One of the basic concepts of the traditional internet is that user endpoints connect to the network through an interface, when they would like to communicate with each other. The data packets are transferred through a single path. The drawback of this solution is that if one of the network nodes or its link fails, then it has an effect on the quality of the service, in the worst-case scenario it can cause a complete failure. Sometimes the network is able to use another path because complex error handling happens in the lower layers, but it could take a lot of time. However, a new approach makes it possible to solve the problem in the transport layer by using and managing multiple parallel paths between the network endpoints. One of the implementations of this approach is the Multipath TCP protocol, which is a multipath transport protocol. The multipath property allows it to send traffic over multiple parallel paths at the same time; this makes it possible to redirect traffic to another path if one path fails so the connection is kept alive. The multipath transmit also allows bandwidth increase, because the bandwidths’ of the paths are added together. The main goal the thesis is to examine how the MPTCP performs during various network issues, can it benefit from using multiple paths. During the research, at first I introduced some of the recently suggested multipath transport protocols: ATLB, Fair TCP, PATTHEL, Concurrent TCP, SCTP. I also showed the main challenges during the creation of the MPTCP. I described the congestion and flow control of the MPTCP. Various test environments were set up using a network emulator tool to analyze the MPTCP. During the tests I inspected how MPTCP reacts to different network issues: delay, packet loss, paths with different bandwidths, appearance of new paths. I also discovered the weak points of the MPTCP, like using the TCP Reno algorithm. I implemented an MPTCP capable proxy server, to prove that MPTCP is fully transparent to applications. I tested that a client without MPTCP capability can gain advantage from the multipath transmission by using the MPTCP capable proxy.