Label Switching Functions

• In label switching, analysis of the layer 3 header is done only once.
• After this analysis, add a fixed length, unstructured value called a label.
• Many different header add to the same label (those headers are have same next hop)
• i.e. a label represents a forwarding equivalence class
• Means a set of packets which are different but they are indistinguishably by the forwarding function.
• The initial choice of label may not depend upon the content of layer 3 packet header
• Ex: Forwarding decisions at subsequent hops can also be based on routing policies.
• The packet header need not be reanalysis  during packet transit through the network.
• Because the label is fixed length and unstructured.
• So the MPLS forwarding table lookup process is straight forward & fast