draft-ietf-fecframe-pseudo-cdp-01.txt   draft-ietf-fecframe-pseudo-cdp-02.txt 
FEC Framework U. Kozat FEC Framework U. Kozat
Internet-Draft DoCoMo USA Labs Internet-Draft DoCoMo USA Labs
Intended status: Standards Track A. Begen Intended status: Standards Track A. Begen
Expires: September 8, 2009 Cisco Systems Expires: May 3, 2012 Cisco
March 7, 2009 October 31, 2011
Pseudo Content Delivery Protocol (CDP) for Protecting Multiple Source Pseudo Content Delivery Protocol (CDP) for Protecting Multiple Source
Flows in FEC Framework Flows in FEC Framework
draft-ietf-fecframe-pseudo-cdp-01 draft-ietf-fecframe-pseudo-cdp-02
Abstract
This document provides a pseudo Content Delivery Protocol (CDP) to
protect multiple source flows with one or more repair flows based on
the FEC Framework and the Session Description Protocol (SDP) elements
defined for the framework. The purpose of the document is not to
provide a full-pledged protocol, but to show how the defined
framework and SDP elements can be combined together to design a CDP.
Status of this Memo Status of this Memo
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This document provides a pseudo Content Delivery Protocol (CDP) to This document may contain material from IETF Documents or IETF
protect multiple source flows with one or more repair flows based on Contributions published or made publicly available before November
the FEC Framework document and the Session Description Protocol (SDP) 10, 2008. The person(s) controlling the copyright in some of this
elements defined for the framework. The purpose of the document is material may not have granted the IETF Trust the right to allow
not to provide a full-pledged protocol, but to show how the defined modifications of such material outside the IETF Standards Process.
framework and SDP elements can be combined together to design a CDP. Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 3 2. Definitions/Abbreviations . . . . . . . . . . . . . . . . . . 3
3. Definitions/Abbreviations . . . . . . . . . . . . . . . . . . 3 3. Construction of a Repair Flow from Multiple Source Flows . . . 3
4. Construction of a Repair Flow from Multiple Source Flows . . . 4 3.1. Example: Two Source Flows Protected by a Single Repair
4.1. Example: Two Source Flows Protected by a Single Repair
Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Reconstruction of Source Flows from Repair Flow(s) . . . . . . 10 4. Reconstruction of Source Flows from Repair Flow(s) . . . . . . 9
5.1. Example: Multiple Source Flows Protected by a Single 4.1. Example: Multiple Source Flows Protected by a Single
Repair Flow . . . . . . . . . . . . . . . . . . . . . . . 10 Repair Flow . . . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
9. Normative References . . . . . . . . . . . . . . . . . . . . . 11 8. Normative References . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction 1. Introduction
The Forward Error Correction (FEC) Framework (described in The Forward Error Correction (FEC) Framework (described in [RFC6363])
[I-D.ietf-fecframe-framework]) and SDP Elements for FEC Framework and SDP Elements for FEC Framework (described in [RFC6364]) together
(described in [I-D.ietf-fecframe-sdp-elements]) together define define mechanisms sufficient enough to build an actual Content
mechanisms sufficient enough to build an actual Content Delivery Delivery Protocol (CDP) with FEC protection. Methods to convey FEC
Protocol (CDP) with FEC protection. Methods to convey FEC Framework Framework Configuration Information (described in
Configuration Information (described in
[I-D.ietf-fecframe-config-signaling]) on the other hand provides the [I-D.ietf-fecframe-config-signaling]) on the other hand provides the
signaling protocols that may be used as part of CDP to communicate signaling protocols that may be used as part of CDP to communicate
FEC Scheme-Specific Information from FEC sender to a single as well FEC Scheme-Specific Information from FEC sender to a single as well
as multiple FEC receivers. This document aims at providing a as multiple FEC receivers. This document aims at providing a
guideline on how the mechanisms defined in guideline on how the mechanisms defined in [RFC6363] and [RFC6364]
[I-D.ietf-fecframe-framework] and [I-D.ietf-fecframe-sdp-elements]
can be sufficiently used to design a CDP over a non-trivial scenario, can be sufficiently used to design a CDP over a non-trivial scenario,
namely protection of multiple source flows with one or more repair namely protection of multiple source flows with one or more repair
flows. flows.
