d adds labels over the IP packet. In IP/MPLS networks, label switching path (LSP) technology is used to pre-provision virtual multi-protocol label switching transport network (VMTN) for each service type (VoIP, IPTV, best-effort Internet traffic, corporate VPN, etc.). This can be performed manually (by setting the forwarding tables for MPLS) or automatically (by using RSVP for MPLS traffic engineering (RSVP-TE) [31], or Constraint-based Label Distribution Protocol (CR-LDP), [32], DiffServ-enabled MPLS traffic engineering (DS-TE) for opti- mization purposes [33], as well as BGP/MPLS with IP VPNs [34] for IP traffic exchange (e.g. peering) between network providers (e.g. telecom operators). Regarding the MPLS network architecture, in short, fixed-length labels are associated to streams of data in the following manner (Figure 2.15): In the ingress edge MPLS router, called LER (label edge router), labels are added IP streams (based on different constraints for traffic differentiation at the network edges). Packet belonging to those streams are forwarded along the LSPs based on their labels (not on IP addresses), SO there is no IP header examination in LSRs (label switching routers), which are used for packet switching in the MPLS network domain (that is, network segment or a whole network which uses and understands the labels added to the packets by LERs). 2.9 Deep Packet Inspection (DPI) Label edge router (LER) add/drop labels to/from IP packets IP packet domain IP packet Labels IP packet LER - Label edge router LSR - Label switching router MPLS - Multi-protocol label switching Figure 2.15 MPLS network architecture. QoS technologies based on the differentiated services architecture by using MPLS with VPN are widely deployed within the transport networks of many providers. 2.9 Deep Packet Inspection (DPI) Deep packet inspection is a type of packet filtering targeted at all headers and all pay- loads from network layer (layer 3) up to application layer (layer 7), i.e. all layers that make up the end-to-end communicati