After AR28 undergoes NAT translation, it is very slow that PC downloads via BIT.

Publication Date:  2012-07-27 Views:  57 Downloads:  0
Issue Description
Once AR28 undergoes NAT, PC in private network downloads in rate of only dozens of Kbye/s via BIT; however, the same PC uses public network IP address to access network, its download rate by BIT could reach hundreds of Kbye/s.

Alarm Information
No

Handling Process
Configure the public network interface of the router with nat server, providing a static TCP port map for BIT listening port of PC in private network; thus, the BIT listening port number is mapped to the IP address of public network:

nat server protocol tcp global X.X.X.X(public network address)15338 inside Y.Y.Y.Y(private network address) 15338listening port

When PC at private network uses BIT to download files, it could initiate BIT connection via seed, and other BIT download operators could establish BIT connections with PC in private network via listening port mapped, so the more the number of BIT connections, the faster the download speed. 

Root Cause

1. The principle of BIT download: the more the connections, the faster the download; additionally, you could upload files while downloading. BIT has two types of connections: one is that initiated by PC, and the other is connection with PC initiated by other download operators.  BIT listening port functions as the port connecting with other download operators.


2. PC at public network could initiate connection with other BIT download operators via seed for download and upload of files, and other BIT download operators could establish connection with BIT listening port of PC at public network for download and upload of files. However, the BIT listening port of PC at private network is invisible at public network, so it could only establish connection with other BIT download operators via seed for download and upload of files. Consequently, the number of BIT connections of PC at private network is less than that at public network, which causes the BIT download rate of PC at private network to be slower than that at public network.  



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