Application Level Framing Research Articles

Adaptive packet video streaming over IP networks: a cross-layer approach

There is an increasing demand for supporting real-time audiovisual services over next-generation wired and wireless networks. Various link/network characteristics make the deployment of such demanding services more challenging than traditional data applications like e-mail and the Web. These audiovisual applications are bandwidth adaptive but have stringent delay, jitter, and packet loss requirements. Consequently, one of the major requirements for the successful and wide deployment of such services is the efficient transmission of sensitive content (audio, video, image) over a broad range of bandwidth-constrained access networks. These media will be typically compressed according to the emerging ISO/IEC MPEG-4 standard to achieve high bandwidth efficiency and content-based interactivity. MPEG-4 provides an integrated object-oriented representation and coding of natural and synthetic audiovisual content for its manipulation and transport over a broad range of communication infrastructures. In This work, we leverage the characteristics of MPEG-4 and Internet protocol (IP) differentiated service frameworks, to propose an innovative cross-layer content delivery architecture that is capable of receiving information from the network and adaptively tune transport parameters, bit rates, and QoS mechanisms according to the underlying network conditions. This service-aware IP transport architecture is composed of: 1) an automatic content-level audiovisual object classification model; 2) a reliable application level framing protocol with fine-grained TCP-Friendly rate control and adaptive unequal error protection; and 3) a service-level QoS matching/packet tagging algorithm for seamless IP differentiated service delivery. The obtained results demonstrate, that breaking the OSI protocol layer isolation paradigm and injecting content-level semantic and service-level requirements within the transport and traffic control protocols, lead to intelligent and efficient support of multimedia services over complex network architectures.

ITP: an image transport protocol for the Internet

Images account for a significant and growing fraction of Web downloads. The traditional approach to transporting images uses TCP, which provides a generic reliable in-order bytestream abstraction, but which is overly restrictive for image data. We analyze the progression of image quality at the receiver with time, and show that the in-order delivery abstraction provided by a TCP-based approach prevents the receiver application from processing and rendering portions of an image when they actually arrive. The end result is that an image is rendered in bursts interspersed with long idle times rather than smoothly.This paper describes the design, implementation, and evaluation of the image transport protocol (ITP) for image transmission over loss-prone congested or wireless networks. ITP improves user-perceived latency using application-level framing (ALF) and out-of-order application data unit (ADU) delivery, achieving significantly better interactive performance as measured by the evolution of peak signal-to-noise ratio (PSNR) with time at the receiver. ITP runs over UDP, incorporates receiver-driven selective reliability, uses the congestion manager (CM) to adapt to network congestion, and is customizable for specific image formats (e.g., JPEG and JPEG2000). ITP enables a variety of new receiver post-processing algorithms such as error concealment that further improve the interactivity and responsiveness of reconstructed images. Performance experiments using our implementation across a variety of loss conditions demonstrate the benefits of ITP in improving the interactivity of image downloads at the receiver.

Application level framing applied to image compression

Two well-known wavelet zerotree encoding algorithms, Embedded Zerotree Encoding (Ezw) and Set Partitioning in Hierarchical Trees (Spiht), provide excellent progressive display when images are transmitted over reliable networks. However, both algorithms are state-dependent and can perform poorly over unreliable networks. We apply the concept of network-conscious image compression to theSpiht wavelet zerotree encoding algorithm, to improve its performance over unreliable networks. Experimental results confirm the utility of network-conscious image compression concept.

