MMUSIC Working Group F. Andreasen
Internet-Draft Cisco Systems
Intended status: Standards Track G. Camarillo
Expires: September 5, 2010 Ericsson
D. Oran
D. Wing
Cisco Systems
March 4, 2010
Connectivity Preconditions for Session Description Protocol (SDP) Media
Streams
draft-ietf-mmusic-connectivity-precon-07.txt
Abstract
This document defines a new connectivity precondition for the Session
Description Protocol (SDP) precondition framework. A connectivity
precondition can be used to delay session establishment or
modification until media stream connectivity has been successfully
verified. The method of verification may vary depending on the type
of transport used for the media. For unreliable datagram transports
such as UDP, verification involves probing the stream with data or
control packets. For reliable connection-oriented transports such as
TCP, verification can be achieved simply by successful connection
establishment or by probing the connection with data or control
packets, depending on the situation.
Status of this Memo
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This Internet-Draft will expire on September 5, 2010.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Connectivity Precondition Definition . . . . . . . . . . . . . 4
3.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Operational Semantics . . . . . . . . . . . . . . . . . . 5
3.3. Status Type . . . . . . . . . . . . . . . . . . . . . . . 5
3.4. Direction Tag . . . . . . . . . . . . . . . . . . . . . . 5
3.5. Precondition Strength . . . . . . . . . . . . . . . . . . 6
4. Verifying Connectivity . . . . . . . . . . . . . . . . . . . . 7
4.1. Media Stream to Dialog Correlation . . . . . . . . . . . . 7
4.2. Explicit Connectivity Verification Mechanisms . . . . . . 8
4.3. Verifying Connectivity for Connection-Oriented
Transports . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Connectivity and Other Precondition Types . . . . . . . . . . 10
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 15
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
9.1. Normative References . . . . . . . . . . . . . . . . . . . 16
9.2. Informative References . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
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1. Introduction
The concept of a Session Description Protocol (SDP) [RFC4566]
precondition in the Session Initiation Protocol (SIP) [RFC3261] is
defined in RFC 3312 [RFC3312] (updated by RFC 4032 [RFC4032]). A
precondition is a condition that has to be satisfied for a given
media stream in order for session establishment or modification to
proceed. When the precondition is not met, session progress is
delayed until the precondition is satisfied or the session
establishment fails. For example, RFC 3312 [RFC3312] defines the
Quality of Service precondition, which is used to ensure availability
of network resources prior to establishing a session (i.e., prior to
starting alerting the callee).
SIP sessions are typically established in order to setup one or more
media streams. Even though a media stream may be negotiated
successfully through an SDP offer-answer exchange, the actual media
stream itself may fail. For example, when there is one or more
Network Address Translators (NATs) or firewalls in the media path,
the media stream may not be received by the far end. In cases where
the media is carried over a connection-oriented transport such as TCP
[RFC0793], the connection-establishment procedures may fail. The
connectivity precondition defined in this document ensures that
session progress is delayed until media stream connectivity has been
verified.
The connectivity precondition type defined in this document follows
the guidelines provided in RFC 4032 [RFC4032] to extend the SIP
preconditions framework.
2. Terminology
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 [RFC2119].
3. Connectivity Precondition Definition
3.1. Syntax
The connectivity precondition type is defined by the string "conn"
and hence we modify the grammar found in RFC 3312 [RFC3312] and RFC
5027 [RFC5027] as follows:
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precondition-type = "conn" / "sec" / "qos" / token
This precondition tag is registered with the IANA in Section 8.
3.2. Operational Semantics
According to RFC 4032 [RFC4032], documents defining new precondition
types need to describe the behavior of UAs (User Agents) from the
moment session establishment is suspended due to a set of
preconditions, until it is resumed when these preconditions are met.
An entity that wishes to delay session establishment or modification
until media stream connectivity has been established uses this
precondition-type in an offer. When a mandatory connectivity
precondition is received in an offer, session establishment or
modification is delayed until the connectivity precondition has been
met (i.e., until media stream connectivity has been established in
the desired direction or directions). The delay of session
establishment defined here implies that alerting of the called party
does not occur until the precondition has been satisfied.
