I have come across a term SDN (software defined network). I have gone through some related webpages and understood that it is basically related to networking virtualisation. I want to understand SDN from an application developer/programmer's perspective. For example, if I have created a set of websites and web services (in .Net), what are the things that would be different in SDN than in a conventional network, in terms of development and deployment.
I would appreciate if somebody could explain this with an example.
Thanks a lot.
Before I say anything I should mention everything I say here might be changed in future. The reason is that this field is still in the research area and might face some modifications in future. Even some use cases may be removed or added.
One thing I should maybe add is that SDN is not just network visualization. It could be more than that. I think it is better to say one of the applications/usages of SDN is network visualization.
Let's consider onos: ONOS is implementing an controller which internet service providers would use to cerate path and links. ISP's just specify the two end points and then ONOS goes and sends flows to different switches in order to make path between them. ONOS calls it "intent", that is an intent is created between two points.
Imagine Datacenter (DC) A wants to backup it's data at 3 am tomorrow. With SDN they can call their ISP and ask for a "path" at 3am tomorrow with bandwidth of 50Gb/s. The two DC may have full view of the network or just a subset of the view. (i.e. visualized view ) The ISP's SDN controller would go and program the required switches using OF commands to create that path for the two DC. SDN is mostly used in programming network. For example:
Another possible usage is the following: Let's say you have your website up and user/client want to connect to your website and browse it. One can say, users need to create a path from client to your server using their ISP. However, I think this maybe by the browser for you. I doubt this is feasible but I've heard this usage too.
In general I think SDN would not make a big change in terms of web browsing and web servers. Usually web browsing is just short connections and packets. I think SDN would make more sense for long time connections like backing up a whole DC or streaming videos. The reason is that configuring a path from client to host is a bit expensive and a bit time consuming (at least with the current technology) so it is worth it for connections over a long period.
I hope it helps.