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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: August 28, 2008 Feb 25, 2008
Support for non-compound RTCP, opportunities and consequences
draft-ietf-avt-rtcp-non-compound-03
Status of this Memo
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
This memo discusses benefits and issues that arise when allowing RTCP
packets to be transmitted as non-compound packets, i.e not follow the
rules of RFC 3550. Based on that analysis this memo proposes changes
to the rules to allow feedback messages to be sent as non-compound
RTCP packets when using the RTP AVPF profile (RFC 4585) under certain
conditions.
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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
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. RTCP Compound Packets . . . . . . . . . . . . . . . . . . . . 3
3. Benefits with non-compound packets . . . . . . . . . . . . . . 4
4. Issues with non-compound RTCP packets . . . . . . . . . . . . 6
4.1. Middle boxes . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Packet Validation . . . . . . . . . . . . . . . . . . . . 6
4.2.1. Old RTCP Receivers . . . . . . . . . . . . . . . . . . 6
4.2.2. Weakened Packet Validation . . . . . . . . . . . . . . 7
4.2.3. Bandwidth consideration . . . . . . . . . . . . . . . 7
4.2.4. Computation of avg_rtcp_size . . . . . . . . . . . . . 7
4.3. Header compression . . . . . . . . . . . . . . . . . . . . 7
4.4. RTP and RTCP multiplex on the same port . . . . . . . . . 7
4.5. Encryption/authentication . . . . . . . . . . . . . . . . 8
5. Use cases for non-compound RTCP . . . . . . . . . . . . . . . 8
5.1. Control plane signaling . . . . . . . . . . . . . . . . . 8
5.2. Codec control signaling . . . . . . . . . . . . . . . . . 8
5.3. Feedback . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.4. Status reports . . . . . . . . . . . . . . . . . . . . . . 9
6. Rules and guidelines for non-compound packets in AVPF . . . . 10
6.1. Verification of the delivery of non-compound packets . . . 10
6.2. Algorithm modifications . . . . . . . . . . . . . . . . . 11
6.2.1. Distinction between compound and non-compound RTCP . . 11
6.2.2. Modified bandwidth algorithms . . . . . . . . . . . . 12
6.2.3. Immediate mode . . . . . . . . . . . . . . . . . . . . 12
6.2.4. Enforcing compound RTCP . . . . . . . . . . . . . . . 12
6.3. Open issues . . . . . . . . . . . . . . . . . . . . . . . 13
6.4. SDP Signalling Attribute . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Normative References . . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . . . 16
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1. 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 2).
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 large amount of resources and
introduce extra delay in the time it takes to completely send the
compound packet in the network. There are also other benefits as
discussed in Section 3.
The use of non-compound packets is not without issues. This is
discussed in Section 4. 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 non-compound packets in a way that would not
substantially affect the mechanisms that compound packets provide.
The connection to AVPF is motivated by the fact that non-compound
RTCP is mainly intended for event driven feedback purposes and that
the AVPF early and immediate modes make this possible.
2. RTCP Compound Packets
Section 6.1 in RFC3550 [RFC3550] specifies that an RTCP packet must
be sent in a compound packet consisting of at least two individual
packets, 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). Lets examine what these RTCP packet types are used for.
1. The sender and receiver reports (see Section 6.4 of RFC 3550
[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 to much bandwidth.
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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 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 RFC 3550 [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 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.
3. Benefits with non-compound packets
As mentioned in the introduction, most advantages of using non-
compound packets exists in cases when the available RTCP bit-rate is
limited. This because non-compound packets will be 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. And if the recommended form of user@host is used, then
most strings will be longer than 20 characters. Thus a non-compound
packets can become at least 70-80 bytes smaller than the compound
packet.
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The following benefits exist for the smaller non-compound packets:
1. 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.
2. For links where the packet loss rate grows with the packet size,
smaller packets will 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, which increases the capacity and coverage for
voice services in a given wireless network. Minimum sized
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 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.
3. Independently of the link type there are additional benefits with
sending feedback in small non-compound RTCP. One such example is
applications that use RTCP AVPF in early or immediate mode to
send frequent event driven feedback. Under these circumstances
non-compound RTCP reduces the risk that the RTCP bandwidth
becomes too high during periods of heavy adaptation feedback
signaling.
