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diff --git a/content/docs/protocols.md b/content/docs/protocols.md new file mode 100644 index 0000000..d7d364f --- /dev/null +++ b/content/docs/protocols.md @@ -0,0 +1,217 @@ +--- +title: "Packet network protocols" +author: "Dimitri Staessens" +description: "protocols" +date: 2019-09-06 +#type: page +draft: false +--- + +# Network protocols + +Packet switched networks move data between two applications using +_network protocols_, which specify where to move the data and how to +do it. The Internet famously uses the Internet Protocol, IP (versions +4 and 6, which are mutually incompatible, so in essence, there is not +a single Internet, there are two!) as the network protocol that +specifies how to move packets from point _A_ to point _B_. + +In order to move a packet from _A_ to _B_, each intermediate node _C_ +in the network will investigate the packet header and, based on the +destination address, forward the packet onward until it reaches _B_. + +The IPv4 protocol is specified in +[RFC791](https://tools.ietf.org/html/rfc791), and its _header_ is +shown here: + +``` + 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 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + |Version| IHL |Type of Service| Total Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Identification |Flags| Fragment Offset | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Time to Live | Protocol | Header Checksum | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Source Address | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Destination Address | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Options | Padding | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +``` + +The IPv6 protocol is specified in +[RFC2460](https://tools.ietf.org/html/rfc2460), and its header format +is: + +``` + 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 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + |Version| Traffic Class | Flow Label | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Payload Length | Next Header | Hop Limit | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + + + + | | + + Source Address + + | | + + + + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + + + + | | + + Destination Address + + | | + + + + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +``` + +For a detailed description of what all the fields in this protocol +mean, we gladly refer you to the RFCs or the wikipedia pages ( +[IPv4](https://en.wikipedia.org/wiki/IPv4) and +[IPv6](https://en.wikipedia.org/wiki/IPv6)). + +The most interesting fact about the jump from IPv4 to IPv6 is that the +protocol got noticeably _simpler_. + +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 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 protocols + +Packet switched networks use transport protocols on top of their +[network protocols](/docs/network_protocols) in order to deal with +lost or corrupted packets. IP has the Transport Control Protocol (TCP) +that takes care of things when IP packets get lost. TCP also does some +other neat things, like making sure that a client does not send faster +than a server can process (_flow control_); and making sure that the +network doesn't get overwhelmed by its users (_congestion control_). + +The TCP protocol is specified in +[RFC793](https://tools.ietf.org/html/rfc793), and its _header_ is +shown here: + +``` + 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 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Source Port | Destination Port | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Sequence Number | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Acknowledgment Number | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Data | |U|A|P|R|S|F| | + | Offset| Reserved |R|C|S|S|Y|I| Window | + | | |G|K|H|T|N|N| | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Checksum | Urgent Pointer | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Options | Padding | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +``` + +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 (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. + +--- +Changelog: + +2019 09 05: Initial version.<br> +2019 09 06: Added section on transport protocol.
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