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{{#seo:
|title=Bitcoin network – Review, p2p structure, payments - zaoniao Wiki
|keywords=Bitcoin network, blockchain, network, payment, p2p, protocol
|description=Bitcoin network is a peer-to-peer (p2p) payment network that operates on a cryptographic protocol. Blockchain network is used as a simple broadcasting network to propagate transactions and blocks.
}}
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[[File:Bitcoinnetwork.png|400px|right|Bitcoin network - Blockchain network]]
'''Bitcoin network''' is a [[peer-to-peer]] payment network that operates on a cryptographic protocol. Users send and receive bitcoins, the units of currency, by broadcasting digitally signed messages to the network using bitcoin cryptocurrency wallet [[software]]. Transactions are recorded into a distributed, replicated public database known as the [[blockchain]], with consensus achieved by a proof-of-work system called mining. Satoshi Nakamoto, the designer of bitcoin claimed that design and coding of bitcoin begun in 2007. The project was released in 2009 as open source software.

The Blockchain network requires minimal structure to share transactions. An ad hoc decentralized network of volunteers is sufficient. Messages are broadcast on a best effort basis, and nodes can leave and rejoin the network at will. Upon reconnection, a node downloads and verifies new blocks from other nodes to complete its local copy of the blockchain.

Bitcoin network is used as a simple broadcasting network to propagate transactions and blocks. All communications are done over TCP. [[Bitcoin]] is fully able to use ports other than 8333 via the -port parameter. IPv6 is [https://bitcointalk.org/index.php?topic=81378.0 supported] with Bitcoind/Bitcoin-Qt v0.7.

== Bitcoin Network Messages ==
{{#ev:youtube|oSP-taqLWPQ|500|right|The Bitcoin and Blockchain Network Explained}}
* ''version'' - Information about program version and block count. Exchanged when first connecting.
* ''verack'' - Sent in response to a version message to acknowledge that we are willing to connect.
* ''addr'' - List of one or more IP addresses and ports.
* ''inv'' - "I have these blocks/transactions: ..." Normally sent only when a ''new'' block or transaction is being relayed. This is only a list, not the actual data.
* ''getdata'' - Request a single block or transaction by hash.
* ''getblocks'' - Request an ''inv'' of all blocks in a range.
* ''getheaders'' - Request a ''headers'' message containing all block headers in a range.
* ''tx'' - Send a transaction. This is sent only in response to a ''getdata'' request.
* ''block'' - Send a block. This is sent only in response to a ''getdata'' request.
* ''headers'' - Send up to 2,000 block headers. Non-generators can download the headers of blocks instead of entire blocks.
* ''getaddr'' - Request an ''addr'' message containing a bunch of known-active peers (for bootstrapping).
* ''submitorder'', ''checkorder'', and ''reply'' - Used when performing an [[IP address|IP transaction]].
* ''alert'' - Send a Bitcoin network alert key.
* ''ping'' - Does nothing. Used to check that the connection is still online. A TCP error will occur if the connection has died.

More information and in-depth technical information is in the Bitcoin Network Protocol Specification.

== Blockchain Network Connection ==
To connect to a peer, you send a ''version'' message containing your version number, block count, and current time. The remote peer will send back a ''verack'' message and his own ''version'' message if he is accepting connections from your version. You will respond with your own ''verack'' if you are accepting connections from his version.

The time data from all of your peers is collected, and the median is used by Bitcoin for all network tasks that use the time (except for other version messages)<ref>[https://www.bitcoinmining.com/getting-started/ Bitcoin Mining Guide - Getting started with Bitcoin mining]</ref>.

You then exchange ''getaddr'' and ''addr'' messages, storing all [[Bitcoin address|addresses]] that you don't know about. ''addr'' messages often contain only one address, but sometimes contain up to 1000. This is most common at the beginning of an [[exchange]].

== Standard relaying ==
When someone sends a transaction, they send an ''inv'' message containing it to all of their peers. Their peers will request the full transaction with ''getdata''. If they consider the transaction valid after receiving it, they will also broadcast the transaction to all of their peers with an ''inv'', and so on. Peers ask for or relay transactions only if they don't already have them. A peer will never rebroadcast a transaction that it already knows about, though transactions will eventually be forgotten if they don't get into a block after a while. The sender and receiver of the transaction will rebroadcast, however.

