Mobile radio group communications by satellite

The protocol design for a mobile radio service supporting half-duplex, push-to-talk, voice communications over mobile satellite systems currently being developed around the world is presented. The service enables a close group of mobile users to communicate among themselves, such that a transmission from any user is received by all. A key issue in the design is the efficient utilization of satellite channels. Demand assignment multiple access (DAMA) is used to allocate channels only to those user-groups in active sessions of conversations. The unique characteristics of the half-duplex, point-to-multipoint group communications necessitate the DAMA protocol proposed for this service. Within a channel assigned to a user-group, access contentions can occur among its members. The resulting loss of capacity due to collisions is exacerbated by the very long round trip delay. A novel access control signal protocol is proposed to detect an resolve across contentions, thus improving channel utilization. Analysis and numerical results are presented to illustrate the efficacy of this protocol. >

The UHF satellite terminal system (USTS) introduces a demand assigned multiple access (DAMA) scheme for efficient sharing of a 5 kHz UHF satellite communication broadcast channel among a large number of users. The 5 kHz UHF DAMA protocols offer simplicity while providing both packet and virtual circuit type services, multiple precedence levels, message acknowledgements, variable-size message packets, several over-the-air burst rates, and multiple-hop routing for global connectivity. The protocols and the UHF waveform developed for the USTS have been used as the basis for a US Department of Defense 5 kHz DAMA waveform standard. The protocols and the waveform are described, and message delay performance simulation results are presented. The analyzed performance indicates that a network shared by 250 users with a typical distribution of link qualities and an aggregate throughput of 1350 messages per hour will operate at 63% efficiency. >

A new integrated demand-assignment multiple-access (DAMA) method for multiple-bus local networks (MBLNs) is proposed and evaluated. The performance of this method is shown to be superior to independent token-passing as well as to previously proposed integrated access schemes. V-STIA, a virtual token-passing extension of a modified explicit token-passing scheme called single-token integrated access (STIA), delivers the best overall performance at medium to heavy loads while achieving good light-load performance without collision detection. Consequently, V-STIA makes the fewest possible demands on interface capabilities for DAMA support in MBLNs. Additionally, V-STIA implementation does not require simultaneous transmit capability for correct operation and greatly reduces design complexity. Performance advantages of MBLNs over an equivalent bandwidth single-bus DAMA system are established. >

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.

A Combined Performance Analysis of Error Control and Multiple Access for a Mobile Radio Channel

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.

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.

A multiple access protocol is a scheme to control the access to a shared communication medium (radio frequency) among various users. Although many access protocols have been proposed and each has its advantages and limitations, very few are suitable for integrated wireless communications. Access protocols can be grouped according to the bandwidth allocation mechanism, which can be static or dynamic, and according to the type of control mechanism implemented. Multiple access protocols can be categorized into three classes: fixed assignment, random assignment, and demand assignment.

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.

Collaboration is used for information sharing and activity coordinating, and it exists broadly in many fields. Group communication enables efficient communication between a set of processes logically organized into groups and communicating via multicast in an asynchronous environment. One of the key technologies for collaborative applications is secure group communication. Current research on secure group communication scarcely considers the existing security mechanism in local systems. As a result, group communication systems couldn 't provide general support for collaborative applications running on a specific system. Based on the existing grid security technologies, we propose an authentication and access control framework at virtual organization (VO) level for group communication in grid environment. By introducing role-based access control (RBAC) and attribute-based approach, we define group management policies and design group control protocols. The protocols are analyzed from three aspects: compatibility, performance, and security. Finally, we implement a prototype based on GridShib.

Security problems in satellite environments are one of the obstacles to the widespread deployment of satellite IP multicast and, more generally, of satellite multimedia applications (Cruickshank et al., 1998). By satellite environments we refer to networks where the satellite plays an essential role. e.g. those where it is used to multicast IP packets to many nodes of a terrestrial network. We also speak of ”Hybrid Satellite/Terrestrial networks” in such cases. The broadcast nature of satellites makes eavesdropping and active intrusion much easier than in terrestrial ルxed or mobile networks. A further issue is speciルc to multicast: the number of members in a multicast group can be very large and, even worse, can change very dynamically. While the process of performing and securing key management for unicast connections is well understood (Harkins & Carrel, 1998), (Maughan et al., 1998), (Orman, 1998), multicast security is still an open ルeld (see par. 2). Protocols that manage the process of distributing keys in a multicast environment are under development (see par. 2.3 and 2.4). Access to the encryption key is controlled by a group key management system, which is responsible for sending the encryption key to authorized new users and for performing multicast group rekeying whenever the key changes. Speciルcally, a group key management system is said to implement two types of access control: backward access control and forward access control. If the system changes the encryption key after a new user joins, the new user will not be able to decrypt past group communications; this is called backward access control. Similarly, if the system rekeys after a current user leaves, or is expelled from the system, the departed user will not be able to access future group communications; this is called forward access control. Many group key management solutions (see par. 2.2, (Jokela, 2006) (Mah, 2004)) have been proposed and a number of classiルcations of the available approaches can be found in the current literature (Dondeti et al., 1999), (Rafaeli & Hutchison, 2003), (Eskicioglu, 2003). Moreover, security mechanisms regarding satellite networks have been investigated in (Howarth et al., 2004), (Noubir & Allmen, 1999) and (Arslan & Alagoz, 2006). Group key management protocols can be categorized as following:

