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Versions: 00 01 draft-ietf-vwrap-intro

Virtual World Region Agent                                    M. Hamrick
Internet-Draft                                                 D. Levine
Intended status: Informational             IBM Thomas J. Watson Research
Expires: November 19, 2010                                        Center
                                                            May 18, 2010

                     VWRAP: Introduction and Goals


   The Virtual World Region Agent Protocol (VWRAP) defines interactions
   between hosts collaborating to create an shared, internet scale
   virtual world experience.  This document introduces the protocol, the
   objectives and requirements it imposes on hosts implementing the
   protocol.  To the extent it affects protocol interactions, this
   document describes the model assumed by the protocol.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on November 19, 2010.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must

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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction and Motivation  . . . . . . . . . . . . . . . . .  3
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  3
   2.  Introducing the Virtual World Region Agent Protocol  . . . . .  3
     2.1.  A Brief Introduction to Virtual Worlds . . . . . . . . . .  3
     2.2.  Architectural Objectives . . . . . . . . . . . . . . . . .  5
     2.3.  Protocol Objectives  . . . . . . . . . . . . . . . . . . .  8
   3.  Virtual World Region Agent Protocol Architecture . . . . . . . 10
     3.1.  Deployment Patterns  . . . . . . . . . . . . . . . . . . . 10
     3.2.  Protocol Elements  . . . . . . . . . . . . . . . . . . . . 11
       3.2.1.  Communicating Application State Using REST-Like
               Resource Accesses  . . . . . . . . . . . . . . . . . . 11
       3.2.2.  Bi-Directional Messaging with the VWRAP Event Queue  . 13
       3.2.3.  Using Capabilities to Simplify Inter-Domain Access
               Control  . . . . . . . . . . . . . . . . . . . . . . . 13
       3.2.4.  Using LLSD to Avoid Version Skew . . . . . . . . . . . 14
   4.  Virtual World Region Agent Protocol Services . . . . . . . . . 15
     4.1.  Authentication . . . . . . . . . . . . . . . . . . . . . . 17
     4.2.  Text and Voice Chat  . . . . . . . . . . . . . . . . . . . 18
     4.3.  Agent Presence . . . . . . . . . . . . . . . . . . . . . . 19
       4.3.1.  Moving Presence  . . . . . . . . . . . . . . . . . . . 20
     4.4.  Digital Asset Access . . . . . . . . . . . . . . . . . . . 21
       4.4.1.  Manipulating Digital Assets  . . . . . . . . . . . . . 21
       4.4.2.  Establishing Presence for Digital Assets . . . . . . . 22
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23
     5.1.  Capabilities . . . . . . . . . . . . . . . . . . . . . . . 24
     5.2.  User Authentication  . . . . . . . . . . . . . . . . . . . 24
     5.3.  Service to Service Authentication  . . . . . . . . . . . . 24
     5.4.  Access Control for Digital Assets  . . . . . . . . . . . . 25
   6.  Accessibility Considerations . . . . . . . . . . . . . . . . . 25
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 25
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 25
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 26
   Appendix A.  Definitions of Important Terms  . . . . . . . . . . . 26
   Appendix B.  Acknowledgements  . . . . . . . . . . . . . . . . . . 27
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27

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1.  Introduction and Motivation

   Virtual Worlds are of increasing interest to the internet community.
   Innumerable examples of virtual world implementations exist; most
   using proprietary protocols.  With roots in games and social
   interaction, virtual worlds are now finding use in business,
   education and information exchange.  This document introduces the
   Virtual World Region Agent Protocol (VWRAP) suite.  This protocol
   suite is intended to carry information about a virtual world: its
   shape, its residents and objects existing within it.  VWRAP's goal is
   to define an extensible set of messages for carrying state and state
   change information between hosts participating in the simulation of
   the virtual world.

   Virtual worlds differ in their capabilities and architectural
   features.  The VWRAP protocol suite is not appropriate for all
   massively multi-participant experiences.  This document provides an
   introduction to virtual worlds and defines characteristics of virtual
   worlds VWRAP explicitly supports.  It also describes the specific
   objectives of the protocol suite.  An overview of the protocol is
   included, including an architectural description and list of services
   defined in a typical virtual world deployment.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Introducing the Virtual World Region Agent Protocol

2.1.  A Brief Introduction to Virtual Worlds

   At its most basic level, the virtual world mirrors the reified world.
   It is inhabited by people and contains objects.  Objects and people
   have a distinct place in the world and respond to external forces.
   The social construction of the virtual world is also similar to the
   reified world.  People meet and interact with others to complete work
   tasks or for simple enjoyment.  People converse, share media, and
   even sing to each other.  A virtual world may allow commerce or
   enable building of virtual assets.  Nearly the complete range of
   human interaction can be replicated in the virtual world.  Properly
   rendered, an experience in a virtual world can carry the same impact
   as one in consensus reality.

   To be relevant to the participant's experience, virtual worlds must
   retain characteristics of the "real world."  Objects in the virtual

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   world are models of familiar shapes and textures, represented using a
   common data format so they may be easily processed by the human
   visual cortex.  At the same time they must carry sufficient
   information to be consumed by participants with visual impairments or
   to be processed by automated systems.  Though the virtual world's
   state is maintained by abstract collections of data, it is rendered
   as recognizable (though occasionally fantastical) physical objects.

   But virtual worlds are not completly faithful mirrors of the world
   our physical bodies inhabit.  Virtual worlds are not limited by
   distance.  With appropriate network connectivity, users may interact
   even if they are on opposite sides of the earth.  Virtual worlds also
   allow participants to "play" with physical constraints.  They provide
   the subjective experience of things not possible in consensus
   reality: participants can fly, the effects of "death" are temporary,
   users may call items into existence, examine the International Space
   Station with friends, examine DNA codon by codon with co-workers, or
   experience with a works of interactive art.

