MMUSIC Working Group T. Guenkova-Luy, Internet-Draft A. Kassler Document:draft-guenkova-mmusic-e2enp-sdpng-00.txt University of Ulm Expires: September 25, 2002 J. Eisl Siemens AG D. Mandato Sony International (Europe) GmbH March 25, 2002 Efficient End-to-End QoS Signaling - concepts and features Status of this Memo This document is an Internet-Draft and is subject to 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/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Abstract This document analyzes issues for providing both sedentary and mobile users of multiparty, multimedia communication services with efficient mechanisms for coping with unstable network conditions and limited resource availability, conforming to the users' QoS requirements and expectations. To this extent, the concept of an efficient end-to-end QoS signaling mechanism is needed, dealing not only with capabilities/QoS negotiation, but also with efficient re-negotiations and coordinated resource management. Requirements of a protocol (thereinafter, the "End-to-End Negotiation Protocol" - E2ENP) [1], as well as a possible Guenkova, et al. Expires September 25, 2002 [Page 1] Efficient End-to-End QoS Signaling - concepts and features Mar 2002 implementation thereof, based on extensions of SDPng [2] and on the use of SIP [3], are then discussed. Finally, differences and/or synergies with existing solutions and proposals (especially with [4] and [5]), as well as security considerations, are provided. Table of Contents 1. Introduction 2 1.1 Motivations 2 1.2 Problem Statement 2 1.3 Scope of this document 3 2. Definition of Terms 4 3. The concept 5 3.1 Coping with unstable environment conditions 6 3.2 Hierarchical QoS Specification 7 3.3 Inter-stream QoS constraints 7 3.4 Planning counteractions ahead 8 3.5 Independence from network aspects 8 3.6 Mapping of the quality settings on codec definition 9 3.7 Third-Party-Assisted Negotiation 9 4. The features 10 5. Security Considerations 11 6. Related Work 11 7. Conclusions 13 8. References 13 9. Author's addresses for comments and discussions 15 10. Acknowledgements 15 1. Introduction 1.1 Motivations The Internet has proven to be a successful architecture for delivering a broad set of electronic services (including - among many others - telephony, electronic messaging, and audio/video (A/V) services), not only to sedentary but also to nomadic users. Micro/macro IP mobility and wireless IP technologies in fact pave the way to the full integration of the Internet with the second and third generation of mobile phone systems. In order to achieve this goal, next generation IP networks and applications will have to address the increasingly important challenges of wireless access, mobility management, the provision of Quality of Service (QoS), and multimedia services. 1.2 Problem Statement A paramount problem that mobile users will face within this context is how to cope with limited amounts of resources at the Guenkova, et al. Expires September 25, 2002 [Page 2] Efficient End-to-End QoS Signaling - concepts and features Mar 2002 end-systems and within the network, under unstable environmental conditions. It is expected that mobile users will no longer be able to rely on their QoS contracts being supported over the whole duration of a session by the network infrastructure, due to various reasons like: wireless link quality degradations, handovers, limited amount of resources. By assuming proper resource overprovision in the backbone, one can expect that these problems will most likely be concentrated in the access network, especially in the radio part thereof, and even on the end-systems. Since users typically have business relationships with specific network providers (e.g. a subscription with an ISP or a prepaid phone card), two possible types of handover may occur: - horizontal handovers: occur within a given administrative domain of a network provider, and within the same type of access network; - vertical handovers: occur across two different types of access networks and/or across the administrative boundary between two network providers. When dealing with handovers, users must be prepared to face changes in network resource availability, depending not only on the type of access network, but also on the type of business relationships the users may have with the various network providers. In some extreme cases, the users might try to access the network owned by a network provider, with which the user has no business relationship at all, or which offers limited amount of resources. Pricing aspects also play a key role. Within this context, multiparty multimedia applications will need an effective and efficient way of handling QoS fluctuations at the network layer. In particular, the sheer negotiation of capabilities (like codecs) is hereby regarded as necessary but not sufficient for meeting the users' QoS expectations. Intelligent, adaptive applications can in fact provide predictive QoS on an end-to-end basis only if end- peers are able to negotiate also QoS aspects directly affecting the application performance, according to the users' QoS expectations. This combined information enables applications effectively choosing the best adaptation strategy in reaction to a given QoS fluctuation [1]. 