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Versions: (draft-fair-ipdvb-ar) 00 01 02 03 04 05 06 RFC 4947

Internet Engineering Task Force                         Gorry Fairhurst
Internet Draft                                   University of Aberdeen
Document: draft-ietf-ipdvb-ar-05.txt               Marie-Jose Montpetit
                                                     Motorola Connected
                                                         Home Solutions



Category: Draft intended as INFO                            August 2006



   Address Resolution Mechanisms for IP Datagrams over MPEG-2 Networks


Status of this Draft

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Drafts.

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   http://www.ietf.org/1id-abstracts.html.

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   Abstract

   This document describes the process of binding/associating IPv4/IPv6
   addresses with MPEG-2 Transport Streams (TS). This procedure is
   known as Address Resolution (AR), or Neighbour Discovery (ND). Such
   address resolution complements the higher layer resource discovery
   tools that are used to advertise IP sessions.

   In MPEG-2 Networks, an IP address must be associated with a Packet
   ID (PID) value and a specific Transmission Multiplex. The document
   reviews current methods appropriate to a range of technologies (DVB,
   ATSC, DOCSIS, and variants). It also describes the interaction with
   well-known protocols for address management including DHCP, ARP, and
   the ND protocol, and provides guidance on usage.




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   Table of Contents

   1. Introduction
   1.1 Bridging and Routing

   2. Convention used in the document

   3. Address Resolution Requirement
   3.1 Unicast Support
   3.2 Multicast Support

   4. MPEG-2 Address Resolution
   4.1 Static configuration.
   4.1.1 MPEG-2 Cable Networks
   4.2 MPEG-2 Table-Based Address Resolution
   4.2.1 IP/MAC Notification Table (INT) and its usage
   4.2.2 Multicast Mapping Table (MMT) and its usage
   4.2.3 Application Information Table (AIT) and its usage
   4.2.4 Address Resolution in ATSC
   4.2.5 Comparison of SI/PSI table approaches
   4.3 IP-based address resolution for TS Logical Channels
   4.3.1 IP-based multicast resolution of TS Logical Channels

   5. Mapping IP addresses to MAC/NPA addresses
   5.1 Uni-directional links supporting uni-directional connectivity
   5.2 Uni-directional links with bi-directional connectivity
   5.3 Bi-directional links
   5.4 AR Server
   5.5 DHCP Tuning
   5.6 IP Multicast AR
   5.6.1 Multicast/Broadcast addressing for UDLR

   6. Link Layer Support
   6.1 ULE without a destination MAC/NPA address (D=1)
   6.2 ULE with a destination MAC/NPA address (D=0)
   6.3 MPE without LLC/SNAP Encapsulation
   6.4 MPE with LLC/SNAP Encapsulation
   6.5 ULE with Bridging Header Extension (D=1)
   6.6 ULE with Bridging Header Extension and NPA Address (D=0)
   6.7 MPE with LLC/SNAP and Bridging

   7. Conclusions

   8. Security Considerations

   9. Acknowledgements
   10. References
   11. Author's Addresses
   12. IPR Notices
   13. Copyright Statements
   14. IANA Considerations



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1. Introduction

   The MPEG-2 Transport Stream (TS) provides a time-division
   multiplexed (TDM) stream that may contain audio, video and data
   information, including encapsulated IP Datagrams [RFC4259], defined
   in specification ISO/IEC 138181 [ISO-MPEG2]. Each Layer-2 (L2)
   frame, known as a TS Packet, contains a 4 byte header and a 184 byte
   payload.  Each TS Packet is associated with a single TS Logical
   Channel, identified by a 13-bit Packet ID (PID) value that is
   carried in the MPEG-2 TS Packet header.

   The MPEG-2 standard also defines a control plane that may be used to
   transmit control information to Receivers in the form of System
   Information (SI) Tables [ETSI-SI], [ETSI-SI1], or Program Specific
   Information (PSI) Tables.

   To utilize the MPEG-2 TS as a Layer-2 (L3) IP link, a sender must
   associate an IP address with a particular Transmission Multiplex,
   and within the multiplex identify the specific PID to be used. This
   document calls this mapping an Address Resolution (AR) function. In
   some AR schemes, the MPEG-2 TS address space is sub-divided into
   logical contexts known as Platforms [ETSI-DAT]. Each Platform
   associates an IP service provider with a separate context that share
   a common MPEG-2 TS (use the same PID value).

   MPEG-2 Receivers may use a Network Point of Attachment (NPA)
   [RFC4259] to uniquely identify a L2 node within an MPEG-2
   transmission network. An example of an NPA is the IEEE Medium Access
   Control (MAC) address. Where such addresses are used, these must
   also be signalled by the AR procedure. Finally, address resolution
   could signal the format of the data being transmitted, for example,
   the encapsulation, any L2 encryption method and any compression
   scheme [RFC4259].

   The numbers of Receivers connected via a single MPEG-2 link may be
   much larger than found in other common LAN technologies, (e.g.
   Ethernet).  This has implications on design/configuration of the
   address resolution mechanisms. Current routing protocols, and some
   multicast application protocols also do not scale to arbitrary large
   numbers of participants. Such networks do not by themselves
   introduce an appreciable subnetwork round trip delay, however many
   practical MPEG-2 transmission networks are built using links that
   may introduce significant path delay (satellite links, use of dial-
   up modem return, cellular return, etc). This higher delay may need
   to be accommodated for by address resolution protocols that use this
   service.

1.1 Bridging and Routing

   The following two figures illustrate the use of AR for a routed and
   a bridged subnetwork. Various other combinations of L2 and L3
   forwarding may also be used over MPEG-2 links (including Receivers


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   that are IP end hosts and end hosts directly connected to bridged
   LAN segments).


                           Broadcast Link AR
                           - - - - - - - - -
                           |               |
                           \/
                            1a            2b        2a
                   +--------+              +--------+
               ----+   R1   +----------+---+   R2   +----
                   +--------+ MPEG-2   |   +--------+
                              Link     |
                                       |   +--------+
                                       +---+   R3   +----
                                       |   +--------+
                                       |
                                       |   +--------+
                                       +---+   R4   +----
                                       |   +--------+
                                       |
                                       |

   Figure 1: A routed MPEG-2 link feeding 3 downstream routers (R2-R4).
   AR takes place at the Encapsulator (R1) to identify each Receiver at
   L2 within the IP subnetwork (R2, etc).

   When considering unicast communication from R1 to R2, several L2
   addresses are involved:

    1a is the L2 (sending) interface address of R1 on the MPEG-2 link
    2b is the L2 (receiving) interface address of R2 on the MPEG-2 link
    2a is the L2 (sending) interface address of R2 on the next hop link

   AR for the MPEG-2 link allows R1 to determine the L2 address (2b)
   corresponding to the next hop Receiver, router R2.

   Figure 2 shows a bridged topology. The Encapsulator associates a
   destination MAC/NPA address with each bridged PDU sent on an MPEG-2
   link. Two methods are defined by ULE [RFC4326]:

   The simplest method uses the L2 address of the transmitted frame.
   This is the MAC address corresponding to the destination within the
   L2 subnetwork (the next hop router, 2b of R2). This requires each
   Receiver (B4) to associate the receiving MPEG-2 interface with the
   set of MAC addresses that exist on the L2 subnetworks that it feeds.
   Similar considerations apply when IP-based tunnels support L1/L2
   services (including the use of UDLR [RFC3077]).

   It is also possible for a bridging Encapsulator (B1) to encapsulate
   a PDU with a link-specific header that contains the MAC/NPA address
   associated with a Receiver L2 interface on the MPEG-2 link (figure
   2). In this case, the destination MAC/NPA address of the

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   encapsulated frame is set to the Receiver MAC/NPA address (y),
   rather than the address of the final L2 destination. At a different
   level, an AR binding is also required for R1 to associate the
   destination L2 address 2b with R2. In a subnetwork using bridging,
   the systems R1, R2 will normally use standard IETF-defined AR
   mechanisms (e.g. IPv4 Address Resolution Protocol, ARP [RFC826] and
   the IPv6 Neighbor Discovery Protocol, ND [RFC2461) edge-to-edge
   across the IP subnetwork.


                                Subnetwork AR
                      - - - - - - - - - - - - - - - -
                      |                             |

                      |        MPEG-2 Link AR       |
                             - - - - - - - - -
                      |      |               |      |
                      \/     \/
                      1a      x              y      2b        2a
             +--------+  +----+              +----+  +--------+
         ----+   R1   +--| B1 +----------+---+ B2 +--+   R2   +----
             +--------+  +----+ MPEG-2   |   +----+  +--------+
                                Link     |
                                         |   +----+
                                         +---+ B3 +--
                                         |   +----+
                                         |
                                         |   +----+
                                         +---+ B4 +--
                                         |   +----+
                                         |

   Figure 2: A bridged MPEG-2 link feeding 3 downstream bridges (B2-
   B4). AR takes place at the Encapsulator (B1) to identify each
   Receiver at L2 (B2-B4). AR also takes place across the IP subnetwork
   allowing the feed router (R1) to identify the downstream Routers at
   L2 (R2, etc).


   Methods also exist to assign IP addresses to Receivers within a
   network (e.g. DHCP [RFC2131], DHC [RFC3736]).  Receivers may also
   participate in remote configuration of the L3 IP addresses used in
   connected equipment (e.g. using DHCP-Relay [RFC3046]).