   Virtual worlds inherit the intellectual property characteristics of
   other digital media.  Implementers wishing to replicate the economy
   of scarcity present in the reified world must take special measures
   to avoid or limit the ramifications of unauthorized content

   The VWRAP suite assumes network hosts, likely operated by distinct
   organizations will collaborate to simulate the virtual world.  It
   also assumes that services originally defined for other environments
   (like the world wide web) will enhance the experience of the virtual
   world.  The virtual world is expected to be simulated using software
   from multiple sources; interoperability standards are essential for
   delivering a robust services and compelling user experiences.  VWRAP
   provides these interoperability standaards.  It may be used with
   large arrays of hosts simulating a vast virtual world, or small
   worlds operated for the benefit a few persons.  It defines a trust
   model so hosts from different organizations may limit access to
   sensitive information.

   VWRAP presupposes a virtual world with the following characteristics:

   1. The virtual world exists independent of the participating

       This is in contrast to systems that dynamically create virtual
       environments for specific social or task-oriented simulation.
       VWRAP assumes the state virtual world is "always on" and does not
       require a specific protocol to establish new virtual worlds.

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   2. Avatars have a single, unique presence in the virtual world.

       Users are represented in the virtual world by a digital
       representation called an avatar.  A user's avatar has an
       existence that mirrors the common physical world.  Like people,
       avatars exist in only one place at one time.  Avatars have a
       single identity that persists between user sessions.  This
       identity may be used to render user-specific avatar shape or as
       the basis for access control.

   3. The virtual world contains persistent objects.

       Objects in the virtual world are governed by a "rational" life-
       cycle.  They are created, persist and are (optionally) destroyed.
       Absent external forces, they tend to keep their current state.

2.2.  Architectural Objectives

   The overall objective of the VWRAP suite is to enable a stable,
   extensible and secure virtual world.  The protocols defined by this
   working group do not mandate a specific system or network
   architecture.  However, previous implementations of large distributed
   systems can yeild clues as to how VWRAP compliant systems will be
   deployed.  Documents produced by this working group reflect the
   consensus view of best common practice for producing large-scale,
   loosely-coupled distributed systems.  VWRAP does not require a
   specific architecture, but it's protocols are defined with a specific
   series of architectural patterns in mind.

   These architectural patterns have the following objectives in mind:

   1. Systems implementing virtual world services should be

       Virtual worlds are inherently distributed systems.  They are
       collaborative tools intended to reduce the effect of distance on
       meaningful social, educational and commercial interaction.
       Typical virtual worlds are envisioned as drawing services from
       network hosts operated by a wide array of organizational
       entities.  Virtual worlds may also be large enough that a single
       system or cluster of systems is not capable of providing all
       services to each client.

       Experience with previous virtual world technologies suggests
       systems implementing the virtual world assume services they
       depend on are provided by distinct hosts in different
       administrative domains.  The virtual world, it's user base and
       the constellation of virtual objects they use are simply too vast

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       and varied to assume a single system or a single provider.

       This does not mean, however, that virtual worlds simulated by the
       VWRAP suite must exist on more than one system.  Quite the
       contrary, all VWRAP components (including the user agent) could
       operate on a single system.  But there is little reason to
       believe the protocol used to exchange information between virtual
       world services must differ between small and large systems.

       Large virtual worlds with many users are certain to implement
       virtual world services differently than small ones.  But the
       protocol used to to communicate between systems implementing the
       virtual world can be the same.  To be sure, optimizations may be
       possible for smaller deployments.  Implementers of these "small"
       systems may find it useful to utilize standard, unoptimized
       protocols to allow for the possibility of growth.

       However large (or small) a virtual world deployment is, or how
       many distinct organizations contribute to its operation, software
       implementing virtual world services MUST assume resources
       required to perform its function are distributed amongst multiple

   2. Services supporting collaboration are hosted on 'central'

       The VWRAP suite assumes a collection of authoritative hosts for
       critical data and services.  This applies to digital assets, user
       accounts, agent presence information and sources for virtual
       world object updates.  This is in contrast to 'peer to peer'
       systems in which authoritative data may travel between hosts,
       depending on which hosts are connected to the network at any
       given moment.  It also contrasts with 'client authoritative' or
       'co-simulation' architectures in which physics simulation and
       agent state change occurs on the client.

       This does not imply there is a single collection of systems
       holding authoritative data for the entire connected Internet.On
       the contrary, it explicitly allows for the simultaneous existance
       of multiple virtual worlds.  It defines the mechanisms by which
       systems cooperate to simulate a virtual world, but does not
       specify a specific instance of those protocols as being any more
       authoritative than any others.

       This objective implies that for any given data item, be it a
       avatar mesh, a region description or object description, there is
       an authorative URL.  Subject to security policy, the data may be
       cached or transferred between domains, but authority over the

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       data rests with administrative ownership of the host identified
       by it's URL.

       This decision was motivated by the realization that network load
       in niave peer-to-peer implementations increases proportionally to
       the factorial of the number of participants.  "Client
       Authoritative" solutions, where clients are first class
       participants in physics simulation or object presence and
       differences are explicitly resolved between clients, was thought
       to introduce undesirable requirements for client connectivity and
       client system performance.

       This is not to say that either peer-to-peer or co-simulation are
       incompatible with systems that might use VWRAP.  But rather, it
       was believed that their specification should be deferred to a
       later time when solutions to perceived problems could be explored
       more fully.

   3. Hosts cooperating to simulate a virtual world should be composed
   of loosely coupled systems.

       This document uses the term "loosely coupled" to mean software
       and systems implementing the virtual world should exhibit strong
       separation of concerns and resiliance in the presence of version
       skew.  For the purposes of this document, "loosely coupled"
       implies system developers should expect multiple revisions of
       message formats to be encountered.  Systems implementing these
       protocols should make a best effort to interpret messages
       received from remote hosts.  Conversely, protocol developers and
       system implementers should carefully craft new revisions of
       messages to avoid confusion for systems expecting earlier message

       The motivation for emphesizing this pattern stems from the
       requirement that systems cooperating to simulate the virtual
       world may be owned by distinct organizations.

