Re: [Bitcoin-development] A bitcoin UDP P2P protocol extension

[Randy Willis <willis.randy@ymail.com>]

Not looked at code yet, some thoughts:

1) In IPv4 max UDP data size is 65507 bytes.
2) What about big messages (block)?
3) I think relay speed can be increased only by reducing network diameter. 

Introducing super-nodes with thousands of connected peers can greatly help here.
4) The only (IMO) UDP advantage: hole punching. But requirement of active 

TCP connection defies it. And hole punching will need protocol extension.
5) unsolicited tx broadcast will increase traffic of nodes (especially well-connected)
and less people will run them.


---- Original Message -----

From: Jeff Garzik <jgarzik@exmulti.com>
To: Bitcoin Development <bitcoin-development@lists.sourceforge.net>
Cc: 
Sent: Saturday, March 23, 2013 7:17 AM
Subject: [Bitcoin-development] A bitcoin UDP P2P protocol extension

Here is a rough draft implementation of a UDP P2P protocol extension
for bitcoin:

    https://github.com/jgarzik/bitcoin/tree/udp
     http://yyz.us/bitcoin/udp-v0.patch

Protocol specification (such that it is):

- UDP, bound to same port as TCP P2P (normally 8333)
- Active, simultaneous TCP P2P connection required (useful against DoS
and other attacks)
- Same message format as TCP P2P, same pchMessageStart conventions,
etc. (my CNetMessage pull req would be helpful here)
- Multiple P2P messages per UDP packet permitted
- Max UDP packet size 100*1024 bytes
- Advertises NODE_UDP in nServices
- New "getudpcook" TCP P2P command returns a "udpcook" message,
containing a yummy cookie
- UDP P2P commands "inv", "tx" and "addr" are handled as if received via TCP
- UDP P2P command "udpsub" sets a mask, that subscribes to one or more
data broadcasts.
- When USM_INV_BCAST mask bit is set, receive "inv" messages via UDP
rather than TCP.

Project and design goals (or, why do this?):

- It is theorized that UDP may be useful for some messages we
broadcast throughout the network
- A productive discussion STARTS with code, otherwise discussion
continues forever.
- Investigate improving "inv" relay speed
- Investigate unconditional "tx" broadcasting via UDP, as "inv"
alternative, for small tx's.
- Investigate improving block relay speed (or perhaps block header relay speed)
- Open up new design avenues, for P2P patterns more suited to UDP than
TCP in general.

-- 
Jeff Garzik
exMULTI, Inc.
jgarzik@exmulti.com

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