Alagu Periyannan

Supporting constant-bit-rate-encoded MPEG-2 transport over local ATM networks

As one of the fast-developing switch-based high-speed networks, asynchronous transfer mode (ATM) is a promising network standard which may satisfy various requirements of multimedia computing. The Moving Picture Experts Group (MPEG) standard was designed to support full motion video stored on digital storage media at compression ratios up to 200:1. MPEG-2 is the second development phase of the MPEG standard and is designed for higher resolutions (including but not restricted to interlaced video) and higher bit rates (up to 20 Mbits/s). In this paper, the ATM adaptation layer type 5 (AAL-5) protocol was used to encapsulate constant-bit-rate-encoded MPEG-2 transport packets because of AAL-5’s general availability. However, there is a mismatch of size between MPEG-2’ s transport packets (188 bytes) and ATM AAL-5’s protocol data units (up to 65 535 bytes). In this paper, we examine and analyze four different packing schemes, 1TP, 2TP, nTP-Tight, and nTP-Loose (the scheme we propose), which encapsulated a certain number of MPEG-2 transport packets into one AAL-5 PDU. nTP-Loose scheme is proposed to have (1) better end-to-end performance than schemes 1TP and 2TP, (2) better error-recovery capability than scheme nTP-Tight, and (3) the same buffer requirement as scheme 2TP. A Power Macintosh ATM platform was used to identify the range of possible ways of packing MPEG-2 transport packets into one ATM AAL-5 PDU, when schemes with more than two MPEG-2 transport packets are chosen. Based on the test results, 10 or 12 MPEG-2 transport packets, which can yield throughputs of 70.36 and 78.98 Mbits/s, respectively, are recommended. Fast forward and backward playing of MPEG-2 movies (several times the video display speed) can be easily achieved via ATM networks.

Key to the success of asynchronous transfer mode: an application programming interface

Asynchronous transfer mode (ATM) networks are scalable via a wide variety of physical link speeds and can be run in both the local and wide areas. Bandwidth reservation and quality of service guarantees make ATM attractive to deliver multimedia information in real-time. Existing protocol suites can be extended. However, they do not give access to those characteristics. Therefore, applications demand an ATM application programming interface (API) to take advantage of those features. This paper covers a special syntax mapping of the ATM API services on top of X/Open Transport Interface (XTI) which is able to give applications access directly to the special quality and traffic services of an ATM network. A particular realization of the API on the XTI environment is proposed and implemented on the MacOS networking platform. It provides a flexible and modular design of the ATM networking. Finally, the paper concludes with one ATM-aware application (video on demand) which requires real-time streaming data.