1.3 Scope of this document Coping with the aforementioned issues, this document presents a concept for negotiation of capabilities and QoS at the application level, triggered by QoS requirements of the end-user (the E2ENP concept), which can be realized by either deriving a new specific protocol, or enhancing existing ones. As an example of the latter option, a possible E2ENP implementation based on extensions of SDPng [2] and on the use of SIP [3] is also discussed. Guenkova, et al. Expires September 25, 2002 [Page 3] Efficient End-to-End QoS Signaling - concepts and features Mar 2002 2. Definition of Terms Adaptation Path (AP) An ordered set of QoS contracts that end-systems use for employing adaptation strategies in a preplanned way. The nominal QoS contract indicates the one the end-system should preferably try to enforce. Should this not (or no longer) be possible, the AP offers alternative QoS contracts (and, optionally, specific rules for choosing them) for degrading the QoS level in a controlled way. Application Level QoS An end-system internal representation of QoS specification (e.g. XML description), derived from User Level QoS specification. Capability The ability to perform certain tasks and/or to handle certain information types. A single capability is associated with a certain amount of hardware and/or software resources (each handling a given information type) and can be configured to produce different QoS levels. On the other hand a given QoS level can be associated with different capability sets (e.g. different codecs can offer the same QoS level). Intermediate Components (IM) Any network element situated on the signaling and/or the data path between two end-systems and which can understand the protocol the end-systems use (at least on the network level). Examples are: routers, proxies, independent services, etc. Mediator The role an end-peer can take for redirecting incoming calls to another end-peer(s) according to some settings in the user profile. A part of this role is to provide QoS satisfaction for the user(s) in a way the Mediator itself (considering the end- peer's multimedia capabilities) cannot handle. Peer A service or an end-device (associated with an end-user). This term has equivalent meaning with the terms end-peer and party, which are interchangeably used throughout this document. QoS change The change of the QoS contract initiated by the service user or by an application within the context of a predefined AP. QoS contract An agreement between a service user and a service provider , specifying QoS requirements and constraints, as well as the policies required to keep track of a single QoS level during the given service execution. Guenkova, et al. Expires September 25, 2002 [Page 4] Efficient End-to-End QoS Signaling - concepts and features Mar 2002 QoS level A discrete region of the multidimensional QoS space characterizing a service. Users perceive distinct QoS levels as the result of applying certain QoS contracts to the given services. QoS parameter A functional representation of a single characteristic of a given QoS aware service (e.g. network bitrate, network overall end-to- end delay, but also parameters like video frame rate, video frame size, audio sampling rate, number of audio channels, etc.), which identifies a measurable QoS related quantity. QoS profile A collection of data specifying the end-peer preferences in terms of QoS, concerning the usage of a given service. The QoS profile is the end-system internal representation of the user's QoS preferences within a QoS aware system. The QoS profile can contain one or several Application Level QoS specifications. QoS violation The violation of one or several QoS contracts within an AP, caused by the network and/or Service Provider and/or local system. User Level QoS specification The QoS as users expect to perceive, eventually expressed in non- crisp terms by non-expert users. This QoS specification is an application-specific issue, depending on user interface aspects. 