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diff --git a/content/en/docs/Concepts/protocols.md b/content/en/docs/Concepts/protocols.md new file mode 100644 index 0000000..16c72cb --- /dev/null +++ b/content/en/docs/Concepts/protocols.md @@ -0,0 +1,130 @@ +--- +title: "The protocols" +author: "Dimitri Staessens" +#description: protocols +date: 2019-09-06 +#type: page +draft: false +description: > + A brief introduction to the main protocols. +--- + +# Network protocol + +As Ouroboros tries to preserve privacy as much as possible, it has an +*absolutely minimal network protocol*: + +``` + 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 and IPv6 (where this field is called + 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). + +* **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. + +# Transport protocol + +Packet switched networks use transport protocols on top of their +network protocol in order to deal with lost or corrupted packets. + +The Ouroboros Transport protocol (called the _Flow and Retransmission +Control Protocol_, FRCP) has only 4 fields: + +``` + 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 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Flags | Window | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Sequence Number | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Acknowledgment Number | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +``` + +* **Flags**: There are 7 flags defined for FRCP. + + - **DATA**: Indicates that the packet is carrying data (this allows + for 0 length data). + + - **DRF** : Data Run Flag, indicates that there are no unacknowledged + packets in flight for this connection. + + - **ACK** : Indicates that this packet carries an acknowledgment. + - **FC** : Indicates that this packet updates the flow control window. + - **RDVZ**: Rendez-vous, this is used to break a zero-window deadlock + that can arise when an update to the flow control window + gets lost. RDVZ packets must be ACK'd. + - **FFGM**: First Fragment, this packet contains the first fragment of + a fragmented payload. + - **MFGM**: More Fragments, this packet is not the last fragment of a + fragmented payload. + +* **Window**: This updates the flow control window. + +* **Sequence Number**: This is a monotonically increasing sequence number + used to (re)order the packets at the receiver. + +* **Acknowledgment Number**: This is set by the receiver to indicate the + highest sequence number that was received in + order. + +# Operation + +The operation of the transport protocol is based on the [Delta-t +protocol]((https://www.osti.gov/biblio/5542785-delta-protocol-specification-working-draft)), +which is a timer-based protocol that is a bit simpler in operation +than the equivalent functionalities in TCP. In contrast with TCP/IP, +Ouroboros does congestion control purely in the network protocol, and +fragmentation and flow control purely in the transport protocol. + + + + +--- Changelog: + +2019 09 05: Initial version.<br> +2019 09 06: Added section on transport protocol.
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