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Network Working Group                                       G. FairhurstRequest for Comments: 5163                        University of AberdeenCategory: Standards Track                              B. Collini-Nocker                                                  University of Salzburg                                                              April 2008Extension Formats for Unidirectional Lightweight Encapsulation (ULE)and the Generic Stream Encapsulation (GSE)Status of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Abstract   This document describes a set of Extension Headers for the   Unidirectional Lightweight Encapsulation (ULE),RFC 4326.   The Extension Header formats specified in this document define   extensions appropriate to both ULE and the Generic Stream   Encapsulation (GSE) for the second-generation framing structure   defined by the Digital Video Broadcasting (DVB) family of   specifications.Table of Contents1. Introduction ....................................................22. Conventions Used in This Document ...............................33. Description of the Method .......................................43.1. MPEG-2 TS-Concat Extension .................................53.2. PDU-Concat Extension .......................................83.3. TimeStamp Extension .......................................124. IANA Considerations ............................................135. Acknowledgments ................................................136. Security Considerations ........................................147. References .....................................................147.1. Normative References ......................................147.2. Informative References ....................................14Appendix A. The Second-Generation DVB Transmission      Specifications .................................................16Fairhurst & Collini-Nocker  Standards Track                     [Page 1]

RFC 5163      Extension Formats for the ULE Encapsulation     April 20081.  Introduction   This document describes three Extension Headers that may be used with   both the Unidirectional Lightweight Encapsulation (ULE) [RFC4326] and   the Generic Stream Encapsulation (GSE) [GSE].  ULE is defined for   links that employ the MPEG-2 Transport Stream, and supports a wide   variety of physical-layer bearers [RFC4259].   GSE has been designed for the Generic Mode (also known as the Generic   Stream (GS)), offered by second-generation DVB physical layers, and   in the first instance for DVB-S2 [ETSI-S2].  The requirements for the   Generic Stream are described in [S2-REQ].  The important   characteristics of this encapsulation are described in the appendix   of this document.  GSE maintains a design philosophy that presents a   network interface that is common to that presented by ULE and uses a   similar construction for SubNetwork Data Units (SNDUs).   The first Extension Header defines a method that allows one or more   TS Packets [ISO-MPEG2] to be sent within a ULE SNDU.  This method may   be used to provide control plane information including the   transmission of MPEG-2 Program Specific Information (PSI) for the   Multiplex.  In GSE, there is no native support for Transport Stream   packets and this method is therefore suitable for providing an MPEG-2   control plane.   A second Extension Header allows one or more PDUs to be sent within   the same ULE SNDU.  This method is designed for cases where a large   number of small PDUs are directed to the same Network Point of   Attachment (NPA) address.  The method may improve transmission   efficiency (by removing duplicated MAC layer overhead).  It can also   reduce processing overhead for a receiver that is not configured to   receive the NPA address associated with an SNDU, allowing this   receiver to then skip several PDUs in one operation.  The method is   defined as a generic Extension Header and may be used for IPv4 or   IPv6 packets.  If, and when, a compression format is defined for ULE   or Ethernet, the method may also be used in combination with this   method.   A third Extension Header provides an optional TimeStamp value for an   SNDU.  Examples of the use of this TimeStamp option include   monitoring and benchmarking of ULE and GSE links.  Receivers that do   not wish to decode (or do not support) the TimeStamp extension may   discard the extension and process the remaining PDU or Extension   Headers.   The appendix includes a summary of key design issues and   considerations relating to the GSE Specification defined by the DVB   Technical Module [GSE].Fairhurst & Collini-Nocker  Standards Track                     [Page 2]

