ISMA eyes standards, open architecture

ISMA eyes standards, open architecture
The Internet Streaming Media Alliance's goal is to provide an open specification for interoperability, allowing end users freedom of choice and vendors the ability to compete in a more open market. Since its inception in 2000 by Apple, Cisco Systems, IBM, Kasenna, Philips and Sun Microsystems, ISMA has received wide industry support from companies interested in developing an open-source approach in these proprietary times.

The mission is simple: to facilitate and promote the adoption of a standards-based end-to-end architecture to stream rich media content over Internet Protocol (IP) infrastructures for greater interoperability among products from multiple vendors.

ISMA is not a standards organization but a nonprofit industry alliance with a diverse membership from all aspects of the streaming workflow. We use already-existing open standards, whenever possible, to develop interoperable specifications, and we invent new technologies only when there is a need to fill a gap due to a lack of an open solution.

ISMA is interested in providing the industry with an "invest once" solution that will eventually drive down the cost of multimedia delivery, whether it is over wired or wireless networks to PCs, PDAs or cell phones.

Last December, the member companies came together to develop the first version of our specification. That specification focuses on rich media delivery over IP networks in an interoperable manner. It provides all the open tools to encode, stream and decode media over networks up to 1.5 Mbits/second. It uses MPEG-4 as the compression standard for audio and video coding, while it refers to IETF protocols (RTP, RTSP, SDP) for media transport and session control. ISMA 1.0 is an implementation specification that provides all the necessary details to implement an end-to-end open media-streaming solution that can interoperate with solutions from other vendors.

Diverse support

Essentially, ISMA 1.0 supports wireless, narrowband- and broadband-quality networks up to 1.5 Mbits/s. The target client devices range from PDAs to desktop computers. To accommodate the varied network and computational resources, ISMA 1.0 defines two hierarchical profiles; Profile 0 and Profile 1. The higher profile, Profile 1, supports all the tools supported by Profile 0 along with some additional tools.

The media content is tagged to comply with one of the two hierarchical profiles, advertised during a media announcement before establishing the session. Only clients that are compliant with an ISMA profile can expect to receive, decode and play media content of that profile in an interoperable manner.

Profile 0 is aimed at streaming audio/video content on wireless and narrowband networks to low-complexity devices with limited viewing and audio capabilities. The target sessions can be a wireless device or a desktop computer connected over a dial-up modem. Profile 0 has a maximum video bit rate of 64 kbits/s. Profile 1 is aimed at streaming content over broadband-quality networks to provide the end user with a richer viewing experience. It is targeted at more powerful devices than those targeted by Profile 0, with a maximum cumulative bit rate of 1.5 Mbits/s.

In the simplest form, the target architecture of ISMA 1.0 involves a media client and a media server with an IP network connecting them. It is assumed that media is transmitted from the media server to the media client in on-demand or broadcast modes.

The architecture that ISMA 1.0 addresses is intentionally kept simple. That allows a mixture of real-time and offline media delivery over different types of network conditions. The architecture, although simple, allows extensions for a range of services between the media server and the media client.

Those services include intermediate storage, load balancing, repurposing, transcoding, mixing, caching and the like. In most cases the systems are transparent to the media servers and clients. In some cases they present a media client interface to the servers while presenting a media server interface to the clients.

These technologies are used in ISMA 1.0, which details the exact features that must be implemented for interoperability.

• Because MPEG-4 is a versatile toolbox standard that is appropriate for many different markets and devices, specific profiles and levels of MPEG-4 video and audio were chosen to be adopted in the ISMA profiles.
  
• The Session Description Protocol (SDP) is the protocol of choice for the session description of media. It should be noted that SDP information could be transmitted using such protocols as HTTP, RTSP, SAP and SIP.
  
• The Real-Time Streaming Protocol (RTSP) is invoked by ISMA 1.0 as the session control protocol for the approach.
  
• SMA 1.0 adopts the Real-time Transport Protocol (RTP) to transport audio and video streams in real-time from the media server to the client.
  
• Although ISMA 1.0 does not use MPEG-4 systems, it outlines some basic MPEG-4 systems support for compatibility with MPEG-4 media sessions that involve MPEG-4 systems.
  

The Internet Streaming Media Alliance is in the process of developing strict conformance guidelines for the 1.0 spec. Last month, the alliance finalized ISMA 1.0. The spec will be released to the public this month.

For additional information, contact www.isma.tv.