RelM: reliable multicast for mobile networks

OMG has published an unreliable multicast specification for distributed applications developed in CORBA (UMIOP). This mechanism can be implemented based on IP Multicast, a best-effort protocol, which provides no guarantees about the message delivery. However, many fault-tolerant or groupware applications demand more restrictive agreement and ordering guarantees (for instance, reliable multicast with FIFO, causal or total ordering) from the available support for group communication. OMG has not yet provided any specification for supporting those requirements. This paper presents an important contribution towards this direction. We proposed the ReMIOP, an extension to the UMIOP/OMG protocol, for the conception of a reliable multicast mechanism in CORBA middleware. Performance measures comparing ReMIOP, UMIOP and UDP sockets for IP multicast communication are presented in order to evidence the costs for adding reliable and unreliable multicast in middleware level.

No doubt, the usages of mobile agent and mobile phone technologies are rapidly increased. The mobile agent has a promising room in the industry area. Unfortunately, this technology faces some security problems from mobile agents and hosts sides. Two of the fundamental issues in designing protocols for message passing between mobile agents (MAs) are tracking the migration of the target agent and forwarding messages to it. Even with an ideal fault-free network-transport mechanism, messages can be dropped during MA migration. Therefore, in order to provide reliable message delivery, protocols need to overcome message loss caused by asynchronous operations of agent migration and message forwarding. As mobile devices and third generation mobile networks have become a reality, location based services are thought to be a major growing area. Mobile devices are given context sensitiveness so that they can be aware of the users/services surrounding physical environment and state. In this paper we propose message forwarding approaches, namely push and pull, are explored to design adaptive and reliable message delivery protocols.Also location aware services scheme by using an agency, which helps in discovering the required services for the mobile users. The agency consists of five agents: Manager Agent (MA), Route Monitoring Agent (RMA), Local Service Management Agent (LSMA), Global Service Management Agent (GSMA) and Area Monitoring Agent (AMA).

Disruption Tolerant Networks (DTNs) are characterized by frequent network partitioning. This causes network connectivity to be opportunistic. In recent years, many collaborative applications have been envisioned for DTNs. These applications rely on the availability of reliable group communication protocols. To address this challenge in DTNs, we propose a scalable multicasting scheme that deterministically guarantees message delivery to all receivers in the group. Also, our scheme makes controlled use of non-multicast nodes to reduce latency of message delivery. Our work introduces a new measure called termination delay, which is the delay incurred in assuring that the receivers have obtained a copy of the message. Simulation results show that the proposed scheme has much smaller delivery latency and termination delay than other schemes in literature.

We present MTCT, a congestion control scheme for large-scale reliable multicast. Congestion control for reliable multicast is important because of its wide applications in multimedia and collaborative computing, yet nontrivial, because of the potentially large number of receivers involved. Many schemes have been proposed to handle the recovery of lost packets in a scalable manner; but there is little work on the design and implementation of congestion control schemes for reliable multicast. We propose new techniques that can effectively handle instances of congestion occurring simultaneously at various parts of a multicast tree. Our protocol incorporates several novel features: (1) hierarchical congestion status reports that distribute the load of processing feedback from all receivers across the multicast group, (2) the relative time delay (RTD) concept which overcomes the difficulty of estimating round-trip times in tree-based multicast environments, (3) window-based control that prevents the sender from transmitting faster than packets leave the bottleneck link an the multicast path through which the sender's traffic flows, (4) a retransmission window that regulates the flow of repair packets to prevent local recovery from causing congestion, and (5) a selective acknowledgment scheme that prevents independent (i.e., non-congestion-related) packet loss from reducing the sender's transmission rate. We have implemented MTCP both on UDP in SunOS 5.6 and on the simulator ns, and we have conducted extensive Internet experiments and simulation to test the scalability and inter-fairness properties of the protocol. The encouraging results we have obtained support our confidence that TCP-like congestion control for large-scale reliable multicast is within our grasp.