Anyone who is generating will collect valid received transactions and work on including them in a block. When someone does find a block, they send an ''inv'' containing it to all of their peers, as above. It works the same as transactions<ref>[https://bitcoin.org Bitcoin - Open P2P money]</ref>.

Everyone broadcasts an ''addr'' containing their own IP address every 24 hours. Nodes relay these messages to a couple of their peers and store the address if it's new to them. Through this system, everyone has a reasonably clear picture of which IPs are connected to the network at the moment. After connecting to the network, you get added to everyone's address database almost instantly because of your initial ''addr''.

Blockchain Network alerts are broadcast with ''alert'' messages. No ''inv''-like system is used; these contain the entire alert. If a received alert is valid (signed by one of the people with the private key), it is relayed to all peers. For as long as an alert is still in effect, it is rebroadcast at the start of every new connection.

== Initial block download ==
At the start of a connection, you send a ''getblocks'' message containing the [[hash]] of the latest block you know about. If Bitcoin p2p doesn't think that this is the latest block, it will send an ''inv'' that contains up to 500 blocks ahead of the one you listed. You will then request all of these blocks with ''getdata'', and the peer will send them to you with ''block'' messages. After you have downloaded and processed all of these blocks, you will send another ''getblocks'', etc., until you have all of the blocks.

== Thin SPV Clients ==
[[BIP 0037]] introduced support for thin or lite clients by way of Simple Payment Verification. SPV clients do not need to download the full block contents to verify the existence of funds in the blockchain, but rely on the chain of block headers and bloom filters to obtain the data they need from other nodes. This method of client communication allows high security trustless communication with full nodes, but at the expensive of some privacy as the peers can deduce which addresses the SPV client is seeking information about.

[[Multibit|MultiBit]] and [[Bitcoin wallet]] work in this fashion using the library [[bitcoinj]] as their foundation.

== Bootstrapping ==
You choose which peers to connect to by sorting your address database by the time since you last saw the address and then adding a bit of randomization.

Bitcoin has three methods of finding peers<ref>[https://bitclubnetwork.com BitClub Network]</ref>.

=== Addr ===
The ''addr'' messages described above create an effect similar to the [[IRC]] bootstrapping method. You know reasonably quickly whenever a peer joins, though you won't know for a while when they leave.

Bitcoin comes with a list of addresses known as "seed nodes". If you are unable to connect to IRC and you've never connected to the network before, the client will update the address database by connecting to one of the nodes from this list.

The -addnode command line option can be used to manually add a node. The -connect option can force bitcoin to connect only to a specific node.

=== DNS ===
Bitcoin looks up the IP Addresses of several host names and adds those to the list of potential addresses. This is the default seeding mechanism, as of v0.6.x and later.

=== IRC ===
As-of version 0.6.x of the Bitcoin client, IRC bootstrapping is no longer enabled by default. The information below is accurate for most versions prior.

Bitcoin joins a random channel between #bitcoin00 and #bitcoin99 on irc.lfnet.org. Your nick is set to an encoded form of your IP address. By decoding all the nicks of all users on the channel, you get a list of all IP addresses currently connected to Bitcoin.

For hosts that cannot make outbound connections on port 6667, the lfnet servers are also [[FAQ#Do_I_need_to_configure_my_firewall_to_run_bitcoin?|listening on port 7777]].

== Heartbeat ==
If thirty minutes or more has passed since the client has transmitted any messages it will transmit a message to keep the connection to the peer node alive.

If ninety minutes has passed since a p2p node has communicated any messages, then the client will assume that connection has closed.

==External links==
* [http://bitcoinstatus.rowit.co.uk/ Historical Network Status (no longer updated)]
* [http://getaddr.bitnodes.io/ Bitnodes.io's network size estimate]
* [http://fullnode.info/howto.html How to run your own cheap full bitcoin node]
* [https://www.bitcoinmining.com/ Bitcoin Mining]
* [https://www.youtube.com/watch?v=GmOzih6I1zs Video: What is Bitcoin Mining]
* [https://en.bitcoin.it/wiki/Network https://en.bitcoin.it/wiki/Network]

== See Also ==
* [[Satoshi Client Node Discovery]]
* [[Anonymity & Security]]
* [[Transaction fee]]
* [[Satoshi Nakamoto]]
* [[Smart contract]]

==References==
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[[Category:Bitcoin]]
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