   The remainder of the document describes current mechanisms and their
   use to associate an IP address with the corresponding TS Multiplex,
   PID value, the MAC/NPA address and/or Platform ID. A range of
   approaches is described, including Layer-2 mechanisms (using MPEG-2
   SI tables), and protocols at the IP level (including ARP [RFC826]
   and the ND [RFC2461]).  Interactions and dependencies between these
   mechanisms and the encapsulation methods are described. The document
   does not propose or define a new protocol, but does provide guidance


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   on issues that would need to be considered to supply IP-based
   address resolution.


2. Conventions used in this document

   AIT: Application Information Table specified by the Multimedia Home
   Platform (MHP) specifications [ETSI-MHP]. This table may carry
   IPv4/IPv6 to MPEG-2 TS address resolution information.

   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 [ISO-MPEG2].

   b: bit. For example, one byte consists of 8b.

   B: Byte. Groups of bytes are represented in Internet byte order.

   DSM-CC: Digital Storage Media Command and Control [ISO-DSMCC].  A
   format for transmission of data and control information carried in
   an MPEG-2 Private Section, defined by the ISO MPEG-2 standard.

   DVB: Digital Video Broadcasting [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.

   DVB-RCS: Digital Video Broadcast Return Channel via Satellite. A bi-
   directional IPv4/IPv6 service employing low-cost Receivers.

   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.

   Feed Router: The router delivering the IP service over a
   Unidirectional Link.

   INT: Internet/MAC Notification Table.  A uni-directional address
   resolution mechanism using SI and/or PSI Tables.

   MAC: Medium Access Control [IEEE-802.3]. A link-layer protocol
   defined by the IEEE 802.3 standard (or by Ethernet v2).

   MAC Address: A 6 byte link layer address of the format described by
   the Ethernet IEEE 802 standard (see also NPA).

   MAC Header: The link-layer header of the IEEE 802.3 standard [IEEE-
   802.3 or Ethernet v2. It consists of a 6 byte destination
   address, 6 byte source address, and 2 byte type field (see also NPA,
   LLC).




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   MHP: Multimedia Home Platform. An integrated MPEG-2 multimedia
   receiver, that may (in some cases) support IPv4/IPv6 services [ETSI-
   MHP].

   MMT: Multicast Mapping Table (proprietary extension to DVB-RCS
   [ETSI-RCS] defining an AR table that maps IPv4 multicast addresses
   to PID values).

   MPE: Multiprotocol Encapsulation [ETSI-DAT; ATSC-DAT; ATSC-DATG]. A
   method that encapsulates PDUs, forming a DSM-CC Table Section. Each
   Section is sent in a series of TS Packets using a single Stream (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/IEC 113818-1) [ISO-MPEG2], and ITU-T (in H.220).

   NPA: Network Point of Attachment. A 6 byte destination address
   (resembling an IEEE MAC address) within the MPEG-2 transmission
   network that is used to identify individual Receivers or groups of
   Receivers [RFC4259].

   PAT: Program Association Table. An MPEG-2 PSI control table. It
   associates each program with the PID value that is used to send the
   associated PMT. The table is sent using the well-known PID value of
   0x000, and is required for an MPEG-2 compliant Transport Stream.

   PDU: Protocol Data Unit.  Examples of a PDU include Ethernet frames,
   IPv4 or IPv6 Datagrams, and other network packets.

   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.

   PMT: Program Map Table. An MPEG-2 PSI control table that associates
   the PID values used by the set of TS Logical Channels/ Streams that
   comprise a program [ISO-MPEG2]. The PID value used to send the PMT
   for a specific program is defined by an entry in the PAT.

   Private Section: A syntactic structure constructed according to
   Table 2-30 of [ISO-MPEG2]. The structure may be used to identify
   private information (i.e. not defined by [ISO-MPEG2]) relating to
   one or more elementary streams, or a specific MPEG-2 program, or the
   entire Transport Stream.  Other Standards bodies, e.g. ETSI, ATSC,
   have defined sets of table structures using the private_section
   structure. A Private Section is transmitted as a sequence of TS
   Packets using a TS Logical Channel. A TS Logical Channel may carry
   sections from more than one set of tables.

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   PSI: Program Specific Information [ISO-MPEG2]. PSI is used to convey
   information about services carried in a TS Multiplex. It is carried
   in one of four specifically identified table section constructs
   [ISO-MPEG2], see also SI Table.

   Receiver: Equipment that processes the signal from a TS Multiplex
   and performs filtering and forwarding of encapsulated PDUs to the
   network-layer service (or bridging module when operating at the
   link-layer).

   SI Table: Service Information Table [ISO-MPEG2]. In this document,
   this term describes a table that is been defined by another
   standards body to convey information about the services carried in a
   TS Multiplex. A Table may consist of one or more Table Sections,
   however, all sections of a particular SI Table must be carried over
   a single TS Logical Channel [ISO-MPEG2].

   SNDU: Subnetwork Data Unit. An encapsulated PDU sent as an MPEG-2
   Payload Unit.

   Table Section: A Payload Unit carrying all or a part of an SI or PSI
   Table [ISO-MPEG2].

   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. See also TS Logical Channel and TS Multiplex.

   TS Logical Channel: Transport Stream Logical Channel. In this
   document, this term identifies a channel at the MPEG-2 level [ISO-
   MPEG2]. This exists at level 2 of the ISO/OSI reference model. All
   packets sent over a TS Logical Channel carry the same PID  value
   (this value is unique within a specific TS Multiplex). The term
   "Stream" is defined in MPEG-2 [ISO-MPEG2]. This describes the
   content carried by a specific TS Logical Channel (see, ULE Stream).
   Some PID values are reserved (by MPEG-2) for specific signaling.
   Other standards (e.g., ATSC, DVB) also reserve specific PID values.

   TS Multiplex: In this document, this term defines a set of MPEG-2 TS
   Logical Channels sent over a single lower layer connection. This may
   be a common physical link (i.e. a transmission at a specified symbol
   rate, FEC setting, and transmission frequency) or an encapsulation
   provided by another protocol layer (e.g. Ethernet, or RTP over IP).
   The same TS Logical Channel may be repeated over more than one TS
   Multiplex (possibly associated with a different PID value)
   [RFC4259], 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-MPEG2]. Each TS Packet carries a 4B header.

   UDL: Unidirectional link: A one-way transmission link. For example,
   and IP over DVB link using a broadcast satellite link.

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   ULE: Unidirectional Lightweight Encapsulation (ULE). A
   scheme that encapsulates PDUs, into SNDUs that are sent in a series
   of TS Packets using a single TS Logical Channel [RFC4326].

   ULE Stream: An MPEG-2 TS Logical Channel that carries only ULE
   encapsulated PDUs. ULE Streams may be identified by definition of a
   stream_type in SI/PSI [RFC4326, ISO-MPEG2].














































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3. Address Resolution Requirements

   The MPEG IP address resolution process is independent of the choice
   of encapsulation and needs to support a set of IP over MPEG-2
   encapsulation formats, including Multi-Protocol Encapsulation (MPE)
   [ETSI-DAT, ETSI-DAT1, ATSC-DAT]) and the IETF-defined Unidirectional
   Lightweight Encapsulation (ULE) [RFC4326].

   The general IP over MPEG-2 AR requirements are summarized below:

        A scalable architecture that may support large numbers of
        systems within the MPEG-2 network [RFC4259].

        A protocol version, to indicate the specific AR protocol in use
        and which may include the supported encapsulation method.

        A method (e.g. well-known L2/L3 address/addresses) to identify
        the AR Server sourcing the AR information.

        A method to represent IPv4/IPv6 AR information (including
        security associations to authenticate the AR information that
        will prevent address masquerading [RFC3756]).

        A method to install AR information associated with clients at
        the AR Server (registration).

        A method for transmission of AR information from an AR Server
        to clients that minimise the transmission cost (link local
        multicast, is preferable to subnet broadcast).

        Incremental update of the AR information held by clients.

        Procedures for purging clients of stale AR information.


   An MPEG-2 transmission network may support multiple IP networks. If
   this is the case, it is important to recognise the scope within
   which an address is resolved, to prevent packets from one addressed
   scope leaking into other scopes [RFC4259]. Examples of overlapping
   IP address assignments include:

      (i)   Private unicast addresses (e.g. in IPv4, 10/8 prefix;
            172.16/12 prefix; 192.168/16 prefix). Packets with these
            addresses should be confined to one addressed area. IPv6
            also defines link-local addresses that must not be
            forwarded beyond the link on which they were first sent.

      (ii)  Local scope multicast addresses.  These are only valid
            within the local area (examples for IPv4 include:
            224.0.0/24; 224.0.1/24). Similar cases exist for some IPv6
            multicast addresses [RFC2375].

      (iii) Scoped multicast addresses [RFC2365] [RFC2375].

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            Forwarding of these addresses is controlled by the scope
            associated with the address.  The addresses are only valid
            within an addressed area (e.g. the 239/8 [RFC2365]).

   Overlapping address assignments may also occur at L2, where the same
   MAC/NPA address is used to identify multiple Receivers [RFC4259]:

      (i)  An MAC/NPA unicast address must be unique within the
           addressed area. The IEEE-assigned MAC addresses used in
           Ethernet LANs are globally unique. If the addresses are
           not globally unique, an address must only be re-used by
           Receivers in different addressed (scoped) areas.

      (ii) The MAC/NPA address broadcast address (an all ones L2
           address). Traffic with this address should be confined to
           one addressed area.

