In this work we survey distributed systems that can provide group communications, including both existing commercial systems and proposed research systems. Distributed systems are compared across multiple architectural characteristics such as fault-tolerance, scalability, security, delivery guarantees, and management as well as contrasted against systems utilizing peer-to-peer systems, application-level multicast, and IP layer multicast. Comparing distributed systems which provide group communications is a step toward developing systems appropriate for military network-centric group communications where more research is needed. A secondary result is an attempt to merge group communications terminology between distributed systems, peer-to-peer, application-layer multicast and IP layer multicast.
An extensible network simulation application was developed to study wireless battlefield communications. The application monitors node mobility and depicts broadcast and unicast traffic as expanding rings and directed links. The network simulation was specially designed to support fault injection to show the impact of air strikes on disabling nodes. The application takes standard ns-2 trace files as an input and provides for performance data output in different graphical forms (histograms and x/y plots). Network visualization via animation of simulation output can be saved in AVI format that may serve as a basis for a real-time battlefield awareness system.
KEYWORDS: Telecommunications, Systems modeling, Network security, Information security, Process modeling, Distributed computing, Computer security, Computing systems, Control systems, Receivers
The importance of group communications and the need to efficiently and reliably support it across a network is an issue of growing importance for the next decade. New group communication services are emerging such as multimedia conferencing/groupware, distributed interactive simulations, sensor fusion systems, command and control centers, and network-centric military applications. While a succession of point-to-point unicast routes could provide group communications, this approach is inherently inefficient and unlikely to support the increased resource requirements of these new services.
There is the lack of a comprehensive process to designing security into group communications schemes. Designing such protection for group communications is best done by utilizing proactive system engineering rather than reacting with ad hoc countermeasures to the latest attack du jour. Threat modeling is the foundation for secure system engineering processes because it organizes system threats and vulnerabilities into general classes so they can be addressed with known protection techniques. Although there has been prior work on threat modeling primarily for software applications, however, to our knowledge this is the first attempt at implementation-independent threat modeling for group communications. We discuss protection challenges unique to group communications and propose a process to create a threat model for group communication systems independent of underlying implementation based on classical security principles (Confidentiality, Integrity, Availability, Authentication, or CIAA). It is our hope that this work will lead to better designs for protection solutions against threats to group communication systems.
KEYWORDS: 3D video compression, Image compression, Video, Video compression, 3D modeling, 3D image processing, Visualization, 3D acquisition, Data modeling, Visual compression
Tele-immersive systems can improve productivity and aid communication by allowing distributed parties to exchange information via a shared immersive experience. The TEEVE research project at the University of Illinois at Urbana-Champaign and the University of California at Berkeley seeks to foster the development and use of tele-immersive environments by a holistic integration of existing components that capture, transmit, and render three-dimensional (3D) scenes in real time to convey a sense of immersive space. However, the transmission of 3D video poses significant challenges. First, it is bandwidth-intensive, as it requires the transmission of multiple large-volume 3D video streams. Second, existing schemes for 2D color video compression such as MPEG, JPEG, and H.263 cannot be applied directly because the 3D video data contains depth as well as color information. Our goal is to explore from a different angle of the 3D compression space with factors including complexity, compression ratio, quality, and real-time performance. To investigate these trade-offs, we present and evaluate two simple 3D compression schemes. For the first scheme, we use color reduction to compress the color information, which we then compress along with the depth information using zlib. For the second scheme, we use motion JPEG to compress the color information and run-length encoding followed by Huffman coding to compress the depth information. We apply both schemes to 3D videos captured from a real tele-immersive environment. Our experimental results show that: (1) the compressed data preserves enough information to communicate the 3D images effectively (min. PSNR > 40) and (2) even without inter-frame motion estimation, very high compression ratios (avg. > 15) are achievable at speeds sufficient to allow real-time communication (avg. ≈ 13 ms per 3D video frame).
Ring-based network overlays have attractive characteristics for group
communications such as inherent reliability and single fault-tolerance.
However, ring networks also generally have longer paths and thus higher delay
and delay jitter. In order to provide scalability as the number of group
members grows, large single rings may be broken into smaller multi-rings
interconnected together at the same level or interconnected in a multi-level
hierarchy of rings.
In this paper we consider different approaches to providing scalable
battlespace group communications using multi-ring techniques -- classifying the
techniques according to the primary military requirements of security and
survivability. For multi-rings at the same level, an optimal number of rings to
cover the group members may be approximated and these rings may then be
interconnected at end systems or bridged via network devices.
For hierarchical rings the number of levels and the number of
rings per level may both be approximated. These results are dependent on
application QoS demands and the underlying network infrastructure in terms of
topology (dense versus sparse) and link bandwidths (bottleneck capacities).
Network-centric warfare is not simply a combination of communication,
intelligence, and signals, but rather warfare that leverages off a common
network to support different purposes. While group communications based on a
single virtual ring overlay may satisfy the most important requirements for
survivability and security, scalability may force redesign. Thus comparing the
characteristics of different multi-ring techniques provides an insight into
which battlespace applications may be supported via virtual rings.
