address and the port number (regarding both sides of the connection, the sending side and the receiving side), usually the following fields are used for classification (called 5-tuple): source address (from the IP header), which identifies the network interface of the sender; destination address (from the IP header), which identifies the network interface of the recipient; protocol type, such as TCP or UDP (read from the field "protocol number" in the IPv4 header or the "next header" field in the IPv6 header); source port (from the transport protocol header, e.g. the TCP or UDP port number); destination port (from the transport protocol header, e.g. the TCP or UDP port number). In IPv6 networks, classification can be performed also with 3-tuple in cases where "Flow Label" in the IPv6 header is used. In such cases the 3-tuple is the: 2.5 Traffic Management Techniques source IPv6 address; destination IPv6 address; "Flow Label" field from the IPv6 header, which identifies the flow, and in which case there is no need for use of port numbers from the transport layer protocol header. After classification of IP packets, the next step is packet marking. The packets are typically classified and marked at the edge routers. After an IP packet enters the core network, core routers check the mark applied by the edge routers. 2.5.3 Packet Scheduling Packet scheduling typically refers to mechanisms in network nodes (e.g. routers) regard- ing how to schedule the IP packets on the same outgoing interface (toward the next hop, which is the next router on their path). There are many scheduling mechanisms defined, and subsets of them are implemented by different vendors (in network equip- ment, such as routers, switches, mobile base stations). The typical default scheduling scheme is FIFO (sometimes called FCFS (first come first served)), which gives prior- ity to the IP packets which first enter the buffer queue for the given outgoing network interface. FIFO suits the best-effort nature of Internet traffic, with the initial low cos