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Versions: 00 01

                                                            D. Petrie
   Internet Draft                                       Pingtel Corp.
   Document: draft-petrie-sip-config-framework-00.txt
   Expires: September 2001                                 March 2001


               A Framework for SIP User Agent Configuration


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
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other documents
   at any time.  It is inappropriate to use Internet-Drafts as
   reference material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
        http://www.ietf.org/ietf/1id-abstracts.txt
   The list of Internet-Draft Shadow Directories can be accessed at
        http://www.ietf.org/shadow.html.


Abstract

   This document defines the application of a set of protocols for
   configuring a SIP user agent.  The SIP user agent must discover how
   and from where to retrieve its initial configuration and be notified
   of changes and updates which impact its configuration.  The
   objective is to define a means for automatically configuring a user
   agent such that it can be functional without user or administrative
   intervention.  The framework for discovery, delivery, notification
   and updates of user agent configuration is defined here.  This
   framework is also intended to ease ongoing administration,
   configuration and upgrading of large scale deployments of SIP user
   agents.  The contents and format of the configuration data to be
   defined is outside the scope of this document.










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Table of Contents

   Status of this Memo................................................1
   Abstract...........................................................1
   1  Overview.......................................................3
   2  Conventions used in this document..............................4
   3  Discovery......................................................4
   3.1  DHCP Option..................................................5
   3.2  DNS SRV......................................................5
   3.3  DNS..........................................................5
   3.4  Multicast....................................................5
   3.5  Manually Provisioned.........................................5
   4  Enrollment and Change Notification.............................6
   4.1  Header Field Definitions.....................................7
   4.1.1 Config-Allow................................................7
   4.1.2 Config-Require..............................................7
   4.1.3 Config-Expires..............................................7
   4.2  SUBSCRIBE....................................................8
   4.2.1 Additional From Field Parameters............................9
   4.3  NOTIFY.......................................................9
   4.3.1 NOTIFY Body Content Format.................................10
   5  Configuration Retrieval.......................................11
   6  Configuration Upload..........................................11
   7  Examples......................................................12
   7.1  Example Message Flows.......................................12
   7.2  Example Messages............................................14
   8  Security Considerations.......................................17
   9  Open Issues...................................................18
   10 References....................................................19
   11 Author's Addresses............................................20























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1  Overview

   This document defines a framework which allows SIP user agents (UA)
   to automatically:
        - discover a configuration server (Discovery)
        - enroll with the configuration server (Enrollment)
        - retrieve configuration data (Configuration Retrieval)
        - receive notification of configuration changes (Change
          Notification)
        - upload configuration data changes back up to the server
          (Configuration Upload)

   The content and format of the data is not defined in this document.
   It is to be defined in configuration data profile(s) in other
   document(s). The goal of this framework is to satisfy the
   requirements defined in [10] and [11] excluding the requirements
   which pertain to configuration data profile content and format.

   Discovery is the process by which a UA SHOULD find the address and
   port at which it SHOULD enroll with the configuration server.  As
   there is no single discovery mechanism which will work in all
   network environments, a number of discovery mechanisms are defined
   with a prescribed order in which the UA SHOULD try them until one
   succeeds.

   Enrollment is the process by which a UA SHOULD make itself known to
   the configuration server. In enrolling the UA MUST provide identity
   information, a named list of requested configuration data profiles
   and supported protocols for configuration retrieval.  It SHOULD also
   SUBSCRIBE to a mechanism for notification of configuration changes.
   As a result of enrollment the UA receives a URL for each of the
   configuration data profiles that the configuration server is able to
   provide.

   Configuration Retrieval is the process of retrieving the content for
   each of the configuration data profiles the UA requested.

   Change Notification is the process by which the configuration server
   notifies the UA that the content of one or more of the configuration
   data profiles has changed. Subsequently the UA SHOULD retrieve the
   data profile from the specified URL upon receipt of the change
   notification.

   Configuration Upload is the process by which a UA or other entity
   pushes a change to a configuration data profile back up to the
   configuration server.

   Today all SIP UA vendors use proprietary means of delivering
   configuration to the UA.  This configuration framework is intended
   to enable a first phase migration to a standard means of configuring
   SIP user agents.  It is expected that UA vendors should be able to
   use this configuration framework as a means of delivering their
   existing proprietary configuration data profiles (i.e. using their

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   existing proprietary binary or text formats).  This in itself is a
   tremendous advantage in that a SIP environment can use a single
   configuration server to deliver configuration data to UAs from
   multiple vendors.  Follow-on standardization activities can: 1)
   define a standard format (e.g. XML or name-value pairs [8]) and 2)
   specify the content (i.e. name the configuration parameters) of the
   configuration data profiles.

