Brief Explanation of P2P download principles

My friend gave me a BT seed and found out that it was the download link of the video. So I asked my friend, "why don't I give the video to the seed ." My friend was speechless and looked at me like an alien creature, so I was unwilling to find out why? The excerpt is as follows:

You have used BT. Now BT can be said to be the most widely used way of file sharing and dissemination After lan, FTP, and HTTP. It can be said that it has been integrated into the lives of the majority of Internet users. BT, full name of BitTorrent, is a P2P download method. Common P2P in addition to BT is eMule (commonly known as the electricity generator, of course, also called the Donkey --, see the difference: http://www.quanyo.com/zt/emule/618.shtml ).

Why can P2P be popular in the world in such a short period of time? Here we should start with its principle. Before introducing the principles of P2P, it is necessary to explain the traditional HTTP download.

Traditional HTTP downloads directly copy data from the server (sever) to the client (PC). The transmission speed is limited by bandwidth. [What is bandwidth? For example, if you use 2 m ADSL, the bandwidth is 2 m. 2 m here refers to 2 Mbps, that is, 250kb/s (2000/8 ). Do you think you have reached the bandwidth when downloading?] because there are more than one client connected to the server, the server bandwidth will be shared [of course, the server bandwidth is much larger than the bandwidth of other users, and it is generally fiber optic; if there are no special restrictions, the server bandwidth is equal.] Assume that the server bandwidth is 100 Mbps, that is, 100 kb/s, and there are client connections, the bandwidth shared by each server is kb/s. It can be seen that the client bandwidth is not fully utilized, in order to make up for this situation, flashget invented multi-thread download and won't go into details here.

But in reality, the situation is much more serious, and the number of visits to large software download sites can be Baidu. There are more and more Internet users. This situation needs to change. P2P is born under such circumstances. The following is P2P:

 

During P2P download, the server (sever) no longer serves as the server in the previous HTTP download. It is only responsible for transferring the basic information of the file between clients and does not store any files. The P2P software divides the file into several blocks, which are assumed to be ~ Z block, the client can download K segments before downloading other, there is no fixed order, as long as the final file is "filled" to complete. The advantage is that when HTTP download goes down, you will not be able to complete it (although there are also resumable transfers, but now there are more and more random addresses -- + ), you don't have to worry about this when using P2P. Even if you don't have m segments, you only need to wait for M segments to be sent to you, you are also sharing the part you have completed to those who do not have this block. Of course, the transmission speed between a single group of clients is very slow, but the more the number of connected users, the theoretical number of users connected to a client can increase, and the download speed is increased, it not only makes full use of bandwidth but also ensures integrity.

The following is a supplement:

1. There is a "seed" in P2P transmission. The so-called "Seed" refers to the people who have downloaded the files, and they have all the blocks. The person who publishes resources is the original seed, and the block obtained from the client that is first connected is from his side until the new seed appears. When the seed disappears, two conditions will occur. One is that the block is missing, and the rest of the client can download to the same progress at most; the other is that the block is exactly complete, it is only distributed on different clients. In this way, someone will download it and become a seed. Therefore, seed is very important. If you have downloaded it, you must develop it on your own. This is the default rule in the P2P world.

2. Upload. When the number of connections is guaranteed, the download speed depends on your bandwidth. However, if you restrict upload, your download speed will be affected. Generally, you can use the software to automatically detect the available upload/download speed, and then slightly limit the upload speed. This will not be too difficult to browse the Web page while downloading.

3. For Intranet and Internet, ICS, UPnP, port ing, etc., please refer to: http://bbs.btchina.net/showthread.php? S = 48fde9c000f98be54974c9538ee9a2fa & threadid = 459806.

4. Common P2P software:

Authentic type: bitcomet, bitspirit, uTorrent, BitTorrent plus! Ii. eMule

Viewing side bottom: funshion, totolook, Blin

Emerging models: thunder and flashget

 

From: http://blog.chinaunix.net/uid-20446794-id-1677434.html

Brief Explanation of P2P download principles