One document matched: draft-ietf-sipping-config-framework-00.txt
D. Petrie
Internet Draft Pingtel Corp.
draft-ietf-sipping-config-framework-00.txt
Expires: Aug 2003 Feb 2003
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-sipping-config-framework-00.txt....4
3.2 Changes from draft-petrie-sip-config-framework-01.txt........4
3.3 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....................................................7
4.4 Manually Provisioned.........................................7
5 Enrollment and Change Notification.............................7
5.1 SUBSCRIBE....................................................8
5.1.1 Additional User Agent Field Parameters......................9
5.2 NOTIFY......................................................10
5.2.1 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...................................................18
11 References....................................................19
12 Author's Address..............................................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 for configuration delivery defined in [10], [11] and
[16] explicitly 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.
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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.
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-sipping-config-framework-00.txt
Changed name to reflect SIPPING work group item
Updated with changes to SIP DHCP [3], SIP [6], SIP Events [7] and
content indirection [15].
Moved the device identity parameters from the From field parameters
to User-Agent header parameters.
Many thanks to Rich Schaaf of Pingtel, Cullen Jennings of Cisco and
Adam Roach of Dyamicsoft for the great comments and input.
3.2 Changes from draft-petrie-sip-config-framework-01.txt
Changed the name as this belongs in the SIPPING work group.
Minor edits
3.3 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
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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.
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 [3]
- DNS A record
- Multicast
- Manual provisioning
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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.
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 deployment of any significant size
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.
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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
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 MIME type in the SUBSCRIBE Accept
header field. The configuration server then delivers a URL (through
content indirection [15]) 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 MIME type must be named for each
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type of profile. The profile(s) MIME type(s) MUST be included in
the SUBSCRIBE Accept header field.
[Is it ok to allow a single SUBSCRIBE to request multiple profile
types in (e.g. for each MIME subtype application/sip-ua-user-profile
and application/sip-ua-device-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.
5.1 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 indicate support for content indirection by
including the MIME type message/external-body in the SUBSCRIBE
Accept header field per [15].
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 SUBSCRIBE 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 to the UA via content
indirection. 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
where each SUBSCRIBE would have a different MIME type in the
Accept header field.
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).
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The user agent forms the From field in the SUBSCRIBE in one of two
ways depending upon the type of profile that it is enrolling to. If
the user agent is enrolling to a device specific profile, the from
addr-spec is formed as: sip:<MAC-address>@<local-domain>. If the
user agent is enrolling to a user specific profile the addr-spec is
formed as the users address of record. In this way the identity for
which the profile is desired is always specified in the From field.
5.1.1 Additional User Agent 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 user agent MUST include
the User-Agent header in the SUBSCRIBE request. The following
additional User-Agent 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
Note: on some hardware such as PCs and servers, there may be
multiple instances of a user agent installed. In these
scenarios only the serial number can be used to uniquely
distinguish instances.
Mac û the token used to identify the MAC address in hex for the UA
From RFC 3261 [6] the User-Agent header field syntax is extended to:
User-Agent = "User-Agent" HCOLON product *( SEMI config-params )
config-params = serial-param / mac-param / generic-param
product = vendor-model [SLASH product-version]
product-version = token
vendor-param = ôVendorö ô=ö token
serial-param = ôSerialö ô=ö token
mac-param = ôMacö ô=ö token
Example:
User-Agent: model-a/1.5.0.1;vendor=acme
The Vendor, Model, Version, Serial and Mac parameters MUST be
provided in the User-Agent header field for the enrollment SUBSCRIBE
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request. Most profiles will either be device or user specific. All
config-params MUST be specified even when enrolling for user
profiles as the device characteristics may impact the content that
the profile server provides.
5.2 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 and make effective as soon as
it is safe to do so (e.g. when there are no active INVITE
dialogs).
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 different Content-ID entity header 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 Content-ID entity header
associated with the configuration data profile with changed content
should be different than that of the previous NOTIFY.
