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Versions: 00                                                            
                                                       Andreas Schrader
   Internet Draft                                    Hannes Hartenstein
   Document: draft-brunner-nsis-req-00.txt                 Ralf Schmitz
   Expires: May 2002                                    Juergen Quittek
                                                        Morihisa Momona
                                                         Marcus Brunner

                                                         Robert Hancock
                                                       Eleanor Hepworth
                                                    Roke Manor Research

                                                     Mathias Rautenberg
                                                      Hannes Tschofenig
                                                       Cornelia Kappler
                                                    Hans-Peter Schwefel
                                                  Christoph Niedermeier
                                                             Siemens AG

                                                            Holger Karl
                                                            Xiaoming Fu
                                                              TU Berlin

                                                        Andreas Kassler
                                                         University Ulm

                                                          November 2001

                 Requirements for QoS Signaling Protocols

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
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   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
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               Requirements for QoS Signaling Protocols  November 2001


   This draft proposes a set of requirements for signaling QoS across
   different network environments. To achieve wide applicability of the
   requirements, the starting point is a diverse set of user scenarios
   concerning both access and core networks, application interactions,
   and use within cellular networks.  We also provide an outline
   structure for the problem, including QoS related terminology. Taken
   with the user scenarios, this allows us to focus more precisely on
   which parts of the overall QoS problem needs to be solved. We
   present the assumptions and the aspects not considered within scope
   before listing the requirements grouped according to areas such as
   architecture and design goals, signaling flows, layering,
   performance, flexibility, security, and mobility. The motivation for
   each requirement is included as well as a distinction between
   requirements that should be met by the core part of the solution and
   those that could be implemented as extensions.

1. Introduction

   In order to derive requirements for QoS signaling it is necessary to
   first have a clear idea of the scope within which they are
   applicable. After defining terminology in Section 2, we therefore
   start in Section 3 with a set of QoS signaling scenarios. These
   scenarios derive from a variety of backgrounds, and help obtain a
   clearer picture of what is in or out of scope of the NSIS work. They
   illustrate the problem of QoS signaling from various perspectives
   (end-system, access network, core network) and for various areas
   (fixed line, mobile, wireless environments). As the NSIS work
   becomes more clearly defined, scenarios will be added or dropped, or
   defined in more detail.

   Based on these scenarios, we are able to define the QoS signaling
   problem on a more abstract level. In Section 4, we thus present a
   simple conceptual model of the QoS signaling problem, describe the
   entities involved in QoS signaling, and typical signaling paths.
   Additionally we list our assumptions and exclusions.

   The model of Section 4 allows deriving requirements from the
   scenarios presented in Section 2 in a coherent and consistent
   manner. Requirements are grouped according to areas such as
   Architecture and design goals, Signaling Flows, Layering,
   Performance, Flexibility, Security and Mobility.

   QoS is a pretty large field with a lot of interaction with other
   protocols, mechanisms, applications etc. In the following, some
   thoughts from an end-system point of view and from an network point
   of view.

   End-system perspective: In future mobile terminals, the support of
   adaptive applications is more and more important. Adaptively can be
   seen as an important technique to react to QoS violations that may
   occur frequently, e.g.,  in wireless environments due to changed
   environmental and network conditions. This may result in degraded

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               Requirements for QoS Signaling Protocols  November 2001

   end-to-end performance. It is then up to adaptive applications to
   react to the new resource availability. Therefore, it is essential
   to define interoperability between media-, mobility- and QoS
   management. While most likely mobile terminals cannot assume, that
   explicit QoS reservation schemes are available, some access networks
   nevertheless may offer such capabilities. Applications subscribed to
   an end-system QoS management system should be supported with a
   dedicated QoS API to set-up, control and adapt media sessions.

   Network perspective: QoS enabled IP networks are expected to handle
   two different kinds of QoS granularities: per-flow QoS and per-
   trunk/per-class QoS. Per-flow QoS might be needed in access networks
   and may there be subject of QoS signaling. However, in the core
   network only per-trunk or per-class QoS can be considered for
   scalability reasons. Therefore there might be different requirements
   on QoS signaling applying to different parts of the network. In the
   access network QoS signaling is an interaction between end systems
   and access routers or access network QoS managers (in the following
   we call them QoS initiator and QoS controller). In the core network
   QoS signaling refers to trunks or classes of traffic between core
   and edge systems or between peering core systems. Please note that
   this does not exclude the transport of per-flow signaling through
   core networks.

   It is clear from these descriptions that the subject of QoS is
   uniquely complex and any investigation could potentially have a very
   broad scope - so broad that it is a challenge to focus work on an
   area which could lead to a concrete and useful result. This is our
   motivation for considering a set of use cases which map out the
   domain of application that we want to address; these use cases are
   given in section 3. It is also the motivation for defining a problem
   structure, which allows us to state the boundaries of what types of
   functionality to consider, and to list background assumptions. This
   structure is given in section 4. The requirements themselves follow
   in section 5. There are several areas of the requirements related to
   networking aspects which are incomplete, for example, interaction
   with host and site multi-homing, use of anycast services, and so on.
   These issues should be considered in any future requirement analysis

2. Terminology

   Aggregate: a group of flows, usually with similar QoS requirements,
   which can be treated together as a whole with a single overall QoS
   requirement for signaling and provisioning. Aggregates and flows can
   be further aggregated together.

   [QoS] Domain: a collection of networks under the same administrative
   control and grouped together for administrative purposes.

   Egress point: the router via which a path exits a domain/subdomain.

   End Host: the end system or host, for whose flows QoS is being
   requested and provisioned.

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   End-to-End QoS: the QoS delivered by the network between two
   communicating end hosts.  End-to-end QoS co-ordinates and enforces
   predefined traffic management policies across multiple network
   entities and administrative domains.

   Edge-to-edge QoS: QoS within an administrative domain that connects
   to other networks rather than hosts or end systems.

   Flow: a traffic stream (sequence of IP packets between two end
   systems) for which a specific level of QoS is to be provided. The
   flow can be unicast (uni- or bi-directional) or multicast.

