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IV. Speed Modes Up Close
30. Quick Optimization Mode - Custom Settings
For advanced users, network engineers, and those used to being able to configure their own settings, ActiveSpeed's Detailed Optimization options are perfect. These manual settings are not intended for use by the average user. You will need to understand what these setting represent to be able to successfully optimize your Internet.
However, any adverse settings can easily be fixed just by re-optimizing under the Intelligent Mode, QuickOptimize Mode, or Standard Mode; so feel free to try tweaking your Internet speeds with these options in complete safety.
Descriptions of MTU, PMTU, TTL, and RWIN are again listed below.
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MTU:
 When you download a file, it is broken into many packets of data before it is sent over the World Wide Web to your computer (where it is then reassembled). The size of these packets is called your MTU value, or the Maximum Transfer Unit. Your downloads will be slow and disappointing if this value is not set correctly.
Each packet that is sent over the Internet contains a header which contains a variety of information about the packet, source, and destination. Setting your computer's MTU value too low would make downloading less efficient because a greater percentage of the packet is taken up by the packet header. However, setting the MTU too high can also decrease efficiency. Other computers on the Internet might not be able to handle MTU values of a certain size. If you set your computer's MTU value too high, some computers along the delivery path would be required to break these packets into smaller pieces before accepting them and passing them to the next computer. This "Stop. Break. Go." processing of packets can dramatically slow down data transfers.
It is usually best to let ActiveSpeed figure out and select this setting for you by using the Intelligent Mode. However, the QuickOptimization panel in ActiveSpeed will let you select the setting you want quicker, without having to go through the entire Learning Phase again. And expert users and experienced network engineers may make their own adjustments by using the Detailed Optimization panel.
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RWIN:
RWIN stands for Receive WINdow. This "window" is a buffer, or holding area, that your computer uses to sort the packets of data received when something is downloaded.
Each packet of data that your computer receives needs to be accepted in a certain order before the file you are downloading can be "put back together" on your end. Although these packets of data are sent out in the correct order, sometimes the packets can take different paths and arrive out of order or get lost altogether.
When the next packet of data your computer receives is not the right one (according to its order), your computer has to stop and send a request back to ask for the missing packet. This request takes time. However, because of the RWIN buffer, your computer downloads the data packets to a storage area first. This storage area can hold more than one packet at a time (usually four to six). If the data is received out of order, your computer will continue to download the data packets to this holding area, waiting for the packet that is supposed to come next. Your computer will only have to send a request for the missing packet if your RWIN fills before the needed data packet arrives.
It takes significantly less time for the data packets to pass from your RWIN buffer to your application's memory than it takes for your computer to make a request for a needed data packet. However, setting your RWIN size too large would result in a slower download process. Your computer's RWIN buffer would have to fill completely before it realized that a packet of data was missing (rather than just out of order) and request a retransmission of the packet.
Custom RWIN settings may have an adverse effect and should only be used by expert users and network engineers.
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TTL:
When you download a file, it is broken into many packets of data before it is sent to your computer (where it is then reassembled). Not all of these data packets use the same path along the Internet to your computer. Some packets may not arrive in a reasonable length of time and some may even become lost. An arrangement of incorrect routing tables could cause a packet to loop endlessly and congest the network. Not good!
Because of this, packets of data are set with an "expiration date" and will be discarded after a certain number of hops (a hop occurs every time a packet is sent from one computer to the next along a path). TTL stands for Time To Live. After a packet is discarded, your computer will have to request the missing packet(s) again from the originator.
Setting your TTL too low would make it impossible for some packets to reach their destination. Setting it too high would cause the network to become congested. This value is set automatically by all three Optimization Modes, although expert users and network engineers are free to make their own adjustments on the Detailed Optimization tab.
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PMTU:
The PMTU settings can be selected, however they are rarely used.
Black Hole Detection detects troublesome routers and attempts to choose another one -- so if you are having connection trouble, you should select this PMTU option.
Automatic Discovery means that your system will attempt to come to an agreement with the server or router, regarding the packet size. However, this agreement may not always be the optimal size.
We recommend using the Intelligent Mode or QuickOptimize Mode in ActiveSpeed. However, expert users and network engineers may make their own adjustments on the Detailed Optimization tab.
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