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Versions: (draft-johansson-avt-rtcp-avpf-non-compound)
00 01 02 03 04 05 06 07 08 09 RFC 5506
Network Working Group I. Johansson
Internet-Draft M. Westerlund
Intended status: Standards Track Ericsson AB
Expires: November 21, 2008 May 20, 2008
Support for reduced size RTCP, opportunities and consequences
draft-ietf-avt-rtcp-non-compound-05
Status of this Memo
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This Internet-Draft will expire on November 21, 2008.
Abstract
This memo discusses benefits and issues that arise when allowing RTCP
packets to be transmitted with reduced size such that mandatory
report types according to the rules outlined in RFC3550 are removed.
Based on that analysis this memo proposes changes to the rules to
allow feedback messages to be sent as reduced size RTCP packets when
using the RTP AVPF profile (RFC 4585) under certain conditions.
Requirements Language
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
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Table of Contents
1. Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. RTCP Compound Packets . . . . . . . . . . . . . . . . . . . . 4
4. Benefits with reduced size RTCP . . . . . . . . . . . . . . . 5
4.1. Low birate links . . . . . . . . . . . . . . . . . . . . . 5
4.2. Higher bitrates . . . . . . . . . . . . . . . . . . . . . 6
4.3. Both high and low bitrate links . . . . . . . . . . . . . 6
5. Use cases for reduced size RTCP . . . . . . . . . . . . . . . 7
5.1. Control plane signaling . . . . . . . . . . . . . . . . . 7
5.2. Codec control signaling . . . . . . . . . . . . . . . . . 7
5.3. Feedback . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.4. Status reports . . . . . . . . . . . . . . . . . . . . . . 8
6. Issues with reduced size RTCP . . . . . . . . . . . . . . . . 8
6.1. Middle boxes . . . . . . . . . . . . . . . . . . . . . . . 8
6.2. Packet Validation . . . . . . . . . . . . . . . . . . . . 8
6.2.1. Old RTCP Receivers . . . . . . . . . . . . . . . . . . 9
6.2.2. Weakened Packet Validation . . . . . . . . . . . . . . 9
6.2.3. Bandwidth considerations . . . . . . . . . . . . . . . 9
6.2.4. Computation of avg_rtcp_size . . . . . . . . . . . . . 10
6.3. Encryption/authentication . . . . . . . . . . . . . . . . 10
6.4. RTP and RTCP multiplex on the same port . . . . . . . . . 10
6.5. Header compression . . . . . . . . . . . . . . . . . . . . 10
7. Rules and guidelines for non-compound packets in AVPF . . . . 10
7.1. Definition of non-compound RTCP . . . . . . . . . . . . . 11
7.2. Algorithm considerations . . . . . . . . . . . . . . . . . 11
7.2.1. Verification of delivery . . . . . . . . . . . . . . . 11
7.2.2. Single vs multiple RTCP in a reduced size RTCP . . . . 12
7.2.3. Enforcing compound RTCP . . . . . . . . . . . . . . . 12
7.2.4. Immediate mode . . . . . . . . . . . . . . . . . . . . 12
7.3. SDP Signalling Attribute . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . 13
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1. Normative References . . . . . . . . . . . . . . . . . . . 14
11.2. Informative References . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . . . 17
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1. Glossary
The naming convention for RTCP is often confusing. Below a list of
RTCP terms and what they mean. See also section 6.1 in [RFC3550] and
section 3.1 in [RFC4585] for details.
o RTCP packet: Can be of different types, contains a fixed header
part followed by structured elements depending on RTCP packet
type.
o Lower layer datagram: Can be interpreted as the UDP payload, it
may however, depending on the transport be TCP or DCCP payload or
something else. Synonymous to "underlying protocol" defined in 3
in [RFC3550].
o Compound RTCP: A collection of two or more RTCP packets. A
compound RTCP is transmitted in a lower layer datagram. It must
contain at least an RTCP RR or SR packet and a SDES packet with
the CNAME item. Often "compound" is left out, the interpretation
of the word RTCP is therefore dependent on the context.
o Minimal compound RTCP: A compound RTCP that contains the RTCP RR
or SR packets and the SDES packet with the CNAME item with a
specified ordering.
o (Full) compound RTCP: A compound RTCP that conforms to the
requirements on minimal compound RTCP packets and contains more
RTCP packets.
o Reduced size RTCP: May contain one or more RTCP packets but does
not follow the minimal compound RTCP rules defined in section 6.1
in [RFC3550].