2  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in
   this document are to be interpreted as described in RFC-2119 [1].

   The syntax and semantics used here extend those defined in SIP (RFC
   2543) [6]. SIP is described in an augmented Backus-Naur form (ABNF).
   See [6, section C] for an overview of ABNF.

3  Discovery

   The first time a UA is plugged in it does not know the address or
   port at which to enroll with the local configuration server.  It
   must discover this address and port.  A UA SHOULD support all of the
   listed discovery mechanisms.  It MUST support at least one of them.
   Once the UA has discovered the address and port and has successfully
   enrolled with the configuration server, the UA SHOULD cache the
   address and port to avoid the need to re-discover the configuration
   server.  However if enrollment, configuration retrieval or
   configuration upload fails at any time, the UA SHOULD apply the
   discovery and enrollment process again.  This provides a means for
   configuration server fail over and load balancing.
   The UA SHOULD use the following mechanisms to discover the host
   address and port at which it SHOULD enroll with the configuration
   server.  Each mechanism should be tried in the following order until
   an address and port is provided which results in successful
   enrollment (i.e. the server responds with a successful 2xx class
   response):
        - DHCP site-specific option [1]
        - DNS SRV
        - DNS A record
        - Multicast
        - Manual provisioning

   The rationale for this order follows.  Assuming that most UAs are
   going to use DHCP for IP configuration anyway, using a DHCP option
   is the least costly in terms of lookup time (i.e. no additional
   messages are required).  Hence DHCP is first.  DNS SRV allows the
   more flexibility than DNS A records.  Hence DNS SRV is tried before
   DNS A records.  Multicast is used last of the automated discovery
   mechanisms as it is the most restricted in terms of network
   environments that support it.  Multicast is included, even though
   the applicable environments are restricted, as it is the only
   mechanism that can be used without the support of the local network

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   administrator (The phone administrator and the network administrator
   are often different people and perhaps in different departments.)

   The UA implementer MAY provide the user or administrator with the
   means to change the order in which these mechanisms are tried.
   However by default without user interaction it SHOULD use the order
   listed above.

3.1 DHCP Option

   It is likely that most UAs in an environment of any significant
   number will use DHCP for IP configuration.  DHCP becomes a
   convenient means to discover the configuration server.  In the same
   DHCP request for basic IP configuration, the UA can add the site-
   specific option [TBD] [1] to the options field.  This indicates a
   request for the configuration server address and port.  If the
   configuration server address and port is not returned in the DHCP
   response or the server does not respond with a successful 2xx class
   response, the next discovery mechanism is attempted.

   [site-specific DHCP option (i.e. > 128)?]
   or
   [DHCP Option for SIP Servers?]

3.2 DNS SRV

   Using the service identifier “sipuaconfig” the DNS SRV records [5]
   are requested for the local domain for the protocols (i.e. UDP
   and/or TCP) that the UA supports.  The UA tries to enroll using the
   search order as prescribed in RFC 2782 [5].  If none of the servers
   respond with a successful 2xx class response (or none are returned
   in the SRV records) the next discovery mechanism is attempted.

3.3 DNS

   The UA SHALL try a DNS A record lookup on the host name
   “sipuaconfig”.  If the server does not respond with a successful 2xx
   class response, the next discovery mechanism is attempted.

3.4 Multicast

   The enrollment request is sent to the multicast address for SIP
   registration [6] "sip.mcast.net" (224.0.1.75).  If a server does not
   respond with a successful 2xx class response to the enrollment
   request, the next discovery mechanism is attempted.

3.5 Manually Provisioned

   The UA SHOULD let the user (or administrator) know if the automatic
   discovery has failed and allow the user or administrator to manually
   (or perhaps using some other out of band means e.g. beam, smart
   card, etc.) enter the configuration server address and port to be
   used for enrollment.

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4  Enrollment and Change Notification

   The enrollment and configuration change notification are paired
   together and provided via the SIP SUBSCRIBE/NOTIFY framework [7].
   This document defines the profile on top of the SUBSCRIBE/NOTIFY
   framework [7] for this purpose.

   UA enrollment with the configuration server is accomplished via the
   SUBSCRIBE request.  A UA MUST enroll with the configuration server
   prior to retrieving configuration data profiles.  As part of the
   enrollment the UA MUST identify itself, its configuration retrieval
   protocol capabilities and configuration data profile requirements.

   The configuration server may use this information to decide how to
   allocate resources (e.g. load balancing) to support the UA for its
   specific configuration retrieval needs.  The configuration server
   may also use the UA enrollment event as the trigger to generate a
   new set of configuration data for the specific UA (e.g. based upon
   provisioned defaults and configuration profile context knowledge for
   the environment).  This would allow the configuration server to
   provide configuration data for a new UA without previously
   provisioning the specific UA on the server.

