Next generation networks (NGNs) are required to support a broad variety of services such as voice and video over IP, file sharing, web browsing, cloud computing, etc. Some of these services have strict Quality of Service (QoS) requirements (ITU-T Y.1541). For example real-time applications demand specific values of the delay to ensure acceptable human perception. In this instance, Quality of Service refers to the control mechanisms which can provide different levels of priority to different applications connecting through the network to guarantee a desired level of performance. The way user's Quality of Service requirements are satisfied has large influence to the way routers serve the traffic. The router's QoS policy may include for example packet scheduling, load balancing, QoS routing, use of reservation protocols or policy servers. Current developments towards NGNs adopt different methods for service guarantees and broadly are divided into IntServ, DiffServ and FAN architectures. The percentage volume of real-time traffic on the Internet is still low but growing from year to year. This will exacerbate problems of traffic controlled on the packet level, because routers investigate every packet regardless of the header. Alternatively traffic can be controlled at the flow level where all packets belonging to the same flow are treated in an identical manner. For reasons of efficiency this method of service appears to be more suitable for the control of large volumes of data and may also be embedded in MPLS or the virtual environment.