Internet Engineering Task Force Gorry Fairhurst
Internet Draft University of Aberdeen, U.K.
Document: draft-ietf-ipdvb-ule-04.txt Bernhard Collini-Nocker
University of Salzburg, A
ipdvb WG
Category: Draft, Intended Standards Track January 2005
Ultra Lightweight Encapsulation (ULE) for transmission of
IP datagrams over MPEG-2/DVB networks
Status of this Draft
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Abstract
The MPEG-2 TS has been widely accepted not only for providing
digital TV services, but also as a subnetwork technology for
building IP networks. This document describes an Ultra Lightweight
Encapsulation (ULE) mechanism for the transport of IPv4 and IPv6
Datagrams and other network protocol packets directly over ISO MPEG-
2 Transport Streams (TS) as TS Private Data. ULE supports an
extension format that allows it to carry both optional (with an
explicit extension length) and mandatory (with an implicit extension
length) header information to assist in network/Receiver processing
of a SNDU.
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Table of Contents
1. Introduction
2. Conventions used in this document
3. Description of method
4. SNDU Format
4.1 Destination Address Present (D) Field
4.2 Length Field
4.3 End Indicator
4.4 Type Field
4.4.1 Type 1: Next-Header Type Fields
4.4.2 Type 2: EtherType Compatible Type Fields
4.5 SNDU Destination Address Field
4.6 SNDU Trailer CRC
4.7 Description of SNDU Formats
4.7.1 End Indicator
4.7.2 IPv4 SNDU Encapsulation
4.7.3 IPv6 SNDU Encapsulation
5. Extension Headers
5.1 Test SNDU
5.2 Bridged Frame SNDU Encapsulation
5.3 Extension-Padding Optional Extension Header
6.Processing at the Encapsulator
6.1 SNDU Encapsulation
6.2 Procedure for Padding and Packing
7. Receiver Processing
7.1 Idle State
7.1.1 Idle State Payload Pointer Checking
7.2 Processing of a Received SNDU
7.2.1 Reassembly Payload Pointer Checking
7.3 Other Error Conditions
8. Summary
9. Acknowledgments
10. Security Considerations
11. References
11.1 Normative References
11.2 Informative References
12. Authors' Addresses
13. IPR Notices
13.1 Intellectual Property Statement
13.2 Disclaimer of Validity
14. Copyright Statement
14.1 Intellectual Property Statement
14.2 Disclaimer of Validity
15. IANA Considerations
15.1 IANA Guidelines
ANNEXE A: Informative Appendix - SNDU Packing Examples
ANNEXE B: Informative Appendix - SNDU Encapsulation
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1. Introduction
This document describes an encapsulation for transport of IP
datagrams, or other network layer packets, over ISO MPEG-2 Transport
Streams [ISO-MPEG; ID-ipdvb-arch]. It is suited to services based
on MPEG-2, for example the Digital Video Broadcast (DVB)
architecture, the Advanced Television Systems Committee (ATSC)
system [ATSC; ATSC-G], and other similar MPEG-2 based transmission
systems. Such systems provide unidirectional (simplex) physical and
link layer standards. Support has been defined for a wide range of
physical media (e.g. Terrestrial TV [ETSI-DVBT; ATSC-PSIP-TC],
Satellite TV [ETSI-DVBS; ATSC-S], Cable Transmission [ETSI-DVBC;
ATSC-PSIP-TC]). Bi-directional (duplex) links may also be
established using these standards (e.g., DVB defines a range of
return channel technologies, including the use of two-way satellite
links [ETSI-RCS] and dial-up modem links [RFC3077]).
Protocol Data Units, PDUs, (Ethernet Frames, IP datagrams or other
network layer packets) for transmission over an MPEG-2 Transport
Multiplex are passed to an Encapsulator. This formats each PDU into
a SubNetwork Data Unit (SNDU) [RFC3819] by adding an encapsulation
header and an integrity check trailer. The SNDU is fragmented into a
series of TS Packets) that are sent over a single TS Logical
Channel.
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2. Conventions used in this document
Adaptation Field: An optional variable-length extension field of the
fixed-length TS Packet header, intended to convey clock references
and timing and synchronization information as well as stuffing over
an MPEG-2 Multiplex [ISO-MPEG].
AFC: Adaptation Field Control [ISO_MPEG]. A pair of bits carried in
the TS Packet header that signal the presence of the Adaptation
Field and/or TS Packet payload.
ATSC: Advanced Television Systems Committee [ATSC]. A framework and
a set of associated standards for the transmission of video, audio,
and data using the ISO MPEG-2 standard.
DSM-CC: Digital Storage Media Command and Control [ISO-DSMCC]. A
format for transmission of data and control information defined by
the ISO MPEG-2 standard that is carried in an MPEG-2 Private
Section.
DVB: Digital Video Broadcast [ETSI-DVB]. A framework and set of
associated standards published by the European Telecommunications
Standards Institute (ETSI) for the transmission of video, audio, and
data, using the ISO MPEG-2 Standard.
Encapsulator: A network device that receives PDUs and formats these
into Payload Units (known here as SNDUs) for output as a stream of
TS Packets.
End Indicator: A value that indicates to the Receiver that there are
no further SNDUs present within the current TS Packet.
MAC: Medium Access and Control. The link layer header of the
Ethernet IEEE 802 standard of protocols, consisting of a 6B
destination address, 6B source address, and 2B type field (see also
NPA).
MPE: Multiprotocol Encapsulation [ETSI-DAT; ATSC-DAT ; ATSC-DATG]. A
scheme that encapsulates PDUs, forming a DSM-CC Table Section. Each
Section is sent in a series of TS Packets using a single TS Logical
Channel.
MPEG-2: A set of standards specified by the Motion Picture Experts
Group (MPEG), and standardized by the International Standards
Organisation (ISO) [ISO-MPEG].
Next-Header: A Type value indicating an Extension Header.
NPA: Network Point of Attachment. In this document, refers to a 6 B
destination address (resembling an IEEE MAC address) within the
MPEG-2 transmission network that is used to identify individual
Receivers or groups of Receivers.
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Packing Threshold: A period of time an Encapsulator is willing to
defer transmission of a partially filled TS-Packet to accumulate
more SNDUs, rather than use Padding. After the Packet Threshold
period, the Encapsulator uses Padding to send the partially filled
TS-Packet.
PDU: Protocol Data Unit. Examples of a PDU include Ethernet frames,
IPv4 or IPv6 datagrams, and other network packets.
PES: Packetized Elementary Steam [ISO-MPEG]. A format of MPEG-2 TS
packet payload usually used for video or audio information.
PID: Packet Identifier [ISO_MPEG]. A 13 bit field carried in the
header of TS Packets. This is used to identify the TS Logical
Channel to which a TS Packet belongs [ISO-MPEG]. The TS Packets
forming the parts of a Table Section, PES, or other Payload Unit
must all carry the same PID value. The all 1s 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.
PP: Payload Pointer [ISO-MPEG]. An optional one byte pointer that
directly follows the TS Packet header. It contains the number of
bytes between the end of the TS Packet header and the start of a
Payload Unit. The presence of the Payload Pointer is indicated by
the value of the PUSI bit in the TS Packet header. The Payload
Pointer is present in DSM-CC, and Table Sections, it is not present
in TS Logical Channels that use the PES-format.
Private Section: A syntactic structure constructed in accordance
with Table 2-30 of [ISO-MPEG]. The structure may be used to identify
private information (i.e. not defined by [ISO-MPEG]) relating to one
or more elementary streams, or a specific MPEG-2 program, or the
entire Transport Stream. Other Standards bodies, e.g. ETSI, ATSC,
have defined sets of table structures using the private_section
structure. A Private Section is transmitted as a sequence of TS
Packets using a TS Logical Channel. A TS Logical Channel may carry
sections from more than one set of tables.
PSI: Program Specific Information [ISO-MPEG]. PSI is used to convey
information about services carried in a TS Multiplex. It is carried
in one of four specifically identified table section constructs
[ISO-MPEG], see also SI Table.
PSI: Program Specific Information [ISO-MPEG]. Tables used to convey
information about the service carried in a TS Multiplex. The set of
PSI tables is defined by MPEG-2 [ISO-MPEG]. See also SI Table.
PU: Payload Unit. A sequence of bytes sent using a TS. Examples of
Payload Units include: an MPEG-2 Table Section or a ULE SNDU.
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PUSI: Payload_Unit_Start_Indicator [ISO-MPEG]. A single bit flag
carried in the TS Packet header. A PUSI value of zero indicates that
the TS Packet does not carry the start of a new Payload Unit. A PUSI
value of one indicates that the TS Packet does carry the start of a
new Payload Unit. In ULE, a PUSI bit set to 1 also indicates the
presence of a one byte Payload Pointer (PP).
