Virtual Multicast Link via Packet Re-entrance in NS2
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Multicast and MPLS are two complementary technologies of forwarding packets in a network. Multicast uses host group address to send and receive multicast traffic within a multicast group. MPLS uses labels for packet forwarding. Combining the two technologies to forward packets in layer 2 will enhance traffic performance and improve scalability. Though these two techniques have been actively used in practice, some of the major network simulators have not adopted the simultaneous simulation of them. Particularly, Network Simulator (NS2) does not have the capability of making such combined simulations because of the lack of simulating a virtual link. In this thesis, we introduce the concept of "packet re-entrance" to simulate a virtual link without making significant changes to the regular functioning of the simulator. We simulate a scenario for multicast routing over an MPLS network using the packet re-entrance technique in NS2. In packet re-entrance, the incoming packets are classified by MPLS classifier as well as multicast classifier before it reaches the next node. We design a network topology based on multicast group of communication with MPLS packet forwarding by modifying the NS2 system to implement the packet re-entrance concept. This new methodology can help researchers to simulate and evaluate MPLS multicast routing in NS2. A simple topology sending packets from source to destination using Multicast protocol is taken for study. When a link failure is introduced in the route, a label switched path (LSP) is installed as an alternate path using MPLS protocol. It is inferred from the simulation that, during a link failure, the packet can be transmitted within layer 2 between the nodes of the failed link through the LSP and leaves the packets to be made available at layer 3. This process makes the packets to follow the multicast tree to reach the destination successfully even after the link failure. We illustrate scenarios validating the feasibility of the packet re-entrance for simulating virtual multicast links.