   4. A persistent, ubituitous identity may accompany requests between

       Many network services are provided anonymously; the nature of the
       service does not require identity authentication prior to it's
       use.  But with the increasing deployment of customizable services
       delivered on the internet, identity is increasingly important.
       Even services that contain information that might not be
       considered "sensitive" require a representation of digital
       identity if for no other reason than to match service requests
       with user preferences.  For example, a web page presenting

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       current weather information may be enhanced by remembering
       locations of interest to each user.  Recent work with "web mash
       ups," where multiple personalized or sensitive resources are used
       in concert with one another points to the utility of a
       "universal" identity.  The representation of this universal
       identity enables independent services to cooperate to present the
       facade of a unified application to the service consumer.  This
       allows service aggregators to more easily integrate "best of
       breed" services into a consistent solution.

       Universal identity is critical to the virtual world.  To achieve
       an internet scale virtual world, user services must be
       distributed amongst multiple hosts.  To achieve a compelling
       experience, it must be easy for service providers to deliver
       their services in the virtual world.  To facilitate a compelling
       social experience in the virtual world, all users must have the
       ability evaluate identity information of other users.  Domains
       responsible for virtual world simulation MUST use a consistent
       representation of identity across all their hosts; simulation
       would otherwise be uncoordinated.  Service providers who deliver
       content into the virtual world MUST use a consistent
       representation of identity to maintain the persistence of the
       virtual manifestation of their service; virtual objects used in
       conjunction with these services might otherwise appear to change
       state without apparent cause.  Users depend on the persistent,
       universal identity of other users; if an avatar's identity
       changed unexpectedly, the result would be a suboptimal virtual
       world experience.

2.3.  Protocol Objectives

   The primary objective of the Virtual World Region Agent Protocol is
   to provide a stable, extensible, secure system for virtual world
   information interchange with the following characteristics:

   1. Flexible presentation of protocol data

       While the primary purpose of the virtual world is to simulate a
       physical or social space, the tools used to access objects in the
       virtual world may be varied.  Using a "3d viewer" is the primary
       mode of interaction with the virtual world, but other tools may
       be better suited for some tasks.  For instance, it may be easier
       for a user to use a web browser to review avatar profile
       information, or to change details of virtual objects.  Further,
       virtual world "mash ups" may prove to be important to some
       communities.  To support the web (where XML and JSON are the
       lingua franca of information exchange) while also supporting
       tools where binary encodings are more appropriate, VWRAP was

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       designed to be "presentation neutral."

       VWRAP protocol exchanges are described in terms of an abstract
       type system using an interface description language.
       Implementations may choose to instantiate actual protocol data
       units using the most appropriate presentation format.  Web-based
       applications may choose to use JSON or XML.  Server-to-server
       interactions may use the VWRAP specific binary serialization
       scheme if implementers and deployers view binary encoding to be
       advantageous.  The decision of which serialization scheme to use
       is ultimately that of the system implementer.  VWRAP has been
       designed to provide this flexibility to system implementers and
       those tasked with deploying VWRAP compatible systems.

   2. Flexible decomposition of concerns and ease of extension

       VWRAP has been daesigned to allow meaningful separation of
       concerns.  In other words, changes in one part of the protocol
       should not appreciably affect other parts.

       For example, the authentication portion of the protocol is
       independent of the part of the protocol that deals with instant
       messaging or instantiating objects in the virtual world.  In
       addition to defining messages for communicating application
       state, the specification also defines pre- and post-conditions.
       Should one particular authentication scheme be found to be
       lacking, it can be modified or replaced without affecting other

       This type of separation of concerns in the protocol specification
       also makes it easy to deploy "related solutions."  While VWRAP
       was designed primarily to communicate the state of the virtual
       world between servers and client applications, a number of
       related applications also exist.  E-Commerce web sites related to
       the virtual world and mobile chat clients allowing instant
       messaging between mobile networks and virtual world participants
       are just two examples of such applications.  Proper separation of
       concerns allows new services to be specified and deployed without
       the need to redefine existing protocol.

   3. Resilience in the face of version skew

       Core to the VWRAP protocol is the idea that different components
       and services may be operated by different administrative
       entities; identity management services might be operated one
       business while simulation services are operated by another.  In
       environments where many different organizations participate,
       version skew can be an important concern.  VWRAP was designed to

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       "degrade gracefully" when two systems running different versions
       of the protocol attempt to communicate.

       VWRAP uses the LLSD abstract type system and the LLIDL interface
       description language to describe the structure and type semantics
       of elements in messages sent between systems.  Because LLSD makes
       extensive use of variable width, clearly delineated data fields,
       services which consume protocol messages may identify and extract
       only those message elements they know how to handle.  While this
       is not a guarantee that message semantics may be preserved in all
       version skew situations, it does eliminate one important cause of
       interoperability failures.

3.  Virtual World Region Agent Protocol Architecture

3.1.  Deployment Patterns

   The VWRAP suite assumes that the services that simulate the virtual
   world will be hosted on multiple network hosts.  Client applications
   that render the virtual world for end users are assumed to be on
   distinct hosts as well.

                             | organization 1      |
                             |                     |
                             | +----------------+  |     +-------------+
                       +------>| service host 1 |<------>]             |
                       |     | +----------------+  |     |   client    |
                       |     |                     | +-->| application |
   +-------------+     |     |                     | |   |             |
   |             |<----+     | +----------------+  | |   +-------------+
   |   client    |<----------->| service host 2 |<---+     ^
   | application |           | +----------------+  |       |
   |             |<----+     +---------------------+       |
   +-------------+     |                                   |
                       |     +---------------------+       |
                       |     | organization 2      |       |
                       |     |                     |       |
                       |     | +----------------+  |       |
                       +------>| service host 3 |<---------+
                             | +----------------+  |

   Figure 1: Protocol Flows in VWRAP

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   Figure 1 above demonstrats a typical virtual world deployment.  In it
   we see multiple client applications connecting to several servers
   operated by multiple organizations.  Each "service host" in this
   diagram exposes an interface to a collection of resources
   representing the state of objects in the virtual world.  It is
   traditional to discuss related resources as exposing "an interface"
   while related interfaces comprise "a service."  Typical services are
   listed in a section below.

