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Versions: 00 01 02                                                      
     Internet Engineering Task Force                         Gorry Fairhurst
     Internet Draft                             University of Aberdeen, U.K.
     Document: draft-fair-ipdvb-ule-01.txt           Bernhard Collini-Nocker
                                                   University of Salzburg, A
     Revision 1d
     
     
     
     Category: Draft -Intended Standards Track                  October 2003
     
     
             Ultra Lightweight Encapsulation (ULE) for transmission of
                     IP datagrams over MPEG-2/DVB networks
     
     Status of this Draft
     
        This document is an Internet-Draft and is in full conformance with
           all provisions of Section 10 of RFC2026.
     
        Internet-Drafts are working documents of the Internet Engineering
        Task Force (IETF), its areas, and its working groups. Note that
        other groups may also distribute working documents as Internet-
        Drafts. Internet-Drafts are draft documents valid for a maximum of
        six months and may be updated, replaced, or obsoleted by other
        documents at any time. It is inappropriate to use Internet- Drafts
        as reference material or to cite them other than as "work in
        progress."
     
        The list of current Internet-Drafts can be accessed at
        http://www.ietf.org/ietf/1id-abstracts.txt
        The list of Internet-Draft Shadow Directories can be accessed at
        http://www.ietf.org/shadow.html.
     
        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.
     
     
     
     
     
     
     
     
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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 Text corrected. Protocol amended following discussion on
        the list.
     
        1) Padding sequence modified to 0x0000, from 0xFFFF, this change
           aligns with other usage by MPEG-2 streams. Treatment remains the
           same as specified for ULE.
     
        2) SDNU Format updated.
     
        3) Procedure added for TS Packet carrying the final part of a SNDU
        with either less than two bytes of unused payload updated.
     
        4) 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.
     
        5) Payload Pointer (PP) description updated.
     
        6) CRC Calculation added.
     
        7) Decapsulator processing revised.
     
        8) Type field split into two parts.
     
        9) References updated
     
        10) Security considerations added (first draft)
     
        11) Appendix added with examples.
     
     
        KNOWN ISSUES (to be addressed by WG):
             (i) No method is mandated to select the SNDU format without MAC
        destination address.
     
     
        [END of RFC EDITOR NOTE]
     
     
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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 Field
          4.2 Length Field
          4.3 End Indicator
          4.4 Type Field
            4.4.1 Type 1: IANA Assigned 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
            4.7.4 Test SNDU
        5. Processing at the Encapsulator and Receiver
        5.1 Encapsulator processing
          5.1.1 Flushing the Bitstream
        5.2 Receiver Processing
          5.2.1 Idle State
          5.2.2 Processing of Received SNDUs
          5.2.3 Payload Pointer Checking
        5.3 SNDU Packing
          5.3.1 Encapsulator Packing
          5.3.2 Processing of Packed SNDUs at the Receiver
        6. Summary
        7. Acknowledgments
        8. Security Considerations
        9. References
        9.1 Normative References
        9.2 Informative References
        10. Authors' Addresses
        11. IANA Considerations
            Appendix A.
     
     
     
     
     
     
     
     
     
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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].  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 typically
        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) 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.
     
     
        [Authorés NOTE: The draft describes a mechanism aimed at a subset of
        the services supported by [DRAFT-ENC].  The format of this document
        resembles [DRAFT-ENC]for ease of comparison and much of the
        background text is common, although the encapsulation protocol is
        different and more lightweight.]
     
     
     
     
     
     
     
     
     
     
     
     
     
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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, 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 Management 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.
     
        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.
     
        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]
     
        NPA: Network Point of Attachment. In this document, refers to a 6 B
        destination address within the MPEG-2 transmission network used to
        identify individual Receivers or groups of Receivers.
     
        PDU: Protocol Data Unit. Examples of PDU include Ethernet frames,
        IPv4 or IPv6 datagrams, and other network packets
     
        PES: Programme Elementary Scheme of MPEG-2 [ISO-MPEG].
     
     
     
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        PID: Packet Identifier. A 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.
     
        PP: Payload Pointer. 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.
     
        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.
     
        PUSI: Payload_Unit_Start_Indicator of MPEG-2 [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).
     
        PRIVATE SECTION: a syntactic structure used for mapping all service
        information (e.g. an SI table) into TS Packets.  A Table may be
        divided into a number of Table Sections, however all Table Sections
        must be carried over a single TS Logical Channel.
     
        PSI: Programme SI. An table used to convey information about the
        service carried in a TS Multiplex. The set of PSI tables is defined
        by [ISO-MPEG], see also SI Table.
     
