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Understanding BitComet

What is BitComet?

BitComet is a powerful, clean, fast, and easy-to-use BitTorrent client running on Windows. You can download torrents, as well as HTTP/FTP and eDonkey/eMule files, using BitComet. Read more about BitComet.


What platform does BitComet support?

Windows only. (Windows 98/Me/2000/XP/2003/Vista/2008)

It supports Unicode in Windows2000/XP, and supports ICS/ICF, UPnP in Windows XP.


Which port does BitComet use?

There are 65,536 ports available to you, and you can choose any one of them for your listen port. No port is better than any other. There is no “BitTorrent port”, or port(s) that BitComet is expected to use, should use, must use or would obtain any advantage from using.

It is better and less confusing to others if you select a port that isn't already commonly used for something else (Example: port 80 is commonly used for web servers, but if you're not running a web server, there's no technological reason why you couldn't use 80. It simply confuses others if you do). Ports above 60000 are not customarily used by something else, and are recommended. (Port 65432 is a good choice because it's pretty hard to forget.)

BitComet uses a single TCP port to “listen” for other peers wishing to contact it. (As of version. 0.55, BitComet uses the same port for TCP and UDP protocols.)

When you select a listen port, your port number is passed to the tracker and to the DHT network for distribution, so that other peers will know which port to contact you on. Your port number need not remain the same from one session to another, and BitComet includes the ability to select a port at random for each session.

   It is up to you to make certain your listen port is not being blocked by a firewall.
   Do not connect to the Internet without a working firewall. 
   Your system is likely be infected very quickly, if you connect without a firewall.

This means that you need to configure your firewall(s) to open your chosen listen port, NOT to hunt for a port that your firewall isn't blocking.

If you are behind a firewall which you cannot control (as is the case with most types of wireless connections, and connections that come with the facility (hotels, dormitories, office buildings), then all ports are probably blocked and you must use “no listen port” mode. This will be considerably slower, but will still work.


I am new to BitComet and to torrents, so how do I use it?

Peers, seeds, torrent, tracker, DHT, Peer Exchange (PEX), Magnet Links; what are all these things?

Click on the following link to see explanations for all these terms: Peers, seeds, torrent, tracker, DHT, Peer Exchange (PEX), Magnet Links.


What do the icons next to the task mean?

: Downloading incomplete .torrent file.
: Downloading incomplete files (BT task, HTTP/FTP task)
: BT task is stopped and incomplete
: BT task is stopped and complete
: BT task Hash Checking
: Seeding complete BT file
: Error occurred, task stopped. (BT & HTTP/FTP task) 【Tip: Hover the mouse over theto see error details in the latest versions of BitComet.】Several things can cause errors; please see this topic for details on the possible causes and solutions.
: HTTP/FTP Task Paused and incomplete
: HTTP/FTP Task Stopped and Complete
: HTTP/FTP or BT task that is waiting in queue for downloading or seeding. (E.g. if you set “Max Concurrent downloading BT task number” as 2, and you started 5 BT tasks, then three BT tasks will wait in a queue to start downloading. The same goes for the HTTP/FTP tasks.)


What's the meaning of the line "[+]-----bt_disconnected(n)" in the Peer tab --> IP column?

This tells you how many peers(n) the client has failed to connect. It's for your information, but there's nothing you need to do about it.


What is "taskname.piece_part.bc!" among my downloaded files?

If you're downloading some, but not all of the files in a torrent, BitComet must create a file containing data about where the file ends within a transferred piece. (Don't worry about it). This data will be saved in a special file: taskname.piece_part.bc!.

Well, if you simply must know, BitTorrent clients exchange data which has been broken down into evenly-sized pieces. That is, at the creation time of a torrent the torrent-making program, virtually concatenates all the files in the torrent, then it divides the resulting data chunk into evenly sized pieces, which are the trading currency of BT protocol. Piece boundaries do not usually match file boundaries, so a piece can contain the end of one file and the beginning of another file. BitTorrent must download the entire piece, probably including the beginning part of a file that was not selected. Hash-checking for errors is done on the entire piece, so the extra data can't be discarded yet. This extra data is stored in these additional files. These files must be present as long as the task is active in BitComet (as well as if, in the future, you need to reseed the torrent). They are not required in order to use the files after downloading. BitComet versions prior to v.1.02 do not use this type of boundary data file and could, in some circumstances, cause valid files to fail a hash-check.

