MMUSIC Working Group Internet Draft X. Mingqiang Expires: 3 May 2006 H. Ishii D. Komiya S. Kawaguchi Brijesh Kumar Panasonic November 3, 2005 Requirements for Service Discovery in the Personal Area Network(PAN) draft-mingqiang-mmusic-servicediscovery-pan-req-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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 The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on May 3, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract Several protocols exist in the industry for device/service discovery. Each of these protocols addresses the aspects of device/service discovery in different network environments. A Service Discovery in a PAN Mingqiang Expires - May, 2006 [Page 1] Service discovery in a PAN November 2005 Personal Area Network (PAN) is dynamic in its nature where devices may join and leave the network very frequently. A PAN, being an ad- hoc network, also differs from fixed networks in many other ways. The current generation of service protocols such as SLP were not designed for such an environment. This document specifies the requirements of a service discovery protocol for PANs, which specifically can be used for applications such as multimedia session transfer between devices within a PAN. Table of Contents 1. Introduction..................................................2 1.1 Background and Motivation.................................2 1.2 Terminology...............................................3 1.3 Scope of this document....................................4 2. PAN Characteristics...........................................4 3. Problems Statement............................................5 4. Requirements..................................................7 5. IANA Considerations...........................................7 6. Security Consideration........................................8 7. Acknowledgements..............................................8 8. References....................................................8 9. Author's Addresses............................................8 1. Introduction 1.1 Background and Motivation A Personal Area Network (PAN) is a computer network where a small number of devices in close proximity communicate with each other. The reachability of a PAN is usually measured in just a few meters, although longer ranges can be reached under certain circumstances. A PAN can be used for communication among the personal devices (intra-PAN communication), or for connecting to a higher-level network, and the Internet through a particular PAN device. A PAN was also proposed as a part of the vision of 3GPP All-IP Networks in [4]. As devices come in close proximity to one another, they need to discover each other and services provided by other devices. SLP [2] is a service discovery protocol developed in IETF that provides a framework and protocol for service discovery and selection of network services. It is reasonably scalable in an enterprise network. SSDP (Simple Service Discovery Protocol)[5] is another service/device discovery protocol, which is a part of the UPnP(Universal Plug and Play) specification. It is primarily aimed Mingqiang Expires May 2006 [Page 2] Service discovery in a PAN November 2005 for service discovery within home networks, and small office network environments. Compared with the network environments where SLP and UPnP are applied, a PAN has the following characteristics: - Devices within a PAN are likely to be deployed dynamically. They may join and leave the network frequently. - Communication between devices within a PAN is likely to be affected by unstable radio connectivity, status change caused by user, battery capacity and so on. - Devices forming a PAN may not belong to the same owner. Hence, it may not always be possible for a user to administratively manage all devices forming a PAN. Due to the dynamics of a PAN, prompt discovery of available services, and adaptation to changes in the availability of any services is necessary for building needed applications such as media session transfer. The changes caused by leaving or joining of devices in a PAN should be promptly visible to other devices. Similarly, monitoring of the device and service status should be also considered. But, neither SLP nor SSDP addresses all these need satisfactorily. This document describes the requirements for a framework to enable the design of an efficient service discovery protocol for the PAN. The availability of a service discovery protocol meeting these requirements is a prerequisite for the fast session transfer as discussed in [6] and in [7]. 1.2 Terminology Personal Area Network (PAN): A PAN is a collection of one or more logically associated devices that share the same physical communication medium within a close proximity of each other. PAN formation: A mechanism that establishes the logical association between devices within a PAN . It basically manages the process of leaving and joining of devices in a PAN. PAN monitoring: A mechanism that monitors dynamically changed statuses of devices/ services/ sessions of devices in a PAN. In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119 [1] and indicate requirement levels for compliant implementations. Mingqiang Expires May 2006 [Page 3] Service discovery in a PAN November 2005 1.3 Scope of this document This document proposes requirements for the framework and protocol of service discovery for PANs, which is aimed to help identifying any need of new standardization activity in the IETF to address the proposed requirements. 