        SI TABLE: Service Information Table. In this document, this term
        describes any table used to convey information about the service
        carried in a TS Multiplex. SI tables are carried in MPEG-2 private
        sections.
     
        SNDU: Subnetwork Data Unit. An encapsulated PDU sent as an MPEG-2
        Payload Unit.
     
        TABLE SECTION: A Payload Unit carrying a part of a MPEG-2 SI Table.
     
        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 LOGICAL CHANNEL: Transport Stream Logical Channel, a channel
        identified 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. According to MPEG-2, some TS
     
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        Logical Channels are reserved for specific signalling purposes.
        Other standards (e.g., ATSC, DVB) also reserve specific TS Logical
        Channels.
     
        TS MULTIPLEX: A set of MPEG-2 TS Logical Channels sent over a single
        common physical link (i.e. a transmission at a specified symbol
        rate, FEC setting, and transmission frequency). The same TS Logical
        Channel may be repeated over more than one TS Multiplex, for example
        to redistribute the same multicast content to two terrestrial TV
        transmission cells.
     
        TS PACKET: A fixed-length 188B unit of data sent over a TS Multiplex
        [ISO-MPEG]. Operation resembles that of cell in  an ATM network, and
        may also be referred to as a TS_Cell.  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 Transport Streams.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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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. If required,
        a 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 differently for PES and PSI packets [ISO-
        MPEG]; for private data, its use is not defined in the MPEG-2
        Standard. In ULE, 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 convenient 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 or Stuffing.
     
        A Receiver processing MPEG-2 Table Sections is aware that when it
        receives a table_id value of 0xFF, this indicates Padding/Stuffing
        occurred 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. The purpose of the adaptation field is primarily to
        carry timing and synchronisation information and may be used to also
        include stuffing bytes before a TS Packet payload. Standard
        Receivers discard TS Packets with an adaptation_field_control field
        value of '00'. 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'. Receivers MUST discard TS Packets
        that carry other AFC values.
     
        [XXX Author's NOTE: The enc encapsulation defines how to use the AF]
     
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     4. SNDU Format
     
        PDUs are encapsulated using ULE to form a SNDU. Each SNDU is sent as
        an MPEG-2 Payload Unit. The encapsulation format to be used for PDUs
        (IP packets and bridged Ethernet frames) is illustrated below:
     
        .--------------------------   SNDU   ---------------------------.
        +---+---------------------------------------------------+--------+
        | R | Length | Type |                 PDU               | CRC-32 |
        +---+---------------------------------------------------+--------+
     
        Figure 1: SNDU Encapsulation
     
        The Length, Type, and Destination fields are transmitted most
        significant byte first (Appendix A provides informative examples of
        usage).
     
     
        4.1 Reserved Field
     
        The most significant bit of the Length Field is reserved. All
        transmitted SNDUs MUST set this to the value 0.  One exception is
        transmission of an End Indicator (see 4.3), in which this bit MUST
        be set to the value of 1.
     
        At the receiver, the value of this bit MUST be checked ignored,
        except for the special case defined in 4.3.
     
     
        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.
        Also note the special case described in 4.3.
     
        4.3 End Indicator
     
        When the first two bytes of a SNDU has the value 0xFFFF, this
        denotes an End Indicator (i.e., all 1és length combined with a
        Reserved Field set to a value of 1). It indicates that there are no
        further SNDU are present within the current TS packet (see section
        5.1). The value 0xFF has specific semantics in MPEG-2 framing, where
        it is used to indicate the presence of stuffing. This use resembles
        this.
     
     
        4.4 Type Field
     
        The 16-bit Type field indicates the type of payload carried in a
        SNDU. The set of values that may be assigned to this field is
        divided into two parts, similar to the allocations for Ethernet.
     
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        Ethertypes were originally by Xerox under the DIX framework. After
        specification of IEEE 802.3, the set of Ethertypes less than 1500,
        assumed the role of a length indicator. Receivers use this feature
        to discriminate LLC format frames. Hence any Ethertype <= 1500
        indicates an LLC frame, and the actual value indicates the length of
        the LLC frame. This mode of identification is not required in ULE,
        since the SNDU format always carries an explicit Length Field.
        Specification of two independent length fields is undesirable, and
        therefore the procedure in ULE is modified, as below:
     
        The first set of ULE Type Field values apply to a Type Field value
        <= 1500.  These Type Field values are IANA assigned (see 4.4.1).
     