Receiver: An equipment that processes the signal from a TS Multiplex
and performs filtering and forwarding of encapsulated PDUs to the
network-layer service (or bridging module when operating at the link
layer).
SI Table: Service Information Table [ISO-MPEG]. In this document,
this term describes a table that is used to convey information about
the services carried in a TS Multiplex, that has been defined by
another standards body. A Table may consist of one or more Table
Sections, however all sections of a particular SI Table must be
carried over a single TS Logical Channel [ISO-MPEG].
SNDU: Subnetwork Data Unit [RFC3819]. An encapsulated PDU sent as an
MPEG-2 Payload Unit.
Table Section: A Payload Unit carrying all or a part of an SI or PSI
Table [ISO-MPEG].
TS: Transport Stream [ISO-MPEG], a method of transmission at the
MPEG-2 level using TS Packets; it represents level 2 of the ISO/OSI
reference model. See also TS Logical Channel and TS Multiplex.
TS Header: The 4 byte header of a TS Packet [ISO-MPEG].
TS Logical Channel: Transport Stream Logical Channel. In this
document, this term identifies a channel at the MPEG-2 level [ISO-
MPEG]. It exists at level 2 of the ISO/OSI reference model. All
packets sent over a TS Logical Channel carry the same PID value
(this value is unique within a specific TS Multiplex). According to
MPEG-2, some TS Logical Channels are reserved for specific
signalling purposes. Other standards (e.g., ATSC, DVB) also reserve
specific TS Logical Channels.
TS Multiplex: In this document, this term defines a set of MPEG-2 TS
Logical Channels sent over a single lower layer connection. This may
be a common physical link (i.e. a transmission at a specified symbol
rate, FEC setting, and transmission frequency) or an encapsulation
provided by another protocol layer (e.g. Ethernet, or RTP over IP).
The same TS Logical Channel may be repeated over more than one TS
Multiplex (possibly associated with a different PID value) [ID-
ipdvb-arch], for example to redistribute the same multicast content
to two terrestrial TV transmission cells.
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TS Packet: A fixed-length 188B unit of data sent over a TS Multiplex
[ISO-MPEG]. Each TS Packet carries a 4B header, plus optional
overhead including an Adaptation Field, encryption details and time
stamp information to synchronise a set of related TS Logical
Channels. The 188B TS Packet incorporates a 4B header with the
following fields (those referenced within this document are marked
with *):
Field Length Name/Purpose
(in bits)
8b Synchronisation pattern equal 0x47
*1b Transport Error Indicator
*1b Payload Unit Start Indicator (PUSI)
1b Transport Priority
*13b Packet IDentifier (PID)
2b Transport scrambling control
*2b Adaptation Field Control (AFC)
*4b Continuity Counter (CC)
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3. Description of the Method
PDUs (IP packets, Ethernet frames or packets from other network
protocols) are encapsulated to form a Subnetwork Data Unit (SNDU).
The SNDU is transmitted over an MPEG-2 transmission network by
placing it either in the payload of a single TS Packet, or if
required, an SNDU may be fragmented into a series of TS Packets.
Where there is sufficient space, the method permits a single TS
Packet to carry more than one SNDU (or part there of), sometimes
known as Packing. All TS Packets comprising a SNDU MUST be assigned
the same PID, and therefore form a part of the same TS Logical
Channel.
The ULE encapsulation is limited to TS private streams only. The
header of each TS Packet carries a one bit Payload Unit Start
Indicator (PUSI) field. The PUSI identifies the start of a payload
unit (SNDU) within the MPEG-2 TS Packet payload. The semantics of
the PUSI bit are defined for PES and PSI packets [ISO-MPEG]; for
private data, its use is not defined in the MPEG-2 Standard. In ULE,
although being private data, the operation follows that of PSI
packets. Hence, the following PUSI values are defined:
0: The TS Packet does NOT contain the start of a SNDU, but
contains the continuation, or end of a SNDU;
1: The TS Packet contains the start of a SNDU, and a one byte
Payload Pointer follows the last byte of the TS Packet header.
If a Payload Unit (SNDU) finishes before the end of a TS Packet
payload, but it is not intended to start another Payload Unit, a
stuffing procedure fills the remainder of the TS Packet payload with
bytes with a value 0xFF [ISO-MPEG2], known as Padding.
A Receiver processing MPEG-2 Table Sections that receives a value of
0xFF in place of the table_id field, interprets this as
Padding/Stuffing and silently discards the remainder of the TS
Packet payload. The payload of the next TS Packet for the same TS
Logical Channel will begin with a Payload Pointer of value 0x00,
indicating that the next Payload Unit immediately follows the TS
Packet header. The ULE protocol resembles this, but differs in the
exact procedure (see the following sections).
The TS Packet Header also carries a two bit Adaptation Field Control
(AFC) value. This adaptation field may extend the TS Packet Header
to carry timing and synchronisation information and may also be used
to include stuffing bytes before a TS Packet payload. Adaptation
Field stuffing is NOT used in this encapsulation method, and TS
Packets from a ULE Encapsulator MUST be sent with an AFC value of
'01'. For TS Logical Channels supporting ULE, Receivers MUST discard
TS Packets that carry other AFC values.
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4. SNDU Format
PDUs (IP packets and bridged Ethernet frames) are encapsulated using
ULE to form a SNDU. (Each SNDU is an MPEG-2 Payload Unit.) The
encapsulation format to be used for PDUs is illustrated below:
< ----------------------------- SNDU ----------------------------- >
+-+-------------------------------------------------------+--------+
|D| Length | Type | PDU | CRC-32 |
+-+-------------------------------------------------------+--------+
Figure 1: SNDU Encapsulation
All multi-byte values in ULE (including Length, Type, and
Destination fields) are transmitted in network byte order (most
significant byte first). The most significant bit of each byte is
placed in the left-most position of the 8-bit field. Appendix A
provides informative examples of usage.
4.1 Destination Address Present (D) Field
The most significant bit of the Length Field carries the value of
the Destination Address Present Field, the D-bit. A value of 0
indicates the presence of the Destination Address Field (see section
4.5). A value of 1 indicates that a Destination Address Field is not
present (i.e. it is omitted).
By default, the D-bit value SHOULD be set to a value of 0 (see 4.5),
except for the transmission of an End Indicator (see 4.3), for which
this bit MUST be set to the value of 1.
4.2 Length Field
A 15-bit value that indicates the length, in bytes, of the SNDU
(encapsulated Ethernet frame, IP datagram or other packet) counted
from the byte following the Type field, up to and including the CRC.
Note the special case described in 4.3.
4.3 End Indicator
When the first two bytes of a SNDU have the value 0xFFFF, this
denotes an End Indicator (i.e., all 1s length combined with a D-bit
value of 1). This indicates to the Receiver that there are no
further SNDUs present within the current TS Packet (see section 6),
and that no Destination Address Field is present. The value 0xFF has
specific semantics in MPEG-2 framing, where it is used to indicate
the presence of Padding. This use resembles [ISO-DSMCC].
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4.4 Type Field
The 16-bit Type field indicates the type of payload carried in a
SNDU, or the presence of a Next-Header. The set of values that may
be assigned to this field is divided into two parts, similar to the
allocations for Ethernet.
EtherTypes were originally specified by Xerox under the DIX
framework for Ethernet. After specification of IEEE 802.3 [LLC], the
set of EtherTypes less than 1536 (0x0600), assumed the role of a
length indicator. Ethernet receivers use this feature to
discriminate LLC format frames. Hence any IEEE EtherType < 1536
indicates an LLC frame, and the actual value indicates the length of
the LLC frame.
There is a potential ambiguous case when a Receiver receives a PDU
with two length fields: The Receiver would need to validate the
actual length and the Length field and ensure that inconsistent
values are not propagated by the network. Specification of two
independent length fields is therefore undesirable. In the ULE
header, this is avoided in the SNDU header by including only one
length value, but bridging of LLC frames re-introduces this
consideration (section 5.2).
The Ethernet LLC mode of identification is not required in ULE,
since the SNDU format always carries an explicit Length Field, and
therefore the procedure in ULE is modified, as below:
The first set of ULE Type field values comprise the set of values
less than 1536 in decimal. These Type field values are IANA
assigned (see 4.4.1), and indicate the Next-Header.
The second set of ULE Type field values comprise the set of values
greater than or equal to 1536 in decimal. In ULE, this value is
identical to the corresponding type codes specified by the IEEE/DIX
type assignments for Ethernet and recorded in the IANA EtherType
registry.
