Recursive networks

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 “Recursive InterNetwork Architecture”, or RINA.

Ouroboros follows the recursive principles of RINA, but deviates quite 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 soure 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.

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.