   There is no restriction on how services map to hosts.  Deployments
   where all resource interfaces are hosted on a single host is just as
   valid as one where resources are spread between a wide array of
   systems.  Client applications should support both.Resource interfaces
   are addressed using URLs.  Clients should treat the URLs for
   resources as opaque resource locations.

   Clients use the "service establishment" process to retrieve URLs to
   various resources.

3.2.  Protocol Elements

   VWRAP utilizes a number of "architectural motifs" or recurring design
   patterns.  Most notably they include:

   o  exposing application state via RESTful resources

   o  using URIs to represent the address of application resources

   o  using HTTP to "carry" message oriented protocol data

   o  defining application state transitions and accesses with an
      interface description language

   o  using an abstract type system to define access semantics of fields
      in protocol messages

   o  using multiple "serializations" of the abstract type system to
      support different categories of consumers; defined serializations
      include XML, JSON and Binary.

3.2.1.  Communicating Application State Using REST-Like Resource

   Contrary to popular opinion, not ALL virtual world interactions must
   be real-time exchanges.  Many common activities like user
   authentication and texture and object transfer do not require "real
   time" semantics in the same way that applications like video-
   conferencing and Voice Over IP (VOIP) do.  While it is generally a

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   better experience if textures download quickly, if they are delayed,
   it does not have the same ramifications as if a voice packet in a
   VOIP system were delayed.  Additionally, some interactions with the
   virtual world are strongly reminiscent of the request / response
   semantics used by popular protocols (like HTTP, POP3, etc.)

   Because many protocol exchanges in the virtual world may be
   represented as non-real-time request / response interactions, VWRAP
   "reuses" the messaging semantics of HTTP.  The justification for this
   is simple.  Were VWRAP to not use HTTP, many of the features of HTTP
   would need to be re-invented or at least re-specified.  Features like
   the use of mime types to identify payload structure; the use of
   message headers to modify the request or response and the use of URIs
   to address and identify resources.  HTTP also has the benefit of
   being well supported by tools vendors and well understood by
   manufacturers of networking equipment.

   Protocol exchanges in VWRAP that utilize request / response semantics
   are described using the LLSD / LLIDL abstract type system
   [I-D.hamrick-vwrap-type-system].  LLSD defines type semantics for
   elements in a protocol data unit as well as rules for converting the
   data into a serialized form suitable for transmission across the
   network.  VWRAP defines HTTP (and HTTPS) as the transports for
   serialized messages.

   Addressable protocol endpoints in VWRAP are represented as URIs
   [RFC3986].  Protocol endpoints generally address RESTful resources.
   The VWRAP protocol uses HTTP verbs to provide read and write access
   to resources which represent the application state of the remote

   To recap, the objective of VWRAP is to communicate application state
   about the virtual world to all participants.  VWRAP messages that
   communicate request / response style messages flow between clients
   and servers, using HTTP(S) as a message transport.  Application
   objects representing the application state expose a RESTful interface
   and are addressed unambiguously using URIs.  The VWRAP message
   formats are described using LLIDL, the interface description language
   defined as part of the LLSD abstract type system.  LLIDL defines
   RESTful resource accesses in terms of the LLSD abstract type system,
   which may be serialized using one of three well defined serialization
   mechanisms: XML, JSON and Binary.  Protocol participants decide
   before interacting which serialization mechanism is most appropriate
   or use the content negotiation mechanisms defined in HTTP.

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3.2.2.  Bi-Directional Messaging with the VWRAP Event Queue

   Not all protocol interactions are easily represented by HTTP's
   request / response semantics.  When the server has a message for the
   client, there is no widely deployed technique for the server to
   initiate a HTTP request to the client.  It is interesting to note
   that this is the same problem developers of "rich web applications"
   see when deploying their applications.  Though VWRAP is not targeted
   for implementation exclusively in web browsers, we can utilize some
   of the techniques common in COMET applications.

   Work is ongoing to define a general solution for "reverse HTTP," but
   many of these solutions require the definition of new protocol and
   deploying new code to web servers.  The current best practice for
   COMET-style interaction is the use of the "long poll."

   To avoid "technology lock in," VWRAP defines an Event Queue
   abstraction that represents the flow of messages from the server to
   the client.  The Event Queue is expected to be implemented using the
   long poll technique.  When additional options such as Reverse HTTP or
   web sockets are specified and in general deployment, the Event Queue
   may be re-implemented using these techniques.  However, the interface
   defined by the Event Queue in the VWRAP Foundation document
   [I-D.lentczner-vwrap-foundation] should not change.

3.2.3.  Using Capabilities to Simplify Inter-Domain Access Control

   Simulated objects and services delivered by VWRAP compliant systems
   will require some level of access control.  Unfortunately,
   distributed access control is a notoriously difficult problem.  VWRAP
   seeks to minimize the drawbacks of distributed access control by use
   of capabilities.  In this context, a capability is an opaque URL,
   some portion of which contains a securely generated,
   cryptographically unguessable sequence of digits.  Capabilities are
   used to define service endpoints and are intended to only be in the
   possession of trusted parties.

   For example, a system may export the capability:


   This URL defines the protocol endpoint used to communicate
   application state changes (or query application state) for a specific
   application object by a specific user (or delegate.)

   Capabilities are required to be effectively unguessable as they
   represent the right to perform a set of operations on a particular
   resource.  Additionally, they must be kept "secret."  While the task

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   of maintaining the confidentiality of a number of web resource
   addresses may be a burden, it does have the advantage of simplifying
   access delegation.  If a subject wishes to delegate access to a third
   party, they simply communicate the capability.

   To reduce the likelihood of successful guessing attacks, inadvertent
   disclosure of a capability and "time of check, time of use" attacks,
   capabilities in VWRAP have a fixed lifetime, after which they expire.
   Systems SHOULD pick capability lifetimes commensurate with their
   security requirements and MUST NOT respond to protocol requests
   directed at a capability's URL after it has expired.  Additionally,
   VWRAP capabilities may be "single use" or "one shot," meaning that
   they may only be used once before expiring.

