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In this paper, we study the impact of node mobility on link duration in multihop mobile networks. In multihop mobile networks, each node is free to move, and each link is established between two nodes. A link between two nodes is established when one node enters the transmission range of the other node, and the link is broken when either node leaves the transmission range of the other. The time interval during which the link remains active is referred to as the link duration. We develop an analytical model for link duration in multihop mobile networks. We find that the link duration for two nodes is determined by the relative speed between the two nodes and the distance during which the link is connected, which are, in turn, determined by the angles between the two nodes' velocities and the angle of one node incident to the other node's transmission range, respectively. The analytical result is then extended to model multipoint links, which appear in existing group mobility models. The accuracy of our framework is validated by simulations based on existing mobility models. The results show that our model can accurately describe the link-duration distribution for point-to-point and multi-point links in multihop mobile networks, particularly when the transmission range of each node is relatively smaller than the entire network coverage. Index Terms--Link duration, multihop mobile networks.

In this paper, we propose a bandwidth-efficient multicast routing mechanism using rectilinear Steiner trees for Internet Protocol (IP)-based low earth orbit (LEO) satellite networks. Different from existing work that minimizes the end-to-end delay, our mechanism minimizes the total bandwidth, i.e., the number of hops, for a multicast tree since the wireless bandwidth in satellite networks is a limited and scarce resource. We formulate the problem as an optimization problem and propose a distributed algorithm and a protocol to support the dynamic group membership for multicasting over LEO satellite networks. Our simulation results show that the trees created by our mechanism consume less bandwidth than the shortest path trees. The difference between the optimal solutions and the solutions obtained by our distributed algorithm is within 5%. Furthermore, our protocol has a limited overhead and can support a large number of group members. Index Terms--Low earth orbit (LEO) satellite, multicast, rectilinear Steiner tree (RST).

In this paper, we model the location-dependent throughput and delay in wireless mesh networks. We analyze the packet-arrival and the packet-departure rates for the forwarding queues at relaying nodes and then derive the per-user throughputs and packet delays experienced by nodes at different hop-count distances from the gateway. Based on this analytical model, we propose two network design strategies to provide fair resource sharing and minimize the end-to-end delay in wireless mesh networks. We then conduct simulations to validate the correctness of our analytical model and evaluate the performance of the proposed network design strategies. The results show that our analytical framework can accurately model the location-dependent throughput and delay in wireless mesh networks and that our proposed strategies effectively and efficiently provide fair throughputs for nodes and reduce the end-to-end packet delay. This paper not only provides a framework for studying the performance of wireless mesh networks but also gives insights into the network design strategy for wireless mesh networks. Index Terms--Delay, throughput, wireless mesh networks.

The significance of hop counts on the throughput and delay performance in multihop wireless networks has been well demonstrated in the literature. However, so far, there has been very little analytical work on determining the expected hop count for packet forwarding in multihop wireless networks. In this paper, we develop an analytical framework for the hop count distribution in a multihop wireless network with an arbitrary node density. We derive the average progress per hop and obtain the path connectivity probability in a network. Together with the derived per-hop progress and the path connectivity probability, we can express the probability distribution for the expected hop count in multihop wireless networks. We also demonstrate that, based on our analytical result, many network design guidelines can be provided. Specifically, the average packet delivery ratio in the network under a hop count limitation can be estimated accurately, and the tradeoff between the flooding cost and the search latency for target location discovery that is commonly used in many ad hoc routing protocols can also be evaluated. Index Terms--Hop count distribution, multihop wireless networks, path connectivity.

