4. Channels, Congestion Control, and Timing
ALC/LCT has a concept of channels and congestion control. There are
four scenarios in which FLUTE is envisioned to be applied.
(a) Use of a single channel and a single-rate congestion control
(b) Use of multiple channels and a multiple-rate congestion control
protocol. In this case, the FDT Instances MAY be delivered on
more than one channel.
(c) Use of a single channel without congestion control supplied by
ALC, but only when in a controlled network environment where
flow/congestion control is being provided by other means.
(d) Use of multiple channels without congestion control supplied by
ALC, but only when in a controlled network environment where
flow/congestion control is being provided by other means. In
this case, the FDT Instances MAY be delivered on more than one
When using just one channel for a file delivery session, as in (a)
and (c), the notion of 'prior' and 'after' are intuitively defined
for the delivery of objects with respect to their delivery times.
However, if multiple channels are used, as in (b) and (d), it is not
straightforward to state that an object was delivered 'prior' to the
other. An object may begin to be delivered on one or more of those
channels before the delivery of a second object begins. However, the
use of multiple channels/layers may mean that the delivery of the
second object is completed before the first. This is not a problem
when objects are delivered sequentially using a single channel.
Thus, if the application of FLUTE has a mandatory or critical
requirement that the first transmission object must complete 'prior'
to the second one, it is RECOMMENDED that only a single channel be
used for the file delivery session.
Furthermore, if multiple channels are used, then a receiver joined to
the session at a low reception rate will only be joined to the lower
layers of the session. Thus, since the reception of FDT Instances is
of higher priority than the reception of files (because the reception
of files depends on the reception of an FDT Instance describing it),
the following are RECOMMENDED:
1. The layers to which packets for FDT Instances are sent SHOULD NOT
be biased towards those layers to which lower-rate receivers are
not joined. For example, it is okay to put all the packets for
an FDT Instance into the lowest layer (if this layer carries
enough packets to deliver the FDT to higher-rate receivers in a
reasonable amount of time), but it is not okay to put all the
packets for an FDT Instance into the higher layers that only
higher-rate receivers will receive.
2. If FDT Instances are generally longer than one Encoding Symbol in
length and some packets for FDT Instances are sent to layers that
lower-rate receivers do not receive, an FEC encoding other than
Compact No-Code FEC Encoding ID 0 [RFC5445] SHOULD be used to
deliver FDT Instances. This is because in this case, even when
there is no packet loss in the network, a lower-rate receiver
will not receive all packets sent for an FDT Instance.
5. Delivering FEC Object Transmission Information
FLUTE inherits the use of the FEC building block [RFC5052] from ALC.
When using FLUTE for file delivery over ALC, the FEC Object
Transmission Information MUST be delivered in-band within the file
delivery session. There are two methods to achieve this: the use of
the ALC-specific LCT Header Extension EXT_FTI [RFC5775] and the use
of the FDT. The latter method is specified in this section. The use
of EXT_FTI requires repetition of the FEC Object Transmission
Information to ensure reception (though not necessarily in every
packet) and thus may entail higher overhead than the use of the FDT,
but may also provide more timely delivery of the FEC Object
The receiver of a file delivery session MUST support delivery of FEC
Object Transmission Information using EXT_FTI for the FDT Instances
carried using TOI value 0. For the TOI values other than 0, the
receiver MUST support both methods: the use of EXT_FTI and the use of
The FEC Object Transmission Information that needs to be delivered to
receivers MUST be exactly the same whether it is delivered using
EXT_FTI or using the FDT (or both). The FEC Object Transmission
Information that MUST be delivered to receivers is defined by the FEC
Scheme. This section describes the delivery using the FDT.
The FEC Object Transmission Information regarding a given TOI may be
available from several sources. In this case, it is RECOMMENDED that
the receiver of the file delivery session prioritize the sources in
the following way (in order of decreasing priority).
1. FEC Object Transmission Information that is available in EXT_FTI.
2. FEC Object Transmission Information that is available in the FDT.
The FDT delivers FEC Object Transmission Information for each file
using an appropriate attribute within the "FDT-Instance" or the
"File" element of the FDT structure.
* "Transfer-Length" carries the "Transfer-Length" Object
Transmission Information element defined in [RFC5052].