      (iii) IP and other protocols may view sets of L3 multicast
           addresses as link-local. This may produce unexpected results
           if frames with the corresponding multicast L2 addresses are
           distributed to systems in a different L3 network or
           multicast scope (sections 3.2 and 5.6).

   Reception of unicast packets destined for another addressed area
   will lead to an increase in the rate of received packets by systems
   connected via the network. Reception of the additional network
   traffic may contribute to processing load, but should not lead to
   unexpected protocol behaviour, providing that systems can be
   uniquely addressed at L2. It does however introduce a potential
   Denial of Service (DoS) opportunity.  When the Receiver operates as
   an IP router, the receipt of such a packet can lead to unexpected
   protocol behaviour.


3.1 Unicast Support

   Unicast address resolution is required at two levels.

   At the lower level, the IP (or MAC) address needs to be associated
   with a specific TS Logical Channel (PID value) and the corresponding
   TS Multiplex (section 4). Each Encapsulator within an MPEG-2 Network
   is associated with a set of unique TS Logical Channels (PID values)
   that it sources [ETSI-DAT, RFC4259]. Within a specific scope, the
   same unicast IP address may therefore be associated with more than
   one Stream, and each Stream contributes different content (e.g. when
   several different IP Encapsulators contribute IP flows destined to
   the same Receiver).  MPEG-2 Networks may also replicate IP packets
   to send the same content (simulcast) to different Receivers or via
   different TS Multiplexes. The configuration of the MPEG-2 Network
   must prevent a Receiver accepting duplicated copies of the same IP
   packet.



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   At the upper level, the AR procedure needs to associate an IP
   address with a specific MAC/NPA address (section 5).


3.2 Multicast Support

   Multicast is an important application for MPEG-2 Transmission
   Networks, since it exploits the advantages of native support for
   link broadcast. Multicast address resolution occurs at the network-
   level in associating a specific L2 address with an IP Group
   Destination Address (section 5.6).  In IPv4 and IPv6 over Ethernet,
   this association is normally a direct mapping, and this is the
   default method also specified in both ULE [RFC4326] and MPE [ETSI-
   DAT].

   Address resolution must also occur at the MPEG-2 level (section 4).
   The goal of this multicast address resolution is the association of
   an IPv4 or IPv6 multicast address with a specific TS Logical Channel
   and the corresponding TS Multiplex.  This association needs to
   permit a large number of active multicast groups, and should
   minimise the processing load at the Receiver when filtering and
   forwarding IP multicast packets (e.g. by distributing the multicast
   traffic over a number of TS Logical Channels). Schemes that allow
   hardware filtering can be beneficial, since these may relieve the
   drivers and operating systems from discarding unwanted multicast
   traffic.

   There are two specific functions required for address resolution in
   IP multicast over MPEG-2 Networks:

   (i)  Mapping IP multicast groups to the underlying MPEG-2 TS Logical
        Channel (PID) and the MPEG-2 TS Multiplex at the Encapsulator.

   (ii) Provide signalling information to allow a Receiver to
        locate an IP multicast flow within an MPEG-2 TS Multiplex.


   Methods are required to identify the scope of an address when an
   MPEG-2 Network supports several logical IP networks and carries
   groups within different multicast scopes [RFC4259].

   Appropriate procedures need to specify the correct action when the
   same multicast group is available on separate TS Logical Channels.
   This could arise when different Encapsulators contribute IP packets
   with the same IP Group Destination Address in the ASM address range.
   Another case arises when a Receiver could receive more than one copy
   of the same packet (e.g. when packets are replicated across
   different TS Logical Channels, or even different TS Multiplexes, a
   method known as Simulcasting [ETSI-DAT]). At the IP level, the
   host/router may be unaware of this duplication and this needs to be
   detected by other means.



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   When the MPEG-2 Network is peered to the multicast-enabled Internet,
   an arbitrarily large number of IP multicast group destination
   addresses may be in use, and the set forwarded on the transmission
   network may be expected to vary significantly with time.  Some uses
   of IP multicast employ a range of addresses to support a single
   application (e.g., ND [RFC2461], LCT [RFC3451], WEBRC [RFC3738]).
   The current set of active addresses may be determined dynamically
   via a multicast group membership protocol (e.g., IGMP [RFC3376], MLD
   [RFC3810]), via multicast routing (e.g., PIM [RFC2362]) and/or other
   means (e.g. [RFC3819], [RFC-IGMP-Proxy]), however each active
   address requires a binding by the AR method. There are therefore
   advantages in using a method that does not need to explicitly
   advertise an AR binding for each IP traffic flow, but is able to
   distribute traffic across a number of L2 TS Logical Channels (e.g.,
   using a hash/mapping that resembles the mapping from IP addresses to
   MAC addresses [RFC1112, RFC2464]). Such methods can reduce the
   volume of AR information that needs to be distributed, and reduce
   the AR processing.

   Section 5.6 describes the binding of IP multicast addresses to
   MAC/NPA addresses.

































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4. MPEG-2 Address Resolution

   The first part of this section describes the role of MPEG-2
   signalling to identify streams (TS Logical Channels [RFC4259])
   within the L2 infrastructure.

   At L2, the MPEG-2 Transport Stream in ISO 13818-1 [ISO-MPEG2]
   identifies the existence and format of a Stream, using a combination
   of two PSI tables: the Programme Association Table (PAT) and entries
   in the program element loop of a Programme Map Table (PMT). PMT
   Tables are sent infrequently, and are typically small in size. The
   PAT is sent using the well-known PID value of 0X000. This table
   provides the correspondence between a program_number and a PID
   value. (The program_number is the numeric label associated with a
   program.) Each program in the Table is associated with a specific
   PID value, used to identify a TS Logical Channel (i.e. a TS).  The
   identified TS is used to send the PMT, which associates a set of PID
   values with the individual components of the programme. This
   approach de-references the PID values when the MPEG-2 Network
   includes multiplexors or re-multiplexors that renumber the PID
   values of the TS Logical Channels that they process.

   In addition to signalling the Receiver with the PID value assigned
   to a Stream, PMT entries indicate the presence of Streams using ULE
   and MPE to the variety of devices that may operate in the MPEG-2
   transmission network (multiplexors, remultiplexors, rate shapers,
   advertisement insertion equipment, etc).

   A multiplexor or remultiplexor may change the PID values associated
   with a Stream during the multiplexing process, the new value being
   reflected in an updated PMT. TS Packets that carry a PID value that
   is not associated with a PMT entry (an orphan PID), may, and usually
   will, be dropped by ISO 13818-1 compliant L2 equipment, resulting in
   the Stream not being forwarded across the transmission network. In
   networks that do not employ any intermediate devices (e.g. scenarios
   C,E,F of [RFC4259]), or where devices have other means to determine
   the set of PID values in use, the PMT table may still be sent (but
   is not required for this purpose).

   Although the basic PMT information may be used to identify the
   existence of IP traffic, it does not associate a Stream with an IP
   prefix/address. The remainder of the section describes IP addresses
   resolution mechanisms relating to MPEG-2.


4.1 Static configuration.

   The static mapping option, where IP addresses or flows are
   statically mapped to specific PIDs is the equivalent to signalling
   "out-of-band". The application programmer, installing engineer, or
   user receives the mapping via some outside means, not in the MPEG-2
   TS. This is useful for testing, experimental networks, small
   subnetworks and closed domains.

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   A pre-defined set of IP addresses may be used within a MPEG-2
   transmission network. Prior knowledge of the active set of addresses
   allows appropriate AR records to be constructed for each address,
   and to pre-assign the corresponding PID value (e.g., selected to
   optimise Receiver processing; to group related addresses to the same
   PID value; and/or to reflect a policy for usage of specific ranges
   of PID values). This presumes that the PID mappings are not modified
   during transmission (section 4).

   A single "well-known" PID is a specialisation of this. This scheme
   is used by current DOCSIS cable modems [DOCSIS], where all IP
   traffic is placed into the specified TS stream. MAC filtering
   (and/or Section filtering in MPE) may be used to differentiate
   subnetworks.


4.1.1 MPEG-2 Cable Networks

   Cable networks use a different transmission scheme for downstream,
   (head-end to cable modem) and upstream (cable modem to head-end)
   transmission.

   IP/Ethernet packets are sent (on the downstream) to the cable
   modem(s) encapsulated in MPEG-2 TS Packets sent on a single well-
   known TS Logical Channel (PID). There is no use of in-band
   signalling tables. On the upstream, the common approach is to use
   Ethernet framing, rather than IP/Ethernet over MPEG-2, although
   other proprietary schemes also continue to be used.

   Until the deployment of DOCSIS and EuroDOCSIS, most address
   resolution schemes for IP traffic in cable networks were
   proprietary, and did not usually employ a table-based address
   resolution method. Proprietary methods continue to be used in some
   cases where cable modems require interaction. In this case,
   equipment at the head-end may act as gateways between the cable
   modem and the Internet. These gateways receive L2 information and
   allocate an IP address.

   DOCSIS uses DHCP for IP client configuration. The Cable Modem
   Terminal System (CMTS) provides a DHCP server that allocates IP
   addresses to DOCSIS cable modems. The MPEG-2 Transmission Network
   provides a L2 bridged network to the cable modem (section 1). This
   usually acts as a DHCP Relay for IP devices [RFC2131], [RFC3046],
   [RFC3256]. Issues in deployment of IPv6 are described in [ID-V6OPS-
   DEPLOY].