        The second set of ULE Type Field values apply to a Type Field value
        > 1500. In ULE, this indicates that the value is identical to the
        corresponding type codes specified by the IEEE/DIX type assignments
        for Ethernet
     
     
        4.4.1 Type 1: IANA Assigned Type Fields
     
        The first part of the Type space corresponds to the values 0x0000 to
        1500 Decimal.  These values are assigned to an IANA registry.
     
        The following types are defined:
     
        [XXX IANA ACTION REQUIRED XXX]
     
        0x0000: Test SNDU, discarded by the Receiver.
        0x0001: Bridged Ethernet Frame (i.e. MAC source address follows)
        0x0002: LLC header follows in SNDU Payload
     
        [XXX END OF IANA ACTION REQUIRED XXX]
     
        [Author NOTE: Type allocation and appropriate IANA Procedure
        to be determined.]
     
        4.4.2 Type 2: Ethertype compatible Type Fields
     
        The second part of the Type space corresponds to the values 1500
        Decimal and 0xFFFF.  This set of type assignments follow DIX/IEEE
        assignments (not including use of LLC) [LLC]. The following types
        are defined in this document for part 2:
     
        0x0800 : IPv4 Payload (according to IANA EtherTypes)
        0x86DD : IPv6 Payload (according to IANA EtherTypes)
     
     All other assignments in part two of this space should be coordinated
     with the values defined for IANA EtherType encapsulations.
     
     
     
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        [Author Note: Suitable values for ROHC types may in future
        need to be added]
     
     
        4.5 SNDU Destination Address Field
     
        [Authorés note: Location of the D-bit, or the use of appropriate
        Type Field allocations within the SNDU header is still to be
        determined by the WG]
     
        The SNDU Destination Address Field is optional.
     
        This field MUST be carried for IP unicast packets destined to
        routers. A sender MAY omit this field 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.
     
        The default SNDU format MUST carry this field,
     
        When the SNDU header indicates the presence of a SNDU destination
        address field, a Network Point of Attachment, NPA, field directly
        follows the SNDU Type Field.  NPA destination addresses are 6 B
        numbers, normally expressed in hexadecimal, used to identify the
        Receiver(s) that should process a received SNDU within a MPEG-2
        transmission network.
     
     
        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
        polynomial to be used is the Reverse CRC-32.  The reverse order of
        calculation (i.e. where the CRC operates on successive bytes,
        processing the lsb of each byte first) is compatible with both a
        hardware or software implementation. The CRC-32 is calculated
        according to the following generator polynomial:
     
        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.
     
        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.
     
         [Author NOTE: We need to specify initial register value!!!]
     
        The Encapsulator calculates a transmit value for the CRC32 including
        all bytes from the start of the SNDU header to the end of the
        trailer, and places this in the CRC Field.  The receiver performs an
        integrity check by independently calculating the CRC value and
     
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        comparing this with the transmitted value in the SNDU trailer. SNDUs
        that do not have a valid CRC-32, are discarded.
     
        The primary purpose of this CRC is to protect the SNDU payload from
        undetected resassembly 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 (these may however, in
        some cases, also be detected by other means).
     
     
        4.7 Description of SNDU Formats
     
        [>>> Authorés Note: The mechanism for communicating the presence of
        the Destination Address Field (D) is to be determined by the WG.
        Early implementers should note the default value of D is 0,
        indicating presence of the Destination Address Field <<<]
     
        The Format of a SNDU is determined by the combination of the
        Destination Address 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 directly preceding the PDU.
     
        The following SNDU Formats are defined here:
     
        End Indicator: The Receiver should enter the Idle State.
     
        IPv4 SNDU: The payload is a complete IPv4 datagram.
     
        IPv6 SNDU: The payload is a complete IPv6 datagram.
     
        Test SNDU: The payload will be discarded by the Receiver.
     
        Bridged SNDU: The payload carries a bridged MAC or LLC frame.
     
     
        All other formats are currently reserved.
     
     
     
     
     
     
     
     
     
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        4.7.1 End Indicator
     
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |1 |                     0x7FFF                 |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |                                               |
          =        Arbitrary number of bytes >= 0         =
          |                                               |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     
        Figure 2: SNDU Formats for an End Indicator.
     
        4.7.2 IPv4 SNDU
     
        IPv4 datagrams are 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 2 and 3.
     
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |R |     Length  (2B)   |     Type = 0x0800     |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |          MAC Destination Address  (6B)        |
          +                       +--+--+--+--+--+--+--+--+
          |                       |                       |
          +--+--+--+--+--+--+--+--+                       +
          |                                               |
          |                IPv4 datagram                  |
          |                                               |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |                   (CRC_32)                    |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     
        Figure 3: SNDU Formats for an IPv4 Datagram using L2 filtering.
     
