Internet Engineering Task Force Internet Draft Nomura/Schulzrinne Fujitsu/Columbia U. draft-nomura-mmusic-img-requirements-00.txt February 24, 2003 Expires: August 2003 Protocol Requirements for Internet Media Guides STATUS OF THIS MEMO This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress". The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt To view the list Internet-Draft Shadow Directories, see http://www.ietf.org/shadow.html. Abstract This memo specifies requirements for a protocol for accessing and updating Internet Media Guide (IMG) information for media-on-demand and multicast applications. The requirements details general protocol operations and description formats transmitted by an uni- or bi- directional transport based on the IMG framework. 1 Introduction An Internet Media Guide (IMG) [1] describes one or more multimedia items, available either for download, streaming or multicast distribution [2]. There may also be meta-guides, i.e., IMGs that describe other IMGs. IMGs allow users to initiate streaming media sessions, schedule delivery of downloadable or multicast content or listen to live multicast sessions. Nomura/Schulzrinne [Page 1] Internet Draft IMG Requirements February 24, 2003 Protocols are needed to request, transmit and update such IMGs, as well as let users know if the IMG has changed. The same host can serve and produce IMG information. This draft classifies the features, protocol components and description formats of the IMG and shows requirements and describes some possible solutions. 2 Terminology The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [3]. Internet Media Guide (IMG): An IMG is a set of meta-data describing the features of multimedia content. For example, meta-data may consist of the URI, title, air time, bandwidth needed, file size, text summary, genre, and access restrictions. IMG source: An IMG source is a logical entity that sends IMGs to one or more IMG receivers. IMG receiver: An IMG receiver is a logical entity that receives IMGs from an IMG source. 3 Overview 3.1 Features of an IMG IMG data may be updated as time elapses because content described in the guide may be changed. For example, the airtime of an event such as a concert or sports event may change, possibly affecting the air time of subsequent medias. Also, content may be made available only temporarily, e.g., via multicast, based on popularity. If a particular program proves to be popular, additional sessions might be added. Similarly, the IMG may be made available for download from a different set of servers. 3.2 Devices Using the IMG We assume that any Internet host can be a source of content and thus meta data. Some of the content sources and sinks may only be connected to the Internet sporadically. Also, a single human user may use many different devices to access meta data, including bandwidth- constrained mobile devices. Thus, we envision that IMGs can be sent and received by, among others, by cellular phones, PDA (Personal Nomura/Schulzrinne [Page 2] Internet Draft IMG Requirements February 24, 2003 Digital Assistant), personal computer, streaming video server, set- top box, video camera, and PVR (Personal Video Recorder). 4 Requirements 4.1 On-demand Retrieval on a Bi-directional Transport Since an IMG may contain a large amount of data, the IMG receiver needs to be able to access the guide when convenient (e.g., when sufficient network bandwidth is available to the user). If the IMG receiver and source does not support a bi-directional transport, the on-demand retrieval is not required. 4.2 Receiving IMGs without a request Instead of requesting the MG periodically, a user may want to simply receive updated versions when they become available [4]. Here, multicast distribution [5] is an efficient mechanism as long as the MG data volume is small. If the IMG receiver and source does not support a multicast transport, this is not required. 4.3 Customized IMG User may require a subset of the IMG according to their preference (type of content, media format, appropriate age group, etc.) and configuration. 4.4 Different Kinds of Devices The protocol is designed to be sufficiently simple so as to be implemented on the small devices such as a cellular phone and PDA. 4.5 Many Kinds of Multimedia Content IMGs may describe a variety of media formats, not just (say) MPEG- derived formats. For example, IMGs may describe a executable binary file such as a game program. IMGs may describe other IMGs. IMGs should be able to describe parts of multimedia streams, e.g., a news story within a news magazine. 4.6 IMG as Web IMGs should allow for a web structure, i.e., where IMG may refer to other guides or actual meta data. Just like the web, links (with meta data about the linked-to entity) and content should be able to appear Nomura/Schulzrinne [Page 3] Internet Draft IMG Requirements February 24, 2003 in the same IMG. 4.7 Change Notification Since IMGs can change at any time, receivers of IMGs should be notified of such changes, without necessarily re-sending the whole IMG. Depending on the size of the guide, the interested party may want to defer retrieving the actual information. The change notification should be addressed to a logical user, not a host, since users may change devices. As an example, consider a storage device requires the up-to-date video file from an IP-reachable video camera but the camera is connected only sporadically. When the camera is connected on the network and has a new video object, the storage device must be notified of its availability immediately. 