   Because capabilities are randomly generated with a short lifetime,
   VWRAP defines a mechanism for securely communicating capabilities and
   re-requesting expired capabilities.

   It is important to note that capabilities do not completely replace
   traditional access control models.  Systems may still use traditional
   Subject-Permission-Object schemes to represent access control for
   objects under their control.  Capabilities provide a mechanism for
   communicating access control decisions among loosely coupled trusted

3.2.4.  Using LLSD to Avoid Version Skew

   It is a common practice in large, complicated software systems to
   divide the system into smaller, more manageable pieces.  The precise
   nature of this partitioning is beyond the scope of this protocol.
   However, practical experience has demonstrated that services
   distributed across multiple co-operating hosts MUST contend with the
   issue of version skew.  Simply stated, version skew is the condition
   where multiple versions of a service are interoperating

   There are many reasons why version skew may be introduced.  In VWRAP,
   agent domain hosts and region domain hosts may be operated by
   different organizations with different deployment schedules.  Or
   perhaps a domain operator is required to support an obsolete version
   of a particular service endpoint for a small number of customers.
   Whatever the cause of version skew, it has, in the past introduced
   difficulties in deploying distributed services.

   VWRAP does not seek to eliminate version skew, but it does attempt to
   reduce it's impact.  VWRAP services are defined in using the LLIDL
   interface description language.  LLIDL defines the type semantics of
   fields inside a protocol message using the LLSD abstract type system.

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   Each of the abstract types defined in LLSD has a default value, and
   common conversions between conformable types are defined.  LLSD
   specifies three standard techniques for serializing a protocol
   message prior to transmission across the network.  Each of the three
   serialization techniques renders protocol messages into a collection
   of variable length fields.  Protocol content is identified by JSON
   syntax, binary tags or XML element semantics, not by it's position in
   the message.  LLIDL does not support the concept of a "required
   field."  If a field defined in a protocol interaction is not present
   in the serialized message, it is semantically equivalent to the field
   being present and containing the default value for the field's type.

   Careful construction of service endpoints allows them to consume
   messages described using LLIDL without fear that version skew induced
   format differences may cause the semantics of the message to be
   unclear.  If a message arrives at a service endpoint with extra
   fields (fields defined in a later revision of the protocol exchange),
   the consumer can still extract those fields it understands.  If a
   message arrives lacking a field described in the protocol exchange,
   the service endpoint SHOULD interpret it as if the field was present
   and contained the default value for it's type.  This implies the
   message consumer cannot depend on the format of the message to
   determine validity, but must examine the contents of the message,
   converting missing fields to present fields with default values, and
   then determine if sufficient information is present to imply
   semantics about the protocol exchange.

   This technique will not eliminate all ramifications of version skew,
   but carefully constructed service descriptions should be able to
   avoid the most common problems found when services interoperate with
   minor revision differences.  While the Virtual World Region Agent
   Protocol itself does not mandate this style of message
   interpretation, it does require that messages be constructed so that
   service endpoints may do so.

4.  Virtual World Region Agent Protocol Services

   Simulation and persistence of virtual objects in VWRAP is managed on
   "central" servers.  Servers maintain interfaces to shared resources
   which represent the state of the virtual world.  Interfaces are
   grouped by function into "services."  Services are available to
   support the access to and distribution of data representing multiple
   facets of the virtual world.  This section defines some services
   defined by VWRAP.

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       Avatar Presence

       When a user authenticates themselves and wishes to interact with
       the virtual world, the user's avatar presence must be
       established.  Simulating a user's avatar is a task shared by the
       agent domain, the region domain and the client application.  The
       agent domain is responsible for establishing the user's presence
       in the virtual world simulated by the region domain, and to
       provide information about the avatar so it may be properly

       Object Presence

       The state of objects in the virtual world (landscapes, avatars,
       virtual "things") must be communicated to all participants.  It
       is the responsibility of the region domain to keep track of each
       object's state.  The landscape can change; clouds in the virtual
       sky may move and change shape; virtual people may move around and
       virtual "things" can undergo any number of state changes.  The
       region domain is responsible for receiving input from virtual
       world inhabitants, evaluating how that input changes the state of
       objects in the virtual world, and then communicating those state
       changes to other observers.

       Physics Simulation

       Simulating the physical behavior of objects in the virtual world
       is a core feature of any virtual world.  Regions may choose
       "earth like" conditions, or may modify gravity and atmospheric
       settings to create the experience of being on a different planet.
       Still other options include simulating quantum effects seen at
       very small scales or the large scale relativistic effects seen on
       galactic scales.  Whatever the "physics" involved, it is the
       individual hosts in the region domain tasked with the simulation.

       Effects of Programmatic Changes

       (aka "scripting.")  Some virtual worlds allow users to modify the
       state of objects using simple programming languages.  The region
       domain is generally responsible for managing and executing
       scripts that modify the state of objects.

       Region Specific Asset Storage

       Though most "assets at rest" are associated with an avatar, it is
       conceptually appropriate for some items to be associated with a
       region; textures associated with landscapes, for instance.  Or in
       some situations, the operator of a region may wish to bind

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       "sensitive" resources to the location to ensure they do not
       follow region visitors to regions outside the originating
       region's administrative authority.

4.1.  Authentication

   User Authentication in the Virtual World Region Agent Protocol is
   intended to verify the user's authorization to control their avatar
   in the virtual world and associated services.  VWRAP currently
   defines three methods for authenticating a user, as well as
   recommendations for integrating some third party authentication
   schemes.  The inputs to authentication are an avatar or account
   identifier and a related authentication token.  Assuming the token is
   successfully authenticated, the output of authentication is a seed
   capability or "seed cap."

   Like most VWRAP protocol exchanges, authentication protocol data is
   represented as LLSD serialized data carried over a secure HTTPS
   transport.  The use of TLS with VWRAP authentication is recommended
   for all deployers who do not employ some other network security
   scheme (IPSec, link encryption, etc.)  Implementers are advised that
   in addition to user's password (or other credential,) the seed
   capability returned after successful authentication is also
   considered "sensitive" and should be protected with appropriate
   network security measures.

