ols LDP, CR-LDP e.g. OSPF, OSPF-TE (present on all links in the figure) Figure 7.19 MPLS terminology and way of working Quality of Service MPLS offers dynamic bandwidth allocation, traffic engineering, scalable IP over ATM support and support for VPNs. MPLS introduces the concept of label-switched paths (LSP) for both individual and aggregated traffic streams. Separate LSPs are used to serve flows with different QoS requirements. LSPs are set up between media gateways based on topology information provided by routing protocols, such as OSPF (open shortest path first). Each LSP car- ries traffic from only one specific service class. The LSPs are created with a specific set of characteristic parameters (carried in MPLS signalling) according to the type of traf- fic (voice, signalling, etc.) it is intended to carry. LSPs may be set up either statically or dynamically according to the actual bandwidth needed between the media gateways. The end-points of an LSP on the border of the MPLS enabled core network are defined as label edge routers (LER). At these points traffic from surrounding networks will be labelled and switching will be carried out based upon the label which is exchanged on a link-by-link basis. The LER function is implemented as part of the media gate- way function. Each LSP carries traffic for a number of users. The number of LSPs as well as the number of calls a LSP is intended to carry is a trade-off between available resources and additional load produced by the MPLS signalling, which is required to maintain the LSPs. Not all types of traffic carried through the network require the use of LSP paths. MPLS trunks are used to apply adequate traffic engineering, security and resource management on the core network. Traffic engineering facilitates performance optimization while utilizing network resources economically, efficiently and reliably. MPLS encompasses techniques for reliability SO that network service outages arising from errors, faults and failures can be minimized. 7.6 QOS AT THE APPLICATION