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48 lines
2.8 KiB
Plaintext
[[communications_protocol]]
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== The communication protocol
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After you discovered the overview of how the lightning network protocol worked in the last chapter we now want to present a few more details about the actual communication that takes place between the nodes to fulfill the most important tasks like opening a channel, forwarding a payment and closing the channel.
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All communication takes place over a secure, encrypted and authenticated connection.
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[NOTE]
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====
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While the specification of how to set up such a connection is part of the lightning network protocol and can be read upon in BOLT08 we will omit this in the book.
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The reason is that BOLT08 mainly follows the handshake patterns from the noise protocol framework which is a standard template system for secure cryptographic handshakes.
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This protocol framework is also used by Whatsapp and Wireguard and is very well documented.
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If you want to learn more we suggest you check out http://www.noiseprotocol.org/
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====
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=== Lightning Messages
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Each Lightning Message contains 2 bytes indicating the *type* of message, and a variable-length *payload*.
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A *payload* needs to be interpreted according the *type*.
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A Lightning Message falls into one of the following groups:
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[cols="3,3,10",options="header"]
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|=======
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| Group | Type | Description
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| Setup & Control | 0~31 | Messages related to connection setup, control, supported features, and error reporting
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| Channel | 32~127 | Messages related to setup and close channels
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| Commitment | 128~255 | Messages related to updating the current commitment transaction
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| Routing | 256~511 | Messages related to node and channel announcements, or active route explorations
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| Custom | 32768~65535 | Experimental or custom messages
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|=======
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Lightning Messages follows two forethoughtful rules: "it's OK to be odd" rule and "ignore additional data" rule. Both of them allow for future extension of Lightning Messages.
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==== "It's OK to be odd" rule
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Lightning Message type follows the _it's ok to be odd_ rule. A node is allowed to send a message of an _odd_-numbered type, but not _even_-numbered type without prior negotiation. Once a node receives an _oddly_-but-unknown-typed message, it should ignore it. However, if it receives an _evenly_-but-unknown-typed message, it is expected to fail the channels.
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==== "Ignore additional data" rule
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The length of a Lightning Message is a 2-byte unsigned int, so the maximum message size is 65535 bytes.
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If a node receives a message with additional data longer than it expects for the corresponding type, the exceeding part will be discarded. On the contrary, if a node receives a message shorter than it expects, it fails the channels.
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=== Opening a Payment channel
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=== forwarding, making and receiving a payment
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=== closing the channel
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