2. Introduction
In RTP [RFC3550] it is currently mandatory to always use RTCP
compound packets containing at least Sender Reports or Receiver
reports, and a SDES packet containing at least the CNAME item. There
are good reasons for this as discussed below (see Section 3).
However this do result in that the minimal RTCP packets are quite
large.
The RTP profile AVPF [RFC4585] specifies new RTCP packet types for
feedback messages. Some of these feedback messages would benefit
from being transmitted with minimal delay and AVPF do provide some
mechanism to enable this.
However for environments with low-bitrate links this still consumes
quite a large amount of resources and introduces extra delay in the
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time it takes to completely send the compound packet in the network.
There are also other benefits as discussed in Section 4.
The use of reduced size RTCP is not without issues. This is
discussed in Section 6. These issues needs to be considered and are
part of the motivation for this document.
In addition this document proposes how AVPF could be updated to allow
the transmission of reduced size RTCP in a way that would not
substantially affect the mechanisms that compound packets provide.
The connection to AVPF is motivated by the fact that reduced size
RTCP is mainly intended for event driven feedback purposes and that
the AVPF early and immediate modes make this possible.
3. RTCP Compound Packets
Section 6.1 in [RFC3550] specifies that an RTCP packet must be sent
as a compound RTCP consisting of at least two individual RTCP, first
an Sender Report (SR) or Receiver Report (RR), followed by additional
packets including a mandatory SDES packet containing a CNAME Item for
the transmitting source identifier (SSRC). Below is a short
description what these RTCP packet types are used for.
1. The sender and receiver reports (see Section 6.4 of [RFC3550])
provides the RTP session participant with the Sender Source
Identifier (SSRC) of all RTCP senders. Having all participants
send these packets periodically allows everyone to determine the
current number of participants. This information is used in the
transmission scheduling algorithm. Thus this is particularly
important for new participants so that they quickly can establish
a good estimate of the group size. Failure to do this would
result in RTCP senders consuming too much bandwidth.
2. The sender and receiver reports contain some basic statistics
usable for monitoring of the transport and thus enable
adaptation. These reports become more useful if sent regularly
as the receiver of a report can perform analysis to find trends
between the individual reports. When used for media transmission
adaptation the information become more useful the more frequently
it is received, at least until one report per round-trip time
(RTT) is achieved. Therefore there are, in most cases, no reason
to not include the sender or receiver report in all RTCP packets.
3. The CNAME SDES item (See Section 6.5.1 of [RFC3550]) exists to
allow receivers to determine which media flows that should be
synchronized with each other between different RTP sessions
carrying different media types. Thus it is important to quickly
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receive this for each media sender in the session when joining an
RTP session.
4. Sender Reports (SR) is used in combination with the above SDES
CNAME mechanism to synchronize multiple RTP streams, such as
audio and video. After having determined which media streams
should be synchronized using the CNAME field, the receiver uses
the Sender Report's NTP and RTP timestamp fields to establish
synchronization.
Reviewing the above it is obvious that both SR/RR and the CNAME are
very important for new session participants to be able to utilize any
received media and to avoid flooding the network with RTCP reports.
In addition, if not sent regularly the dynamic nature of the
information provided would make it less and less useful.
4. Benefits with reduced size RTCP
As mentioned in the introduction, most advantages of using reduced
size RTCP packets exists in cases when the available RTCP bitrate is
limited. This because they can become substantially smaller than
compound packets. A compound packet is forced to contain both an RR
or an SR and the CNAME SDES item. The RR containing a report block
for a single source is 32 bytes, an SR is 52 bytes. Both may be
larger if they contain report blocks for multiple sources. The SDES
packet containing a CNAME item will be 10 bytes plus the CNAME string
length. Here it is reasonable that the CNAME string is at least 10
bytes to get a decent collision resistance. If the recommended form
of user@host is used, then most strings will be longer than 20
characters. Thus a reduced size RTCP can become at least 70-80 bytes
smaller than the compound packet.