Packets may be both sent and received on the media streams in
question. However, such packets SHOULD be limited to packets that
are necessary to verify connectivity between the two endpoints
involved on the media stream. That is, the underlying media stream
SHOULD NOT be cut through. For example, ICE connectivity checks
[I-D.ietf-mmusic-ice] and TCP SYN and ACK packets can be exchanged on
media streams that support them as a way of verifying connectivity.
Some media streams are described by a single 'm' line but,
nevertheless, involve multiple addresses. For example, RFC 5109
[RFC5109] specifies how to send FEC (Forward Error Correction)
information as a separate stream (the address for the FEC stream is
provided in an 'a=fmtp' line). When a media stream consists of
multiple destination addresses, connectivity to all of them MUST be
verified in order for the precondition to be met.
3.3. Status Type
RFC 3312 [RFC3312] defines support for two kinds of status types,
namely segmented and end-to-end. The connectivity precondition-type
defined here MUST be used with the end-to-end status type; use of the
segmented status type is undefined.
3.4. Direction Tag
The direction attributes defined in RFC 3312 [RFC3312] are
interpreted as follows:
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o send: the party that generated the session description is sending
packets on the media stream to the other party, and the other
party has received at least one of those packets. That is, there
is connectivity in the forward (sending) direction.
o recv: the other party is sending packets on the media stream to
the party that generated the session description, and this party
has received at least one of those packets. That is, there is
connectivity in the backwards (receiving) direction.
o sendrecv: both the send and recv conditions hold.
Note that a "send" connectivity precondition from the offerer's point
of view corresponds to a "recv" connectivity precondition from the
answerer's point of view, and vice versa. If media stream
connectivity in both directions is required before session
establishment or modification continues, the desired status needs to
be set to "sendrecv".
3.5. Precondition Strength
Connectivity preconditions may have a strength-tag of either
"mandatory" or "optional".
When a mandatory connectivity precondition is offered and the
answerer cannot satisfy the connectivity precondition (e.g., because
the offer does not include parameters that enable connectivity to be
verified without media cut through) the offer MUST be rejected as
described in RFC 3312 [RFC3312].
When an optional connectivity precondition is offered, the answerer
MUST generate its answer SDP as soon as possible. Since session
progress is not delayed in this case, it is not known whether the
associated media streams will have connectivity. If the answerer
wants to delay session progress until connectivity has been verified,
the answerer MUST increase the strength of the connectivity
precondition by using a strength-tag of "mandatory" in the answer.
Note that use of a "mandatory" precondition requires the presence of
a SIP "Require" header with the option tag "precondition". Any SIP
UA that does not support a mandatory precondition will reject such
requests. To get around this issue, an optional connectivity
precondition and the SIP "Supported" header with the option tag
"precondition" can be used instead.
Offers with connectivity preconditions in re-INVITEs or UPDATEs
follow the rules given in Section 6 of RFC 3312 [RFC3312]. That is:
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"Both user agents SHOULD continue using the old session parameters
until all the mandatory preconditions are met. At that moment,
the user agents can begin using the new session parameters."
4. Verifying Connectivity
Media stream connectivity is ascertained by use of a connectivity
verification mechanism between the media endpoints. A connectivity
verification mechanism may be an explicit mechanism, such as ICE
[I-D.ietf-mmusic-ice] or ICE TCP [I-D.ietf-mmusic-ice-tcp], or it may
be an implicit mechanism, such as TCP. Explicit mechanisms provide
specifications for when connectivity between two endpoints using an
offer/answer exchange is ascertained, whereas implicit mechanisms do
not. The verification mechanism is negotiated as part of the normal
offer/answer exchange, however it is not identified explicitly. More
than one mechanism may be negotiated, but the offerer and answerer
need not use the same. The following rules guide which connectivity
verification mechanism to use:
1. if an explicit connectivity verification mechanism (e.g., ICE) is
negotiated, the precondition is met when the mechanism verifies
connectivity successfully, otherwise
2. if a connection-oriented transport (e.g., TCP) is negotiated, the
precondition is met when the connection is established, otherwise
3. if an implicit verification mechanism is provided by the
transport itself or the media stream data using the transport,
the precondition is met when the mechanism verifies connectivity
successfully, otherwise
4. connectivity cannot be verified reliably and the connectivity
precondition will never be satisfied if requested.