   The three authentication schemes defined in the VWRAP Trust Model and
   User Authentication [I-D.hamrick-vwrap-authentication] specification
   use a cryptographic hashes to demonstrate the user is in possession
   of the shared secret associated with their account.  Recommendations
   also exist for using transport authentication mechanisms (such as TLS
   client certificates) in place of shared secrets.  Also, work is
   currently underway to define protocol messages for use with Secure
   Remote Password (SRP).

   The authentication mechanisms described above are believed to be
   sufficient at the time of this writing.  It is an unfortunate truth,
   however, that cryptographic primitives are occasionally shown to be
   less secure than originally believed.  For this reason, VWRAP
   Authentication was designed to be extensible; allowing future users
   to define new authentication schemes without invalidating other
   authentication components.  A further benefit of flexibility is the
   ability to integrate other authentication schemes into an VWRAP
   context.  OpenID and SAML, for instance, are popular identity and
   user authentication technologies that are defined outside the IETF.
   VWRAP's flexible authentication system allows organizations
   responsible for these standards to define their use with VWRAP
   without having to change the text of the VWRAP Authentication

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   A typical flow of events for user authentication follows.  This is a
   simplified version; readers with an interest in authentication are
   referred to the VWRAP Trust Model and User Authentication
   [I-D.hamrick-vwrap-authentication] specification.

   1.  The end user presents their account identifier (either avatar
       name or account name) and an authenticator to the authentication
       services of the agent domain.  Endpoints for user authentication
       protocol messages are typically well defined, public URLs.

   2.  The authentication service authenticates the authenticator.  If
       the credentials cannot be authenticated, an error condition is

   3.  The authentication service generates a seed capability and
       returns it to the user.

   4.  The user queries the "seed cap," requesting capabilities for
       other services the user is authorized to use.

   It is important to note that in the last step listed above, the
   client is free to request a subset of services offered by the agent
   domain.  This allows the same authentication service to be used by
   restricted clients (for instance, a group-chat only client) as well
   as traditional 3d viewers.

4.2.  Text and Voice Chat

   Virtual worlds are social spaces; efficent communication between
   users is a critical component of the virtual world experience.  VWRAP
   virtual worlds support four types of text communication:

   1. User to User  Akin to traditional "instant message" systems, User-
       to-User Text Chat includes two participants, the sender and the

   2. Group  Group Text Chat is the process of delivering text messages
       to members of a pre-defined group.  Group Text Chat groups are
       frequently defined by an external authority and have a well known
       name, discoverable by a search function.

   3. Ad Hoc Group  Ad Hoc Group Text Chat involves delivering text
       message to a group created in an ad-hoc fashion.  Membership in
       an Ad Hoc Text Chat group is defined by the message sender.  The
       group typically does not have an externally locatable name.

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   4. Proximal Chat  When a user "virtually" chats to an avatar near it
       in the virtual world, it is making use of Proximal Chat.  The
       endpoint for Proximal Chat messages is a location in the virtual
       world rather than a particular usre or group.  Users whose
       avatars are within the proximity of the chatting user's avatar
       will receive text chat from that user.

   Significant effort has been invested in developing protocols capable
   of efficiently deliverign textual information between users and
   groups.  Protocols such as XMPP, SIMPLE and IRC may be used to carry
   text chat messages while VWRAP defined messages are used to establish
   and destroy text chat sessions.

   Though the protocols used to implement voice communication in the
   virtual world are no doubt different from those that carry text
   messages, the scenarios for voice communication mirror those of for
   text.  Four types of voice chat exist: User-to-User, Group, Ad Hoc
   Group and Proximal.

4.3.  Agent Presence

   Once authenticated, the client application has established "agent
   presence."  Once in possession of a valid seed capability, the client
   application may request a set of capabilities representing services
   offered by the agent domain: digital asset management, instant
   message and voice chat support as well as placing the user's avatar
   into the virtual world.

   Placing an avatar in the virtual world begins with the client
   exercising the "place my avatar in a region" capability.  As part of
   this transaction, the client provides the URI representing a region.
   Upon receipt of this request, the agent domain determines the
   validity of the URL provided, and if the URL resolves to a trusted
   region domain begins the protocol between the agent domain and the
   region domain to place the user's avatar in the region.

   The precise exchange of messages between each party is beyond the
   scope of this document, but is described in the VWRAP Teleport
   specification But a few important points should be noted:

   o  The protocol endpoint used by the client application to place the
      user's avatar in a region is managed by the agent presence service
      and provided by the authentication service following successful
      authentication.  It is not a publicly defined, fixed URL.

   o  Regions in VWRAP are represented with a URL.  After
      authentication, the client uses this URL to tell the agent
      presence service where to place the user's avatar.

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   o  The agent presence service MAY apply a local policy to the URI and
      reject the request before attempting to connect with a region.
      For instance, a "behind the firewall" agent presence service may
      limit clients to regions known to be hosted by systems inside the
      local intranet.

   o  The agent presence service MAY apply a local policy and reject the
      request after it makes an initial communication request with the
      remote region. (for example, if the region domain is operating
      servers with expired TLS certificates, or if those certificates
      are issued by a certifying authority the agent domain does not
      trust, it may reject the request.)

   o  The process of placing the avatar in the region results in
      capabilities from the region being communicated back to the agent
      presence service and the client application.  These capabilities
      are used to by the client to control the user's avatar and to
      access region-specific services.

   o  The process also results in the agent presence service issuing
      capabilities to the region, allowing it limited access to
      information about the avatar such as the avatar's shape and

   After an avatar is "placed" or "rezzed" in a region, the agent
   presence service is responsible for maintaining it's presence in a
   single location.  That is to say, after the avatar has been
   successfully been placed in a region, the agent presence service MUST
   refuse to allow a second region to "take" the avatar's presence
   without removing the avatar from its current region.

4.3.1.  Moving Presence

   When an avatar moves between regions, special care must be taken that
   the agent presence service and both the source and destination
   regions agree where avatar is located.

