One document matched: draft-petrie-sipping-config-framework-00.txt
D. Petrie
Internet Draft Pingtel Corp.
draft-petrie-sipping-config-framework-00.txt
Expires: Dec 2002 June 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
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http://www.ietf.org/ietf/1id-abstracts.txt
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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 Changes from Previous Draft....................................4
3.1 Changes from draft-petrie-sip-config-framework-01.txt........4
3.2 Changes from draft-petrie-sip-config-framework-00.txt........4
4 Discovery......................................................5
4.1 DHCP Option..................................................6
4.2 DNS..........................................................6
4.3 Multicast....................................................6
4.4 Manually Provisioned.........................................6
5 Enrollment and Change Notification.............................7
5.1 Header Field Definitions.....................................8
5.1.1 Config-Allow................................................8
5.2 SUBSCRIBE....................................................8
5.2.1 Additional From Field Parameters............................9
5.3 NOTIFY......................................................10
5.3.1 NOTIFY Body Content Format.................................11
6 Configuration Retrieval.......................................11
7 Configuration Upload..........................................11
8 Examples......................................................12
8.1 Example Message Flows.......................................12
8.2 Example Messages............................................14
9 Security Considerations.......................................17
10 Open Issues...................................................17
11 References....................................................19
12 Author's Addresses............................................20
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1 Overview
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
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.
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 to the server
(Configuration Upload)
The content and format of the data is not defined in this document.
It will 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, name requested configuration data profile 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.
Each profile requires a separate enrollment or SUBSCRIBE session.
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
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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.
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 Changes from Previous Draft
3.1 Changes from draft-petrie-sip-config-framework-01.txt
Changed the name as this belongs in the SIPPING work group.
Minor edits
3.2 Changes from draft-petrie-sip-config-framework-00.txt
Many thanks to those who contributed and commented on the previous
draft. Detailed comments were provided by Henning Schulzrinne from
Columbia U., Cullen Jennings from Cisco, Rohan Mahy from Cisco, Rich
Schaaf from Pingtel.
Split the enrollment into a single SUBSCRIBE dialog for each
profile. The 00 draft sent a single SUBSCRIBE listing all of the
desired. These have been split so that each enrollment can be
routed differently. As there is a concept of device specific and
user specific profiles, these may also be managed on separate
servers. For instance in a roaming situation the device might get
itÆs configuration from a local server which knows the LAN specific
configuration. At the same time the user specific profiles might
come from the userÆs home environment configuration server.'
Removed the Config-Expires header as it is largely superfluous with
the SUBSCRIBE Expires header.
Eliminated some of the complexity in the discovery mechanism.
Suggest caching information discovered about a configuration server
to avoid an avalanche problem when a whole building full of devices
powers up.
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Added the User-Profile From header field parameter so that the
device can a request a user specific profile for a user that is
different from the deviceÆs default user.
4 Discovery
The purpose of discovery is to figure out how to address the
configuration server so that the device can enroll. The enrollment
process involves sending a SIP SUBSCRIBE. Prior to this the
discovery process must find the address to use in the URL for the
URI and To header field. The URL SHOULD use the user id:
sipuaconfig. From a SIP perspective the configuration server is
simply a user agent. By using the well known user id, this makes it
easy for proxy servers to be provisioned to route the enrollment
requests from devices to the appropriate configuration server for
the domain.
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 option for SIP [1]
- 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. 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 administrator.
The phone administrator and the network administrator are often
different people and perhaps in different departments.
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The UA implementer MAY provide the user or administrator with the
means to change the order in which these mechanisms are tried. This
includes the ability to manually override the discovery process.
However by default without user interaction the UA SHOULD use the
order listed above.
Once discovery is successful the device SHOULD persistently cache
the address to avoid avalanche problems when a whole building full
of devices powers up at once. The characteristic of the profile may
dictate this behavior. For example device specific profiles may
need to change when the device is moved to a different location.
User specific profiles may be independent of the LAN, network or
device location.