This community service activity is motivated by the local potential of Darungan Hamlet in utilizing herbal plants as health drinks, but is still limited in the aspects of processing, packaging, and marketing. This condition results in low product added value and limited economic opportunities for the community, especially members of the Catleya 3 Dasawisma Group. Motivating the mothers of the Catleya 3 Dasawisma members to become productive individuals will be an opportunity to improve and enhance the quality of family life economically. One effort that can be done is by providing scientific provisions that they can apply by creating something that has economic value. One of these is by making a health drink by utilizing natural resources that can grow well and are abundantly available in Jember. The goal of this activity is to increase the knowledge, skills, and economic independence of the community through innovative herbal dip products and the use of digital technology in marketing. The methods used include socialization, pre-tests and post-tests, training in making herbal dip with three flavors, application of production and packaging technology, and training in creating e-commerce-based marketing accounts. The target of the activity was members of the Catleya 3 Dasawisma Group located in the RT 04/RW 08 area of ​​Darungan Hamlet with a total of 20 participants. The increase in participants' understanding of the use of herbal medicines increased as seen from the average post-test score (80.53±15.80) which was higher than the pre-test score (59.47±13.93). Participants were able to produce herbal dip hygienically and of good quality, package products with attractive labels, and have knowledge related to product marketing through Shopee and Tokopedia. In addition, participants demonstrated independence in managing small businesses based on local potential with the support of production facilities and group communication. This activity succeeded in increasing community knowledge regarding the benefits of traditional medicinal ingredients and how to utilize them, entrepreneurial skills, and expanding participants' knowledge to create e-commerce accounts. Thus, the purpose of community service was achieved, namely the realization of increasing community skills in producing herbal dip sustainably.

In machine-type communications (MTC), contention-based random access is employed to support a number of MTC devices with a limited number of resource blocks (RBs). Since multiple active devices may transmit signals in the same RB or channel, the collision caused by the presence of multiple signals is inevitable and the detection of collision becomes important. Furthermore, if the arrival time and the number of multiple signals can be estimated, successive interference cancellation (SIC) can be employed in time domain to improve the throughput. In this paper, we focus on the estimation of round-trip delays (RTD) of multiple signals in non-orthogonal random access (NORA) based on the maximum likelihood (ML) criterion. Since the computational complexity of the ML approach is high, we propose a low-complexity approach based on variational inference, which is widely used in machine learning. We also show that the number of signals can be reliably estimated from the estimated RTDs.

Computer and wireless mobile communication need Internet accessibility at anytime and anywhere and this includes in high-speed wireless environment such as in high speed trains, fast moving cars as vehicle-to-infrastructure (V2I) communication. However, wireless qualities of service (QoS) provisioning in such environment are more challenging. This increases the development of numerous schemes concerning the need of smooth handoff of the mobile nodes. Transport layer protocols can support seamless handover in such high speed mobility. This paper highlights on the issues of moving users in WiMAX network. A cross-layer design of Transport Layer protocol which is called cross-layer design of Stream Control Transmission Protocol and BS handover messages (SCTPcd) is able to guarantee and maintain QoS for high-speed vehicle. The cross-layer allows information to be exchanged and shared across layer boundaries in order to enable efficient and robust mobility aware protocols.

Access control is an important component in the security of communication systems. While cryptography has rightfully been a significant component in the design of large scale communication systems, its relation to access control, especially its complementarity, has not often been brought out in full. With the wide availability of SELinux, a comprehensive model of access control has all the more become important. In many large scale systems, access control and trust management have become important components in the design. In survivable systems, models of group communication systems may have to be integrated with access control models. In this paper, we discuss the problem of integrating various formalisms often encountered in large scale communication systems, especially in connection with dynamic access control policies as well as trust management.