In this paper we describe state-of-the-art peer-to-peer systems and analyze them according to multiple characteristics highlighting (1) scalability, (2) security and (3) fault tolerance. Peer-to-Peer systems are inherently scalable since they create fully decentralized environments across the Internet while simultaneously reducing complexity because each server handles a local set of clients. Peer-to-peer system security has depended primarily on user trust - the fact that any peer can contact any other peer in the system introduces issues of insider attacks from malicious users or external attacks through the Internet. Lastly, while peer-to-peer systems are evolving in response to peer unreliability, fault tolerance/survivability for general-purpose military group communications may require additional middleware.
Comparing these characteristics across different peer-to-peer systems is a step towards understanding which system may be appropriate for military group communications and where further research is needed. A secondary result of our comparison is an attempt to move towards common terminology and models between peer-to-peer, application-layer multicast, IP layer multicast, and distributed systems approaches for group communications.
Multicasting is the enabling technology for group communication. However, network-layer multicasting (e.g., IP multicast) has not been widely adopted more than 10 years of its invention due to the concerns related to deployment, scalability and network management. Application-layer multicast (ALM) has been proposed as an alternative for IP multicast. In ALM, group communications take place on an overlay network in which each edge corresponds to a direct unicast path between two group members. ALM protocols differ in, among other aspects, the topology of the underlying overlay network (e.g., tree, mesh or ring). Ring-based ALM protocols have the advantages of
providing a constant node degree, and enabling the implementation of reliable and totally-ordered message delivery through the use of a ring with a token that contains ordering and flow control information. In addition, a ring overlay network topology is inherently reliable to
single node failures. In this paper, we provide a survey and a taxonomy of several ring-building group communication protocols. Investigating the major characteristics of ring-building network protocols is an important step towards understanding which of them are suitable for command
and control group communications.
KEYWORDS: Computer security, Data storage, Multimedia, Databases, Network security, Multimedia encryption, Data centers, Digital photography, Video, Information security
Protecting multimedia data from malicious computer users continues to grow in importance. Whether preventing unauthorized access to digital photographs, ensuring compliance with copyright regulations, or guaranteeing the integrity of a video teleconference, all multimedia applications require increased security in the presence of talented intruders. Specifically, as more and more files are preserved on disk the requirement to provide secure storage has become more important. This paper presents a survey of techniques for securely storing multimedia data, including theoretical approaches, prototype systems, and existing systems ready for employment. Due to the wide variety of potential solutions available, a prospective customer can easily become overwhelmed while researching an appropriate system for multimedia requirements. Since added security measures inevitably result in slower system performance, certain storage solutions provide a better fit for particular applications along a security/performance continuum. This paper provides an overview of the prominent characteristics of several systems to provide a foundation for selecting the most appropriate solution. Initially, the paper establishes a set of criteria for evaluating a storage solution based on confidentiality, integrity, availability, and performance. Then, using these criteria, the paper explains the relevant characteristics of select storage systems providing a comparison of the major differences. Finally, the paper examines specific applications of storage devices in the multimedia environment.
Tamper-resistant storage techniques provide varying degrees of authenticity and integrity for data. This paper surveys five implemented tamper-resistant storage systems that use encryption, cryptographic hashes, digital signatures and error-correction primitives to provide varying levels of data protection. Five key evaluation points for such systems are: (1) authenticity guarantees, (2) integrity guarantees, (3) confidentiality guarantees, (4) performance overhead attributed to security, and (5) scalability concerns. Immutable storage techniques can enhance tamper-resistant techniques. Digital watermarking is not appropriate for tamper-resistance implemented in the storage system rather than at the application level.
Security of storage and archival systems has become a basic necessity in recent years. Due to the increased vulnerability of the existing systems and the need to comply with government regulations, different methods have been explored to attain a secure storage system. One of the primary problems to ensuring the integrity of storage systems is to make sure a file cannot be changed without proper authorization. Immutable storage is storage whose content cannot be changed once it has been written. For example, it is apparent that critical system files and other important documents should never be changed and thus stored as immutable. In multimedia systems, immutability provides proper archival of indices as well as content. In this paper we present a survey of existing techniques for immutability in file systems.
Multicasting at the IP layer has not been widely adopted due to a combination of technical and non-technical
issues. End-system multicast (also called application-layer multicast) is an attractive alternative to IP layer
multicast for reasons of user management (set-up and control) and attack avoidance. Sessions can be established
on demand such that there are no static points of failure to target in advance.
In end-system multicast, an overlay network is built on top of available network services and packets are
multicasted at the application layer. The overlay is organized such that each end host participating in a multicast
communication re-sendsmulticasted messages to some of its peers, but not all of them. Thus end-system multicast
allows users to manage multicast sessions under varying network conditions without being dependent on specific
network conditions or specific network equipment maintaining multicast state information.
In this paper we describe a variety of proposed end-system multicast solutions and classify them according to
characteristics such as overlay building technique, management, and scalability. Comparing these characteristics
across different end-system multicast solutions is a step toward understanding which solutions are appropriate
for different battlespace requirements and where further research is needed.
Applications in high speed ATM networks will specify quality of service (QoS) requirements on an end-to-end basis. Typical application QoS metrics are cell loss rate, delay jitter, throughput, and maximum delay. Obviously, the individual network control components will need to provide more stringent quality of service than specified by the applicaiton. In this ppaer, we study (via simulation) how end-to-end QoS parameters provided by the application can be mapped into the QoS numbers used by the individual network control components.
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