Optimizing the Transmission Bittorrent Client for Speed

Optimizing a Bittorrent client, like Transmission, for speed is an easy process: Choose a proper port, clear that port through software firewall and router and adjust internal settings based upon upload capacity of the internet connection.  I am on a Windows system, so I cannot install Transmission.  The screenshots of Transmission herein have been obtained from the web and the numbers within will not match the numbers shown in the Upload Calcualtor, below.  Although I do not have Transmission installed, the steps set forth herein are uniformly suggested by developers of bittorrent programs and should result in increased download speed in your Transmission as the principles are the same for all bittorrent clients.  Avoid any program which claims to optimize speed in Transmission as those programs can do no more than these basic steps (probably less) and generally contain spyware and adware.

Note When viewing this guide in Internet Explorer the Mac command key symbol appears as a box.  I do not know why yet.
This guide is now for Transmission 1.33, thanks to the anonymous poster below who provided the screen shots.

Choosing a proper port  Azureus-Wiki:  Port is Blacklisted
A single port within the 49152-65534 range should be chosen to avoid ISP blocks and possible conflicts with other applications.  The setting of the port in Transmission is at Preferences (⌘ + ,) or (Ctrl+,)>Network -"Network: Peer listening port":

Forwarding the Port:  Essentially this is about setting permission in your software firewall and router for your bittorrent client to send and receive communications.

Software firewall – The best place to look is in the help file of your software firewall. There are some guides at the µTorrent forum (substitute Vuze/Transmission when necessary) and also at PortForward.com Firewall Guides (choose firewall and then program- see Note).  Communications should be allowed for TCP and UDP in both directions.

Router (or modem with firewall) - There are two choices here, Universal Plug n Play (UPnP) or manual forwarding. The choice is basically convenience versus security. UPnP is easy, but has security issues. A router blocks unknown incoming connections at the hardware level and provides significant protection for your computer. Enabling UPnP allows any program to create a port mapping through the router without consent of the owner. I would suggest to at least try manual port forwarding through the router as it is not as difficult as it may seem (especially with the guides) and is safer. In any event, read the following section on UPnP as it is an either/or situation and UPnP will have to be disabled if manually forwarding. 

UPnP (NAT-PMP - Apple)  Must be enabled/disabled in client and router.  In Transmission this setting is at Preferences (⌘ + ,) or (Ctrl+,)>Network “Automatically Map Port” 

Manual Port Forwarding:  Portforward.com Router Index

Again, the router documentation is the best place to look for this information. PortForward.com Router Index has guides for almost all routers and bittorrent programs. Choose the make and model of your router and then your bittorrent program and you will be taken to a page with a guide specific to your client and router.  Many of the bittorrent client screenshots will be out of date as the clients are constantly updated, but the information should still apply.  Make certain to also check the Static IP Guide.

Note:  PortForward does not have guides specific to Transmission. Transmission users can use the guides for Azureus/uTorrent substituting Transmission for Azureus/uTorrent. Also, the Transmission help file, along with the firewall or router manuals may contain helpful information.

When finished, you can test to see if your port is properly forwarded at Can you see me?.

Adjusting Internal Settings:  This involves taking a speed test, using the calculator to determine the settings that should be used and inputing those settings in your client.  The most important setting is to cap upload at no more than 80% of your overall upload capacity as there needs to be room for communications to the tracker or else download speeds will suffer.  Download could also be capped (at 90%), but this is not necessary as this is rarely an issue.

Speed Test: Speedtest.net
First the upload capacity of your internet connection must be determined by taking an online speed test. You should stop all internet activity, including torrents, before taking the test and the test should be taken a few times to obtain a reliable average. Speedtest.net has test locations worldwide and will highlight the one closest to you. Note that the result of Speedtest.net is in kilobits (kb) and bittorrent clients show speeds in kilobytes (kB). This is important as 8kb = 1kB. See Azureus-Wiki: Data Units

Calculator:  Azureus Upload Settings Calculator
Once you have an average upload speed for your connection go to the online Azureus Upload Settings Calculator. Although designed for Azureus, this calculator will work for all bittorrent clients. Enter your average upload speed in the appropriate box and the calculator will automatically give the proper figures to adjust various options in Transmission

Transmission Settings

Preferences (⌘ + ,) or (Ctrl+,)>Bandwidth

The "Speed Limit Mode" is a scheduler and should not be enabled at this time.  If you are with and ISP that limits bandwidth usage at certain times of day, this would be useful.

Preferences (⌘ + ,) or (Ctrl+,)>Peers

The three options below the connections options should be enabled.  Peer Exchange (PEX) allows Transmission to seek seeds/peers outside of the tracker.  This will obviously help torrent health and speeds.  Transmission does not have DHT (Distributed Hash Table) capability at this time.  DHT, like PEX seeks additional seeds/peers outside of the tracker.  In my readings at their forum, it appears that there recently has been some work on this and it may be included in the future.  However, it is not one of their priorities.
The "Prefer Encrypted Peers" option means that Transmission will accept all seeds/peers, but will first attempt to contact via an encrypted connection.  Clients like Vuze/uTorrent will switch to encrypted automatically upon such contact.
The "Prevent known bad peers from connecting" option utilizes a blocklist of known anti-P2P IPs, to prevent them from connecting and possibly interfering with transfers.  I do not have information on setting up the list as of yet.

Preferences (⌘ + ,) or (Ctrl+,)>Transfers>Management

Transmission does not have the "Max Active Torrents" setting, enter the number in the Seeding maximum above.

The above settings should work well most of the time.  Downloads of individual torrents depends on other factors.  See Good Torrents

After setting up your Transmission, you might want to check out my article Searching for Torrents, which lists, with comments, some of the more popular torrent search sites.  I have also prepared an article Finding Legal (and Free) Torrents which lists, with comments, sites which offer only legally downloadable and distributable content.

If you have any questions or suggestions, you may post in the comments below or in our Bittorrent Client forum.

This guide was created on August 1, 2008.