Traffic-Shaping
Traffic shaping ( also traffic shaping ) refers to a type of queue management in packet switched data networks are delayed or discarded in the data packets according to certain criteria in order to meet specific requirement profiles. This function is carried out by a network scheduler and is basically a form of data rate limitation. Traffic Shaping is unidirectional, ie it works as opposed to flow control without control information of the opposite side.
With traffic shaping network traffic is divided into different areas. These classifications are, for example, applications and protocols, transmission directions between client and host, time and type of connection.
Example of use
In the Transmission Control Protocol (TCP ) of the receipt of a certain amount of data from the opposite side must be confirmed before the sender is allowed to send new data. If these receipts not fast enough, the sender has to wait and there will be delays and declines the transfer rate. Especially for ADSL, it may happen that you slow down a download by the return channel (which in any case the smaller bandwidth has ) overloaded with an upload, so that there is not enough transmission capacity for immediate shipment of the receipts of the downloads available. The acknowledgment packets are buffered ( inside the machine and also within the DSL modem ) and have, although they are very small, at worst, wait until all packets generated from them have been sent. The larger the buffer the higher the resulting delay through them. In continuous overloading of the power capacity it also happens that packets are discarded, which increases the delay again.
To compensate for this effect, raise some DSL driver or tuning applications, the TCP window size, so that the sender can send more data before it must wait for an acknowledgment. This advantage is however the expense of a significant increase in the latency ( ping times ), so that surfing during a data transfer is unusually slow. ( If the TCP window size is adjusted to about 65,535 bytes, TCP window scaling must be activated simultaneously, since otherwise the TCP window size increased throughput can be achieved accordingly. Without TCP window scaling, the maximum throughput of about 5 mbps with 100 ms round-trip time. )
Traffic shaping is now analyzing the resulting data traffic in both directions (with the greater effect in uploads) and sorts the waiting data packets so that the data transfer is less hindered in the opposite direction. If under the to be mailed packages are those that should only confirm the receipt of data, they will be brought forward, so sent first. Thus, the phases are shortened, in which the other party does not send data, the transmission rate increases. As a side effect is largely prevented, that of all these packets are dropped due to congestion. To maximize this effect, as well as the entire data stream is slowed down, so that the computer sends its data a little slower than the DSL modem it can transmit. This means that the buffer in the DSL modem are always empty and data sent by the computer to the modem, be transmitted immediately. Means, there are no delays in the buffer in the modem. This has the following advantages:
- Higher download rate despite Uploads
- Higher download rate of some downloads and uploads
- Shorter response times, eg surfing ( better ping times, important eg for online games)
Algorithms
The most widely used algorithms for queue management are the leaky bucket algorithm and the token bucket algorithm.
Hardware / provider used
The offered router firmware can be based on Linux, BSD or VxWorks. For the network scheduler commonly available algorithms with your own settings or self-developed algorithms. With the help of the Linux distribution OpenWrt can even bring the latest techniques on low-cost routers to use, such as packet sniffer.
The firmware for the Fritz! Box by AVM set to true on Linux, the core of which, however, is dsld a proprietary in-house development.
From the cFos Software GmbH are available with the product cFosSpeed a software traffic shaper for Microsoft Windows, which can be cooperatively installed on all Windows clients a homogeneous local Windows network.