This document does not mandate any particular connectivity
verification mechanism; however, in the following, we provide
additional considerations for verification mechanisms.
4.1. Media Stream to Dialog Correlation
SIP and SDP do not provide any inherent capabilities for associating
an incoming media stream packet with a particular dialog. Thus, when
an offerer is trying to ascertain connectivity, and an incoming media
stream packet is received, the offerer may not know which dialog had
its "recv" connectivity verified. Explicit connectivity verification
mechanisms therefore typically provide a means to correlate the media
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stream, whose connectivity is being verified, with a particular SIP
dialog. However, some connectivity verification mechanisms may not
provide such a correlation. In the absence of a dialog-to-media-
stream correlation mechanism (e.g., ICE), a UAS (User Agent Server)
MUST NOT require the offerer to confirm a connectivity precondition.
4.2. Explicit Connectivity Verification Mechanisms
Explicit connectivity verification mechanisms typically use probe
traffic with some sort of feedback to inform the sender whether
reception was successful. Below we provide two examples of such
mechanisms, and how they are used with connectivity preconditions:
Interactive Connectivity Establishment (ICE) [I-D.ietf-mmusic-ice]
provides one or more candidate addresses in signaling between the
offerer and the answerer and then uses STUN Binding Requests to
determine which pairs of candidate addresses have connectivity. Each
STUN Binding Request contains a password which is communicated in the
SDP as well; this enables correlation between STUN Binding Requests
and candidate addresses for a particular media stream. It also
provides correlation with a particular SIP dialog.
ICE implementations may be either Full or Lite (see
[I-D.ietf-mmusic-ice]). Full implementations generate and respond to
STUN Binding Requests, whereas Lite implementations only respond to
them. With ICE, one side is a controlling agent, and the other side
is a controlled agent. A Full implementation can take on either
role, whereas a Lite implementation can only be a controlled agent.
The controlling agent decides which valid candidate to use and
informs the controlled agent of it by identifying the pair as the
nominated pair. This leads to the following connectivity
precondition rules:
o A Full implementation ascertains both "send" and "recv"
connectivity when it operates as a STUN client and has sent a STUN
Binding Request that resulted in a successful check for all the
components of the media stream (as defined further in ICE).
o A Full or a Lite implementation ascertains "recv" connectivity
when it operates as a STUN server and has received a STUN Binding
Request that resulted in a successful response for all the
components of the media stream (as defined further in ICE).
o A Lite implementation ascertains "send" and "recv" connectivity
when the controlling agent has informed it of the nominated pair
for all the components of the media stream.
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A simpler and slightly more delay-prone alternative to the above
rules is for all ICE implementations to ascertain "send" and "recv"
connectivity for a media stream when the ICE state for that media
stream has moved to Completed.
Note that there is never a need for the answerer to request
confirmation of the connectivity precondition when using ICE: the
answerer can determine the status locally. Also note, that when ICE
is used to verify connectivity preconditions, the precondition is not
satisfied until connectivity has been verified for all the component
transport addresses used by the media stream. For example, with an
RTP-based media stream where RTCP is not suppressed, connectivity
MUST be ascertained for both RTP and RTCP; this is a tightening of
the general operational semantics provided in Section 3.2, which is
imposed by ICE. Finally, it should be noted, that although
connectivity has been ascertained, a new offer/answer exchange may be
required before media can flow (per ICE).
The above are merely examples of explicit connectivity verification
mechanisms. Other techniques can be used as well. It is however
RECOMMENDED that ICE be supported by entities that support
connectivity preconditions. Use of ICE has the benefit of working
for all media streams (not just RTP) as well as facilitate NAT and
firewall traversal, which may otherwise interfere with connectivity.
Furthermore, the ICE recommendation provides a baseline to ensure
that all entities that require probe traffic to support the
connectivity preconditions have a common way of ascertaining
connectivity.