In particular, we provide clarifications and descriptions on how: In particular, we provide clarifications and descriptions on how:
o source and repair flows may be uniquely identified, o source and repair flows may be uniquely identified,
o source blocks may be generated from one or more source flows, o source blocks may be generated from one or more source flows,
o repair flows may be paired with the source flows, o repair flows may be paired with the source flows,
o the receiver explicitly and implicitly identifies individual o the receiver explicitly and implicitly identifies individual
flows, flows,
o source blocks are regenerated at the receiver and the missing o source blocks are regenerated at the receiver and the missing
source symbols in a source block are recovered. source symbols in a source block are recovered.
2. Requirements Notation 2. Definitions/Abbreviations
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 [RFC2119].
3. Definitions/Abbreviations
This document uses the following definitions. For further
definitions that apply to FEC Framework in general, see
[I-D.ietf-fecframe-framework].
CDP: Content Delivery Protocol.
FEC: Forward Error Correction.
Source Flow: The packet flow or flows to which FEC protection is to
be applied.
Repair Flow: The packet flow or flows carrying FEC data.
Transport Protocol: The protocol used for transport of the source
data flow being protected.
FEC Scheme: A specification which defines the additional protocol
aspects required to use a particular FEC code with the FEC
framework.
Source Block: The group of source data packets which are to be FEC
protected as a single block.
Source FEC Payload ID: An FEC Payload ID specifically for use with
source packets.
Repair FEC Payload ID: An FEC Payload ID specifically for use with This document uses all the definitions and abbreviations from Section
repair packets. 2 of [RFC6363].
4. Construction of a Repair Flow from Multiple Source Flows 3. Construction of a Repair Flow from Multiple Source Flows
At the sender side, CDP constructs the source blocks (SB) by At the sender side, CDP constructs the source blocks (SB) by
multiplexing transport payloads from multiple flows (See Figure 1 and multiplexing transport payloads from multiple flows (See Figure 1 and
Figure 2). According to the FEC Framework, each source block is FEC Figure 2). According to the FEC Framework, each source block is FEC-
protected separately. Each source block is given to the specific FEC protected separately. Each source block is given to the specific FEC
encoder used within the CDP as input and as the outputs Explicit encoder used within the CDP as input and as the outputs Explicit
Source FEC Payload ID, Repair FEC Payload ID, and Repair Payloads Source FEC Payload ID, Repair FEC Payload ID, and Repair Payloads
corresponding to that source block are generated. Note that Explicit corresponding to that source block are generated. Note that Explicit
Source FEC payload ID is optional and if CDP has implicit means of Source FEC payload ID is optional and if CDP has implicit means of
constructing the source block at the sender/receiver (e.g., by using constructing the source block at the sender/receiver (e.g., by using
any existing sequence numbers in the payload), the Explicit Source any existing sequence numbers in the payload), the Explicit Source
FEC payload ID might not be output. FEC payload ID might not be output.
+------------+ +------------+
s_1 --------> | | s_1 --------> | |
. Source | Source | +--------+ +--------+ +--------+ . Source | Source | +--------+ +--------+ +--------+
. Flows | Block |=> ..|SB_(j+1)| | SB_j | |SB_(j-1)| .. . Flows | Block |==> ..|SB_(j+1)| | SB_j | |SB_(j-1)| ..
s_n --------> | Generation | +--------+ +--------+ +--------+ s_n --------> | Generation | +--------+ +--------+ +--------+
+------------+ +------------+
Figure 1: Source Block generation for an FEC scheme Figure 1: Source Block generation for an FEC scheme
Figure 2 shows the structure of a source block. A CDP MUST clearly Figure 2 shows the structure of a source block. A CDP must clearly
specify which payload corresponds to which source flow and the length specify which payload corresponds to which source flow and the length
of each payload. of each payload.