RFC 5163      Extension Formats for the ULE Encapsulation     April 20082.  Conventions Used in This Document   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described inRFC 2119 [RFC2119].   b: bit.  For example, one byte consists of 8b.   B: byte.  Groups of bytes are represented in Internet byte order.   BBFrame payload: The data field part of a Baseband frame  [ETSI-S2]   that may be used for the communication of data.  Typical BBFrames   range in size from 3072 to 58192 bits according to the choice of   modulation format and Forward Error Correction (FEC) in use.   DVB: Digital Video Broadcasting.  A framework and set of associated   standards published by the European Telecommunications Standards   Institute (ETSI) for the transmission of video, audio, and data.   E: A one-bit flag field defined in GSE [GSE].   Encapsulator: A network device [RFC4259] that receives PDUs and   formats these into Payload Units (known here as SNDUs) for output in   DVB-S or the Generic Mode of DVB-S2.   GS: Generic Stream.  A stream of BBFrames identified by a common   Input Stream Identifier, and which does not use the MPEG-2 TS format   [ETSI-S2].  It represents layer 2 of the ISO/OSI reference model.   GSE: Generic Stream Encapsulation [GSE].  A method for encapsulating   PDUs to form a Generic Stream, which is sent using a sequence of   BBFrames.  This encapsulation format shares the same extension format   and basic processing rules of ULE and uses a common IANA Registry.   LT: A two-bit flag field defined in GSE [GSE].   MAC: Medium Access Control [IEEE-802.3].  A link-layer protocol   defined by the IEEE 802.3 standard.   MPEG-2: A set of standards specified by the Motion Picture Experts   Group (MPEG), and standardized by the International Organization for   Standardization (ISO/IEC 113818-1) [ISO-MPEG2], and ITU-T (in H.220).   Next-Header: A Type value indicating an Extension Header [RFC4326].Fairhurst & Collini-Nocker  Standards Track                     [Page 3]

RFC 5163      Extension Formats for the ULE Encapsulation     April 2008   NPA: Network Point of Attachment [RFC4326].  In this document, refers   to a destination address (resembling an IEEE MAC address) within the   DVB-S/S2 transmission network that is used to identify individual   Receivers or groups of Receivers.   PID: Packet Identifier  [ISO-MPEG2].  A 13-bit field carried in the   header of each TS Packet.  This identifies the TS Logical Channel to   which a TS Packet belongs [ISO-MPEG2].  The TS Packets that form the   parts of a Table Section or other Payload Unit must all carry the   same PID value.  The all-ones PID value indicates a Null TS Packet   introduced to maintain a constant bit rate of a TS Multiplex.  There   is no required relationship between the PID values used for TS   Logical Channels transmitted using different TS Multiplexes.   PDU: Protocol Data Unit [RFC4259].  Examples of a PDU include   Ethernet frames, IPv4 or IPv6 datagrams, and other network packets.   PSI: Program Specific Information [ISO-MPEG2].   S: A one-bit flag field defined in [GSE].   SI Table: Service Information Table [ISO-MPEG2].  In this document,   this term describes a table that is been defined by another standards   body to convey information about the services carried on a DVB   Multiplex.   SNDU: SubNetwork Data Unit [RFC4259].  In this document, this is an   encapsulated PDU sent using ULE or GSE.   Stream: A logical flow from an Encapsulator to a set of Receivers.   TS: Transport Stream [ISO-MPEG2], a method of transmission at the   MPEG-2 level using TS Packets; it represents layer 2 of the ISO/OSI   reference model.   ULE: Unidirectional Lightweight Encapsulation (ULE) [RFC4326].  A   method that encapsulates PDUs into SNDUs that are sent in a series of   TS Packets using a single TS Logical Channel.  The encapsulation   defines an extension format and an associated IANA Registry.3.  Description of the Method   In ULE, a Type field value that is less than 1536 in decimal   indicates an Extension Header.  This section describes a set of three   extension formats for the ULE encapsulation.  [GSE] uses a Type field   that adopts the same semantics as specified byRFC 4326.  TheFairhurst & Collini-Nocker  Standards Track                     [Page 4]