4.3. Verifying Connectivity for Connection-Oriented Transports
Connection-oriented transport protocols generally provide an implicit
connectivity verification mechanism. Connection establishment
involves sending traffic in both directions thereby verifying
connectivity at the transport protocol level. When a three-way (or
more) handshake for connection establishment succeeds, bi-directional
communication is confirmed and both the "send" and "recv"
preconditions are satisfied whether requested or not. In the case of
TCP for example, once the TCP three-way handshake has completed (SYN,
SYN-ACK, ACK), the TCP connection is established and data can be sent
and received by either party (i.e., both a send and a receive
connectivity precondition has been satisfied). SCTP [RFC4960]
connections have similar semantics as TCP and SHOULD be treated the
same.
When a connection-oriented transport is part of an offer, it may be
passive, active, or active/passive [RFC4145]. When it is passive,
the offerer expects the answerer to initiate the connection
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establishment, and when it is active, the offerer wants to initiate
the connection establishment. When it is active/passive, the
answerer decides. As noted earlier, lack of a media-stream-to-dialog
correlation mechanism can make it difficult to guarantee with whom
connectivity has been ascertained. When the offerer takes on the
passive role, the offerer will not necessarily know which SIP dialog
originated an incoming connection request. If the offerer instead is
active, this problem is avoided.
5. Connectivity and Other Precondition Types
The role of a connectivity precondition is to ascertain media stream
connectivity before establishing or modifying a session. The
underlying intent is for the two parties to be able to exchange media
packets successfully. Connectivity by itself however may not fully
satisfy this. Quality of Service for example may be required for the
media stream; this can be addressed by use of the "qos" precondition
defined in RFC 3312 [RFC3312]. Similarly, successful security
parameter negotiation may be another prerequisite; this can be
addressed by use of the "sec" precondition defined in RFC 5027
[RFC5027].
6. Examples
The first example uses the connectivity precondition with TCP in the
context of a session involving a wireless access medium. Both UAs
use a radio access network that does not allow them to send any data
(not even a TCP SYN) until a radio bearer has been setup for the
connection. Figure 1 shows the message flow of this example (the
required PRACK transaction has been omitted for clarity):
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A B
| INVITE |
| a=curr:conn e2e none |
| a=des:conn mandatory e2e sendrecv |
| a=setup:holdconn |
|----------------------------------->|
| |
| 183 Session Progress |
| a=curr:conn e2e none |
| a=des:conn mandatory e2e sendrecv |
| a=setup:holdconn |
|<-----------------------------------|
| |
| UPDATE |
| a=curr:conn e2e none |
| a=des:conn mandatory e2e sendrecv |
A's radio | a=setup:actpass |
bearer is +----------------------------------->|
up | |
| 200 OK |
| a=curr:conn e2e none |
| a=des:conn mandatory e2e sendrecv |
| a=setup:active |
|<-----------------------------------|
| |
| |
| |
| | B's radio
|<---TCP Connection Establishment--->+ bearer is up
| | B sends TCP SYN
| |
| |
| 180 Ringing | TCP connection
|<-----------------------------------+ is up
| | B alerts the user
| |
Figure 1: Message flow with two types of preconditions
A sends an INVITE requesting connection-establishment preconditions.
The setup attribute in the offer is set to holdconn [RFC4145] because
A cannot send or receive any data before setting up a radio bearer
for the connection.
B agrees to use the connectivity precondition by sending a 183
(Session Progress) response. The setup attribute in the answer is
also set to holdconn because B, like A, cannot send or receive any
data before setting up a radio bearer for the connection.
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When A's radio bearer is ready, A sends an UPDATE to B with a setup
attribute with a value of actpass. This attribute indicates that A
can perform an active or a passive TCP open. A is letting B choose
which endpoint will initiate the connection.
Since B's radio bearer is not ready yet, B chooses to be the one
initiating the connection and indicates so with a setup attribute
with a value of active. At a later point, when B's radio bearer is
ready, B initiates the TCP connection towards A.
Once the TCP connection is established successfully, B knows the
"sendrecv" precondition is satisfied, and B proceeds with the session
(i.e., alerts the Callee), and sends a 180 (Ringing) response.
The second example shows a basic SIP session establishment using SDP
connectivity preconditions and ICE (the required PRACK transaction
and some SDP details have been omitted for clarity). The message
flow for this scenario is shown in Figure 2 below.