* "FEC-OTI-FEC-Encoding-ID" carries the "FEC Encoding ID" Object
Transmission Information element defined in [RFC5052], as carried
in the Codepoint field of the ALC/LCT header.
* "FEC-OTI-FEC-Instance-ID" carries the "FEC Instance ID" Object
Transmission Information element defined in [RFC5052] for
Under-Specified FEC Schemes.
* "FEC-OTI-Maximum-Source-Block-Length" carries the
"Maximum-Source-Block-Length" Object Transmission Information
element defined in [RFC5052], if required by the FEC Scheme.
* "FEC-OTI-Encoding-Symbol-Length" carries the
"Encoding-Symbol-Length" Object Transmission Information element
defined in [RFC5052], if required by the FEC Scheme.
* "FEC-OTI-Max-Number-of-Encoding-Symbols" carries the
"Max-Number-of-Encoding-Symbols" Object Transmission Information
element defined in [RFC5052], if required by the FEC Scheme.
* "FEC-OTI-Scheme-Specific-Info" carries the "encoded
Scheme-specific FEC Object Transmission Information" as defined in
[RFC5052], if required by the FEC Scheme.
In FLUTE, the FEC Encoding ID (8 bits) for a given TOI MUST be
carried in the Codepoint field of the ALC/LCT header. When the FEC
Object Transmission Information for this TOI is delivered through the
FDT, then the associated "FEC-OTI-FEC-Encoding-ID" attribute and the
Codepoint field of all packets for this TOI MUST be the same.
6. Describing File Delivery Sessions
To start receiving a file delivery session, the receiver needs to
know transport parameters associated with the session. Interpreting
these parameters and starting the reception therefore represent the
entry point from which thereafter the receiver operation falls into
the scope of this specification. According to [RFC5775], the
transport parameters of an ALC/LCT session that the receiver needs to
* The source IP address;
* The number of channels in the session;
* The destination IP address and port number for each channel in the
* The Transport Session Identifier (TSI) of the session;
* An indication that the session is a FLUTE session. The need to
demultiplex objects upon reception is implicit in any use of
FLUTE, and this fulfills the ALC requirement of an indication of
whether or not a session carries packets for more than one object
(all FLUTE sessions carry packets for more than one object).
Optionally, the following parameters MAY be associated with the
session (note that the list is not exhaustive):
* The start time and end time of the session;
* FEC Encoding ID and FEC Instance ID when the default FEC Encoding
ID 0 is not used for the delivery of the FDT;
* Content encoding format if optional content encoding of the FDT
Instance is used, e.g., compression;
* Some information that tells receiver, in the first place, that the
session contains files that are of interest;
* Definition and configuration of a congestion control mechanism for
* Security parameters relevant for the session;
* FLUTE version number.
It is envisioned that these parameters would be described according
to some session description syntax (such as SDP [RFC4566] or XML
based) and held in a file that would be acquired by the receiver
before the FLUTE session begins by means of some transport protocol
(such as the Session Announcement Protocol (SAP) [RFC2974], email,
HTTP [RFC2616], SIP [RFC3261], manual preconfiguration, etc.).
However, the way in which the receiver discovers the above-mentioned
parameters is out of scope of this document, as it is for LCT and
ALC. In particular, this specification does not mandate or exclude
7. Security Considerations
7.1. Problem Statement
A content delivery system is potentially subject to attacks. Attacks
* the network (to compromise the routing infrastructure, e.g., by
* the Content Delivery Protocol (CDP) (e.g., to compromise the
normal behavior of FLUTE), or
* the content itself (e.g., to corrupt the files being transmitted).
These attacks can be launched either:
* against the data flow itself (e.g., by sending forged packets),
* against the session control parameters (e.g., by corrupting the
session description, the FDT Instances, or the ALC/LCT control
parameters) that are sent either in-band or out-of-band, or
* against some associated building blocks (e.g., the congestion
In the following sections, we provide more details on these possible
attacks and sketch some possible countermeasures. We provide
recommendations in Section 7.5.
7.2. Attacks against the Data Flow
Let us consider attacks against the data flow first. At the least,
the following types of attacks exist:
* attacks that are meant to give access to a confidential file
(e.g., in the case of non-free content) and
* attacks that try to corrupt the file being transmitted (e.g., to
inject malicious code within a file, or to prevent a receiver from
using a file, which is a kind of denial of service (DoS)).