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.
5.2.1 NOTIFY Body Content Format
The NOTIFY request MUST contain a single part body with content
indirection [15]. The request MUST have a Content-Type header field
with the MIME type of message/external-body. The Content-Type MUST
also have a URL parameter specifying the URL at which to retrieve the
profile. The body MUST contain a Content-Type entity header with the
MIME type of the profile as the value. The body MUST also contain a
Content-ID entity header which SHOULD change to a new unique value each
time the content of the URL changes. The Content-ID entity header
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.
Example:
NOTIFY sip:00df1e004cd0@acme.com SIP/2.0
From: sip:sipuaconfig@sipuaconfig.acme.com;tag=1234
To: sip:00df1e004cd0@acme.com;tag=abcd
Call-ID: 3573853342923422@10.1.1.123
CSeq: 2131 INVITE
Content-Type: message/external-body;
ACCESS-TYPE=URL;
URL="https://acme.com/profiles/vendor-x/00df1e004cd0"
Content-Length: ...
Content-Type: application/foo-profile
Content-Disposition: session
Content-ID: <1000957853@acme.com>
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 accept uploads via the same URL the UA
used to retrieve the configuration data profile. 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
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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 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 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 server SHOULD
include a Content-ID header in the HTTP/HTTPS response. The
configuration server SHOULD send out a NOTIFY for this change, using
the same Content-ID entity header value as in the HTTP/HTTPS
response. 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 (i.e. it is safe to ignore the
NOTIFY as the Content-ID is the same).
[Alteratively the Content-ID could be put in the content as opposed
to the HTTP/HTTPS response]
[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 SIP [3] 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 serverÆs 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
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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
behalf of the administrator, sends a NOTIFY (change notification)
request to the UA with Content-ID entity header for the profile. As
the Content-ID value 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-config
==================================================>
200 OK
<==================================================
SIP NOTIFY Event: sip-config 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
.
.
.
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Change Notification
SIP NOTIFY Event: sip-config w/ changed profile URL
<==================================================
200 OK
==================================================>
HTTP GET
==================================================>
200 OK (profile data in body)
<==================================================
.
.
.
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
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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
sip-config. The UA tells the configuration server that it would
like the configuration data profile of type: sip-ua-device-config in
the Accept 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 addr-spec and User-Agent parameters: Vendor/Model,
Version, Serial, Mac. In this example the UserProfile parameter is
not included in the From field as the sip-config profile is device
specific not user specific.
UA => Config. Server
SUBSCRIBE sip: sipuaconfig@config.localdomain.com SIP/2.0
To: sip:sipuaconfig@sipuaconfig.localdomain.com
From: sip:000aaa1234cd@localdomain.com;tag=aslkjhd
User-Agent: acme-model-a/1.5.0.1;Serial=1234567890;Mac=000aaa1234cd
Call-Id: 987654321@10.1.1.123
Cseq: 1 SUBSCRIBE
Event: sip-config
Expires: 86400
Content-Length: 0
Accept: message/external-body application/sip-ua-device-config
The following is an example response to the above enrollment
request.
Config. Server => UA
SIP/2.0 202 Accepted
To: sip:sipuaconfig@sipuaconfig.localdomain.com;tag=owiu1234
From: sip:000aaa1234cd@localdomain.com;tag=aslkjhd
Call-Id: 987654321@10.1.1.123
Cseq: 1 SUBSCRIBE
Content-Length: 0
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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@sipuaconfig.localdomain.com SIP/2.0
To: sip:sipuaconfig@sipuaconfig.localdomain.com
From: sip:fredsmith@localdomain.com;tag=klhfkjncd
User-Agent: acme-model-a/1.5.0.1;Serial=1234567890;Mac=000aaa1234cd
Call-Id: 11111111@10.1.1.123
Cseq: 1 SUBSCRIBE
Event: sip-config
Expires: 86400
Content-Length: 0
Accept: message/external-body application/sip-ua-user-config
The following is an example response to the above enrollment
request.