RFC 5163      Extension Formats for the ULE Encapsulation     April 2008   encapsulation format differs in that GSE does not include a Cyclic   Redundancy Check (CRC) for each SNDU, has different header flags, and   utilizes a different SNDU length calculation [GSE].   There is a natural ordering of Extension Headers, which is determined   by the fields upon which the Extension Header operates.  A suitable   ordering for many applications is presented in the list below (from   first to last header within an SNDU).  This does not imply that all   types of Extensions should be present in a single SNDU.  The   presented ordering may serve as a guideline for optimization of   Receiver processing.   +----------------------------------+-------------------------------+   |Fields related to Extension Header| Example Extension Headers     |   +----------------------------------+-------------------------------+   | Link framing and transmission    | TimeStamp Extension           |   +----------------------------------+-------------------------------+   | Entire remaining SNDU Payload    | Encryption Extension          |   +----------------------------------+-------------------------------+   | Group of encapsulated PDUs       | PDU-Concat or TS-Concat       |   +----------------------------------+-------------------------------+   | Specific encapsulated PDU        | IEEE-defined type             |   |                                  | Test or MAC bridging Extension|   +----------------------------------+-------------------------------+            Table 1: Recommended ordering of Extension Headers3.1.  MPEG-2 TS-Concat Extension   The MPEG-2 TS-Concat Extension Header is specified by an IANA-   assigned H-Type value of 0x0002 in hexadecimal.  This is a Mandatory   Extension Header.   The extension is used to transport one or more MPEG-2 TS Packets   within a ULE SNDU.  The number of TS Packets carried in a specific   SNDU is determined from the size of the remainder of the payload   following the MPEG-2 TS Extension Header.  The number of TS Packets   contained in the SNDU is therefore (Length-N-10+D*6) / 188, where N   is the number of bytes associated with Extension Headers that precede   the MPEG-2 TS-Concat Extension (zero if there are none) and D is the   value of the D-bit.   A Receiver MUST check the validity of the Length value prior to   processing the payload.  A valid Length corresponds to an integral   number of TS Packets.  An invalid Length (a remainder from the   division by 188) MUST result in the discard of all encapsulated TS   Packets and SHOULD be recorded as TS-Concat size mismatch error.Fairhurst & Collini-Nocker  Standards Track                     [Page 5]

RFC 5163      Extension Formats for the ULE Encapsulation     April 2008    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |0|           Length  (15b)     |         Type = 0x0002         |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |            Receiver Destination NPA Address  (6B)             |   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                               |                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |   |                   TS-Packet 1                                 |   =                                                               =   |                                                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                   TS-Packet 2 (if Length > 2*188)             |   =                                                               =   |                              etc.                             |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                             (CRC-32)                          |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+         Figure 1: ULE/SNDU Format for a TS-Packet Payload (D=0)   Figure 1 illustrates the format of this Extension Header for ULE with   a value D=0, which indicates the presence of an NPA address   [RFC4326].  In this case, the valid payload Length for a ULE SNDU   with no other extensions is (Length-10) / 188.   The method used to define the Length in GSE differs to that of ULE.   The equivalent case for GSE would result in a payload Length value of   (Length-6) / 188 (Figure 2).    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |S|E|0 0|      Length  (12b)    |         Type = 0x0002         |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |            Receiver Destination NPA Address  (6B)             |   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                               |                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |   |                   TS-Packet 1                                 |   =                                                               =   |                                                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                   TS-Packet 2 (if Length > 2*188)             |   =                                                               =   |                              etc.                             |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+        Figure 2: GSE/SNDU Format for a TS-Packet Payload (LT=00)Fairhurst & Collini-Nocker  Standards Track                     [Page 6]