   Flow Administration: represents the policy associated with how flows
   should be treated in the network, for example whether and how the
   flows should be aggregated.  It may consist of both user and local
   network management information.

   Higher Layers: the higher layer (transport protocol and application)
   functions that request QoS from the network layer. The request might
   be a trigger generated within the end system, or the trigger might
   be provided by some entity within the network (e.g. application
   proxy or policy server).

   Indication: feedback from QoS provisioning to indicate the current
   QoS being provided to a flow or aggregate, and whether any
   violations have been detected by the QoS technology being used
   within the local domain/subdomain.

   Ingress point: the router via which a path enters a

   Mapping: the act of transforming parameters from QSCs to values that
   are meaningful to the actual QoS technology in use in the

   Path: the route across the networks taken by a flow or aggregate,
   i.e. which domains/subdomains it passes through and the
   egress/ingress points for each.

   Path segment: the segment of a path within a single

   QoS Administration Function: a generic term for all functions
   associated with admission control, policy control, traffic
   engineering etc.

   QoS Control Information: the information the governs the QoS
   treatment to be applied to a flow or aggregate, including the QSC,
   flow administration, and any associated security or accounting

   QoS Controller: this is responsible for interpreting the signaling
   carrying the user QoS parameters, optionally inserting/modifying the

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               Requirements for QoS Signaling Protocols  November 2001

   parameters according to local network QoS management policy, and
   invoking local QoS provisioning mechanisms.

   QoS Initiator: this is responsible for generating the QSCs for
   traffic flow(s) based on user or application requirements and
   signaling them to the network as well as invoking local QoS
   provisioning mechanisms.  This can be located in the end system, but
   may reside elsewhere in network.

   QoS Provisioning: the act of actually allocating resources to a flow
   or aggregate of flows, may include mechanisms such as LSP initiation
   for MPLS, packet scheduler configuration within a router, and so on.
   The mechanisms depend on the overall QoS technology being used
   within the [sub]domain.

   QoS Service Classes (QSC): specify the QoS requirements of a traffic
   flow or aggregate.  Can be further sub-divided into user specific
   and network related parameters

   QoS Signalling: a way to communicate QSCs and QoS management
   information between hosts, end systems and network devices etc.  May
   include request and response messages to facilitate negotiation/re-
   negotiation, asynchronous feedback messages (not delivered upon
   request) to inform End Hosts, QoS initiators and QoS controllers
   about current QoS levels, and QoS querying facilities.

   [QoS] Subdomain: a network within an administrative domain using a
   uniform technology/QoS provisioning function to provision resources.

   QoS Technology: a generic term for a set of protocols, standards and
   mechanisms that can be used within a QoS domain/subdomain to manage
   the QoS provided to flows or aggregates that traverse the domain.
   Examples might include MPLS, DiffServ, and so on. A QoS technology
   is associated with certain QoS provisioning techniques.

   QoS Violation: occurs when the QoS applied to a flow or aggregate
   does not meet the requested and negotiated QoS agreed for it.

   Resource: something of value in a network infrastructure to which
   rules or policy criteria are first applied before access is granted.
   Examples of resources include the buffers in a router and bandwidth
   on an interface.

   Resource Allocation: part of a resource that has been dedicated for
   the use of a particular traffic type for a period of time through
   the application of policies

   For terminology in IP paging etc. see RFC 3132 [1] and in mobility
   see [3].

3. Scenarios

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   In the following we describe some scenarios, which are important to
   cover, and which allow us to discuss various requirements. Note that
   the NSIS working group might choose to explicitly not cover some of

3.1. Scenario 1: Terminal Mobility

   The scenario we are looking at is the case where a mobile terminal
   (MT) changes from one access point to another access point. The
   access points are located in separate QoS domains. We assume Mobile
   IP to handle mobility on the network layer in this scenario and
   consider the various extensions (i.e., IETF proposals) to Mobile IP,
   in order to provide 'fast handover' for roaming Mobile Terminals.
   The goal to be achieved lies in providing, keeping, and adapting the
   requested QoS for the ongoing IP sessions in case of handover.
   Furthermore, the negotiation of QoS parameters with the new domain
   via the old connection might be needed, in order to support the
   different 'fast handover' proposals within the IETF.

   The entities involved in this scenario include a mobile terminal,
   access points, a access network manager, communication partners of
   the MT (the other end(s) of the communication association).
   From a technical point of view, terminal mobility means changing the
   access point of a mobile terminal (MT). However, technologies might
   change in various directions (access technology, QoS technology,
   administrative domain). If the access points are within one specific
   QoS technology (independent of access technology) we call this
   intra-QoS technology handoff. In the case of an inter-QoS technology
   handoff, one changes from e.g. a DiffServ to an IntServ domain,
   however still using the same access technology. Finally, if the
   access points are using different access technologies we call it
   inter-technology hand-off.

   The following issues are of special importance in this scenario:

   1) Handoff decision

   - The QoS management requests handoff. The QoS management can decide
   to change the access point, since the traffic conditions of the new
   access point are better supporting the QoS requirements. The metric
   may be different (optimized towards a single or a group/class of
   users). Note that the MT or the network (see below) might trigger
   the handoff.

   - The mobility management forces handoff. This can have several
   reasons. The operator optimizes his network, admission is no longer
   granted (e.g. emptied prepaid condition). Or another example is when
   the MT is reaching the focus of another base station. However, this
   might be detected via measurements of QoS on the physical layer and
   is therefore out of scope of QoS signaling in IP. Note again that
   the MT or the network (see below) might trigger the handoff.

   - This scenario shows that local decisions might not be enough. The
   rest of the path to the other end of the communication needs to be

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   considered as well. Hand-off decisions in a QoS domain, does not
   only depend on the local resource availability, e.g., the wireless
   part, but involves the rest of the path as well. Additionally,
   decomposition of an end-to-end reservation might be needed, in order
   to change only parts of it.

   2) Trigger sources

   - Mobile terminal: If the end-system QoS management identifies
   another (better suited) access point, it will request the handoff
   from the terminal itself. This will be especially likely in the case
   that two different provider networks are involved. Another important
   example is when the current access point bearer disappears (e.g.
   removing the Ethernet cable). In this case, the QoS initiator is
   basically located on the mobile terminal.