The following benefits exist for reduced size RTCP,
4.1. Low birate links
For low bitrate links the benefits are as follows.
o For links where the packet loss rate grows with the packet size,
smaller packets are be less likely to be dropped. An example of
such links are radio links. In the cellular world there exist
links that are optimized to handle RTP packets sized for carrying
compressed speech. This increases the capacity and coverage for
voice services in a given wireless network. Minimal compound RTCP
packets are commonly 2-3 times the size of a RTP packet carrying
compressed speech. If the speech packet over such a bearer has a
packet loss probability of p, then the RTCP packet will experience
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a loss probability of 1-(1-p)^x where x is the number of fragments
the compound packet will be split on the link layer, i.e. commonly
into 2 or 3 fragments.
o Shorter serialization time, i.e the time it takes the link to
transmit the packet. For slower links this time can be
substantial. For example transmitting 120 bytes over an link
interface capable of 30 kbps takes 32 milliseconds (ms) assuming
uniform transmission rate.
In cases when reduced size RTCP carry important and time sensitive
feedback, both shorter serialization time and the lower loss
probability are important to enable the best possible functionality.
Having a packet loss rate that is much higher for the feedback
packets compared to media packets hurts when trying to perform media
adaptation, to for example handle the changed performance present at
the cell border in a cellular system.
4.2. Higher bitrates
For high bitrate applications there is usually no problem to supply
RTCP with sufficient bitrates. When using AVPF one can use the "trr-
int" parameter to restrict the regular reporting interval to
approximately once per RTT or less often. As in most cases there is
little reason to provide with regular reports of higher density than
this. Any additional bandwidth can then be used for feedback
messages. The benefit of reduced size RTCP in this case is limited,
but exists. One typical example is video using generic NACK in cases
where the RTT is low. Using reduced size RTCP would reduce the total
amount of bits used for RTCP. This is primarily applicable if the
number of reports is large. This would also result in lower
processing delay and less complexity for the feedback packets as they
do not need to query the RTCP database to construct the right
messages.
As message size is generally a smaller issue at higher bitrates, it
is also possible to transmit multiple RTCP in each lower layer
datagram in these cases. The motivation behind reduced size RTCP in
this case is not size, rather it is to avoid the extra overhead
caused by inclusion of the SR/RR and SDES CNAME items in each
transmitted RTCP.
4.3. Both high and low bitrate links
Independently of the link type there are additional benefits with
sending feedback in small reduced size RTCP.
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o Applications that use RTCP AVPF in early or immediate mode to send
frequent event driven feedback. Under these circumstances, the
risk that the RTCP bandwidth becomes too high during periods of
heavy adaptation feedback signaling is reduced.
o In cases when regular feedback is needed, such as the profile
under development for TCP friendly rate control (TFRC) for RTP
[I-D.ietf-avt-tfrc-profile], the size of compound RTCP can result
in very high bandwidth requirements if the round trip time is
short. For this particular application reduced size RTCP gives a
very substantial improvement.
5. Use cases for reduced size RTCP
Below are listed a few use cases for reduced size RTCP. The current
use of reduced size RTCP is very application specific. A general
definition of the use of it for e.g control plane or codec control
signaling would probably need to be specified in the IETF.
5.1. Control plane signaling
Open Mobile Alliance (OMA) Push-to-talk over Cellular (PoC) [OMA-PoC]
makes use of reduced size RTCP when transmitting certain events. The
OMA POC service is primarily used over cellular links capable of IP
transport, such as the GSM GPRS.
5.2. Codec control signaling
Examples of codec control usage for reduced size RTCP are found in
[3GPP-MTSI].
Another example that can be used with reduced size RTCP is e.g TMMBR
messages as specified in [RFC5104] which signal a request for a
change in codec bitrate. The benefit of its use for these messages
is that in bad channel conditions as they are much more likely to be
successfully received than larger compound RTCP. This is critical as
these messages are likely to occur when channel conditions are poor.
5.3. Feedback
An example of a feedback scenario that would benefit from reduced
size RTCP is Video streams with generic NACK. In cases where the RTT
is shorter than the receiver buffer depth, generic NACK can be used
to request retransmission of missing packets, thus improving playout
quality considerably. If the generic NACK packets are transmitted as
reduced size RTCP, the bandwidth requirement for RTCP will be
minimal, enabling more frequent feedback. Like in the Codec control
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case it is important that these packets can be transmitted with as
little delay as possible.
Another interesting use for reduced size RTCP is in cases when
regular feedback is needed, as described in Section 4.3.