RFC 5163      Extension Formats for the ULE Encapsulation     April 2008   Fragmented GSE SNDUs are protected by a CRC-32 carried in the final   fragment.  After reassembly, this CRC-32 is removed and the resulting   SNDU carries a Total Length field.  The fields labeled S and E are   defined by [GSE] and contain control flags used by the GSE link   layer.  The Label Type (LT) field specifies the presence and format   of the GSE label.  The LT field is only specified for the first   fragment (or a non-fragmented) GSE SNDU (i.e., when S=1).   In ULE, a value of D=1 is also permitted and indicates the absence of   an NPA address (Figure 3).  A similar format is supported in GSE.    0                   1                   2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |1|           Length  (15b)     |         Type = 0x0002         |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                   TS-Packet 1                                 |   =                                                               =   |                                                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                   TS-Packet 2 (if Length > 2*188)             |   =                                                               =   |                              etc.                             |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                             (CRC-32)                          |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+         Figure 3: ULE/SNDU Format for a TS-Packet Payload (D=1)   The TS-Concat extension may be used to transport one or more MPEG-2   TS Packets of arbitrary content, interpreted according to [ISO-   MPEG2].  One expected use is for the transmission of MPEG-2 SI/PSI   signalling [RFC4259].   NULL TS Packets [ISO-MPEG2] SHOULD NOT be sent using this   encapsulation.  To reduce transmission overhead and processing, an   Encapsulator SHOULD specify a maximum period of time that it can wait   before sending all queued TS Packets.  This is known as the TS   Packing Threshold.  This value MUST be bounded and SHOULD be   configurable in the Encapsulator.  A larger value can improve   efficiency, but incurs higher jitter and could increase the   probability of corruption.  If additional TS Packets are NOT received   within the TS Packing Threshold, the Encapsulator MUST immediately   send any queued TS Packets.   The use of this format to transfer MPEG-2 clock references (e.g., a   Network Clock Reference, NCR) over ULE/GSE framing raises timing   considerations at the encapsulation gateway, including the need toFairhurst & Collini-Nocker  Standards Track                     [Page 7]

RFC 5163      Extension Formats for the ULE Encapsulation     April 2008   update/modify the timing information prior to transmission by the   physical layer.  These issues are not considered here, but this   operation may be simplified in GSE by ensuring that all SNDUs that   carry this Extension Header are placed before other data within the   BBFrame DataField [GSE].   This document does not specify how TS Packets are to be handled at   the Receiver.  However, it notes:   * A Receiver needs to consistently associate all TS Packets in a     Stream with one TS Logical Channel (Stream).  If an Encapsulator     transmits more than one Stream of TS Packets each encapsulated at a     different level or with a different NPA address, a Receiver needs     to ensure that each is independently demultiplexed as a separate     Stream (Section 3.2 [RFC4259]).   * If an Encapsulator transmits service information encapsulated at     different levels or with different NPA addresses, the Receivers     need to ensure each Stream is related to the corresponding SI table     information (if any).  A RECOMMENDED way to reduce signaling     interactions is to ensure each PID value uniquely identifies a     Stream within a TS Multiplex carrying ULE and also any TS Packets     encapsulated by a ULE/GSE Stream.   The need for consistency in the use of PIDs and the related service   information is described insection 4.2 of [RFC4947].3.2.  PDU-Concat Extension   The PDU-Concat Extension Header is specified by an IANA-assigned   H-Type value of 0x0003 in hexadecimal.  This is a Mandatory Next-   Header Extension.  It enables a sequence of (usually short) PDUs to   be sent within a single SNDU Payload.   The base header contains the Length of the entire SNDU.  This carries   the value of the combined length of all PDUs to be encapsulated,   including each set of encapsulation headers.  The base header MAY be   followed by one or more additional Extension Headers that precede the   PDU-Concat Extension Header.  These Extension Headers (e.g., a   TimeStamp Extension) apply to the composite concatenated PDU.   The Extension Header also contains a 16-bit ULE Type field describing   the encapsulated PDU, PDU-Concat-Type.  Although any Type value   specified in the ULE Next-Header Registry (including Extension Header   Types) may be assigned to the encapsulated PDU (except the recursive   use of a PDU-Concat type), all concatenated PDUs MUST have a common   ULE Type (i.e., all concatenated PDUs passed by the network layerFairhurst & Collini-Nocker  Standards Track                     [Page 8]

