Internet Engineering Task Force Gorry Fairhurst
Internet Draft University of Aberdeen
Expires November 2007 B. Collini-Nocker
University of Salzburg
Category: WG Draft intended for PS May 2007
Extension Formats for Unidirectional Lightweight Encapsulation (ULE)
and the Generic Stream Encapsulation (GSE)
draft-ietf-ipdvb-ule-ext-02.txt
Status of this Draft
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Abstract
This document describes a set of Extension Headers for the
Unidirectional Lightweight Encapsulation (ULE), RFC4326.
The Extension Header formats defined in this document define new
extensions that are common extensions to both ULE and the Generic
Stream Encapsulation (GSE) defined to support the second generation
framing structure defined by Digital Video Broadcasting (DVB) family
of specifications.
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Table of Contents
1. Introduction
2. Conventions used in this document
3. Description of method
3.1 MPEG-2 TS-Concat Extension
3.2 PDU-Concat Extension
3.3 TimeStamp Extension
4. IANA Considerations
5. Acknowledgements
6. Security Considerations
7. References
7.1 Normative References
7.2 Informative References
8. Authors' Addresses
9. IPR Notices
9.1 Intellectual Property Statement
9.2 Disclaimer of Validity
10. Copyright Statement
Appendix: The Second Generation DVB Transmission Specifications
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1. Introduction
This document describes three new Header Extensions that may be used
with both Unidirectional Lightweight Encapsulation, ULE, [RFC4326]
and the Generic Stream Encapsulation (GSE) [GSE]. ULE is defined for
links that employ the MPEG-2 Transport Stream, and supports a wide
variety of physical-layer bearers [RFC4259].
GSE has been designed for the Generic Mode (also known as the
Generic Stream (GS)), offered by second-generation DVB physical
layers, and in the first instance for DVB-S2 [ETSI-S2]. The
requirements for the Generic Stream are described in [ID-S2-REQ].
The important characteristics of this encapsulation are described in
an Appendix to this document. GSE maintains a design philosophy that
presents a common network interface to that of ULE and uses a
similar construction for Subnetwork Data Unit (SNDUs).
The first Extension Header defines a method that allows one or more
TS-Packets [ISO-MPEG2] to be sent within a ULE SNDU. This method may
be used to provide control plane information including the
transmission of MPEG-2 Program Specific Information (PSI) for the
Multiplex. In GSE, there is no native support for transport stream
packets and this method is therefore suitable for providing an MPEG-
2 control plane.
A second Extension Header allows one or more PDUs to be sent within
the same ULE SNDU. This method is designed for cases where a large
number of small PDUs are directed to the same Network Point of
Attachment (NPA) address. The method may improve transmission
efficiency (by removing duplicated MAC layer overhead). It can also
reduce processing overhead for receivers that are not addressed by
the NPA, since these receivers may then skip several PDUs in one
operation. The method is defined as a generic Extension Header and
may be used for IPv4 or IPv6 packets. If and when a compression
format is defined for ULE or Ethernet, the method may also be used
in combination with this method.
A third Extension Header provides an optional timestamp value for an
SNDU. Examples of the use of this timestamp option include
monitoring and benchmarking of ULE and GSE links. Receivers that do
not wish to decode (or do not support) the timestamp extension may
discard the extension and process the remaining PDU or Extension
Headers.
An appendix includes a summary of key design issues and
considerations based on the GSE Specification defined by the DVB
Technical Module [GSE].
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2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
RFC 2119 [RFC2119].
b: bit. For example, one byte consists of 8b.
B: Byte. Groups of bytes are represented in Internet byte order.
BBFrame payload [ETSI-S2]: The data field part of a Baseband frame
that may be used for the communication of data. Typical BBFrames
range in size from 3072 to 58192 bits according to the choice of
modulation format and FEC in use.
DVB: Digital Video Broadcasting. A framework and set of
associated standards published by the European Telecommunications
Standards Institute (ETSI) for the transmission of video, audio, and
data.
E: A one-bit flag field defined in [GSE].
Encapsulator: A network device that receives PDUs and formats these
in to Payload Units (known here as SNDUs) for output in DVB-S or the
Generic Mode of DVB-S2.
GS: Generic Stream [ETSI-S2]. A stream of BBFrames identified by a
common Input Stream Identifier, and which does not use the MPEG-2 TS
format.
