One document matched: draft-ietf-p2psip-sip-04.xml
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<rfc category="std" docName="draft-ietf-p2psip-sip-04"
ipr="pre5378Trust200902">
<front>
<title abbrev="RELOAD SIP Usage">A SIP Usage for RELOAD</title>
<author fullname="Cullen Jennings" initials="C." surname="Jennings">
<organization>Cisco</organization>
<address>
<postal>
<street>170 West Tasman Drive</street>
<street>MS: SJC-21/2</street>
<city>San Jose</city>
<region>CA</region>
<code>95134</code>
<country>USA</country>
</postal>
<phone>+1 408 421-9990</phone>
<email>fluffy@cisco.com</email>
</address>
</author>
<author fullname="Bruce B. Lowekamp" initials="B. B." role="editor"
surname="Lowekamp">
<organization>MYMIC LLC</organization>
<address>
<postal>
<street>1040 University Blvd., Suite 100</street>
<city>Portsmouth</city>
<region>VA</region>
<code>23703</code>
<country>USA</country>
</postal>
<email>bbl@lowekamp.net</email>
</address>
</author>
<author fullname="Eric Rescorla" initials="E.K." surname="Rescorla">
<organization>Network Resonance</organization>
<address>
<postal>
<street>2064 Edgewood Drive</street>
<city>Palo Alto</city>
<region>CA</region>
<code>94303</code>
<country>USA</country>
</postal>
<phone>+1 650 320-8549</phone>
<email>ekr@networkresonance.com</email>
</address>
</author>
<author fullname="Salman A. Baset" initials="S.A." surname="Baset">
<organization>Columbia University</organization>
<address>
<postal>
<street>1214 Amsterdam Avenue</street>
<city>New York</city>
<region>NY</region>
<country>USA</country>
</postal>
<email>salman@cs.columbia.edu</email>
</address>
</author>
<author fullname="Henning Schulzrinne" initials="H.G."
surname="Schulzrinne">
<organization>Columbia University</organization>
<address>
<postal>
<street>1214 Amsterdam Avenue</street>
<city>New York</city>
<region>NY</region>
<country>USA</country>
</postal>
<email>hgs@cs.columbia.edu</email>
</address>
</author>
<date day="8" month="March" year="2010" />
<area>RAI</area>
<workgroup>P2PSIP</workgroup>
<abstract>
<t>This document defines a SIP Usage for REsource LOcation And Discovery
(RELOAD), The SIP Usage provides the functionality of a SIP proxy or
registrar in a fully-distributed system. The SIP Usage provides lookup
service for AoRs stored in the overlay. The SIP Usage also defines GRUUs
that allow the registrations to map an AoR to a specific node reachable
through the overlay. The AppAttach method is used to establish a direct
connection between nodes through which SIP messages are exchanged.</t>
</abstract>
</front>
<middle>
<section title="Overview">
<t>The SIP Usage of RELOAD allows SIP user agents to provide a
peer-to-peer telephony service without the requirement for permanent
proxy or registration servers. In such a network, the RELOAD overlay
itself performs the registration and rendezvous functions ordinarily
associated with such servers.</t>
<t>The SIP Usage involves two basic functions: <list style="hanging">
<t hangText="Registration: ">SIP UAs can use the RELOAD data storage
functionality to store a mapping from their AOR to their Node-ID in
the overlay, and to retrieve the Node-ID of other UAs.</t>
<t hangText="Rendezvous: ">Once a SIP UA has identified the Node-ID
for an AOR it wishes to call, it can use the RELOAD message routing
system to set up a direct connection which can be used to exchange
SIP messages.</t>
</list></t>
<t>For instance, Bob could register his Node-ID, "1234", under his AOR,
"sip:bob@dht.example.com". When Alice wants to call Bob, she queries the
overlay for "sip:bob@dht.example.com" and gets back Node-ID 1234. She
then uses the overlay to establish a direct connection with Bob and can
use that direct connection to perform a standard SIP INVITE. The way
this works is as follows:</t>
<t><list style="numbers">
<t>Bob, operating Node-ID 1234, stores a mapping from his URI to his
Node-ID in the overlay. I.e., "sip:bob@dht.example.com ->
1234".</t>
<t>Alice, operating Node-ID 5678, decides to call Bob. She looks up
"sip:bob@dht.example.com" in the overlay and retrieves "1234".</t>
<t>Alice uses the overlay to route an AppAttach message to Bob's
peer. Bob responds with his own AppAttach and they set up a direct
connection, as shown below.</t>
</list></t>
<figure>
<artwork><![CDATA[
Alice Peer1 Overlay PeerN Bob
(5678) (1234)
-------------------------------------------------
AppAttach ->
AppAttach ->
AppAttach ->
AppAttach ->
<- AppAttach
<- AppAttach
<- AppAttach
<- AppAttach
<------------------ ICE Checks ----------------->
INVITE ----------------------------------------->
<--------------------------------------------- OK
ACK -------------------------------------------->
<------------ ICE Checks for media ------------->
<-------------------- RTP ---------------------->
]]></artwork>
</figure>
<t>It is important to note that RELOAD's only role here is to set up the
direct SIP connection between Alice and Bob. As soon as the ICE checks
complete and the connection is established, then ordinary SIP is used.