<------------------ Source Block (SB) -------------------> <------------------ Source Block (SB) ------------------->
+-------...-----+-------...-----+- -+-------...-----+ +-------...-----+-------...-----+- -+-------...-----+
| Payload_1 | Payload_2 | . . . | Payload_n | | Payload_1 | Payload_2 | . . . | Payload_n |
+-------...-----+-------...-----+- -+-------...-----+ +-------...-----+-------...-----+- -+-------...-----+
\______ _______|______ _______| |______ _______| \______ _______|______ _______| |______ _______|
\/ \/ \/ \/ \/ \/
FID_1,Len_1 FID_2,Len_2 FID_n,Len_n FID_1,Len_1 FID_2,Len_2 FID_n,Len_n
Figure 2: Structure of a Source Block Figure 2: Structure of a Source Block
Flow ID (FID) value provides a unique short-hand identifier for the Flow ID (FID) value provides a unique short-hand identifier for the
source flows. FID is specified and associated with the possibly source flows. FID is specified and associated with the possibly
wildcarded tuple of {Source IP Address, Destination IP Address, wildcarded tuple of {source IP address, source port, destination IP
Source Transport Port, Destination Transport Port, Transport address, destination port, transport protocol} in the SDP
Protocol} in the SDP file. When wildcarded, certain fields in the description. When wildcarded, certain fields in the tuple are not
tuple are not needed for distinguishing the source flows. The tuple needed for distinguishing the source flows. The tuple is carried in
is carried in the IP and transport headers of the source packets. the IP and transport headers of the source packets. Since FID is
Since FID is utilized by the CDP and FEC scheme to distinguish utilized by the CDP and FEC scheme to distinguish between the source
between the source packets, the tuple MUST have a one-to-one mapping packets, the tuple must have a one-to-one mapping to a valid FID.
to a valid FID. This point will be clearer in the specific example This point will be clearer in the specific example given later in
given later in this section. The length of FID must be a priori this section. The length of FID must be a priori fixed and known to
fixed and known to both the receiver and sender. Alternatively, it both the receiver and sender. Alternatively, it might be specified
might be specified in the FEC-Scheme-Specific Information field in in the FEC-Scheme-Specific Information field in the SDP element
the SDP element [I-D.ietf-fecframe-sdp-elements]. [RFC6364].
The payload length (Len) information is needed to figure out how many The payload length (Len) information is needed to figure out how many
bits, bytes, or symbols (depending on the FEC scheme) from a bits, bytes, or symbols (depending on the FEC scheme) from a
particular source flow are included in the source block. If the particular source flow are included in the source block. If the
payload is not an integer multiple of the specified symbol length, payload is not an integer multiple of the specified symbol length,
the remaining portion is padded with zeros (See Figure 3 and the remaining portion is padded with zeros (See Figure 3 and
Figure 4). Figure 4).
+------+ +------+
+--------+ +--------+ +--------+ | | -------> r_1 +--------+ +--------+ +--------+ | | -------> r_1
.. |SB_(j+1)| | SB_j | |SB_(j-1)| .. --> | FEC | Repair . .. |SB_(j+1)| | SB_j | |SB_(j-1)| .. ==> | FEC | Repair .
+--------+ +--------+ +--------+ |Scheme| Flows . +--------+ +--------+ +--------+ |Scheme| Flows .
| | -------> r_k | | -------> r_k
+------+ +------+
Figure 3: Repair flow generation by an FEC scheme Figure 3: Repair flow generation by an FEC scheme
<------------------ Source Block (SB) -------------------> <------------------ Source Block (SB) ------------------->
| | | | | | | | | | | |
+-------...-----+-------...-----+- -+-------...-----+ | +-------...-----+-------...-----+- -+-------...-----+ |
| Payload_1 | Payload_2 | . . . | Payload_n |0| | Payload_1 | Payload_2 | . . . | Payload_n |0|
skipping to change at page 6, line 42 skipping to change at page 6, line 5
can uniquely specify their location in the source block, an Explicit can uniquely specify their location in the source block, an Explicit
Source FEC Payload ID may not be generated for these payloads. Source FEC Payload ID may not be generated for these payloads.