GSE: Generic Stream Encapsulation [GSE]. A method that encapsulates
PDUs that form a Generic Stream, which is sent using a sequence of
BBFrames. This encapsulation format shares the same extension
format, and basic processing rules of ULE and uses a common IANA
Registry.
LT: A two-bit flag field defined in [GSE].
MAC: Medium Access Control [IEEE-802.3]. A link layer protocol
defined by the IEEE 802.3 standard (or by Ethernet v2).
MPEG-2: A set of standards specified by the Motion Picture Experts
Group (MPEG), and standardized by the International Standards
Organisation (ISO/IEC 113818-1) [ISO-MPEG2], and ITU-T (in H.220).
Next-Header: A Type value indicating an Extension Header [RFC4326].
NPA: Network Point of Attachment [RFC4326]. In this document, refers
to a destination address (resembling an IEEE MAC address) within the
DVB-S/S2 transmission network that is used to identify individual
Receivers or groups of Receivers.
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PID: Packet Identifier [ISO-MPEG2]. A 13 bit field carried in the
header of each TS Packet. This identifies the TS Logical Channel to
which a TS Packet belongs [ISO-MPEG2]. The TS Packets that form the
parts of a Table Section, or other Payload Unit must all carry the
same PID value. The all ones PID value indicates a Null TS Packet
introduced to maintain a constant bit rate of a TS Multiplex. There
is no required relationship between the PID values used for TS
Logical Channels transmitted using different TS Multiplexes.
PDU: Protocol Data Unit [RFC4259]. Examples of a PDU include
Ethernet frames, IPv4 or IPv6 datagrams, and other network packets.
PSI: Program Specific Information [ISO-MPEG2].
S: A one-bit flag field defined in [GSE].
SI Table: Service Information Table [ISO-MPEG2]. In this document,
this term describes a table that is been defined by another
standards body to convey information about the services carried on a
DVB Multiplex.
SNDU: Subnetwork Data Unit [RFC4259]. In this document this is an
encapsulated PDU sent using ULE or GSE.
Stream: A logical flow from an Encapsulator to a set of Receivers.
TS: Transport Stream [ISO-MPEG2], a method of transmission at the
MPEG-2 level using TS Packets; it represents layer 2 of the ISO/OSI
reference model.
ULE: Unidirectional Lightweight Encapsulation (ULE) [RFC4326]. A
method that encapsulates PDUs, into SNDUs that are sent in a series
of TS Packets using a single TS Logical Channel. The encapsulation
defines an extension format and an associated IANA Registry.
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3. Description of the Method
In ULE, a Type field value that is less than 1536 Decimal indicates
an Extension Header. This section describes a set of two extension
formats for the ULE encapsulation. The GSE [GSE] follows the same
format as used in the ULE Type field. The encapsulation format
differs in that GSE does not include a per-SNDU CRC, has different
header flags, and utilises a different SNDU length calculation
[GSE].
3.1 MPEG-2 TS-Concat Extension
The MPEG-2 TS-Concat Extension Header is specified by an IANA
assigned H-Type value of 0x0002 in hexadecimal. This is a Mandatory
Next-Header Extension.
The extension is used to transport one or more MPEG-2 TS Packets
within a ULE SNDU. The number of TS Packets carried in a specific
SNDU is determined from the size of the remainder of the payload
following the MPEG-2 TS Extension Header. The number of TS Packets
contained in the SNDU is therefore (Length-N-10+D*6) / 188, where N
is the number of bytes associated with Extension Headers that
precede the MPEG-2 TS-Concat Extension (zero if there are none).
A Receiver MUST check that the validity of the value of the payload
Length prior to processing. Any mismatch (remainder from the
division) MUST result in discard of all encapsulated PDUs and SHOULD
be recorded as TS-Concat size mismatch error.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Length (15b) | Type = 0x0002 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Destination NPA Address (6B) |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| TS-Packet 1 |
= =
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TS-Packet 2 (if Length > 2*188) |
= =
| etc. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (CRC-32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: ULE/SNDU Format for a TS-Packet Payload (D=0)
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Figure 1 illustrates the format of this Extension Header for ULE
with a value D=0, which indicates the presence of a NPA address
[RFC4326]. In this case, the valid payload Length for a ULE SNDU
with no other extensions is (Length-10) / 188.
The method used to define the Length in GSE differs to that of ULE.
The equivalent case for GSE would result in a payload Length value
of (Length-6) / 188 (Figure 2).
