Ruuhkanhallinta-algoritmien toiminta haasteellisissa tietoverkoissa

Abstract

The focus of this Master's thesis is to research the behaviour of different congestion control algorithms by different packet drop and latency values. Seven different transport layer protocol variants were researched. Five of them were TCP variants and two DCCP variants. Used research method was systematic simulation that was performed by Ns2-simulator.

Congestion control algorithms try to avoid congestion and permit as efficient usage of the network as possible. Congestion control algorithms are also responsible about the fairness between different network users. Selfish and aggressive network protocol may seem efficient from its own perspective but for the overall efficiency such behaviour is questionable.

Congestion control is based on noticing and reacting for congestion by tuning the transfer rate. There are many different methods to become aware of congestion but all of them are incapable to distinguish the reason for the interference at the transmission. The most common indication about congestion is a packet loss. Unfortunately there is no mechanism to know exactly the reason for the packet loss. Ali indications about congestion cause same congestion control behaviour and therefore algorithms may sometimes react incorrectly. A good example about this is an uncongested wireless network which has high packet drop rate.

The simulations were divided into two parts. At the first part the good put of different TCP and DCCP variants through an uncongested bottleneck 1mk was researched by computer simulations. At the second part of the simulations the fairness of different TCP and DCCP variants at a bottleneck 1mk were researched.