7.2.1. Access to Confidential Files
Access control to the file being transmitted is typically provided by
means of encryption. This encryption can be done over the whole
file, i.e., before applying FEC protection (e.g., by the content
provider, before submitting the file to FLUTE), or can be done on a
packet-by-packet basis (e.g., when IPsec/ESP [RFC4303] is used; see
Section 7.5). If confidentiality is a concern, it is RECOMMENDED
that one of these solutions be used.
7.2.2. File Corruption
Protection against corruptions (e.g., if an attacker sends forged
packets) is achieved by means of a content integrity verification/
sender authentication scheme. This service can be provided at the
file level, i.e., before applying content encoding and FEC encoding.
In that case, a receiver has no way to identify which symbol(s)
is(are) corrupted if the file is detected as corrupted. This service
can also be provided at the packet level, i.e., after applying
content encoding and FEC encoding, on a packet-by-packet basis. In
this case, after removing all corrupted packets, the file may be in
some cases recovered from the remaining correct packets.
Integrity protection applied at the file level has the advantage of
lower overhead, since only relatively few bits are added to provide
the integrity protection compared to the file size. However, it has
the disadvantage that it cannot distinguish between correct packets
and corrupt packets, and therefore correct packets, which may form
the majority of packets received, may be unusable. Integrity
protection applied at the packet level has the advantage that it can
distinguish between correct and corrupt packets, at the cost of
additional per-packet overhead.
Several techniques can provide this source authentication/content
* At the file level, the file MAY be digitally signed (e.g., by
using RSA Probabilistic Signature Scheme Public-Key Cryptography
Standards version 1.5 (RSASSA-PKCS1-v1_5) [RFC3447]). This
signature enables a receiver to check the file's integrity once
the file has been fully decoded. Even if digital signatures are
computationally expensive, this calculation occurs only once per
file, which is usually acceptable.
* At the packet level, each packet can be digitally signed
[RFC6584]. A major limitation is the high computational and
transmission overheads that this solution requires. To avoid this
problem, the signature may span a set of symbols (instead of a
single one) in order to amortize the signature calculation, but if
a single symbol is missing, the integrity of the whole set cannot
* At the packet level, a Group-Keyed Message Authentication Code
(MAC) [RFC2104] [RFC6584] scheme can be used; an example is using
HMAC-SHA-256 with a secret key shared by all the group members,
senders, and receivers. This technique creates a
cryptographically secured digest of a packet that is sent along
with the packet. The Group-Keyed MAC scheme does not create
prohibitive processing load or transmission overhead, but it has a
major limitation: it only provides a group authentication/
integrity service, since all group members share the same secret
group key, which means that each member can send a forged packet.
It is therefore restricted to situations where group members are
fully trusted (or in association with another technique as a
* At the packet level, Timed Efficient Stream Loss-Tolerant
Authentication (TESLA) [RFC4082] [RFC5776] is an attractive
solution that is robust to losses, provides a true authentication/
integrity service, and does not create any prohibitive processing
load or transmission overhead. However, checking a packet
requires a small delay (a second or more) after its reception.
* At the packet level, IPsec/ESP [RFC4303] can be used to check the
integrity and authenticate the sender of all the packets being
exchanged in a session (see Section 7.5).
Techniques relying on public key cryptography (digital signatures and
TESLA during the bootstrap process, when used) require that public
keys be securely associated to the entities. This can be achieved by
a Public Key Infrastructure (PKI), or by a Pretty Good Privacy (PGP)
Web of Trust, or by pre-distributing the public keys of each group
Techniques relying on symmetric key cryptography (Group-Keyed MAC)
require that a secret key be shared by all group members. This can
be achieved by means of a group key management protocol, or simply by
pre-distributing the secret key (but this manual solution has many
It is up to the developer and deployer, who know the security
requirements and features of the target application area, to define
which solution is the most appropriate. Nonetheless, in case there
is any concern of the threat of file corruption, it is RECOMMENDED
that at least one of these techniques be used.
7.3. Attacks against the Session Control Parameters and Associated
Let us now consider attacks against the session control parameters
and the associated building blocks. The attacker has at least the
following opportunities to launch an attack:
* the attack can target the session description,
* the attack can target the FDT Instances,
* the attack can target the ALC/LCT parameters, carried within the
LCT header, or
* the attack can target the FLUTE associated building blocks (e.g.,
the multiple-rate congestion control protocol).