5.4. Status reports
One proposed idea is to transmit small measurement or status reports
in reduced size RTCP, and to be able to split the minimal compound
RTCP and transmit the individual RTCP separately. The status reports
can be used either by the endpoints or by other network monitoring
boxes in the network.
The benefit is that with some radio access technologies small packets
are more robust to poor radio conditions than large packets.
Additionally, with small (report) packets there is a smaller risk
that the report packets will affect the channel that they report
upon.
Another benefit is that it is, with reduced size RTCP, possible to
allow e.g anonymous status reporting to be transmitted unencrypted.
Something that may be beneficial for e.g network monitoring purposes.
6. Issues with reduced size RTCP
This section describes the known issues with reduced size RTCP and
also a brief analysis.
6.1. Middle boxes
Middle boxes in the network may discard RTCP that do not follow the
rules outlined in section 6.1 of RFC3550. Newer report types may be
interpreted as unknown by the middle box. For instance if the
payload type number is 207 instead of 200 or 201 it may be treated as
unknown. The effect of this might for instance be that compound RTCP
would get through while the reduced size RTCP would be lost.
Verification of the delivery of reduced size RTCP is discussed in
Section 7.2.1.
6.2. Packet Validation
A reduced size RTCP will be discarded by the packet validation code
in Appendix A of [RFC3550]. This has several impacts as described in
the following sub sections.
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6.2.1. Old RTCP Receivers
Any RTCP receiver without updated packet validation code will discard
the reduced size RTCP which means that the receiver will not see e.g
the contained feedback messages. The effect of this depends on the
type of feedback message and the role of the receiver. For example
this may cause complete function loss in the case of attempting to
use a reduced size NACK message (see Section 6.2.1 of [RFC4585]) to
non updated media sender in a session using the retransmission scheme
defined by [RFC4588].
This type of discarding would also effect the feedback suppression
defined in AVPF. The result would be a partitioning of the receivers
within the session between old ones only seeing the compound RTCP
feedback messages and the newer ones seeing both. Where the old ones
may send feedback messages for events already reported on in reduced
size RTCP.
6.2.2. Weakened Packet Validation
The packet validation code needs to be rewritten to accept reduced
size RTCP. This in particular affects section 9.1 in [RFC3550] in
the sense that the header verification must take into account that
the payload type numbers for the (first) RTCP in the lower layer
datagram may differ from 200 or 201 (SR or RR).
One potential effect of this change is much weaker validation that
received packets actually are RTCP, and not packets of some other
type being wrongly delivered. Thus some consideration should be done
to ensure the best possible validation is available. For example
restricting reduced size RTCP to contain only some specific RTCP
packet types, that is preferably signalled on a session basis.
6.2.3. Bandwidth considerations
The discarding of reduced size RTCP would effect the RTCP
transmission calculation in the following way: the avg_rtcp_size
value would become larger than for RTP receivers that exclude the
reduced size RTCP in this calculation (assuming that reduced size
RTCP are smaller than compound ones). Therefore these senders would
under-utilize the available bitrate and send with a longer interval
than updated receivers. For most sessions this should not be an
issue. However for sessions with a large portion of reduced size
RTCP may result in that the updated receivers time out non-updated
senders prematurely. A solution to this is presented in Section 7.2.
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6.2.4. Computation of avg_rtcp_size
Long intervals between compound RTCP and many reduced size RTCP in
between may lead to a computation of a value for avg_rtcp_size that
varies greatly over time. This is discussed more in Section 7.2.
6.3. Encryption/authentication
SRTP presents a problem for reduced size RTCP. Section 3.4 in
[RFC3711] states "SRTCP MUST be given packets according to that
requirement in the sense that the first part MUST be a sender report
or a receiver report".
However the same text also states that the encryption prefix that is
present in the receiver and sender reports should not be used by
SRTP. The conclusion is therefore that it is possible to use reduced
size RTCP with SRTP.
6.4. RTP and RTCP multiplex on the same port
In applications which multiplex RTP and RTCP on the same port, as
defined in [I-D.ietf-avt-rtp-and-rtcp-mux], care must be taken to
ensure that the de-multiplexing is done properly even though RTCP are
reduced size.
