 The content delivery networks are not mere static content, sometimes there is dynamic generation of content as well. So a question arises, can we do anything about dynamically assigning the functions of the CDN by identifying the components there and distributing these across the physical servers and could we achieve some kind of acceleration in terms of distribution and overall management? Let's start. Content delivery networks require dynamically generated and static content. Sometimes this dynamically generated content is also personalized according to user profiles. The main functions of modern web system are all incorporated there. For instance, there is a front end, there is a back end, then there's a database server. Now, a fundamental question arises, could the delivery of the content be improved while keeping the system scalable? How can we do that? We can think about the replication of the functions of the multi-tier web-based system. I have just mentioned a three-tier system in which we have the front end, we have the back end and we have the database over the nodes of CDN. CDN nodes can be thought of as the origin server and the edge servers. These are the part of the overall web infrastructure, physically speaking. These are involved in content delivery. If we think about the replication of functions across the servers, what can we do with regard to front end? We can think about replication of front end layer by considering the edge servers as surrogate servers, which are only replicating the content such as the HTML pages, which are generated by the web server. Now, this is nothing but a file system level replication. Then we can think about the replication of application layer. Replication of application layer actually is more like an active engine replication. We can think about the dynamically generated content that is being generated at the application layer. If that has to be replicated, we can think about it as edge computing, because it moves the web application programs and the components on edge servers, which are closer to the clients. Here we are going to make use of our understanding of the cloud infrastructure, where we had the platform as a service, software as a service, etc, etc. Now, this is essentially a very different way of looking at exactly the same thing. Then we can think about replication of back end layer. The back end layer is nothing but the database, original database. The original database is primarily responsible for the management of infrastructure and it hosts the original or the master copy of the data. So it means that the primary management is being overseen by the back end layer. So if you want to replicate, it means we can think about some kind of origin server to origin server update. Then we can also think about the user profile. The user profiles are mostly personalized file content, which is hosted in the original content server. If it has to be replicated, then edge servers can make use of this user data to provide a more personalized content in real time. Now let's look at it in three steps. Whatever we've discussed, we can think about all these as the logical layers of a web system where we have the clients talking to the front end layer, which in turn interacts with the application layer. The application layer is connected to the back end layer and the user profile layer. The application layer is running dynamic applications and is generating the content which is at the front end layer. We've talked about replicating all of these one by one. Now the diagram in the middle is the visualization of what is the relationship between the core server and the edge servers. The edge servers are the replication servers, which provide replication facility to all these logical components. So it means we are now going to look at the translation or mapping of web system logical layers on CDN infrastructure. We can see from the top, starting from the left hand side, we have the replication of front end layer, replication of application layer, back end layer and user profile layers. Essentially, all the things or all the concepts that we've discussed visually being represented here. The reference is again by the same book, Content Delivery Networks by Raj Kumar Bhaiya in 2008.