The consequences of these attacks are potentially serious, since they
might compromise the behavior of the content delivery system itself.
7.3.1. Attacks against the Session Description
A FLUTE receiver may potentially obtain an incorrect session
description for the session. The consequence of this is that
legitimate receivers with the wrong session description are unable to
correctly receive the session content, or that receivers
inadvertently try to receive at a much higher rate than they are
capable of, thereby possibly disrupting other traffic in the network.
To avoid these problems, it is RECOMMENDED that measures be taken to
prevent receivers from accepting incorrect session descriptions. One
such measure is source authentication to ensure that receivers only
accept legitimate session descriptions from authorized senders. How
these measures are achieved is outside the scope of this document,
since this session description is usually carried out-of-band.
7.3.2. Attacks against the FDT Instances
Corrupting the FDT Instances is one way to create a DoS attack. For
example, the attacker changes the MD5 sum associated to a file. This
possibly leads a receiver to reject the files received, no matter
whether the files have been correctly received or not.
Corrupting the FDT Instances is also a way to make the reception
process more costly than it should be. This can be achieved by
changing the FEC Object Transmission Information when the FEC Object
Transmission Information is included in the FDT Instance. For
example, an attacker may corrupt the FDT Instance in such a way that
Reed-Solomon over GF(2^^16) would be used instead of GF(2^^8) with
FEC Encoding ID 2. This may significantly increase the processing
load while compromising FEC decoding.
More generally, because FDT Instance data is structured using the XML
language by means of an XML media type, many of the security
considerations described in [RFC3023] and [RFC3470] also apply to
It is therefore RECOMMENDED that measures be taken to guarantee the
integrity and to check the sender's identity of the FDT Instances.
To that purpose, one of the countermeasures mentioned above
(Section 7.2.2) SHOULD be used. These measures will either be
applied on a packet level or globally over the whole FDT Instance
object. Additionally, XML digital signatures [RFC3275] are a way to
protect the FDT Instance by digitally signing it. When there is no
packet-level integrity verification scheme, it is RECOMMENDED to rely
on XML digital signatures of the FDT Instances.
7.3.3. Attacks against the ALC/LCT Parameters
By corrupting the ALC/LCT header (or header extensions), one can
execute attacks on the underlying ALC/LCT implementation. For
example, sending forged ALC packets with the Close Session flag (A)
set to one can lead the receiver to prematurely close the session.
Similarly, sending forged ALC packets with the Close Object flag (B)
set to one can lead the receiver to prematurely give up the reception
of an object.
It is therefore RECOMMENDED that measures be taken to guarantee the
integrity and to check the sender's identity of the ALC packets
received. To that purpose, one of the countermeasures mentioned
above (Section 7.2.2) SHOULD be used.
7.3.4. Attacks against the Associated Building Blocks
Let us first focus on the congestion control building block, which
may be used in the ALC session. A receiver with an incorrect or
corrupted implementation of the multiple-rate congestion control
building block may affect the health of the network in the path
between the sender and the receiver. That may also affect the
reception rates of other receivers who joined the session.
When the congestion control building block is applied with FLUTE, it
is RECOMMENDED that receivers be required to identify themselves as
legitimate before they receive the session description needed to join
the session. How receivers identify themselves as legitimate is
outside the scope of this document. If authenticating a receiver
does not prevent this receiver from launching an attack, this
authentication will enable the network operator to identify him and
to take countermeasures.
When the congestion control building block is applied with FLUTE, it
is also RECOMMENDED that a packet-level authentication scheme be
used, as explained in Section 7.2.2. Some of them, like TESLA, only
provide a delayed authentication service, whereas congestion control
requires a rapid reaction. It is therefore RECOMMENDED [RFC5775]
that a receiver using TESLA quickly reduce its subscription level
when the receiver believes that congestion did occur, even if the
packet has not yet been authenticated. Therefore, TESLA will not
prevent DoS attacks where an attacker makes the receiver believe that
congestion occurred. This is an issue for the receiver, but this
will not compromise the network. Other authentication methods that
do not feature this delayed authentication could be preferred, or a
Group-Keyed MAC scheme could be used in parallel with TESLA to
prevent attacks launched from outside of the group.