Please note that also, in version 0.85 or above, BitComet introduced an Align File to Piece Boundary function into its Torrent Maker, as a previous means to deal with pieces overlapping two different files. When enabled, the function makes sure that BT pieces do not span over more files. It does that by inserting empty padding files of the exact size as the remainder of space into every “last” piece for all the files into the torrent.


How do I change my default download directory?

Please make sure there is no task running before you change the default download directory. There are two ways to change the download directory for all tasks:

  • Go to Options → Directories → Directories (or in Preferences → Task, for older versions), click the browse button to change another directory as the default download directory. Or
  • In the main bar, click Tools → Default Directory → Other Directory, and choose the destination you want to be as download directory.

Note: Once one task is started, the above operation will be invalid for that task. If you want to change a saved location for a task that is running, try the following two ways:

  • Stop the task, right-click it and choose: Files Move to… (Version 0.71 and later);
  • Stop the task, right-click it and choose Properties. Then on the General tab you change the Save path parameter to whatever you want. When you hit the OK button a prompt will appear asking you to choose whether to move the downloaded files to the new location. (Version 1.07 and later).

What is UPnP Auto Port Mapping?

To get the best speed, P2P applications like BitComet need a public listening port. However, if you use a router with an active firewall, or use Windows Internet Connection Sharing (ICS), you will need to configure port mapping (port forwarding from gateway/router or sharing computer, to your computer). BitComet takes advantage of UPnP (Universal Plug and Play) technology, and will attempt to automatically configure the port mapping for you when the session begins.

Please note: UPnP is only supported in Windows XP or above, and your hardware router must both support UPnP and have it enabled. By default, BitComet won't release the port-mapping when you exit, but you may configure it to do so in Options → Connections Dialogs. This technology has not been consistently implemented among manufacturers and sometimes does not work. In that event, the router must be manually configured.

If you do not use a router and do not use ICS, then port-forwarding, UPnP and port-mapping do not apply to you. The option should be disabled in BitComet. Read more here about UPnP port mapping.


What is Disk Cache in BitComet?

The function of our Intelligent Disk Cache is an important reason to choose BitComet. The disk-cache is designed to speed up downloads and reduce mechanical wear of the hard-disk. When the transfer rate exceeds a certain value, a carefully-designed disk cache mechanism in BitComet buffers writing to the hard disk. This can greatly improve performance, by decreasing the frequency of Reads/Writes to disk. This also contributes to longer service life of your disk. Some statistics of the operation of the cache are available in the Log View (e.g. Hit/Ratio, Read/Write Request Frequency, Actual Disk Read/Write Frequency) where you can see the improved performance.


What is NAT Traversal in BitComet?

Network Address Translation means that a packet passes through a gateway that changes its IP address when it passes traffic onwards either way. If you are behind such a gateway then it isn't possible to initiate contact with you directly – all contact with you must be through the gateway.

This means that other peers can't initiate contact with you, because while the gateway knows where to route replies to your requests, it doesn't know where on the network to send this unsolicited incoming traffic. Your computer's address is not “publicly routable”, but must be routed privately, by that gateway, on its own subnetwork.

Non-firewalled clients and clients on publicly routable IP addresses are able to help clients which ARE behind such a gateway, to communicate in spite of this, when transferring the same torrent.

A server is needed to assist in setting up this communication (so that it “looks like” a reply to both parties) which server BitComet provides for its clients. BitComet does an even better job for users behind such gateways, by enabling them to contact each other via one-way UDP. If other peers can initiate contact with you despite the gateway, your download rate will increase because you can now connect with more peers. NAT traversal is not as fast as having an open listen port, but is notably faster than no-listen-port mode.

Bitcomet needs no configuration to auto-detect your Internet connection (to find out if you are behind a translating gateway, and will try to do this automatically. You can control this feature in the Options →Connections→Port Mapping dialog.