     
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |R |     Length  (2B)   |     Type = 0x0800     |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |                                               |
          |                IPv4 datagram                  |
          |                                               |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |                   (CRC_32)                    |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     
     Figure 4: SNDU Formats for an IPv4 Datagram using L3 filtering.
     
     
     
     
     
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        4.7.3 IPv6 SNDU Encapsulation
     
        IPv6 datagrams are 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 4 and 5.
     
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |R |     Length  (2B)   |     Type = 0x086DD    |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |          MAC Destination Address  (6B)        |
          +                       +--+--+--+--+--+--+--+--+
          |                       |                       |
          +--+--+--+--+--+--+--+--+                       +
          |                                               |
          |                IPv6 datagram                  |
          |                                               |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |                   (CRC_32)                    |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     
        Figure 5: SNDU Formats for an IPv6 Datagram using L2 filtering.
     
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |R |     Length  (2B)   |     Type = 0x86DD     |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |                                               |
          |                IPv6 datagram                  |
          |                                               |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |                   (CRC_32)                    |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     
        Figure 6: SNDU Formats for an IPv6 Datagram using L3 filtering.
     
     
     
     
     
     
     
     
     
     
     
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        4.7.4 Test SNDU
     
        A Test SNDU is of Type 1 (figure 6). 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.
     
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |R |     Length  (2B)   |     Type = 0x0000     |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |                                               |
          =         Data (ignored by Receivers)           =
          |                                               |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |                                               |
          +                 ULE CRC-32  (4B)              +
          |                                               |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     
        Figure 7: SNDU Format for a Test SNDUs
     
     
        4.7.5 Bridge Frame SNDU Encapsulation
     
        A bridged SNDU is of Type 1.  The payload includes a MAC source and
        Ether-Type field together with the contents of a bridged MAC frame.
        The SNDU has the format shown in figure 8.
     
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |R |     Length  (2B)   |     Type = 0x0800     |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |          MAC Destination Address  (6B)        |
          +                       +--+--+--+--+--+--+--+--+
          |                       |                       |
          +--+--+--+--+--+--+--+--+                       +
          |            MAC Source Address  (6B)           |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |     EtherType (2B)    |                       |
          +--+--+--+--+--+--+--+--+                       |
          =                                               =
          |        (Contents of bridged MAC frame)        |
          |                                               |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
          |                                               |
          +                 ULE CRC-32  (4B)              +
          |                                               |
          +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     
        Figure 8: SNDU Format for a Bridged Payload
     
        The MAC addresses are those specified in the frame being bridged and
        are SHOULD be assigned according to the rules specified by the IEEE
     
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        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 frame
        is defined according to Ethernet/LLC [LLC].
     
        In normal operation, it is expected that any padding appended to the
        Ethernet frame will be removed prior to forwarding. This requires
        the sender to be aware of such padding.
     
        Most bridged frames will also carry a Local Area Network Frame Check
        sequence, LAN FCS, field (e.g. CRC-32 for Ethernet). The LAN-FCS
        value of all received frames MUST be checked by the Encapsulator
        prior to processing.  Frames received with an invalid LAN FCS MUST
        be discarded. 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 may be appended to the bridged frame prior
        to onward transmission.
     
        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).
     
        [Author Note: Is dest address signaled by the type or by the D-
        bit.  What is required in this case? - or should D=1 signify a MPEG-
        2 transmission network MAC + and Ethernet dst MAC? - i.e. two
        addresses - does this have nay practical sue - e.g. In Skyplex/RCS
        scenarios?]
     
     
     
     
     
     
     
     
     
     
     
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     5. Processing at the Encapsulator and Receiver
     
        The Encapsulator forms the PDUs awaiting transmission into SNDUs and
        then segments these 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.
     
                    +----------------------------------------------+
                    |Encap Header|  SubNetwork Data Unit  | CRC-32 |
                    +----------------------------------------------+
                   /         /                               \      \
                  /         /                                 \      \
                 /         /                                   \      \
         +------+----------+    +------+----------+    +------+----------+
         |MPEG-2| MPEG-2   |... |MPEG-2| MPEG-2   |... |MPEG-2| MPEG-2   |
         |Header| Payload  |    |Header| Payload  |    |Header| Payload  |
         +------+----------+    +------+----------+    +------+----------+
     
        Figure 9: Encapsulation of a SNDU into a series of TS Packets
     
        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 is performed
        independently for each TS Logical Channel.
     
     
        5.1 Encapsulator Processing
     
        The Encapsulator adds a header and trailer to each PDU to form a
        SNDU. This SNDU is then segmented into a series of MPEG-2 TS Packets
        belonging to the same logical TS Logical Channel. This set is sent
        as a sequence over a TS Multiplex.
     