4.8 Reliable Message Exchange If the IMG receiver and source supports a bi-directional transport, this protocol should support a reliable message exchange. 4.9 Multiple Sources Users should be able to obtain IMGs from any number of sources, i.e., there is no (single) root node in the tree. 5 Protocol Components 5.1 General Operations Protocols for IMG access can be divided into three operations [4]: IMG RETRIEVE: A user can obtain an IMG listing one or more multimedia resources, selecting an appropriate subset. IMG SUBSCRIBE: A user can subscribe to change notifications for meta-data elements of interest, or new IMG elements matching a profile. IMG NOTIFY: When the IMG source and receiver supports the uni- directional transport and detects a change in IMG, the source simply sends a notification message to the receiver. When the IMG source and receiver supports the bi- directional transport, and detects a change in the IMG, which has been subscribed to by a receiver, the source sends a notification message to the receiver. The receiver Nomura/Schulzrinne [Page 4] Internet Draft IMG Requirements February 24, 2003 replies with an acknowledgement. This message may be forwarded to a suitable device. 5.2 IMG Data Format An IMG may refer multiple content, and content may consist of sub- content. Each sub-content is described by a set of parameters. Thus, an IMG is structured data [4]. An IMG may refer (via URI) to other IMGs. Such references improve flexibility and scalability and simplifies decentralized management of IMGs. However, it makes update notifications somewhat more challenging. 5.3 User Preferences A user may specify his preferences in the IMG SUBSCRIBE message and may want to keep a particular part of the IMG up-to-date. A user should be able to select parts of the IMG by using an IMG RETRIEVE. If an XML-based format is used, this appears to be a special case of an XML query operation (http://www.w3.org/XML/Query). Unlike for presence, where likely only the last state is of interest, update notifications for disconnected users may need to be queued. 6 Related Protocols SDPng [6] can describe meta-data for content by using XML. Since SDPng addresses multiparty multimedia conferences, it is necessary to extend the XML schema in order to describe general multimedia content. MPEG-7 [7] can describe meta-data of content by using XML. It defines an XML schema for general multimedia content and has a IMG structure. SAP [5] distributes session descriptions via multicast. It does not support fine-grained meta data selection and update notifications, as it always sends the whole meta data. Given the lack of a wide-area multicast infrastructure, it is likely only deployable within a local area network. SIP [8] and SIP-specific event notification [9] can be used to notify subscribers of the update of the IMG. Since IMGs are likely to be referencable by URLs, [10] describes a means to notify users of changes in those URLs. Nomura/Schulzrinne [Page 5] Internet Draft IMG Requirements February 24, 2003 HTTP or SOAP can be used to request a IMG. SOAP could be used to define queries. 7 Security Considerations TBD 8 Acknowledgements The authors would like to thank Juka-Pekka Luoma (Nokia), Rod Walsh (Nokia) and Toni Paila (Nokia) for thier comments on the draft. 9 Bibliography [1] Y. Nomura and H. Schulzrinne, "A framework for Internet Media Guides," internet draft, Internet Engineering Task Force, Feb. 2003. Work in progress. [2] B. Quinn and K. Almeroth, "IP multicast applications: Challenges and solutions," RFC 3170, Internet Engineering Task Force, Sept. 2001. [3] S. Bradner, "Key words for use in rfcs to indicate requirement levels," RFC 2119, Internet Engineering Task Force, Mar. 1997. [4] J. Luoma, "MUPPET: Internet media guide unidirectional," internet draft, Internet Engineering Task Force, Dec. 2002. Work in progress. [5] M. Handley, C. E. Perkins, and E. Whelan, "Session announcement protocol," RFC 2974, Internet Engineering Task Force, Oct. 2000. [6] D. Kutscher, J. Ott, and C. Bormann, "Session description and capability negotiation," internet draft, Internet Engineering Task Force, July 2002. Work in progress. [7] ISO (International Organization for Standardization), "Overview of the MPEG-7 standard," ISO Standard ISO/IEC JTC1/SC29/WG11 N4509, International Organization for Standardization, Geneva, Switzerland, Dec. 2001. [8] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. R. Johnston, J. Peterson, R. Sparks, M. Handley, and E. Schooler, "SIP: session initiation protocol," RFC 3261, Internet Engineering Task Force, June 2002. [9] A. B. Roach, "Session initiation protocol (sip)-specific event notification," RFC 3265, Internet Engineering Task Force, June 2002. Nomura/Schulzrinne [Page 6] Internet Draft IMG Requirements February 24, 2003 [10] X. Wu and H. Schulzrinne, "Use SIP MESSAGE method for shared web browsing," internet draft, Internet Engineering Task Force, Nov. 2001. Work in progress. 10 Author's Addresses Yuji Nomura Fujitsu Laboratories Ltd. 4-1-1 Kamikodanaka, Nakahara-ku, Kawasaki 211-8588 Japan Email: nom@flab.fujitsu.co.jp Henning Schulzrinne Dept. of Computer Science Columbia University 1214 Amsterdam Avenue New York, NY 10027 USA Email: schulzrinne@cs.columbia.edu Nomura/Schulzrinne [Page 7]