   Configuration Change Notification is communicated to the UA via a
   NOTIFY request from the configuration server.  The NOTIFY request is
   used by the configuration server to convey the URLs that the UA MUST
   use to retrieve its requested configuration data profiles.  The
   NOTIFY is used immediately after enrollment.  It MAY be subsequently
   used by the configuration server to identify the list of
   configuration data profile URLs which have changed (i.e. change
   notification).

   The SUBSCRIBE request for enrollment is sent to the address(es)
   identified in the discovery process until the first successful 2xx
   class response is received.  As part of the binding of the
   SUBSCRIBE/NOTIFY framework this document defines a new Event token:
   “Config-Event”.  The Event header field is mandatory in SUBSCRIBE
   and NOTIFY requests and MUST contain this token value when used for
   the purpose of enrollment and configuration change notification.

   [Does Config-Event need to be registered with IANA?]

   If enrollment fails (i.e. no 2xx response to SUBSCRIBE), the UA
   SHOULD re-discover the configuration server address and port as
   described in section 3.

   The following new header fields are defined for use in SUBSCRIBE and
   NOTIFY requests for the purpose of enrollment and configuration
   change notification:

   The keys used the following table:
   R – request

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   r – response
   m – mandatory
   o – optional
   - - not applicable

   Header                    Where    SUBSCRIBE NOTIFY
   ------                    -----    --------- ------
   Config-Allow                 R         m        -
   Config-Require               R         m        -
   Config-Expires               R         -        o


4.1 Header Field Definitions

4.1.1   Config-Allow

   The Config-Allow header field is used by the UA in the enrollment
   request (SUBSCRIBE) to list the protocols that it is capable of
   using to retrieve configuration data.  The configuration server MUST
   adhere to the protocol capabilities of the UA when providing the
   list of URLs for the configuration profiles in the NOTIFY request.

   Syntax:
        Config-Allow  =  "Config-Allow" ":" 1#config-protocol
        config-protocol  = “tftp” | “http” | “https” | token

4.1.2   Config-Require

   The Config-Require header field contains the names of all of the
   configuration data profiles that the UA requires.  The name(s) of
   the configuration profiles are to be defined in a future document(s)
   specifying the content and format of the specific profile.

   Syntax:
        Config-Require  =  “Config-Require” “:” 1#config-profile-name
        config-profile-name  =  token

   [experimental: x-… ?]
   [IANA ?]

4.1.3   Config-Expires

   The optional Config-Expires header field defines the lease length of
   the configuration data.  If Config-Expires was present in the last
   NOTIFY received from the configuration server and the UA has not
   received a notification from the configuration server within this
   period of time, the UA SHOULD re-enroll by sending a new SUBSCRIBE
   message to the configuration server.  If the enrollment fails, the
   UA SHOULD re-discover the configuration server using the mechanisms
   described in section 3.  The configuration server SHOULD send a
   NOTIFY before the lease expires with the event Config-Event, a
   renewed lease length in the Config-Expires header field and the
   complete list of configuration data profile URLs in the  request

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   body for the UA’s configuration data.  The configuration data
   profile URLs SHOULD have the same sequence numbers if the content
   has not changed.  The sequence numbers MUST be different for
   profiles whose content has changed.  The absence of the Config-
   Expires header field in the lease renewal indicates an indefinite
   expiration.

   Note: the Config-Expires header field sets a lease that the UA
   observes to determine when its configuration is stale.  This lease
   is renewed with every NOTIFY message from the configuration server.
   The Expires header field in the SUBSCRIBE request describes the
   duration that the configuration server will continue to send change
   notifications to the UA.  This is renewed with every SUBSCRIBE
   request from the UA.

   Syntax:
        Config-Expires  =  “Config-Expires” “:” delta-seconds

4.2 SUBSCRIBE

   The SUBSCRIBE request is used by the UA to enroll in the
   configuration domain of the configuration server.  It uniquely
   identifies the UA with vendor, model and serial number information.
   The UA also MUST specify its capabilities for configuration
   retrieval as well as the configuration data profiles that it
   requires.  That is the UA MUST include the Config-Allow and Config-
   Require header fields and each MUST contain at least one token.  The
   configuration server MUST not send an error if it is not able to
   provide all of the configuration data profiles listed in the
   SUBSCRIBE request Config-Require header field.  The configuration
   server SHOULD provide the configuration data profile that it is able
   to or desires (see example at the end of section 4.3) to deliver to
   the UA.  If the configuration server sends a 301 Moved Permanently
   response to the enrollment SUBSCRIBE, the UA SHOULD cache the URL
   contained in the response Contact header field in place of the
   address and port found during discovery for future enrollment.

