Internet Architecture

The topic on this entry is how the Internet is structured: the main actors, organizations implied in Internet architecture and the problem with IPv4.

Internet is a global system of interconnected computer networks that use the TCP/IP suite protocol to connect users and applications, and the way to access the net is through an ISP. Them provide connectivity to the users, corporative networks and others Internet Service Provider.

The Internet Assigned Numbers Authority (IANA) is responsible for the global coordination of the Internet Domains, Number Resources and Protocol Assignments. In other words, is the responsible of making the Internet works correctly without centralizing the Internet control. IANA is divided in Regional, National and Local Internet Registries in order to solve the legislation of the different countries. The RIR, which are distributed in continents, manage the distribution of IPv4 and IPv6 address blocks and AS number to the LIR, which are the ISP, that assign  these resources to the end users.

An Autonomous System is a group of IP networks run by one or more networks operators with a single, clearly defined routing policy. So, all the ISP must be in an AS and have an AS number assigned. The relationships between these networks are generally separated in:

• Transit: you pay to another network for Internet access.
• Peer: two networks exchange traffic between each other's customers freely, and for mutual benefit.
• Customer: another networks pay you to provide them with Internet access.

The Internet Service Providers are organized in three levels:

• Tier 1: also called Default Free Zone, which is a network that can reach every other network on the Internet without purchasing IP transit, and without costs.  
• Tier 2: a network that peers with some networks, but still purchases IP transit to reach at least some portion of the Internet. They are the ISP which are to provide access to Internet to a region. 
• Tier 3: a network that solely purchases transit from other networks to reach the Internet. They are the local providers.

On the actual Internet the main kind of network are peer-networks, so normally, the connections are going to be between Tier 3-ISP, and to avoid travelling through the three ISP levels has been created the Internet eXchange Point. It consists in routing Tier 2 or 3 ISP instead of going to an international connection (Tier 1). Some companies refuse it because it is complicated to manage the traffic and charge taxes to the end-user.

Another way to organize the ISP is based on what is offered to the user: services or content. The Content Service Providers are also divided into three groups:

• Network Operator Content Networks: the operator stores content in caches in order to offer better access services. 
• User Content Networks: such as peer-to-peer networks, which store content in a local network.
• Content Providers Content Networks: are divided in Farm servers, which store content in local networks, Mirrors, distributed servers in geographical localizations, but the user has to choose the server, and Content Distribution Networks, distributed servers, just as Mirrors, but with a dynamic pointing.

The CDN networks, are networks based in the idea of joining the users and the content, and shorting the delivery path via global networks of strategically placed servers. This kind of networks are capable of managing and maintaining the networks' elements that deliver Web content, and also provide to value added services, such as customization and adaptation of content, virus scanning and ad insertion. Thereby, these networks achieve reduced latency, high scalability and high availability.