4. 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 non-compound RTCP gives a
very substantial improvement.
In cases when non-compound packets 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 cellular system.
For high bit-rate applications there is usually no problem of
supplying RTCP with sufficient bit-rates. 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
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cases there are no reasons to provide regular reports with higher
density than this. Any additional bandwidth can then be used for
feedback messages. The benefit of non-compound packets in this case
is limited, but exists. One typical example is video using generic
NACK in cases where the RTT is low. Using non-compound packets would
reduce the total amount of bits used for RTCP. This is primarily
applicable if the number of non-compound packets 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.
4. Issues with non-compound RTCP packets
This section describes some of the known issues with non-compound
RTCP packets
4.1. Middle boxes
Middle boxes in the network may discard RTCP packets that do not
follow the rules outlined in section 6.1 of RFC3550. The effect of
this might for instance be that compound RTCP packets would get
through while the non-compound feedback packets would be lost.
4.2. Packet Validation
A non-compound packet will be discarded by the packet validation code
in Appendix A of RFC 3550 [RFC3550]. This has several impacts as
described in the following sub sections.
4.2.1. Old RTCP Receivers
Any RTCP receiver without updated packet validation code will discard
the non-compound packets. Thus these receivers will not see the
feedback contained in the these non-compound packets. 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 non-compound NACK message (see Section
6.2.1 of RFC 4585 [RFC4585]) to non updated media sender in a session
using the retransmission scheme defined by RFC 4588 [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 non-
compound packets.
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4.2.2. Weakened Packet Validation
The packet validation code needs to be rewritten to accept non-
compound packets. One potential effect of this change is much weaker
validation that received packets actually are RTCP packets, 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 non-compound packets to
contain only some specific RTCP packet types, that is preferably
signalled on a session basis. A solution to this is presented in
Section 6.2
4.2.3. Bandwidth consideration
The discarding of non-compound RTCP packets 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
non-compound in this calculation (assuming that non-compound packets
are smaller than compound ones). Therefore these senders would
under-utilize the available bit-rate 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 non-compound
packets may result in that the updated receivers time out non-updated
senders prematurely. A solution to this is presented in Section 6.2.
4.2.4. Computation of avg_rtcp_size
Long intervals between compound RTCP packets and many non-compound
RTCP packets 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 6.2.
4.3. Header compression
The classifiers for header compression algorithms such as RoHC
[RFC3095] and its profiles must be aware of the fact that, with the
proposed non-compound RTCP packets, the first RTCP packet type might
differ from 200 or 201. Otherwise they would likely wrongly classify
the packets as something else than RTCP. However, as no header
compression technology defined in IETF compresses RTCP, this should
have no real impact.
4.4. 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
packets are non-compound.
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4.5. Encryption/authentication
SRTP presents a problem for non-compound 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 non-
compound RTCP with SRTP.
Non-compound RTCP also 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 packet may differ from 200 or 201
(SR or RR).
5. Use cases for non-compound RTCP
Below are listed a few use cases for non-compound RTCP. It is worth
noting here that the current uses of non-compound RTCP are thoroughly
specified in other standardization bodies and are limited to specific
services such as PoC or 3GPP-MTSI. A general definition of the use
of non-compound RTCP for e.g control plane or codec control signaling
would probably need to be specified within the IETF.
5.1. Control plane signaling
Open Mobile Alliance (OMA) Push-to-talk over Cellular (PoC) [OMA-PoC]
makes use of non-compound packets 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 non-compound RTCP are found in
[3GPP-MTSI].
Another example that can be used with non-compound RTCP is e.g TMMBR
messages as specified in [I-D.ietf-avt-avpf-ccm] which signal a
request for a change in codec bitrate. The benefit of non-compound
RTCP for these messages is that in bad channel conditions, a non-
compound RTCP can be considerably more likely to be received than
larger compound RTCP messages. This is critical as these messages
predominantly occur when channel conditions are poor.