4.1 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 address. In
the same DHCP request for basic IP configuration, the UA can add the
option for SIP[3] [1] to the options field. This indicates a
request for the default SIP proxy server address and port. For
example if the DHCP option for SIP returns an address of
sip.acme.com and a port of 5080, the following URL is constructed:
sip:sipuaconfig@sip.acme.com:5080. If the proxy server address and
port is not returned in the DHCP response or the server does not
respond to the enrollment request with a successful 2xx class
response, the next discovery mechanism is attempted.
4.2 DNS
The UA SHOULD construct a fully qualified host name using
ôsipuaconfigö as the host and the local domain if defined. It
SHOULD try a DNS A record lookup on the fully qualified host name.
If the name resolves in DNS it should then attempt enrollment. For
example the URL constructed in the local domain of acme.com would
look like: sip:sipuaconfig@sipuaconfig.acme.com. If the server does
not respond to enrollment with a successful 2xx class response, the
next discovery mechanism is attempted.
4.3 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.
4.4 Manually Provisioned
The UA MAY indicate to the user (or administrator) that automatic
discovery has failed. The UA SHOULD allow the user or administrator
to manually (perhaps using some out of band method e.g. beam, smart
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card, etc.) enter the configuration server address and port to be
used for enrollment.
5 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 allows the configuration server to provide
configuration data for a new UA without previously provisioning the
specific UA on the server.
Each profile that the device requires is obtained via a separate
enrollment or SUBSCRIBE request and SIP dialog. That is for each
different profile a device enrolls for, a different Call-Id is used.
The device names the profile in the SUBSCRIBE Event header field.
The configuration server then delivers a URL at which the device can
retrieve the profile in a subsequent NOTIFY request. Changes to the
profile are indicated in additional NOTIFY requests sent from the
configuration server.
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 a new Event token must be named for each
type of profile.
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 field is defined for use in SUBSCRIBE and
NOTIFY requests for the purpose of enrollment and configuration
change notification:
The keys used in the following table are:
R û request
r û response
m û mandatory
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o û optional
- - not applicable
Header Where SUBSCRIBE NOTIFY
------ ----- --------- ------
Config-Allow R m -
5.1 Header Field Definitions
5.1.1 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 URL
for the configuration profile in the NOTIFY request.
Syntax:
Config-Allow = "Config-Allow" ":" config-protocol
*(ô,ö config-protocol)
config-protocol = ôtftpö | ôhttpö | ôhttpsö | token
5.2 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. The UA MUST include the Config-Allow header field which
MUST contain at least one token. The configuration server SHOULD
not send an error if it is temporarily not able to provide the
configuration data profile listed in the SUBSCRIBE request Event
header field. In the first time out of the box case, the SUBSCIRBE
dialog may be the only means of communicating with the device as it
does not yet have configuration. The configuration server SHOULD
send a 403 response to the SUBSCRIBE if is not willing to provide
the requested configuration profile to the device. 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 device may request many configuration data profiles by
sending multiple SUBSCRIBE requests each in a different SIP
dialog. This may be useful if the device requires user
specific profiles for multiple users. In this case the
UserProfile parameter would vary for each SUBSCRIBE.
Alternately the device may require multiple types of profiles
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where each SUBSCRIBE would have a different Event header field
token.
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).
5.2.1 Additional From Field Parameters
When the device first starts up out of the box, it has no user or
local configuration. The device MUST provide a unique identity such
that it is possible for the configuration server to generate
configuration profile for the device. The following additional From
field parameters are defined for the purpose of identifying the UA
device:
Vendor û a token used to identify the UA vendor name
Model û a token used to identify the UA hardware/software model
Version û a token used to identify the firmware/software version
currently installed on the UA
Serial û the token used to identify the serial number for the UA
Mac û the token used to identify the MAC address in hex for the UA
From RFC 2543 bis [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 | user-profile-param
vendor-parm = ôVendorö ô=ö token
model-parm = ôModelö ô=ö token
version-parm = ôVersionö ô=ö token
serial-parm = ôSerialö ô=ö token
mac-parm = ôMacö ô=ö token
user-profile-param = ôUserProfileö ô=ö SIP-URL
The Vendor, Model, Version, Serial and Mac parameters MUST be
provided in the From URL for the enrollment SUBSCRIBE request. Most
profiles will either be device or user specific. If the profile is
user specific and the device knows the user for which it is to
retrieve, the profile UserProfile MUST be provided. If the profile
is device specific or the device does not know whose user profile it
should retrieve, the device SHOULD not provide the UserProfile
parameter. The profile is user specific and UserProfile is not
present the configuration server assumes the default user for the
device.
