Group Communication Over LTE

The bicycling recently has gained a lot of popularity in many applications, such as transportation, recreation, and exercise. Bikers may ride in different speeds due to their body strengthes and bike performance such that group members using smart phones form two-tier vehicular long-thin networks along the common cycling path, which consist of a 3G/3.5G high-tier interface and an IEEE 802.11-based low-tier interface. In this paper, we design a Google Android and Maps-based solution for cycling group communications. On the handset side, an Android program is developed for group member localization, communication, and transmission. In addition, the augmented reality interface is integrated to show the biker information on real-time camera views of smart phones. On the web side, a biker community site is built for the biker interaction, grouping, and dedicated album. To provide efficient group communications and reduce the transmission delay, ad-hoc communications are adopted to locally exchange data among bikers. Also, a dynamic grouping mechanism has been designed to maintain the stable member connectivity in ad-hoc environments. Furthermore, the gateway selection in a group has taken the similar mobility pattern of members into account for minimizing 3G/3.5G communications.

Current group communication services have mostly been implemented on a homogeneous, distributed computing environment. This limits their applicability because most modern distributed computing environment are heterogeneous in nature. This paper describes the design, implementation, and performance evaluation of a CORBA group communication service. Using CORBA to implement a group communication service enables that group communication service to operate in a heterogeneous, distributed computing environment. To evaluate the effect of CORBA on the performance of a group communication service, this paper provides a detailed comparison of the performance measured from three implementations of an atomic broadcast protocol and a group membership protocol. Two of these implementations use CORBA, while the third uses UDP sockets for interprocess communication. The main conclusion is that heterogeneity can be achieved in group communication services by implementing them using CORBA, but there is a substantial performance cost. This performance cost can be reduced to a certain extent by carefully choosing a design and tuning various protocol parameters such as buffer sizes and timer values.

The paper investigates the use of group communication to improve the efficiency of load balancing in interconnected LANs. Conventional load balancing techniques usually assume point-to-point connections among the computers and typically work on a single LAN only. This may waste network bandwidth and lengthen the load balancing time in LANs that support group communication such as the Ethernet. To tackle this problem a two level algorithm is proposed. At the LAN level, all computers in a LAN maintain loading information in the entire LAN using a globally ordered group channel. The workload in the different LANs is balanced by moving load from the overloaded LANs to the underloaded ones. It is proved that the proposed algorithm converges to the state of global balance geometrically. Experimental results show that the algorithm reduces load balancing time and network utilization significantly, compared to the single level algorithm without group communication.

Object replication is a technique to enhance fault tolerance and high availability. Group communication is a useful mechanism guaranteeing the consistency among replicated objects. We propose a generic group communication framework that allows transparent plug-in of various group communication protocols with no modification of existing CORBA. For this, we extend the Open Communications Interface (OCI) to support interoperability, reusability of existing group communication, and independency on ORB and OS. The proposed scheme is composed of group membership, group IOR, and group multicast. Experimental results show that group object invocation using the proposed scheme performs substantially better than group object invocations using IIOP as the number of members in a group increases.

Group communication is a one-to-many communication pattern that distributes data from one sender to multiple receivers. Multicast as a group communication method is extensively employed in content distribution scenarios, such as IP-based cable TV, live streaming, video conference, data delivery, etc. Since application-layer multicast cannot touch network elements, it suffers from inefficient network utilization. Some existing network-assisted multicast are limited by scalability issues caused by the inability to maintain a sharply increased per-flow state in individual network elements. Moreover, existing network-assisted multicast is unable to meet the newly emerging need, such as load balancing and traffic engineering. This paper presents a novel multicast technique called Carrier-Grade Minimalism Multicast (CGM2). Through a string of bits, the bitmap, nodes are instructed to locally replicate packets and forward them over several interfaces without maintaining a per-flow state. Bitmaps of nodes along the multicast path are encapsulated in the recursive format as a binary in-packet tree for explicit forwarding path.

Group communication services typically generate large multicast data streams. Delivering such massive data streams to the end system nodes at the edge of the Internet has been a challenging problem in terms of high stress on the network links and high demand on network resources and routing node capacities. Most of existing research has been dedicated on geo-distance based routing with various optimizations to alleviate the performance impact on geo-distance based routing due to unpredictable network dynamics. Most representative techniques are targeted at reducing the delivery path length or optimizing routing path by utilizing network locality. In this paper, we identify the inefficiency of geo-distance based routing protocols in many existing multicast overlay networks in terms of both resource utilization and group communication efficiency. To address this issue, we develop a utility-based routing scheme (UDR) that can provide efficient group communication services in a decentralized geographical overlay network. Our approach makes three unique contributions. First, we introduce a utility function to refine the geo-distance based routing in such a way that the routing path selection can carefully incorporate both geo-distance based metric and the network latency. Second, we enhance our utility driven routing scheme with self-adaptive capability by considering the nodes' state and network density. Thus, nodes in the multicast network can dynamically accommodate the changes of network conditions based solely on their local knowledge about the network. Third, we devise a suite of optimization techniques to minimize the maintenance cost and computational complexity of our self-adaptive and utility-drive routing scheme. We evaluate our approach through extensive experiments based on a realistic network topology model and show that the UDR method is highly scalable and it effectively enhances the multicast delivery efficiency for large scale group communication services compared to existing geo-distance based routing protocols.