Config. Server => UA
SIP/2.0 202 Accepted
To: sip:sipuaconfig@sipuaconfig.localdomain.com;tag=oqieu983
From: sip:fredsmith@localdomain.com;tag=klhfkjncd
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 above 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.
Config. Server => UA
NOTIFY sip:10.1.1.123 SIP/2.0
To: sip:sipuaconfig@sipuaconfig.localdomain.com;tag=owiu1234
From: sip:000aaa1234cd@localdomain.com;tag=aslkjhd
Call-Id: 987654321@10.1.1.123
Cseq: 22 NOTIFY
Event: sip-config
Content-Type: message/external-body;ACCESS-TYPE=URL;
URL="http://config.localdomain.com/device/000aaa1234cd/dev-prof
Content-Length: ...
Content-Type: application/sip-ua-device-config
Content-ID: 000aaa1234cd-3254@localdomain.com
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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:sipuaconfig@sipuaconfig.localdomain.com;tag=owiu1234
From: sip:000aaa1234cd@localdomain.com;tag=aslkjhd
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-config 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:sipuaconfig@sipuaconfig.localdomain.com;tag=owiu1234
From: sip:000aaa1234cd@localdomain.com;tag=aslkjhd
Call-Id: 987654321@10.1.1.123
Event: sip-config
Cseq: 23 NOTIFY
Content-Type: message/external-body;ACCESS-TYPE=URL;
URL="http://config.localdomain.com/device/000aaa1234cd/dev-prof
Content-Length: ...
Content-Type: application/sip-ua-device-config
Content-ID: 000aaa1234cd-3255@localdomain.com
The following is an example response to the above request.
UA => Config. Server
SIP/2.0 200 Ok
To: sip:sipuaconfig@sipuaconfig.localdomain.com;tag=owiu1234
From: sip:000aaa1234cd@localdomain.com;tag=aslkjhd
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
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User Agent Configuration
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
[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] H.Schulzrinne , ôDynamic Host Configuration Protocol (DHCP-
for-IPv4)ö, Request for Comments (Draft Standard) 3361, Internet
Engineering Task Force, Aug. 2002.
[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] Rosenberg, et. al., ôSIP: session initiation protocol,ö
Request for Comments 3261, Internet Engineering Task Force, June
2002
[7] A. Roach, ôEvent Notification in SIPö, Request for Comments
3265, Internet Engineering Task Force, June 2002
[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-ietf-sip-config-framewk-reqs-00.txt>, IETF;
Feb. 2003, 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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User Agent Configuration
[14] T. Dierks, C. Allen, ôThe TLS Protocol Version 1.0ö, Request
for Comments 2246, Internet Engineering Task Force, Jan. 1999
[15] S. Olson ôA Mechanism for Content Indirection in Session
Initiation Protocol (SIP) Messagesö, <draft-ietf-sip-content-
indirect-mech-01>, IETF; Nov. 2002, Work in progress
[16] H. Sinnreich, ôSIP Telephony Device Requirements,
Configuration and Dataö, <draft-sinnreich-sipdev-req-00.txt>,
IETF; Nov. 2002, Work in progress
[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
[14] T. Dierks, C. Allen, ôThe TLS Protocol Version 1.0ö, Request
for Comments 2246, Internet Engineering Task Force, Jan. 1999
[15] S. Olson ôA Mechanism for Content Indirection in Session
Initiation Protocol (SIP) Messagesö, <draft-ietf-sip-content-
indirect-mech-01>, IETF; Nov. 2002, Work in progress
12 Author's Address
Dan Petrie
Pingtel Corp.
400 W. Cummings Park Phone: +1 781 938 5306
Woburn, MA USA Email: dpetrie@pingtel.com
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