 Thus far, we've assumed that content delivery networks are pretty resource provisioned and they are autonomous, but this may not always be true. So do they have an interplay or interdependence with each other? For that, let's look at how the content delivery networks reach out to each other. This area is known as CDN internet working. So we'll start off with the need for such internet working or peering. We'd look at an interesting scenario and we'll look at the architecture. It is obvious that people subscribe to cloud services and services over the internet for high quality content. Now, the requirement for providing high quality with global outreach is indeed challenging. Now, this challenge is very, very serious for new CDN providers and it's not even viable for existing ones. So that is why we've seen over the years that somehow collaboration acquisition mergers take place which results into very few players which are the movers and shakers in CDN. For instance, we know of Akamai, we know of Amazon and we know of Netflix. So it means we don't know of hundreds and thousands of such CDN providers. Why? Because some kind of mergers and consolidations do take place. Why? Because some kind of coordination is required for these CDNs to remain commercially viable. And as you well know that sometimes the demand is not real. It appears as a flash crowd or as a certain increase in demand which is not representative of the customer base in that particular CDN jurisdiction. So for that, the CDNs have to get into some kind of peering arrangement. So what is that? Peering arrangement is basically a commitment by the CDNs to cooperate with each other. Now, this helps them to facilitate the sharing of infrastructure for cooperation that is sharing the resources and to make sure that the services are delivered efficiently by all the participating peers. Now, some questions would arise. For instance, if a CDN has to pair with others or internet work with others, then whom to pair with? When to pair and on what conditions to pair? Now, this is actually when to pair is basically the circumstances when a certain CDN finds itself unable to provide the same quality of service to the customers. How to pair is interaction between different entities, the SLA, the service level agreement and whom to pair with basically is a multi criteria decision making process that is the exact incumbent requirements which are being faced by a CDN, CDN I, then it must look for the CDN which is within its proximity under certain constraints that best fulfills its requirements. Now, let's look at an interesting scenario. In fact, two scenarios which motivate us to look for internet working. Now, everyone in Pakistan who's fond of watching cricket must have referred to the ESPN Crick Info website. Now, the Crick Info origin server basically is actually being requested by a client to provide the live update, say between Pakistan and Sri Lanka. Now, this origin server sends the request to the Akamai server. Now, the Akamai server has the content. So, it looks for the appropriate content, chooses the web server in the premises of a certain cluster and then let's say it finds that the part of the requests that are being made by the users can be accommodated from the edge servers. Let's say a server is placed in candy Sri Lanka where the match is being played. So, edge server in that particular area would be used, would be redirected to provide the content to the users. Now, if there is an additional requirement, in that case Akamai as the content delivery network will have to replicate servers, let's say somewhere, let's say in Trinidad and Tobago, like St. Lucia. There, a new server has to be deployed. It's known as the point of presence. A new point of presence will have to be deployed. It means new investment has to be made by Akamai as a singular content delivery network. Now, the users are now being provisioned from the edge servers, from the newly placed servers. This means more cost, but if we look at peering arrangement between CDN providers, now the Akamai content delivery network has relationship or an MOU or a service level agreement with the mirror image, let's say another company, which has a point of presence in candy. The example here is of Trinidad and Tobago. So, it means if they already have a server there, Akamai doesn't have to invest to have another server in Trinidad and Tobago or candy for that matter. In that case, the users are now being served the content from the mirror image edge server because that particular edge server has the content and is the best suited delivery site. So, the users are being provisioned from there. In this case, you can see if Akamai wants to expand globally, it has to join hands with another content delivery network provider. Now, let's look at some terms. Then we are going to look at the architecture that is used to realize such internet working or peering. We have the web server that is the original content provider, which has the original objects. Then we have the mediator. mediator is the one that is a software artifact that has the rules for negotiation and management between multiple CDNs. Then we have the registry. Registry is basically the record of the resources and policies which are being used by different CDNs which want to reach out to each other and have a peering relationship. Then we have peering agent that is basically a software module that helps to discover the resources which are available in the CDN community. Then we have policies or the rules like web server specific rules, mediator specific rules and the peering rules. Now, these are the typical terminologies which one would come across if one were to look into how CDNs internet work with each other. The consequent architecture of an entire system in which the peers can support each other and can take benefit out of each other is going to be like this. Here we have the content requester and the content provider. The content requester is let's say a certain client, individual client and the content provider is going to be the web server. But which web server and which particular CDN to be used? It all depends upon the availability of content, the proximity, the relationship between these CDNs and what policies are implemented on these CDNs. So, let's look at a particular CDN, let's say CDN 1. So, we have web server, then we have policies for the web server, we have the registry, we have the mediator, we have the policy registry and then we have the peering agent. So, it means it is the peering agent that works on behalf of the CDN to talk to another peering agent who is representing another CDN on its behalf. So, it means these peering agents are going to look for the particular CDN that best suits the requirements for the requesting CDN.