What is Virtual private network (VPN)

Internet streaming media changed the Web from a static medium into a multimedia platform, which supports audio and video content delivery. In our days streaming media turns into the standard way of global media broadcasting and distribution. The low costs, worldwide accessibility, and technical simplicity of this telecommunication way make media streams very attractive for content providers. Streaming works by cutting the compressed media content into packets, which are sent to the receiver. Packets are reassembled and decompressed on the receiver side into a format that can be played by the user. To achieve smooth playback, packets are buffered on the receiver side. However, in case of a network congestion, the stream of packets slows down, and the player application runs out of data, which results in poor playback quality. This article presents the comparison of different transport level congestion control schemes, including variants of the TCP. The protocol mechanisms, implemented in various protocols, are hard to investigate in a uniform manner; therefore, the simulator SimCast (Simulator for multiCast) is developed for traffic analysis of the unicast and multicast streams. In this article the TCP and other transport protocol mechanisms will be compared using the SimCast simulator (Orosz & Tegze, 2001). The simulated results are presented through examples. Due to spreading of traffic lacking end-to-end congestion control, congestion collapse may arise in the Internet (Floyd & Fall, 1999). This form of congestion collapse is caused by congested links that are sending packets to be dropped only later in the network. The essential factor behind this form of congestion collapse is the absence of end-to-end feedback. On the one hand an unresponsive flow fails to reduce its offered load at a router in response to an increased packet drop rate, and on the other hand a disproportionate-bandwidth flow uses considerably more bandwidth than other flows in time of congestion. In order to achieve accurate multicast traffic simulation—being not so TCP-friendly yet—the effects of the flow control of the TCP protocol should be determined (Postel, 1981). However, there are many different kinds of TCP and other unicast transport protocol implementations with various flow control mechanisms, which make this investigation rather difficult (He, Vicat-Blanc Primet, & Welzl, 2005).