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|E|0 0| Length (12b) | Type = 0x0002 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Destination NPA Address (6B) |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| TS-Packet 1 |
= =
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TS-Packet 2 (if Length > 2*188) |
= =
| etc. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: GSE/SNDU Format for a TS-Packet Payload (LT=00)
Note that fragmented GSE SNDUs are protected by a CRC-32 carried in
the final fragment. The fields labelled S and E are defined by [GSE}
and contains control flags used by the GSE link layer. The Label
Type field (LT) specifies the presence and format of the GSE label.
In ULE, a value of D=1, is also permitted and indicates the absence
of a NPA address (Figure 3). A similar format is supported in GSE.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| Length (15b) | Type = 0x0002 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TS-Packet 1 |
= =
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TS-Packet 2 (if Length > 2*188) |
= =
| etc. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (CRC-32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: ULE/SNDU Format for a TS-Packet Payload (D=1)
This extension may be used to transport one or more MPEG-2 TS
Packets of arbitrary content, interpreted according to [ISO-MPEG2].
One expected use is for the transmission of MPEG-2 SI/PSI
signalling.
NULL TS Packets are not normally sent using this encapsulation. To
reduce transmission overhead and processing, an Encapsulator SHOULD
specify a maximum period of time that it can wait before sending all
queued TS Packets. This is known as the TS Packing Threshold. This
value MUST be bounded and SHOULD be configurable in the
Encapsulator. A larger value can improve efficiency, but incurs
higher jitter and could increase the probability of corruption. If
additional TS Packets are NOT received within the TS Packing
Threshold, the Encapsulator MUST immediately send any queued TS
Packets.
The use of this format to transfer MPEG-2 clock references (e.g. a
Network Clock Reference, NCR, SI Table) over ULE/GSE framing raises
timing considerations at the encapsulation gateway, including the
need to update/modify the timing information prior to transmission
by the physical layer. These issues are not considered here, but
this operation may be simplified in GSE by ensuring that all SNDUs
that carry this Extension Header are placed before other data within
the BBFrame DataField [GSE].
This document does not specify how TS Packets are to be handled at
the Receiver, however it notes that a poorly configured Encapsulator
could lead to a Multiplex carrying multiple (possibly conflicting)
sets of TS Logical Channels and SI information encapsulated at
different levels or with different NPA addresses. The need for
consistency in the use of PIDs and the related SI information is
described in [RFCxARx].
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3.2 PDU-Concat Extension
The PDU-Concat Extension Header is specified by an IANA assigned H-
Type value of 0x0003 in hexadecimal. This is a Mandatory Next-Header
Extension. It enables a sequence of (usually short) PDUs to be sent
within a single SNDU payload.
The base header contains the Length of the entire SNDU. This carries
the value of the combined length of all PDUs to be encapsulated,
including each set of encapsulation headers. The base header MAY be
followed by one or more additional Extension Headers preceding the
PDU-Concat Extension Header. These Extension Headers (e.g. a
TimeStamp Extension) apply to the composite concatenated PDU.
The Extension Header also conatains a 16-bit ULE Type field
describing the encapsulated PDU, CONCAT-PDU-Type. Although any Type
value specified in the ULE Next-Header Registry (including Extension
Header Types) may be assigned to the encapsulated PDU, all
concatenated PDUs MUST have a common ULE Type (i.e. all concatenated
PDUs passed by the network layer must be associated with the same
Type value). This simplifies the receiver design, and reduces the
transmission overhead for common use cases.
Each PDU is prefixed by its length in bytes (shown as PDU-Length in
the following diagrams). Encapsulated PDUs are of arbitrary length
(in bytes) and are not necessarily aligned to 16-bit or 32-bit
boundaries within the SNDU (as shown in the figure). The most
significant bit of the first byte is reserved, R, and this
specification requires that this MUST be set to zero. The length of
each PDU MUST be less than 32758 bytes, but will generally be much
smaller.