   - Network (access network manager): Sometimes, the handoff trigger
   will be issued from the network management to optimize the overall
   load situation. Most likely this will result in changing the base-
   station of a single providers network. Most likely the QoS initator
   is located on a system within the network.

   3) Integration with other protocols

   - Interworking with other protocol must be considered in one or the
   other form. E.g., it might be worth combining QoS signaling between
   different QoS domains with mobility signaling at hand-over.

3.2. Scenario 2: Cellular Networks

   In this scenario, the user is using the packet service of a 3rd
   generation cellular system, e.g. using UMTS. The region between the
   End Host and the edge node connecting the cellular network to
   another QoS domain (e.g. the GGSN in UMTS or the PDSN in 3GPP2) is
   considered to be a single QoS domain [4][5].

   Cellular systems provide their own QoS technology with specialized
   parameters to co-ordinate the QoS provided by both the radio access
   and access network. For example, in a UMTS network, one aspect of
   GPRS is that it can be considered as a QoS technology; provisioning
   of QoS within GPRS is described mainly in terms of things called
   UMTS bearer classes.  This QoS technology needs to be invoked with
   suitable parameters when a request for QoS is triggered by higher
   layers, and this therefore involves mapping the requested IP QoS
   onto these UMTS bearer classes. This request for resources triggers
   IP signaling messages that pass across the cellular system, and
   possibly other QoS domains, to negotiate for network resources.
   Typically, cellular system specific messages invoke the underlying
   cellular system QoS technology in parallel with the IP QoS
   negotiation, to allocate the resources within the cellular system.

   The QoS initiator could be located at the End Host (triggered by
   applications), the GGSN/PDSN, or at a node not directly on the data
   path, such as a bandwidth broker. In the second case, the GGSN/PDSN

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   could either be acting as a proxy on behalf of an End Host with
   little capabilities, and/or managing aggregate resources within its
   QoS domain (the UMTS core network). The IP signaling messages are
   interpreted by the QoS controllers, which may be located at the
   GGSN/PDSN, and in any QoS sub-domains within the cellular system.
   IP-level QoS re-negotiation may be initiated by either the End Host,
   or by the network, based on current network loads.

   Note that in comparison to the former scenario, the emphasis is much
   less on the mobility aspects, because mobility is mainly handled on
   the lower layer.

3.3. Scenario 3: Session mobility

   In this scenario, a session is moved from one end-system to another.
   Ongoing sessions are kept and QoS parameters need to be adapted,
   since it is very likely that the new device provides different
   capabilities. Note that it is open which entity initiates the move,
   which implies that the QoS initiator might be triggered by different

   User mobility (i.e., a user changing the device and therefore moving
   the sessions to the new device) is considered to be a special case
   within the session mobility scenario.

   Note that this scenario is different from terminal mobility. Not the
   terminal (end-system) has moved to a different access point. Both
   terminals are still connected to an IP network at their original
   points. Keeping the QoS guarantees negotiated implies that the end-
   point(s) of communication are changed without changing the

3.4. Scenario 4: QoS reservations/negotiation from access to core

   The scenario includes the signaling between access networks and core
   networks in order to setup and change reservations together with
   potential negotiation.

   The issues to be solved in this scenario are different from previous
   ones. The entity of reservation is most likely an aggregate, and the
   time scales of reservations might be different (long living
   reservations of aggregates, rarer re-negotiation). However, the
   specification of the traffic, a particular QoS is guaranteed for,
   needs to be changed. E.g., in case additional flows are added to the
   aggregate, the traffic specification of the flow needs to be added
   if it is not already included in the aggregates specification.

3.5. Scenarios 5: QoS reservation/negotiation over administrative

   Signaling between two or more core networks to provide QoS is
   handled in this scenario. The might also include access to core
   signaling over administrative boundaries. Compare to the previous

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               Requirements for QoS Signaling Protocols  November 2001

   one it adds the case, the two networks are not in the same
   administrative domain. Basically, it is the inter-domain/inter
   provider signaling which is handled in here.

   The domain boundary is the critical issue to be resolved. Normally,
   only basic information should be exchanged, if the signaling is
   between competing administrations. Specifically information about
   core network internals (e.g., topology, technology, etc.) should not
   be exchanged. Some information exchange about the "access points" of
   the core networks (which is topology information as well) may need
   to be exchanged.

   Additionally, as in scenario 4, signaling most likely is based on

4. Problem Statement and Scope

   We provide in the following a preliminary architectural picture as a
   basis for discussion. We will refer to it in the following
   requirement section.

   The overall problems to be solved have been given at a top level by
   the use cases/scenarios of section 3. However, the problem of QoS
   has an extremely wide scope and there is a great deal of work
   already done to provide different components of the solution, such
   as QoS technologies for example. A basic goal should be to re-use
   these wherever possible, and to focus requirements work at an early
   stage on those areas where a new solution is needed (e.g. an
   especially simple one). We also try to avoid defining requirements
   related to internal implementation aspects.

   In this section, we present a simple conceptual model of the overall
   QoS problem in order to identify the applicability to NSIS of
   requirements derived from the use cases, and to clarify the scope of
   the work, including any open issues. This model also identifies
   further sources of requirements from external interactions with
   other parts of an overall QoS solution, clarifies the terminology
   used, and allows the statement of design goals about the nature of
   the solution (see section 5).

   Note that this model is intended not to constrain the technical
   approach taken subsequently, simply to allow concrete phrasing of
   requirements (e.g. requirements about placement of the QoS
   initiator, or ability to 'drive' particular QoS technologies.)

4.1. Problem Discussion Model

   A simple layer model covering a single path segment is shown in
   figure 1, using the terminology from Section 2.

   Roughly, the scope of NSIS within the context of this diagram is
   assumed to be the interaction between the initiator and
   controller(s), including selection of signaling protocols to carry

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               Requirements for QoS Signaling Protocols  November 2001

   the QoS information, and the syntax/semantics of the information
   that is exchanged. Further statements on assumptions/exclusions are
   given below. The main elements shown are:

   1. Something that starts the request for QoS, the QoS Initiator.
   This might be in the end system or within some part of the network.
   The distinguishing feature of the QoS initiator is that it acts on
   triggers coming (directly or indirectly) from the higher layers in
   the end systems, mapping the QoS requested by them, and also
   provides feedback information to the higher layers which might be
   used by transport layer rate management or adaptive applications.