RFC 5163      Extension Formats for the ULE Encapsulation     April 2008   must be associated with the same Type value).  This simplifies the   receiver design, and reduces the transmission overhead for common use   cases.   Each PDU is prefixed by its length in bytes (shown in the following   diagrams as PDU-x-Length for the xth PDU).  Encapsulated PDUs are of   arbitrary length (in bytes) and are not necessarily aligned to 16-bit   or 32-bit boundaries within the SNDU (as shown in the figures 4, 5,   and 6).  The most significant bit of the first byte is reserved, R,   and this specification requires that this MUST be set to zero.   Receivers MUST ignore the value of the R bit.  The length of each PDU   MUST be less than 32758 bytes, but will generally be much smaller.   When the SNDU header indicates the presence of an SNDU Destination   Address field (i.e., D=0 in ULE), a Network Point of Attachment, NPA,   field directly follows the fourth byte of the SNDU header.  NPA   destination addresses are 6 byte numbers, normally expressed in   hexadecimal, used to identify the Receiver(s) in a transmission   network that should process a received SNDU.  When present, the   Receiver MUST associate the same specified MAC/NPA address with all   PDUs within the SNDU Payload.  This MAC/NPA address MUST also be   forwarded with each PDU, if required by the forwarding interface.    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |0|           Length  (15b)     |         Type = 0x0003         |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |            Receiver Destination NPA Address  (6B)             |   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                               |        PDU-Concat-Type        |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |R|      PDU-1-Length  (15b)    |                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +   =                        PDU-1                                  =   |                                                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |R|      PDU-2-Length  (15b)    |                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +   =                        PDU-2                                  =   |                                                               |                              More PDUs as required   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                             (CRC-32)                          |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+         Figure 4: ULE/SNDU Format for a PDU-Concat Payload (D=0)Fairhurst & Collini-Nocker  Standards Track                     [Page 9]

RFC 5163      Extension Formats for the ULE Encapsulation     April 2008    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |S|E|0 0|      Length  (12b)    |         Type = 0x0003         |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |            Receiver Destination NPA Address  (6B)             |   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                               |        PDU-Concat-Type        |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |R|      PDU-1-Length  (15b)    |                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +   =                        PDU-1                                  =   |                                                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |R|      PDU-2-Length  (15b)    |                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +   =                        PDU-2                                  =   |                                                               |                              More PDUs as required   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+        Figure 5: GSE/SNDU Format for a PDU-Concat Payload (LT=00)   When the SNDU header indicates the absence of an SNDU Destination   Address field (i.e., D=1 in ULE), all encapsulated PDUs MUST be   processed as if they had been received without an NPA address.   The value of D in the ULE header indicates whether an NPA/MAC address   is in use [RFC4326].  A similar format is supported in GSE (using the   LT field).Fairhurst & Collini-Nocker  Standards Track                    [Page 10]

RFC 5163      Extension Formats for the ULE Encapsulation     April 2008    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |1|           Length  (15b)     |         Type = 0x0003         |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |         PDU-Concat-Type       |R|      PDU-1-Length  (15b)    |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   =                        PDU-1                                  =   |                                                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |R|      PDU-2-Length  (15b)    |                               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +   =                        PDU-2                                  =   |                                                               |                              More PDUs as required   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                             (CRC-32)                          |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+         Figure 6: ULE/SNDU Format for a PDU-Concat Payload (D=1)   To reduce transmission overhead and processing, an Encapsulator   SHOULD specify a maximum period of time it will wait before sending a   Concatenated PDU.  This is known as the PDU Packing Threshold.  This   value MUST be bounded and SHOULD be configurable in the Encapsulator.   A larger value can improve efficiency, but incurs higher jitter and   could increase the probability of corruption.  If additional PDUs are   NOT received within the PDU Packing Threshold, the Encapsulator MUST   immediately send all queued PDUs.   The Receiver processes this Extension Header by verifying that it   supports the specified PDU-Concat Type (unsupported Types MUST be   discarded, but the receiver SHOULD record a PDU-Type error   [RFC4326]).  It then extracts each encapsulated PDU in turn.  The   Receiver MUST verify the Length of each PDU.  It MUST also ensure   that the sum of the Lengths of all processed PDUs equals the Length   specified in the SNDU base header.  A Receiver SHOULD discard the   whole SNDU if the total and PDU sizes are not consistent and thisFairhurst & Collini-Nocker  Standards Track                    [Page 11]