4.4.1 Type 1: Next-Header Type Fields
The first part of the Type space corresponds to the values 0 to 1535
Decimal. These values may be used to identify link-specific
protocols and/or to indicate the presence of Extension Headers that
carry additional optional protocol fields (e.g. a bridging
encapsulation). Use of these values is co-ordinated by an IANA
registry.
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The following types are defined in this document:
[XXX IANA ACTION REQUIRED XXX]
0x0000: Test SNDU, discarded by the Receiver.
0x0001: Bridged Ethernet Frame (i.e. MAC source address follows)
0x0100: Padding, ignored by the Receiver.
[XXX END OF IANA ACTION REQUIRED XXX]
The remaining values within the first part of the Type space are
reserved for Next-Header values allocated by the IANA.
4.4.2 Type 2: EtherType Compatible Type Fields
The second part of the Type space corresponds to the values between
0x600 (1536 decimal) and 0xFFFF. This set of type assignments
follow DIX/IEEE assignments (but exclude use of this field as a
frame length indicator) [LLC]. All assignments in this space MUST
use the values defined for IANA EtherType, the following two Type
values are used as examples (taken from the IANA EtherTypes
registry):
0x0800 : IPv4 Payload
0x86DD : IPv6 Payload
4.5 SNDU Destination Address Field
The SNDU Destination Address Field is optional (see 4.1). This field
MUST be carried (i.e. D=0) for IP unicast packets destined to
routers that are sent using shared links (i.e., where the same link
connects multiple Receivers). A sender MAY omit this field (D=1) for
an IP unicast packet and/or multicast packets delivered to Receivers
that are able to utilise a discriminator field (e.g. the IPv4/IPv6
destination address), which in combination with the PID value, could
be interpreted as a Link-Level address.
When the SNDU header indicates the presence of a SNDU Destination
Address field (i.e. D=0), 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 MPEG-2
transmission network that should process a received SNDU. The value
0x00:00:00:00:00:00, MUST NOT be used as a destination address in a
SNDU. The least significant bit of the first byte of the address is
set to 1 for multicast frames, and the remaining bytes specify the
link layer multicast address. The specific value 0xFF:FF:FF:FF:FF:FF
is the link broadcast address, indicating this SNDU is to be
delivered to all Receivers.
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4.6 SNDU Trailer CRC
Each SNDU MUST carry a 32-bit CRC field in the last four bytes of
the SNDU. This position eases CRC computation by hardware. The CRC-
32 polynomial is to be used. Examples where this polynomial is also
employed include Ethernet, DSM-CC section syntax [ISO-DSMCC] and
AAL5 [ITU3563]. This is a 32 bit value calculated according to the
generator polynomial represented 0x104C11DB7 in hexadecimal:
x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x^1+x^0.
The Encapsulator initialises the CRC-32 accumulator register to the
value 0xFFFF FFFF. It then accumulates a transmit value for the
CRC32 that includes all bytes from the start of the SNDU header to
the end of the SNDU (excluding the 32-bit trailer holding the CRC-
32), and places this in the CRC Field. In ULE, the bytes are
processed in order of increasing position within the SNDU, the order
of processing bits is NOT reversed. This use resembles, but is
different to that in SCTP [RFC3309].
The Receiver performs an integrity check by independently
calculating the same CRC value and comparing this with the
transmitted value in the SNDU trailer. SNDUs that do not have a
valid CRC, are discarded, causing the Receiver to enter the Idle
State.
This description may be suited for hardware implementation, but this
document does not imply any specific implementation. Software-based
table-lookup or hardware-assisted software-based implementations are
also possible. Annexe B provides an example of an Encapsulated PDU
that includes the computed CRC-32 value.
The primary purpose of this CRC is to protect the SNDU (header, and
payload) from undetected reassembly errors and errors introduced by
unexpected software / hardware operation while the SNDU is in
transit across the MPEG-2 subnetwork and during processing at the
encapsulation gateway and/or the Receiver. It may also detect the
presence of uncorrected errors from the physical link (however,
these may also be detected by other means, e.g. section 7.3).
4.7 Description of SNDU Formats
The format of a SNDU is determined by the combination of the
Destination Address Present bit (D) and the SNDU Type Field. The
simplest encapsulation places a PDU directly into a SNDU payload.
Some Type 1 encapsulations may require additional header fields.
These are inserted in the SNDU following the NPA destination address
and directly preceding the PDU.
The following SNDU Formats are defined here:
End Indicator: The Receiver should enter the Idle State (4.7.1).
IPv4 SNDU: The payload is a complete IPv4 datagram (4.7.2)
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IPv6 SNDU: The payload is a complete IPv6 datagram (4.7.3).
Test SNDU: The payload will be discarded by the Receiver (5.1).
Bridged SNDU: The payload carries a bridged MAC or LLC frame (5.2).
Other formats may be defined through relevant assignments in the
IEEE and IANA registries.
4.7.1 End Indicator
The format of the End Indicator is shown in figure 2. This format
MUST carry a D-bit value of 1.
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| 0x7FFF |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
= Arbitrary number (>= 0) bytes with value 0xFF =
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SNDU Format for an End Indicator.
4.7.2 IPv4 SNDU
IPv4 datagrams are directly transported using one of the two
standard SNDU structures, in which the PDU is placed directly in the
SNDU payload. The two encapsulations are shown in figures 3 and 4.
(Note that in this, and the following figures, the IP datagram
payload is of variable size, and is directly followed by the CRC-
32).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Length (15b) | Type = 0x0800 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Destination NPA Address (6B) |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
= IPv4 datagram =
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (CRC-32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: SNDU Format for an IPv4 Datagram using L2 filtering (D=0).
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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 = 0x0800 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
= IPv4 datagram =
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (CRC-32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: SNDU Format for an IPv4 Datagram using L3 filtering (D=1).
4.7.3 IPv6 SNDU Encapsulation
IPv6 datagrams are directly transported using one of the two
standard SNDU structures, in which the PDU is placed directly in the
SNDU payload. The two encapsulations are shown in figures 5 and 6.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Length (15b) | Type = 0x086DD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Destination NPA Address (6B) |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
= IPv6 datagram =
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (CRC-32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: SNDU Format for an IPv6 Datagram using L2 filtering (D=0).
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 = 0x086DD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
= IPv6 datagram =
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (CRC-32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: SNDU Format for an IPv6 Datagram using L3 filtering (D=1)
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5. Extension Headers
This section describes an extension format for the ULE
encapsulation. In ULE, a Type field value less than 1536 Decimal
indicates an Extension Header. These values are assigned from a
separate IANA registry defined for ULE.
The use of a single Type/Next-Header field simplifies processing and
eliminates the need to maintain multiple IANA registries. The cost
is that each Extension Header requires at least 2 bytes. This is
justified, on the basis of simplified processing and maintaining a
simple lightweight header for the common case when no extensions are
present.
A ULE Extension Header is identified by a 16-bit value in the Type
field. This field is organised as a 5-bit zero prefix, a 3-bit H-LEN
field and an 8-bit H-Type field, as follows:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0|H-LEN| H-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Structure of ULE Next-Header Field.
The H-LEN Assignment is described below:
0 Indicates a Mandatory Extension Header
1 Indicates an Optional Extension Header of length 2B
2 Indicates an Optional Extension Header of length 4B
3 Indicates an Optional Extension Header of length 6B
4 Indicates an Optional Extension Header of length 8B
5 Indicates an Optional Extension Header of length 10B
>=6 the combined H-LEN and H-TYPE values indicate the EtherType
of a PDU that directly follows this Type field.
A H-LEN of zero indicates a Mandatory Extension Header. Each
Mandatory Extension Header has a pre-defined length that is not
communicated in the H-LEN field. No additional limit is placed on
the maximum length of a Mandatory Extension Header. A Mandatory
Extension Header MAY modify the format or encoding of the enclosed
PDU (e.g. to perform encryption and/or compression).
The H-Type is a one byte field that is either one of 256 Mandatory
Header Extensions or one of 256 Optional Header Extensions. The set
of currently permitted values for both types of Extension Headers
are defined by an IANA Registry (section 15). Registry values for
Optional Extensions are specified in the form H=1 (i.e. a decimal
number in the range 256-511), but may be used with an H-Length value
in the range 1-5 (see example in 5.3).
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Two examples of Extension Headers are the Test_SNDU and the use of
Extension-Padding. The Test-SNDU Mandatory Extension Header results
in the entire PDU being discarded. The Extension-Padding Optional
Extension Header results in the following (if any) option header
being ignored (i.e. a total of H-LEN 16-bit words).