In particular, the establishment of the media channel for the phone call
happens via the usual SIP mechanisms, and RELOAD is not involved. Media
never goes over the overlay. After the successful exchange of SIP
messages, call peers run ICE connectivity checks for media.</t>
<t>As well as allowing mappings from AORs to Node-IDs, the SIP Usage
also allows mappings from AORs to other AORs. For instance, if Bob
wanted his phone calls temporarily forwarded to Charlie, he could store
the mapping "sip:bob@dht.example.com -> sip:charlie@dht.example.com".
When Alice wants to call Bob, she retrieves this mapping and can then
fetch Charlie's AOR to retrieve his Node-ID.</t>
<!-- -->
<!-- -->
</section>
<section title="Terminology">
<t>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 <xref
target="RFC2119">RFC 2119</xref>.</t>
<t>We use the terminology and definitions from <xref
target="I-D.ietf-p2psip-concepts">Concepts and Terminology for Peer to
Peer SIP</xref> and the <xref target="I-D.ietf-p2psip-base">RELOAD Base
Protocol</xref> extensively in this document.</t>
</section>
<!-- -->
<section title="Registering AORs">
<t>In ordinary SIP, a UA registers its AOR and location with a
registrar. In RELOAD, this registrar function is provided by the overlay
as a whole. To register its location, a RELOAD peer stores a
SipRegistration structure under its own AOR. This uses the
SIP-REGISTRATION Kind-ID, which is formally defined in <xref
target="sec.sip-reg-kind"></xref>. <list style="hanging">
<t hangText="Note:">GRUUs are handled via a separate mechanism, as
described in <xref target="sec-gruus"></xref>.</t>
</list></t>
<t>As a simple example, if Alice's AOR were "sip:alice@dht.example.com"
and her Node-ID were "1234", she might store the mapping
"sip:alice@example.org -> 1234". This would tell anyone who wanted to
call Alice to contact node "1234".</t>
<t>RELOAD peers MAY store two kinds of SIP mappings:</t>
<t><list style="symbols">
<t>From AORs to destination lists (a single Node-ID is just a
trivial destination list.)</t>
<t>From AORs to other AORs.</t>
</list></t>
<t>The meaning of the first kind of mapping is "in order to contact me,
form a connection with this peer." The meaning of the second kind of
mapping is "in order to contact me, dereference this AOR". This allows
for forwarding. For instance, if Alice wants calls to her to be
forwarded to her secretary, Sam, she might insert the following mapping
"sip:alice@dht.example.org -> sip:sam@dht.example.org".</t>
<t>The contents of a SipRegistration structure are as follows:</t>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
enum {sip_registration_uri (1), sip_registration_route (2),
(255)} SipRegistrationType;
select (SipRegistration.type) {
case sip_registration_uri:
opaque uri<0..2^16-1>;
case sip_registration_route:
opaque contact_prefs<0..2^16-1>;
Destination destination_list<0..2^16-1>;
/* This type can be extended */
} SipRegistrationData;
struct {
SipRegistrationType type;
uint16 length;
SipRegistrationData data;
} SipRegistration;
]]></artwork>
</figure>
<t>The contents of the SipRegistration PDU are:</t>
<t><list style="hanging">
<t></t>
<t hangText="type "></t>
<t>the type of the registration</t>
<t></t>
<t hangText="length "></t>
<t>the length of the rest of the PDU</t>
<t></t>
<t hangText="data "></t>
<t>the registration data</t>
</list></t>
<t><list style="symbols">
<t>If the registration is of type "sip_registration_uri", then the
contents are an opaque string containing the URI.</t>
<t>If the registration is of type "sip_registration_route", then the
contents are an opaque string containing the callee's contact
preferences and a destination list for the peer.</t>
</list></t>
<t>RELOAD explicitly supports multiple registrations for a single AOR.