A B
| |
|-------------(1) INVITE SDP1--------------->|
| |
|<------(2) 183 Session Progress SDP2--------|
| |
|<~~~~~ Connectivity check to A ~~~~~~~~~~~~~|
|~~~~~ Connectivity to A OK ~~~~~~~~~~~~~~~~>|
| |
|~~~~~ Connectivity check to B ~~~~~~~~~~~~~>|
|<~~~~ Connectivity to B OK ~~~~~~~~~~~~~~~~~|
| |
|-------------(3) UPDATE SDP3--------------->|
| |
|<--------(4) 200 OK (UPDATE) SDP4-----------|
| |
|<-------------(5) 180 Ringing---------------|
| |
| |
Figure 2: Connectivity precondition with ICE Connectivity Checks
SDP1: A includes a mandatory end-to-end connectivity precondition
with a desired status of "sendrecv"; this will ensure media stream
connectivity in both directions before continuing with the session
setup. Since media stream connectivity in either direction is
unknown at this point, the current status is set to "none". A's
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local status table (see [RFC3312]) for the connectivity precondition
is as follows:
Direction | Current | Desired Strength | Confirm
-----------+----------+------------------+----------
send | no | mandatory | no
recv | no | mandatory | no
and the resulting offer SDP is:
a=ice-pwd:asd88fgpdd777uzjYhagZg
a=ice-ufrag:8hhY
m=audio 20000 RTP/AVP 0
c=IN IP4 192.0.2.1
a=curr:conn e2e none
a=des:conn mandatory e2e sendrecv
a=candidate:1 1 UDP 2130706431 192.0.2.1 20000 typ host
SDP2: When B receives the offer, B sees the mandatory sendrecv
connectivity precondition. B can ascertain connectivity to A ("send"
from B's point of view) by use of the ICE connectivity check, however
B wants A to inform it about connectivity in the other direction
("recv" from B's point of view). B's local status table therefore
looks as follows:
Direction | Current | Desired Strength | Confirm
-----------+----------+------------------+----------
send | no | mandatory | no
recv | no | mandatory | no
Since B wants to ask A for confirmation about the "recv" (from B's
point of view) connectivity precondition, the resulting answer SDP
becomes:
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a=ice-pwd:qrCA8800133321zF9AIj98
a=ice-ufrag:H92p
m=audio 30000 RTP/AVP 0
c=IN IP4 192.0.2.4
a=curr:conn e2e none
a=des:conn mandatory e2e sendrecv
a=conf:conn e2e recv
a=candidate:1 1 UDP 2130706431 192.0.2.4 30000 typ host
Meanwhile, B performs a successful send connectivity check to A by
sending an ICE connectivity check packet to A and receiving the
corresponding response. B's local status table is updated as
follows:
Direction | Current | Desired Strength | Confirm
-----------+----------+------------------+----------
send | yes | mandatory | no
recv | no | mandatory | no
Since the "recv" connectivity precondition (from B's point of view)
is still not satisfied, session establishment remains suspended.
SDP3: When A receives the answer SDP, A notes that confirmation was
requested for B's "recv" connectivity precondition, which is the
"send" precondition from A's point of view. A performs a successful
send connectivity check to B by sending an ICE connectivity check to
B and receiving the corresponding response. A's local status table
becomes:
Direction | Current | Desired Strength | Confirm
-----------+----------+------------------+----------
send | yes | mandatory | yes
recv | no | mandatory | no
Since B asked for confirmation about the "send" connectivity (from
A's point of view), A now sends an UPDATE (5) to B to confirm the
connectivity from A to B:
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a=ice-pwd:asd88fgpdd777uzjYhagZg
a=ice-ufrag:8hhY
m=audio 20000 RTP/AVP 0
c=IN IP4 192.0.2.1
a=curr:conn e2e send
a=des:conn mandatory e2e sendrecv
a=candidate:1 1 UDP 2130706431 192.0.2.1 20000 typ host
B has both send and recv connectivity confirmed at this point and the
session can continue.
7. Security Considerations
General security considerations for preconditions are discussed in
RFC 3312 [RFC3312] and RFC 4032 [RFC4032]. As discussed in RFC 4032
[RFC4032], it is strongly RECOMMENDED that integrity protection be
applied to the SDP session descriptions. S/MIME [RFC3853]
protection, as described in RFC 3261 [RFC3261]. When the user agent
provides identity services (rather than the proxy server), the SIP
identity mechanism specified in RFC 4474 [RFC4474] provides an
alternative end-to-end integrity protection. Additionally, the
following security issues relate specifically to connectivity
preconditions.