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5.3. Feedback
The feedback scenario is best presented as a Video stream 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 play out quality considerably. If
the generic NACK packets are transmitted as non-compound packets, the
bandwidth requirement for RTCP will be minimal, enabling more
frequent feedback. Like in the Codec control case it is important
that these packets can be transmitted with as little delay as
possible. The RTCP bandwidth reduction and transmission speed are
equally useful when retransmission is not used for loss recovery.
Another interesting use for non-compound RTCP is 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 for the feedback when the round trip time is short. For
this particular application non-compound RTCP may give a very
substantial improvement.
5.4. Status reports
One idea proposed is to transmit small measurement or status reports
in non-compound RTCP, and to be able to split the sub-packets of a
minimum compound RTCP and transmit them 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.
Even though this may be an interesting use case a few issues needs to
be considered.
o A risk exists that it opens up for a whole set of incompatible
metrics and reports devised in various standardization fora
leading to a potential interoperability problems.
o Middle boxes or third party network monitoring equipment may fail
to understand the new reports or even discard these new report
types.
o There may arise a need to verify that these "special" reports
reach the intended recipient in case middle boxes in the network
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discards unknown reports. In many cases it is difficult to verify
that for instance sender reports are received correctly, missing
SR may as well be an indication that the other endpoint has
terminated.
6. Rules and guidelines for non-compound packets in AVPF
Based on the above analysis it seems feasible to allow transmission
of non-compound RTCP under some restrictions. First of all it is
important that compound packets are regularly sent to ensure 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 packets also are used to establish the
synchronization, any newly joining participant in a session would
need to receive a compound packet from the media sender. In summary
the regular usage of compound packets must be maintained throughout
the complete session. Thus non-compound packets should be restricted
to be used as extra feedback packets sent in cases when a regular
compound packet would not have been sent.
The usage of non-compound RTCP packet SHALL only be done in RTP
sessions operating in AVPF [RFC4585] Early RTCP or Immediate feedback
mode. Non-compound packets SHALL NOT be sent until at least one
compound packet has been sent. In Immediate feedback mode all
feedback messages MAY be sent as non-compound packets. In early RTCP
mode a feedback message scheduled for transmission as an Early RTCP
packet, i.e not a Regular RTCP packet, MAY be sent as a non-compound
packet. All packets that scheduled for transmission as Regular RTCP
packets SHALL be sent as (full) compound RTCP packets as indicated by
AVPF [RFC4585].
6.1. Verification of the delivery of non-compound packets
If an application is to use non-compound packets it is important to
verify that they actually reaches the session participants. As
outlined above in Section 4.1 and Section 4.2 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 non-compound packets or not. The middle
box issue is more difficult and here one will be required to use
heuristics to determine if the non-compound packets are delivered or
not. However in many cases the feedback messages sent using non-
compound packets 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 Bit-rate Notification message
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resulting from a Temporary Maximum Media Bit-rate Request
[I-D.ietf-avt-avpf-ccm], or the presence of a Decoder Refresh Point
[I-D.ietf-avt-avpf-ccm] in the video media stream resulting from the
Full Intra Request sent.
A proposed algorithm to detect consistent failure of delivery of non-
compound packets needs to be written. The details of this algorithm
is application dependent and therefore outside the scope of this
document.
An optional method to detect if non-compound RTCP are discarded is to
send a non-compound SR packet, then check that the timestamp is
echoed back in the corresponding RR packet.
If the verification fails it is strongly RECOMMENDED that only
compound RTCP according to the rules outlined in RFC3550 is
transmitted.
6.2. Algorithm modifications
6.2.1. Distinction between compound and non-compound RTCP
One question that arise is how to distinguish between small (non-
compound) and large (compound) RTCP. A few alternatives:
o Payload type: A non-compound RTCP may have a (first) PT number
that differs from the PT numbers for SR or RR. This may be a weak
alternative as some interest to be able to split minimum compound
RTCP is expressed, see Status reports (Section 5.4). A possible
problem here is also that this distinction does not actually tell
the size of the RTCP.
o Fixed size, set in specification. For instance one may base the
distinction on the likely minimum size of a minimal compound RTCP.