   The configuration server MAY use the enrollment (SUBSCRIBE request)
   as the stimulus to generate a new instance of a configuration data
   profile unique to the UA.  Alternately the configuration server MAY
   be provisioned ahead of time to know about new UAs and their
   specific configuration data content (for example based upon serial
   number, MAC address).

   [Request URI should not contain a user id?  The user may not be
   known yet.]
   [ What happens when the config server receives multiple SUBSCRIBE
   requests from the same UA but for different list of profiles.  Does
   the last request supercede all previous ones?]
   [ What happens when the config server receives multiple SUBSCRIBE
   requests from the same IP address but for different devices?  This
   might happen if some entity is acting as a proxy for a bunch of
   other devices.  It might also happen if the IP address for a UA gets

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   reused for some other UA (the DHCP lease timeout may be much shorter
   than the SUBSCRIBE/NOTIFY lease timeouts). The SUBSCRIBE lease
   SHOULD not exceed the DHCP lease?  The UA SHOULD reenroll if its IP
   address changes?]

4.2.1   Additional From Field Parameters

   In the enrollment and configuration change notification messages
   (i.e. SUBSCRIBE and NOTIFY requests and responses) the SIP-URL [6]
   MUST not contain userinfo if the default UA user is not known (e.g.
   first time startup of new UA out of the box).

   The following additional From field parameters are defined for the
   purpose of identifying the UA device:

   Vendor –a token used to identify the UA vendor name

   Model –a token used to identify the UA hardware/software model

   Version –a token used to identify the firmware/software version
   currently installed on the UA

   Serial –the token used to identify the serial number for the UA

   Mac –the token used to identify the MAC address in hex for the UA

   From RFC 2543 [6] the From header field syntax is extended to
   include:
   from-param  =  tag-param | generic-param | device-param
   device-param  =  vendor-parm | model-parm | version-parm |
                        serial-parm | mac-parm
   vendor-parm  =  “Vendor” “=” token
   model-parm  =  “Model” “=” token
   version-parm  =  “Version” “=” token
   serial-parm  =  “Serial” “=” token
   mac-parm  =  “Mac” “=” token

4.3 NOTIFY

   The NOTIFY message is sent by the configuration server to convey the
   URLs at which the UA can retrieve the requested configuration data
   profiles.  This occurs in two contexts:

     Immediately following the enrollment SUBSCRIBE the configuration
     server MUST send a NOTIFY providing URLs for the configuration
     data profiles requested by the UA in the Config-Require header
     field of the SUBSCRIBE request.  If the configuration server is
     not able to provide some specific configuration data profiles or
     it does not want the UA to retrieve some specific configuration
     profiles at that point in time, it MAY exclude those URL(s) from
     the NOTIFY.  At a later time when the configuration server is able
     to provide the data profile(s) or it wishes the UA to retrieve the
     data profiles at that point in time, the configuration server MAY

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     send a NOTIFY request containing the URL(s) for the configuration
     data profile(s) which the UA SHOULD retrieve immediately.

     If the configuration server becomes aware of a configuration
     change that it wishes to be effective immediately on the UA, the
     configuration server SHOULD send a NOTIFY message containing the
     complete list of URLs for the configuration data profiles that the
     UA requested when it enrolled.  The configuration data profiles
     with changed content SHOULD have sequence number larger than that
     of the last NOTIFY request.  The UA SHOULD retrieve and make
     effective the changed configuration URLs immediately upon receipt
     of the NOTIFY request.  The UA MAY choose to wait to make the
     changes effective (e.g. to prevent the change from disrupting
     active calls on the UA).

     [Do we need an option for the configuration server to tell the UA
     that it MUST make the change immediately regardless of state?
     Should this be the default?]

   The UA SHOULD send a 200 response to the NOTIFY immediately upon
   receipt and validation of the solicited request.  The configuration
   server SHOULD include, in the change notification NOTIFY request,
   the complete list of the configuration data profile URLs.  The
   sequence numbers associated with the configuration data profiles
   with changed content should be larger than those in the previous
   NOTIFY. These configuration data profile URLs MUST be among those
   the UA named in the Config-Requires header field in the most recent
   enrollment (SUBSCRIBE request). The URLs listed in the NOTIFY
   request MUST use one of the protocols the UA listed in the Config-
   Allow header field provided during enrollment in the most recent
   SUBSCRIBE request.  The sequence numbers for the configuration data
   profile URLs are positive integers chosen by the configuration
   server.  The sequence number value MUST increase monotonically as
   modifications are made to a data profile.
   This mechanism may be used by the configuration server to provide
   firmware updates.  For example on a UA that caches or has a
   persistent firmware image: if the server realizes (e.g. from the
   enrollment information) the UA is running the most currently
   available firmware version, it would not provide the URL for the
   firmware.  However at a later point in time when a new firmware
   version was available the configuration server could send a NOTIFY
   with the URL for the new firmware version, indicating the UA SHOULD
   upgrade now.
4.3.1   NOTIFY Body Content Format