RFC 5163      Extension Formats for the ULE Encapsulation     April 2008   event SHOULD be recorded as a PDU-Concat size mismatch error.  A   receiver MUST NOT forward a partial PDU with an indicated PDU-Length   greater than the number of unprocessed bytes remaining in the SNDU   payload field.3.3.  TimeStamp Extension   The TimeStamp Extension Header is an Optional Extension Header that   permits an Encapsulator to add a TimeStamp field to an SNDU.  The   TimeStamp Extension Header is specified by the IANA-assigned H-Type   value of 257 decimal.  This extension is an Optional Extension Header   ([RFC4326], Section 5).   This extension is designed to support monitoring and measurement of   the performance of a link to indicate the quality of an operational   ULE link.  This may be useful for GSE links (e.g., where significant   complexity exists in the scheduling provided by the lower layers).   Possible uses of this extension include:   * Validation of in-sequence ordering per Logical Channel   * Measurement of one-way delay (when synchronized with the sender)   * Measurement of PDU Jitter introduced by the link   * Measurement of PDU loss (with additional information from sender)   Figure 7 shows the format of this extension with a HLEN value of 3   indicating a TimeStamp of length 4B with a Type field (there is no   implied byte-alignment).   0               7               15              23              31   +---------------+---------------+---------------+---------------+   |     0x03      |      0x01     |        TimeStamp HI           |   +---------------+---------------+---------------+---------------+   |          TimeStamp LO         |            Type               |   +---------------+---------------+---------------+---------------+        Figure 7: Format of the 32-bit TimeStamp Extension Header   The extension carries a 32-bit value (TimeStamp HI plus TimeStamp   LO).  The specified resolution is 1 microsecond.  The value therefore   indicates the number of 1-microsecond ticks past the hour in   Universal Time when the PDU was encapsulated.  This value may be   earlier than the time of transmission, due for example to Packing,   queuing, and other Encapsulator processing.  The value is right-   justified to the 32-bit field.  Systems unable to insert TimeStamps   at the specified resolution MUST pad the unused least-significant   bits with a value of zero.Fairhurst & Collini-Nocker  Standards Track                    [Page 12]

RFC 5163      Extension Formats for the ULE Encapsulation     April 2008   The last two bytes carry a 16-bit Type field that indicates the type   of payload carried in the SNDU or the presence of a further Next-   Header ([RFC4326], Section 4.4).   Receivers MAY process the TimeStamp when the PDU encapsulation is   removed.  Receivers that do not implement, or do not wish to process,   the TimeStamp Extension MAY skip this Extension Header.  Receivers   MUST continue to process the remainder of the SNDU, forwarding the   encapsulated PDU.4.  IANA Considerations   IANA has assigned three new Next-Header Type values from the IANA ULE   Next-Header Registry.  These options are defined for specific use   cases envisaged by GSE, but are compatible with ULE.   The following assignments have been made in this document and   registered by IANA:       Type      Name                             Reference       2:        TS-ConcatSection 3.1       3:        PDU-ConcatSection 3.2       Type      Name                    H-LEN    Reference       257:      TimeStamp                3Section 3.3   The TS-Concat Extension is a Mandatory next-type Extension Header,   specified inSection 3.1 of this document.  The value of this next-   header is defined by an IANA assigned H-Type value of 0x0002.   The PDU-Concat Extension is a Mandatory next-type Extension Header   specified inSection 3.2 of this document.  The value of this next-   header is defined by an IANA assigned H-Type value of 0x0003.   The TimeStamp Extension is an Optional next-type Extension Header   specified inSection 3.3 of this document.  The value of this next-   header is defined by an IANA assigned H-Type value of 257 decimal.   This documents defines the format for an HLEN value of 0x3.5.  Acknowledgments   The authors gratefully acknowledge the inputs, comments, and   assistance offered by the members of the DVB-GBS ad hoc group on   DVB-S2 encapsulation, in particular contributions on DVB-S2   transmission aspects from Rita Rinaldo, Axel Jahn, and Ulrik De Bie.Fairhurst & Collini-Nocker  Standards Track                    [Page 13]