The registrations are stored in a Dictionary with the dictionary keys
being Node-IDs. Consider, for instance, the case where Alice has two
peers:</t>
<t><list style="symbols">
<t>her desk phone (1234)</t>
<t>her cell phone (5678)</t>
</list></t>
<t>Alice might store the following in the overlay at resource
"sip:alice@dht.example.com".</t>
<t><list style="symbols">
<t>A SipRegistration of type "sip_registration_route" with
dictionary key "1234" and value "1234".</t>
<t>A SipRegistration of type "sip_registration_route" with
dictionary key "5678" and value "5678".</t>
</list></t>
<t>Note that this structure explicitly allows one Node-ID to forward to
another Node-ID. For instance, Alice could set calls to her desk phone
to ring at her cell phone. It's not clear that this is useful in this
case, but may be useful if Alice has two AORs.</t>
<t>In order to prevent hijacking, registrations are subject to access
control rules. Before a Store is permitted, the storing peer MUST check
that:</t>
<t><list style="symbols">
<t>The certificate contains a username that is a SIP AOR that hashes
to the Resource-ID it is being stored at.</t>
<t>The certificate contains a Node-ID that is the same as the
dictionary key it is being stored at.</t>
</list></t>
<t>Note that these rules permit Alice to forward calls to Bob without
his permission. However, they do not permit Alice to forward Bob's calls
to her. See <xref target="sec-security-malicious-retargeting"></xref>
for more on this point.</t>
</section>
<section title="Looking up an AOR">
<t>When a RELOAD user wishes to call another user, starting with a
non-GRUU AOR, he follows the following procedure. (GRUUs are discussed
in <xref target="sec-gruus"></xref>).</t>
<t><list style="numbers">
<t>Check to see if the domain part of the AOR matches the domain
name of an overlay of which he is a member. If not, then this is an
external AOR, and he MUST do one of the following: <list
style="symbols">
<t>Fail the call.</t>
<t>Use ordinary SIP procedures.</t>
<t>Attempt to become a member of the overlay indicated by the
domain part, if that overlay is a RELOAD overlay.)</t>
</list></t>
<t>Perform a Fetch for kind SIP-REGISTRATION at the Resource-ID
corresponding to the AOR. This Fetch SHOULD NOT indicate any
dictionary keys, so that it will fetch all the stored values.</t>
<t>If any of the results of the Fetch are non-GRUU AORs, then repeat
step 1 for that AOR.</t>
<t>Once only GRUUs and destination lists remain, the peer removes
duplicate destination lists and GRUUs from the list and forms a SIP
connection to the appropriate peers as described in the following
sections. If there are also external AORs, the peer follows the
appropriate procedure for contacting them as well.</t>
</list></t>
</section>
<section title="Forming a Direct Connection">
<t>Once the peer has translated the AOR into a set of destination lists,
it then uses the overlay to route AppAttach messages to each of those
peers. The "application" field MUST be 5060 to indicate SIP. If
certificate-based authentication is in use, the responding peer MUST
present a certificate with a Node-ID matching the terminal entry in the
route list. Note that it is possible that the peers already have a
RELOAD connection between them. This MUST NOT be used for SIP messages.
However, if a SIP connection already exists, that MAY be used. Once the
AppAttach succeeds, the peer sends SIP messages over the connection as
in normal SIP.</t>
</section>
<section anchor="sec-gruus" title="GRUUs">
<t>GRUUs do not require storing data in the Overlay Instance. Rather,
they are constructed by embedding a base64-encoded destination list in
the gr URI parameter of the GRUU. The base64 encoding is done with the
alphabet specified in table 1 of RFC 4648 with the exception that ~ is
used in place of =. An example GRUU is
"sip:alice@example.com;gr=MDEyMzQ1Njc4OTAxMjM0NTY3ODk~". When a peer
needs to route a message to a GRUU in the same P2P network, it simply
uses the destination list and connects to that peer.</t>
<t>Because a GRUU contains a destination list, it MAY have the same
contents as a destination list stored elsewhere in the resource
dictionary.</t>
<t>Anonymous GRUUs are done in roughly the same way but require either
that the enrollment server issue a different Node-ID for each anonymous
GRUU required or that a destination list be used that includes a peer
that compresses the destination list to stop the Node-ID from being
revealed.</t>
</section>
<section anchor="sec.sip-reg-kind"
title="SIP-REGISTRATION Kind Definition">
<t>This section defines the SIP-REGISTRATION kind.</t>
<t><list style="hanging">
<t></t>
<t hangText="Name">SIP-REGISTRATION</t>
<t></t>
<t hangText="Kind IDs">The Resource Name for the SIP-REGISTRATION
Kind-ID is the AOR of the user. The data stored is a
SipRegistrationData, which can contain either another URI or a
destination list to the peer which is acting for the user.</t>
<t></t>
<t hangText="Data Model">The data model for the SIP-REGISTRATION
Kind-ID is dictionary. The dictionary key is the Node-ID of the
storing peer. This allows each peer (presumably corresponding to a
single device) to store a single route mapping.</t>
<t></t>