3. The concept This section defines requirements for an efficient end-to-end QoS signaling mechanism for dealing with multiparty, multimedia services. This concept also embraces the case of multi-streams applications like online-games combined with A/V sessions. The "handling of QoS" shall be achieved through the negotiation of hardware/software configuration information and the negotiation and enforcement of QoS contracts, which are derived from the user preferences : - a QoS contract shall capture user's QoS expectations, as well as network provider policies for enabling a comprehensive QoS adaptation process (this means for instance to control that the QoS levels fit into the predefined policies, or to control the amount of resources by up-/downgrading QoS upon detection of QoS changes / QoS violations); - a QoS contract shall also capture configuration information concerning network resources, as well as the resources and capabilities of the involved QoS aware end-systems (for instance, some codecs like variable bitrate video-codecs can be differently preset to produce different QoS directly perceivable by the user: the sheer definition of codecs is thus not sufficient for Guenkova, et al. Expires September 25, 2002 [Page 5] Efficient End-to-End QoS Signaling - concepts and features Mar 2002 determining the amount of local and network resources to reserve when QoS should be supported). Before starting a negotiation, each end-peer shall derive the negotiable QoS contracts from existing information concerning both users' QoS expectations and type/amount of available resources, by possibly applying the following refinement/validation process: 1. users specify the User Level QoS; 2. applications derive Application Level QoS by mapping User Level QoS into QoS contracts detailing specific aspects (e.g. video frame rate, video frame size, image quality, etc); 3. the mapping of Application Level QoS on the end-system capabilities (i.e. the end-system hardware and software configuration - e.g. supported codecs), originates QoS contract Sketches, which represent the Application Level QoS that the end- system can theoretically support; 4. the validation of QoS contract Sketches against network provider policies for supporting QoS, originates Validated Application Level QoS contracts. These valid contracts constitute a common vocabulary, which the local and the remote end-systems can use for negotiating the establishment of QoS aware communications, and for efficiently dealing with QoS re- negotiations thereof. Those Application Level QoS which have failed the validation, could still be used in special cases like vertical handovers, dynamic end-system changes (e.g. due to end- system up-/downgrading), etc. For the sake of simplicity, this document refers thereinafter to "Validated Application Level QoS contracts" as "Application Level QoS". These are the negotiable QoS contracts end-peers are expected to deal with during QoS negotiations and QoS re- negotiations. In order to allow end-peers reserving network resource in a coordinated manner, during the negotiation process the sender side can derive network-level QoS contracts (e.g. the TI(Traffic Information) and SI(Sensitivity Information) information presented in [4]) from the negotiable Application Level QoS. 3.1 Coping with unstable environment conditions In order to allow users achieving QoS with limited amounts of resources at the end-system and in the network, under unstable environment conditions, the application developers and the users shall be prepared to increase renegotiation speed, for instance by proactively planning proper actions at negotiation time. As aforementioned, QoS Contract information is complementary to capability information. As such, the E2ENP may advantageously negotiate QoS Contracts and capabilities independently. For instance some codecs might be dynamically downloadable: having negotiated QoS contracts independently of such codes, allows end- Guenkova, et al. Expires September 25, 2002 [Page 6] Efficient End-to-End QoS Signaling - concepts and features Mar 2002 peers saving time (critical aspect of re-negotiations), by simply referencing the pre-negotiated QoS contracts and binding the newly available codecs with those contracts. 3.2 Hierarchical QoS Specification Grouping streams is mainly useful for allowing QoS aware applications to handle groups as a whole when balancing quality to resource availability under certain environmental conditions. For instance, in online gaming applications it can make sense to augment the gaming experience by allowing each player to keep in audio/visual contact with the other players. To this extent, it is possible to distinguish (and therefore treat differently) various groups of streams, each grouping all the streams between the given player and another player. The description of these groups of streams is subject to negotiation. Furthermore, the developers and the users of multiparty multimedia applications dealing with multiple streams may advantageously arrange streams by recursively applying the grouping process, based on high-level criteria aiming to improve resources orchestration among multiple streams. For instance, a player can arrange the A/V streams by identifying multiple concurrent instances of audio- or videoconferences, one with the own team members and one with each other team. This optional form of streams grouping is managed locally by the end-peers (and thus is not subject to negotiation). The resulting hierarchical structure is topologically equivalent to a tree, where each leaf represents a stream, and each internal node represents a group of streams (or, recursively, of groups). 