Assuming that such a packet will contain at least an SR (32 bytes)
and a SDES CNAME (likely 16 bytes or more) one can conclude that
48 bytes (+IP/UDP overhead) is probably the smallest realistic
size of a compound RTCP.
o Fixed size, set in session setup : Some sessions may e.g use
RTCP-XR or some other RTCP reporting on occasions that may give
very large packet sizes, it may be desirable to adjust the
threshold
o Variable size: As non-compound RTCP is by definition RTCP that
does not follow the rules for compound RTCP as they are specified
in RFC3550, the size can be determined "on the fly".
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o Comparison against total UDP packet size: If the size of the first
RTCP packet is + possible SRTCP overhead is smaller than the UDP
packet size it is a compound RTCP. If the sizes match then it is
a non-compound RTCP. This method is an indication of the number
of RTCP packets in a given UDP payload, if 2 RTCP packets or more
then it is a compound RTCP.
Of the above alternatives the last one is the most straightforward
and simple. The exception is if one need to know if it is a non-
compound SRTCP without decrypting it (for instance in a middle box).
6.2.2. Modified bandwidth algorithms
The use of non-compound RTCP does not imply any specific need for
algorithm modifications. A few possible algorithm modifications have
been tested and even though the modifications may improve the
performance when feedback is transmitted the benefits are not judged
large enough to justify the relatively large changes in the
algorithms.
A more extensive report covering various test-cases and different
algorithm modifications can be downloaded from:
http://www.ijdata.com/rtcp-non-compound-rtcp-evaluation.doc
The report also covers tests with other averaging factors than the
specified 1/16, and it shows that it is beneficial to use slower
averaging (1/32 or 1/64) as it makes the estimate avg_rtcp_size more
stable and does not degrade the feedback transmission performance.
This modification is however not critical.
6.2.3. 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 feedback using
non-compound RTCP becomes smaller it opens up for a more liberal use
of immediate mode.
6.2.4. Enforcing compound RTCP
As discussed earlier it is important that the sending of compound
RTCP packets do happen at regular interval. 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
packets must be full compound RTCP packets. Note that also in
immediate mode is there a requirement on sending regular RTCP
packets.
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6.3. Open issues
This section contains a list of the yet unresolved issues. Currently
no open issues.
6.4. SDP Signalling Attribute
We request to define the a "a=rtcp-nc" [RFC4566] attribute to
indicate if the session participant is capable of supporting non-
compound packets. It is a required that a participant that proposes
the use of non-compound RTCP itself supports the reception of non-
compound RTCP.
An offering client that wish to use non-compound RTCP MUST include
the attribute "a=rtcp-nc" in the SDP offer. If the other client does
not support non-compound RTCP the attribute MUST be removed from the
answer SDP.
7. IANA Considerations
IANA will be required to register the SDP signalling attribute
defined in Section 6.4.
8. Security Considerations
The security considerations of RTP [RFC3550] and AVPF [RFC4585] will
apply also to non-compound packets. The reduction in validation
strength for received packets on the RTCP port may result in a higher
degree of acceptance of spurious data as real RTCP packets. This
vulnerability can mostly be addressed by usage of an security
mechanism that provide authentication, e.g. SRTP[RFC3711].
9. 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.
10. References
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10.1. 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.
10.2. Informative References
[3GPP-MTSI]
3GPP, "Specification : 3GPP TS 26.114 (v7.1.0
preliminary), http://www.3gpp.org/ftp/tsg_sa/WG4_CODEC/
Specs_update_after_SA36/26114-710.zip", March 2007.
[I-D.ietf-avt-avpf-ccm]
Wenger, S., Chandra, U., Westerlund, M., and B. Burman,
"Codec Control Messages in the RTP Audio-Visual Profile
with Feedback (AVPF)", draft-ietf-avt-avpf-ccm-10 (work
in progress), October 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
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.
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[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.
Authors' Addresses
Ingemar Johansson
Ericsson AB
Laboratoriegrand 11
SE-971 28 Lulea
SWEDEN
Phone: +46 73 0783289
Email: ingemar.s.johansson@ericsson.com
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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