Editing Gnutella2 (section)

== Protocol features ==

Gnutella2 has an extensible binary packet format, comparable to an [[XML]] document tree, which was conceived as an answer for some of gnutella's less elegant parts. The packet format was designed so that future network improvements and individual vendor features could be added without worry of causing [[Software bug|bugs]] in other clients on the network.<ref>{{cite web| url=http://g2.trillinux.org/index.php?title=Packet_Structure| title=Packet Structure| publisher=Gnutella2 Wiki| access-date=2007-11-07| archive-date=2007-12-19| archive-url=https://web.archive.org/web/20071219232211/http://g2.trillinux.org/index.php?title=Packet_Structure| url-status=live}}</ref>

For the purpose file identification and secure [[Data integrity|integrity]] check of files it employs [[SHA-1]] [[Cryptographic hash function|hashes]]. To allow for a file to be reliably [[download]]ed in parallel from multiple sources, as well as to allow for the reliable uploading of parts while the file is still being downloaded (swarming), [[Merkle tree|Tiger tree hashes]] are used.<ref name="G2 standard">{{cite web| url=http://g2.trillinux.org/index.php?title=Gnutella2_Standard| title=Gnutella2 Standard| publisher=Gnutella2 wiki| access-date=2007-11-07| archive-date=2007-12-19| archive-url=https://web.archive.org/web/20071219232205/http://g2.trillinux.org/index.php?title=Gnutella2_Standard| url-status=live}}</ref>

To create a more [[Robustness (computer science)|robust]] and complete system for searching, Gnutella2 also has a [[metadata]] system for more complete labeling, rating, and quality information to be given in the search results than would simply be gathered by the file names.<ref>{{cite web| url=http://g2.trillinux.org/index.php?title=Simple_Query_Language_and_Metadata| title=Simple Query Language and Metadata| publisher=Gnutella2 Wiki| access-date=2007-11-07| archive-date=2007-12-19| archive-url=https://web.archive.org/web/20071219232217/http://g2.trillinux.org/index.php?title=Simple_Query_Language_and_Metadata| url-status=live}}</ref> Nodes can even share this information after they have deleted the file, allowing users to mark [[Computer virus|viruses]] and [[Computer worm|worms]] on the network, without requiring them to keep a copy.

Gnutella2 also utilizes [[HTTP compression|compression]] in its network connections to reduce the bandwidth used by the network.<ref name="G2 standard"/>

[[Shareaza]] has the additional feature to request previews of [[image]]s and [[Video file format|video]]s though only FilesScope takes limited advantage of this.

[[gtk-gnutella]] extended the protocol to further reduce the gap between [[Gnutella]] and G2.  In particular, the semi-reliable UDP layer was enhanced to add cumulative and extended acknowledgments in a way that is backward compatible with legacy G2 clients.<ref>{{cite web |url=http://g2.doxu.org/index.php/UDP_Transceiver#Extension_Proposal |title=UDP Transceiver - Gnutella2 |publisher=G2.doxu.org |access-date=2014-08-06 |archive-date=2014-07-19 |archive-url=https://web.archive.org/web/20140719083104/http://g2.doxu.org/index.php/UDP_Transceiver#Extension_Proposal |url-status=live }}</ref> Further extensions include the "A" string in /Q2/I <ref>{{cite web |url=http://g2.doxu.org/index.php/Q2#.2FQ2.2FI_-_Interest |title=Q2 - Gnutella2 |publisher=G2.doxu.org |date=2014-02-25 |access-date=2014-08-06 |archive-date=2014-07-14 |archive-url=https://web.archive.org/web/20140714124310/http://g2.doxu.org/index.php/Q2#.2FQ2.2FI_-_Interest |url-status=live }}</ref> and the introduction of /QH2/H/ALT, /QH2/H/PART/MT, /QH2/HN, /QH2/BH and /QH2/G1 in the query hits.<ref>{{cite web |url=http://g2.doxu.org/index.php/QH2 |title=QH2 - Gnutella2 |publisher=G2.doxu.org |date=2014-03-12 |access-date=2014-08-06 |archive-date=2013-12-13 |archive-url=https://web.archive.org/web/20131213030530/http://g2.doxu.org/index.php/QH2 |url-status=live }}</ref>