Otherwise, Explicit Source FEC Payload IDs are generated for each Otherwise, Explicit Source FEC Payload IDs are generated for each
payload and indicate the order the payloads appear in the source payload and indicate the order the payloads appear in the source
block. block.
Note that FID and length information are not actually transmitted Note that FID and length information are not actually transmitted
with the source payloads since both information can be gathered by with the source payloads since both information can be gathered by
other means as it will be clear in the next sections. other means as it will be clear in the next sections.
4.1. Example: Two Source Flows Protected by a Single Repair Flow 3.1. Example: Two Source Flows Protected by a Single Repair Flow
In this section, we present an example of source flow and repair flow In this section, we present an example of source flow and repair flow
generation by the CDP. We have two source flows with flow IDs of 0 generation by the CDP. We have two source flows with flow IDs of 0
and 1 to be protected by a single repair flow (See Figure 5). The and 1 to be protected by a single repair flow (See Figure 5). The
first source flow is multicast to 224.1.1.1 and the second source first source flow is multicast to 233.252.0.1 and the second source
flow is multicast to 224.1.1.2. Both flows use the port number flow is multicast to 233.252.0.2. Both flows use the port number
30000. The SDP description below states that the source flow defined 30000. The SDP description below states that the source flow defined
by the tuple {*,224.1.1.1,*,30000} is identified with FID=0 and the by the tuple {*,*,233.252.0.1,30000} is identified with FID=0 and the
source flow defined by the tuple {*,224.1.1.2,*,30000} is identified source flow defined by the tuple {*,*,233.252.0.2,30000} is
with FID=1. The SDP description also states that the repair flow is identified with FID=1. The SDP description also states that the
to be received at the multicast address of 224.1.2.1 and at port repair flow is to be received at the multicast address of 233.252.0.3
30000. and at port 30000.
SOURCE FLOWS | INSTANCE #1 SOURCE FLOWS
0: Source Flow |_________| 2: Repair Flow S1: Source Flow | | INSTANCE #1
1: Source Flow | |---------| R3: Repair Flow
S2: Source Flow |
Figure 5: Example: Two source flows and one repair flow Figure 5: Example: Two source flows and one repair flow
v=0 v=0
o=ali 1122334455 1122334466 IN IP4 fec.example.com o=ali 1122334455 1122334466 IN IP4 fec.example.com
s=FEC Framework Examples s=FEC Framework Examples
t=0 0 t=0 0
a=group:FEC S1 S2 R1 a=group:FEC-FR S1 S2 R3
m=video 30000 RTP/AVP 100 m=video 30000 RTP/AVP 100
c=IN IP4 224.1.1.1/127 c=IN IP4 233.252.0.1/127
a=rtpmap:100 MP2T/90000 a=rtpmap:100 MP2T/90000
a=fec-source-flow: id=0 a=fec-source-flow: id=0
a=mid:S1 a=mid:S1
m=video 30000 RTP/AVP 101 m=video 30000 RTP/AVP 101
c=IN IP4 224.1.1.2/127 c=IN IP4 233.252.0.2/127
a=rtpmap:101 MP2T/90000 a=rtpmap:101 MP2T/90000
a=fec-source-flow: id=1 a=fec-source-flow: id=1
a=mid:S2 a=mid:S2
m=application 30000 udp/fec m=application 30000 UDP/FEC
c=IN IP4 224.1.2.1/127 c=IN IP4 233.252.0.3/127
a=fec-repair-flow: encoding-id=0; ss-fssi=5hu= a=fec-repair-flow: encoding-id=0; ss-fssi=n:7,k:5
a=repair-window: 200 a=repair-window:150ms
a=mid:R1 a=mid:R3
Figure 6 shows the first and the second source blocks (SB_1 and SB_2) Figure 6 shows the first and the second source blocks (SB_1 and SB_2)
generated from these two source flows. In this example, SB_1 is of generated from these two source flows. In this example, SB_1 is of