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5.3 NOTIFY
The NOTIFY message is sent by the configuration server to convey the
URL at which the UA can retrieve the requested configuration data
profile. This occurs in two contexts:
Immediately following the enrollment SUBSCRIBE the configuration
server MUST send a NOTIFY providing the URL for the configuration
data profile requested by the UA in the Event header field of the
SUBSCRIBE request. If the configuration server is not able to
provide the specific configuration data profile or it does not
want the UA to retrieve the specific configuration profile at that
time, it MAY defer sending NOTIFY. Later when the configuration
server is able to provide the data profile or it wishes the UA to
retrieve the data profile, the configuration server MAY send a
NOTIFY request containing the URL for the configuration data
profile which the UA SHOULD retrieve as soon as it is safe to do
so.
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
URL for the configuration data profile that the UA requested when
it enrolled. The configuration data profile with changed content
SHOULD have a sequence number larger than that of the last NOTIFY
request. The UA SHOULD retrieve and make effective the changed
configuration URL 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 MUST include, in the change notification NOTIFY request, the
configuration data profile URL. The sequence numbers associated
with the configuration data profile with changed content should be
larger than those in the previous NOTIFY. The URL 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 number for the configuration
data profile URL MUST be a positive integer 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 could defer sending the NOTIFY with
the URL for the firmware. However at a later time when a new
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firmware version is available the configuration server could send
a NOTIFY with the URL for the new firmware version, indicating the
UA SHOULD upgrade as soon as it is safe to do so.
5.3.1 NOTIFY Body Content Format
The NOTIFY request contains a body of Content-Type: text/plain. The
content is formatted according to RFC 822 [8]. It contains a header
field with the same name as the configuration data profile indicated
in the Event header. 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 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 ô:ö Seq-Param ô;ö Url-Param
Seq-Param = ôSequenceö ô=ö 1*digit
Url-Param = ôUrlö ô=ö tftp-url | Http-url | Https-url
Tftp-url [need reference]
Http-Url as defined in [12, section 3.3]
Https-Url [need reference]
Example:
X-Acme-Special: Sequence=1234567;Url=http://www.acme.com/config.txt
6 Configuration Retrieval
The UA MUST retrieve its configuration data profile using the URL
specified by the configuration server in the NOTIFY request. If the
retrieval fails, the UA SHOULD not re-enroll until the SUBSCRIBE
session expires to avoid a cascade effect if the server goes down
temporarily. The device MAY re-try the profile retrieve of the
profile from the URL before the SUBSCRIBE expires. Should the re-
enrollment fail, the UA SHOULD re-discover the configuration server
as described in section 4.
7 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
is not permitted to make the changes on the configuration server the
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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 û in 403 case restrict and provide feedback as to what
specifically is not allowed to be modified by the UA or user]
8 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.
8.1 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 lookup
for the configuration service within the local domain. It gets a
response from the DNS server for the configuration server fully
qualified host name. The UA then enrolls with the configuration
server by sending a SUBSCRIBE request for the profile type indicated
in the Event header. The configuration server sends back a
successful response. The configuration server then sends a NOTIFY
request with the URL for the configuration data profile that the UA
named in the enrollment SUBSCRIBE request. The UA sends a 200
response to the NOTIFY. The UA then downloads the configuration
data profile via the URL from the NOTIFY request. This process may
be repeated in parallel for each of the required profiles. 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
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behalf of the administrator, sends a NOTIFY (change notification)
request to the UA with an incremented sequence number for the
profile. As the sequence number has changed, the UA downloads the
configuration data profile from the given URL.
UA DHCP Server DNS Server Config. Server
Discovery
IP config. req.
==============>
IP config. wo/ local option
<==============
DNS A record req. for sipuaconfig host in local domain
=============================>
A record IP address returned for Host
<=============================
Enrollment
SIP SUBSCRIBE Event: Sip-Device
==================================================>
200 OK
<==================================================
SIP NOTIFY Event: Sip-Device w/ requested profile URL
<==================================================
200 OK
==================================================>
Configuration retrieval
HTTP GET
==================================================>
200 OK (specific profile data in body)
<==================================================
.