3.3 Inter-stream QoS constraints Multi-media applications may deal with multiple streams of different types (i.e. audio, video, and data). To this extent, users of such applications may wish to specify their QoS preferences for each single stream, but also any parameter that might determine inter-stream behavior. Typically, videoconference applications deal with voice and video streams, which must be synchronized (time synchronization). If the media codec and stream format itself does not provide means for synchronizing, it is a requirement that inter-stream correlation information is available and negotiated. This correlation can be generalized by introducing the specification of QoS constraints applicable to a given bundle of streams (QoS correlation). The decision of what level of correlation should be enforced at the QoS level among a set of streams, depends on the scenario and the requirements of the application. The introduction of the time synchronization and QoS correlation aspects augment the overall possibilities to specify and manage QoS within a QoS aware system. Guenkova, et al. Expires September 25, 2002 [Page 7] Efficient End-to-End QoS Signaling - concepts and features Mar 2002 3.4 Planning counteractions ahead A possible way to cope with otherwise unpredictable events resulting from QoS changes / QoS violations, is to enable the mobile users' applications to efficiently and timely react to those events, by planning proper counteractions ahead, in a coordinated manner with the remote end-peers. In this manner, whenever QoS changes / QoS violations occur, agreements on how to most effectively adapt to the mutated conditions can be timely reached among the peers. These counteractions include: - negotiating multiple alternative QoS levels for a stream; - negotiating multiple alternative QoS levels for a group of streams, to capture time synchronization, QoS correlation, and other inter-stream QoS constraints; - coordinating local-, remote-, and network-resource management. 3.5 Independence from network aspects The end-peers are in general connected over one or a multiplicity of interconnected networks, including also Intermediate Components (IM). In terms of SIP the SIP-proxies are considered as IM. Taking in account the functionality of the SIP-proxies [3], [6] and their ability to interfere with the communication between two end-peers, it is desirable that the E2ENP operates based on an abstraction of the underlying network, in order to provide real end-to-end negotiation and conformance of the so delivered QoS information. Since the IMs offer services that not only may influence the information that end-peers eventually negotiate via E2ENP, but also may enforce the results of the E2ENP process, IMs should be informed about the decision made by the end-peers. IMs may be informed by providing them with some standard-profile information before the start of E2ENP, and/or by publishing the agreed QoS contracts, e.g. via a directory service. In order to best satisfy the user QoS expectations and the network provider QoS policies, the following is suggested: - the E2ENP should be able to be used in combination with (but independently from) IM, which may result effective in preparing and/or guaranteeing the QoS contracts agreed by the end-peers; - the exchange of information (e.g. profiles, security, authentication, provider policies, etc.) not directly affecting the E2ENP-process, rather influencing the information that is going to be negotiated, should be carried out before the E2ENP starts. In general the flows carrying E2ENP messaging (the signaling-path) and the flows carrying the actual streams (the data-path) could be routed differently, depending not only on network-related issues, but also on application/service specific reasons. Thus the E2ENP signaling-paths and the corresponding data-paths between any two Guenkova, et al. Expires September 25, 2002 [Page 8] Efficient End-to-End QoS Signaling - concepts and features Mar 2002 given end-peers should be in general considered different. Every time a signaling-path and/or data-path is built, there may be some IMs (proxies, directory services, etc.) located along the path, whose usage is application-specific, and which might "understand" some of the protocols used by the end-peers. Some of these entities might thus be able to "interfere" with the E2ENP, thus disrupting the very "End-to-End" nature of the E2ENP. In order to avoid this threat, it is suggested that: - with respect to the E2ENP, Intermediate Components should operate based only on information provided - directly or indirectly - by the peers, in order to carry out application specific tasks; - exception cases when the involvement of the IMs is inevitable, should also be considered. Thus the IMs should be allowed to interfere with the E2ENP only by explicitly notifying the end- peers about the occurred problems, and only when end-peers misbehave, e.g. by disregarding system policies and/or in case of system failure conditions. 