length 10000 bytes. Suppose that the FEC scheme uses a symbol length length 10000 bytes. Suppose that the FEC scheme uses a symbol length
of 512 bytes. Then SB_1 can be divided into 20 symbols after padding of 512 bytes. Then SB_1 can be divided into 20 symbols after padding
the source block for 240 bytes. Assume that the FEC scheme is the source block for 240 bytes. Assume that the FEC scheme is
rate-2/3 erasure code, hence, it generates 10 repair symbols from 20 rate-2/3 erasure code, hence, it generates 10 repair symbols from 20
original symbols for SB_1. On the other hand, SB_2 is 7000-byte long original symbols for SB_1. On the other hand, SB_2 is 7000-byte long
and can be divided into 14 symbols after padding 168 bytes. Using and can be divided into 14 symbols after padding 168 bytes. Using
the same encoder, suppose that 7 repair symbols are generated for the same encoder, suppose that 7 repair symbols are generated for
SB_2. SB_2.
<-------- Source Block 1 --------> <-------- Source Block 1 -------->
+------------+-------------------+ +------------+-------------------+
| $1 $2 $3 $4| #1 #2 #3 #4 #5 #6 | 0..00 | $1 $2 $3 $4| #1 #2 #3 #4 #5 #6 | 0..00
+------------+-------------------+ +------------+-------------------+
\__________________ __________________/ \__________________ __________________/
\/ \/
@1 @2 @3 @4 @5 @6 @7 @8 @9 @10 @1 @2 @3 @4 @5 @6 @7 @8 @9 @10
<---- Source Block 2 ----> <---- Source Block 2 ---->
+----------------+-------+ +----------------+-------+
| $5 $6 $7 $8 $9 | #7 #8 |0..00 | $5 $6 $7 $8 $9 | #7 #8 |0..00
+----------------+-------+ +----------------+-------+
\______________ _____________/ \______________ _____________/
\/ \/
@11 @12 @13 @14 @15 @16 @17 @11 @12 @13 @14 @15 @16 @17
$: 1000-byte payload from source flow 1 $: 1000-byte payload from source flow 1
#: 1000-byte payload from source flow 2 #: 1000-byte payload from source flow 2
@: Repair symbol @: Repair symbol
Figure 6: Source block with two source flows Figure 6: Source block with two source flows
The information on the unit of payload length, FEC scheme, symbol The information on the unit of payload length, FEC scheme, symbol
size, and coding rates can be specified in the FEC Scheme-Specific size, and coding rates can be specified in the FEC Scheme-Specific
Information (FSSI) field of the SDP element. If the values of the Information (FSSI) field of the SDP element. If the values of the
payload lengths from each source flow and the order of appearance of payload lengths from each source flow and the order of appearance of
source flows in every source block are fixed during the session, source flows in every source block are fixed during the session,
these values may be also provided in the FSSI field. To carry FSSI these values may be also provided in the FSSI field. To carry FSSI
information to the FEC receivers, one may utilize the signaling information to the FEC receivers, one may use the signaling methods
methods described in [I-D.ietf-fecframe-config-signaling]. In our described in [I-D.ietf-fecframe-config-signaling]. In our example,
example, we will consider the case where the ordering is fixed and we will consider the case where the ordering is fixed and known both
known both at the sender and the receiver, but the payload lengths at the sender and the receiver, but the payload lengths will be
will be variable from one source block to another. We assume that variable from one source block to another. We assume that the
the payload of a source flow with an FID smaller than another flow's payload of a source flow with an FID smaller than another flow's FID
FID precedes other payloads in a source block. precedes other payloads in a source block.