6.5. Header compression
Two issues are related to header compression:
o Payload type number identification: The RoHC header compression
algorithm [RFC3095] needs to create different compression contexts
for RTP and RTCP for optimum performance. If RTP and RTCP are
multiplexed on the same port the classification may be based on
payload type numbers. The classification algorithm must here
acknowledge the fact that the payload type number for (the first)
RTCP may differ from 200 or 201.
o Compression of RTCP: No IETF defined header compression method
compress RTCP, however if such methods are developed in the
future, these methods must take reduced size RTCP in account.
7. Rules and guidelines for non-compound packets in AVPF
Based on the above analysis it seems feasible to allow transmission
of reduced size RTCP under some restrictions.
First of all it is important that compound RTCP are transmitted at
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regular intervals to ensure that the feedback reporting works. The
tracking of session size and number of participants is also important
as this ensures that the RTCP bandwidth remain bounded independent of
the number of session participants.
As the compound RTCP are also used to establish and maintain
synchronization between media, any newly joining participant in a
session would need to receive compound RTCP from the media sender(s).
In summary the regular usage of compound RTCP must be maintained
throughout the complete session. Thus reduced size RTCP should be
restricted to be used as extra RTCP (e.g feedback) sent in cases when
a regular compound RTCP would not have been sent.
The usage of reduced size RTCP SHALL only be done in RTP sessions
operating in AVPF [RFC4585] Early or Immediate mode. Reduced size
RTCP SHALL NOT be sent until at least one compound RTCP has been
sent. In Immediate mode all feedback messages MAY be sent as reduced
size RTCP. In early mode a feedback message scheduled for
transmission as an Early RTCP, i.e not a Regular RTCP, MAY be sent as
reduced size RTCP. All RTCP that are scheduled for transmission as
Regular RTCP SHALL be sent as (full) compound RTCP as indicated by
AVPF [RFC4585].
7.1. Definition of non-compound RTCP
A reduced size RTCP deviates from the rules regarding (minimal)
compound RTCP given in RFC3550/4585 in the aspect that they don't
contain both the mandatory elements SR/RR and SDES-CNAME. The
definition does not make any distinction based on size. This means
that it is possible to transmit multiple RTCP in one lower layer
datagram.
7.2. Algorithm considerations
7.2.1. Verification of delivery
If an application is to use reduced size RTCP it is important to
verify that they actually reach the session participants. As
outlined above in Section 6.1 and Section 6.2 packets may be
discarded along the path or in the end-point.
The end-points can be resolved by introducing signaling that informs
if all session participants are capable of reduced size RTCP.
The middle box issue is more difficult and here one will be required
to use heuristics to determine if the reduced size RTCP are delivered
or not. However in many cases the feedback messages sent using
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reduced size RTCP will result in either explicit or implicit
indications that they have been received. Example of such are the
RTP retransmission [RFC4588] that result from a NACK message
[RFC4585], the Temporary Maximum Media Bitrate Notification message
resulting from a Temporary Maximum Media Bitrate Request [RFC5104],
or the presence of a Decoder Refresh Point [RFC5104] in the video
media stream resulting from the Full Intra Request sent.
An algorithm to detect consistent failure of delivery of reduced size
RTCP must be used by any application using it. The details of this
algorithm is application dependent and therefore outside the scope of
this document.
A method to detect if reduced size RTCP are discarded is to send a
single SR packet in a lower layer datagram, then check that the
timestamp is echoed back in the corresponding RR packet. This
verification method is not completely safe however as it SR is still
one of the expected packet types.
If the verification fails it is strongly RECOMMENDED that only
compound RTCP according to the rules outlined in RFC3550 is
transmitted.
7.2.2. Single vs multiple RTCP in a reduced size RTCP
The result of the definition in Section 7.1 may be that the resulting
size of reduced size RTCP can become larger than a normal compound
RTCP. For applications that use access types that are sensitive to
packet size (see Section 4.1) it is strongly RECOMMENDED that the use
of reduced size RTCP is limited to the transmission of single RTCP in
each lower layer datagram.
The methods to determine the need for this is outside the scope of
this draft.
7.2.3. Enforcing compound RTCP
As discussed earlier it is important that the transmission of
compound RTCP occurs at regular intervals. However, this will occur
as long as the RTCP senders follow the AVPF scheduling algorithm
defined in Section 3.5 in [RFC4585]. This as all regular RTCP must
be full compound RTCP. Note that also in immediate mode is there a
requirement on sending regular RTCP.