Tunable reliable multicast for periodic information dissemination

Existing reliable transport protocols for periodic information dissemination ignore application semantics while attempting to be 100% reliable. "Application Level Framing" (ALF) suggests that taking application semantics into account when designing transport protocols can result in performance that is highly optimized for the network. We apply this principle in designing a policy-based TUNAble semi-reliable multicast protocol (TUNA) for periodic information dissemination. Specifically, TUNA is not constrained to guarantee full reliability, but allows the receiving application to selectively request retransmissions of lost portions of the data stream, based on user-level policies. TUNA uses statistical properties of the data stream to adaptively guide receivers in dynamically altering their reliability policies. This is particularly well matched for satellite systems, where end node to satellite bandwidth is limited, especially when shared by large community of end nodes. Our simulation results show that TUNA is made highly scalable by reducing the number of NACKs sent back to the information source, while keeping the staleness of received data within application-specified bounds. Under large session sizes, TUNA yields a factor of 1.5 to 6 improvement over a fully reliable scheme; for high loss rates, it results in a factor of 1.5 to 5 improvement. TUNA is also able to reduce contention for retransmission request bandwidth in a multiple access backchannel environment. We have implemented TUNA and a prototype application called InfoCaster in the MASH toolkit.

Scalable, error-resilient, and high-performance video communications in mobile wireless environments

A novel mobile communications system is proposed, which provides not only effective but also efficient video access for mobile users when communicating over low-bandwidth error-prone wireless links. The middleware implemented by a mobile proxy server at the mobile support station is designed for the seamless integration of mobile users with video servers, so the specific details of the underlying protocols and source/channel coding techniques are hidden to both the video server and mobile client. Based on the concept of application-level framing, the application (video codec in our case) plays a significant role in network communications that most of functionalities of the system are implemented as part of the application. As such, at the application layer, adaptive source- and channel-coding techniques are developed to jointly provide the user with the highest possible video quality. For efficient source coding, our high-performance low-complexity video-coding algorithm called a 3-D significance-linked connected component analysis (3D-SLCCA) is chosen. Due to its high robustness against channel-error propagation, 3D-SLCCA is well suited for wireless environments. For error-resilient channel coding, a multilayer transmission error-control mechanism is developed. Since there is no additional requirement imposed on either the mobile client or the video server, mobile users interact with the server in exactly the same way as stationary users. Extensive computer experiments demonstrate the effectiveness of the proposed system.

Network-conscious GIF image transmission over the Internet

Traditional image compression techniques seek the smallest possible file size for a given level of image quality. By contrast, network-conscious image compression techniques take into account the fact that a compressed image will be transmitted over a packet-switched network that may lose and reorder packets. We describe GIFNCa, a network-conscious revision of the popular GIF89a standard. As with GIF89a, GIFNCa compresses an image using LZW encoding, however GIFNCa does so using an Application Level Framing approach. The data is segmented into path MTU-size data units, each of which can be independently decompressed and displayed on its own. Under lossy network conditions, when used in combination with an unordered transport protocol, GIFNCa permits faster progressive display at the receiver than GIF89a over an ordered transport protocol. This advantage comes in exchange for a small penalty in overall compression. This paper defines GIFNCa, and presents preliminary experimental data concerning this tradeoff. The overall goal of this research is to illustrate (1) the value of considering network characteristics in designing image formats, and (2) the value of unordered transport service.

Impact of out-of-sequence processing on the performance of data transmission

Application Level Framing (ALF) was proposed by Clark and Tennenhouse as an important design principle for developing high performance applications. ALF relies in part on the ability of applications and protocols to process packets independently one from the other. Thus, performance gains one might expect from the use of ALF are clearly related to performance gains one might expect from applications that can handle and process packets received out-of-sequence, as compared to application that require in-sequence delivery (FTP, TELNET, etc.). In this paper, we examine how the ability to process out-of-sequence packets impacts the efficiency of data transmission. We consider both the impact of application parameters such as the time to process a packet by the application, as well as network parameters such as network transmission delay, network loss rate and flow and congestion control characteristics. The performance measure of interest are total latency, buffer requirements, and jitter. We show, using experimental and simulation results, that out-of-sequence processing is beneficial only for very limited ranges of transmission delays and application processing time. We discuss the impact of this on the architecture of communication systems dedicated to distributed multimedia applications.