The FEC scheme gets the source blocks as input and generates the The FEC scheme gets the source blocks as input and generates the
parity blocks for each source block to protect the whole source parity blocks for each source block to protect the whole source
block. In the example, the repair payloads for SB_1 consist of 512- block. In the example, the repair payloads for SB_1 consist of 512-
byte symbols, denoted by @1 to @10. Similarly @11 to @17 constitute byte symbols, denoted by @1 to @10. Similarly @11 to @17 constitute
the repair payloads for SB_2. The FEC scheme outputs the repair the repair payloads for SB_2. The FEC scheme outputs the repair
payloads along with the Repair FEC Payload IDs. In our example, payloads along with the Repair FEC Payload IDs. In our example,
Repair FEC Payload ID provides information on the source block Repair FEC Payload ID provides information on the source block
sequence number and the order the repair symbols are generated. For sequence number and the order the repair symbols are generated. For
instance @3 is the third FEC repair symbol for SB_1 and the three instance @3 is the third FEC repair symbol for SB_1 and the three
tuple {@3, SB_1,3} can uniquely deliver this information. In our tuple {@3,SB_1,3} can uniquely deliver this information. In our
example, the FEC scheme also provides Explicit Source FEC Payload IDs example, the FEC scheme also provides Explicit Source FEC Payload IDs
that carry information to indicate which source symbols correspond to that carry information to indicate which source symbols correspond to
which source block sequence number and its relative position in the which source block sequence number and the relative position in the
source block. For instance the two tuple {SB_2,2} can be attached to source block. For instance the two tuple {SB_2,2} can be attached to
$6 as the Explicit Source FEC Payload ID to indicate that $6 is $6 as the Explicit Source FEC Payload ID to indicate that $6 is
protected together with packets belonging to SB_2, and $6 is the protected together with packets belonging to SB_2, and $6 is the
second payload in SB_2. second payload in SB_2.
The source packets are generated from the source symbols by The source packets are generated from the source symbols by
concatenating consecutive symbols in one packet. There SHOULD NOT be concatenating consecutive symbols in one packet. There should not be
any fragmentation of a source symbol, e.g., symbols #7 and #8 can be any fragmentation of a source symbol, e.g., symbols #7 and #8 can be
concatenated in one transport payload of 2000-bytes (The concatenated in one transport payload of 2000-bytes (The
implementation SHOULD make sure that the size of the resulting source implementation should make sure that the size of the resulting source
packet - payload plus the overhead - is not larger than the path packet - payload plus the overhead - is not larger than the path
MTU), but one portion of symbol #7 SHOULD NOT be put in one source MTU), but one portion of symbol #7 should not be put in one source
packet and the remaining portion in another source packet. The packet and the remaining portion in another source packet. The
simplest implementation is to place each source symbol in a different simplest implementation is to place each source symbol in a different
source packet as shown in Figure 7. source packet as shown in Figure 7.
+------------------------------------+ +------------------------------------+
| IP header {224.1.1.1} | | IP header {233.252.0.1} |
+------------------------------------+ +------------------------------------+
| Transport header {30000} | | Transport header {30000} |
+------------------------------------+ +------------------------------------+
| Original Transport Payload {$6} | | Original Transport Payload {$6} |
+------------------------------------+ +------------------------------------+
| Source FEC Payload ID {SB_2,2} | | Source FEC Payload ID {SB_2,2} |
+------------------------------------+ +------------------------------------+
Figure 7: Example of a source packet Figure 7: Example of a source packet
The repair packets are generated from the repair symbols belonging to The repair packets are generated from the repair symbols belonging to
the same source block by grouping consecutive symbols in one packet. the same source block by grouping consecutive symbols in one packet.
