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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.

In this paper, we study the contention behavior of DOCSIS in cable TV networks. Specifically, we focus on the behavior of TCP over DOCSIS. We determine the expected access delay for TCP transmissions in CATV networks. The access delay here is defined as the interval between the time when a data packet arrives at a Cable Modem (CM) and the time when that packet is successfully sent by the CM. The analytical model is comprised of two parts. The first part is to calculate the probability that a CM sends a request in a randomly selected minislot, and the second part is to derive the expected access delay based on the probability derived in the first part. The accuracy of the analytical model is validated by simulations. The results show that our analytical model can accurately model the contention behavior of DOCSIS in CATV networks. Index Terms--CATV, contention access, DOCSIS, TCP.

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.

IP multicasting is an efficient group communication mechanism. It avoids transmitting packets from a sender to each of the receivers separately. Under the current IP multicast model, once having joined a group, the host will receive all data destined to the group from any source, irrespective of whether it wishes to receive them. This paper studies source filtering (SF) in IP multicasting. Source filtering allows individual hosts to specify the reception of packets sent to a multicast group only from a list of source addresses or to explicitly identify a list of the sources whose data the hosts do not want to receive. We investigate the issue of source filtering in the context of multicast routing protocols, and provide support of source filtering for shared-tree based IP multicast routing. We also discuss how source filtering improves the performance of existing work on IP multicast. Finally, we provide analysis and conduct simulations to evaluate the performance of the proposed SF mechanism. The results show that our mechanism allows better bandwidth utilization and scalability than those without the capability of source filtering, thus achieving a truly efficient use of resources for IP multicasting. Index Terms--IP multicasting, source filtering.

This paper studies the impact of the data-over-cable service interface specification (DOCSIS) media-access control (MAC) protocol on the performance of the transmission control protocol (TCP) in hybrid fiber coax (HFC) broadband access networks. We find that the asymmetry ratio expressed in existing work cannot adequately explain the behavior of TCP in DOCSIS-based networks. To better capture the effect of DOCSIS on TCP, we express the asymmetry ratio (denoted by [eta]) in another way (denoted by k), considering the time-division multiple-access-like MAC layer operation of DOCSIS. When [eta] > 1, TCP behaves as in a symmetric network, and when [eta] [less than or equal to] 1, the system acts as in an asymmetric network, and the performance of TCP degrades. We find that the number of simultaneous TCP transfers significantly affects the asymmetry ratio. When the number of active transfers is below two times the maximum number of pending requests in a transmission period, the value of [eta] is larger than one, regardless of the value of k. However, when the number of active transfers becomes very large, the effect of DOCSIS on TCP becomes negligible, and the asymmetry ratio is determined by the bandwidth ratio of the channels times the length ratio of data and acknowledgement packets. Based on [eta], we develop the round-trip delay of sending a data packet for both one-way and two-way transfers, and discuss the buffer requirement at the head end. The accuracy of the analytical model is validated by ns-2 simulations. The analytical result can provide useful guidelines in the design of slot allocation or scheduling mechanisms for any DOCSIS-based broadband access networks, including the emerging IEEE 802.16 WiMAX networks. Index Terms--Broadband access networks, community antenna television (CATV), data-over-cable service interface specification (DOCSIS), transmission control protocol (TCP).

This paper proposes a new group management protocol called Received-initiated Group Membership Protocol (RGMP) for IP multicasting. The dominant group management protocol on the Internet to date is the Internet Group Management Protocol (IGMP). Unlike IGMP based on a query/reply model, an RGMP host actively takes responsibility to refresh group membership on the neighboring multicast routers. Each RGMP host maintains a 'refresh' timer per group. The refresh timer is reset once the suppression rule holds true for a received report message, where the report may be a join, departure, state change, or refresh message. The RGMP refresh timer is adjusted in a way to be adaptive and self-synchronized. This receiver-initiated, serf-synchronized approach makes the RGMP suppression mechanism superior to that of IGMP v1/v2, because the latter can be applied only to periodical refresh messages. As a result, RGMP protocol overhead is significantly reduced over a wide variety of service scenarios compared to IGMP v3. In addition to the reduced protocol overhead, RGMP is robust, scalable and adaptive to serve as a group management protocol. Index Terms--Group management protocol, IGMP, IP multicast, RGMP.

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.

In this letter, a new transport layer mechanism is proposed to improve the performance of transport control protocol (TCP) in mobile networks. The proposed mechanism is comprised of two parts: a loss classifier (LC) and a congestion window extrapolator (CWE). Based on LC, the cause of packet loss during roaming is determined. If the loss is considered to be caused by congestion in the wireline, the congestion window is halved; otherwise, the packet is considered to be lost in the last hop, the wireless portion, and the sender adjusts the size of the congestion window based on CWE. We conduct simulations to evaluate the performance of the proposed mechanism. The results show that our mechanism significantly improves TCP performance as compared with existing solutions for mobile networks. Index Terms--Mobile networks, wireless transport control protocol (TCP).