When the SNDU header indicates the presence of an SNDU Destination
Address field (i.e. D=0 in ULE), a Network Point of Attachment, NPA,
field directly follows the fourth byte of the SNDU header. NPA
destination addresses are 6 Byte numbers, normally expressed in
hexadecimal, used to identify the Receiver(s) in a transmission
network that should process a received SNDU. When present the
Receiver MUST associate the same specified MAC/NPA address with all
PDUs within the SNDU Payload. This MAC/NPA address MUST also be
forwarded with each PDU, if required by the forwarding interface.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Length (15b) | Type = 0x0003 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Destination NPA Address (6B) |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | CONCAT-PDU-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| PDU-Length-1 (15b) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
= PDU-1 =
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| PDU-Length-2 (15b) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
= PDU-2 =
| |
More PDUs as required
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (CRC-32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: ULE/SNDU Format for a PDU-Concat Payload (D=0)
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|E|0 0| Length (12b) | Type = 0x0003 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Destination NPA Address (6B) |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | CONCAT-PDU-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| PDU-Length-1 (15b) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
= PDU-1 =
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| PDU-Length-2 (15b) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
= PDU-2 =
| |
More PDUs as required
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: GSE/SNDU Format for a PDU-Concat Payload (LT=00)_
The value of D in the ULE header idicates whether a NPA/MAC address
is in use [RFC4326]. A similar format is supported in GSE.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| Length (15b) | Type = 0x0003 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CONCAT-PDU-Type |R| PDU-Length-1 (15b) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
= PDU-1 =
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| PDU-Length-2 (15b) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
= PDU-2 =
| |
More PDUs as required
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (CRC-32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: ULE/SNDU Format for a PDU-Concat Payload (D=1)
To reduce transmission overhead and processing, an Encapsulator
SHOULD specify a maximum period of time it will wait before sending
a Concatenated PDU. This is known as the PDU Packing Threshold. This
value MUST be bounded and SHOULD be configurable in the
Encapsulator. A larger value can improve efficiency, but incurs
higher jitter and could increase the probability of corruption. If
additional PDUs are NOT received within the PDU Packing Threshold,
the Encapsulator MUST immediately send any queued PDUs.
The Receiver processes this Extension Header by verifying that it
supports the specified CONCAT-PDU Type (unsupported Types MUST be
discarded but the receiver SHOULD record a PDU-Type error). It then
extracts each encapsulated PDU in turn. The Receiver MUST verify the
Length of each PDU. It MUST also ensure that the sum of the Lengths
of all processed PDUs equals the Length specified in the SNDU base
header. A Receiver SHOULD discard the whole SNDU if the total and
PDU sizes are not consistent and this event SHOULD be recorded as a
PDU-Concat size mismatch error.
3.3 Timestamp Extension
The Timestamp Extension Header permits an Encapsulator to add a
timestamp field to an SNDU. This is designed to support monitoring
and measurement of ULE performance over a link to indicate the
quality of an operational ULE link. This may be useful for GSE links
(where significant complexity exists in the scheduling provided by
the lower layers). This extension may be (optionally) checked at the
Receiver.
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Possible uses of this extension include:
* Validation of in-sequence ordering per Logical Channel,
* Measurement of one-way delay (when synchronised with the sender)
* Measurement of PDU Jitter introduced by the link,
* PDU loss (with additional information from the sender).
The Timestamp Extension Header is specified by the IANA-assigned H-
Type value of 257 decimal. This extension is an Optional Extension
Header ([RFC4326], Section 5).
Figure 7 shows the format of this extension with a HLEN value of 3
indicating a timestamp of length 4B with a Type field (there is no
implied byte-alignment).
0 7 15 23 31
+---------------+---------------+---------------+---------------+
| 0x03 | 0x01 | time stamp HI |
+---------------+---------------+---------------+---------------+
| time stamp LO | Type |
+---------------+---------------+---------------+---------------+
Figure 7 The format of the 32-bit Timestamp Extension Header
The extension carries a 32-bit value (time stamp HI plus time stamp
LO). The specified resolution is 1 microsecond. The value therefore
indicates the number of 1 microsecond ticks past the hour in
Universal Time when the PDU was encapsulated. This value may be
earlier than the time of transmission due for example to Packing,
queueing and other Encapsulator processing. The value is right-
justified to the 32-bit field. Systems unable to insert timestamps
at the specified resolution may use an arbitrary (and varying) value
to pad the unused least-significant bits.
The last two bytes carry a 16-bit Type field that indicates the type
of payload carried in the SNDU, or the presence of a further Next-
Header ([RFC4326], Section 4.4).
This is an Optional Extension Header. Receivers SHOULD process the
timestamp when the PDU is decapsulated. Receivers that do not
implement, or do not wish to process, the Timestamp Extension MAY
skip this extension and continue to process the remainder of the
SNDU, forwarding the encapsulated PDU.