   2. Something that assists in managing QoS further along the path,
   the QoS controller. The QoS controller does not interact with higher
   layers, but interacts with the QoS initiator and possibly more QoS
   controllers on the path, edge to edge or possibly end to end.

   3. The QoS initiator and controller(s) interact with each other,
   path segment by path segment. This interaction involves the exchange
   of data (QoS control information) over some signaling protocol.

   4. The path segment traverses an underlying network (QoS domain or
   subdomain) covering one or more IP hops. The underlying network uses
   some local QoS technology. This QoS technology has to be provisioned
   appropriately for the flow, and this is done by the QoS initiator
   and controller(s), mapping their QoS control information to
   technology-related QoS parameters and receiving indications about
   success or failure in response.

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               Requirements for QoS Signaling Protocols  November 2001

   ..............   ................
   .  request/  .   .  response/   .
   .trigger from.   . feedback to  .
   .higher layer.   .higher layers .
   ..............   ................
            |         ^
            |         |
            |         |        ...............
            |         |        . QoS Control .
            V         |        . Information .
       +----------------+      ...............     +----------------+
   --->|                |------------------------->|                |->
       |                |      QoS signalling      |                |
       | QoS Initiator  |     (request/query,      | QoS Controller |
       |                |   response/error etc.)   |                |
   <---|                |<-------------------------|                |<-
       +----------------+                          +----------------+
        ^              |                            ^              |
        |              |                            |              |
        | ............ |                            | ............ |
        |     QoS      |                            |     QoS      |
        | provisioning |                            | provisioning |
        |  commands &  |                            |  commands &  |
        |  responses   |                            |  responses   |
        | ............ |                            | ............ |
        |              |                            |              |
        |              |                            |              |
        |              V                            |              V
      |                  QoS (sub)domain using any                   |
      |                        Qos technology                        |
      |                                                              |
      |     +------+       +------+                     +------+     |
      |     |Router|       |Router|                     |Router|     |
   =========|      |=======|      |=====================|      |=======
      |     |      |       |      |       flow path     |      |     |
      |     +------+       +------+                     +------+     |

   Figure 1: Generic scope of signaling

   A second diagram, figure 2, concentrates more on the overall end to
   end (multiple QoS domains) aspects, in particular:

   1. The QoS initiator need not be located at the end system, and the
   QoS controllers are not assumed to be located on the flow path.
   However, they must be able to identify the ingress and egress points
   for the flow path as it traverses the domain/subdomain. Any
   signalling protocol must be able to find the appropriate QoS
   controller and carry this ingress/egress point information.

   2. We see the network at the level of domains/subdomains rather than
   individual routers (except in the special case that the domain

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               Requirements for QoS Signaling Protocols  November 2001

   contains one link). Domains are assumed to be administrative
   entities, so security requirements apply to the signaling between
   them. Subdomains are introduced to allow the fact a given QoS
   provisioning mechanism may only be used within a part of a domain,
   typically for a particular subnetwork technology boundary.
   Aggregation can also take place at subdomain boundaries.

   3. Only a unicast flow is shown, with the QoS initiator at or near
   one end. However, we do not exclude bi-directional flows with the
   QoS requested by either end. Further QoS initiators may exist on the
   path. Multicast or anycast flows or flows with variable paths within
   a subdomain (e.g. to a mobile end system) are also logically

   4. Any domain may contain QoS administration functions (e.g. to do
   with traffic engineering, admission control, policy and so on).
   These are assumed to interact with the QoS initiator and controllers
   (and end systems) using standard mechanisms.

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               Requirements for QoS Signaling Protocols  November 2001

                            |        QoS Domain        |
   +----+    flow path     +-+                        +-+
   +----+                  +-+                        +-+          ||
                            | \                      / |           ||
                            |  \+----+        +----+/  |           ||
                            |   |QoS |        |QoS |   |           ||
                            |   |cont|        |init|   |           ||
                            |   +----+        +----+   |           ||
                            |      ^            ^      |           ||
                            |      |            |      |           ||
                            |      V            V      |           ||
                            |   +------------------+   |           ||
                            |   |QoS administration|   |           ||
                            |   |    functions     |   |           ||
                            |   +------------------+   |           ||
                            +--------------------------+           ||
                   +-----------------------------------------+     ||
                   |           +--------------------+        |     ||
                   |     +-----|   QoS controller   |--+     |     ||
                   |    /      +--------------------+   \    |     ||
                   |   /                                 \   |     ||
                   |  /     +--------------------------+  \  |     ||
                   | /      |      QoS Subdomain       |   \ |     ||
    +----+        +-+      +-+                        +-+   +-+    ||
    +----+        +-+      +-+     aggregate path     +-+   +-+
                   |        | \                      / |     |
                   |        |  \+----+        +----+/  |     |
                   |        |   |QoS |        |QoS |   |     |
                   |        |   |init|        |cont|   |     |
                   |QoS     |   +----+        +----+   |     |
                   |Domain  +--------------------------+     |

   Figure 2: Signaling in a multiple (QoS)domains

4.2. Assumptions and Non-Assumptions

   1. The NSIS signaling could run end to end, end to edge, or edge to
   edge, or network-to-network ((between providers), depending on what
   point in the network acts as the initiator, and how far towards the
   other end of the network the signaling propagates. One extreme would
   be to have the initiator at the end system and the scope of
   signaling only as far as the first hop router; another would be to
   have signaling edge to edge across an interior QoS domain, triggered
   e.g. by a application layer proxy.

   2. It does not make much sense to consider 'pure' end-to-end QoS
   signaling that is not interpreted anywhere within the network.

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   Mainly in the area of mobility it is essential to decompose the path
   into path segments (see scenario 1,2,3). This is part of the
   transport or application layers.

