Wpływ mechanizmów protokołu TCP oraz algorytmów kolejkowania na transmisję danych w sieci Internet

At the beginning of the Internet, the speed transmission does not allow to predict that it will ever be possible to transfer audio, video and other multimedia content. Consequences of the project, which was characterized by reliability and low cost of the connections proved to be a barrier at a time when the Internet became available in almost every home and in every place on the globe. Scientists developing in the 70s the base of the family of  TCP/IP protocols not predicted the challenges for these protocols which bring technologies and solutions created several decades later. The most serious barrier appeared to be an Internet Protocol IP (Based on the connectionless datagram model). This model is not a good solution for the data bandwidth, delay or loosing packets sensitive transmissions. Fortunately, the structure of the Internet allowed to make changes, which initially can be implemented in a small area and then eventually  spread to the larger areas. For adapt the network possibilities to the needs of its users a number of network mechanisms were created. The mission of this mechanisms is the best possible performance of the network links ensuring. The most important elements of the network traffic control are: the packets incoming management,  the packets rejection in the queue, and  the transmitter sending packets speed control at the transport protocol level. The standard queue behavior handle different streams according to the rule "best effort" (FIFO queue).  Nowadays, the queuing algorithms that divide a link between parallel transmissions were introduced. This algorithms rank the packets preserving a queuing discipline (e.g. WFQ, WRR, DRR, CBQ). A major problem, which appeared with the development of the Internet was the network overload. They manifested by a lack of space in the   routers queues. Queue overflow causes packet losses and consequently, the data retransmissions. The traditional approach implied rejection of incoming packets from the queue only after overflow. Mechanisms of active queue management introduced a new approach to this issue. According to the rules AQM earlier, preventive packet rejection is possible. These mechanisms depend on monitoring link status by monitoring the number of data in the queue. On this basis, the decision to remove the incoming packet is taken. In addition, AQM mechanisms use some TCP feature (congestion window mechanism). A congestion control method mechanism is simple, and therefore very efficient. Congestion window size is dependent on the number of received acknowledgments and grows until the sent data is accepted. Rejection of the incoming packet in the router is also an information for the sender suggesting a transmission speed reduction.The most popular AQM mechanisms increase the dropping packet probability with the queue length. In the Internet layer model there are two transport protocols UDP and TCP. TCP is incomparably more complex than UDP. The better part of Internet traffic uses the TCP protocol. TCP has  the control data flow and control the correctness of the transmitted data mechanisms. Also congestion control mechanisms have been introduced in this protocol. With the development of the Internet the better congestion control  mechanisms were created. Currently, there are dozens  adapted to a variety of network conditions mechanisms. The control of the speed generation, acting efficiently under all reasonable network conditions is not a trivial problem. This feature of the transport protocol is extremely important in the era of heterogeneous network consisting of various transmission media (wireless, satellite, optical, or simply cable).