want* to solve these problems, as the economic interests of the ISP's may not map to the interests of the country involved. These interests go well beyond Ministries of Education, so proper solutions may be time consuming and politically difficult. Note that in this example, such situations may complicate content distribution, requiring multiple delivery networks.

Technologies

Content Distribution Networks (CDN's)

There are many content distribution networks of which Akamai may be best known. There are open source CDN's as well, less well known, including CoDeeN and Coral. These provide geographic distribution and replication of content. CDN's may prefetch content they have reason to believe will become popular (to handle the flash crowd effect); certainly topical news requires such distribution, as does the core curricula; on the first day of school, the first unit of a national curricula had better be well distributed.

With thousands, tens of thousands, and eventually hundreds of thousands of schools in a country, CDN's will certainly become necessary.

Enabling publishing of interesting content and activities is also essential; creative teachers and students are everywhere, and a flash crowd could easily bring a school's network connection to its knees.

CDN's generally use caching web proxies as components. They may use techniques such as multicast or other peer-to-peer technologies (e.g. DHT's) to locate and distribute content efficiently.

Offline Caching

--Jim 17:34, 30 July 2008 (UTC)