Ouroboros Data Transfer Protocol

The Ouroboros Data Transfer Protocol is the hop-by-hop protocol that forwards packets to their destination.

As Ouroboros tries to preserve privacy as much as possible, it has an absolutely minimal network protocol. The field widths are not that important:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
+                      Destination Address                      +
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time-to-Live  |      QoS      |     ECN       |     EID       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                              EID                              +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The 5 fields in the Ouroboros network protocol are:

   Destination address: This specifies the address to forward the packet to. The width of this field is configurable based on various preferences and the size of the envisioned network. The Ouroboros default is 64 bits. Note that there is no source address, this is agreed upon during flow allocation.

   Time-to-Live: Similar to IPv4 (in IPv6 this field is replaced by the Hop Limit), this is decremented at each hop to ensures that packets don’t get forwarded forever in the network, for instance due to (transient) loops in the forwarding path. The Ouroboros default for the width is one octet (byte), limiting the Maximum Packet Lifetime in the network to 255 seconds. The initial TTL value for a flow can be based on the maximum delay requested by the application.

   QoS: Ouroboros supports Quality of Service via a number of methods (out of scope for this page), and this field is used to prioritize scheduling of the packets when forwarding. For instance, if the network gets congested and queues start filling up, higher priority packets (e.g. a voice call) get scheduled more often than lower priority packets (e.g. a file download). By default this field takes one octet.

   ECN: This field specifies Explicit Congestion Notification (ECN), with similar intent as the ECN bits in the Type-of-Service field in IPv4 / Traffic Class field in IPv6. The Ouroboros ECN field is by default one octet wide, and its value is set to an increasing value as packets are queued deeper and deeper in a congested routers’ forwarding queues. Ouroboros enforces Forward ECN (FECN).

   EID: The Endpoint Identifier (EID) field specified the endpoint for which to deliver the packet. The width of this field is configurable (the figure shows 16 bits). The values of this field is chosen by the endpoints, usually at flow allocation. It can be thought of as similar to an ephemeral port. However, in Ouroboros there is no hardcoded or standardized mapping of an EID to an application. For security, this field should be sufficiently large. For efficiency, it should be easy to map to a flow descriptor at the endpoints.