Gnutella Forums - Question regarding UDP

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Question regarding UDP

Please pardon my ignorance. I'm sure this question have been answered before (I tried search but was flooded with posts about UDP). Why doesn't the Gnutella network use the UDP protocol for searching and other small data transfers? How come other private networks like Blubster and File Spree can use UDP for searching with great success?

Thanks.

Some firewalls, including the ones where I work, don't allow some or all UDP out, so you would be preventing many people from being able to use the network.

But this problem can be circumvented by a TCP "proxy-out" mechanism. Here's how Blubster's author deals with it:

Quote:

How are we going to enable everybody to connect with Blubster if they can’t use UDP? The answer is “Guide Nodes”. Guide nodes will be normal Blubster peers that will be acting like a guide for non-UDP-enabled peers.

The idea is that, when a peer (peer-A) that can’t use UDP tries to connect, it will “ask” for a UDP-enabled peer (peer-B) to be his/her gateway to the network. A normal TCP/IP connection is now between the two peers. The peer-A will see through peer-B. When peer-A needs to search for something, it passes the search to peer-B, who will process it, resending it -using the normal UDP transmissions- to the network. Peer-B will then receive the results and will forward them to peer-A. This is similar to the router port forwarding, but we will do it in a different layer.

The pros for this method are that everybody will be able to connect with Blubster. If you can navigate the web then you can connect to a Guide Node. The cons are the TCP/IP connection needed. TCP/IP transmissions are reliable, which means that guided peers will not be anonymous. Guide Nodes will sacrifice about 20% of performance receiving, processing and sending data to the guided peer.

The performance hit for those who use this method shouldn't be that bad, IMHO.

UDP is a connectionless protocol. If you use it, you have no idea if the person you are sending to is still there anymore. For instance, you may send a search request to a person, but if he signs off right now, you still keep sending him data. Wasting your time and bandwidth. TCP is a more "expensive" protocol but is alot better for the needs of the network.

So how does Blubster utilize UDP successfully? Is it more efficient with the search packets so that there is very little wastage? If you look at the statistics in the Blubster client, you will see that there are very few bad packets. Is it the case that Gnutella must optimize the searching and handshake methods before it can utilize UDP?

The problem is the broadcast UDP address. In most cases it is disabled. In addition to the other mentioned issues, this will make UDP usability very limited. It's been discussed before, many times...

problems problems problems