4.2 MPEG-2 Table-Based Address Resolution

   The information about the set of MPEG-2 Transport Streams carried
   over a TS Multiplex can be distributed via SI/PSI Tables. These
   tables are usually sent periodically (section 4). This design
   requires access to and processing of the SI Table information by

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   each Receiver [ETSI-SI], [ETSI-SI1].  This scheme reflects the
   complexity of delivering and co-ordinating the various Transport
   Streams associated with multimedia TV. A TS Multiplex may provide AR
   information for IP services by integrating additional information
   into the existing control tables or by transmitting additional SI
   Tables that are specific to the IP service.

   Examples of MPEG-2 Table usage to allow an MPEG-2 Receiver to
   identify the appropriate PID and multiplex associated with a
   specific IP address include:

   (i)  IP/MAC Notification Table (INT) in the DVB Data standard
        [ETSI-DAT]. This provides uni-directional address resolution of
        IPv4/IPv6 multicast addresses to an MPEG-2 TS.

   (ii) Application Information Table (AIT) in the Multimedia Home
        Platform (MHP) specifications [ETSI-MHP].

   (iii) Multicast Mapping Table (MMT) an MPEG-2 Table employed by some
         DVB-RCS systems to provide uni-directional address resolution
         of IPv4 multicast addresses to an MPEG-2 TS.

   The MMT and AIT are used for specific applications, whereas the INT
   [ETSI-DAT] is a more general DVB method that supports MAC, IPv4, and
   IPv6 AR when used in combination with the other MPEG-2 tables
   (section 4).


4.2.1 IP/MAC Notification Table (INT) and its usage

   The INT provides a set of descriptors to specify addressing in a DVB
   network. Use of this method is specified for Multi-Protocol
   Encapsulation (MPE) [ETSI-DAT]. It provides a method for carrying
   information about the location of IP/L2 flows within a DVB network.
   A Platform_ID, identifies the addressing scope for a set of IP/L2
   streams and/or Receivers. A Platform may span several Transport
   Streams carried by one or multiple TS Multiplexes and represents a
   single IP network with a harmonized address space (scope). This
   allows for the coexistence of several independent IP/MAC address
   scopes within an MPEG-2 Network.

   The INT allows both fully-specified IP addresses and prefix
   matching, to reduce the size of the table (and hence enhance
   signalling efficiency). An IPv4/IPv6 "subnet mask" may be specified
   in full form or using a slash notation (e.g. /127). IP multicast
   addresses can be specified with or without a source (address or
   range), although if a source address is specified, then only the
   slash notation may be used for prefixes.

   In addition to identification and security descriptors, the
   following descriptors are defined for address binding in INT tables:

   (i)   target_MAC_address_descriptor: A descriptor to describe a

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         single or set of MAC addresses (and their mask).

   (ii)  target_MAC_address_range_descriptor: A descriptor that may be
         used to set filters.

  (iii)  target_IP_address_descriptor: A descriptor describing a
         single or set of IPv4 unicast or multicast addresses (and
         their mask).

   (iv)   target_IP_slash_descriptor:  Allows definition and
          announcement of an IPv4 prefix.

   (v)    target_IP_source_slash_descriptor: Uses source and
          destination addresses to target a single or set of systems.

   (vi)   IP/MAC  stream_location_descriptor: A descriptor that locates
          an IP/MAC stream in a DVB network.

   The following descriptors provide corresponding functions for IPv6
   addresses:

        target_IPv6_address_descriptor
        target_IPv6_slash_descriptor
        and target_IPv6_source_slash_descriptor

   The ISP_access_mode_descriptor allows specification of a second
   address descriptor to access an ISP via an alternative non-DVB
   (possibly non-IP) network.

   One key benefit is that the approach employs MPEG-2 signalling
   (section 4) and is integrated with other signalling information.
   This allows the INT to operate in the presence of (re)multiplexors
   [RFC4259] and to refer to PID values that are carried in different
   TS Multiplexes. This makes it well-suited to a Broadcast TV Scenario
   [RFC4259].

   The principal drawback is a need for an Encapsulator to introduce
   associated PSI/SI MPEG-2 control information. This control
   information needs to be processed at a Receiver. This requires
   access to information below the IP layer. The position of this
   processing within the protocol stack makes it hard to associate the
   results with IP Policy, management and security functions. The use
   of centralized management prevents the implementation of a more
   dynamic scheme.


4.2.2 Multicast Mapping Table (MMT) and its usage

   In DVB-RCS, unicast AR is seen as a part of a wider configuration
   and control function and does not employ a specific protocol.

   A Multicast Mapping Table (MMT) may be carried in an MPEG-2 control
   table that associates a set of multicast addresses with the

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   corresponding PID values.  This table allows a DVB-RCS Forward Link
   Subsystem (FLSS) to specify the mapping of IPv4 multicast addresses
   to PID values within a specific TS Multiplex. Receivers (DVB-RCS
   Return Channel Satellite Terminals, RCSTs) may use this table to
   determine the PID values associated with an IP multicast flow that
   it requires to receive. The MMT is not specified as a part of the
   DVB-RCS specification.


4.2.3 Application Information Table (AIT) and its usage

   The DVB Multimedia Home Platform (MHP) specification [ETSI-MHP] does
   not define a specific AR function. However, an Application
   Information Table (AIT) is defined that allows MHP Receivers to
   receive a variety of control information. The AIT uses an MPEG-2
   signalling table providing information about data broadcasts, the
   required activation state of applications carried by a broadcast
   stream, etc. This information allows a broadcaster to request that a
   Receiver change the activation state of an application, and to
   direct applications to receive specific multicast packet flows
   (using IPv4 or IPv6 descriptors).  In MHP, AR is not seen as a
   specific function, but as a part of a wider configuration and
   control function.


4.2.4 Address Resolution in ATSC

   ATSC [ATSC-G] defines a system that allows transmission of IP
   packets within an MPEG-2 Network. An MPEG-2 Program (defined by the
   PMT) may contain one or more applications [ATSC-A90] that include IP
   multicast streams [ATSC-A92]. IP multicast data are signalled in the
   PMT using a stream_type indicator of value 0x0D. A MAC address list
   descriptor [SCTE-1] may also be included in the PMT.

   The approach focuses on applications that serve the transmission
   network. A method is defined that uses MPEG-2 SI Tables to bind the
   IP multicast media streams and the corresponding Session Description
   Protocol (SDP) announcement streams to particular MPEG-2 Program
   Elements.  Each application constitutes an independent network. The
   MPEG-2 Network boundaries establish the IP addressing scope.


4.2.5 Comparison of SI/PSI table approaches

   The MPEG-2 methods based on SI/PSI meet the specified requirements
   of the groups that created them and each has their strength:  the
   INT in terms of flexibility and extensibility, the MMT in its
   simplicity, the AIT in its extensibility. However, they exhibit
   scalability constraints, represent technology specific solutions and
   do not fully adopt IP-centric approaches that would enable easier
   use of the MPEG-2 bearer as a link technology within the wider
   Internet.


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4.3 IP-based address resolution for TS Logical Channels

   As MPEG-2 Networks evolve to become multi-service networks, the use
   of IP protocols is becoming more prevalent. Most MPEG-2 Networks now
   use some IP protocols for operations, control and data delivery,
   address resolution information could also be sent using IP
   transport.  At the time of writing there is no standards-based IP-
   level AR protocol that supports the MPEG-2 TS.

   There is an opportunity to define an IP-level method that could use
   an IP multicast protocol over a well-known IP multicast address to
   resolve an IP address to a TS Logical Channel (i.e. a Transport
   Stream). The advantages of using an IP-based address resolution
   include:

   (i) Simplicity:
   The AR mechanism does not require interpretation of Layer 2 tables;
   this is an advantage especially in the growing market share for home
   network and audio video networked entities.

   (ii) Uniformity:
   An IP-based protocol can provide a common method across different
   network scenarios for both IP to MAC address mappings and to map to
   TS Logical Channels (PID value associated with a Stream).

   (iii) Extensibility:
   IP-based AR mechanisms allow an independent evolution of the AR
   protocol. This includes dynamic methods to request address
   resolution and the ability to include other L2 information (e.g.
   Encryption keys).

   (iv) Integration
   The information exchanged by IP-based AR protocols can easily be
   integrated as a part of the IP network layer, simplifying support
   for AAA, policy, OAM, mobility, configuration control, etc. that
   combine AR with security.


   The drawbacks of an IP-based method include:

   (i) It can not operate over an MPEG-2 Network that uses MPEG-2
   remultiplexors [RFC4259] that modify the PID values associated with
   the TS Logical Channels during the multiplexing operation (section
   4). This makes the method unsuitable for use in deployed broadcast
   TV networks [RFC4259].

   (ii) IP-based methods can introduce concerns about the integrity of
   the information and authentication of the sender [RFC4259]. (These
   concerns are also applicable to MPEG-2 Table methods, but in this
   case the information is confined to the L2 network, or parts of the
   network where gateway devices isolate the MPEG-2 devices from the
   larger Internet creating virtual MPEG-2 private networks.) IP-based

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   solutions should therefore implement security mechanisms that may be
   used to authenticate the sender and verify the integrity of the AR
   information, as a part of a larger security framework.