The general format for an SNDU with Extension Headers is:
< -------------------------- SNDU ------------------------- >
+---+--------------------------------------------------+--------+
|D=0| Length | T1 | NPA Address | H1 | T2 | PDU | CRC-32 |
+---+--------------------------------------------------+--------+
< ULE base header > < ext 1 >
Figure 8: SNDU Encapsulation with one Extension Header (for D=0).
Where:
D is the ULE D_bit (in this example D=0, however NPA addresses may
also be omitted when using Extension Headers).
T1 is the base header Type field. In this case, specifying a
Next-Header value.
H1 is a set of fields defined for header type T1. There may be 0
or more bytes of information for a specific ULE Extension Header.
T2 is the Type field of the next header, or an EtherType > 1535 B
indicating the type of the PDU being carried.
< -------------------------- SNDU ------------------------- >
+---+---------------------------------------------------+--------+
|D=1| Length | T1 | H1 | T2 | H2 | T3 | PDU | CRC-32 |
+---+---------------------------------------------------+--------+
< ULE base header >< ext 1 >< ext 2 >
Figure 9: SNDU Encapsulation with two Extension Headers (D=1).
Using this method, several Extension Headers MAY be chained in
series. Figure 12 shows an SNDU including two Extension Headers. The
values of T1 and T2 are both less than 1536 Decimal, each indicates
the presence of an Extension Header, rather than a directly
following PDU. T3 has a value > 1535 indicating the EtherType of the
PDU being carried. Although an SNDU may contain an arbitrary number
of consecutive Extension Headers, it is not expected that SNDUs will
generally carry a large number of extensions.
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5.1 Test SNDU
A Test SNDU (figure 10) is of Type 1. The structure of the Data
portion of this SNDU is not defined by this document. All Receivers
MAY record reception in a log file, but MUST then discard any Test
SNDUs. The D-bit MAY be set in a TEST SNDU.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|D| Length (15b) | Type = 0x0000 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
= Data (not forwarded by a Receiver) =
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (CRC-32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: SNDU Format for a Test SNDU
5.2 Bridge Frame SNDU Encapsulation
A bridged SNDU is of Type 1. The payload includes MAC address and
Ether-Type fields together with the contents of a bridged MAC frame.
The SNDU has the format shown in figures 11 and 12.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Length (15b) | Type = 0x0001 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Destination NPA Address (6B) |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| MAC Destination Address (6B) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Source Address (6B) |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | EtherType (2B) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
= (Contents of bridged MAC frame) =
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (CRC-32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: SNDU Format for a Bridged Payload (D=0)
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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 = 0x0001 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Destination Address (6B) |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| MAC Source Address (6B) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EtherType (2B) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
= (Contents of bridged MAC frame) =
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (CRC-32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: SNDU Format for a Bridged Payload (D=1)
Note: The final two bytes of the bridging header also carry a Type
field (see section 5). In this special case, the extension mandatory
header format permits this to carry a LLC Length field, specified by
IEEE 802 [LLC] rather than an IANA assigned value.
When an NPA address is specified (D=0), Receivers MUST discard all
SNDUs that carry an NPA destination address that does NOT match
their own NPA address (or a broadcast/multicast address), the
payload of the remaining SNDUs are processed by the bridging rules
that follow. An SNDU without an NPA address (D=1) results in a
Receiver performing bridging processing on the payload of all
received SNDUs.
The MAC addresses in the frame being bridged SHOULD be assigned
according to the rules specified by the IEEE and may denote unknown,
unicast, broadcast, and multicast link addresses. These MAC
addresses denote the intended recipient in the destination LAN, and
therefore have a different function to the NPA addresses carried in
the SNDU header. The EtherType field of a frame is defined according
to Ethernet/LLC [LLC].
A frame Type < 1536 for a bridged frame, introduces a LLC Length
field. The Receiver MUST check this length and discard any frame
with a length greater than permitted by the SNDU payload size.
In normal operation, it is expected that any padding appended to the
Ethernet frame SHOULD be removed prior to forwarding. This requires
the sender to be aware of such Ethernet padding (e.g. LLC).
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Ethernet frames received at the Encapsulator for onward transmission
over ULE carry a Local Area Network Frame Check sequence, LAN FCS,
field (e.g. CRC-32 for Ethernet). The Encapsulator MUST check the
LAN-FCS value of all frames received, prior to further processing.
Frames received with an invalid LAN FCS MUST be discarded. After
checking, the LAN FCS is then removed (i.e., it is NOT forwarded in
the bridged SNDU). As in other ULE frames, the Encapsulator appends
a CRC-32 to the transmitted SNDU. At the Receiver, an appropriate
LAN-FCS field will be appended to the bridged frame prior to onward
transmission on the Ethernet interface.
This design is readily implemented using existing network interface
cards, and does not introduce an efficiency cost by transmitting two
integrity check fields for bridged frames. However, it also
introduces the possibility that a frame corrupted within the
processing performed at an Encapsulator and/or Receiver may not be
detected by the final recipient(s) (i.e. such corruption would not
normally result in an invalid LAN FCS).
5.3 Extension-Padding Optional Extension Header
The Extension-Padding Optional Extension Header is specified by an
IANA assigned H-Type value of 0x100. As in other Optional
Extensions, the total length of the extension is indicated by the H-
LEN field (specified in 16-bit words). The extension field is formed
of a group of 1-5 16-bit fields.
For this specific option, only the last 16-bit word has an assigned
value, the sender SHOULD set the remaining values to 0x0000. The
last 16-bit field forms the Next-Header Type field. A Receiver MUST
interpret the Type field, but MUST ignore any other fields of this
Extension Header.
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6. Processing at the Encapsulator
The Encapsulator forms the PDUs queued for transmission into SNDUs
by adding a header and trailer to each PDU (section 4). It then
segments the SNDU into a series of TS Packet payloads (figure 9).
These are transmitted using a single TS Logical Channel over a TS
Multiplex. The TS Multiplex may be processed by a number of MPEG-2
(re)multiplexors before it is finally delivered to a Receiver [ID-
ipdvb-arch].
+------+--------------------------------+------+
| ULE | Protocol Data Unit | ULE |
|Header| |CRC-32|
+------+--------------------------------+------+
/ / \ \
/ / \ \
/ / \ \
+--------+---------+ +--------+---------+ +--------+---------+
|MPEG-2TS| MPEG-2 |...|MPEG-2TS| MPEG-2 |...|MPEG-2TS| MPEG-2 |
| Header | Payload | | Header | Payload | | Header | Payload |
+--------+---------+ +--------+---------+ +--------+---------+
Figure 13: Encapsulation of a SNDU into a series of TS Packets
6.1 SNDU Encapsulation
When an Encapsulator has not previously sent a TS Packet for a
specific TS Logical Channel, or after an Idle period, it starts to
send a SNDU in the first available TS Packet. This first TS Packet
generated MUST carry a PUSI value of 1. It MUST also carry a Payload
Pointer value of zero indicating the SNDU starts in the first
available byte of the TS Packet payload.
The Encapsulation MUST ensure that all TS Packets set the MPEG-2
Continuity Counter carried in the TS Packet header, according to
[ISO-MPEG]. This value MUST be incremented by one (modulo 16) for
each successive fragment/complete SNDU sent using a TS Logical
Channel.
An Encapsulator MAY decide not to immediately send another SNDU,
even if space is available in a partially filled TS Packet. This
procedure is known as Padding (figure 11). It informs the Receiver
that there are no more SNDUs in this TS Packet payload. The End
Indicator is followed by zero or more unused bytes until the end of
the TS Packet payload. All unused bytes MUST be set to the value of
0xFF, following current practice in MPEG-2 [ISO-DSMCC]. The Padding
procedure trades decreased efficiency against improved latency.
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+-/------------+
| SubNetwork |
| DU 3 |
+-/------------+
\ \
\ \
\ \
+--------+--------+--------+----------+
|MPEG-2TS| End of | 0xFFFF | Unused |
| Header | SNDU 3 | | Bytes |
+--------+--------+--------+----------+
PUSI=0 ULE
End
Indicator
Figure 14: A TS Packet carrying the end of SNDU 3, followed by an
End Indicator.
Alternatively, when more packets are waiting at an Encapsulator, and
a TS Packet has sufficient space remaining in the payload, the
Encapsulator can follow a previously encapsulated SNDU with another
SNDU using the next available byte of the TS Packet payload (see
6.2). This is called Packing (figure 15).
+-/----------------+ +----------------/-+
| Subnetwork | | Subnetwork |
| DU 1 | | DU 2 |
+-/----------------+ +----------------/-+
\ \ / /\
\ \ / / \
\ \ / / \. . .