There should not be any fragmentation of a repair symbol, e.g., There should not be any fragmentation of a repair symbol, e.g.,
symbols @4, @5, and @6 can be concatenated in one transport payload symbols @4, @5, and @6 can be concatenated in one transport payload
of 1536-bytes, but @6 SHOULD NOT be divided into smaller sub-symbols of 1536-bytes, but @6 should not be divided into smaller sub-symbols
and spread over multiple repair packets. The Repair FEC Payload ID and spread over multiple repair packets. The Repair FEC Payload ID
MUST carry sufficient information for the decoding process and in our must carry sufficient information for the decoding process and in our
example indicating source block sequence number, length of each example indicating source block sequence number, length of each
source payload, and the order that the first parity block in a repair source payload, and the order that the first parity block in a repair
packet is generated are sufficient. The exact header format of packet is generated are sufficient. The exact header format of
Repair FEC Payload ID may be specified in the FSSI field of the SDP Repair FEC Payload ID may be specified in the FSSI field of the SDP
element. In Figure 8 for instance, the repair symbols @4, @5, and @6 element. In Figure 8 for instance, the repair symbols @4, @5, and @6
are concatenated together. The Payload ID {SB_1,4,4,6} states that are concatenated together. The Payload ID {SB_1,4,4,6} states that
the repair symbols protect SB_1, the first repair symbol in the the repair symbols protect SB_1, the first repair symbol in the
payload is generated as the 4th symbol and the source block consists payload is generated as the 4th symbol and the source block consists
of two source flows carrying 4 and 6 packets from each. of two source flows carrying 4 and 6 packets from each.
+------------------------------------+ +------------------------------------+
| IP header {224.1.2.1} | | IP header {233.252.0.3} |
+------------------------------------+ +------------------------------------+
| Transport header {30000} | | Transport header {30000} |
+------------------------------------+ +------------------------------------+
| Repair FEC Payload ID {SB_1,4,4,6} | | Repair FEC Payload ID {SB_1,4,4,6} |
+------------------------------------+ +------------------------------------+
| Repair Symbols {@4,@5,@6} | | Repair Symbols {@4,@5,@6} |
+------------------------------------+ +------------------------------------+
Figure 8: Example of a repair packet Figure 8: Example of a repair packet
5. Reconstruction of Source Flows from Repair Flow(s) 4. Reconstruction of Source Flows from Repair Flow(s)
5.1. Example: Multiple Source Flows Protected by a Single Repair Flow 4.1. Example: Multiple Source Flows Protected by a Single Repair Flow
At the receiver, source flows 1 and 2 are received at At the receiver, source flows 1 and 2 are received at
{224.1.1.1,30000} and {224.1.1.2,30000}, while the repair flow is {233.252.0.1,30000} and {233.252.0.2,30000}, while the repair flow is
received at {224.1.2.1,30000}. The CDP can map these tuples to the received at {233.252.0.3,30000}. The CDP can map these tuples to the
flow IDs using the SDP elements. Accordingly, the payloads received flow IDs using the SDP elements. Accordingly, the payloads received
at {224.1.1.1,30000} and {224.1.1.2,30000} are mapped to flow IDs 0 at {233.252.0.1,30000} and {233.252.0.2,30000} are mapped to flow IDs
and 1, respectively. 0 and 1, respectively.