   The NOTIFY request contains a body of Content-Type: text/plain.  The
   content is formatted according to RFC 822 [8].  For each of the
   named configuration data profiles which the configuration server is
   able to provide, the body contains a header field with the same name
   as the configuration data profile.  The value of the header field
   MUST contain a URL and a sequence number as described in the syntax
   below.  The protocol of the URL MUST be one of those listed in the
   Config-Allow header field provided by the UA in the enrollment

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   SUBSCRIBE request.  The sequence number associated with the URL is
   intended to allow the UA to decide if it has the latest content of
   the configuration data profile without having to download and
   compare the contents.

   Syntax:
   config-profile  =  token “:”  Seq-Param “;” Url-Param
   Seq-Param  =  “Sequence” “=” 1*digit
   Url-Param =  “Url” “=” tftp-url | Http-url | Https-url
   Tftp-url [need reference]
   Http-Url as defined in [12, section 3.3]
   Httpsw-Url [need reference]


   Example:

   X-Acme-Special: Sequence=1234567;Url=http://www.acme.com/config.txt

5  Configuration Retrieval

   The UA MUST retrieve its configuration data profiles using the URLs
   specified by the configuration server in the NOTIFY request.  If any
   of the retrievals fail, the UA SHOULD re-enroll as described in
   section 4.  Should the enrollment fail, the UA SHOULD re-discover
   the configuration server as described in section 3.

   [Is this a good idea?  It might cause a nasty cascade effect if the
   server for a bunch of URLs goes down.  In all likelihood, the
   configuration server won’t check whether the server is available for
   each of the URLs it hands out – that would probably be too
   expensive.  The effect will be to have a bunch of UA spinning back
   and forth between hitting the configuration server and hitting the
   failed server for the URL.  What are the alternatives?  Leave the
   precise procedure up to the UA since some may need more
   sophisticated cutover mechanisms than others.  Retry fetching the
   URL using an exponential backoff timer between attempts up to some
   maximum interval.  When that limit is reached, the UA can try to re-
   enroll.  However, if the configuration server gives it the same
   failing URL, it should continue to retry after waiting the maximum
   interval timeout.]


6  Configuration Upload

   If the UA or another entity wishes to modify a configuration data
   profile it MAY make the change persistent on the configuration
   server if it is authorized to do so.  The configuration server
   SHOULD support the ability to upload via the same URL the UA used to
   retrieve the configuration data profile.  For TFTP the UA does a put
   [9].  For HTTP and HTTPS the UA does a POST with a multipart MIME
   attachment containing any URL parameters in one part and the changed
   configuration data profile [whole or changes only ?? define in
   profiles ??] in another part as defined in [?].  If the UA or user

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   is not permitted to make the changes on the configuration server the
   configuration server returns an HTTP error response code of 403
   Forbidden.  If the configuration server returns a 403 the UA SHOULD
   disallow the changes from being effective on the UA.   The UA SHOULD
   not make the changes effective until it receives a successful
   response (e.g. for HTTP 2xx).

   If the URL is for HTTP/HTTPS the server MUST return the changed
   configuration data profile in the response (assuming it was
   allowed). The configuration server SHOULD include an incremented
   sequence number in the HTTP/HTTPS response if the configuration data
   profile contents changed [Sip-Ua-Config-Seq header field?].  The UA
   SHOULD use the configuration data profile contents from the HTTP
   response as opposed to the data that was pushed in the request as
   changes may occur from other sources.  The configuration server
   SHOULD send out a NOTIFY for this change, using the same sequence
   number in the configuration data profile URL parameter.  This allows
   the UA to know that it already has the current contents of the
   configuration data profile and SHOULD not download that
   configuration data profile.
   [TBD – in 403 case restrict and provide feedback as to what
   specifically is not allowed to be modified by the UA or user]

7  Examples

   Below is an example high level message flow for a new UA discovering
   and using configuration data from a configuration server.  Following
   the high level message flows are some specific SIP messages
   illustrating SUBSCRIBE and NOTIFY messages from enrollment and
   configuration change notification.