2. PAN Characteristics A PAN has several unique characteristics such as: Small Scale: A PAN consists of a relatively small number of devices. For example, a piconet of Bluetooth can consist of 1-7 devices. Dynamic Configuration: A PAN configuration can be dynamic since not all devices can be available and active at all times. Some devices may join a PAN only for a limited duration to accomplish a short- term task (e.g., a picture transfer from a digital camera to a portable media player). Device Capability Heterogeneity: Each PAN device may have different memory, battery and computing capabilities. Exact capabilities of devices may not be known a priori or advertised to other devices in the PAN. The service discovery protocol should be designed to take advantage of devices with more resources/capabilities over those with less resources/capabilities. Unconscious Communications: A PAN can be formed based on the user profile that includes the needs of user and so on. Using such a profile, a device may establish association with other devices in a PAN without a user becoming aware of the association. For example, a mobile handset may automatically download pictures from its local memory to a server as soon as a user enters his or her home. PAN Device Ownership: All devices in a PAN need not be necessarily owned by the same user. The association is generally established based on valid credentials of a device rather than the physical ownership of devices. Unreliable Communication Links: Wireless communication is highly affected by interference from other communication sources. Presence of interference may result in high packet losses, and hence unreliable communication link between devices in a PAN. Mingqiang Expires May 2006 [Page 4] Service discovery in a PAN November 2005 3. Problems Statement Two application scenarios are presented for analyzing the problems in current service discovery protocols when applied to a PAN environment. Application scenario 1 Dynamic configuration of a PAN: A user is attending a meeting in an office building which she is not familiar to. She wants to discover a printer around to print a document from her laptop PC. She strolls in the office with her laptop PC installed with an UWB(Ultra Wide Band) interface to find a suitable one in the office. +--------+ +---------+ +---------+ +---------+ |Printer1| |Printer2 | |Printer3 | |Printer4 | +--------+ +---------+ +---------+ +---------+ | | | | +---------- ----+ +---------------+ | Laptop | -----> | Laptop | +----------- ---+ Moving +---------------+ Figure 1 Printers accessed by laptop PC In this scenario, the user's laptop computer forms a PAN with the printers around her that can be accessed by a short-distance wireless communication such as UWB. Because the user is moving, the printers that belong to the PAN formed by her laptop computer are changing dynamically, namely, some printers join the PAN while the other printers may be leaving the PAN. As Figure 1 shows, the printers available to a user while moving change from printer 1 and 2 to printer 3 and 4. Even when the laptop is not moving, printers in the PAN may change too, because unstable radio link may disconnect printers and the laptop. In the current SLP framework and protocol, dynamic connectivity of devices of a PAN is not taken into consideration. For example, if a new device joins the network after a service discovery request is sent, the sender of the request would not know about the device that has the requested service capability. In addition, fast response of service discovery query is expected in this scenario because the user is moving, but existing service discovery protocols may take too much time to get responses; for example, SLP is primarily designed for discovering printers and servers originally and the default times for various timers are in Mingqiang Expires May 2006 [Page 5] Service discovery in a PAN November 2005 the level of seconds and minutes. For example, SLP sets 2 seconds for CONFIG_RETRY that is the wait interval before initial retransmission of multicast or unicast requests. Thus it is difficult for SLP to ensure fast responses without adjusting the default and minimum allowed timer values for various protocol timers. In this scenario, we can also see no fixed and centralized controller or lookup service exists, as devices join and leave frequently. Relying on fixed and pre-configured DAs(Directory Agents) for gathering service advertisements together, as is the case in SLP, is not appropriate for a PAN environment. Application scenario 2 Unexpected device/service status change in a PAN: A user is using her mobile phone and enjoying a Video on Demand (VOD) service. While she comes into her house, at the entrance, she finds that two PCs (PC 1, PC 2) and a TV that are located in her house, are shown as detected on her mobile phone. She decides to transfer the VOD session to PC 1. But, her son begins to use PC 1 at that moment. When she selects PC 1 from her mobile phone for VOD session transfer, a warning message appears that the PC 1 is being used now and is not available for VOD session transfer. In this application scenario, her mobile phone forms a PAN