     
        5.1.1 Flushing the Bitstream
     
        MPEG-2 multiplexers do not usually flush their buffers, but store TS
        Packets until the buffer fills, assuming that the data comes in a
        more or less continuous stream. In the case of data traffic, this
        assumption no longer holds, leading to the problem that the last IP
        datagram will be only partly transmitted unless a special "push" TS
        Packet is appended. This introduces additional overhead.
     
        [Author Note: Do we need to specify functionality here ???]
     
     
     
     
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        5.2 Receiver Processing
     
        Receipt of a TS Packet with a non-zero PUSI value indicates that the
        TS Packet contains the start of a new SNDU.  It also indicates the
        presence of the Payload Pointer. The Payload Pointer value indicates
        that there are Payload Pointer bytes of the SNDU currently being
        reassembled at the start of the TS Packet payload. A Payload Pointer
        value equal to greater than 183 is illegal in ULE, and the SNDU
        reassembly MUST be aborted. This event SHOULD be recorded as an
        error.
     
        A Receiver reassembles SNDUs from the TS Packets received from a 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.
     
        [Author Note: Should we validate the CC field in TS Packet- or
        ignore this. The strong CRC-32 suggests this is unnecessary, and it
        does increase the required complexity of the (re)multiplexor - WG
        thoughts please?]
     
        5.2.1 Idle State
     
        After initialisation or on receipt of an End Indicator, the Receiver
        enters the Idle State. In this state, the Receiver discards the
        contents of the Current SNDU buffer and waits for the start of the
        next SNDU by waiting for a TS Packet with a PUSI value of 1.  All
        other TS Packets are discarded in this mode.
     
        A PUSI value of 1, indicates the presence of a Payload Pointer. For
        the first TS Packet received, the Payload Pointer will also have a
        value of 0.  Following a loss of synchronisation, values between 1
        and 182 are permitted, in which case the receiver MUST discard the
        number of bytes indicated by the Payload Pointer, before starting
        reassembly of the next SNDU.
     
     
        5.2.2 Processing of Received SNDUs
     
        The Receiver reads the SNDU Length field from the current SNDU. If
        this Length is less than or equal to 3, the Receiver discards the
        Current SNDU and the remaining TS Packet payload and returns to the
        search mode waiting for the next TS Packet with a PUSI value of 1.
     
        If the Length of the Current SNDU is greater than 4, it then 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. When Length bytes are received, the receiver MUST
        calculate and verify the CRC value. SNDUs that contain an invalid
        CRC value MUST be discarded. After receiving a valid SNDU, the
        receiver MUST check the Type Field. The SNDU payload is then passed
     
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        to the next protocol layer specified. An SNDU with an unknown Type
        value MUST be discarded. This error event SHOULD be recorded in a
        log file.
     
        The receiver then starts reassembly of the next SNDU. This MAY
        directly follow the previously reassembled SNDU within the TS Packet
        Payload.
     
        If there is either 0 or 1 byte of payload data remaining in the TS
        Packet after completion of the Current SNDU, the receiver MUST
        discard this remaining TS payload, and wait for the next TS Packet
        with the PUSI value set to 1 (the Idle State).
     
        If there is more than one byte of payload data remaining in the TS
        Packet after completion of the Current SNDU, the Receiver MUST
        accept the next bytes as the start of the next SNDU (or an End
        Indicator), and continue with processing the next SNDU.
     
     
        5.2.3 Payload Pointer Checking
     
        An idle Receiver (i.e. one that is not currently reassembling a PDU)
        MUST check the PUSI value in the header of all received TS Packets.
        If it receives a TS Packet with a PUSI value of 1, and MUST discard
        a number of bytes equal to the Payload Pointer value from the start
        of the TS Packet payload, before it commence reassembly of a new
        SNDU at this point. Normally, the Payload Pointer will have a value
        of 0.
     
        A Receiver that has partially received a SNDU (in the Current SNDU
        buffer) MUST check the PUSI value in the header of all received TS
        Packets. 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 also discard a number of bytes
        equal to the Payload Pointer value from the start of the TS Packet
        payload, and commence reassembly of a new SNDU at this point.
     
     
        5.2.4 Other Error Conditions
     
        [Author Note: Should we check the MPEG-2 CC??]
     
        The Receiver SHOULD also check the MPEG-2 Continuity Counter carried
        in the TS Packet header.  This value MUST be incremented by one for
        each TS Packet sent using a TS Logical Channel. If the received
        value does not increment by one in successive TS Packets (modulo
     
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        16), the Receiver has detected a continuity error. Any partially
        received SNDU MUST be discarded. The receiver then enters a mode to
        wait for the next TS Packet with a PUSI value of 1.
     