RFC 5163      Extension Formats for the ULE Encapsulation     April 2008   Juan Cantillo provided a significant contribution to the informative   appendix.  The authors thank Christian Praehauser for his insight and   contribution on Extension Header processing issues.6.  Security Considerations   Security considerations for ULE are described in [RFC4326], and   further information on security aspects of using ULE are described in   the security considerations of [RFC4259] and [Sec-Req].   An attacker that is able to inject arbitrary TS Packets in a ULE or   GSE Stream may modify layer 2 signalling information transmitted by   the MPEG-2 TS-Concat extension.  Since this attack requires access to   the link and/or layer 2 equipment, such an attack could also directly   attack signalling information sent as native TS Packets (not   encapsulated by ULE/GSE).  Security issues relating to the   transmission and interpretation of layer 2 signalling information   (including Address Resolution) within a TS Multiplex are described in   [RFC4947].  The use of security mechanisms to protect the MPEG-2   signalling information is discussed by [Sec-Req].7.  References7.1.  Normative References   [RFC2119]    Bradner, S., "Key words for use in RFCs to Indicate                Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC4326]    Fairhurst, G. and B. Collini-Nocker, "Unidirectional                Lightweight Encapsulation (ULE) for Transmission of IP                Datagrams over an MPEG-2 Transport Stream (TS)",RFC4326, December 2005.   [GSE]        TS 102 606 "Digital Video Broadcasting (DVB); Generic                Stream Encapsulation (GSE) Protocol, "European                Telecommunication Standards, Institute (ETSI), 2007.7.2.  Informative References   [ETSI-S2]    EN 302 307, "Digital Video Broadcasting (DVB); Second                generation framing structure, channel coding and                modulation systems for Broadcasting, Interactive                Services, News Gathering and other broadband satellite                applications", European Telecommunication Standards                Institute (ETSI).Fairhurst & Collini-Nocker  Standards Track                    [Page 14]

RFC 5163      Extension Formats for the ULE Encapsulation     April 2008   [S2-REQ]     Cantillo, J. and J. Lacan, "A Design Rationale for                Providing IP Services over DVB-S2 Links", Work in                Progress, December 2006.   [Sec-Req]    Cruickshank, H., Iyengar, S., and P. Pillai, "Security                requirements for the Unidirectional Lightweight                Encapsulation (ULE) protocol", Work in Progress,                November 2007.   [IEEE-802.3] "Local and metropolitan area networks - Specific                requirements Part 3: Carrier sense multiple access with                collision detection (CSMA/CD) access method and physical                layer specifications", IEEE 802.3, IEEE Computer                Society, (also ISO/IEC 8802-3), 2002.   [ISO-MPEG2]  ISO/IEC DIS 13818-1:2000, "Information Technology;                Generic Coding of Moving Pictures and Associated Audio                Information Systems", International Organization for                Standardization (ISO), 2000.   [RFC4259]    Montpetit, M.-J., Fairhurst, G., Clausen, H., Collini-                Nocker, B., and H. Linder, "A Framework for Transmission                of IP Datagrams over MPEG-2 Networks",RFC 4259,                November 2005.   [RFC4947]    Fairhurst, G. and M. Montpetit, "Address Resolution                Mechanisms for IP Datagrams over MPEG-2 Networks",RFC4947, July 2007.Fairhurst & Collini-Nocker  Standards Track                    [Page 15]