.
.
Administrative change on configuration server via user interface
.
.
.
Change Notification
SIP NOTIFY Event: Sip-Device w/ changed profile URL
<==================================================
200 OK
==================================================>
HTTP GET
==================================================>
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)
<==================================================
.
.
.
8.2 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 profile named: sip-device in the Event 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
with the URL for the configuration data profile which changed. The
UA has identified the specifics about itself in the From field
parameters: Vendor, Model, Version, Serial, Mac. In this example
the UserProfile parameter is not included in the From field as the
Sip-Device profile is device specific not user specific.
UA => Config. Server
SUBSCRIBE sip: sipuaconfig@config.localdomain.com SIP/2.0
To: sip:sipuaconfig@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: Sip-Device
Config-Allow: tftp, http, https
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
In the following example the device is requesting a user specific
profile Sip-User. The device specifies that it want the profile for
the user: sip:fredsmith@localdomain.com.
UA => Config. Server
SUBSCRIBE sip: sipuaconfig@config.localdomain.com SIP/2.0
To: sip:sipuaconfig@config.localdomain.com
From: sip:10.1.1.123;Vendor=acme;Model=model-a
;Version=1.5.0.1;Serial=1234567890;Mac=000aaa1234cd
;UserProfile=sip%3Afredsmith%40localdomain.com
Call-Id: 11111111@10.1.1.123
Cseq: 1 SUBSCRIBE
Event: Sip-Device
Config-Allow: tftp, http, https
Expires: 86400
Content-Length: 0
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
;UserProfile=sip%3Afredsmith%40localdomain.com
Call-Id: 11111111@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 URL
in the request body is for the configuration data profile the UA
named in the Event header field in the above SUBSCRIBE request from
the UA.
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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: Sip-Device
Content-Type: text/plain
Content-Length: 79
Sip-Device: Sequence=1
;Url=http://config.localdomain.com/device/1234567890
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
Assume at some later 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 or content in the request body with a
higher sequence number.
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: Sip-Device
Cseq: 23 NOTIFY
Content-Type: text/plain
Content-Length: 79
Sip-Device: Sequence=2
;Url=http://config.localdomain.com/device/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
9 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. There is a chicken and egg problem. Since 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.
10 Open Issues
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[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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11 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 , ôDHCP Option for SIP Serversö,
<draft-ietf-sip-dhcp-04.txt>, IETF; Mar. 2001, 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, ôA DNS RR for
specifying the location of services (DNS SRV),ö Request for
Comments 2782, Internet Engineering Task Force, Feb. 2000.
[6] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg,
ôSIP: session initiation protocol,ö <draft-ietf-sip-rfc2543bis-
05.txt>, IETF; Oct. 2001, Work in progress.
[7] A. Roach, ôEvent Notification in SIPö, <draft-ietf-sip-
events-01.txt>, IETF; Nov. 2001, Work in progress.
[8] D. Crocker, ôSTANDARD FOR THE FORMAT OF ARPA INTERNET TEXT
MESSAGESö, Request for Comments 822, Internet Engineering Task
Force, Aug. 1982
[9] K. Sollins, ôTHE TFTP PROTOCOL (REVISION 2)ö, Request for
Comments 1350, Internet Engineering Task Force, Jul. 1992
[10] H Schulzrinne, ôConfiguring IP Telephony End Systemsö,
<schulzrinne-sip-config-00.txt>, IETF; Dec. 2000, Work in
progress
[11] D. Petrie, ôRequirements for a SIP User Agent Configuration
Frameworkö, <draft-petrie-sip-config-framewk-reqs-00.txt>, IETF;
Feb. 2001, Work in progress
[12] T. Berners-Lee et al, ôUniform Resource Locators (URL)ö,
Request for Comments 1738, Internet Engineering Task Force, Dec.
1994
[13] E. Rescorla, ôHTTP Over TLSö, Request for Comments 2818,
Internet Engineering Task Force, May 2000
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[14] T. Dierks, C. Allen, ôThe TLS Protocol Version 1.0ö, Request
for Comments 2246, Internet Engineering Task Force, Jan. 1999
12 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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