        The Receiver SHOULD check the MPEG-2 Transport Error indicator
        carried in the TS Packet header.  This flag indicates a transmission
        error for a TS Logical Channel. If the flag is set to a value of
        one, an error event SHOULD be recorded. Any partially received SNDU
        MUST be discarded. The Receiver then enters the Idle State.
     
     
        5.3 SNDU Packing
     
        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.
     
        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.
     
        If there are at least two bytes remaining in the TS Packet payload
        after processing the Current SNDU and further PDUs are queued at an
        Encapsulator, it MAY append the bytes of the next SNDU directly to
        the preceding one before segmentation (figure 9). This procedure is
        known as Packing. If there are no further SNDUs available, an
        Encapsulator MAY wait for additional PDUs to fill the incomplete TS
        Packet.
     
        [Author Note: Should this waiting period be bounded?]
     
           +------------------+       +------------------+
           |   Subnetwork     |       |   Subnetwork     |
           |      DU 1        |       |      DU 2        |
           +------------------+       +------------------+
                      \        \     /          /\
                       \        \   /          /  \
                        \        \ /          /    \
         +------+--------+--------+----------+
         |MPEG-2| Payload| end of | start of |
         |Header| Pointer| SNDU 1 | SNDU 2   |
         +------+--------+--------+----------+
                    |              ^
         PUSI=1     |              |
                    +--------------+
     
        Figure 10: A TS Packet with the end of SNDU 1, followed by SNDU 2
     
     
     
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        If an Encapsulator decides NOT to wait for another SNDU, it MUST
        instead transmit an End Indicator directly after the end of the last
        SNDU. This informs the Receiver that there are no more SNDUs in this
        TS Packet payload. The End Indicator is followed by stuffing bytes
        until the end of the TS Packet payload (figure 10). The latter
        procedure trades decreased efficiency against improved latency.
     
     
        +-------------+
        | Subnetwork  |
        |      DU 3   |
        +-------------+
              \        \
               \        \
                \        \
         +------+--------+--------+----------+
         |MPEG-2| End of | 0xFFFF |  Unused  |
         |Header| SNDU 3 |        |  Bytes   |
         +------+--------+--------+----------+
     
         PUSI=0            End
                           Indicator
     
        Figure 10: A TS Packet carrying the end of SNDU 3, followed by an
        End Indicator
     
        [Author Note: Should we mandate ALL stuffing bytes are 0xFF???
        Why?]
     
     
        5.3.1 Encapsulator Packing
     
        If more packets are waiting at the Encapsulator, and a TS Packet has
        more than two bytes of unused payload, it MAY start the next SNDU in
        the next available byte of the TS Packet payload. The PUSI MUST be
        set, if not already set. When an Encapsulator packs a further SNDU
        into an already formed TS Packet, this may require the PUSI value in
        the TS Packet header to be updated, also requiring a Payload Pointer
        to be inserted in the TS Packet.
     
        If the PUSI is set by this operation, the 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. The value 0x00
        indicates that a SNDU starts immediately after the Payload Pointer.
     
        If the TS Packet carrying the final part of a SNDU has less than two
        bytes of unused payload, 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.) This rule
        provides a simple mechanism to resolve the complex behaviour that
        may arise when the TS Packet has no PUSI set.  In ULE, this would
     
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        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.
     
        When a SNDU is less than the size of a TS Packet payload, a TS
        Packet may be formed which carries a PUSI value of one and also an
        End Indicator.
     
     
        5.3.2 Processing of Packed SNDUs at the Receiver
     
        All Receivers MUST support the use of the Packing method for any
        received SNDU. Use of the Packing method by an Encapsulation Gateway
        is optional, and may be determined on a per session, per-packet, or
        per-SNDU basis.
     
        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 enter the
        Idle State.
     
     
     6. 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.
     
     
     7. 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, and Alain Ritoux.
     
     
     8. Security Considerations
     
        There is a known security issue with un-initialised stuffing bytes.
     
        There are also a potential security issue when an encapsulation
        permits two length fields - as in the use of bridged LLC packets.
        The Encapsulator and Receiver MUST validate the actual length and
        the Length field and ensure that inconsistent values are not
        propagated by the network.
     
     
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        There are known integrity issues with the removal of the LAN FCS in
        a bridged networking environment. The removal exposes the traffic to
        potentially undetected corruption while being processed by the
        Encapsulator and/or Receiver.
     