The CDP passes the flow IDs and received payloads along with the The CDP passes the flow IDs and received payloads along with the
Explicit Source FEC Payload ID to the FEC scheme defined in the SDP Explicit Source FEC Payload ID to the FEC scheme defined in the SDP
description. The CDP also passes the received repair packet payloads description. The CDP also passes the received repair packet payloads
and Repair FEC Payload ID to the FEC scheme. The FEC scheme can and Repair FEC Payload ID to the FEC scheme. The FEC scheme can
construct the original source block with missing packets by using the construct the original source block with missing packets by using the
information given in the FEC Payload IDs. The FEC Repair Payload ID information given in the FEC Payload IDs. The FEC Repair Payload ID
provides the information that SB_1 has packets from two flows with 4 provides the information that SB_1 has packets from two flows with 4
packets from the first one and 6 packets from the second one. Flow packets from the first one and 6 packets from the second one. Flow
IDs state that the packets from source flow 0 precedes the packets IDs state that the packets from source flow 0 precedes the packets
skipping to change at page 11, line 16 skipping to change at page 10, line 17
+------------+-------------------+ +------------+-------------------+
| $1 $2 X X | #1 X #3 #4 #5 #6 | | $1 $2 X X | #1 X #3 #4 #5 #6 |
+------------+-------------------+ +------------+-------------------+
O: Symbols received from the source flow 1 for SB_1 O: Symbols received from the source flow 1 for SB_1
#: Symbols received from the source flow 2 for SB_1 #: Symbols received from the source flow 2 for SB_1
X: Lost source symbols X: Lost source symbols
Figure 9: Source block regeneration Figure 9: Source block regeneration
When the FEC scheme can recover any missing block while more repair When the FEC scheme can recover any missing symbol while more repair
symbols are arriving, it provides the recovered blocks along with the symbols are arriving, it provides the recovered blocks along with the
source flow IDs of the recovered blocks as outputs to the CDP. The source flow IDs of the recovered blocks as outputs to the CDP. The
receiver knows how long to wait to repair the remaining missing receiver knows how long to wait to repair the remaining missing
packets (e.g., specified by the 'repair-window' attribute in the SDP packets (e.g., specified by the 'repair-window' attribute in the SDP
description). After the associated timer expires, the CDP hands over description). After the associated timer expires, the CDP hands over
whatever could be recovered from the source flow to the application whatever could be recovered from the source flow to the application
layer and continues with processing the next source block. layer and continues with processing the next source block.
6. Security Considerations 5. Security Considerations
For the general security considerations related to the FEC Framework, For the general security considerations related to the FEC Framework,
refer to [I-D.ietf-fecframe-framework]. There are no additional refer to [RFC6363]. There are no additional security considerations
security considerations that apply to this document. that apply to this document.
7. IANA Considerations 6. IANA Considerations
There are no IANA related issues considered in this document. There are no IANA related issues considered in this document.
8. Acknowledgments 7. Acknowledgments
The authors would like to thank the FEC Framework Design Team for The authors would like to thank the FEC Framework Design Team for
their inputs, suggestions and contributions. their inputs, suggestions and contributions.
9. Normative References 8. Normative References
[I-D.ietf-fecframe-framework] [RFC6363] Watson, M., Begen, A., and V. Roca, "Forward Error
Watson, M., "Forward Error Correction (FEC) Framework", Correction (FEC) Framework", RFC 6363, October 2011.
draft-ietf-fecframe-framework-03 (work in progress),
October 2008.
[I-D.ietf-fecframe-sdp-elements] [RFC6364] Begen, A., "Session Description Protocol Elements for the
Begen, A., "SDP Elements for FEC Framework", Forward Error Correction (FEC) Framework", RFC 6364,
draft-ietf-fecframe-sdp-elements-02 (work in progress), October 2011.
November 2008.
[I-D.ietf-fecframe-config-signaling] [I-D.ietf-fecframe-config-signaling]
Asati, R., "Methods to convey FEC Framework Configuration Asati, R., "Methods to convey FEC Framework Configuration
Information", draft-ietf-fecframe-config-signaling-01 Information", draft-ietf-fecframe-config-signaling-06
(work in progress), November 2008. (work in progress), September 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
Authors' Addresses Authors' Addresses
Ulas C. Kozat Ulas C. Kozat
DoCoMo USA Labs DoCoMo USA Labs
3240 Hillview Avenue 3240 Hillview Avenue
Palo Alto, CA 94304-1201 Palo Alto, CA 94304-1201
USA USA
Phone: +1 650 496 4739 Phone: +1 650 496 4739
Email: kozat@docomolabs-usa.com Email: kozat@docomolabs-usa.com
Ali Begen Ali Begen
Cisco Systems Cisco
170 West Tasman Drive 181 Bay Street
San Jose, CA 95134 Toronto, ON M5J 2T3
USA Canada
Email: abegen@cisco.com Email: abegen@cisco.com
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