7.4. Other Security Considerations
The security considerations that apply to, and are described in, ALC
[RFC5775], LCT [RFC5651], and FEC [RFC5052] also apply to FLUTE, as
FLUTE builds on those specifications. In addition, any security
considerations that apply to any congestion control building block
used in conjunction with FLUTE also apply to FLUTE.
Even if FLUTE defines a purely unidirectional delivery service,
without any feedback information that would be sent to the sender,
security considerations MAY require bidirectional communications.
For instance, if an automated key management scheme is used, a
bidirectional point-to-point channel is often needed to establish a
shared secret between each receiver and the sender. Each shared
secret can then be used to distribute additional keys to the
associated receiver (e.g., traffic encryption keys).
As an example, [MBMSsecurity] details a complete security framework
for the Third Generation Partnership Project (3GPP) Multimedia
Broadcast/Multicast Service (MBMS) that relies on FLUTE/ALC for
Download Sessions. It relies on bidirectional point-to-point
communications for User Equipment authentication and for key
distribution, using the Multimedia Internet KEYing (MIKEY) protocol
[RFC3830]. Because this security framework is specific to this use
case, it cannot be reused as such for generic security
recommendations in this specification. Instead, the following
section introduces minimum security recommendations.
7.5. Minimum Security Recommendations
We now introduce a mandatory-to-implement, but not necessarily to
use, security configuration, in the sense of [RFC3365]. Since FLUTE
relies on ALC/LCT, it inherits the "baseline secure ALC operation" of
[RFC5775]. More precisely, security is achieved by means of IPsec/
ESP in transport mode. [RFC4303] explains that ESP can be used to
potentially provide confidentiality, data origin authentication,
content integrity, anti-replay, and (limited) traffic flow
confidentiality. [RFC5775] specifies that the data origin
authentication, content integrity, and anti-replay services SHALL be
supported, and that the confidentiality service is RECOMMENDED. If a
short-lived session MAY rely on manual keying, it is also RECOMMENDED
that an automated key management scheme be used, especially in the
case of long-lived sessions.
Therefore, the RECOMMENDED solution for FLUTE provides per-packet
security, with data origin authentication, integrity verification,
and anti-replay. This is sufficient to prevent most of the in-band
attacks listed above. If confidentiality is required, a per-packet
encryption SHOULD also be used.
8.3. Registration of the application/fdt+xml Media Type
IANA has registered the following in the "Application Media Types"
registry at http://www.iana.org/assignments/media-types/application/.
Type name: application
Subtype name: fdt+xml
Required parameters: none
Optional parameters: charset="utf-8"
Encoding considerations: binary (the FLUTE file delivery protocol
does not impose any restriction on the objects it carries and in
particular on the FDT Instance itself)
Restrictions on usage: none
Security considerations: fdt+xml data is passive and does not
generally represent a unique or new security threat. However, there
is some risk in sharing any kind of data, in that unintentional
information may be exposed, and that risk applies to fdt+xml data as
Interoperability considerations: None
Published specification: [RFC6726], especially noting Section 3.4.2.
The specified FDT Instance functions as an actual media format of use
to the general Internet community, and thus media type registration
under the Standards Tree is appropriate to maximize interoperability.
Applications that use this media type: file and object delivery
applications and protocols (e.g., FLUTE).
Magic number(s): none
File extension(s): ".fdt" (e.g., if there is a need to store an
FDT Instance as a file)
Macintosh File Type Code(s): none
Person and email address to contact for further information:
Toni Paila (email@example.com)
Intended usage: Common
Author/Change controller: IETF
8.4. Creation of the FLUTE Content Encoding Algorithms Registry
IANA has created a new registry, "FLUTE Content Encoding Algorithms",
with a reference to [RFC6726]; see Section 3.4.3. The registry
entries consist of a numeric value from 0 to 255, inclusive, and may
be registered using the Specification Required policy [RFC5226].