<t hangText="Access Control">USER-NODE-MATCH. Note that this matches
the SIP AOR against the rfc822Name in the X509v3 certificate. The
rfc822Name does not include the scheme so that "sip:" prefix needs to
be removed from the SIP AOR before matching. </t>
</list></t>
<t>Data stored under the SIP-REGISTRATION kind is of type
SipRegistration. This comes in two varieties: <list style="hanging">
<t></t>
<t hangText="sip_registration_uri "></t>
<t>a URI which the user can be reached at.</t>
<t></t>
<t hangText="sip_registration_route "></t>
<t>a destination list which can be used to reach the user's
peer.</t>
</list></t>
<!-- -->
</section>
<section title="Security Considerations">
<section title="Overview">
<t>RELOAD provides a generic storage service, albeit one designed to
be useful for P2PSIP. In this section we discuss security issues that
are likely to be relevant to any usage of RELOAD. In <xref
target="section.sip-issues"></xref> we describe issues that are
specific to SIP.</t>
</section>
<section anchor="section.sip-issues" title="SIP-Specific Issues">
<section title="Fork Explosion">
<t>Because SIP includes a forking capability (the ability to
retarget to multiple recipients), fork bombs are a potential DoS
concern. However, in the SIP usage of RELOAD, fork bombs are a much
lower concern because the calling party is involved in each
retargeting event and can therefore directly measure the number of
forks and throttle at some reasonable number.</t>
</section>
<section anchor="sec-security-malicious-retargeting"
title="Malicious Retargeting">
<t>Another potential DoS attack is for the owner of an attractive
number to retarget all calls to some victim. This attack is
difficult to ameliorate without requiring the target of a SIP
registration to authorize all stores. The overhead of that
requirement would be excessive and in addition there are good use
cases for retargeting to a peer without there explicit
cooperation.</t>
</section>
<section title="Privacy Issues">
<t>All RELOAD SIP registration data is public. Methods of providing
location and identity privacy are still being studied.</t>
</section>
</section>
</section>
<section title="IANA Considerations">
<t>IANA [shall register/has registered] code point TBD to represent the
SIP-REGISTRATION kind, as described in <xref
target="sec.sip-reg-kind"></xref>.</t>
</section>
<section title="Acknowledgments">
<t>This draft is a merge of the "REsource LOcation And Discovery
(RELOAD)" draft by David A. Bryan, Marcia Zangrilli and Bruce B.
Lowekamp, the "Address Settlement by Peer to Peer" draft by Cullen
Jennings, Jonathan Rosenberg, and Eric Rescorla, the "Security
Extensions for RELOAD" draft by Bruce B. Lowekamp and James Deverick,
the "A Chord-based DHT for Resource Lookup in P2PSIP" by Marcia
Zangrilli and David A. Bryan, and the Peer-to-Peer Protocol (P2PP) draft
by Salman A. Baset, Henning Schulzrinne, and Marcin Matuszewski.</t>
<t>Thanks to Michael Chen for his contributions.</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
<reference anchor="I-D.ietf-p2psip-base">
<front>
<title>REsource LOcation And Discovery (RELOAD) Base
Protocol</title>
<author fullname="Cullen Jennings" initials="C" surname="Jennings">
<organization></organization>
</author>
<author fullname="Bruce Lowekamp" initials="B" surname="Lowekamp">
<organization></organization>
</author>
<author fullname="Eric Rescorla" initials="E" surname="Rescorla">
<organization></organization>
</author>
<author fullname="Salman Baset" initials="S" surname="Baset">
<organization></organization>
</author>
<author fullname="Henning Schulzrinne" initials="H"
surname="Schulzrinne">
<organization></organization>
</author>
<date day="27" month="October" year="2008" />
<abstract>
<t>This document defines REsource LOcation And Discovery (RELOAD),
a peer-to-peer (P2P) signaling protocol for use on the Internet. A
P2P signaling protocol provides its clients with an abstract
storage and messaging service between a set of cooperating peers
that form the overlay network. RELOAD is designed to support a P2P
Session Initiation Protocol (P2PSIP) network, but can be utilized
by other applications with similar requirements by defining new
usages that specify the kinds of data that must be stored for a
particular application. RELOAD defines a security model based on a
certificate enrollment service that provides unique identities.
NAT traversal is a fundamental service of the protocol. RELOAD
also allows access from "client" nodes which do not need to route
traffic or store data for others.</t>
</abstract>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-p2psip-base-00" />
<format target="http://www.ietf.org/internet-drafts/draft-ietf-p2psip-base-00.txt"
type="TXT" />
</reference>
</references>
<references title="Informative References">
<?rfc include="reference.I-D.ietf-p2psip-concepts"?>
</references>
<section anchor="sec-changes" title="Change Log">
<section title="Changes since draft-ietf-p2psip-reload-00">
<t><list style="symbols">
<t>Split SIP Usage from combined draft into new draft.</t>
</list></t>
</section>
</section>
<!-- -->
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</back>
</rfc>
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