Multicasting, the transmission of a packet to a group of hosts, is an important service for improving the efficiency and robustness of distributed systems and applications. Although multicast capability is available and widely used in local area networks, when those LANs are interconnected by storeand-forward routers, the multicast service is usually not offered across the resulting internetwork. To address this limitation, we specify extensions to two common internetwork routing algorithmsdistance-vector routing and link-state routing-to support low-delay datagram multicasting beyond a single LAN. We also describe modifications to the single-spanning-tree routing algorithm commonly used by link-layer bridges, to reduce the costs of multicasting in large extended LANs. Finally, we discuss how the use of multicast scope control and hierarchical multicast routing allows the multicast service to scale up to large internetworks.

Wireless networks are vulnerable to many identity-based attacks in which a malicious device uses forged MAC addresses to masquerade as a specific client or to create multiple illegitimate identities. For example, several link-layer services in IEEE 802.11 networks have been shown to be vulnerable to such attacks even when 802.11i/1X and other security mechanisms are deployed. In this paper we show that a transmitting device can be robustly identified by its signalprint, a tuple of signal strength values reported by access points acting as sensors. We show that, different from MAC addresses or other packet contents, attackers do not have as much control regarding the signalprints they produce. Moreover, using measurements in a testbed network, we demonstrate that signalprints are strongly correlated with the physical location of clients, with similar values found mostly in close proximity. By tagging suspicious packets with their corresponding signalprints, the network is able to robustly identify each transmitter independently of packet contents, allowing detection of a large class of identity-based attacks with high probability.

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This paper gives a method for finding a minimum spanning tree in an undirected graph. If the problem graph has n vertices and e edges, the algorithm runs in 0(e log log n) time. This time bound is the same as that of a new algorithm by Yao, but Yao's method seems more complicated to implement. A modification of the method improves the l+€ running time to 0(e), if e is fl(n) for some positive constant 6. Another algorithm finds a minimum spanning tree of a planar graph in 0(n) time. The paper also presents some results which suggest that any method for finding a minimum spanning tree requires ft(e log log n) comparisons in the worst case.

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