7.1 Example Message Flows

   The following high level message flows illustrate the configuration
   process of discovery, enrollment, configuration retrieval and change
   notification with associated configuration retrieval.  The UA uses
   DHCP with the local option requesting the configuration server
   address and port.  The DHCP server does not provide the
   configuration server address or port.  The UA then does a DNS SRV
   lookup for the configuration service within the local domain.  It
   gets a response with one configuration server address and port.  The
   UA then enrolls with the configuration by sending a SUBSCRIBE
   request for the Config-Event.  The configuration server sends back a
   successful response.  The configuration server then sends a NOTIFY
   request with the list of URLs for all the configuration data
   profiles that the UA named in the enrollment SUBSCRIBE request.  The
   UA sends a 200 response to the NOTIFY.  The UA then downloads all of
   the configuration data profiles via the URLs from the NOTIFY
   request.  The UA is now configured as prescribed.

   Later ... an administrator makes a change to the configuration for
   the UA on the configuration server.  The configuration server on
   behalf of the administrator, sends a NOTIFY (change notification)

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   request to the UA listing the configuration data profiles that
   changed (the minimum subset of the list of configuration data
   profiles the UA requested during enrollment).  The UA downloads the
   configuration data profiles that changed.

   UA           DHCP Server     DNS Server      Config. Server

   Discovery

   IP config. req.
   ==============>
   IP config. wo/ local option
   <==============
   DNS SRV req. for sipuaconfig service in local domain
   =============================>
   Host and port for config. server returned
   <=============================

   Enrollment

   SIP SUBSCRIBE Config-Event w/ requested profile names
   ==================================================>
   200 OK
   <==================================================
   SIP NOTIFY Config-Event w/ requested profile URLs
   <==================================================
   200 OK
   ==================================================>

   Configuration retrieval

   HTTP GET (For each profile URL)
   ==================================================>
   200 OK (specific profile data in body)
   <==================================================
   .
   .
   .

   Administrative change on configuration server via user interface
   .
   .
   .

   Change Notification

   SIP NOTIFY Config-Event w/ changed profile URLs
   <==================================================
   200 OK
   ==================================================>
   HTTP GET (for each changed profile)
   ==================================================>
   200 OK (profile data in body)

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   <==================================================
   .
   .
   .

   User changes data in a profile on the user agent
   .
   .
   .

   Configuration Upload

   HTTP POST (changed profile attached as multipart MIME)
   ==================================================>
   200 OK (profile data in body, as change confirmation)
   <==================================================
   .
   .
   .

7.2 Example Messages

   The following SUBSCRIBE request example is from a UA enrolling with
   a configuration server.  As this SUBSCRIBE request is for
   configuration enrollment the Event header field contains the token
   Config-Event.  The UA tells the configuration server that it
   supports the TFTP, HTTP, HTTPS protocols for retrieving
   configuration data profiles in the Config-Allow header field.  The
   UA tells the configuration server that it would like the
   configuration data profiles named: sip-device, sip-user, x-acme-
   special in the Config-Require header field.  The UA tells the
   configuration server that it is enrolling for 86400 seconds via the
   Expires header field.  During this period of time the configuration
   server MUST send a change notification listing the configuration
   data profiles which have changed.  The UA has identified the
   specifics about itself in the From field parameters: Vendor, Model,
   Version, Serial, Mac.


   UA => Config. Server

   SUBSCRIBE sip:config.localdomain.com SIP/2.0
   To: sip:config.localdomain.com
   From: sip:10.1.1.123;Vendor=acme;Model=model-a
     ;Version=1.5.0.1;Serial=1234567890;Mac=000aaa1234cd
   Call-Id: 987654321@10.1.1.123
   Cseq: 1 SUBSCRIBE
   Event: Config-Event
   Config-Allow: tftp, http, https
   Config-Require: Sip-Device, Sip-User, X-Acme-Special, X-Acme-Kernel
   Expires: 86400
   Content-Length: 0


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   The following is an example response to the above enrollment
   request.

   Config. Server => UA

   SIP/2.0 202 Accepted
   To: sip:config.localdomain.com
   From: sip:10.1.1.123;Vendor=acme;Model=model-a
     ;Version=1.5.0.1;Serial=1234567890;Mac=000aaa1234cd
   Call-Id: 987654321@10.1.1.123
   Cseq: 1 SUBSCRIBE
   Content-Length: 0

   The following example is the immediate NOTITY request the
   configuration server sent to the UA following enrollment.  The
   Config-Expires header field indicates the lease length of the
   configuration data profiles.  After that period of time if the UA
   had not received an additional NOTIFY request from the configuration
   server it should re-retrieve the configuration data profiles from
   the provided URLs.  The URLs are listed in the request body for each
   of the named configuration data profiles the UA listed in the
   Config-Require header field in the above SUBSCRIBE request from the
   UA, that the configuration server is able or wishes to provide.
   Note that the configuration server did not provide a URL for X-Acme-
   Kernel (perhaps it decided that the kernel image on the UA was
   already current).