+--------+--------+--------+----------+
|MPEG-2TS| Payload| end of | start of |
| Header | Pointer| SNDU 1 | SNDU 2 |
+--------+--------+--------+----------+
PUSI=1 | ^
| |
+--------------+
Figure 15: A TS Packet with the end of SNDU 1, followed by SNDU 2.
6.2 Procedure for Padding and Packing
Five possible actions may occur when an Encapsulator has completed
encapsulation of an SNDU:
(i) If the TS Packet has no remaining space, the Encapsulator
transmits this TS Packet. It starts transmission of the next SNDU in
a new TS Packet. (The standard rules [ISO-MPEG] require the header
of this new TS Packet to carry a PUSI value of 1, and a Payload
Pointer value of 0x00.)
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(ii) If the TS Packet carrying the final part of a SNDU has one byte
of unused payload, the Encapsulator MUST place the value 0xFF in
this final byte, and transmit the TS Packet. This rule provides a
simple mechanism to resolve the complex behaviour that may arise
when the TS Packet has no PUSI set. To send another SNDU in the
current TS Packet, would otherwise require the addition of a Payload
Pointer that would consume the last remaining byte of TS Packet
payload. The behaviour follows similar practice for other MPEG-2
payload types [ISO-DSMCC]. The Encapsulator MUST start transmission
of the next SNDU in a new TS Packet. (The standard rules require the
header of this new TS Packet to carry a PUSI value of 1 and a
Payload Pointer value of 0x00.)
(iii) If the TS Packet carrying the final part of a SNDU has exactly
two bytes of unused payload, and the PUSI was NOT already set, the
Encapsulator MUST place the value 0xFFFF in this final two bytes,
providing an End Indicator (section 4.3), and transmit the TS
Packet. This rule prevents fragmentation of the SNDU Length Field
over two TS Packets. The Encapsulator MUST start transmission of the
next SNDU in a new TS Packet. (The standard rules require the header
of this new TS Packet to carry a PUSI value of 1 and a Payload
Pointer value of 0x00.)
(iv) If the TS Packet has more than two bytes of unused payload, the
Encapsulator MAY transmit this partially full TS Packet but MUST
first place the value 0xFF in all remaining unused bytes (i.e.
setting an End Indicator followed by Padding). The Encapsulator MUST
start transmission of the next SNDU in a new TS Packet. (The
standard rules [ISO-MPEG] require the header of this new TS Packet
to carry a PUSI value of 1 and a Payload Pointer value of 0x00.)
(v) If at least two bytes are available for payload data in the TS
Packet payload (i.e. three bytes if the PUSI was NOT previously set,
and two bytes if it was previously set), the Encapsulator MAY
encapsulate further queued PDUs, by starting the next SNDU in the
next available byte of the current TS Packet payload. The PUSI MUST
be set. When the Encapsulator packs further SNDUs into a TS Packet
where the PUSI has NOT already been set, this requires the PUSI to
be updated (set to 1) and an 8-bit Payload Pointer MUST be inserted
in the first byte directly following the TS Packet header. The value
MUST be set to the position of the byte following the end of the
first SNDU in the TS Packet payload. If no further PDUs are
available, an Encapsulator MAY wait for additional PDUs to fill the
incomplete TS Packet. The maximum period of time an Encapsulator can
wait, known as the Packing Threshold, MUST be bounded and SHOULD be
configurable in the Encapsulator. If sufficient additional PDUs are
NOT received to complete the TS Packet within the Packing Threshold,
the Encapsulator MUST insert an End Indicator (using rule iv).
Use of the Packing method (v) by an Encapsulator is optional, and
may be determined on a per-session, per-packet, or per-SNDU basis.
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When a SNDU is less than the size of a TS Packet payload, a TS
Packet may be formed that carries a PUSI value of one and also an
End Indicator (using rule iv).
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7. Receiver Processing
A Receiver tunes to a specific TS Multiplex and sets a receive
filter to accept all TS Packets with a specific PID. These TS
Packets are associated with a specific TS Logical Channel and are
reassembled to form a stream of SNDUs. A single Receiver may be
able to receive multiple TS Logical Channels, possibly using a range
of TS Multiplexes. In each case, reassembly MUST be performed
independently for each TS Logical Channel. To perform this
reassembly, the Receiver may use a buffer to hold the partially
assembled SNDU, referred to here as the Current SNDU buffer. Other
implementations may choose to use other data structures, but MUST
provide equivalent operations.
Receipt of a TS Packet with a PUSI value of 1 indicates that the TS
Packet contains the start of a new SNDU. It also indicates the
presence of the Payload Pointer (indicating the number of bytes to
the start of the first SNDU in the TS-Packet currently being
reassembled). It is illegal to receive a Payload Pointer value
greater than 181, and this MUST cause the SNDU reassembly to be
aborted and the Receiver to enter the Idle State. This event SHOULD
be recorded as a payload pointer error.
A Receiver MUST support the use of both the Packing and Padding
method for any received SNDU, and MUST support reception of SNDUs
with or without a Destination Address Field (i.e. D=0 and D=1).
7.1 Idle State
After initialisation, errors, or on receipt of an End Indicator, the
Receiver enters the Idle State. In this state, the Receiver discards
all TS Packets until it discovers the start of a new SNDU, when it
then enters the Reassembly State. Figure 16 outlines these state
transitions:
+-------+
| START |
+---+---+
|
\/
+----------+
\| Idle |/
+-------/| State |\-------+
Insufficient | +----+-----+ |
unused space | | PUSI set | MPEG-2 TS Error
or | \/ | or
End Indicator| +----------+ | SNDU Error
| |Reassembly| |
+--------| State |--------+
+----------+
Figure 16: Receiver state transitions
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7.1.1 Idle State Payload Pointer Checking
A Receiver in the Idle State MUST check the PUSI value in the header
of all received TS Packets. A PUSI value of 1 indicates the presence
of a Payload Pointer. Following a loss of synchronisation, values
between 0 and 181 are permitted, in which case the Receiver MUST
discard the number of bytes indicated by the Payload Pointer from
the start of the TS Packet payload, before leaving the Idle State.
It then enters the Reassembly State, and starts reassembly of a new
SNDU at this point.
7.2 Processing of a Received SNDU
When in the Reassembly State, the Receiver reads a 2 byte SNDU
Length Field from the TS Packet payload. If the value is less than
or equal to 4, or equal to 0xFFFF, the Receiver discards the Current
SNDU and the remaining TS Packet payload and returns to the Idle
State. Receipt of an invalid Length Field is an error event and
SHOULD be recorded as an SNDU length error.
If the Length of the Current SNDU is greater than 4, the Receiver
accepts bytes from the TS Packet payload to the Current SNDU buffer
until either Length bytes in total are received, or the end of the
TS Packet is reached (see also 7.2.1). When Current SNDU length
equals the value of the Length Field, the Receiver MUST calculate
and verify the CRC value (see 4.6). SNDUs that contain an invalid
CRC value MUST be discarded. Mismatch of the CRC is an error event
and SHOULD be recorded as a CRC error. The under-lying physical-*
layer processing (e.g. forward error correction coding) often
results in patterns of errors, rather than since bit errors, so the
Receiver needs to be robust to arbitrary patterns of corruption to
the TS Packet and payload, including potential corruption of the
PUSI, PP, and SNDU Length fields. Therefore, a Receiver SHOULD
discard the remaining TS Packet payload (if any) following a CRC
mismatch and return to the Idle State.
When the Destination Address is present (D=0), the Receiver accepts
SNDUs that match one of a set of addresses specified by the Receiver
(this includes the NPA address of the Receiver, the NPA broadcast
address and any required multicast NPA addresses). The Receiver MUST
silently discard an SNDU with an unmatched address.
After receiving a valid SNDU, the Receiver MUST check the Type Field
(and process any Type 1 Extension Headers). The SNDU payload is then
passed to the next protocol layer specified. An SNDU with an unknown
Type value < 1536 MUST be discarded. This error event SHOULD be
recorded as a SNDU type error.
The Receiver then starts reassembly of the next SNDU. This MAY
directly follow the previously reassembled SNDU within the TS Packet
payload.
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(i) If the Current SNDU finishes at the end of a TS Packet payload,
the Receiver MUST enter the Idle State.
(ii) If only one byte remains unprocessed in the TS Packet payload
after completion of the Current SNDU, the Receiver MUST discard this
final byte of TS Packet payload. It then enters the Idle State. It
MUST NOT record an error when the value of the remaining byte is
identical to 0xFF.