with the devices in her house, finds that PC 1, PC 2 and a TV are available for a VOD session, and lists them on its screen as devices available. But the status of PC 1 changes abruptly,thereby making it unavailable for the VOD session transfer. Such an abrupt status change of service availability needs to be notified by PC 1 or discovered by the user's mobile phone in time. Poor and unstable radio link may disconnect devices and they may not be able to send any messages to announce their departure from the PAN. In addition, the connection between two devices in a PAN may be in an intermittent state. As a result, a device can not access the discovered device when it needs to access the discovered device. Thus, availability of devices in a PAN should be checked. General subscription/ notification mechanism can be used to catch such changes, but it is not guaranteed that the status of device/ service status has been subscribed before it changes. Service discovery requests can be sent periodically to catch a change of status, but it may not be efficient; thus a lightweight monitoring mechanism, that is integrated within the service discovery protocol, may be necessary. Mingqiang Expires May 2006 [Page 6] Service discovery in a PAN November 2005 4. Requirements The requirements of a framework and protocol for service discovery in PAN environments to support application scenarios as described in the previous section are presented below. The framework of a complete service discovery process for a PAN is composed of three components: a generic service discovery, PAN formation, and PAN monitoring. Section 4.1 focuses on generic requirements whereas section 4.2 and 4.3 summarize requirements mainly based on application scenario 1 and application scenario 2,respectively. 4.1 Generic requirements - The size of service discovery protocol for a PAN SHOULD be small enough to be installed in devices with only limited resources. - A service discovery protocol SHOULD provide fast response for service lookup (e.g., desirable in the order of 100ms). - A service discovery protocol for a PAN SHOULD be lightweight and minimize the overall control traffic in PAN networks. - A service discovery protocol MUST provide its own security mechanisms. Link layer security mechanisms may not be available, activated or unsuitable. 4.2 PAN Formation - A PAN formation mechanism SHOULD be able to support notification when a device leaves and joins the PAN network. - A PAN formation mechanism SHOULD be able to support discovery of multiple PANs present at any one location. 4.3 PAN Monitoring: - A PAN monitoring mechanism SHOULD support monitoring of statuses of various entities such as devices, as well as services and sessions of a device. - A PAN monitoring mechanism SHOULD be lightweight in traffic. 5. IANA Considerations Mingqiang Expires May 2006 [Page 7] Service discovery in a PAN November 2005 There is no need for IANA considerations in current version of this document. 6. Security Consideration Secure service discovery is strictly required in PANs. But the service discovery protocol MUST NOT rely on physical link security between devices. Service discovery framework and protocol SHOULD include the security mechanism. This document currently concentrates on the requirements for service discovery for PANs. The security concerns will be addressed in the future revision. 7. Acknowledgements We thankfully acknowledge the help of our colleague Mahfuz Rahman of PDNL, who made many useful suggestions to improve the contents of this draft. 8. References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Guttman, E., Perkins, C., Veizades, J. and M. Day, "Service Location Protocol", RFC 2608, July 1999. [3] Guttman, E., Perkins, C. and J. Kempf, "Service Templates and service: Schemes", RFC 2609, July 1999. [4] Sachno, ed., "All-IP Network (AIPN) Feasibility Study, Release 7", 3GPP TR22.978, 2005. [5] UPnP Service Specification, UPnP Forum, http://www.upnp.org [6] Sacham, et al., "Session Initiation Protocol (SIP) Session Mobility" Internet Draft (work in progress), draft-shacham- sipping-session-mobility-01, July, 2005. [7] Mingqiang, et al., " Extensions of Session Description Protocol (SDP) for Seamless Session Mobility", Internet Draft (work in progress), draft-mingqiang-mmusic-session-mobility- attribute-01.txt,October, 2005. 9. Author's Addresses Xu Mingqiang Mingqiang Expires May 2006 [Page 8] Service discovery in a PAN November 2005 Matsushita Electric Industrial Co., Ltd.(Panasonic) 4-5-15 Higashi-shinagawa Shinagawa-ku, Tokyo Japan Email: xu.mingqiang@jp.panasonic.com Hidenori Ishii Matsushita Electric Industrial Co., Ltd.(Panasonic) 4-5-15 Higashi-shinagawa Shinagawa-ku, Tokyo Japan Email: hidenori ishii@jp.panasonic.com Daisaku Komiya Matsushita Electric Industrial Co., Ltd.(Panasonic) 4-5-15 Higashi-shinagawa Shinagawa-ku, Tokyo Japan Email: komiya.daisaku@jp.panasonic.com Sachiko Kawaguchi Matsushita Electric Industrial Co., Ltd.(Panasonic) 4-5-15 Higashi-shinagawa Shinagawa-ku, Tokyo Japan Email: kawaguchi.sachiko@jp.panasonic.com Brijesh Kumar Panasonic R&D Corporation of America Two Research Way, 3rd Floor Princeton, NJ 08540 USA Phone: +1 609 734 7329 Email: kumarb@research.panasonic.com IPR Disclosure Acknowledgement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. 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