   Config. Server => UA

   NOTIFY sip:10.1.1.123 SIP/2.0
   To: sip:10.1.1.123;Vendor=acme;Model=model-a
     ;Version=1.5.0.1;Serial=1234567890;Mac=000aaa1234cd
   From: sip:config.localdomain.com
   Call-Id: 987654321@10.1.1.123
   Cseq: 22 NOTIFY
   Event: Config-Event
   Config-Expires: 43200
   Content-Type: text/plain
   Content-Length: 175

   Sip-Device: Sequence=1
     ;Url=http://config.localdomain.com/device/1234567890
   Sip-User: Sequence=1;Url=http://config.localdomain.com/user/fred
   X-Acme-Special: Sequence=1
    ;Url=http://www.acme.com/special/config/1234567890









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   The following is an example response from the UA for the above
   request.

   UA => Config. Server

   SIP/2.0 200 Ok
   To: sip:10.1.1.123;Vendor=acme;Model=model-a
     ;Version=1.5.0.1;Serial=1234567890;Mac=000aaa1234cd
   From: sip:config.localdomain.com
   Call-Id: 987654321@10.1.1.123
   Cseq: 22 NOTIFY
   Content-Length: 0


   Assuming at some later point in time, an administrator makes a
   change to the content of the Sip-Device configuration data profile
   for the UA.  The configuration server sends a NOTIFY request to the
   UA for the configuration change notification.  This example request
   below indicates the changed URL(s) in the request body with a higer
   sequence number.  In this case only one URL has changed, that for
   the configuration data profile named: Sip-Device.  The configuration
   server extends the configuration lease to 43200 seconds from when
   this request is received.  This lease applies to all of the
   configuration data profiles that the UA requested when it last
   enrolled.  If the UA does not receive another NOTIFY request from
   the configuration server before the lease expires, the UA SHOULD
   download all of the configuration data profiles from the most recent
   URLs provided for each of the configuration data profiles listed in
   the enrollment SUBSCRIBE Config-Require header field.

   Config. Server => UA

   NOTIFY sip:10.1.1.123 SIP/2.0
   To: sip:10.1.1.123;Vendor=acme;Model=model-a
     ;Version=1.5.0.1;Serial=1234567890;Mac=000aaa1234cd
   From: sip:config.localdomain.com
   Call-Id: 987654321@10.1.1.123
   Event: Config-Event
   Cseq: 23 NOTIFY
   Config-Expires: 43200
   Content-Type: text/plain
   Content-Length: 64

   Sip-Device: Sequence=2
     ;Url=http://config.localdomain.com/device/1234567890
   Sip-User: Sequence=1;Url=http://config.localdomain.com/user/fred
   X-Acme-Special: Sequence=1
    ;Url=http://www.acme.com/special/config/1234567890






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   The following is an example response to the above request.

   UA => Config. Server

   SIP/2.0 200 Ok
   To: sip:10.1.1.123;Vendor=acme;Model=model-a
     ;Version=1.5.0.1;Serial=1234567890;Mac=000aaa1234cd
   From: sip:config.localdomain.com
   Call-Id: 987654321@10.1.1.123
   Cseq: 23 NOTIFY
   Content-Length: 0

8  Security Considerations

   [This section needs to be greatly expanded and elaborated]

   SIP basic and digest authentication [6] MAY be used for
   SUBSCRIBE/NOTIFY messages used for enrollment and configuration
   change notification.  As there is a chicken and egg problem as well
   and the content of SUBSCRIBE/NOTIFY messages are transported in the
   clear, the credentials that the UA uses in the SUBSCRIBE 401
   challenge, or that the configuration server uses in the NOTIFY 401
   challenge must be provisioned out of band (i.e. user or
   administrator manual input, beamed via PDA, smart card, etc.) via a
   secure means.

   Configuration data profile URLs are communicated in the clear in the
   NOTIFY requests from the configuration server.  The security risk of
   unauthorized access of the URL content can be mitigated if the
   configuration server and UA both support basic authentication and
   HTTP or HTTPS.  There is a chicken and egg problem here as well
   since the content of SUBSCRIBE/NOTIFY messages are transported in
   the clear.  Accordingly,the credentials that the UA uses for the
   HTTP/HTTPS GET/POST 401 challenge must be provisioned out of band
   (i.e. user or administrator manual input, beamed via PDA, smart
   card, etc.) via a secure means.