(iii) If two or more bytes of TS Packet payload data remain after
completion of the Current SNDU, the Receiver accepts the next 2
bytes and examines if this is an End Indicator. When an End
Indicator is received, a Receiver MUST silently discard the
remainder of the TS Packet payload and transition to the Idle State.
Otherwise this is the start of the next Packed SNDU, and the
Receiver continues by processing this SNDU.
7.2.1 Reassembly Payload Pointer Checking
A Receiver that has partially received a SNDU (in the Current SNDU
buffer) MUST check the PUSI value in the header of all subsequent TS
Packets with the same PID (i.e. same TS Logical Channel). If it
receives a TS Packet with a PUSI value of 1, it MUST then verify the
Payload Pointer. If the Payload Pointer does NOT equal the number of
bytes remaining to complete the Current SNDU, i.e., the difference
between the SNDU Length field and the number of reassembled bytes,
the Receiver has detected a delimiting error.
Following a delimiting error, the Receiver MUST discard the
partially assembled SNDU (in the Current SNDU buffer), and SHOULD
record a reassembly error. It MUST then re-enter the Idle State.
7.3 Other Error Conditions
The Receiver SHOULD check the MPEG-2 Transport Error Indicator
carried in the TS Packet header [ISO-MPEG]. This flag indicates a
transmission error for a TS Logical Channel. If the flag is set to a
value of one, a transmission error event SHOULD be recorded. Any
partially received SNDU MUST be discarded. The Receiver then enters
the Idle State.
The Receiver MUST check the MPEG-2 Continuity Counter carried in the
TS Packet header [ISO-MPEG]. If two (or more) successive TS Packets
within the same TS Logical Channel carry the same Continuity Counter
value, the duplicate TS Packets MUST be silently discarded. If the
received value is NOT identical to that in the previous TS Packet,
and it does NOT increment by one for successive TS Packets (modulo
16), the Receiver has detected a continuity error. Any partially
received SNDU MUST be discarded. A continuity counter error event
SHOULD be recorded. The Receiver then enters the Idle State.
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Note that an MPEG2-2 Transmission network is permitted to carry
duplicate TS Packets [ISO-MPEG], which are normally detected by the
MPEG-2 Continuity Counter. A Receiver that does not perform the
above Continuity Counter check, would accept duplicate copies of TS
Packets to the reassembly procedure. In most cases, the SNDU CRC-32
integrity check will result in discard of these SNDUs, leading to
unexpected PDU loss, however in some cases, duplicate PDUs (fitting
into one TS Packet) could pass undetected to the next layer
protocol.
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8. Summary
This document defines an Ultra Lightweight Encapsulation (ULE) to
perform efficient and flexible support for IPv4 and IPv6 network
services over networks built upon the MPEG-2 Transport Stream (TS).
The encapsulation is also suited to transport of other protocol
packets and bridged Ethernet frames.
ULE also provides an Extension Header format and defines an
associated IANA registry for efficient and flexible support of both
mandatory and optional SNDU headers. This allows for future
extension of the protocol, while providing backwards capability with
existing implementations. In particular, Optional Extension Headers
may safely be ignored by Receiver drivers that do not implement
them, or choose not to process them.
9. Acknowledgments
This draft is based on a previous draft authored by: Horst D.
Clausen, Bernhard Collini-Nocker, Hilmar Linder, and Gorry
Fairhurst. The authors wish to thank the members of the ip-dvb
mailing list for their input provided. In particular, the many
comments received from Patrick Cipiere, Wolgang Fritsche, Hilmar
Linder, Alain Ritoux, and William Stanislaus. Alain also provided
the original examples of usage.
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10. Security Considerations
The security considerations for ULE resemble those that arise when
the existing Multi-Protocol Encapsulation (MPE) is used. ULE does
not add specific new threats that will impact the security of the
general Internet.
There is a known security issue with un-initialised stuffing bytes.
In ULE, these bytes are set to 0xFF (normal practice in MPEG-2).
There are known integrity issues with the removal of the LAN FCS in
a bridged networking environment. The removal for bridged frames
exposes the traffic to potentially undetected corruption while being
processed by the Encapsulator and/or Receiver.
There is a potential security issue when a Receiver receives a PDU
with two length fields: The Receiver would need to validate the
actual length and the Length Field and ensure that inconsistent
values are not propagated by the network. In direct encapsulation of
IPv4/IPv6 in ULE, this is avoided by including only one SNDU Length
Field. However, this issue still arises in bridged LLC frames, and
frames with a LLC Length greater than the SNDU payload size MUST be
discarded, and a SNDU payload length error SHOULD be recorded.
A ULE Mandatory Extension Header may in future be used to define a
method to perform link encryption of the SNDU payload. This is as an
additional security mechanism to IP, transport or application layer
security - not a replacement [ID-ipdvb-arch]. The approach is
generic and decouples the encapsulation from future security
extensions. The operation provides functions that resemble those
currently used with the MPE encapsulation.
Additional security control fields may be provided as a part of this
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 SNDU 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.
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11. References
11.1 Normative References
[ISO-MPEG] ISO/IEC DIS 13818-1 "Information technology -- Generic
coding of moving pictures and associated audio information:
Systems", International Standards Organisation (ISO).
[RFC2026] Bradner, S., "The Internet Standards Process - Revision
3", BCP 9, RFC 2026, BCP 9, 1996.
[RFC2119] Bradner, S., "Key Words for Use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, 1997.
[RFC3667] Bradner, S., "IETF Rights in Contributions", BCP 78, RFC
3667, February 2004.
[RFC3668] Bradner, S., "Intellectual Property Rights in IETF
Technology", BCP 79, RFC 3668, February 2004.
11.2 Informative References
[ID-ipdvb-arch] "Requirements for transmission of IP datagrams over
MPEG-2 networks", Internet Draft, Work in Progress.
[ATSC] A/53, "ATSC Digital Television Standard", Advanced Television
Systems Committee (ATSC), Doc. A/53 Rev.C, 2004
[ATSC-DAT] A/90, "ATSC Data Broadcast Standard", Advanced Television
Systems Committee (ATSC), Doc. A/090, 2000.
[ATSC-DATG] A/91, "Recommended Practice: Implementation Guidelines
for the ATSC Data Broadcast Standard", Advanced Television Systems
Committee (ATSC), Doc. A/91, 2001.
[ATSC-G] A/54, "Guide to the use of the ATSC Digital Television
Standard", Advanced Television Systems Committee (ATSC), Doc. A/54,
1995.
[ATSC-PSIP-TC] A/65A, "Program and System Information Protocol for
Terrestrial Broadcast and Cable", Advanced Television Systems
Committee (ATSC), Doc. A/65A, 23 Dec 1997, Rev. A, 2000.
[ATSC-S] A/80, "Modulation and Coding Requirements for Digital TV
(DTV) Applications over Satellite", Advanced Television Systems
Committee (ATSC), Doc. A/80, 1999.
[CLC99] Clausen, H., Linder, H., and Collini-Nocker, B., "Internet
over Broadcast Satellites", IEEE Commun. Mag. 1999, pp.146-151.
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INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB January 2005
[ETSI-DAT] EN 301 192 "Specifications for Data Broadcasting",
European Telecommunications Standards Institute (ETSI).
[ETSI-DVBC] EN 300 800 "Digital Video Broadcasting (DVB); DVB
interaction channel for Cable TV distribution systems (CATV)",
European Telecommunications Standards Institute (ETSI).
[ETSI-DVBS] EN 301 421 "Digital Video Broadcasting (DVB); Modulation
and Coding for DBS satellite systems at 11/12 GHz", European
Telecommunications Standards Institute (ETSI).
[ETSI-DVBT] EN 300 744 "Digital Video Broadcasting (DVB); Framing
structure, channel coding and modulation for digital terrestrial
television (DVB-T)", European Telecommunications Standards Institute
(ETSI).
[ETSI-RCS] ETSI 301 791 "Digital Video Broadcasting (DVB);
Interaction Channel for Satellite Distribution Systems", European
Telecommunications Standards Institute (ETSI).
[ISO-DSMCC] ISO/IEC IS 13818-6 "Information technology -- Generic
coding of moving pictures and associated audio information -- Part
6: Extensions for DSM-CC", International Standards Organisation
(ISO).
[ITU-I363] ITU-T I.363.5 B-ISDN ATM Adaptation Layer Specification
Type AAL5, International Standards Organisation (ISO), 1996.
[LLC] "IEEE Logical Link Control" (ANSI/IEEE Std 802.2/ ISO 8802.2),
1985.