The initial contents of the registry are as follows, with unspecified
values available for new registrations:
| Value | Algorithm Name | Reference |
| 0 | null | [RFC6726] |
| 1 | ZLIB | [RFC1950] |
| 2 | DEFLATE | [RFC1951] |
| 3 | GZIP | [RFC1952] |
8.5. Registration of LCT Header Extension Types
IANA has registered two new entries in the "Layered Coding Transport
(LCT) Header Extension Types" registry [RFC5651], as follows:
| Number | Name | Reference |
| 192 | EXT_FDT | [RFC6726] Section 3.4.1 |
| 193 | EXT_CENC | [RFC6726] Section 3.4.3 |
The following persons have contributed to this specification: Brian
Adamson, Mark Handley, Esa Jalonen, Roger Kermode, Juha-Pekka Luoma,
Topi Pohjolainen, Lorenzo Vicisano, Mark Watson, David Harrington,
Ben Campbell, Stephen Farrell, Robert Sparks, Ronald Bonica, Francis
Dupont, Peter Saint-Andre, Don Gillies, and Barry Leiba. The authors
would like to thank all the contributors for their valuable work in
reviewing and providing feedback regarding this specification.
Tampere University of Technology
P.O. Box 553 (Korkeakoulunkatu 1)
Tampere University of Technology
P.O. Box 553 (Korkeakoulunkatu 1)
SE-164 80 Stockholm
Ericsson Research (EDD)
Ericsson Allee 1
11. Change Log
11.1. RFC 3926 to This Document
Incremented the FLUTE protocol version from 1 to 2, due to concerns
about backwards compatibility. For instance, the LCT header changed
between RFC 3451 and [RFC5651]. In RFC 3451, the T and R fields of
the LCT header indicate the presence of Sender Current Time and
Expected Residual Time, respectively. In [RFC5651], these fields
MUST be set to zero and MUST be ignored by receivers (instead, the
EXT_TIME Header Extensions can convey this information if needed).
Thus, [RFC5651] is not backwards compatible with RFC 3451, even
though both use LCT version 1. FLUTE version 1 as specified in
[RFC3926] MUST use RFC 3451. FLUTE version 2 as specified in this
document MUST use [RFC5651]. Therefore, an implementation that
relies on [RFC3926] and RFC 3451 will not be backwards compatible
with FLUTE as specified in this document.
Updated dependencies to other RFCs to revised versions; e.g., changed
ALC reference from RFC 3450 to [RFC5775], changed LCT reference from
RFC 3451 to [RFC5651], etc.
Added clarification for the use of FLUTE for unicast communications
in Section 1.1.4.
Clarified how to reliably deliver the FDT in Section 3.3 and the
possibility of using out-of-band delivery of FDT information.
Clarified how to address FDT Instance expiration time wraparound with
the notion of the NTPv4 "epoch" in Section 3.3.
Clarified what should be considered erroneous situations in
Section 3.4.1 (definition of FDT Instance ID). In particular, a
receiver MUST be ready to handle FDT Instance ID wraparounds and
missing FDT Instances.
Updated Section 7.5 to define IPsec/ESP as a mandatory-to-implement
Removed the 'Statement of Intent' from Section 1. The statement of
intent was meant to clarify the "Experimental" status of [RFC3926].
It does not apply to this document.
Added clarification of "XML-DSIG" near the end of Section 3.
In Section 3.2, replaced "complete FDT" with text that is more
Clarified Figure 1 with regard to "Encoding Symbol(s) for FDT
Clarified the text regarding FDT Instance ID wraparound at the end of
Clarified "complete FDT" in Section 3.4.2.
Added semantics for the case where two TOIs refer to the same
Content-Location. It is now in line with the way that 3GPP and
Digital Video Broadcasting (DVB) standards interpret this case.
In Section 3.4.2, the XML Schema of the FDT Instance was modified per
advice from various sources. For example, extension by element was
missing but is now supported. Also, the namespace definition was
changed to URN format.
Clarified FDT-schema extensibility at the end of Section 3.4.2.
The CENC value allocation has been added at the end of Section 3.4.3.
Section 5 has been modified so that EXT_FTI and the FEC issues were
replaced by a reference to the ALC specification [RFC5775].
Added a clarifying paragraph on the use of the Codepoint field at the
end of Section 5.
Reworked Section 8 -- IANA Considerations; it now contains six IANA
* Registration of the FDT Instance XML Namespace.
* Registration of the FDT Instance XML Schema.
* Registration of the application/fdt+xml Media Type.
* Registration of the Content Encoding Algorithms.