   An IP-level method could use an IP multicast protocol running an AR
   Server (see also section 5.4) over a well-known (or discovered) IP
   multicast address. To satisfy the requirement for scalability to
   networks with large number of systems (section 1), a single packet
   needs to transport multiple AR records, and define the intended
   scope for each address. Methods that employ prefix matching (e.g.
   where a range of source/destination addresses are matched to a
   single entry are desirable), as also are methods that allow a range
   of IP addresses to mapped to a set of TS Logical Channels (a hashing
   technique similar to the mapping of IP Group Destination Addresses
   to Ethernet MAC addresses may be beneficial).






































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5. Mapping IP addresses to MAC/NPA addresses

   This section reviews IETF protocols that may be used to assign and
   manage the mapping of IP addresses to/from MAC/NPA addresses over
   MPEG-2 Networks.

   An IP Encapsulator requires AR information to select an appropriate
   MAC/NPA address in the SNDU header [RFC4259] (section 6). The
   information to complete this header may be taken directly from a
   neighbour/arp cache, or may require the Encapsulator to retrieve the
   information using an AR protocol. The way in which this information
   is collected will depend upon whether the Encapsulator functions as
   a Router (at L3) or a Bridge (at L2) (section 1.1).

   Two IETF-defined protocols for mapping IP addresses to MAC/NPA
   addresses are the Address Resolution Protocol, ARP [RFC826], and the
   Neighbor Discovery protocol, ND [RFC2461], respectively for IPv4 and
   IPv6. Both protocols are normally used in a bi-directional mode,
   although both also permit unsolicited transmission of mappings. The
   IPv6 mapping defined in [RFC2464] can result in a large number of
   active MAC multicast addresses (e.g. one for each end host).

   ARP requires support for L2 broadcast packets. A large number of
   Receivers can lead to a proportional increase in ARP traffic, a
   concern for bandwidth-limited networks. Transmission delay can also
   impact protocol performance.

   ARP also has a number of security vulnerabilities. ARP spoofing is
   where a system can be fooled by a rogue device that sends a
   fictitious ARP response that includes the IP address of a legitimate
   network system, and the MAC of a rogue system. This causes
   legitimate systems on the network to update their ARP tables with
   the false mapping and then send future packets to the rogue system
   instead of the legitimate system. Using this method, a rogue system
   can see (and modify) packets sent through the network.

   Secure ARP (SARP) uses a secure tunnel (e.g. between each client and
   a server at a wireless access point or router) [RFC2246]. The router
   ignores any ARP responses not associated with clients using the
   secure tunnels. Therefore, only legitimate ARP Responses are used
   for updating ARP tables. SARP requires the installation of software
   at each client. It suffers from the same scalability issues as the
   standard ARP.

   The ND protocol uses a set of IP multicast addresses. In large
   networks, many multicast addresses are used, but clients typically
   only listen to a restricted set of group destination addresses and
   little traffic is usually sent in each group. Layer-2 AR for MPEG-2
   Networks therefore must support this in a scalable manner.

   A large number of ND Router Solicitation messages may cause a large
   demand for performing asymmetric operations. The base ND protocol


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   limits the rate at which multicast responses to solicitations can be
   sent, configurations may need to be tuned when operating with large
   numbers of Receivers.

   The default parameters specified in RFC 2461 for the ND protocol can
   introduce interoperability problems (e.g. a failure to resolve when
   the link RTT exceed 3 seconds) and performance degradation
   (duplicate ND messages with a link RTT > 1 second) when used in
   networks were the link RTT is significantly larger than experienced
   by Ethernet LANs. Tuning of the protocol parameters (e.g.
   RTR_SOLICITATION_INTERVAL) is therefore recommended when using
   network links with appreciable delay (Section 6.3.2 of [RFC2461]).

   ND has similar security vulnerabilities to ARP. The Secure Neighbor
   Discovery, SEND [RFC3971] was developed to address known security
   vulnerabilities in ND [RFC3756]. It can also reduce the AR traffic
   compared to ND. SEND also does not impact the IPsec architecture and
   implementations, and provides improved support for security
   decisions based on application state. This allows co-existence of
   SEND and insecure ND on the same link.


5.1 Uni-directional links supporting uni-directional connectivity

   MPEG-2 Networks may provide a Uni-Directional broadcast Link (UDL),
   with no return path. Such links may be used for unicast applications
   that do not require a return path (e.g. based on UDP), but commonly
   are used for IP multicast content distribution.

                                           /-----\
                         MPEG-2 Uplink    /MPEG-2 \
                      ###################( Network )
                      #                   \       /
                 +----#------+             \--.--/
                 |  Network  |                |
                 |  Provider +                v MPEG-2 downlink
                 +-----------+                |
                                        +-----v------+
                                        |   MPEG-2   |
                                        |  Receiver  |
                                        +------------+

                Figure 3: Uni-directional connectivity

   The ARP and ND protocols require bi-directional L2/L3 connectivity.
   They do not provide an appropriate method to resolve the remote
   (destination) address in a uni-directional environment.

   Unidirectional links therefore require a separate out-of-band
   configuration method to establish the appropriate AR information at
   the Encapsulator and Receivers. ULE [RFC4326] defines a mode in
   which the MAC/NPA address is omitted from the SNDU. In some
   scenarios, this may relieve an Encapsulator of the need for L2 AR.

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5.2 Uni-directional links with bi-directional connectivity

   Bi-directional connectivity may be realised using a uni-directional
   link in combination with another network path. Common combinations
   are a Feed link using MPEG-2 satellite transmission and a return
   link using terrestrial network infrastructure. This topology is
   often known as a Hybrid network, and has asymmetric network routing.

                                           /-----\
                         MPEG-2 uplink    /MPEG-2 \
                      ###################( Network )
                      #                   \       /
                 +----#------+             \--.--/
                 |  Network  |                |
                 |  Provider +-<-+            v MPEG-2 downlink
                 +-----------+   |            |
                                 |      +-----v------+
                                 +--<<--+   MPEG-2   |
                               Return   |  Receiver  |
                               Path     +------------+

                Figure 4: Bi-directional connectivity

   The Uni-Directional Link Routing, UDLR [RFC3077] protocol may be
   used to overcome issues associated with asymmetric routing. The
   Dynamic Tunnel Configuration Protocol (DTCP) enables automatic
   configuration of the return path.  UDLR hides the uni-directional
   routing from the IP and upper layer protocols, by providing a L2
   tunnelling mechanism that emulates a bi-directional broadcast link
   at L2. A network using UDLR has a topology where a Feed Router and
   all Receivers form a logical Local Area Network. Encapsulating L2
   frames allows them to be sent through an Internet Path (i.e.
   bridging).

   Since many uni-directional links employ wireless technology for the
   forward (Feed) link (e.g., [ETSI-DAT]), there may be an appreciable
   cost associated with forwarding traffic on the Feed link. Therefore,
   it is often desirable to prevent forwarding unnecessary traffic,
   (e.g. for multicast this implies control of which groups are
   forwarded). The implications of forwarding in the return direction
   must also be considered (e.g., asymmetric capacity and loss
   [RFC3449]). This suggests a need to minimise the volume and
   frequency of control messages.

   Three different AR cases may be identified (each considers sending
   an IP packet to a next-hop IP address that is not currently cached
   by the sender):

   (i) A Feed Router needs a Receiver MAC/NPA address.



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   This occurs when a Feed Router sends an IP packet using the Feed UDL
   to a Receiver whose MAC/NPA address is unknown. In IPv4, the Feed
   Router sends an ARP REQUEST with the IP address of the Receiver. The
   Receiver that recognises its IP address replies with an ARP RESPONSE
   to the MAC/NPA address of the Feed Router (e.g. using a UDLR
   tunnel). The Feed Router may then address IP packets to the unicast
   MAC/NPA address associated with the Receiver. The ULE packet format
   also permits packets to be sent without specifying a MAC/NPA
   address, where this is desirable (section 6.1, 6.5).

   (ii) A Receiver needs the Feed Router MAC/NPA address.

   This occurs when a Receiver sends an IP packet to a Feed Router
   whose MAC/NPA address is unknown. In IPv4, the Receiver sends an ARP
   REQUEST with the IP address of the Feed Router (e.g. using a UDLR
   tunnel). The Feed Router replies with an ARP RESPONSE using the Feed
   UDL. The Receiver may then address IP packets to the MAC/NPA address
   of the recipient.

   (iii) A Receiver needs another Receiver MAC/NPA address.

   This occurs when a Receiver sends an IP packet to another Receiver
   whose MAC/NPA address is unknown. In IPv4, the Receiver sends an ARP
   REQUEST with the IP address of the remote Receiver (e.g. using a
   UDLR tunnel to the Feed Router). The request is forwarded over the
   Feed UDL.  The target Receiver replies with an ARP RESPONSE (e.g.
   using a UDLR tunnel). The Feed Router forwards the response on the
   UDL. The Receiver may then address IP packets to the MAC/NPA address
   of the recipient.


   These 3 cases allow any system connected to the UDL to obtain the
   MAC/NPA address of any other system. Similar exchanges may be
   performed using the ND protocol for IPv6.

   A long round trip delay (via the UDL and UDLR tunnel) impacts the
   performance of the reactive address resolution procedures provided
   by ARP, ND and SEND. In contrast to Ethernet, during the interval
   when resolution is taking place, many IP packets may be received
   that are addressed to the AR Target address. The arp specification
   allows an interface to discard these packets while awaiting the
   response to the resolution request. An appropriately sized buffer
   would however prevent this loss.

   In case (iii), the time to complete address resolution may be
   reduced by use of an AR Server at the Feed (section 5.4).