   Moving between regions is typically initiated by the client.  The
   process is largely the same as the initial avatar placement, but with
   the important added step of removing the avatar from it's source
   location before rezzing it in it's destination.  (In fact, the
   initial placement of an avatar can be thought of as a transfer from

   The process of moving between regions is described in the VWRAP
   Teleport specification, thought implementers should keep the
   following important considerations in mind:

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   o  The client signals to the agent presence service it's desire to
      move from one region to another by accessing the same capability
      as is used for initial placement of the avatar.

   o  The agent presence service must again check that local policy
      allows movement to the new destination, and MUST receive a
      capability for placing the client into the new region before it
      removes the avatar from it's current location.

   o  The agent presence service MUST also remove the avatar from it's
      current location before placing the avatar in the destination
      location.  Capabilities granted to the current region MUST be
      revoked as part of this process.

   o  The location of the avatar MUST be unambiguous and the agent
      presence service MUST NOT represent the avatars location as being
      in two places at once.  If required, for the short period between
      removing the avatar from one region and placing it in another, the
      avatar's location may be "in transit."

4.4.  Digital Asset Access

   The virtual world is filled with virtual objects: conference tables,
   houses, airships, dragons, etc.  These objects may or may not be
   instantiated in the virtual world.  Digital descriptions of objects
   to be placed in the virtual world should be made available to clients
   by way of the "Asset Access Protocol."  Services that wish to display
   or manipulate digital assets query servers using this protocol.

   The asset access protocol defined in VWRAP differs significantly from
   legacy protocols defined by previous virtual world systems.  It has
   been designed to more easily integrate existing collections of
   digital assets using standard protocols such as HTTP.  All assets
   used by VWRAP, including avatar meshes, scene graphs and virtual
   object descriptions are accessed using this protocol.

4.4.1.  Manipulating Digital Assets

   A number of useful manipulations of digital assets "at rest" are
   defined by VWRAP.  Where appropriate, asset metadata may be altered
   by directly communicating with the network host with authority for
   that asset.  This host may be part of the user's agent domain, or in
   the case of region-specific assets, it could be associated with a
   region domain.  It is important to note, however, that not all
   metadata is modifiable by all users, even the asset's owner.
   Specifically, the semantics of the creator metadata do not allow the
   owner to change the creator's identity.  Group membership may carry
   some rights like the ability to manipulate the size, shape and

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   texture of an asset, but not an asset's owner.

   The ability to access or manipulate digital assets is based on the
   accessor's identity.  Accessing and manipulating digital assets is
   performed via capabilities which expose the state of the asset to an
   authorized client.  This requires positive identification of the
   accessor prior to access.  In the case where an asset service is
   owned by the same authority as the authentication service, this
   access may be as simple as providing the proper capability after user
   authentication.  In cases where the asset service is owned by a
   different authority, systems for deferred authentication may be
   necessary.  Work is currently underway to integrate OAuth and SAML
   into VWRAP for this purpose.

   At a gross level, the types of resources exposed by a digital asset
   server would include:

   o  a resource for searching an agent's inventory

   o  a resource for iterating across an agent's inventory

   o  a resource for accessing or manipulating a digital asset's

   o  a resource for uploading new digital assets, or changes to an
      existing asset.

   o  a resource for removing a digital asset from the authority of the
      asset service

   o  a resource for transferring the asset or a copy of the asset to a
      remote asset service

   o  a resource for instantiating (or "rezzing") an object "in world"

4.4.2.  Establishing Presence for Digital Assets

   Digital assets are intended to be used "in world," meaning there must
   be a way for a user to direct a simulation host to take an asset from
   an asset store and imbue it with presence in the virtual world.  The
   separation between agent based services and region based services is
   fundamental to VWRAP and implies the authority for the system
   maintaining the asset "at rest" may be distinct from that which
   simulates the asset "in world."  In practical terms, a region
   simulator may need to communicate with an asset server owned by a
   different person or company.  In situations like this, trust is
   paramount.  Because an asset's metadata may limit the owner's right
   to make copies of an asset, the agent domain MUST be able to trust

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   the region domain will honor that metadata.

   There are two levels of trust defined when working with digital
   assets: host-based trust and user-based trust.  The former represents
   one system's expectation that the other will honor the metadata
   regarding ownership, creatorship and rights and restrictions implied
   by these concepts.  Host based trust is carried by X.509 / PKIX
   certificates and implies a managed PKI.  User-based trust represents
   the expectation the asset server will expose sensitive resources only
   to users with the right to access such resources.

   Provided trust is established between the asset server and a
   simulation host, and the simulation host can demonstrate it is acting
   on behalf of a user with rights to access a particular resource,
   VWRAP defines a protocol for transferring a representation of the
   digital asset for simulation.  As part of this protocol, access to a
   digital asset may be restricted while the object exists "in world."
   This is the case for objects whose creators or owners specify that
   only one copy of the asset may exist at a time.

5.  Security Considerations

   As mentioned previously, the concept of a persistent, ubiquitous
   identity in the virtual world is core to the user experience.
   Keeping agent based services distinct from region or object based
   services has advantages for scalability and flexibility.  However, it
   does have ramifications for the security of the virtual world as a

   Most notably, this structure puts the authentication service in the
   role of a trust broker.  As the authentication service must collect
   capabilities for the benefit of the client, is trusted by both client
   applications and peer services.  A transitive trust relationship
   exists between the peer services and end users by way of the
   authentication service.  The administrators of peer services trust
   the authentication service to properly identify end users, and
   potentially to ensure they are members of a particular class.  The
   end users trust the authentication service to properly identify peer
   services and to limit the transfer of digital assets to only those
   entities that explicitly agree to honor asset permissions meta-data.

   VWRAP does not REQUIRE services to adhere to any preset policy,
   however.  It instead provides a mechanism for communicating identity
   information so that such a policy MAY be enforced.

