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diff --git a/content/en/docs/Concepts/what.md b/content/en/docs/Concepts/what.md new file mode 100644 index 0000000..bacd4d6 --- /dev/null +++ b/content/en/docs/Concepts/what.md @@ -0,0 +1,146 @@ +--- +title: "What is a recursive network?" +author: "Dimitri Staessens" + +date: 2019-07-06 +weight: 1 +description: > + Introduction to recursive networks. +--- + +# The current networking paradigm +{{<figure width="40%" src="/docs/concepts/aschenbrenner.png">}} + +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. + +{{<figure width="50%" src="/docs/concepts/layers.jpg">}} + +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, followed by a Virtual Private Network and on top a tunnel +that supports the application. 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.
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