     
     9. References
     
     9.1 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, October 1996.
     
        [RFC2119] Bradner, S., "Key Words for Use in RFCs to Indicate
        Requirement Levels", BCP 14, RFC 2119, March 1997.
     
     
        9.2 Informative References
     
        [ATSC] A/53, "ATSC Digital Television Standard", Advanced Television
        Systems Committee (ATSC), Doc. A/53, 1995.
     
        [ATSC-DAT] A/90, "ATSC Data Broadcast Standard", Advanced Television
        Systems Committee (ATSC), Doc. A/090, 26 July 00
     
        [ATSC-DATG] A/91, "Recommended Practice: Implementation Guidelines
        for the ATSC Data Broadcast Standard", Advanced Television Systems
        Committee (ATSC),Doc. A/91. 10 June 2001
     
        [ATSC-G] A/54, "Guide to the use of the ATSC Digital Television
        Standard", Advanced Television Systems Committee (ATSC), Doc. A/54,
        4 Oct 95
     
        [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 - 31 May 2000
     
        [ATSC-S] A/80, "Modulation and Coding Requirements for Digital TV
        (DTV) Applications  over Satellite", Advanced Television Systems
        Committee (ATSC), Doc. A/80, 17 July 99
     
        [CLC99] Clausen, H., Linder, H., and Collini-Nocker, B., "Internet
        over Broadcast Satellites", IEEE Commun. Mag. 1999, pp.146-151.
     
        [DRAFT-ENC] IETF Work in Progress, draft-clausen-ipdvb-enc-XX.txt
     
        [ETSI-DAT]  EN  301  192  "Specifications  for  Data  Broadcasting",
        European Telecommunications Standards Institute (ETSI).
     
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        [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] XXX Reference Required XXX
     
        [ISO-DSMCC] ISO/IEC IS 13818-6 "Information technology -- Generic
        coding of moving pictures and associated audio information -- Part
        6:  Extensions  for  DSM-CC  is  a  full  software  implementation",
        International Standards Organisation (ISO).
     
        [ISO-MPEG] ISO/IEC DIS 13818-1 "Information technology -- Generic
        coding  of  moving  pictures  and  associated  audio  information:
        Systems", International Standards Organisation (ISO).
     
        [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.
     
        [RFC3095] C. Bormann, et al, "RObust Header Compression (ROHC):
        Framework and four profiles: RTP, UDP ESP and uncompressed",
        RFC3095.
     
        [SI-DAT] SI-DAT group, "Second Draft DVB Specification for Data
        Broadcasting", Geneva, 15 Jan. 1997
     
     
     10.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
        Institute of Computer Sciences
        University of Salzburg
     
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        Jakob Haringer Str. 2
        5020 Salzburg
        Austria
        Email: [bnocker]@cosy.sbg.ac.at
        Web: http://www.cosy.sbg.ac.at/cs/
     
     Full Copyright Statement
     
        "Copyright (C) The Internet Society (date). All Rights Reserved.
        This document and translations of it may be copied and furnished to
        others, and derivative works that comment on or otherwise explain it
        or assist in its implementation may be prepared, copied, published
        and distributed, in whole or in part, without restriction of any
        kind, provided that the above copyright notice and this paragraph
        are included on all such copies and derivative works. However, this
        document itself may not be modified in any way, such as by removing
        the copyright notice or references to the Internet Society or other
        Internet organizations, except as needed for the purpose of
        developing Internet standards in which case the procedures for
        copyrights defined in the Internet Standards process must be
        followed, or as required to translate it into languages other than
        English.
     
        The limited permissions granted above are perpetual and will not be
        revoked by the Internet Society or its successors or assigns.
     
     
     11. IANA Considerations
     
     
        This document will require IANA involvement.
     
        The payload type field defined in this document must be aligned with
        an existing IANA registry or the following values need to be
        assigned by the IANA:
     
             Payload Type Field
     
     
     
     
     
     
     
     
     
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     INTERNET DRAFT  Encapsulation for IP over MPEG-2/DVB     October 2003
     
     
        ANNEXE A: Informative Appendix
     
        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)
     
        [XXX Editor note: Can someone please  provide us with a hex-dump
        including the TS Packet headers for these examples??? XXX]
     
        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 | 0xC8 | ... | A182 |
         +-----+----*-+-*----+------+-   -+------+
         PUSI=1     *   *
                    *****
                                               SNDU
                 PP=16                        Length
         +-----+------+------+-   -+--- --+------+------+-   -+------+
         | HDR | 0x10 | A183 | ... | A199 | 0x00 | 0xC0 | ... | B165 |
         +-----+----*-+------+-   -+------+-*----+------+-   -+------+
         PUSI=1     *                       *
                    *************************
     