   Using HTTPS over TLS[13] the configuration server MAY request the
   certificate of the UA [14].  If this level of authentication is
   desired, the UA vendor SHOULD ship the UA with a digital certificate
   or provide a means by which this can be installed out of band.  The
   configuration server MUST be provisioned with the certificates of
   authority allowed for each model of UA to be supported.

   Using HTTPS the UA MAY request the certificate of the configuration
   server.  If this level of authentication is desired the UA must be
   provisioned with the allowed certificate(s) of authority and
   identities for the configuration server out of band (i.e. user or
   administrator manual input, beamed via PDA, smart card, etc.) via a
   secure means.




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9  Open Issues

   Local DHCP option (i.e. > 128)?
   or
   DHCP Option for SIP Servers?

   How does the configuration server give feedback to a new UA that it
   SHOULD/MAY prompt the user for or provide configuration data
   specifics?

   [Request URI should not contain a user id?  The user may not be
   known yet.]

   [ What happens when the config server receives multiple SUBSCRIBE
   requests from the same UA but for different list of profiles.  Does
   the last request supercede all previous ones?]

   [ What happens when the config server receives multiple SUBSCRIBE
   requests from the same IP address but for different devices?  This
   might happen if some entity is acting as a proxy for a bunch of
   other devices.  It might also happen if the IP address for a UA gets
   reused for some other UA (the DHCP lease timeout may be much shorter
   than the SUBSCRIBE/NOTIFY lease timeouts).  The SUBSCRIBE lease
   SHOULD not exceed the DHCP lease?  The UA SHOULD re-enroll if its IP
   address changes?]

   [Do we need an option for the configuration server to tell the UA
   that it MUST make the change immediately regardless of state?
   Should this be the default?]

   [Upload to configuration server configuration data profiles whole or
   changes only ?? define in profiles ??]

   [Security considerations section needs much elaboration]




















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10 References

      [1] R. Droms, "Dynamic host configuration protocol," Request for
      Comments (Draft Standard) 2131, Internet Engineering Task Force,
      Mar. 1997.

      [2] S. Alexander and R. Droms, "DHCP options and BOOTP vendor
      extensions," Request for Comments (Draft Standard) 2132, Internet
      Engineering Task Force, Mar. 1997.

      [3] G.Nair, H.Schulzrinne , “DHCP Option for SIP Servers”,
      <draft-ietf-sip-dhcp-01.txt>, IETF; Apr. 2000, Work in progress.

      [4] S. Bradner, "Key words for use in RFCs to indicate
      requirement levels," Request for Comments (Best Current Practice)
      2119, Internet Engineering Task Force, Mar. 1997.

      [5] A. Gulbrandsen, P. Vixie, and L. Esibov, “A DNS RR for
      specifying the location of services (DNS SRV),” Request for
      Comments 2782, Internet Engineering Task Force, Feb. 2000.

      [6] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg,
      “SIP: session initiation protocol,” Request for Comments 2543,
      Internet Engineering Task Force, Mar. 1999.

      [7] A. Roach, “Event Notification in SIP”, <draft-roach-sip-
      subscribe-notify-03.txt>, IETF; Feb. 2001, Work in progress.

      [8] D. Crocker, “STANDARD FOR THE FORMAT OF ARPA INTERNET TEXT
      MESSAGES”, Request for Comments 822, Internet Engineering Task
      Force, Aug. 1982

      [9] K. Sollins, “THE TFTP PROTOCOL (REVISION 2)”, Request for
      Comments 1350, Internet Engineering Task Force, Jul. 1992


      [10] H Schulzrinne, “Configuring IP Telephony End Systems”,
      <schulzrinne-sip-config-00.txt>, IETF; Dec. 2000,  Work in
      progress

      [11] D. Petrie, “Requirements for a SIP User Agent Configuration
      Framework”, <draft-petrie-sip-config-framewk-reqs-00.txt>, IETF;
      Feb. 2001, Work in progress

      [12] T. Berners-Lee et al, “Uniform Resource Locators (URL)”,
      Request for Comments 1738, Internet Engineering Task Force, Dec.
      1994

      [13] E. Rescorla, “HTTP Over TLS”, Request for Comments 2818,
      Internet Engineering Task Force, May 2000



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      [14] T. Dierks, C. Allen, “The TLS Protocol Version 1.0”, Request
      for Comments 2246, Internet Engineering Task Force, Jan. 1999



11 Author's Addresses

   Dan Petrie
   Pingtel Corp.
   400 W. Cummings Park         Phone:  +1 781 938 5306
   Woburn, MA USA               Email:  dpetrie@pingtel.com










































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