Connectivity preconditions rely on mechanisms beyond SDP such as TCP
[RFC0793] connection establishment, or ICE connectivity checks
[I-D.ietf-mmusic-ice] to establish and verify connectivity between an
offerer and an answerer. An attacker that prevents those mechanisms
from succeeding (e.g., by keeping ICE connectivity checks from
arriving to their destination) can prevent media sessions from being
established. While this attack relates to connectivity
preconditions, it is actually an attack against the connection
establishment mechanisms used by the endpoints. This attack can be
performed in the presence or in the absence of connectivity
preconditions. In their presence, the whole session setup will be
disrupted. In their absence, only the establishment of the
particular stream under attack will be disrupted. This specification
does not provide any mechanism against attackers able to block
traffic between the endpoints involved in the session because such an
attacker will always be able to launch DoS (Denial of Service)
attacks.
Instead of blocking the connectivity checks, the attacker can
generate forged connectivity checks that would cause the endpoints to
assume that there was connectivity when there was actually no
connectivity. This attack would result in a poor user's experience
because the session would be established without all the media
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streams being ready. The same attack can be used, regardless of
whether or not connectivity preconditions are used, to attempt to
hijack a connection. The forged connectivity checks would trick the
endpoints into sending media to the wrong direction. To prevent
these attacks, it is RECOMMENDED that the mechanisms used to check
connectivity are adequately secured by message authentication and
integrity protection. For example, Section 2.5 of
[I-D.ietf-mmusic-ice] discusses how message integrity and data origin
authentication are implemented in ICE connectivity checks.
8. IANA Considerations
IANA is hereby requested to register a new precondition type under
the Precondition Types used with SIP subregistry, which is located
under the Session Initiation Protocol (SIP) Parameters registry.
Precondition-Type Description Reference
----------------- ----------------------------------- ---------
conn Connectivity precondition [RFCxxxx]
[Note to the RFC Editor: replace RFCxxxx with the number assigned to
this RFC.]
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3312] Camarillo, G., Marshall, W., and J. Rosenberg,
"Integration of Resource Management and Session Initiation
Protocol (SIP)", RFC 3312, October 2002.
[RFC3853] Peterson, J., "S/MIME Advanced Encryption Standard (AES)
Requirement for the Session Initiation Protocol (SIP)",
RFC 3853, July 2004.
[RFC4032] Camarillo, G. and P. Kyzivat, "Update to the Session
Initiation Protocol (SIP) Preconditions Framework",
Andreasen, et al. Expires September 5, 2010 [Page 16]
Internet-Draft Connectivity Precondition March 2010
RFC 4032, March 2005.
[RFC4474] Peterson, J. and C. Jennings, "Enhancements for
Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 4474, August 2006.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC5027] Andreasen, F. and D. Wing, "Security Preconditions for
Session Description Protocol (SDP) Media Streams",
RFC 5027, October 2007.
[I-D.ietf-mmusic-ice]
Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols",
draft-ietf-mmusic-ice-19 (work in progress), October 2007.
9.2. Informative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981.
[RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in
the Session Description Protocol (SDP)", RFC 4145,
September 2005.
[RFC4960] Stewart, R., "Stream Control Transmission Protocol",
RFC 4960, September 2007.
[RFC5109] Li, A., "RTP Payload Format for Generic Forward Error
Correction", RFC 5109, December 2007.
[I-D.ietf-mmusic-ice-tcp]
Perreault, S. and J. Rosenberg, "TCP Candidates with
Interactive Connectivity Establishment (ICE)",
draft-ietf-mmusic-ice-tcp-08 (work in progress),
October 2009.
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Authors' Addresses
Flemming Andreasen
Cisco Systems, Inc.
499 Thornall Street, 8th Floor
Edison, NJ 08837
USA
Email: fandreas@cisco.com
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Gonzalo.Camarillo@ericsson.com
David Oran
Cisco Systems, Inc.
7 Ladyslipper Lane
Acton, MA 01720
USA
Email: oran@cisco.com
Dan Wing
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
USA
Email: dwing@cisco.com
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