<p>I assume Satoshi here refers to the broadcast of the standalone transaction to the network as the first one, and the broadcast of a valid block containing the transaction as the second one.</p>
<p><a href="https://github.com/bitcoin/bips/blob/master/bip-0152.mediawiki" rel="noreferrer">Compact block relay</a> has since improved this by not redundantly broadcasting transactions from a block that a peer has already seen.</p>

CC BY-SA 4.0
2023-09-28T09:19:19.977Z
2023-09-28T09:24:59.473Z
2023-09-28T09:24:59.473Z
Antoine Poinsot
<p>Here is a part of <a href="https://www.metzdowd.com/pipermail/cryptography/2008-November/014815.html" rel="nofollow noreferrer">this mail</a> in the mailing list from Satoshi:</p>
<blockquote>
<p>The bandwidth might not be as prohibitive as you think.  A typical
transaction would be about 400 bytes (ECC is nicely compact).  Each
transaction has to be broadcast twice, so lets say 1KB per
transaction.  Visa processed 37 billion transactions in FY2008, or an
average of 100 million transactions per day.  That many transactions
would take 100GB of bandwidth, or the size of 12 DVD or 2 HD quality
movies, or about $18 worth of bandwidth at current prices.</p>
</blockquote>
<p>I don't quite understand why every transaction is broadcast twice. The first time clearly is when the client broadcast its transaction to the network, but what's the second time? (Is it considering broadcast of the mined block itself the second time because it contains the transaction?)</p>

<network><transaction-propagation>
Why is each transaction broadcast twice in the Bitcoin network?
Amir reza Riahi
# Why is each transaction broadcast twice in the Bitcoin network?

(Asked by: username_0 on 2023-09-28)

Here is a part of [this mail](https://www.metzdowd.com/pipermail/cryptography/2008-November/014815.html) in the mailing list from Satoshi:

> The bandwidth might not be as prohibitive as you think. A typical
> transaction would be about 400 bytes (ECC is nicely compact). Each
> transaction has to be broadcast twice, so lets say 1KB per
> transaction. Visa processed 37 billion transactions in FY2008, or an
> average of 100 million transactions per day. That many transactions
> would take 100GB of bandwidth, or the size of 12 DVD or 2 HD quality
> movies, or about $18 worth of bandwidth at current prices.

I don't quite understand why every transaction is broadcast twice. The first time clearly is when the client broadcast its transaction to the network, but what's the second time? (Is it considering broadcast of the mined block itself the second time because it contains the transaction?)

**Tags:** network, transaction-propagation


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## 1 answers

### Answer by username_1 on 2023-09-28. Score: 12 | Accepted answer

I assume Satoshi here refers to the broadcast of the standalone transaction to the network as the first one, and the broadcast of a valid block containing the transaction as the second one.

[Compact block relay](https://github.com/bitcoin/bips/blob/master/bip-0152.mediawiki) has since improved this by not redundantly broadcasting transactions from a block that a peer has already seen.


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