   3. Where the signaling does cover several QoS domains or subdomains,
   we do not exclude that different signaling protocols are used in
   each path segment. We only place requirements on the universality of
   the QoS control information that is being transported. (The goal
   here would be to allow the use of signaling protocols which are
   matched to the characteristics of the portion of the network being
   traversed.) Note that the outcome of NSIS work might result in
   various protocols or various flavors of the same protocol. This
   implies the need for the translation of information into QoS domain
   specific format as well.

4.3. Exclusions

   1. Development of specific mechanisms and algorithms for application
   and transport layer adaptation are not considered, nor are the
   protocols that would support it.

   2. Specific mechanisms (APIs and so on) for interaction between
   transport/applications and the network layer are not considered,
   except to clarify the requirements on the negotiation capabilities
   and information semantics that would be needed of the signaling
   protocol. The same applies to application adaptation mechanisms.

   3. Specific mechanisms for QoS provisioning within a
   domain/subdomain are not considered. It should be possible to
   exploit these mechanisms optimally within the end to end context.
   Consideration of how to do this might generate new requirements for
   NSIS however. For example, the information needed by an QoS
   controller to manage a radio subnetwork needs to be provided by the
   NSIS solution.

   4. Specific mechanisms (APIs and so on) for interaction between the
   network layer and underlying QoS provisioning mechanisms are not

   5. Interaction with QoS administration capabilities is not
   considered. Standard protocols should be used for this (e.g. COPS).
   This may imply requirements for the sort of information that should
   be exchanged between the NSIS network QoS entities.

   6. Security issues related to multicasting are outside the scope of
   the QoS signaling protocol.

   Since multicasting is currently not an issue for the QoS protocol,
   security issues related to multicast are outside the scope.
   Multicast security may additionally be an application issue which is
   also outside the scope of the QoS protocol.

   7. Protection of non-QoS signaling messages are outside the scope of
   the QoS protocol

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   Security protection of data messages transmitted along the establish
   QoS path are outside the scope of the QoS protocol. These security
   properties are likely to be application specific and may be provided
   by the corresponding application layer protocol.

5. Requirements

   This section defines more detailed requirements for a QoS signaling
   solution, derived from consideration of the use cases/scenarios, and
   respecting the framework, scoping assumptions, and terminology
   considered earlier. The requirements are in subsections, grouped
   roughly according to general technical aspects: architecture and
   design goals, topology issues, QoS parameters, performance,
   security, information, and flexibility.

   Two general (and potentially contradictory) goals for the solution
   are that it should be applicable in a very wide range of scenarios,
   and at the same time lightweight in implementation complexity and
   resource requirements in nodes. One approach to this is that the
   solution could deal with certain requirements via modular components
   or capabilities, which are optional to implement in individual
   nodes. Requirements which could be handled this way are labeled
   [Extension] in what follows.

   There may be a better label than [Extension], but we think it has
   the right implications: it doesn't imply 'optional to solve in the
   work of the group' (like 'option' would) but it does not need to be
   part of a 'core' solution.

   Some of the requirements are technically contradictory. Depending on
   the scenarios a solution apply to one or the other requirement is
   applicable. We believe that the working group needs to decide first
   on the scenarios to be covered, and which one to exclude.

5.1. Architecture and Design Goals

   This section contains requirements related to desirable overall
   characteristics of a solution, e.g. enabling flexibility, or
   independence of parts of the framework.

   1) Signaling must be applicable for different QoS technologies.
   This includes sufficient QoS information. The information exchanged
   over the signaling protocol must be in such detail and quantity that
   it is useful for various QoS technologies.

   2) Resource availability information on request [Extension]
   In some scenarios, e.g., the mobile terminal scenario, it is
   required to query, whether resources are available, without
   performing a reservation on the resource. Feedback

   3) Modularity

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   A modular design should allow for more lightweight implementations,
   if fewer features are needed. Mutually exclusive solutions are
   supported. Examples for modularity:
   - Work over any kind of network (narrowband / broadband, error-prone
   / reliable...) - This implies low bandwidth signaling and redundant
   information must be supported if necessary.

   - In case QoS requirements are soft (e.g. banking transactions,
   gaming), fast and lightweight signaling (e.g., not more than one
   round-trip time)
   - Uni- and bi-directional reservations are possible

   4) Decoupling of protocol and information it is carrying
   The signaling protocol(s) used should be clearly separated from the
   QoS control information being transported. This provides for the
   independent development of these two aspects of the solution, and
   allows for this control information to be carried within other
   protocols, including application layer ones, to be developed in the
   future. The gained flexibility in the information transported allows
   for the applicability of the same protocol in various scenarios.
   However, note that the information carried needs to be the same.
   Otherwise interoperability is difficult to achieve.

   5) Reuse of existing QoS provisioning
   Reuse existing QoS functions and protocols for QoS provisioning
   within a domain/subdomain unchanged. (Motivation: 'Don't re-invent
   the wheel'.)

   6) Avoid duplication of [sub]domain signaling functions
   The specification of the NSIS signaling protocol should be optimised
   to avoid duplication of existing [sub]domain QoS signaling and to
   minimise the overall complexity. (Motivation: we don't want to
   introduce duplicate feedback or negotiation mechanisms, or
   complicate the work by including all possible existing QoS signaling
   in some form. The function will be placed in the new part if it has
   to be end-to-end, universal to all network types
   ('simple/lightweight'), or if it has to be protected by upper layer
   security mechanisms.)

   The point here is that the QoS technology (lower layer stuff) gets
   re-used unchanged, and we have new signaling above it. But, in many
   cases the local QoS technology will contain equivalent functions to
   the NSIS-required ones, just in a technology specific form. Examples
   of these functions would be error/QoS violation notifications,
   ability to query for resources and so on. So, there is a danger that
   our 'lightweight' signaling ends up trying to carry all this
   information all over again, and (even worse) that the
   initiator/controller functions have to weigh up nearly equivalent
   information coming from two directions. However, the basic problem
   here is that the boundary between new and re-used stuff is pretty
   shaky. The requirement is trying to scope our problem (a) to
   eliminate the potential overlap, and (b) to keep the new NSIS stuff

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   7) Avoid modularity with large overhead (in various dimensions)
   The protocols used for transporting signaling information over
   various path segments do not need to be the same. Only the QoS
   control information needs to be interworked between each segment.
   (Motivation: the protocol can be chosen optimally for the
   characteristics of the QoS domain being traversed. Also, we allow a
   choice of protocols in end systems and networks without forcing
   everyone to implement all choices; the network implementer's choice
   of protocol can be local.)