In this paper, we propose an interframe-space (IFS)-based distributed-fair-queuing (IDFQ) mechanism to provide proportional fairness service for IEEE 802.11 wireless local-area networks (WLANs). IDFQ is designed to emulate self-clocked fair queuing in a distributed manner. It eliminates the backoff process as implemented in existing work and introduces a new mechanism to assign the IFS value to each station. IDFQ is immune from the implementation problem suffered by existing IFS-based mechanisms and is adaptive to the collision state in the system. Moreover, it can be used to eliminate the performance-anomaly problem of 802.11 medium-access control. The performance of IDFQ is validated by ns-2 simulations. The simulation results show that IDFQ supports fairness service for flows in proportion to their weights and outperforms existing mechanisms in terms of fairness and stability, rendering IDFQ an excellent candidate to provide weighted fairness in IEEE 802.11 WLANs. Index Terms--Distributed fair queuing (DFS), IEEE 802.11 wireless local-area networks (WLANs).

In this paper, we analyze the behavior of floodingbased packet forwarding in a densely populated mobile ad hoc network. Specifically, we develop the probability distribution of hop count distance for a source--destination pair in the network, given that all nodes are roaming. The behavior of packet forwarding in such an environment is analogous to the ripples radiating from the source when one drops a stone into a pond. Due to node mobility, the number of hops traversed by each packet is not simply equal to the number of ripples from source to destination. In this paper, node mobility is represented as a growing circle centered at the destination node. The moving behavior of intermediate nodes can be ignored in a flooding-based ad hoc network with high node density since there is always a node available in the transmission direction to forward packets. The analytical model is validated via simulations. We further demonstrate that based on the proposed analytical model, one can estimate the flooding cost and search latency of target location discovery commonly used in most existing on-demand ad hoc routing protocols, and learn the impact of different flooding schemes on target discovery. Index Terms--Flooding, hop count distance, mobile ad hoc networks.

In this paper, a new protocol, called Family ACK Tree (FAT), is proposed to support reliable multicast service for mobile ad hoc networks. For each reliable multicast protocol, a recovery scheme is used to ensure end-to-end delivery of unreliable multicast packets for all group members. FAT employs a tree-based recovery mechanism that localizes ACKs and retransmissions to avoid feedback implosion. To cope with node movements, FAT constructs an ACK tree on which each node maintains reachability information to three generations of nodes on the ACK tree. When a tree is fragmented due to a departed node, the fragments will be glued back to the tree using the underlying multicast routing protocol. FAT then adopts an adaptive scheme to recover missed packets that have been multicast to the group during fragmentation and are not repaired by the new reliability agent. We have conducted simulations to compare the performance of FAT with existing solutions. The results show that FAT achieves better performance for the provision of reliable service in ad hoc networks, in terms of reliability, scalability, and delivery efficiency. Index Terms--Family ACK tree (FAT), mobile ad hoc network, reliable multicast.

This paper studies mobility extensions to ITU-T Rec. H.323 for the support of mobile internet telephony. Internet telephony, also known as voice-over internet protocol (IP) (VoIP), requires the transmission of two-way and real-time traffic over IP-based networks. The current version of H.323 allows IP telephony and the interoperability of the internet with switched circuit networks (SCN). However, until recently, VoIP mobility has not been widely considered, where VoIP mobility refers to the mobility within the scope of IP telephony. In this paper, we focus on terminal mobility for VoIP. We investigate the influence of mobility on the H.323 layer and propose an H.323 mobility solution to be implemented over the IP layer. Two approaches to mobility extensions to H.323 are described in the paper: using ad hoc multipoint conference expansion and using IP multicasting to emulate mobility. Besides, we have also shown that the proposed ad hoc expansion approach shares many properties with the alternative of using IP multicasting for mobility. Hence, the call signaling procedure for the ad hoc expansion approach is also applicable to the multicasting approach. Since ad hoc multipoint expansion has been defined in H.323, our solution introduces no additional entities to H.323 and requires minimal modifications to the existing H.323 protocol. Such mobility extensions can serve as a value-added feature for the internet telephony systems compliant to the H.323 standard. Index Terms--H.323 mobility, mobile extensions to H.323, mobile internet telephony, voice over internet protocol (VoIP) mobility.