7.2.4. Immediate mode
Section 3.3 in RFC4585 gives the option to use AVPF Immediate mode as
long as the groupsize is below a certain limit. As transmission
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using reduced size RTCP may become reduce the bandwidth demand it
opens up for a more liberal use of immediate mode.
7.3. SDP Signalling Attribute
We request to define the "a=rtcp-rsize" [RFC4566] attribute to
indicate if the session participant is capable of supporting reduced
size RTCP. It is a required that a participant that proposes the use
of reduced size RTCP itself supports the reception of reduced size
RTCP.
An offering client that wish to use reduced size RTCP MUST include
the attribute "a=rtcp-rsize" in the SDP offer. If "a=rtcp-rsize" is
present in the offer SDP, the answerer that supports reduced size
RTCP and wish to use it SHALL include the "a=rtcp-rsize" attribute in
the answer.
8. IANA Considerations
Following the guidelines in [RFC4566], the IANA is requested to
register one new SDP attribute:
o Contact name, email address and telephone number: Authors of
RFCXXXX
o Attribute-name: rtcp-rsize
o Long-form attribute name: Reduced size RTCP
o Type of attribute: media-level
o Subject to charset: no
This attribute defines the support for reduced size RTCP, i.e the
possibility to transmit RTCP that does not conform to the rules for
compund RTCP defined in RFC3550. It is a property attribute, which
does not take a value.
Note to RFC Editor: please replace "RFC XXXX" above with the RFC
number of this memo, and remove this note.
9. Security Considerations
The security considerations of RTP [RFC3550] and AVPF [RFC4585] will
apply also to reduced size RTCP. The reduction in validation
strength for received packets on the RTCP port may result in a higher
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degree of acceptance of spurious data as real RTCP. This
vulnerability can mostly be addressed by usage of any security
mechanism that provide authentication, one example such mechanism is
SRTP [RFC3711].
10. Acknowledgements
The authors would like to thank all the people who gave feedback on
this document.
This document also contain some text copied from [RFC3550],
[RFC4585]and [RFC3711]. We take the opportunity to thank the authors
of said documents.
11. References
11.1. Normative References
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
"Extended RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
July 2006.
11.2. Informative References
[3GPP-MTSI]
3GPP, "Specification : 3GPP TS 26.114 (v7.4.0), http://
www.3gpp.org/ftp/Specs/archive/26_series/26.114/
26114-740.zip", March 2007.
[I-D.ietf-avt-rtp-and-rtcp-mux]
Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
Control Packets on a Single Port",
draft-ietf-avt-rtp-and-rtcp-mux-07 (work in progress),
August 2007.
[I-D.ietf-avt-tfrc-profile]
Gharai, L., "RTP with TCP Friendly Rate Control",
draft-ietf-avt-tfrc-profile-10 (work in progress),
July 2007.
[OMA-PoC] Open Mobile Alliance, "Specification : Push to talk Over
Johansson & Westerlund Expires November 21, 2008 [Page 14]
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Cellular User Plane, http://www.openmobilealliance.org/
release_program/docs/PoC/V1_0_1-20061128-A/
OMA-TS-PoC-UserPlane-V1_0_1-20061128-A.pdf",
November 2006.
[RFC3095] Bormann, C., Burmeister, C., Degermark, M., Fukushima, H.,
Hannu, H., Jonsson, L-E., Hakenberg, R., Koren, T., Le,
K., Liu, Z., Martensson, A., Miyazaki, A., Svanbro, K.,
Wiebke, T., Yoshimura, T., and H. Zheng, "RObust Header
Compression (ROHC): Framework and four profiles: RTP, UDP,
ESP, and uncompressed", RFC 3095, July 2001.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
Hakenberg, "RTP Retransmission Payload Format", RFC 4588,
July 2006.
[RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman,
"Codec Control Messages in the RTP Audio-Visual Profile
with Feedback (AVPF)", RFC 5104, February 2008.
Authors' Addresses
Ingemar Johansson
Ericsson AB
Laboratoriegrand 11
SE-971 28 Lulea
SWEDEN
Phone: +46 73 0783289
Email: ingemar.s.johansson@ericsson.com
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Magnus Westerlund
Ericsson AB
Torshamnsgatan 21-23
SE-164 83 Stockholm
SWEDEN
Phone: +46 8 7190000
Email: magnus.westerlund (AT) ericsson.com
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