[RFC3077] E. Duros, W. Dabbous, H. Izumiyama, Y. Zhang, "A Link
Layer Tunneling Mechanism for Unidirectional Links", RFC3077,
Proposed Standard, 2001.
[RFC3309] Stone, J., R. Stewart, D. Otis. "Stream Control
Transmission Protocol (SCTP) Checksum Change". RFC3095, Proposed
Standard, 2001.
[RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. Wood,
"Advice for Internet Subnetwork Designers", BCP 89, RFC 3819, July
2004.
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12. 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 Scientific Computing
University of Salzburg
Jakob Haringer Str. 2
5020 Salzburg
Austria
Email: bnocker@cosy.sbg.ac.at
Web: http://www.scicomp.sbg.ac.at/
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13. IPR Notices
13.1 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
rights might or might not be available; nor does it represent that
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
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use
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
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
13.2 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 AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
14. Copyright Statement
Copyright (C) The Internet Society (2004). 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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15. IANA Considerations
This document will require IANA involvement.
The ULE Next-Header type field defined in this document requires
creation of a registry:
ULE Next-Header registry
This registry allocates values 0-512 (decimal).
15.1 IANA Guidelines
The following contains the IANA guidelines for management of the ULE
Next-Header registry. This registry allocates values 0-512 decimal
(0x0000-0x01FF, hexadecimal). It MUST NOT allocate values greater
than 0x01FF (decimal).
It subdivides the Next-Header registry in the following way:
1) 0-255 (decimal) IANA assigned values indicating Mandatory
Extension Headers (or link-dependent type fields) for ULE,
requiring expert review leading to prior issue of an IETF RFC.
This specification must define the value, and the name associated
with the Extension Header. It must also define the need for the
extension and the intended use. The size of the Extension Header
must also be specified.
Assignments made in this document:
Type Name Reference
0: Test-SNDU Section 4.7.4.
1: Bridged-SNDU Section 4.7.5.
2) 256-511 (decimal) IANA assigned values indicating Optional
Extension Headers for ULE, requiring expert review leading to
prior issue of an IETF RFC. This specification must define the
value, and the name associated with the Extension Header. The
entry must specify range of allowable H-LEN values that are
permitted (in the range 1-5). It must also define the need for the
extension and the intended use.
Assignments made in this document:
Type Name H-LEN Reference
256: Extension-Padding 1-5 Section 5.
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ANNEXE A: Informative Appendix - SNDU Packing Examples
This appendix provides some examples of use. The appendix is
informative. It does not provide a description of the protocol. The
examples provide the complete TS Packet sequence for some sample
encapsulated IP packets.
The specification of the TS Packet header operation and field values
is provided in [ISO-MPEG]. The specification of ULE is provided in
the body of this document.
The key below is provided for the following examples.
HDR 4B TS Packet Header
PUSI Payload Unit Start Indicator
PP Payload Pointer
*** TS Packet Payload Pointer (PP)
Example A.1: Two 186B PDUs.
SNDU A is 200 bytes (including destination MAC address)
SNDU B is 200 bytes (including destination MAC address)
The sequence comprises 3 TS Packets:
SNDU
PP=0 Length
+-----+------+------+------+- -+------+
| HDR | 0x00 | 0x00 | 0xC4 | ... | A182 |
+-----+----*-+-*----+------+- -+------+
PUSI=1 * *
*****
SNDU
PP=17 CRC for A Length
+-----+------+------+- -+--- --+------+------+- -+------+
| HDR | 0x11 | A183 | ... | A199 | 0x00 | 0xC4 | ... | B165 |
+-----+----*-+------+- -+------+-*----+------+- -+------+
PUSI=1 * *
*************************
End Stuffing
CRC for A Indicator Bytes
+-----+------+- -+------+----+----+- -+----+
| HDR | B166 | ... | B199 |0xFF|0xFF| ... |0xFF|
+-----+------+- -+------+----+----+- -+----+
PUSI=0
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Example A.2: Usage of last byte in a TS-Packet
SNDU A is 183 bytes
SNDU B is 182 bytes
SNDU C is 181 bytes
SNDU D is 185 bytes
The sequence comprises 4 TS Packets:
SNDU
PP=0 Length CRC for A
+-----+------+------+------+- -+------+
| HDR | 0x00 | 0x00 | 0x63 | ... | A182 |
+-----+----*-+-*----+------+- -+------+
PUSI=1 * *
*****
SNDU Unused
PP=0 Length CRC for B byte
+-----+------+------+------+- -+------+------+
| HDR | 0x00 | 0x00 | 0x62 | ... | B181 | 0xFF |
+-----+---*--+-*----+------+- -+------+------+
PUSI=1 * *
******
SNDU SNDU
PP=0 Length CRC for C Length
+-----+------+------+------+- -+------+------+------+
| HDR | 0x00 | 0x00 | 0x61 | ... | C180 | 0x00 | 0x65 |
+-----+---*--+-*----+------+- -+------+------+------+
PUSI=1 * *
****** Unused
byte
+-----+------+- -+------+------+
| HDR | D002 | ... | D184 | 0xFF |
+-----+------+- -+------+------+
PUSI=0
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Example A.3: Large SNDUs
SNDU A is 732 bytes
SNDU B is 284 bytes
The sequence comprises 6 TS Packets:
SNDU
PP=0 Length
+-----+------+------+------+- -+------+
| HDR | 0x00 | 0x02 | 0xD8 | ... | A182 |
+-----+---*--+-*----+------+- -+------+
PUSI=1 * *
******
+-----+------+- -+------+
| HDR | A183 | ... | A366 |
+-----+------+- -+------+
PUSI=0
+-----+------+- -+------+
| HDR | A367 | ... | A550 |
+-----+------+- -+------+
PUSI=0
SNDU
PP=181 CRC for A Length
+-----+------+------+- -+------+------+------+
| HDR | 0xB5 | A551 | ... | A731 | 0x01 | 0x18 |
+-----+---*--+------+- -+------+*-----+------+
PUSI=1 * *
*************************
+-----+------+- -+------+
| HDR | B002 | ... | B185 |
+-----+------+- -+------+
PUSI=0
End Stuffing
Indicator Bytes
+-----+------+- -+------+------+------+- -+------+
| HDR | B186 | ... | B283 | 0xFF | 0xFF | ... | 0xFF |
+-----+------+- -+------+------+------+- -+------+
PUSI=0
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Example A.4: Packing of SNDUs
SNDU A is 200 bytes
SNDU B is 60 bytes
SNDU C is 60 bytes
The sequence comprises two TS Packets:
SNDU
PP=0 Length
+-----+------+------+------+- -+------+
| HDR | 0x00 | 0x00 | 0xC4 | ... | A182 |
+-----+----*-+-*----+------+- -+------+
PUSI=1 * * + +
***** ++++++++
+
+++++++++++++++++
+ SNDU
PP=17 CRC for A + Length
+-----+------+------+- -+------+-+----+------+-
| HDR | 0x11 | A183 | ... | A199 | 0x00 | 0x38 | ...
+-----+----*-+------+- -+------+*-----+------+-
PUSI=1 * * + +
************************ +++++++++
+
+++++++++++++++++++++++++++++++++++++++
+
+ SNDU End Stuffing
+ Length Indicator bytes
+ -+------+------+------+ -+------+------+------+- -+------+
+ ... | B59 | 0x00 | 0x38 |...| C59 | 0xFF | 0xFF |...| 0xFF |
+ -+------+-+----+------+ -+------+-+----+------+- -+------+
+ + + + +
+ + ++++++++ +
+ + + +
++++++++++++++++ ++++++++++++++++++++++
*** TS Packet Payload Pointer (PP)
+++ ULE Length Indicator
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Example A.5: Three 44B PDUs.
SNDU A is 52 bytes (no destination MAC address)
SNDU B is 52 bytes (no destination MAC address)
SNDU C is 52 bytes (no destination MAC address)
The sequence comprises 1 TS Packet:
SNDU
PP=0 Length
+-----+------+------+------+- -+-----+------+-----+- -+-----+-
| HDR | 0x00 | 0x80 | 0x34 | ... | A51 |0x80 | 0x34 | ... | B51 | ..
+-----+----*-+-*----+------+- -+-----+-*----+-----+- -+-----+-
PUSI=1 * *
*****
End Stuffing
Indicator bytes
-----+------+- -+-----+---------+- -+------+
... 0x80 | 0x34 | ... | C51 |0xFF|0xFF| | 0xFF |
-*---+------+- -+-----+---------+- -+------+
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ANNEXE B: Informative Appendix - SNDU Encapsulation
An example of ULE encapsulation carrying an ICMPv6 packet generated
by ping6.
