content: Add section on recursive networks

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 recent_posts_number = 2
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diff --git a/content/docs/what.md b/content/docs/what.md
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+---
+title: "What is a recursive network?"
+author: "Dimitri Staessens"
+description: "what"
+date:  2019-07-06
+#type:  page
+draft: false
+---
+
+Ouroboros has the objective to greatly simplify the creation and
+management of distributed applications, through a single, unified API.
+The API is completely agnostic of where the applications are running,
+whether the destination application is running locally on your
+machine, or remotely over the internet, the API calls are exactly the
+same.
+
+It is based on the __recursive networks__ paradigm.
+
+# The current networking paradigm
+
+<center> {{<figure
+class="w-80"
+src="/images/aschenbrenner.png">}}
+</center>
+
+Every computer science class that deals with networks explains the
+[7-layer OSI model](https://www.bmc.com/blogs/osi-model-7-layers/).
+Open Systems Interconnect (OSI) defines 7 layers, each providing an
+abstraction for a certain *function* that a network application may
+need.
+
+From top to bottom, the layers provide (roughly) the following
+functions:
+
+The __application layer__ implements the details of the application
+protocol (such as HTTP), which specifies the operations and data that
+the application understands (requesting a web page).
+
+The __presentation layer__ provides independence of data representation,
+and may also perform encryption.
+
+The __session layer__ sets up and manages sessions (think of a session
+as a conversation or dialogue) between the applications.
+
+The __transport layer__ handles individual chunks of data (think of them
+as words in the conversation), and can ensure that there is end-to-end
+reliability (no words or phrases get lost).
+
+The __network layer__ forwards the packets across the network, it
+provides such things as addressing and congestion control.
+
+The __datalink layer__ encodes data into bits and moves them between
+hosts. It handles errors in the physical layer. It has two sub-layers:
+Media access control layer (MAC), which says when hosts can transmit
+on the medium, and logical link control (LLC) that deals with error
+handling and control of transmission rates.
+
+Finally, the __physical layer__ is responsible for translating the
+bits into a signal (e.g. laser pulses in a fibre) that is carried
+between endpoints.
+
+This functional layering provides a logical order for the steps that
+data passes through between applications. Indeed, every existing
+(packet) network goes through these steps in roughly this order
+(however, some may be skipped). There can be some small variations on
+where the functions are implemented. For instance, TCP does congestion
+control, but is a Layer 4 protocol.
+
+However, when looking at current networking solutions, things are not
+as simple as these 7 layers seem to indicate. Just consider this
+realistic scenario for a software developer working remotely. Usually
+it goes something like this: You connect to the company __Virtual
+Private Network__ (VPN), setup an SSH __tunnel__ over the development
+server to your virtual machine and then SSH into that virtual machine.
+
+The use of VPNs and various tunneling technologies draw a picture
+where the __functions__ of Layers 2, 3, and 4, and often layers 5 and
+6 (encryption) are __repeated__ a number of times in the actual
+functional path that data follows through the network stack.
+
+Enter __*recursive networks*__.
+
+# The recursive network paradigm
+
+The functional repetition in the network stack is discussed in
+detail in the book __*"Patterns in Network Architecture: A Return to
+Fundamentals"*__. From the observations in the book, a new architecture
+was proposed, called the "__R__ecursive __I__nter__N__etwork
+__A__rchitecture", or [__RINA__](http://www.pouzinsociety.org).
+
+__Ouroboros__ follows the recursive principles of RINA, but deviates
+quit a bit from its internal design. There are resources on the
+Internet explaining RINA, but here we will focus
+on its high level design and what is relevant for Ouroboros.
+
+Let's look at a simple scenario of an employee contacting an internet
+corporate server over a Layer 3 VPN from home. Let's assume for
+simplicity that the corporate LAN is not behind a NAT firewall. All
+three networks perform (among some other things):
+
+__Addressing__: The VPN hosts receive an IP address in the VPN, let's
+say some 10.11.12.0/24 address. The host will also have a public IP
+address, for instance in the 20.128.0.0/16 range . Finally that host
+will have an Ethernet MAC address. Now the addresses __differ in
+syntax and semantics__, but for the purpose of moving data packets,
+they have the same function: __identifying a node in a network__.
+
+__Forwarding__: Forwarding is the process of moving packets to a
+destination __with intent__: each forwarding action moves the data
+packet __closer__ to its destination node with respect to some
+__metric__ (distance function).
+
+__Network discovery__: Ethernet switches learn where the endpoints are
+through MAC learning, remembering the incoming interface when it sees
+a new SRC address; IP routers learn the network by exchanging
+informational packets about adjacency in a process called *routing*;
+and a VPN proxy server relays packets as the central hub of a network
+connected as a star between the VPN clients and the local area
+network (LAN) that is provides access to.
+
+__Congestion management__: When there is a prolonged period where a
+node receives more traffic than can forward forward, for instance
+because there are incoming links with higher speeds than some outgoing
+link, or there is a lot of traffic between different endpoints towards
+the same destination, the endpoints experience congestion. Each
+network could handle this situation (but not all do: TCP does
+congestion control for IP networks, but Ethernet just drops traffic
+and lets the IP network deal with it. Congestion management for
+Ethernet never really took off).
+
+__Name resolution__: In order not having to remember addresses of the
+hosts (which are in a format that make it easier for a machine to deal
+with), each network keeps a mapping of a name to an address. For IP
+networks (which includes the VPN in our example), this is done by the
+Domain Name System (DNS) service (or, alternatively, other services
+such as *open root* or *namecoin*). For Ethernet, the Address
+Resolution Protocol maps a higher layer name to a MAC (hardware)
+address.
+
+<center>
+{{<figure class="fl w-90"
+          src="/images/layers.jpg">}}
+</center>
+
+Recursive networks take all these functions to be part of a network
+layer, and layers are mostly defined by their __scope__. The lowest
+layers span a link or the reach of some wireless technology. Higher
+layers span a LAN or the network of a corporation e.g. a subnetwork or
+an Autonomous System (AS). An even higher layer would be a global
+network. An even higher one a Virtual Private Network. An even higher
+one a tunnel, etc. Each layer being the same in terms of
+functionality, but different in its choice of algorithm or
+implementation. Sometimes the function is just not implemented
+(there's no need for routing in a tunnel!), but logically it could be
+there.
+
+
+---
+Changelog:
+
+2019 07 09: Initial version.
\ No newline at end of file
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