   Using DHCP requires prior establishment of the L2 connectivity to a
   DHCP server. The delay in establishing return connectivity in UDLR
   networks that use DHCP, may make it beneficial to increase the
   frequency of the DTCP HELLO message. Further information about
   tuning DHCP is provided in section 5.5.


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5.3 Bi-directional Links

   Bi-directional IP networks can be and are constructed by a
   combination of two MPEG-2 transmission links. One link is usually a
   broadcast link that feeds a set of remote Receivers. Links are also
   provided from Receivers so that the combined link functions as a
   full duplex interface. Examples of this use include two-way DVB-S
   satellite links and the DVB-RCS system.


5.4 AR Server

   An AR Server can be used to distribute AR information to Receivers
   in an MPEG-2 Network. In some topologies this may significantly
   reduce the time taken for Receivers to discover AR information.

   The AR Server can operate as a proxy responding on behalf of
   Receivers to received AR requests. When an IPv4 AR request is
   received (e.g. Receiver ARP REQUEST), an AR Server responds by
   (proxy) sending an AR response providing the appropriate IP to
   MAC/NPA binding (mapping the IP address to the L2 address).

   Information may also be sent unsolicited by the AR Server using
   multicast/broadcast to update the arp/neighbor cache at the
   Receivers without the need for explicit requests. The unsolicited
   method can improve scaling in large networks. Scaling could be
   further improved by distributing a single broadcast/multicast AR
   message that binds multiple IP and MAC/NPA addresses. This reduces
   the network capacity consumed and simplifies client
   processing/server in networks with large numbers of clients.

   An AR Server can be implemented using IETF-defined Protocols by
   configuring the subnetwork so that AR Requests from Receivers are
   intercepted rather than forwarded to the Feed/broadcast link.  The
   intercepted messages are sent to an AR Server.  The AR Server
   maintains a set of MAC/NPA address bindings. These may be configured
   or may learned by monitoring ARP messages sent by Receivers.
   Currently defined IETF protocols only allow one binding per message,
   (i.e. there is no optimisation to conserve L2 bandwidth).

   Equivalent methods could provide IPv6 AR. Procedures for
   intercepting ND messages are defined in [RFC4389]. To perform an AR
   Server function, the AR information must also be cached. A caching
   AR proxy stores system state within a middle-box device. This
   resembles a classic man-in-the-middle security attack; interactions
   with SEND are described in [ID-SP-ND].

   Methods are needed to purge stale AR data from the cache. The
   consistency of the cache must also be considered when the receiver
   bindings can change (e.g. IP mobility, network topology changes, or
   intermittent Receiver connectivity). In these cases, the use of old
   (stale) information can result in IP packets being directed to an
   inappropriate L2 address, with consequent packet loss.

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   Current IETF-defined methods provide bindings of IP addresses to
   MAC/NPA, but do not allow the bindings to other L2 information
   pertinent to MPEG-2 Networks, requiring the use of other methods for
   this function (section 4).  AR Servers can also be implemented using
   non-IETF AR protocols to provide the AR information required by
   Receivers.


5.5 DHCP Tuning

   DHCP [RFC2131] may be used over MPEG-2 Networks. DHCP consists of
   two components: a protocol for delivering system-specific
   configuration parameters from a DHCP server to a DHCP client (e.g.
   default router, DNS server) and a mechanism for allocation of
   network addresses to systems. DHCP messages  (e.g. DHCPDISCOVER,
   DHCPREQUEST, DHCPOFFER) may include options [RFC2131].

   The configuration of DHCP Servers and Clients should take into
   account the local link round trip delay (possibly including the
   additional delay from bridging, e.g. using UDLR). A larger delay
   makes it desirable to tune the DHCP lease duration and the size of
   the address pool. Appropriate timer values should also be selected:
   the DHCP messages retransmission timeout, and the maximum delay that
   a DHCP Server waits before deciding that the absence of an ICMP echo
   response indicates that the relevant address is free.

   DHCP Clients may retransmit DHCP messages if they do not receive a
   response. Some client implementations specify a timeout for the
   DHCPDISCOVER message that is small (e.g. suited to Ethernet delay,
   rather than appropriate to a MPEG-2 Network) providing insufficient
   time for a DHCP Server to respond to a DHCPDISCOVER retransmission
   before expiry of the check on the lease availability (by an ICMP
   echo request), resulting in potential address conflict.  This value
   may need to be tuned for MPEG-2 networks.


5.6 IP Multicast AR

   Section 3.2 describes multicast address resolution requirements.
   This section describes L3 address bindings when the destination
   network layer address is an IP multicast Group Destination Address.

   In MPE [ETSI-DAT], a mapping is specified for the MAC Address based
   on the IP multicast address for IPv4 [RFC1112] and IPv6 [RFC2464].
   (A variant of DVB (DVB-H) uses a modified MAC header [DVB_DAT]).

   In ULE [RFC4326], the L2 NPA address is optional, and is not
   necessarily required when the Receiver is able to perform efficient
   L3 multicast address filtering. When present, a mapping is defined
   based on the IP multicast address for IPv4 [RFC1112] and IPv6
   [RFC2464].


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   The L2 group addressing method specified in [RFC1112] and [RFC2464]
   can result in more than one IP destination addresses mapping to the
   same L2 address. In Source-Specific Multicast, SSM [RFC3569],
   multicast groups are identified by the combination of the IP source
   and IP destination addresses. Senders may therefore independently
   select an IP group destination address that could map to the same L2
   address if forwarded onto the same L2 link. The resulting addressing
   overlap at L2 can increase the volume of traffic forwarded to L3,
   where it then needs to be filtered.

   These considerations are the same as for Ethernet LANs, and may not
   be of concern to Receivers that can perform efficient L3 filtering.
   Section 3 noted that a MPEG-2 Network may need to support multiple
   addressing scopes at the network and link layers.  Separation of the
   different groups into different Transport Streams is one remedy
   (with signalling of IP to PID value mappings). Another approach is
   to employ alternate MAC/NPA mappings to those defined in [RFC1112]
   and [RFC2464], but such mappings need to be consistently bound at
   the Encapsulator and Receiver using AR procedures in a scalable
   manner.


5.6.1 Multicast/Broadcast addressing for UDLR

   UDLR is a layer 2 solution, in which a Receiver may send
   multicast/broadcast frames that are subsequently forwarded natively
   by a Feed Router (using the topology in figure 2), and are finally
   received at the feed interface of the originating Receiver.  This
   multicast forwarding does not include the normal L3 Reverse Path
   Forwarding (RPF) check or L2 spanning tree checks, the processing of
   the IP Time To Live (TTL) field, or the filtering of
   administratively scoped multicast addresses. This raises a need to
   carefully consider multicast support.  To avoid forwarding loops,
   RFC3077 notes that a Receiver needs to be configured with
   appropriate filter rules to ensure it discards packets that
   originate from an attached network and are later received over the
   feed link.

   When the encapsulation includes an MAC/NPA source address, such
   packets may be filtered at the link-layer using a filter that
   discards L2 addresses that are local to the Receiver. In some
   circumstances, systems can send packets with an unknown (all zero)
   MAC source address (e.g. IGMP Proxy Queriers [RFC-IGMP-Proxy]),
   where the source at L2 can not be determined at the Receiver, these
   packets need to be silently discarded, which may prevent running the
   associated services on the Receiver.

   Some encapsulations do not include an MAC/NPA source address (Table
   2).  Multicast packets may therefore alternatively be discarded at
   the IP layer if their IP source address matches a local IP address
   (or address range).  Systems can send packets with an all zero IP
   source address (e.g. BOOTP [RFC951], DHCP [RFC2131] and ND
   [RFC2461]), where the source at L3 can not be determined at the

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   Receiver these packets need to be silently discarded.  This may
   prevent running the associated services at a Receiver, e.g.
   participation in IPv6 Duplicate Address Detection, or running a DHCP
   server.


















































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6. Link Layer Support

   This section considers link-layer (L2) support for address
   resolution in MPEG-2 Networks. It considers two issues: The code-
   point used at L2 and the efficiency of encapsulation for
   transmission required to support the AR method. The table below
   summarises the options for both MPE [ETSI-DAT] and ULE [RFC4326]
   encapsulations.

      +-------------------------------+--------+----------------------+
      |                               | PDU    |L2 Frame Header Fields|
      | L2 Encapsulation              |overhead+----------------------+
      |                               |[bytes] |src mac|dst mac| type |
      +-------------------------------+--------+-------+-------+------+
      |6.1 ULE without dst MAC address| 8      |   -   |  -    | x    |
      |6.2 ULE with dst MAC address   | 14     |   -   |  x    | x    |
      |6.3 MPE without LLC/SNAP       | 16     |   -   |  x    | -    |
      |6.4 MPE with LLC/SNAP          | 24     |   -   |  x    | x    |
      |6.5 ULE with Bridging extension| 22     |   x   |  x    | x    |
      |6.6 ULE with Bridging & NPA    | 28     |   x   |  x    | x    |
      |6.7 MPE+LLC/SNAP+Bridging      | 38     |   x   |  x    | x    |
      +-------------------------------+--------+-------+-------+------+

   Table showing L2 support and overhead (x=supported, -=not supported)

   The remainder of the section describes IETF-specified AR methods for
   use with these encapsulation formats.