ULE SNDU Length : 63 decimal
D-bit value : 0 (NPA Present)
ULE Protocol Type : 0x86dd (IPv6)
Destination ULE NPA Address: 00:01:02:03:04:05
ULE CRC32 : 0x4709a744
Source IPv6: 2001:660:3008:1789::5
Destination IPv6: 2001:660:3008:1789::6
SNDU contents (including CRC-32):
0000: 00 3f 86 dd 00 01 02 03 04 05 60 00 00 00 00 0d
0016: 3a 40 20 01 06 60 30 08 17 89 00 00 00 00 00 00
0032: 00 05 20 01 06 60 30 08 17 89 00 00 00 00 00 00
0048: 00 06 80 00 9d 8c 06 38 00 04 00 00 00 00 00 47
0064: 09 a7 44
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[RFC EDITOR NOTE:
This section must be deleted prior to publication]
DOCUMENT HISTORY
Draft 00
This draft is intended as a study item for proposed future work by
the IETF in this area. Comments relating to this document will be
gratefully received by the author(s) and the ip-dvb mailing list at:
ip-dvb@erg.abdn.ac.uk
--------------------------------------------------------------------
DRAFT 01 (Protocol update)
* Padding sequence modified to 0xFFFF, this change aligns with other
usage by MPEG-2 streams. Treatment remains the same as specified for
ULE.
* SDNU Format updated to include R-bit (reserved).
* Procedure for TS Packet carrying the final part of a SNDU with
either less than two bytes of unused payload updated.
* A Receiver MUST silently discard the remainder of a TS Packet
payload when two or less bytes remain unprocessed following the end
of a SNDU, irrespective of the PUSI value in the received TS Packet.
It MUST NOT record an error when the value of the remaining byte(s)
is identical to 0xFF or 0xFFFF. The Receiver MUST then wait for a
TS Packet with a PUSI value set to 1.
* Payload Pointer description updated.
* CRC Calculation added.
* Decapsulator processing revised.
* Type field split into two.
* References updated.
* Security considerations added (first draft).
* Appendix added with examples.
--------------------------------------------------------------------
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DRAFT - 02 (Improvement of clarity)
* Corrected CRC-32 to follow standard practice in DSM-CC.
* Removed LLC frame type, now redundant by Bridge-Type (==1)
* Defined D-bit to use the reserved bit field (R ) - Gorry, Alain,
Bernhard
* Changes to description of minimum payload length. Gorry
* MPEG-2 Error Indicator SHOULD be used.Hilmar & Gorry
* MPEG-2 CC MAY be used (since CRC-32 is strong anyway). Hilmar &
Gorry
* Corrected CRC-32 to now follow standard practice in DSM-CC. Gorry,
Hilmar, Alain.
* Changed description of Encapsulator action for Packing. Gorry &
Hilmar.
* Changed description of Receiver to clarify packing. Gorry & Alain.
* Stuff/Pad of unused bytes MUST be 0xFF, to align with MPEG.
Hilmar/Bernhard.
* Recommend removal of section on Flushing bit stream. Gorry
* Updated SNDU figures to reflect D-bit and correct a mistake in the
bridged type field. Alain
* Reorganised section 5 to form sections 5 and 6, separating
encapsulation and receiver processing. Gorry, Hilmar, Alain.
* Added concept of Idle State and Reassembly State to the Receiver.
Renumbered sections 5,6 and following. Gorry.
* Nits from Alain, Hilmar and Gorry.
Moved security issue on the design of the protocol to appropriate
sections, since this is not a concern for deployment: Length field
usage and padding initialisation.
* Changed wording: All multi-byte values in ULE (including Length,
Type, and Destination fields) are transmitted in network byte order
(most significant byte first). old NiT from Alain, now fixed.
* Frame byte size in diagrams now updated to -standard- format, and
D bit action corrected, as requested by Alain.
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* Frame format diagrams, redrawn to 32-bit format below:
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
* Additional diagram requested by Alain for D=0 bridging (added, and
subsequent figures renumbered).
* Diagrams of encapsulation process, redrawn for clarity (no change
to meaning). Gorry.
* Reworded last para of CRC description.
* Clarification to the statements in the CRC coverage - to make it
clear that it is the entire SNDU (header AND payload) that is
checksummed. (Fritsche@iabg.de, hlinder@cosy.sbg.ac.at).
* References added for RCS (spotted by Alain) and AAL5 (provided by
Anthony Ang).
* Removed informative reference to MPEG part 1.Alain.
Spelling correction -> Allain to Alain.
* Added description of Receiver processing of the address
field.Gorry
* Added caution on LLC Length in bridged Packets thanks.
Gorry/wolfgang
* Removed Authors notes from text after their discussion on the list
Gorry
* Corrected text to now say maximum value of PP = 182 in ULE. Gorry
* Tidied diagrams at end (again) - Gorry,
Revision with following changes:
* Re issue as working group draft (filename change)
* Refinement of the text on CRC generation to be unambiguous.
* Revised CC processing at Encapsulator (B C-N/GF/A.Allison)
* Revised CC processing at Receiver (from List: A.Allison; et al )
* Corrections to length/PP field in Examples (M Sooriyabandara,
Alain)
* Corrections to pointer in Example 3 SNDU C (M Jose-Montpetit)
* Section 4.5 only SHARED routed links require D=0
* Packing Threshold defined
* Next-Layer-Header defined (Now called Next-Header)
* Addition of Appendix B (to aide verification of SNDFU format)
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Working Group ID rev 01
Issues addressed:
* Typographical
* Types > 1500 should be passed to the next higher protocol (Hilmar)
* The second part of the Type space corresponds to the values 1500
COMMENT: ~Range should be 1536 Decimal Decimal to 0xFFFF.
* IANA has already defined IP and IPv6 types - corrected text!
Added more security considerations (-01d).
* Should we allow an Adaptation Field within ULE (request for DVB-
RCS compatibility)? Requirement to be clarified! Implementation
impact to be evaluated!
Current Recommendation: The current spec does not preclude use of
AF, it simply says that this is not the standard for ULE. The use
case and requirement for this mode are not currently clear, based on
this there is no current intention to add this to ULE - text for
requirements would be welcome.
* Verify the minimum value allocated to DIX Ethernet Header Types.
Draft updated to align with IEEE Registry assignments.
--------------------------------------------------------------------
Working Group ID rev 02
Revised IPR disclosure
Revised copyright notice
Section 5 added to ULE to define optional Extension Headers (see
xule)
Correction of figure numbering.
Correction to capitalisation in Transport Stream definition of fields
Inserted space character after 1536 in line 2 of 4.4.2
Replaced } with ] after ISO_DSMCC
Replace reference to section 6.3 with section 7.3 at end of section
4.6.
Reference in 4.7.4 was changed to refer to figure 7 (not 6).
Note added after figure 9.
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Working Group ID rev 03
Changes with this revision of the document:
(i) The worked hexadecimal example in the annexe was reworked to
include a valid MAC address for an IPv6 unicast packet. -
(BCN)
(ii) The IANA procedures revised, based on inputs from IANA to
improve consistency of the term Next-Header and to add the
HLEN field to the IANA registry record for OPTIONAL headers.
(GF)
(iii) 7.2 Change to revert wording in the second para to MUST enter
IDLE after CRC failure of SNDU check.
(iv) In normal operation, it is expected that any padding appended
to a bridged Ethernet frame SHOULD be removed prior to
forwarding. This requires the sender to be aware of such
Ethernet padding (e.g. LLC). (Made this a SHOULD). (GF)
NiTS:
(v) Format of page Breaks was updated. (GF)
(vi) Check for <- -> sequences of characters. (GF)
(vii) Update refs to add RFC3667 / 3668. (GF)
(viii) Changed text defining M in DSMCC definition to the word Media
(ix) 7.1.1 Range of PP values corrected to 0-181.
(x) Definition of END INDICATOR corrected in section 2 - this is
not a TYPE value, but a LENGTH value.
(xi) Next-Header used throughout the document to replace
next-layer-header, and various other forms of wording.
(xii) In section 7.2, added a ref the section on PP checking
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Working Group ID rev 04
This rev followed WGLC comments, which are defined in the ipdvb
mailing list. Important changes included:
(i) This text was moved to an appendix
(ii) ToC was updated and section headers made consistent
(iii) Revised definition text
(iv) Improved clarity with respect to terms defined in ISO 18181-1
(v) Bridging and Extension-Padding formats move to section 5
(vi) Clarification of the NPA in packet headers
(vii) Clarification of placement of NPA address with extension headers.
[END of RFC EDITOR NOTE]
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