                                       End     Stuffing
                                    Indicator   Bytes
         +-----+------+-   -+------+----+----+-   -+
         | HDR | B166 | ... | B199 |0xFF|0xFF| ... |
         +-----+------+-   -+------+----+----+-   -+
         PUSI=0
     
     
     
     Expires April 2004                                           [page 26]


     INTERNET DRAFT  Encapsulation for IP over MPEG-2/DVB     October 2003
     
     
        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:
     
                  PP=0
          +-----+------+------+-   -+------+
          | HDR | 0x00 | A000 | ... | A182 |
          +-----+----*-+-*----+-   -+------+
          PUSI=1     *   *
                     *****
                                            Unused
                  PP=0                       byte
          +-----+------+------+-   -+------+------+
          | HDR | 0x00 | B000 | ... | B181 | 0xFF |
          +-----+---*--+-*----+-   -+------+------+
          PUSI=1    *    *
                    ******
     
                  PP=0
          +-----+------+------+-   -+------+------+------+
          | HDR | 0x00 | C000 | ... | C180 | D000 | D001 |
          +-----+---*--+-*----+-   -+------+------+------+
          PUSI=1    *    *
                    ******           Unused
                                      byte
          +-----+------+-   -+------+------+
          | HDR | D002 | ... | D184 | 0xFF |
          +-----+------+-   -+------+------+
           PUSI=0
     
     
     
     
     
     
     
     
     
     
     Expires April 2004                                           [page 27]


     INTERNET DRAFT  Encapsulation for IP over MPEG-2/DVB     October 2003
     
     
        Example A.3: Large SNDUs
     
             SNDU A is 732 bytes
             SNDU B is 284 bytes
     
        The sequence comprises 6 TS Packets:
     
     
                 PP=0
          +-----+------+------+-   -+------+
          | HDR | 0x00 | A000 | ... | A182 |
          +-----+---*--+-*----+-   -+------+
          PUSI=1    *    *
                    ******
     
          +-----+------+-   -+------+
          | HDR | A183 | ... | A366 |
          +-----+------+-   -+------+
          PUSI=0
     
     
          +-----+------+-   -+------+
          | HDR | A367 | ... | A550 |
          +-----+------+-   -+------+
          PUSI=0
     
     
                  PP=181
          +-----+------+------+-   -+------+------+------+
          | HDR | 0xB5 | A551 | ... | A731 | B000 | B001 |
          +-----+---*--+------+-   -+------+*-----+------+
          PUSI=1    *                       *
                    *************************
     
          +-----+------+-   -+------+
          | HDR | B002 | ... | B186 |
          +-----+------+-   -+------+
          PUSI=0
     
                                         End       Stuffing
                                      Indicator     Bytes
          +-----+------+-   -+------+------+------+-   -+
          | HDR | B187 | ... | B283 | OxFF | 0xFF | ... |
          +-----+------+-   -+------+------+------+-   -+
          PUSI=0
     
     
     
     
     
     Expires April 2004                                           [page 28]


     INTERNET DRAFT  Encapsulation for IP over MPEG-2/DVB     October 2003
     
     
        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:
     
     
                 PP=0   SNDU A Length
          +-----+------+------+------+-   -+------+
          | HDR | 0x00 | A000 | A001 | ... | A182 |
          +-----+----*-+-*----+------+-   -+------+
          PUSI=1     *   *  +      +
                     *****  ++++++++
                             +
                             +++++++++++++++++
                                             +
                 PP=17                       +SNDU B Length
          +-----+------+------+-   -+------+-+----+------+-
          | HDR | 0x11 | A183 | ... | A199 | B000 | B001 | ...
          +-----+----*-+------+-   -+------+*-----+------+-
          PUSI=1     *                      *  +       +
                     ************************  +++++++++
                                                +
            +++++++++++++++++++++++++++++++++++          End       Stuffing
            +               SNDU C Length              Indicator      bytes
            +      -+------+------+------+    -+------+------+------+-   -+
            +   ... | B059 | C000 | C001 | ... | C059 | 0xFF | 0xFF | ... |
            +      -+------+-+----+------+    -+------+-+----+------+-   -+
            +                +  +      +                +
            +                +  ++++++++                +
            +                +   +                      +
            ++++++++++++++++++   ++++++++++++++++++++++++
     
        *** TS Packet Payload Pointer (PP)
        +++ ULE Length Indicator
     
     
     
     
     
     
     
     
     
     
     Expires April 2004                                           [page 29]