Classification and overview of existing P2P protocols

(1) Common P2P protocols
1. Napster: the world's first large-scale P2P application network; centralized and collapsed.
Napster, a popular sharing service at the time, is mainly used to find MP3 files. It has a server used to store the link location of MP3 files and provide retrieval, while the real MP3 files are stored in
On thousands of PCs, files searched for are directly shared among PCs through P2P. The disadvantage of this method is that a server is needed, and the competition for MP3 file copyright is booming.
On behalf of Napster, Napster soon became the target of the public, and was forced to close due to copyright infringement by numerous recording companies. Of course, the server will no longer exist once it passes through Napster.

2. Gnutella and gnutella2 (gnutella2 is an improvement and extension of Gnutella): Open source. The first non-central, non-structured P2P network, and file query adopts the flood mode.
Gnutella learned from Napster's failure and pushed the idea of P2P further: it does not have a central directory server, and all the information is stored on a personal computer. Once the software
is installed, the user immediately turns his computer into a server capable of providing complete directory and file services, and will automatically search for other similar servers, thus forming a super server network composed of countless PCs. The server and client of the traditional
network are redefined in front of it.
3. FastTrack:
the first client is Kazaa. The Protocol is similar to Gnutella. The largest user network in-03 years, and the third place in 05 years. The reason for the decline is that this network cannot be used by many users at the same time, and there are Copyright Owners Pollution and spyware problems.
imesh is also based on FastTrack.
4. eDonkey, Overnet, and Kad:
when using P2P software, selfish people only want to "get", rather than "share ", the development of P2P has encountered the bottleneck of Consciousness Development. However, a "donkey" quickly changed the game rules. This is the e-donkey-eDonkey, which introduced the forced sharing mechanism.
edeonkey divides network nodes into the server layer and customer layer, and blocks files to improve the download speed. The most popular P2P client Program In the eDonkey network is
edonkey2000 and eMule. EMule is the successor of eDonkey, but it is better. It uses DHT to build the underlying network topology. Currently, it is very popular with P2P file sharing software
.
Overnet is designed to replace eDonkey. It has no central server, but has fewer users than eDonkey.
the kademlia protocol is called the KAD network and uses UDP for communication. Similar to Overnet, it is used by almost only eDonkey users.
5. BitTorrent: uses a distributed server to provide a hybrid P2P network that shares file indexes and downloads files in multiple parts.
the download speed is high and the search function is not available. The seed has a timeliness. It combines the stability of the central directory server with optimized distributed file management.

BitTorrent means PNP download, also called abnormal download. BT download is an extension of P2P download and PP download. The two P Pairs in PNP refer to the personal computers of netizens and are abstracted as a point on the Internet. N is 1, 2, 3 ,...... N in N is infinite. PNP means many-to-many connections between a PC and a PC over the network. Why is BT download commonly known as abnormal download? This is because this download method is different from the traditional method of relying solely on the website server as the download source. It adopts the idea that everyone's computer is a server. The more people download, the more people share, the faster the download speed is. The BitTorrent download tool is the latest P2P download tool. It adopts the Multi-Point-to-multi-point principle. Generally, BitTorrent is called abnormal download. This software is quite special. Generally, files or software are downloaded from the HTTP site or FTP site. If many people download the software at the same time, based on the factors of the server bandwidth, the speed slows down a lot, but the software is different. On the contrary, the more people you download at the same time, the faster you download, because it adopts the Multi-Point-to-multi-point transmission principle.

6. Direct Connect:
A protocol commonly used in small networks and intra-university networks. It is applicable to small network environments. DC ++ is a common client.
7. Ares: similar to the Gnutella network.

(2) main fields and development directions of existing P2P technologies
(1) provides P2P networks that share files and other content, such as Napster, gnotella, Freenet, CAN, eDonkey, eMule, and BitTorrent.
(2) P2P-based collaborative processing and service sharing platforms, such as JXTA, Magi, groove, and. netmy service.
(3) instant messaging, including ICQ, OICQ, and Yahoo Messenger.
(4) Secure P2P communication and information sharing. Leveraging P2P's decentralized features, it can provide new technical means for privacy protection and anonymous communication. For example, cliquenet, crowds, and onion routing.
(5) Speech and streaming media: due to the use of P2P technology, a large number of users access streaming media servers at the same time, and the server will not be paralyzed due to heavy load. Skype and coolstream are typical examples.

(6) grid computing, mining P2P distributed computing capabilities. P2P technology is used to centralize idle CPU time segments, memory space, and hard disk space of computers connected to the network to replace "supercomputer
". For example, SETI @ Home, avaki, and popular
Power, distributed.net, etc. The purpose of grid computing is to connect tens of thousands of computing nodes all over the world through the high-speed internet and organize them into a giant system.
It can complete complex computing tasks transparently and efficiently.
(7) IBM, Microsoft, and Arba are also working on a project named UDDI to standardize B2B e-commerce.
(8) eazel is building the next-generation Linux Desktop.
(9) jabber has developed an XML-based and open instant messaging standard. Jabber is considered to be a standard for the future use of P2P data exchange.
(10) groove created by developers of Lotus Notes tries to "help people communicate in a new way ".
(11) intel is also promoting its P2P technology to help more effectively use the computing power of chips.
(3) P2P resource locating
To locate resources in a P2P network, you must first solve the problem. Generally, three methods are used:
(1) centralized indexing
Each node registers its shared content to one or more centralized directory servers. When searching for resources, first locate the resource through the server, and then directly communicate between the two nodes. For example, early Napster. This type of network is easy to implement, but it often requires support from large directory servers, and the robustness of the system is not good.
(2) broadcast mode
Without any index information, content submission and Content Search are directly broadcast and transmitted through adjacent nodes. For example, Gnutella. In general, P2P networks using this method have high requirements on the bandwidth of participating nodes.
(3) Dynamic hash table

The above two positioning methods can be selected based on different P2P application environments, but DHT (Distributed Hash) is widely favored.
Table. To some extent, the DHT-Based P2P network can directly locate the content. A conflicting problem is that if a node provides shared content, the more complex the content is
The more complex the hash function is, the more complex the network topology is. However, if the content is simple, the content cannot be positioned based on the content. Currently, most DHT-Based P2P
The expression of shared content provided by the network to the node is very simple, generally only for the file name.
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