3.6 Mapping of the quality settings on codec definition When user-defined audio quality settings are associated with codecs according to the standard static payload-type definitions of the codecs [7], each QoS level can be mapped to one audio payload type expressing such QoS level. On the other hand a single variable bitrate video-codec can produce multiple QoS levels with respect to the quality of the single video frame and - in some cases - the quality of the color of a single frame. A user-defined QoS level can be applied to a video by defining a compression percentage for the performance of the video codec. However, some video codecs have different number of compression levels. When an application based on the users requirements selects a constant video quality and accepts a variable bitrate coder, the application would derive from the QoS level "visually perceivable quality = X", an unique number expressing the compression level for the video codec. Thus, in order to better apply QoS settings to a codec, it is suggested that: - applications should share a numbering range for the user perceivable quality specification (overall visual quality and color quality, if the user wants to specify a certain color quality), in order to be able to uniquely map video quality to a given codec; - the numbering range for the user perceivable quality specification should have enough resolution to uniquely map to the compression levels of a given codec. 3.7 Third-Party-Assisted Negotiation End-peers may leverage services like directory, allocation, presence, etc. for redirecting connections over alternative end- Guenkova, et al. Expires September 25, 2002 [Page 9] Efficient End-to-End QoS Signaling - concepts and features Mar 2002 systems, which can more appropriately meet users' QoS expectations because of more appropriate capabilities. In these cases, end-peers should be able to negotiate on behalf of other end-peers, according to specific user profile information. This type of negotiation is called third-party-assisted negotiation. By third-party-assisted negotiation a pure Mediator should only facilitate the delegation of a connection without actively taking part in it. 4. The features A possible E2ENP implementation can be realized by combining special extensions of SDPng [2] with a particular use of SIP. The following list indicates the proposed SDPng extensions. - An important part of the implementation is the use of modularity for the elements by applying SDPng and extensions of it. This would enable to use SDPng with and without the new extensions. - The modularity of the SDPng extensions should enable the end- to-end negotiating parties to quickly reach agreements on common codecs, payload types and codec parametrizations thus possibly optimizing the decisions on commonly supported QoS contracts. - For describing the QoS contracts it is necessary to have SDPng elements for mapping the Application Level QoS descriptions onto the codecs and the payload types. A single QoS contract would be in these terms the QoS settings of a single media stream. - It is suggested to enrich at the sender side the negotiated Application Level QoS contracts with the TI and SI information presented in [4], for allowing the end-peers to perform resource reservation in a coordinate manner. - It is necessary to distinguish between the different streams (audio, video) and data types (data, control) in the definition of the QoS contracts for a communication session. - Considering the video codecs, the parametrization indicated in [7] is not sufficient to fully characterize the given codec from a QoS perspective. That is why it is necessary to introduce codec parametrization attributes like frame-rate, frame-size, color- quality-range, overall-quality-range, etc. which should be uniquely interpreted by the end-systems. - It is necessary to introduce descriptions and parametrizations for non-streaming data. - It is necessary to provide means for managing user, system, and provider policy information at least by defining which of the proposed QoS contracts the QoS aware system may support during a negotiation. - For defining APs new SDPng elements are needed for formally configuring the adaptation process correspondingly, in accordance with the envisioned QoS changes and/or violations. - For defining stream grouping it is necessary to introduce new Guenkova, et al. Expires September 25, 2002 [Page 10] Efficient End-to-End QoS Signaling - concepts and features Mar 2002 SDPng elements with respect to (eventually hierarchical) group definition, and QoS correlation / time synchronization aspects. The following SIP features for implementing the E2ENP processes are identified: - Signaling for carrying out the negotiation and re-negotiation - Means for coordinating resource management among multiple parties (common example given in [8]) - Transporting and recognizing the E2ENP content expressed as SDPng content 5. Security Considerations This chapter discusses some aspects considering security with respect to SDPng and SIP performance. If the contents of the SIP message body (SDPng) are private and should be treated according to security policies they might be encrypted. The use of Digital Certificates with and within SDPng message bodies can serve the unique identification of the sent information for both end-peers and IM. This would enable the end-peers and IM verify and best satisfy the user, system and provider policies. Additional techniques for confidentiality and integrity support, with respect to the negotiated information, should also be considered. On the issue of firewalls, further thorough investigations concerning IMs are required. 