Multimedia Communications Session Management 1

Multimedia Communications involves itself with the communications of highly distributed multimedia data objects that require precise timing at and between multiple locations. This paper proposes a way to handle this level of communications through enhancements made at the Session Layer of the OSI protocol standard. The approach taken starts with a definition of multimedia data objects and then develops the required elements for the Session Layer. Detailed implementations are presented and discussions on their performance comparisons are discussed. 1.0 Introduction Multimedia Communications is a discipline that combines the ideas of the human senses, disparate storage and data structures, varying interfaces and complex communications systems. The basis concept of a multimedia environment has evolved from that of the single media data focused world of the computer specialist to the need to provide a fully integrated system for a human user to interact with using information stored on may different storage media. Multimedia consists of a matching of the three elements of the senses, the storage media and the interface devices. It has been argued elsewhere (see McGarty, 17) that multimedia should not be confined to merely the storage of information of multiple storage devices. Rather, multimedia must include the senses and the interfaces as well. In fact, for the purpose of this paper we define multimedia as the confluence of storage, senses and interfaces. Specifically, multimedia relates to constructs of not only information storage but also information processing and communications. It encompasses all of the senses, although we currently only focus on the senses of sight, sound and touch. The definition that we take of multimedia in this paper is an expansive definition. It has been taken to provide a basis for the next step which is multimedia communications, which takes the multimedia paradigm and adds multiple human elements and as such transcends the prototypical computer communications view of the world. When we introduce the communications concepts, we do so in the context of having multiple users share in the use of the multimedia objects. Thus multimedia communications requires that multiple human users have sensory interfaces to multiple versions of complex objects stored on multiple storage media. In contrast to data communications in the computer domain, where humans are a secondary after thought, and optimization is made in accordance with the machine to machine connection, multimedia a communications is a human to many other human communications process that must fully integrate the end user into the environment. Multimedia communications thus generates a sense of conversationality, it is sustainable over longer periods, and it has an extreme fluidity of interaction. Various authors have recently addressed the issue of multimedia communications with an architectural approach. (See Little and Ghafoor, Nicolaou, and Steinmetz). The current approaches focus on one of two extremes, either on broadband communications and the transport mechanism or on the multimedia storage aspects of the system design. Little and Ghafoor have attempted to integrate the presentation and data object side of the problem and have at a higher level, attempted to address the communications issues. Nicolaou has developed a communications architecture that follows the OSI standards but in attempting to 1This paper was prepared while the author was on the Faculty of MIT in the Academic Year of 1989-1990. 6/8/2005 4:25 PM C:\Papers\List By Date\1989_12_01_MMSess.doc introduce the multimedia issues has been forced to introduce several new constructs. Various other researchers in this area have focused on the lower protocol layers and have specifically been concerned with transport layer problems and below. One of the major challenges to multimedia communications is that today there are broadband architectures that are developed that provide higher speed communications using direct extensions of the techniques developed in the data world of packet communications. Specifically such techniques as ATM and SMDS, as well as FDDI are direct offshoots of local area networks and packet technology. The fail to understand the paradigm that we are developing in this paper that relates to the structure of the multimedia object and the conversationality of multimedia communications. In this paper, we concentrate on three issues in the area of multimedia communications; the data objects, the conversationality of the interaction and the overall communications architecture. We first note that the data structures in multimedia environments are dramatically different than those in normal computer data communications. Specifically, Mullender has shown that typical data file sizes that are transferred in a UNIX environment are on the order of 2K bits whereas in a multimedia environment the file size may average 100 Mbits. Secondly, a multimedia environment needs to handle real time data interaction such as that in real time voice and video. As is well known, such transport protocols as TCP/IP are not adequate from a delay perspective to support these types of data objects. The conversationality aspect of the multimedia environment is key to effective communications. In this paper we focus on utilizing the Session layer from the OSI format for the delivery of the multi-user conversationality. Historically, the session layer (See Tannenbaum) has been relegated to a secondary position in the OSI hierarchy. In a multimedia environment, we show that the session functionality, refined and expanded, provides the essential integrating capability for conversationality. The remaining communications services, at OSI layer 4 and below, become, at best, delimiting factors in the communications environment. In this paper we show that there are certain underlying performance factors of the lower four layers, that when combined control the overall end to end performance as viewed from the users perspective. As a major point in this paper, we argue that the standard approach to communications system design, from the physical layer and up is the wrong way to proceed for multimedia. Specifically, in a multimedia environment, one must, perforce of user acceptance, design the system from the top layers and down. 2.0 Multimedia Data Objects In a more standard computer communications environment, the data objects have significant structure and they are frequently integrated into a system wide data base management system that ensures the overall integrity of the data structures. In a multimedia environment, the data elements are more complex, taking the form of video, voice, text, images and may be real time in nature or can be gathered from a stored environment. More importantly, the separate data objects may combined into more complex forms so that the users may want to create new objects by concatenating several simpler objects into a complex whole. Thus we can conceive of a set of three objects composed of an image, a voice annotation and a pointer motion annotating the voice annotation. The combination of all three of these can also be viewed as a single identifiable multimedia object. Before commencing on the issues of communications, it is necessary to understand the data objects that are to be communicated. We can consider a multimedia data object to be composed of several related multimedia data objects which are a voice segment, an image and a pointer movement (e.g. mouse movement). As we have just described, these can be combined into a more complex object. We call the initial objects Simple Multimedia Objects (SMOs) and the combination of several a Compound Multimedia Object (CMO). In general a multimedia communications process involves one or multiple SMOs and possibly several CMOs.