Internet DRAFT - draft-mingqiang-mmusic-servicediscovery-pan-req
draft-mingqiang-mmusic-servicediscovery-pan-req
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
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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
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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
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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.
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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.
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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
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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.
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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
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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
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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
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