4.. IANA Considerations
This document requires IANA involvement for the assignment of two
new Next-Header Type values from the IANA ULE Next-Header Registry.
These options are defined for specific use cases envisaged by GSE,
but are compatible with ULE.
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The TS-Concat Extension is a Mandatory next-type Extension Header,
specified in section 3.1 of this document. The value of this next-
header is defined by an IANA assigned H-Type value of 0x0002.
The PDU-Concat Extension is a Mandatory next-type Extension Header
specified in section 3.2 of this document. The value of this next-
header is defined by an IANA assigned H-Type value of 0x0003.
The Timestamp Extension is an Optional next-type Extension Header
specified in section 3.3 of this document. The value of this next-
header is defined by an IANA assigned H-Type value of 257 decimal.
This documents defines format for a HLEN value of 0x3.
5. Acknowledgments
The author gratefully acknowledges the inputs, comments and
assistance offered by the members of the DVB-GBS ad hoc group on
DVB-S2 encapsulation, in particular contributions on DVB-S2
transmission aspects from Rita Rinaldo, Axel Jahn, and Ulrik De Bie.
Juan Cantillo provided a significant contribution to the informative
annexe. The authors thank Christian Praehauser for his insight and
contribution on header extension processing issues.
6. Security Considerations
No specific security issues are raised within this document.
Additional security control fields may be provided as a part of a
link encryption Extension Header, e.g. to associate an SNDU with one
of a set of Security Association (SA) parameters. As a part of the
encryption process, it may also be desirable to authenticate
some/all of the headers. The method of encryption and the way in
which keys are exchanged is beyond the scope of this specification,
as also are the definition of the SA format and that of the related
encryption keys.
7. References
7.1 Normative References
[RFC2119] Bradner, S., "Key Words for Use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, 1997.
[RFC4326] Fairhurst, G. and B. Collini-Nocker, "Unidirectional
Lightweight Encapsulation (ULE) for transmission of IP datagrams
over an MPEG-2 Transport Stream", RFC 4326, December 2005.
[GSE] "Generic Stream Encapsulation", DVB Document A116, DVB
Technical Module (GBS Group), May 2007.
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7.2 Informative References
[ETSI-S2] EN 302 307, "Digital Video Broadcasting (DVB); Second
generation framing structure, channel coding and modulation systems
for Broadcasting, Interactive Services, News Gathering and other
broadband satellite applications", European Telecommunication
Standards Institute (ETSI).
[ID-S2-REQ] "Requirements for transmission of IP datagrams over DVB-
S2", Internet Draft <draft-cantillo-ipdvb-s2encaps-01.rxr>, Work in
Progress.
[IEEE-802.3] "Local and metropolitan area networks - Specific
requirements Part 3: Carrier sense multiple access with collision
detection (CSMA/CD) access method and physical layer
specifications", IEEE 802.3, IEEE Computer Society, (also ISO/IEC
8802-3), 2002.
[ISO-MPEG2] ISO/IEC DIS 13818-1:2000, "Information Technology;
Generic Coding of Moving Pictures and Associated Audio Information
Systems", International Standards Organisation (ISO).
[RFC4259] Montpetit, M.-J., Fairhurst, G., Clausen, H., Collini-
Nocker, B., and H. Linder, "A Framework for Transmission of IP
Datagrams over MPEG-2 Networks", RFC 4259, November 2006.
[RFCxARx] Montpetit, M.-J., Fairhurst, G., "Address Resolution
Mechanisms for IP Datagrams over MPEG-2 Networks", RFC Ed Queue,
<draft-ietf-ipdvb-ar-xx.txt>, 2007.
8. Authors' Addresses
Godred Fairhurst
Department of Engineering
University of Aberdeen
Aberdeen, AB24 3UE
UK
Email: gorry@erg.abdn.ac.uk
Web: http://www.erg.abdn.ac.uk/users/Gorry
Bernhard Collini-Nocker
Department of Computer Sciences
University of Salzburg
Jakob Haringer Str. 2
5020 Salzburg
Austria
EMail: bnocker@cosy.sbg.ac.at
Web: http://www.cosy.sbg.ac.at/
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10. IPR Notices
9.1 Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed
to pertain to the implementation or use of the technology described
in this document or the extent to which any license under such
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it has made any independent effort to identify any such rights.