6. Related Work This section discusses existing solutions and/or proposals in the field of QoS aware end-to-end negotiations, and highlights the shortcomings of the respective existing signaling mechanisms (in- band, SIP) and description methods (SDPng) for QoS. The authors of [7] and [9] describe possibilities of quick re- negotiations via in-band signaling. However this kind of signaling concerns only change of codecs and the redundant support of differently coded media without considering the respective effects when QoS should be supported. The authors of [8] and [10] present a multi-phase call-setup mechanism that makes network QoS and security establishment a precondition to sessions initiated by the SIP and described by the SDP. Thus the resource management is done only for the network resources. However [8], [10] do not consider pre-negotiation of QoS and the integration of local and peer resource management. The authors of [11] describe a complete model for one-to-one capabilities negotiation with SDP. However this model has problems Guenkova, et al. Expires September 25, 2002 [Page 11] Efficient End-to-End QoS Signaling - concepts and features Mar 2002 by the definition of mutually referred information and information on grouping streams because of the flat structure of the SDP. Additionally this model concerns only capability negotiation but no QoS support and QoS adaptation. Ongoing work in [12] identifies the requirements of a framework dealing with session description and endpoint capability negotiation in multiparty multimedia conferencing scenarios. Depending on user preferences, system capabilities, or other constraints, different configurations can be chosen for the conference. The need of a negotiation process among the end-peers for determining a common set of potential system configurations and for selection of one or many common configurations to be used is identified, but not described. The authors of [12] also identify the need for network resource reservation coupled with session setup. The proposal in [12] deals only with capability negotiations and does neither consider a negotiation protocol for determining a common set of QoS configuration nor integrate local, peer and network resource reservation. The most recent versions of SDPng proposal [2], [13] provide detailed XML Schema specification and a prototype of the Audio Codec and RTP Profiles. Additionally [13] describes a capability negotiation process for establishing of a common capability vocabulary between end-peers. However the proposals in [2], [13] still do not consider the QoS specific issues. In [5] an End-to-End User Perceived Quality of Service Negotiation is described, with the assumption that some IMs and services may strongly be involved in the end-decision about the negotiated QoS information of the end-peers. The decision about QoS configurations in [5] may be taken over some standard "contract types". Although [5] mentions that signaling and data packets may flow along different paths throughout the network, the authors of [5] suggest that some IMs along the negotiation path may influence the negotiation, though in general having nothing to do with the data. According to such a protocol model the network is not transparent. The negotiation process presented in [5] does not allow incremental negotiations, and furthermore [5] leverages static APs with fixed transitions among capability configurations/network- level QoS contracts only. The model of [5] suggests negotiations of QoS only at stream level without considering some stream dependencies like groups and stream hierarchies. The most recent work on the problem of User Perceived QoS [4] introduces SDPng schema for defining traffic throughput and sensitivity information. This information considers only the Guenkova, et al. Expires September 25, 2002 [Page 12] Efficient End-to-End QoS Signaling - concepts and features Mar 2002 network reservation process without taking in account the necessity for local (peer) QoS specific configurations and reservations. The model in [4] is not taking in account the Application Level QoS definitions, with respect to codec configuration and a flexible adaptation process. However the E2ENP can incorporate this proposal, by allowing senders to derive TI/SI from Application Level QoS contracts, and to