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5.1.  Capabilities

   VWRAP makes extensive use of RESTful resources accessed via HTTP.
   Application state is communicated and changed by accessing web based
   resources.  One characteristic of such resources is they have a well
   defined URL, many of which are formatted as URL-based capabilities.
   [I-D.lentczner-vwrap-foundation] Capabilities have the characteristic
   that possession of the URL implies the right to access the resource
   it identifies.  It is important that capability URLs are shared only
   with trusted participants.  The VWRAP Base document defines the
   characteristics of URL-based capabilities, including the requirement
   that they include an unpredictable random component in the URL.
   Implementers need also ensure that these URLs are protected using
   suitable mechanisms (such as TLS, IPSec or link encryption.)

5.2.  User Authentication

   Prior to granting an end user access to sensitive resources, the
   client MUST be authenticated.  The VWRAP Authentication specification
   defines three techniques for using shared secrets to authenticate end
   users.  The agent_login resource used for end user authentication
   provides an extensible mechanism, allowing the development and use of
   additional authentication techniques (SRP, TLS Client Certificates,
   SASL, etc.)

   Again, it should be noted that VWRAP as currently defined does not
   REQUIRE an authentication service to support a particular
   authentication scheme (shared secret, public key, secure remote
   password, etc.)  But it does define the mechanism for three shared
   secret options.

   Once a user is successfully authenticated, their client application
   is passed a seed capability (as described in the VWRAP Base
   specification.)  This seed capability is used by the client
   application to request access to resources and services managed by
   the agent domain (including services like "place my avatar in the
   virtual world.")

5.3.  Service to Service Authentication

   Authenticating one service to another uses an X.509 PKI.  Prior to
   communicating, the originating service generates a key pair for each
   host under their control and requests a certificate from each the
   peer service with which they wish to interact.  The peer service
   returns a signed certificate the originating service uses in
   subsequent communication with the region.

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5.4.  Access Control for Digital Assets

   In addition to security characteristics addressing traditional
   network and user security issues, the raison d'etre of VWRAP is to
   communicate state concerning items inhabiting a virtual world.  Some
   of these items may have access control restrictions within the scope
   of the applications used to simulate and render the virtual world.
   VWRAP defines an extensible permissions model which allows
   permissions meta-data to be associated with virtual items.

6.  Accessibility Considerations

   This document makes extensive reference to the visual properties of
   objects.  It is important to note that semantic cues may be more
   important to persons with visual deficits.  The VWRAP suite includes
   the ability to annotate objects with situaltional or semantic meta-
   data to provide a meaningful experience to non-sighted users.
   Implementers are are encouraged to consider that client applications
   favored by non-blind users may query the state of the virtual world
   differently; the VWRAP suite SHOULD be sufficently expressive to
   support multiple modes of interaction with the virtual world.

   Implementers are also encouraged to consider the wide range of human
   capability and to design interaction experiences applicable to all.

7.  IANA Considerations

   This memo includes no request to IANA.

8.  References

8.1.  Normative References

              Chu, T., Hamrick, M., and M. Lentczner, "VWRAP Trust Model
              and User Authentication",
              draft-hamrick-vwrap-authentication-00 (work in progress),
              February 2010.

              Brashears, A., Hamrick, M., and M. Lentczner, "VWRAP :
              Abstract Type System for the Transmission of Dynamic
              Structured Data", draft-hamrick-vwrap-type-system-00 (work
              in progress), February 2010.

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              Lentczner, M., "Virtual World Region Agent Protocol:
              Foundation", draft-lentczner-vwrap-foundation-00 (work in
              progress), February 2010.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

8.2.  Informative References

   [RFC1822]  Lowe, J., "A Grant of Rights to Use a Specific IBM patent
              with Photuris", RFC 1822, August 1995.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2817]  Khare, R. and S. Lawrence, "Upgrading to TLS Within
              HTTP/1.1", RFC 2817, May 2000.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

Appendix A.  Definitions of Important Terms

       agent domain

       The agent domain is the administrative authority responsible for
       managing services related to avatars and users.  Identity
       management, group membership, avatar appearance, profile
       information, user authentication and group messaging are examples
       of services and information maintained by the agent domain.

       agent host

       A network host maintained by the agent domain is called an "agent


       The avatar is the representation of a user in the virtual world.
       The avatar's shape and appearance are used by other users to
       render a graphical representation of the inhabited virtual world.
       The user's view of the virtual world is rendered from the
       perspective of their avatar.

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       client application

       A client application is any application that is operated for the
       benefit of the user.  Common client applications might include a
       "viewer" that renders the virtual world on the user's workstation
       or a web application used to manipulate the user's digital
       assets.  VWRAP does not provide a canonical list of client
       application categories, but if an application is not a part of an
       agent domain or a region domain and it is manipulating user data
       or an avatar on behalf of a user, with the user's permission, it
       is a client application.

       region domain

       The region domain is the administrative authority responsible for
       managing services related to presence in the virtual world and
       it's simulation.  Typical services exposed by a region domain
       would include physics simulation, avatar presence and virtual
       object presence lifecycle management (i.e. - the creation,
       manipulation and destruction of objects in the virtual world.)

       region host

       A network host maintained by the region domain is called a
       "region host", though the historical term "simulator" is still
       very common.


       The entity controlling an avatar in world is the "user".

Appendix B.  Acknowledgements

   The author gratefully acknowledges the contributions of: Mark
   Lentczner, David Levine, David Crocker, Larry Mastiner, Joshua Bell,
   Barry Leiba, Kevin Flynn, Morgaine Dinova, Joe Hildebrand, Lora
   Baines, Alan Bradley, Chris Newman, Katherine Mancuso and Jon

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Internet-Draft        VWRAP: Introduction and Goals             May 2010

Authors' Addresses

   Meadhbh Siobhan Hamrick
   P.O. Box 783
   Boulder Creek, CA  95006

   Phone: +1 650 283 0344
   Email: OhMeadhbh@gmail.com

   David W. Levine
   IBM Thomas J. Watson Research Center
   19 Skyline Drive
   Hawthorn, NY  10532

   Phone: +1 914 784 7427
   Email: dwl@us.ibm.com

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