An ALF communication architecture: design and automated implementation

The application level framing (ALF) principle states that information should be packetized by the application into application data units (ADUs), each of which should be at the same time a unit of transmission, a unit of control, and a unit of processing. This paper describes a communication system architecture based on the ALF principle, which then attempts to maximize what might be gained from using ADUs. In this architecture, protocols are tailored to application requirements, i.e., to ADU types. In a first approximation, we consider three specific requirements, namely, in-order delivery, reliable delivery, and real-time delivery. ALF-based systems promise performance gains; however, implementing them in practice might be a complex task. Therefore, we have developed a compiler that automatically generates ALF-based communication systems starting from formal specification of applications. We have used this compiler to generate protocols tailored to three specific applications. Experimental results show that the gains are linked to application "complexity".

Network text editor (NTE)

IP Multicast, Lightweight Sessions and Application Level Framing provide guidelines by which multimedia conferencing tools can be designed, but they do not provide specific solutions. In this paper, we use these design principles to guide the design of a multicast based shared editor, and examine the consequences of taking a loose consistency approach to achieve good performance in the face of network failures and losses.

High-performance protocol architecture

The development of high-speed networking applications requires improvements to data communication protocols in order to efficiently provide the required services to the applications. In this survey paper, we will first give a rapid presentation of protocol optimization techniques and of some high-speed transport protocols developed for specific application needs. We will then present a new protocol architecture based on the “Application Level Framing” (ALF) and “Integrated Layer Processing” (ILP) concepts. ALF states that applications send data as a sequence of autonomous “frames”, which will be at the same time the unit of transmission, the unit of control and the unit of processing. This allows for efficient design of application specific protocols. It also enables ILP, i.e., the integration of multiple transmission control layers in a single loop, maximizing the efficiency of modern processors. We will present both the architectural design aspects and the corresponding implementation problems. Practical experimentations with ALF and ILP will also be described and their benefits and limitations assessed. We will also present a new approach to network architecture namely the active networks approach, and discuss its pros and cons.

A reliable multicast framework for light-weight sessions and application level framing

This paper describes scalable reliable multicast (SRM), a reliable multicast framework for light-weight sessions and application level framing. The algorithms of this framework are efficient, robust, and scale well to both very large networks and very large sessions. The SRM framework has been prototyped in wb, a distributed whiteboard application, which has been used on a global scale with sessions ranging from a few to a few hundred participants. The paper describes the principles that have guided the SRM design, including the IP multicast group delivery model, an end-to-end, receiver-based model of reliability, and the application level framing protocol model. As with unicast communications, the performance of a reliable multicast delivery algorithm depends on the underlying topology and operational environment. We investigate that dependence via analysis and simulation, and demonstrate an adaptive algorithm that uses the results of previous loss recovery events to adapt the control parameters used for future loss recovery. With the adaptive algorithm, our reliable multicast delivery algorithm provides good performance over a wide range of underlying topologies.

Internet protocols for multimedia communications. II. Resource reservation, transport, and application protocols

Part I (ibid., July-Oct. 1997) surveyed the evolution of Internet protocols and applications and described the Internet protocol IPv6 in detail. This part discusses new developments at the upper layers that support real-time Internet multimedia, such as audio and video conferencing and shared whiteboard applications. Application-level framing (ALF), proposed in 1990 for protocol and application design, now forms the basis for many new Internet protocols and applications, including Real-time Transport Protocol (RTP) and Mbone multimedia applications. RTP supports real-time applications that adapt to changing network situations to maintain the quality of service (QoS). The Resource Reservation Protocol (RSVP) provides new Internet services with higher quality than best-effort by means of resource reservations.