Note: Not all versions of BitComet currently support NAT Traversal

'History of NAT Traversal in BitComet' - (from release notes)
Nat Traversal was removed from BitComet v. 1.03 (Core Improved: removed NAT Traversal via UDP, in order to improve TCP transfer efficiency)
Nat Traversal was automatically disabled when not needed in v. 0.90 (Core Improved: disabled NAT Traversal via UDP automatically for WAN IP user, in order to improve TCP transfer efficiency)
Nat Traversal was updated in v. 0.86 (Core Improved: improved NAT Traversal via UDP component, decreased CPU usage)
Nat Traversal reintroduced with Encryption enabled in v. 0.83 (Core Improved: reconstruction of NAT Traversal via UDP using encryption connections)
Nat Traversal was removed, temporarily, in v. 0.71 (Core change: Chat, Proxy, NAT Traversal via UDP, IP block rules removed temporarily)
Early implementation of this technology was on an experimental basis in v.0.54 (Core Improved: NAT pass-through by UDP! (still experimental)


What does the peer status "DUdu" or "IciC" mean?

D— downloading data from peer now

U— uploading data from peer now

d— I request data from peer, want to download from peer ( peer has data that I need )

u— peer request data from me, asking for me to upload ( I have data that the peer needs )

In the latter versions, replaced with the symbols: {I, i, C, c, _}. See here a full description of all status meanings for different combinations of these symbols.


What is P2PCache (in Advanced Options)?

P2PCache can enable your Internet Service Provider to improve content delivery and acceleration of internet traffic by using caching technologies. (If your ISP does not support P2PCache, then it will not work for you.)

For further information, please visit www.p2pcache.org


What to do when garbled text appears in the CometID pane

This problem is usually caused by the corruption of Outlook. You may also find that any .mht file can't be open by IE correctly. Please try Method 1 first, if the problem still exists, please then try method 2.

Method 1:
Step[1]: Windows Start menu → run → regsvr32 inetcomm.dll
Step[2]: If last step failed due to missing inetcomm.dll, try to restore it from c:\windows\system32\dllcache\ to c:\windows\system32\
Step[3]: Repeat step[1], if still faild due to “module missing”, try to find msoert2.dll and inetres.dll, copy them to c:\windows\system32\
Step[4]: Repeat step[1], and it should work.

Method 2:
Download the mht file from here, extract it and double-click the file named mht.reg.


How to change the default media player to play/preview a file from the task list?

Go to OptionsAdvanced, click on ui.preview_program_path to select the default program to play/preview the media file in task list.

More information about preview while downloading can be read HERE.

What is the encryption option in BitComet and what effects does it have on the operation of the client?

The encryption option in BitComet (just as in other clients) has the purpose of obfuscating BitTorrent traffic in order to render it undetectable (or at least less detectable) to traffic shaping applications which some ISPs use, in order to throttle BitTorrent traffic.
BitComet uses the MSE/PE encryption method introduced by Azureus and (when encryption is activated) it encrypts both protocol header and message payload.

For more detailed information on this subject, as well as for a description of the effect each encryption level chosen in the client has on connections read this topic.

What is web-seeding and how can I make use of it?

Simply put, web-seeding is a technology which allows a BitTorrent swarm to use a web server as a peer of the swarm. In other words if you have content you want to distribute through a web server, you can use web-seeding to create a BitTorrent swarm around that content and offload the burden from the web-server, as it would act a simple seed in that swarm maintaining it alive for as long as you share that content, but as soon as there are more than one downloaders, they will actually be peers in the swarm and download all from each other and the server (thus sharing the load) not all of them just from the server.

Currently there are two web-seeding specifications available out there:

  • BitTornado style web-seeding (needs a special web server to be set up, which serves content by info-hash and piece rather than file name);
  • GetRight style web-seeding (can use a standard HTTP web server, with no additional setup required).

In order to benefit from the presence of a web-seeding server in the torrent swarm, a BitTorrent client must support web-seeding.
BitComet supports GetRight style web-seeding since v.1.14. For details on how to create a torrent with a web-seeding server check this topic.


What is Anonymous Download?

Anonymous Download service is basically a private connection to a high-speed seedbox, downloading all torrents anonymously. Instead of only accelerating regular BitTorrent transfers through Bitcomet’s servers, the “anonymous” downloads will be handled by BitComet’s VIP servers exclusively, hiding the IP-address of the user.

If VIP members enable anonymous downloads the remote servers will initiate all peer and tracker communications and download the data on behalf of the VIP member, so the member’s actual IP address isn’t shared with any of the peers or trackers. Members who enable Anonymous Download will only get data tranfered from VIP server and LT-Seed(if enabled).


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understanding_bitcomet.txt · Last modified: 2011/08/23 06:43 by ariel
 
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