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doc:howto:packet.scheduler:packet.scheduler.theory [2012/11/19 16:59] uvray313 |
doc:howto:packet.scheduler:packet.scheduler.theory [2012/11/19 21:50] (current) uvray313 |
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| Activating QoS is not necessary with Linux as it is already active by default. The standard packet scheduler that manages egress queues in Linux, is "pfifo_fast", which means "prioritized first in first out". It is based on the QoS/TOS flags in the packet headers. | Activating QoS is not necessary with Linux as it is already active by default. The standard packet scheduler that manages egress queues in Linux, is "pfifo_fast", which means "prioritized first in first out". It is based on the QoS/TOS flags in the packet headers. | ||
| - | Network interface are serial devices. Packets leave the queue one a time, and are transmitted one after the other, single file. The task of the scheduler is to decide which packet leaves next. It does this by ordering the packets according to an algorithm and its configuration. In the case of "pfifo_fast", the first packet to the enter the buffer is the first to leave. | + | Network interfaces are serial devices. Packets leave the queue one a time, and are transmitted one after the other, single file. The task of the scheduler is to decide which packet leaves next. It does this by ordering the packets according to an algorithm and its configuration. In the case of "pfifo_fast", the first packet to the enter the buffer is the first to leave. |
| == Ingress Queue == | == Ingress Queue == | ||
| - | Unlike the egress buffer, the ingress queue has limited control over the packets it receives. Other than forwarding packets as they are received it's only other capability is to drop packets. This can be used to advantage though with TCP traffic which uses flow and congestion control but has no effect on UDP packets. | + | Unlike the egress queue, the ingress queue has limited control over the packets it receives. Other than forwarding packets as they are received it's only other capability is to drop packets. This can be used to advantage though with the TCP protocol which uses flow and congestion control. Dropping TCP "ACK" packets will imply congestion to the transmission source which will reduce it's transmission rate. There is no similar mechanism available for UDP packets however. |
doc/howto/packet.scheduler/packet.scheduler.theory.txt · Last modified: 2012/11/19 21:50 by uvray313