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. Expires April 2004 [page 1] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 [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] Expires April 2004 [page 2] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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. Expires April 2004 [page 3] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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. [AuthorĒs 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.] Expires April 2004 [page 4] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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]. Expires April 2004 [page 5] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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 Expires April 2004 [page 6] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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. Expires April 2004 [page 7] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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] Expires April 2004 [page 8] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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 1Ēs 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. Expires April 2004 [page 9] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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. Expires April 2004 [page 10] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 [Author Note: Suitable values for ROHC types may in future need to be added] 4.5 SNDU Destination Address Field [AuthorĒs 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 Expires April 2004 [page 11] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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 [>>> AuthorĒs 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. Expires April 2004 [page 12] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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. Expires April 2004 [page 13] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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. Expires April 2004 [page 14] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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 Expires April 2004 [page 15] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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?] Expires April 2004 [page 16] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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 ???] Expires April 2004 [page 17] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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 Expires April 2004 [page 18] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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 Expires April 2004 [page 19] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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 Expires April 2004 [page 20] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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 Expires April 2004 [page 21] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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. Expires April 2004 [page 22] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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). Expires April 2004 [page 23] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 [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 Expires April 2004 [page 24] INTERNET DRAFT Encapsulation for IP over MPEG-2/DVB October 2003 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 Expires April 2004 [page 25] 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]