   8) Possibility to use the signaling protocol for existing local
   It needs to be possible to use the new signaling as another local
   QoS technology in its own right. For example, the treatment of
   aggregates but possibly for other reasons also. Note that figure 2
   shows precisely this case, it is being used there to support
   signaling QoS for the aggregates.

5.2. Signaling Flows

   This section contains requirements related to the possible signaling
   flows that should be supported, e.g. over what parts of the flow
   path, between what entities (end-systems, routers, middleboxes,
   management systems), in which direction.

   1) The protocol(s) must work in various scenarios end-to-end, edge-
   to-edge, (e.g., just within one providers domain), user-to-network
   (from end system into the network, ending, e.g., at the entry to the
   network and vice versa),  network-to-network (e.g., between
   providers). In the figures of section 4, this means the location of
   QoS Initiator and QoS Controllers can be chosen freely.

   2) QoS signaling and QoS Controllers must not be constrained to be
   in the data path.

   3) Concealment of topology
   In various scenarios, topology information should be hidden for
   various reasons. From a business point of view, some administrations
   don't want to reveal the topology and technology used.

   4) Optional transparency of QoS signaling to network
   It should be possible for the QoS signaling for some flows to
   traverse path segments transparently, i.e. without interpretation at
   QoS controllers within the network. An example would be a subdomain
   within a core network, which only interpreted signaling for
   aggregates established at the domain edge, with the flow-related
   signaling passing transparently through it.

5.3. Additional information beyond signaling of QoS information

   This section contains the desired signaling (messages) for other
   purpose other than that for conveying QoS parameters.

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   1) Explicit release of resources
   When a QoS reservation is no longer necessary, e.g. because the
   application terminates, or because a mobile host experienced a hand-
   off, it must be possible to explicitly release resources.

   2) Ability to signal life-time of a reservation
   Information about the life-time of a reservation allows to reduce
   the reservation update frequency in case of soft state based
   signaling. Note however, that we do not require in advance
   reservation, only the expected duration of the reservation should be

   3) Possibility for automatic release of resources after failure
   When the QoS Initiator goes down, the resources it requested should
   be released, since they will no longer be necessary.

   4) Possibility for automatic re-setup of resources after recovery
   In case of a failure, the reservation can get setup again
   automatically. It enables sort of a persistent reservation, if the
   QoS Initiator requests it. In scenarios where the reservations are
   on a longer time scale, this could make sense to reduce the
   signaling load in case of failure and recovery.

   5) Prompt notification of QoS violation in case of error / failure
   to QoS Initiator and QoS Controllers

   6) Feedback about the actually received level of QoS guarantees
   The feedback must be independent of streaming technology used.
   In some scenarios it might be requested to receive statistics about
   the QoS received. E.g., feedback information might be used as input
   to adaptation mechanisms.

   7) Automatic notification on available resources not been granted
   before [Extension]
   In many cases, a QoS initiator does want to get a notification if
   the resource he requested for some time ago, gets free. In order to
   keep it simple, information on how long a request is kept and
   notified. It implies keeping state about requests, which have been

5.4. Layering

   This section contains requirements related to the way the signaling
   being considered interacts with upper layer functions (users,
   applications, and QoS administration), and lower layer QoS

   1) The signaling protocol and QoS control information should be
   application independent. However, opaque application information
   should get transported in the signaling message, without being
   handled in the network. Development and deployment of new
   applications should be possible without impacting the network

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   infrastructure. Additionally, QoS protocols are expected to conform
   to the Internet principles.

5.5. QoS Control Information

   This section contains requirements related to the QoS control
   information that needs to be exchanged.

   1) Mutability information on parameters
   It should be possible for the initiator to control the mutability of
   the QSC information. This prevents from being changed in a non-
   recoverable way. The initiator should be able to control what is
   requested end to end, without the request being gradually mutated as
   it passes through a sequence of domains. This implies that in case
   of changes made on the parameters, the original requested ones must
   still be available.

   2) Possibility to add and remove local domain information
   It should be possible for the QoS control functions to add and
   remove local scope elements. E.g., at the entrance to a QoS domain
   domain-specific information is added, which is used in this domain
   only, and the information is removed again when a signaling message
   leaves the domain. The motivation is in the economy of re-use the
   protocol for domain internal signaling of various information. Where
   additional information is needed for QoS control within a particular
   domain, it should be possible to carry this at the same time as the
   'end to end' information.)

   3) The QoS service classes should be defined taking into account how
   they will be mapped to QoS provisioning or upper layer parameters.
   (Motivation: the simpler and more direct this mapping, the more
   faithful the overall QoS provided to the application.)

   4) Aggregation method specification
   The initiator should be able to specify the aggregation method that
   will be applied to the flow. Since the aggregation method implicitly
   affects the QoS that applies to the flows, the initiator must be
   able to influence this.

   The point in this requirement is that a reservation for a flow may
   make sense in isolation, but for scalability we need to aggregate
   flows together (as we all know). The treatment of the flow within
   the aggregate won't match the original reservation exactly - there
   has to most likely be an information loss - but the user (QoS
   initiator) should be able to at least indicate how the aggregation
   takes place.

   As an example, we use a controlled load service request for NRT
   traffic as an example. the initiator is happy to have just some sort
   of fair sharing with other flows within the aggregate rather than
   precise matching of the leaky bucket parameters at every hop along
   the aggregate path. a second more direct aspect is that a user might
   want to make a set of reservations but indicate the way they get

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   aggregated together (e.g. set of reservations which are all intended
   to share a common resource).

   As another example, say a user has multiple web sessions running and
   wants anything sent to him on port 80 to be aggregated onto a single
   reservation where possible (so that he doesn't have to pay for
   individual reservations for each session).  The requirement is to
   allow the user to specify a minimum aggregation that he would like
   for his flows, but without preventing each individual domain from
   further aggregating flows according to their own QoS technology.