We report the design, implementation and evaluation of Merged Hybrid ARQ with staggered FEC (MHARQ) system for video multicast over wireless LANs. MHARQ combines the advantages of receiver-driven staggered FEC and hybrid ARQ schemes to compensate the large dynamic range of WLAN channels and to achieve high reliability, scalability and wireless bandwidth efficiency for video multicast. The FEC packets generated by a cross-packet FEC code are divided into multiple streams according to the pre-configured overhead and are transmitted in different multiple IP multicast groups. Certain FEC streams are delayed from the original video stream. The receivers dynamically join/leave the FEC multicast groups based on the channel conditions. For efficient utilization of WLAN bandwidth, FEC data for a multicast group would not be transmitted by the APs in wireless networks if no receiver joins this group. The time shift between the video stream and the FEC streams introduces temporal diversity and compensates for the client join delay and handoff interruption. In addition, when delayed FEC packets are not enough to recover the lost packets, the receivers can send a hybrid ARQ request to the video server. We design a channel estimation algorithm for a receiver to dynamically determine the delayed FEC multicast groups to join and/or send ARQ NACK to request for retransmission. Using the ORBIT radio grid testbed, we have investigated the performance of the proposed MHARQ system with various numbers of users per AP and different number of APs per video server. It is demonstrated via real system implementation on ORBIT that MHARQ improves wireless bandwidth efficiency and scalability for reliable video multicast, compared with existing reliable multicast schemes.

Reliable multicast in wireless ad hoc networks is important for the applications such as distributed computing, chat, and whiteboard. Due to the wireless channel characteristics, obtaining the reliability in multicast packet transmission is a difficult and challenging task. Even though IEEE 802.11 is widely adopted medium access control (MAC) protocol in wireless ad hoc networks, it does not support reliable multicast. Thus, several MAC layer protocols have been proposed that can provide reliable multicast. In this paper, we propose the reliable multicast MAC protocol which is based on the orthogonal frequency division multiple access (OFDMA) systems. The proposed method reduces the overhead required for control packets. Analysis results validate the reliability and efficiency of our multicast MAC protocol.KeywordsMedium Access ControlMedium Access Control ProtocolPacket DelayControl PacketOrthogonal Frequency Division Multiple AccessThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The current resource reservation protocol (RSVP) design has no reliability mechanism for the delivery of control messages. Instead, RSVP relies on periodic refresh between routers to maintain reservation states. This approach has several problems in a congested network. End systems send PATH and RESV messages to set up RSVP connections. If the first PATH or RESV message from an end system is accidentally lost in the network, a copy of the message will not be retransmitted until the end of a refresh interval, causing a delay of 30 seconds or more until a reservation is established. If a congested link reuses a tear-down message (PATHTEAR or RESVTEAR) to be dropped, the corresponding reservation will not be removed from the routers until the RSVP cleanup timer expires. We present an RSVP enhancement called staged refresh timers to support fast and reliable message delivery that ensures hop-by-hop delivery of control messages without violating the soft-state design. The enhancement is backwards-compatible and can be easily added to current implementations. The new approach can speed up the delivery of trigger messages while reducing the amount of refresh messages. The approach is also applicable to other soft-state protocols.

In this paper we examine the impact of widely spread multicast groups on the performance of reliable multicast protocols. In a brief analysis we show that transmission cost for reliable multicast increases rapidly with the distance between retransmitting and receiving hosts. Since this distance is not considered by existing protocols, which are based on retransmissions originated at the sender or receiver, the performance often is rather poor and a new error recovery concept has to be developed. Our approach. the Scalable and Reliable Multicast Transport protocol (SRMT), allows retransmissions by extended multicast routers to limit the path length for error recovery. Moreover, the retransmission load can be further reduced by an XOR combination of packets. SRMT is defined as an overlay network model and therefore can be applied to any existing multicast protocol.

Multicasting plays an important role in internet networks. Supporting wavelength division multiplexed (WDM) multicasting in an IP over WDM network poses interesting problems because some WDM switches may be incapable of switching an incoming signal to more than one output interface. Although some multicast applications, such as audio/video conferencing can tolerate packet error or loss, other applications such as one-to-many file transfer and military applications do not. Hence, an inevitable need for reliable multicasting arises. The reliable multicast protocol ensures the eventual delivery of multicast data to all multicast group members. The reliable multicast is receiver initiated NACK-based and it makes use of feedback suppression in order to avoid NACK and retransmission implosion. The loss recovery burden is distributed over the multicast group members in order to reduce recovery latency and end-to-end delay. The proposed protocol is evaluated in terms of performance metrics for an IP/WDM optical network which will be the candidate for the next generation internet networks.