6.1 ULE without a destination MAC/NPA address (D=1)

   The ULE encapsulation supports a mode (D=1) where the MAC/NPA
   address is not present in the encapsulated frame. This mode may be
   used with both IPv4 and IPv6.  When used, the Receiver is expected
   to perform L3 filtering of packets based on their IP destination
   address [RFC4326]. This requires careful consideration of the
   network topology when a receiver is an IP router, or delivers data
   to an IP router (a simple case where this is permitted arises in the
   connection of stub networks that have no connectivity to other
   networks). Since there is no MAC/NPA address in the SNDU, ARP and
   NDP are not required.

   IPv6 systems can automatically configure their IPv6 network address
   based upon a local MAC address [RFC2462]. To use auto-configuration,
   the IP driver at the Receiver may need to access the MAC/NPA address
   of the receiving interface, even though this value is not being used
   to filter received SNDUs.







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6.2 ULE with a destination MAC/NPA address (D=0)

   The IPv4 Address Resolution Protocol (ARP) [RFC826] is identified by
   an IEEE EtherType and may be used over ULE [RFC4326]. Although no
   MAC source address is present in the ULE SNDU, the ARP protocol
   still communicates the source MAC (hardware) address in the ARP
   record payload of any query messages that it generates.

   The IPv6 ND protocol is supported. The protocol uses a block of IPv6
   multicast addresses, which need to be carried by the L2 network. The
   protocol does not require specification of a MAC source address,
   although this is required for a node to participate in Duplicate
   Address Detection (DAD) [RFC2462].


6.3 MPE without LLC/SNAP Encapsulation

   This is the default (and sometimes only) mode specified by most MPE
   Encapsulators. MPE does not provide an EtherType field and therefore
   can not support the Address Resolution Protocol (ARP) [RFC826].

   IPv6 is not supported in this encapsulation format, and therefore it
   is not appropriate to consider the ND protocol.


6.4 MPE with LLC/SNAP Encapsulation

   The LLC/SNAP format of MPE provides an EtherType field and therefore
   may support the ARP [RFC826]. There is no specification to define
   how this is performed. No MAC source address is present in the SNDU,
   although the protocol still communicates the source MAC address in
   the ARP record payload of any query messages that it generates.

   The IPv6 ND protocol is supported using The LLC/SNAP format of MPE.
   This requires specific multicast addresses to be carried by the L2
   network. The MAC source address permits the node to participate in
   DAD [RFC2462].


6.5 ULE with Bridging Header Extension (D=1)

   The ULE encapsulation supports a bridging extension header that
   supplies both a source and destination MAC address.  This can be
   used without an NPA address (D=1). When no other Extension Headers
   are present, the MAC destination address has the same position in
   the ULE SNDU as that used for an NPA destination address.  The
   Receiver may optionally be configured so that the MAC destination
   address value is identical to a Receiver NPA address.

   At the Encapsulator, the ULE MAC/NPA destination address is
   determined by a L2 forwarding decision.  Received frames may be
   forwarded or may be addressed to the Receiver itself. As in other L2
   LANs, the Receiver may choose to filter received frames based on a

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   configured MAC destination address filter. ARP and ND messages may
   be carried within a PDU that is bridged by this encapsulation
   format.


6.6 ULE with Bridging Header Extension and NPA Address (D=0)

   The combination of a NPA address (D=0) and a bridging extension
   header are allowed in ULE. This SNDU format supplies both a source
   and destination MAC address and a NPA destination address (i.e.
   Receiver MAC/NPA address).

   At the Encapsulator, the value of the ULE MAC/NPA destination
   address is determined by a L2 forwarding decision. At the Receiver,
   frames may be forwarded or may be addressed to the Receiver itself.
   As in other L2 LANs, the Receiver may choose to filter received
   frames based on a configured MAC destination address filter. ARP and
   ND messages may be carried within a PDU that is bridged by this
   encapsulation format.


6.7 MPE+LLC/SNAP+Bridging

   The LLC/SNAP format MPE frames may optionally support an IEEE
   bridging header [LLC]. This header supplies both a source and
   destination MAC address, at the expense of larger encapsulation
   overhead. The format defines two MAC destination addresses, one
   associated with the MPE SNDU (i.e. Receiver MAC address) and one
   with the bridged MAC frame (i.e. the MAC address of the intended
   recipient in the remote LAN).

   At the Encapsulator, the MPE MAC destination address is determined
   by a L2 forwarding decision. A Receiver may forward frames or they
   may be addressed to the Receiver itself. As in other L2 LANs, the
   Receiver may choose to filter received frames based on a configured
   MAC destination address filter. ARP and ND messages may be carried
   within a PDU that is bridged by this encapsulation format. The MPE
   MAC destination address is determined by a L2 forwarding decision.
















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7. Conclusions

   This document describes addressing and address resolution issues for
   IP protocols over MPEG-2 transmission networks using both wired and
   wireless technologies. A number of specific IETF protocols are
   discussed along with their expected behaviour over MPEG-2
   transmission networks. Recommendations for their usage are provided.

   There is no single common approach used in all MPEG-2 networks. A
   static binding may be configured for IP addresses and PIDs (as in
   some cable networks).  In broadcast networks, this information is
   normally provided by the Encapsulator/Multiplexor and carried in
   signalling tables (e.g. AIT in MHP, the IP Notification Table, INT,
   of DVB and the DVB-RCS Multicast Mapping Table, MMT). This document
   has reviewed the status of these current address resolution
   mechanisms in MPEG-2 transmission networks and defined their usage.

   The document also considers a unified IP-based method for AR that
   could be independent of the physical layer, but does not define a
   new protocol. It examines the design criteria for a method, with
   recommendations to ensure scalability and improve support for the IP
   protocol stack.


8. Security Considerations

   The normal security issues relating to the use of wireless links for
   transmission of Internet traffic should be considered.

   L2 signalling in MPEG-2 transmission networks is currently provided
   by (periodic) broadcasting of information in the control plane using
   PSI/SI tables (section 4). A loss or modification of the SI
   information may result in an inability to identify the TS Logical
   Channel (PID) that is used for a service. This will prevent
   reception of the intended IP packet stream.

   There are known security issues relating to the use of unsecured
   address resolution [RFC3756].  Readers are also referred to the
   known security issues when mapping IP addresses to MAC/NPA addresses
   using ARP [RFC826] and ND [RFC2461]. It is recommended that AR
   protocols support authentication of the source of AR messages and
   the integrity of the AR information, this avoids known security
   vulnerabilities resulting from insertion of unauthorised AR messages
   within a L2 infrastructure.  For IPv6, the SEND protocol [RFC3971]
   may be used in place of ND. This defines security mechanisms that
   can protect AR.

   AR protocols can also be protected by the use of L2 security methods
   (e.g. Encryption of the ULE SNDU [ID-IPDVB-SEC]). When these methods
   are used, the security of ARP and ND can be comparable to that of a
   private LAN: A Receiver will only accept ARP or ND transmissions
   from the set of peer senders that share a common group encryption


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   and common group authentication key provided by the L2 key
   management.

   AR Servers (section 5.4) are susceptible to the same kind of
   security issues as end hosts using unsecured AR.  These issues
   include hijacking traffic and denial-of-service within the subnet.
   Malicious nodes within the subnet can take advantage of this
   property, and hijack traffic.  In addition, an AR Server is
   essentially a legitimate man-in-the-middle, which implies that there
   is a need to distinguish such proxies from unwanted man-in-the-
   middle attackers. This document does not introduce any new
   mechanisms for the protection of these AR functions (e.g.
   authenticating servers, or defining AR Servers that interoperate
   with the SEND protocol [ID-SP-ND]).


9. Acknowledgments

   The authors wish to thank the ipdvb WG members for their inputs and
   in particular, Rod Walsh, Jun Takei, and Michael Mercurio. The
   authors also acknowledge the support of the European Space Agency.
   Martin Stiemerling contributed descriptions of scenarios,
   configuration, and provided extensive proof reading. Hidetaka
   Izumiyama contributed on UDLR and IPv6 issues. A number of issues
   discussed in the UDLR working group have also provided valuable
   inputs to this document (summarised in draft-ietf-udlr-experiments-
   01.txt).



























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10. References

10.1 Normative References

   [ETSI-DAT]  EN 301 192, "Specifications for Data Broadcasting",
   v1.3.1, European Telecommunications Standards Institute (ETSI), May
   2003.

   [ETSI-MHP] TS 101 812, "Digital Video Broadcasting (DVB); Multimedia
   Home Platform (MHP) Specification", v1.2.1, European
   Telecommunications Standards Institute (ETSI), June 2002.

   [ETSI-SI] EN 300 468, "Digital Video Broadcasting (DVB);
   Specification for Service Information (SI) in DVB systems", v1.7.1,
   European Telecommunications Standards Institute (ETSI), December
   2005.

   [ISO-MPEG2] ISO/IEC IS 13818-1, "Information technology -- Generic
   coding of moving pictures and associated audio information -- Part
   1: Systems", International Standards Organisation (ISO), 2000.

   [RFC826] Plummer, D., "An Ethernet Address Resolution Protocol", RFC
   826, IETF, November 1982.

   [RFC1112] Deering, S.E., "Host Extensions for IP Multicasting",
   RFC1112, (STD05), August 1989.

   [RFC2246] T. Dierks, C. Allen, "The TLS Protocol Version 1.0",
   RFC2246, January 1999.

   [RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
   Discovery for IP Version 6 (IPv6), RFC 2461, December 1998.

   [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
   Networks", RFC 2464, December 1998.

   [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
   2131, March 1997.

   [RFC3077] Duros, E., Dabbous, W., Izumiyama, H., Fujii, N., and Y.
   Zhang, "A Link-Layer Tunneling Mechanism for Unidirectional Links",
   RFC 3077, March 2001.