   5) Multiple levels of detail
   The QSC should allow for multiple levels of detail in description.
   (Motivation: someone interpreting the request can tune its own level
   of complexity by going down to more or less levels of detail. A
   lightweight implementation within the core could consider only the
   coarsest level.)

   6) Ranges in specification
   The QSC should allow for specification of minimum required QoS
   and/or desirable QoS. (Motivation: The QoS Service Classes should
   allow optionally for ranges to be indicated, to minimize negotiation
   latency and suppress error notifications during handover events.)

   7) Independence of reservation identifier
   A reservation identifier must be used, which is independent of the
   flow identifier, the IP address of the QoS Initiator, and the flow
   end-points. Various scenarios in the mobility area require this
   independence because flows resulting from handoff might have changed
   end-points etc. but still have the same QoS requirement.

   8) Seamless modification of already reserved QoS
   In many case, the reservation needs to be updated (up or downgrade).
   This must happen seamlessly without service interruption. At least
   the signaling protocol must allow for it, even if some data path
   elements might not be capable of doing so.

   9) Signaling must support quantitative, qualitative, and relative
   QoS specifications

   10) QoS conformance specification
   The initiator should be able to indicate how faithfully the QoS
   provided by the network should conform to that requested.
   (Motivation: this allows for some flexibility in the level of QoS
   fulfilled by the network compared to that requested by the initiator
   deep inside the network.)

5.6. Performance

   This section discusses performance requirements and evaluation
   criteria and the way in which these could and should be traded off
   against each other in various parts of the solution.

   1) Scalability

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   Scalability is a must anyway. However, depending on the scenario the
   question to which extend the protocol must be scalable. The protocol
   must be scalable:
   - in the number of messages received by a signaling communication
   partner (QoS initiator and controller)
   - in number of hand-offs
   - in the number of interactions for setting up a reservation
   - in the number of state per entity (QoS initiators and QoS

   2) Low latency
   Low latency is only needed in scenarios, where reservations are in a
   short time scale (e.g. mobile environments), or where human
   interaction is immediately concerned (e.g., voice communication
   setup delay)

   3) Low bandwidth consumption
   Again only small sets of scenarios call for low bandwidth, mainly
   those where wireless links are involved.

   Note that many of the performance issues are heavily dependent on
   the scenario assumed and are normally a trade-off between speed,
   reliability, complexity, and scalability. The trade-off varies in
   different parts of the network. For example, in radio access
   networks low bandwidth consumption will overweight the low latency
   requirement, while in core networks it may be reverse.

5.7. Flexibility

   This section lists the various ways the protocol can flexibly be

   1) Aggregation capability, including the capability to select and
   change the level of aggregation.

   2) Flexibility in the placement of the QoS initiator
   It might be the sender or the receiver of content. But also network
   initiated reservations are required in various scenarios.

   3) Flexibility in the initiation of re-negotiation (QoS change
   Again the sender or the receiver of content might initiate a re-
   negotiation due to various reasons, such as local resource shortage
   (CPU, memory on end-system) or a user changed application
   preference/profiles. But also network-initiated re-negotiation is
   required in cases, where the network is not able to further
   guarantee resources etc.

   4) Uni / bi-directional reservation
   Both uni-directonal as well as bi-direction reservations must be

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5.8. Security

   This section includes security-related requirements.

   1) The QoS protocol must provide strong authentication

   A QoS protocol must make provision for enabling various entities to
   be authenticated against each other using data origin and/or entity
   authentication. The QoS protocol must enable mutual authentication
   between the two communicating entities.  The term strong
   authentication points to the fact that weak plaintext password
   mechanisms must not be used for authentication.

   2) The QoS protocol must provide means to authorize resource

   This requirement demands a hook to interact with a policy entity to
   request authorization data. This allows an authenticated entity to
   be associated with authorization data and to verify the resource
   request. Authorization prevents reservations by unauthorized
   entities, reservations violating policies, theft of service and
   additionally limit denial of service attacks against parts of the
   network or the entire network.

   3) The QoS signaling messages must provide integrity protection.

   The integrity protection of the transmitted signaling messages
   prevent an adversary from mounting denial of service attacks against
   network elements participating in the QoS protocol, from hijacking a
   connection and from forging reservation requests and the
   corresponding replies.

   4) The QoS signaling messages must provide protection against replay

   To prevent replay of previous signaling messages the QoS protocol
   must provide means to detect old messages. A solution must cover
   issues of synchronization problems in the case of a restart or a
   crash of a participating network element.

   5) The QoS signaling protocol must allow for hop-by-hop security.

   Hop-by-Hop security is a well-known and proven concept in QoS
   protocols that allows intermediate nodes that actively participate
   in the QoS protocol to modify the messages as required by the QoS
   processing. Note that this requirement does not exclude end-to-end
   security of a QoS reservation request. End-to-End security between
   the initiator and the responder may be used to provide protection of
   non-mutable data fields. Since the QoS protocol makes no provision
   to establish an end-to-end security association such an end-to-end
   protection cannot be a must-requirement.

   6) The QoS protocol should allow identity confidentiality and
   location privacy.

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   Identity confidentiality enables privacy and avoids profiling of
   entities by an adversary eavesdropping the signaling traffic along
   the path. The identity used in the process of authentication may
   also be hidden to a limited extent from a network to which the
   initiator is attached. It is however required that the identity
   provides enough information for the access network to collect
   accounting data. Location privacy is an issue for the initiator who
   triggers the QoS protocol. In some scenarios the initiator may not
   be willing to reveal location information to the responder.

   7) The QoS protocol should provide hooks for AAA protocols

   The security mechanism should be developed with respect to be able
   to collect usage records from one or more network elements.

   8) The QoS protocol should prevent denial-of-service attacks against
   signaling entities.

   To effectively prevent denial-of-service attacks the QoS protocol
   and the used security mechanisms should not force to do heavy
   computation to verify a resource request. The QoS protocol and the
   used security mechanisms should not require large resource
   consumption for example main memory to take place.