An increasing number of mobile users (MUs) share common interests in general information, such as traffic information, weather forecast, and domestic/international news. However, the centralized infrastructure-based system has not been designed for efficiently disseminating the information of common interest (IoCI) to numerous requesters. Thanks to the rapid development of mobile devices equipped with large storage and multiple communication modes, opportunistic communication between a pair of MUs can be readily realized. With the aid of opportunistic networks formed by MUs, we can improve the connectivity of cellular networks in the rural areas, we can offload the tele-traffic from the overloaded cellular networks, and we can efficiently disseminate the IoCI in the densely populated areas. We commence with a detailed survey on the cross-disciplinary research area of social network analysis aided telecommunication networking. We continue by focusing our attention on the family of integrated cellular and large-scale opportunistic networks, whose performance is dominated by the inter-contact duration as well as the contact duration between any pairs of MUs. A continuous-time-pure-birth Markov chain is invoked for analyzing the relevant performance. We demonstrate that the delivery ratio of the IoCI before it expires becomes higher than 90% with the aid of opportunistic networks consisting of 20 MUs. Moreover, our experiments based on the InfoCom 2006 mobility trace show that the opportunistic networks are capable of offloading 58% of the tele-traffic from the cellular networks. Thereafter, we propose a hybrid information dissemination scheme for the integrated cellular and small-scale opportunistic networks, which is comprised of two main stages: 1) the base station-aided single-hop multicast (BSSHM) stage and 2) the cooperative multicast aided spontaneous dissemination stage. In contrast to their large-scale counterparts, in small-scale opportunistic networks, the information dissemination is mainly affected by the mobility of the MUs, by the wireless channel attenuation and by the resource scheduling, where a discrete-time-pure-birth Markov chain is utilized for characterizing the relevant performance. We demonstrate that our hybrid information dissemination scheme outperforms the traditional BSSHM in terms of various delay metrics, despite consuming less energy.

Although the mobile agent paradigm provides great potential advantages ever traditional approaches in distributed computing applications, there are still several issues to be addressed before the technology can be widely accepted. The performance of the communication protocol is one of the critical issues in mobile agent systems. A practical communication protocol for mobile agents must satisfy three basic requirements: location transparency, reliability and efficiency. Although many communication protocols have been proposed for mobile agent systems and most of them are location transparent, these protocols usually compromise some aspects of reliability and efficiency. In this research we develop a communication scheme for efficient location tracking of agents and reliable message delivery in mobile agent systems by using a proxy-based scheme. The location update and message delivery protocols are developed and shown to be reliable even when agents migrate during message delivery. A simulation model is developed to estimate the performance relative to a (nonproxy-based) home-server protocol. Sensitivity analysis is used to reveal the important circumstances (domain/agent dimensions and exogenous demand/movement characteristics) for efficient communication performance.

Tree-based reliable multicast protocols are well-known for being scalable for one-to-many sessions, but their behaviour in terms of throughput and bandwidth requirements has not been identifed for many-to-many sessions. In this paper, existing tree-based reliable multicast protocols are categorised into four classes according to their feedback/retransmission mechanisms. Analysing and comparing them using a new spatial multicast loss model that considers the correlation of packet loss events can yield realistic analysis results. The analysis reveals that for many-to-many sessions, tree-based protocols with unicast NACK, unicast retransmission, and periodic polling are most scalable with respect to throughput and network bandwidth for practical session sizes. The result is contrary to the one-to-many case and it is shown that the reason is that reducing the sender's processing time is a key factor for scaling one-to-many reliable multicast, whereas reducing the receiver's processing time is far more important factor for scalability of many-to-many reliable multicasts.

Understanding the Design of Mobile Social Networking

Performance evaluation of DTN protocols to deliver sms in dense mobile network : Empirical proofs

Patient monitoring is becoming a requirement for offering a better healthcare to an increasing number of patients in nursing homes and hospitals. During the monitoring, vital signs of patients could fluctuate significantly and/or match certain undesirable patterns and therefore alerts or emergency messages must be delivered to healthcare professionals. There has been some work in using infrastructure-oriented wireless networks for transmission of emergency messages, however, the network coverage and reliability of message delivery have not been satisfactory. To overcome these, we propose that ad hoc networks can be formed among patients’ devices for improved transmission of emergency messages. We also propose several design enhancements to improve the quality and coverage of patient monitoring. The performance results for the proposed ad hoc network based architecture show that reliable message delivery and low monitoring delays can be achieved by using multicast or broadcast-based routing schemes.