forward this information as part of a proposal/counter-proposal to the receiver(s). The model of [4] is static in terms of adaptation, insofar as it reuses the fixed prioritization of alternative options derived from SDP, thus losing the powerful flexibility featured by XML. The description of the payload types in [4] is not in accordance with the payload types as described in [7], since the codec parametrization of the audio codecs is already pre-defined for the static payload types. One interesting aspect in [4] is the introduction of QoS Class format as a form of predefined interoperable application level QoS definition. However such a definition would also need high level QoS specification considering the usage of different possible QoS configurations of a single codec/payload type. 7. Conclusions This document has introduced the concept and requirements of the End-to-End QoS Negotiation Protocol (E2ENP). The E2ENP is a signaling mechanism for effectively and efficiently performing end-to-end QoS negotiations/re-negotiations and resource management coordination, when dealing with multiparty multimedia services under unstable network conditions. Special features are the negotiation of common vocabulary and adaptation paths, that describe alternative QoS contracts to be applied, when QoS violations occur. Furthermore, the E2ENP allows developers and/or users to capture and enforce time synchronization and QoS correlation (and even more complex) constraints among multiple streams, thus allowing adaptation at different levels. This is envisioned to be a key benefit in terms of QoS for current and future applications. By modularly extending SDPng, and by properly defining SIP usages, the authors expect that the induction of the E2ENP concept will smoothly blend with legacy solutions, along the path towards the next generation of QoS aware multiparty, multimedia services. 8. References [1] IST-1999-10050 BRAIN Deliverable 1.2, Concepts for Service adaptation, scalability and QoS handling on mobility enabled networks, 31.03.2001 (http://www.ist-brain.org/) Guenkova, et al. Expires September 25, 2002 [Page 13] Efficient End-to-End QoS Signaling - concepts and features Mar 2002 [2] D. Kutscher et al.: Session Description and Capability Negotiation, IETF Internet-Draft, Work-in-progress, . [3] IETF RFC 2543, SIP: Session Initiation Protocol, M. Handley et al, ACIRI, March 1999. [4] L. Bos, et al: SDPng extensions for Quality of service negotiation, IETF Internet-Draft, Work-in-progress,. [5] L. Bos, et al: A Framework for End-to-End User Perceived Quality of Service Negotiation, IETF Internet-Draft, Work-in- progress,. [6] Rosenberg et al.: SIP: Session Initiation Protocol, IETF SIP working group, Work-in-progress, . [7] H. Schulzrinne et al.: RTP Profile for Audio and Video Conferences with Minimal Control, Columbia U., Work-in-progress, . [8] W. Marshall et al.: Integration of Resource Management and SIP - SIP Extensions for Resource Management, IETF SIP working group, Work-in-progress, . [9] IETF RFC 2198, RTP Payload for Redundant Audio Data, C. Perkins et al., Network Working Group, September 1997. [10] W.Marshall et al., SIP Extensions for Resource Management, IETF draft , November 2000. [11] J.Rosenberg, H.Schulzrinne.: An Offer/Answer Model with SDP, IETF Internet-Draft, Work-in-progress, . [12] D. Kutscher et al.: Requirements for Session Description and Capability Negotiation, IETF Internet-Draft, Work-in-progress, . [13] D. Kutscher et al.: Session Description and Capability Negotiation, IETF Internet-Draft, Work-in-progress, . Guenkova, et al. Expires September 25, 2002 [Page 14] Efficient End-to-End QoS Signaling - concepts and features Mar 2002 9. Author's addresses for comments and discussions Teodora Guenkova-Luy Dept. Distributed Systems, University of Ulm, Oberer Eselsberg, 89069 Ulm, Germany Tel: +49 (0)731 502-4148 Fax: +49 (0)731 502-4142 e-Mail: guenkova@vs.informatik.uni-ulm.de Andreas Kassler Dept. Distributed Systems, University of Ulm, Oberer Eselsberg, 89069 Ulm, Germany Tel: +49 (0)731 502-4146 Fax: +49 (0)731 502-4142 e-Mail: kassler@informatik.uni-ulm.de Jochen Eisl Siemens Mobile Networks Research & Concepts Dep. Tel: +49 (0)89 722 62710 Fax: +49 (0)89 722 21882 e-Mail: jochen.eisl@icn.siemens.de Davide Mandato Broadband Wireless Technology Research (BWTR) Sony International (Europe) GmbH Advanced Technology Center Stuttgart Heinrich-Hertz-Str. 1 70327 Stuttgart, Germany Tel: +49 (0)711 5858-797 Fax: +49 (0)711 5858-468 e-mail: mandato@sony.de 10. Acknowledgements This work has been performed in the framework of the IST project IST-2000-28584 MIND, which is partly funded by the European Union. The authors would like to acknowledge the contributions of their colleagues, especially Markku Kojo. The authors would also like to thank their colleagues from TZI, University of Bremen, from Sony International (Europe), Stuttgart and University of Ulm for their support. Guenkova, et al. Expires September 25, 2002 [Page 15]