   9) The QoS protocol should not disclose the network topology

   The QoS protocol should allow hiding the internal structure of a QoS
   domain from end-nodes and from other networks. Hence an adversary
   should not be able to learn the internal structure of a network with
   the help of the QoS protocol.

   10) The QoS protocol may support confidentiality of signaling

   Based on the signaling information exchanged between nodes
   participating in the QoS protocol an adversary may learn both the
   identities and the content of the QoS messages. To prevent this from
   happening, confidentiality of the QoS requests in a hop-by-hop
   manner may be provided. Note that hop-by-hop is always required
   whenever entities actively participating in the protocol must be
   able to read and eventually modify the content of the QoS messages.
   This does not exclude the case where one or more network elements
   are not required to read the information of the transmitted QoS

   11) The QoS protocol should provide hooks to interact with
   authentication and key management negotiation protocols

   The negotiation of an authentication and key management protocols
   within the QoS protocol is outside the scope of the QoS protocol.
   The goal of such a negotiation step is to determine which
   authentication and key management protocol to use is executed prior
   to the execution of the chosen key management protocol. A QoS

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   protocol should however provide a way to interact with these
   negotiation protocols.

   12) The QoS protocol should provide means to interact with key
   management protocols

   Key management protocols typically require a larger number of
   messages to be transmitted to allow a session key and the
   corresponding security association to be derived. To avoid the
   complex issue of mapping individual authentication and key
   management protocols to a QoS protocol such a protocol is outside
   the scope of the QoS protocol. Although the key management protocol
   may be independent there must be a way for the QoS protocol to
   exploit existing security associations to avoid executing a separate
   key management protocol (or instance of the same protocol) for
   protocols that closely operate together. If no such security
   association exists then there should be means for the QoS protocol
   to trigger a key management protocol to dynamically create the
   required security associations.

5.9. Mobility

   Mobility related requirements are already covered in [2], and are
   not repeated here.

    Interworking with other protocols and techniques

   Hooks must be provided to enable efficient interworking between
   various protocols and techniques including:

   1) Policies, traffic engineering, network management, accounting,
   Session signaling (particularly SIP proxy), Context transfer

   2) The solution should not constrain either to IPv4 or IPv6

   3) Combination with Mobility management
   Combining mobility and QoS signaling should be supported for
   economic signaling behavior (e.g., negotiation with the new access
   network: Mobile IP message to acquire new care-of address and query
   for QoS information could be combined, in order to preserve
   bandwidth and reduce latency).

   4) Independence from charging model
   Signaling must not be constrained by charging models or the charging
   infrastructure used. However, the end-system should be able to query
   current pay statistics and to specify user cost functions.

6. References

   [1] Kempf, J., "Dormant Mode Host Alerting ("IP Paging") Problem
   Statement", RFC 3132, June 2001.

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   [2] Chaskar, H., "Requirements of a QoS Solution for Mobile IP",
   draft-ietf-mobileip-qos-requirements-01.txt, Work in Progress,
   August 2001

   [3] Manner. J., et al, "Mobility Related Terminology", draft-manner-
   seamoby-terms-02.txt, Work In Progress, July 2001.

   [4] 3GPP, "General Packet Radio Service (GPRS); Service Description
   Stage 2 v 7.7.0", TS 03.60, June 2001

   [5] 3GPP2, "Network Reference Model for cdma2000 Spread Spectrum
   System, revision B", S.R0005-B, May 2001

   [6] Bradner, S., Mankin, A., "Report of the Next Steps in Signaling
   BOF", draft-bradner-nsis-bof-00.txt, Work in Progress, July 2001

   [7] Partain, D., et al, "Resource Reservation Issues in Cellular
   Radio Access Networks", draft-westberg-rmd-cellular-issues-00.txt,
   Work in Progress, June 2001

7. Acknowledgments

   Quite a number of people have been involved in the discussion of the
   draft, adding some ideas, requirements, etc. We list them without a
   guarantee on completeness: Changpeng Fan, Krishna Paul, Maurizio
   Molina, Mirko Schramm.

8. Author's Addresses

   Andreas Schrader, Hannes Hartenstein, Ralf Schmitz, Juergen Quittek,
   Marcus Brunner
   NEC Europe Ltd.
   Network Laboratories
   Adenauerplatz 6
   D-69115 Heidelberg
   E-Mail: brunner@ccrle.nec.de (contact)

   Morihisa Momona
   NEC Corporation
   E-Mail: momona@ccm.cl.nec.co.jp

   Robert Hancock, Eleanor Hepworth
   Roke Manor Research Ltd
   Romsey, Hants, SO51 0ZN
   United Kingdom
   E-Mail: [robert.hancock|eleanor.hepworth]@roke.co.uk

   Cornelia Kappler
   Siemens AG
   Berlin  13623

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               Requirements for QoS Signaling Protocols  November 2001

   Phone: +49-30-386-32894
   E-Mail: cornelia.kappler@icn.siemens.de

   Holger Karl, Xiaoming Fu
   Technical University Berlin
   Sekr. 5-2, Einsteinufer 25
   Berlin  10587
   Phone: +49-30-314-23826
   E-Mail: [karl|fu]@ee.tu-berlin.de

   Hans-Peter Schwefel
   Siemens AG
   Phone +49-89-722-59890
   E-Mail: hans.schwefel@icn.siemens.de

   Mathias Rautenberg
   Siemens AG
   Hofmannstr. 51
   81359 Munchen
   E-Mail: Mathias.Rautenberg@icn.siemens.de

   Hannes Tschofenig
   Siemens AG
   Otto-Hahn-Ring 6
   81739 Munchen
   Email: Hannes.Tschofenig@mchp.siemens.de

   Dr. Christoph Niedermeier
   CT SE 2
   Siemens AG
   D-81730 Muenchen,
   phone:  ++49-89/636-45783
   fax:    ++49-89/636-40898
   email: Christoph.Niedermeier@mchp.siemens.de

   Andreas Kassler
   Dept. Distributed Systems
   University of Ulm
   Oberer Eselsberg
   89069 Ulm
   Tel.: ++49 731 502 4139
   Fax.: ++49 731 502 4142
   eMail: kassler@informatik.uni-ulm.de

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