Information on the procedures with respect to rights in RFC
documents can be found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
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of such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository
at http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
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this standard. Please address the information to the IETF at ietf-
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9.2 Disclaimer of Validity
This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE
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10. Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
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INTERNET DRAFT Extension Formats for the ULE Encapsulation May 2007
APPENDIX: The Second Generation DVB Transmission Specifications
This section provides informative background to the network layer
requirements of the second generation DVB Transmission
Specifications. The second generation waveforms specified by the
Digital Video Broadcasting project offer two main enhancements.
First, more efficient physical layer methods that employ higher
order modulation with stronger FEC and permit adaptive coding and
modulation response to changes in traffic and propagation
conditions. Second, at the link layer, they offer greater
flexibility in framing. Support is provided for a range of stream
formats including the classical Transport Stream (TS) [RFC4259]. In
addition, a new method called Generic Streams (GS) (or the Generic
Mode) is supported. A GS can be packetized or continuous and is
intended to provide native transport of other network-layer
services. One such method is that provided by the Generic Stream
Encapsulation (GSE) [GSE].
A transmission link sequentially multiplexes a series of baseband
frames (BBFrames). Each BBFrame comprises a fixed-size 10B header
and a payload. The payload carries a DataField and uses padding to
fill any unused space. A stream comprises a sequence of BBFrames
associated with an Input Stream Identifier (ISI) that is carried in
the header of each BBFrame. The simplest scheme uses a single
stream (with just one ISI value), but multiple streams are
permitted. The BBFrames forming a stream may be of variable size
(selected from a set of allowed sizes), and must use the same stream
format (e.g. TS or GSE). Each stream represents an independently
link with independent address resolution [RFCxARx].
GSE provides functions that are equivalent to those of the
Unidirectional Lightweight Encapsulation (ULE) [RFC4326]. It
supports the transmission of IP packets and other network-layer
protocols. The network-layer interface resembles that of ULE, where
it adopts common mechanisms for a Length field, a 16-bit Type field,
support for Extension Headers, and addressing using a 6-byte NPA and
a suppressed NPA address (functionally equivalent to D=1 in ULE). In
addition GSE also supports other addressing modes. It employs a CRC
method in which a CRC is placed at the end of a BBFrame, covering
multiples SNDUs. This is a result of more advanced physical layer
coding and a larger link frame size differ than used by the MPEG-2
TS. In some systems the CRC may be suppressed and replaced by cross-
layer signalling from the physical layer.
GSE also provides more flexible fragmentation at the interface to
the physical layer. This adapts the SNDUs to a variable-sized link-
layer frame, and reflects the more complex requirements in terms of
fragmentation and assembly that arise when using point-to-multipoint
adaptive physical layers.
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INTERNET DRAFT Extension Formats for the ULE Encapsulation May 2007
[RFC EDITOR NOTE:
This section must be deleted prior to publication]
DOCUMENT HISTORY
Individual Draft 00
This draft complements a study item in the DVB-GBS in this area to
define a Generic Stream Encapsulation (GSE). Comments relating to
this document will be gratefully received by the author(s) and may
also be sent to ip-dvb mailing list at: ip-dvb@erg.abdn.ac.uk
Individual Draft 01
Co-Author Added.
This draft updates the language and format.
This draft fixes problems with the concatenation mode, and defines a
new header format that restricts the use of the Type field so that
all concatenated PDUs MUST have the same Type.
Future versions of this draft may define additional Extension
Headers, proposals and ideas are welcome via the IETF ipdvb mailing
list. Possible extensions include those for encapsulation FEC, Link
parameter negotiation (e.g. for header compression), and support for
ATM/ULE.
Working Group Draft 00
Fixed editorial mistakes from Christian Praehauser and ID style for
WG adoption.
Working Group Draft 01
Corrected contact info for Bernhard.
Added TimeStamp Options
Corrected NITS in draft
Working Group Draft 01
Amended diagrams and text to follow tentative IANA assignments for
the codepoints.
Working Group Draft 01
Ammended text to follow IANA assignments for the codepoints.
Added issues raised at ipdvb meeting by C Praehauser.
Revised annexe with text from GSE Spec, J Cantillo, et al.
Revised wording to clarify corner cases.
Removed references to documents not in public domain.
Updated conventions and abbreviations for consistency.
Updated text referencing ULE.
[END of RFC EDITOR NOTE]
Fairhurst Expires July 2007 [page 17]