Service resilience, defined as the continued availability of a service despite failures and other negative changes in its environment, is vital in many systems. It is typically achieved by state machine replication using group communication middleware for coordination of service replicas. In this paper we focus on systems that represent critical data as Web resources identified by Uniform Resource Identifiers (URIs). The best examples of such systems are RESTful web services. We present RESTGroups : a group communication front-end for RESTful web services. Our system is based on Spread --- a popular group communication toolkit. Contrary to Spread and other such toolkits, we represent group communication services as resources on the Web, addressed by URIs. In the paper, we describe the system architecture and the API.

We have developed a cost-effective regional computer communication network system and examined its implementation. The system provides a LAN environment and group communication services to the customers. The main system components are: the intelligent bridge circuit, called the low-end card (LEC), the center brouter (bridging router), and the management server. The LEC is set up in the subscriber's household and provides the popular Ethernet interface (10 Base-T). The leased circuits are connected between the LEC and the center brouter. The LEC and the brouter are controlled by the management server to function as the group communication system. The brouter, which has a multiplex subscriber-port interface, is required to accommodate a lot of customers cost effectively. This paper presents the system design of a large-capacity brouter having a SDH/SONET multiplex-port interface and its operation. The brouter can accommodate up to approximately 2700 subscribers. Ethernet packets are transferred through each subscriber channel between the LEC and the brouter using the HDLC protocol. A group communication mechanism based on packet filtering via the MAC addresses of PCs is presented. The Ethernet packets are filtered by the brouter to eliminate all packets except those from/to the same group members. The group management operation among the center brouter, the LEC, and the management server is discussed.

We discuss a group protocol which supports applications with group communication service when QoS supported by networks or required by applications is changed. An autonomic group protocol is realised by cooperation of multiple autonomous agents. Each agent autonomously takes a class of each protocol function so as to support only and all QoS required. A group is composed of views for scalability. Each view is a subset of the agents where the agents autonomously take protocol classes consistent with each other. We make clear what combination of classes can be autonomously taken by agents in a view.

In distributed systems, high service availability can be achieved by letting a group of servers replicate the service state; if some servers fail, the surviving ones know the service state and can continue to provide the service. Group communication services, such as membership and atomic broadcast, have been proposed to solve the problem of maintaining server state replica consistency. Group membership achieves agreement on the history of server groups that provide the service over time, while atomic broadcast achieves agreement on the history of state updates performed in each group.

In this paper, we propose the design of an extension of the Java distributed object model based on the group communication paradigm for building replicated fault-tolerant servers. Maintaining the correctness and integrity of replicated servers is supported by the group manager object instantiated with each replica to form a logical group and the group membership algorithms to maintain a consistent group view and a reliable multicast mechanism to communicate with other group managers. Group manager object enables the creation of groups of remote objects that cooperate towards some common goal using a join/leave group communication service. Remote object groups simulate the behavior of standard remote objects by implementing a set of remote interfaces and by enabling clients to remotely invoke the methods defined in these interfaces through the standard Java RMI mechanism. For the first time, communication among senders forming a group is based on group method invocations as well, offering a completely object-oriented framework for programmers. And then, it is completed by a state merging service, which simplifies the development of state merging mechanism needed to re-establish a consistent state after the disappearing of join/leave properties

Software based Distributed Shared Memory (DSM) systems have been the focus of considerable research effort, primarily in improving performance and consistency protocols. Unfortunately, computer clusters present a number of challenges for any DSM systems that are not solvable through consistency protocols alone. These challenges relate to the ability of DSM systems to adjust to load fluctuations, computers being added/removed from the cluster, to deal with faults, and the ability to use DSM objects larger than the available physical memory. We present here a proposal for the Synergy Distributed Shared Memory System and its integration with the virtual memory, group communication and process migration services of the Genesis Cluster Operating System.

The so-called media convergence to the Internet is foreseen. As a consequence of this convergence, MANs will face new demands not only in terms of bandwidth, but also in terms of services. To meet these new demands, new MAN architectures are required. WDM-based MAN architectures that tackle the first problem are available not only in the literature, but also on the market. In this paper we deal with the second problem. Specifically, we describe a novel WDM-based MAN architecture that supports group communication, a service that is expected to increase considerably as new applications converge to the Internet. Based on packet switching, the architecture supports both point-to-point and point-to-multipoint communication in the optical domain.

Mobile radio group communications enable a closed group of users to communicate among themselves using push-to-talk (PTT), half duplex transmissions, such that one's transmission is received by all. New protocol designs are presented which support group communications over mobile satellite systems. A new demand assignment multiple access (DAMA) protocol is necessitated by the inappropriateness of call-based channel assignments. Channels are assigned to individual user-groups engaged in active conversations. As members of a user-group contend for access to the assigned channel, access control by the usual manual methods is ineffective due to the very long round trip delay. A novel signaling protocol which automates access control is proposed. Carrier sensing, signal capture, and collision detection are employed to minimize access contentions. The throughput and holding time of the assigned channel are analyzed. Numerical results show that the access control protocol improves the capacity of the assigned channel by up to 65%. >

Group communications are commonly used in parallel and distributed environment. However, existing migration mechanisms do not support group communications. This weakness prevents migrationbased proactive fault tolerance, among others, to be applied to MPI applications. In this study, we propose distributed migration protocols with group membership management to support process migration with group changing. We design and implement a process migration enabling MPI library, named MPIMitten, to verify the protocols and enhance current MPI platforms for reliability and usability. MPI-Mitten is based on MPI standard and can be applied to any MPI-2 implementations. Experimental results show the proposed distributed process migration protocols are solid and the MPI-Mitten system is effective and is uniquely supporting migration-based fault tolerance.