RFC 5163      Extension Formats for the ULE Encapsulation     April 2008Appendix A.  The Second-Generation DVB Transmission Specifications   This section provides informative background to the network-layer   requirements of the second-generation DVB Transmission   Specifications.  The second-generation waveforms specified by the   Digital Video Broadcasting project offer two main enhancements.   First, more efficient physical-layer methods that employ higher-order   modulation with stronger FEC and permit adaptive coding and   modulation response to changes in traffic and propagation conditions.   Second, at the link layer, they offer greater flexibility in framing.   Support is provided for a range of stream formats including the   classical Transport Stream (TS) [RFC4259].  In addition, a new method   called Generic Stream (GS) (or the Generic Mode) is supported.  A GS   can be packetized or continuous and is intended to provide native   transport of other network-layer services.  One such method is that   provided by the Generic Stream Encapsulation (GSE) [GSE].   For example, the DVB-S2 [ETSI-S2] transmission link sequentially   multiplexes a series of baseband frames (BBFrames).  Each BBFrame   comprises a fixed-size 10B header and a payload.  The payload carries   a DataField and uses padding to fill any unused space.  A stream   comprises a sequence of BBFrames associated with an Input Stream   Identifier (ISI) that is carried in the header of each BBFrame.  The   simplest scheme uses a single stream (with just one ISI value), but   multiple streams are permitted.  The BBFrames forming a stream may be   of variable size (selected from a set of allowed sizes), and must use   the same stream format (i.e., TS or GSE).  Each stream represents an   independent link with independent address resolution [RFC4947].   GSE provides functions that are equivalent to those of the   Unidirectional Lightweight Encapsulation (ULE) [RFC4326].  It   supports the transmission of IP packets and other network-layer   protocols.  The network-layer interface resembles that of ULE, where   it adopts common mechanisms for a Length field, a 16-bit Type field,   and support for Extension Headers.  As in ULE, GSE permits multiple   address formats, indicated by the LT field (functionally equivalent   to the D field in ULE).  The default addressing mode uses a 6-byte   NPA and a suppressed NPA address (functionally equivalent to D=1 in   ULE).   GSE also provides more flexible fragmentation at the interface to the   physical layer (using the S and E flags).  This adapts the SNDUs to a   variable-sized link-layer frame, and reflects the more complex   requirements in terms of fragmentation and assembly that arise when   using point-to-multipoint adaptive physical layers.  The integrity of   a reassembled SNDU is validated using a CRC-32 in the last fragment   for the corresponding PDU.Fairhurst & Collini-Nocker  Standards Track                    [Page 16]

RFC 5163      Extension Formats for the ULE Encapsulation     April 2008Authors' Addresses   Godred Fairhurst   School of Engineering,   University of Aberdeen,   Aberdeen, AB24 3UE   UK   EMail: gorry@erg.abdn.ac.uk   URI:http://www.erg.abdn.ac.uk/users/gorry   Bernhard Collini-Nocker   Department of Computer Sciences,   University of Salzburg,   Jakob Haringer Str. 2,   5020 Salzburg,   Austria   EMail: bnocker@cosy.sbg.ac.at   URI:http://www.cosy.sbg.ac.atFairhurst & Collini-Nocker  Standards Track                    [Page 17]

RFC 5163      Extension Formats for the ULE Encapsulation     April 2008Full Copyright Statement   Copyright (C) The IETF Trust (2008).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Fairhurst & Collini-Nocker  Standards Track                    [Page 18]