High performance protocol architectures – HIPPARCH project and workshop

The objective of the HIPPARCH project is to study and design high performance communication architectures and implementations, based particularly on the Application Level Framing and Integrated Layer Processing concepts. The HIPPARCH project holds annual workshops at which papers from leading communications research centers are presented. The papers in this issue of JHSN represent early results of the project and other groups engaged in similar research. 1. Introdnction HIPPARCH is an EC ESPRIT Basic Resarch project which began in january 1994 and is tasked with establishing a novel architectural design for communications protocols to be used for distributed applications over high speed networks. The project partners, INRIA, SICS, UCL and UTS, are all longstanding members of the research community working on improving our understanding and implementation of communications systems. The requirement for a new architecture is clear. Traditional layered protocol architectures such as the ISO OSI model (see for example [3]) and the ARPA Internet model (see for example [4]), are reaching the very end of their extended lifetimes. The problem can partly be blamed on an artificial separation of concerns in layers that represented interfaces between different service providers: The service/protocol concept derives historically from the model X.25 originally presented to the user of a network as inteiface. There would be a link, network, transport and session provider, perhaps all of which would be different potential vendors. This absurd extreme view of a potential in layers in the stack has proved one thing: The costs of such a market in inefficiency mean buyers go to other markets the workable market appears to be in three layers: end system hardware and operating systems; end systems communications stacks; finally transmission networks. HIPPARCH concentrates its efforts on the second of these, to focus on end-to-end transmission control mechanisms and architecture. We are seeing a frantic flurry of effort piggybacked on the IPng effort to introduce a new architecture. Examples of such attempts include [5] and [6]. Some of these have led to partial attempts to address transport protocol problems as well [2]. While these address the network layer, they do not provide an integrated approach to designing the whole stack. We have adopted Application Level Framing and Integrated Layer Processing as intuitively reasonable guiding principles for selecting a new architecture that does address whole protocol stack design. In the initial year, we have carried out a number of tasks to deconstruct the problem. These fall roughly under the following headings: Adaptable transmission control mechanisms. Networks and End systems are and will probably always be heterogeneous. We should design systems that can operate for a large range of applications as well as TCP does now for a small one. 0926-6801/96/$8.00 © 1996 lOS Press. All rights reserved 106 1. Crowcr()ft / High peiformance protocol architectures HIPPARCH project and workshop Novel implementation techniques. We want to gather as many manual implementation techniques together as the basis of our decision on an architecture we want to maximise the gene pool diversity of the communications eco-system we are trying to build. In particular, we want to avoid pitfalls present in hidden assumptions about operating system structures (Unix, OS/2, Windows NT, etc) and about processor/memory architectures (uni versus multi, shared versus distributed memory) in the end system. In general, the final goal is a novel communication support architecture. This is not limited to implementation architecture, but to gain more from implementation techniques, the architecture itself has to be modified. Experiences with ALFIILP. While we seek new techniques, we would like to gain as much experience as possible using these particular guiding principles. Tools and description languages for protocol implementation. Initially, a lot of our efforts have involved manual programming of our new stacks. However, the objective is to eventually provide descriptions of application requirements, and automatically synthesize new protocols and protocol stacks to support the applications. To this end, initially, we wish to describe protocols and modules, and automatically generate working systems. Later this will permit verification/[8] and validation [8].

A reliable multicast framework for light-weight sessions and application level framing

This paper describes SRM (Scalable Reliable Multicast), a reliable multicast framework for application level framing and light-weight sessions. The algorithms of this framework are efficient, robust, and scale well to both very large networks and very large sessions. The framework has been prototyped in wb, a distributed whiteboard application, and has been extensively tested on a global scale with sessions ranging from a few to more than 1000 participants. The paper describes the principles that have guided our design, including the IP multicast group delivery model, an end-to-end, receiver-based model of reliability, and the application level framing protocol model. As with unicast communications, the performance of a reliable multicast delivery algorithm depends on the underlying topology and operational environment. We investigate that dependence via analysis and simulation, and demonstrate an adaptive algorithm that uses the results of previous loss recovery events to adapt the control parameters used for future loss recovery. With the adaptive algorithm, our reliable multicast delivery algorithm provides good performance over a wide range of underlying topologies.

Architectural considerations for a new generation of protocols

The current generation of protocol architectures, such as TCP/IP or the ISO suite, seem successful at meeting the demands of todays networks. However, a number of new requirements have been proposed for the networks of tomorrow, and some innovation in protocol structuring may be necessary. In this paper, we review some key requirements for tomorrow's networks, and propose some architectural principles to structure a new generation of protocols. In particular, this paper identifies two new design principles, Application Level Framing and Integrated Layer Processing. Additionally, it identifies the presentation layer as a key aspect of overall protocol performance.