Architecture: add high level view section

docs/architecture.md

@@ -2,6 +2,41 @@
 
 This page contains advanced info regarding XCP-ng architecture.
 
+## High level view
+
+Here you can find a high level view of how XCP-ng is interacted with by users and other applications, as well as the various blocks that it is made of. This part follows the [c4 model](http://c4model.com) principle for its diagrams.
+
+### Interactions
+
+The Hypervisor runs on a host, and is managed by its user directly via CLI, or through other administration applications such as [Xen Orechestra](https://xen-orchestra.com/#!/xo-home)j or [XCP-ng Center](https://github.com/xcp-ng/xenadmin)
+![c4 system context diagram of XCP-ng](../assets/img/architecture/XCP-ng-SystemContext.svg)
+
+### Main Building Blocks
+
+Inside the hypervisor, there are various parts allowing its main features:
+- Controlling and configuring XCP-ng
+- Controlling and configuring the VMs
+- Making network and Storage work for the host and guests
+- Fetching information about the host and the guests
+
+Here is how they organize and interface with each others:
+
+![c4 container diagram of XCP-ng](../assets/img/architecture/XCP-ng-Container.svg)
+
+## Network
+
+This parts focuses on XCP-ng and Para-Virtualized VMs.
+
+In XCP-ng, at the dom0 level, most of the networking is handled by [Open vSwitch](http://www.openvswitch.org/) for routing, filtering, tunneling and more. It hooks early in the Linux network stack, and the PV drivers handle the devices and their communication with the VMs.
+
+![c4 component diagram of XCP-ng's Network Stack](../assets/img/architecture/Network-Stack-Component.svg)
+
+The VIF driver is splitted in two parts:
+- the backend that runs on the dom0 and creates network interfaces named `vif[…].0`, like `vif1.0`
+- the frontend that runs on the guest VM and creates `enX0`
+
+This driver communicates between the two sides through shared memory pages.
+
 ## Storage
 
 ### Virtual disks on HVMs and PV guests