witholding transaction fees...

[CliffordM]

I'm sure this has been raised already, but surely miners are incentivised not to forward transactions with transaction fees?

This isn't a big deal at the moment, but as transaction fees become juicier per block, won't miners (and in particular, big pools) try
to keep transactions with fees for inclusion in the blocks they solve rather than broadcast them to other miners ?

[realnowhereman]

But the sender is incentivised so will maintain wide connections and non miner nodes are neutral so will forward if they aren't malicious.

[CliffordM]

What incentivises the sender to relay hi-fee transactions rather than hold into them ? 

[Gabi]

The sender usually isn't a miner, so it has to make sure the transactions reach as more miners as possible.

[realnowhereman]

What incentivises the sender to relay hi-fee transactions rather than hold into them ? 

Erm... it's their transaction.  Why would they even create it if they didn't want it in the blockchain?

It's in the sender's interest to have their transaction worked on by as many miners as possible, so that the time-to-inclusion is as low as possible.

[interlagos]

There has been a research paper by Microsoft Research on how to solve this problem in the future:

News article:
http://coderrr.wordpress.com/2011/11/13/simplified-summary-of-microsoft-researchs-bitcoin-paper-on-incentivizing-transaction-propagation/

Original paper:
research.microsoft.com/pubs/156072/bitcoin.pdf

Or just google "Bitcoin and Red Balloons"

[cbeast]

It was discussed here:
https://bitcointalk.org/index.php?topic=51712.0
https://bitcointalk.org/index.php?topic=51662.0

[PrintCoins]

I'm sure this has been raised already, but surely miners are incentivised not to forward transactions with transaction fees?

This isn't a big deal at the moment, but as transaction fees become juicier per block, won't miners (and in particular, big pools) try
to keep transactions with fees for inclusion in the blocks they solve rather than broadcast them to other miners ?

Transactions without fees take much longer to get included in a block. The reality is that all nodes bounce around transactions, so if a miner kept a transaction secret, someone else would pass it around.

[casascius]

A similar argument would be that Bittorrent users have no motivation to seed files, and therefore Bittorrent will collapse.  That hasn't happened.

I don't think this will ever become an issue.  If it does, people would start inviting others to send their transactions directly to them, bypassing the port 8333 bitcoin network.  The whole internet is a giant P2P network - nothing says that a transaction creator couldn't blast their outgoing transactions to thousands of nodes on a list by direct connection to their IP.  And one advantage Bitcoin has over Bittorrent is that transactions are always small - nobody should have a problem blasting out their own transactions to a large number of nodes on even the slowest internet connection.