* Registration of two LCT Header Extension Types and corresponding
values in the LCT Header Extension Types Registry (192 for EXT_FDT
and 193 for EXT_CENC).
Added Section 10 -- Contributors.
Revised lists of both Normative and Informative references.
Added a clarification that the receiver should ignore reserved bits
of Header Extension type 193 upon reception.
Elaborated on what kinds of networks cannot support FLUTE congestion
control (Section 1.1.4).
In Section 3.2, changed "several" (meaning 3-n vs. "couple" = 2) to
"multiple" (meaning 2-n).
Moved the requirement in Section 3.3 (to send FDT more reliably than
files) to a bulleted RECOMMENDED requirement, making check-off easier
In Section 3.3, sharpened the definition that future FDT file
instances can "augment" (meaning enhance) rather than "complement"
(sometimes meaning negate, which is not allowed) the file parameters.
Elaborated in Sections 3.3 and 4 that FEC Encoding ID = 0 is Compact
No-Code FEC, so that the reader doesn't have to search other RFCs to
understand these protocol constants used by FLUTE.
Required in Section 3.3 that FLUTE receivers SHALL NOT attempt to
decode FDTs if they do not understand the FEC Encoding ID.
Removed the restriction of Section 3.3, in bullet #4, that TOI = 0
for the FDT, to be consistent with Appendix A step 6 and elsewhere.
An FDT is signaled by an FDT Instance ID, NOT only by TOI = 0.
Standardized on the term "expiration time", and avoided using the
redundant and possibly confusing term "expiry time".
To interwork with experimental FLUTE, stipulated in Section 3.1 that
only 1 instantiation of all 3 protocols -- FLUTE, ALC, and LCT -- can
be associated with a session (source IP Address, TSI), and mentioned
in Section 6 that one may (optionally) derive the FLUTE version from
the file delivery session description.
Used a software writing tool to lower the reading grade level and
simplify Section 3.1.
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5775] Luby, M., Watson, M., and L. Vicisano, "Asynchronous
Layered Coding (ALC) Protocol Instantiation", RFC 5775,
[RFC5651] Luby, M., Watson, M., and L. Vicisano, "Layered Coding
Transport (LCT) Building Block", RFC 5651, October 2009.
[RFC5052] Watson, M., Luby, M., and L. Vicisano, "Forward Error
Correction (FEC) Building Block", RFC 5052, August 2007.
[RFC5445] Watson, M., "Basic Forward Error Correction (FEC)
Schemes", RFC 5445, March 2009.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
Thompson, H., Beech, D., Maloney, M., and N. Mendelsohn,
"XML Schema Part 1: Structures Second Edition",
W3C Recommendation, October 2004,
Biron, P. and A. Malhotra, "XML Schema Part 2: Datatypes
Second Edition", W3C Recommendation, October 2004,
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226, May 2008.
[RFC3738] Luby, M. and V. Goyal, "Wave and Equation Based Rate
Control (WEBRC) Building Block", RFC 3738, April 2004.
Note: The RFC 3738 reference is to a target document of a
lower maturity level. Some caution should be used, since
it may be less stable than the present document.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
12.2. Informative References
[RFC3926] Paila, T., Luby, M., Lehtonen, R., Roca, V., and R. Walsh,
"FLUTE - File Delivery over Unidirectional Transport",
RFC 3926, October 2004.
[RFC2357] Mankin, A., Romanow, A., Bradner, S., and V. Paxson, "IETF
Criteria for Evaluating Reliable Multicast Transport and
Application Protocols", RFC 2357, June 1998.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC3470] Hollenbeck, S., Rose, M., and L. Masinter, "Guidelines for
the Use of Extensible Markup Language (XML)
within IETF Protocols", BCP 70, RFC 3470, January 2003.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC1950] Deutsch, P. and J-L. Gailly, "ZLIB Compressed Data Format
Specification version 3.3", RFC 1950, May 1996.
[RFC1951] Deutsch, P., "DEFLATE Compressed Data Format Specification
version 1.3", RFC 1951, May 1996.
[RFC1952] Deutsch, P., "GZIP file format specification version 4.3",
RFC 1952, May 1996.
IANA, "Message Header Fields",
[RFC2974] Handley, M., Perkins, C., and E. Whelan, "Session
Announcement Protocol", RFC 2974, October 2000.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5,
RFC 1112, August 1989.
Holbrook, H., "A Channel Model for Multicast", Ph.D.
Dissertation, Stanford University, Department of Computer
Science, Stanford, California, August 2001.
[RFC3365] Schiller, J., "Strong Security Requirements for Internet
Engineering Task Force Standard Protocols", BCP 61,
RFC 3365, August 2002.
[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message
Specification", RFC 5751, January 2010.
[RFC3275] Eastlake 3rd, D., Reagle, J., and D. Solo, "(Extensible
Markup Language) XML-Signature Syntax and Processing",
RFC 3275, March 2002.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
Version 2.1", RFC 3447, February 2003.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
[RFC4082] Perrig, A., Song, D., Canetti, R., Tygar, J., and B.
Briscoe, "Timed Efficient Stream Loss-Tolerant
Authentication (TESLA): Multicast Source Authentication
Transform Introduction", RFC 4082, June 2005.
[RFC5776] Roca, V., Francillon, A., and S. Faurite, "Use of Timed
Efficient Stream Loss-Tolerant Authentication (TESLA) in
the Asynchronous Layered Coding (ALC) and NACK-Oriented
Reliable Multicast (NORM) Protocols", RFC 5776,
[RFC6584] Roca, V., "Simple Authentication Schemes for the
Asynchronous Layered Coding (ALC) and NACK-Oriented
Reliable Multicast (NORM) Protocols", RFC 6584,
[RFC3830] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and K.
Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830,
3GPP, "3rd Generation Partnership Project; Technical
Specification Group Services and System Aspects; 3G
Security; Security of Multimedia Broadcast/Multicast
Service (MBMS) (Release 10)", December 2010,
Appendix A. Receiver Operation (Informative)
This section gives an example of how the receiver of the file
delivery session may operate. Instead of a detailed state-by-state
specification, the following should be interpreted as a rough
sequence of an envisioned file delivery receiver.
1. The receiver obtains the description of the file delivery session
identified by the (source IP address, Transport Session
Identifier) pair. The receiver also obtains the destination IP
addresses and respective ports associated with the file delivery
2. The receiver joins the channels in order to receive packets
associated with the file delivery session. The receiver may
schedule this join operation utilizing the timing information
contained in a possible description of the file delivery session.
3. The receiver receives ALC/LCT packets associated with the file
delivery session. The receiver checks that the packets match the
declared Transport Session Identifier. If not, the packets are
4. While receiving, the receiver demultiplexes packets based on
their TOI and stores the relevant packet information in an
appropriate area for recovery of the corresponding file.
Multiple files can be reconstructed concurrently.
5. The receiver recovers an object. An object can be recovered when
an appropriate set of packets containing Encoding Symbols for the
transmission object has been received. An appropriate set of
packets is dependent on the properties of the FEC Encoding ID and
FEC Instance ID, and on other information contained in the FEC
Object Transmission Information.
6. Objects with TOI = 0 are reserved for FDT Instances. All FDT
Instances are signaled by including an EXT_FDT Header Extension
in the LCT header. The EXT_FDT header contains an FDT Instance
ID (i.e., an FDT version number). If the object has an FDT
Instance ID 'N', the receiver parses the payload of the instance
'N' of the FDT and updates its FDT database accordingly.
7. If the object recovered is not an FDT Instance but a file, the
receiver looks up its FDT database to get the properties
described in the database, and assigns the file the given
properties. The receiver also checks that the received content
length matches with the description in the database. Optionally,
if an MD5 checksum has been used, the receiver checks that the
calculated MD5 matches the description in the FDT database.
8. The actions the receiver takes with imperfectly received files
(missing data, mismatching content integrity digest, etc.) are
outside the scope of this specification. When a file is
recovered before the associated file description entry is
available, a possible behavior is to wait until an FDT Instance
is received that includes the missing properties.
9. If the file delivery session end time has not been reached, go
back to step 3. Otherwise, end.
Appendix B. Example of FDT Instance (Informative)
<?xml version="1.0" encoding="UTF-8"?>
Nokia/Tampere University of Technology
P.O. Box 553 (Korkeakoulunkatu 1)
Qualcomm Technologies, Inc.
2030 Addison Street, Suite 420
Berkeley, CA 94704
655, av. de l'Europe
ST ISMIER cedex 38334