   [RFC4326] Fairhurst, G., Collini-Nocker, B., "Unidirectional
   Lightweight Encapsulation (ULE) for transmission of IP datagrams
   over an MPEG-2 Transport Stream", RFC 4326, December 2005.


10.2 Informative References

   [ATSC] A/53C, "ATSC Digital Television Standard", Advanced
   Television Systems Committee (ATSC), Doc. A/53C, 2004.


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   [ATSC-G] A/54A, "Guide to the use of the ATSC Digital Television
   Standard", Advanced Television Systems Committee (ATSC), Doc. A/54A,
   2003.

   [ATSC-A90] A/90, "ATSC Data Broadcast Standard", Advanced Television
   Systems Committee (ATSC), Doc. A/90, 2000.

   [ATSC-A92] A/92,  "Delivery of IP Multicast Sessions over ATSC Data
   Broadcast", Advanced Television Systems Committee (ATSC), Doc. A/92,
   2002.

   [DOCSIS] "Data-Over-Cable Service Interface Specifications, DOCSIS
   2.0, Radio Frequency Interface Specification", CableLabs, document
   CM-SP-RFIv2.0-I10-051209, 2005.

   [DVB] Digital Video Broadcasting (DVB) Project. http://www.dvb.org

   [ETSI-SI1] TR 101 162, "Digital Video Broadcasting (DVB); Allocation
   of Service Information (SI) codes for DVB systems", European
   Telecommunications Standards Institute (ETSI).

   [ETSI-RCS]  EN 301 790, "Digital Video Broadcasting (DVB);
   Interaction channel for satellite distribution Systems", European
   Telecommunications Standards Institute (ETSI).

   [ISO-DSMCC] ISO/IEC IS 13818-6, "Information technology -- Generic
   coding of moving pictures and associated audio information -- Part
   6: Extensions for DSM-CC is a full software implementation",
   International Standards Organisation (ISO), 2002.

   [ID-IPDVB-SEC] H.Cruickshank, S. Iyengar, L. Duquerroy, P. Pillai,
   "Security requirements for the Unidirectional Lightweight
   Encapsulation (ULE) protocol", Work in Progress, draft-cruickshank-
   ipdvb-sec-req-xx.txt.

   [ID-V6OPS-DEPLOY] Asadullah, S., Ahmed, A., Popoviciu, C., "ISP IPv6
   Deployment Scenarios in Broadband Access Networks"
   draft-ietf-v6ops-bb-deployment-scenarios-04.txt, Work in Progress,
   v6ops WG. XXX Publication Requested XX

   [ID-SP-ND] Daley, G., "Securing Proxy Neighbour Discovery Problem
   Statement", Work in progress, draft-daley-send-spnd-prob-01.txt,
   February 2005.

   [LLC] ISO/IEC 8802.2, "Information technology; Telecommunications
   and information exchange between systems; Local and metropolitan
   area networks; Specific requirements; Part 2: Logical Link Control",
   International Standards Organisation (ISO), 1998.

   [RFC951] Croft, W. and J. Gilmore, "Bootstrap Protocol", RFC 951,
   September 1985.



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   [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
   2131, March 1997.

   [RFC2362]  Estrin, D., Farinacci, D., Helmy, A., Thaler, D.,
   Deering, S., Handley, M., Jacobson, V., Liu, C., Sharma, P., and L.
   Wei, "Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol
   Specification", RFC 2362, June 1998.

   [RFC2365] Meyer, D., "Administratively Scoped IP Multicast", BCP 23,
   RFC 2365, July 1998.

   [RFC2375] Hinden, R. and S. Deering, "IPv6 Multicast Address
   Assignments", RFC 2375, July 1998.

   [RFC2462]  Thomson, S. and T. Narten, "IPv6 Stateless Address
   Autoconfiguration", RFC 2462, December 1998.

   [RFC3046] Patrick, M., "DHCP Relay Agent Information Option", RFC
   3046, January 2001.

   [RFC3256] Jones, D. and R. Woundy, "The DOCSIS (Data-Over-Cable
   Service Interface Specifications) Device Class DHCP (Dynamic Host
   Configuration Protocol) Relay Agent Information Sub-option", RFC
   3256, April 2002.

   [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
   Thyagarajan, "Internet Group Management Protocol, Version 3", RFC
   3376, October 2002.

   [RFC3449] Balakrishnan, H., Padmanabhan, V., Fairhurst, G., and M.
   Sooriyabandara, "TCP Performance Implications of Network Path
   Asymmetry", BCP 69, RFC 3449, December 2002.

   [RFC3451] Luby, M., Gemmell, J., Vicisano, L., Rizzo, L., Handley,
   M., and J. Crowcroft, "Layered Coding Transport (LCT) Building
   Block", RFC 3451, December 2002.

   [RFC3569] Bhattacharyya, S., "An Overview of Source-Specific
   Multicast (SSM)", RFC 3569, July 2003.

   [RFC3736] Droms, R., "Stateless Dynamic Host Configuration Protocol
   (DHCP) Service for IPv6", RFC 3736, April 2004.

   [RFC3756] Nikander, P., Kempf, J. and E. Nordmark, "IPv6 Neighbor
   Discovery (ND) Trust Models and Threats", RFC 3756, May 2004.

   [RFC3738] Luby, M. and V. Goyal, "Wave and Equation Based Rate
   Control (WEBRC) Building Block", RFC 3738, April 2004.

   [RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery
   Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.



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   [RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D.,
   Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. Wood,
   "Advice for Internet Subnetwork Designers", BCP 89, RFC 3819, July
   2004.

   [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
   Neighbor Discovery (SEND)", RFC 3971, March 2005.

   [RFC4259] Montpetit, M.J., Fairhurst, G., Clausen, H.D., Collini-
   Nocker, B., and H. Linder, "Architecture for IP transport
   over MPEG-2 Networks".

   [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
   Proxies (ND Proxy)", RFC 4389, April 2006.

   [RFC-IGMP-Proxy] B. Fenner,H. He, B. Haberman, H. Sandick,
   l"IGMP/MLD-based Multicast Forwarding ("IGMP/MLD Proxying")", RFC
   XXX, 2006. <currently draft-ietf-magma-igmp-proxy-06.txt>

   [SCTE-1] "IP Multicast for Digital MPEG Networks", SCTE DVS 311r6,
   March 2002.



11. Authors' Addresses

     Godred Fairhurst
     Department of Engineering
     University of Aberdeen
     Aberdeen, AB24 3UE
     UK
     gorry@erg.abdn.ac.uk
     http://www.erg.abdn.ac.uk/users/gorry

     Marie-Jose Montpetit
     Motorola Connected Home Solutions
     Advanced Technology
     55 Hayden Avenue , 3rd Floor
     Lexington
     Massachusetts
     02421
     USA
     mmontpetit@motorola.com

12. IPR Notices


12.1 Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed
   to pertain to the implementation or use of the technology described
   in this document or the extent to which any license under such

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   rights might or might not be available; nor does it represent that
   it has made any independent effort to identify any such rights.
   Information on the procedures with respect to rights in RFC
   documents can be found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use
   of such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository
   at http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at ietf-
   ipr@ietf.org.


12.2 Disclaimer of Validity

   This document and the information contained herein are provided on
   an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
   REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
   INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
   IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


13. Copyright Statement

   Copyright (C) The Internet Society (2006).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.


14. IANA Considerations

   This document does not define a protocol or protocol extension.  No
   action is required by the IANA.











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INTERNET DRAFT  AR Mechanisms for IP over MPEG-2 Networks   August 2006


   >>> NOTE to RFC Editor: Please remove this appendix prior to
   publication]

Document History

     -00 This draft is intended as a study item for proposed future
   work by the IETF in this area.
     -01 Review of initial content, major edit and refinement of
   concepts
     -02 fairly important review; took out all new protocol reference;
   added one author; added contribution on real implementation
     -02 Added content to respond to 61st IETF comments;
   refined ID goals; rewrote section 4.2 and 4.3; added cable
   information.
     -03 Major reorganise to align with Charter, and clearly identify
   IP issues.
     -04 restructured the draft (major rewrite) and added discussion of
   arp and ND related to specific cases for use.

   WG -00
   Reformatted as WG Draft.
   Added inputs from UDLR working group on UDLR, DHCP, etc.

   WG-01
   This rev. included a number of changes:
   * Added the case for large no. of groups/dynamic join to 3.2
   * ISO MPEG-2 table requirements added to section 4, following
   discussion on the list.
   * Added AR Authentication note to security considerations.

   WG-02
   * Major editorial work to bring this up tro DRAFT RFC format
   * Removed duplication of scoping discussion with ipdvb-arch
   * Reworded UDLR section to separate protocol issues from UDLR
   specifics.
   * Added SI security discussion.
   * Minor corrections
   * Added text from A/92 on scoping.
   * Aligned definitions with ipdvb-arch.
   * Fixed Reference format
   * Removed markers for additional contributions
   * No contributions received on PPPoE (removed).

   WG-03
   * Sections restructured to offer clearer advice on IETF-defined
   protocols.
   * Section added on bridging v routing cases
   * Section added on AR Server and use with arp and ND.
   * Section added to collect issues relating to DHCP
   * English improved to prepare for WGLC.



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INTERNET DRAFT  AR Mechanisms for IP over MPEG-2 Networks   August 2006


   WG-04
   * Fixed spelling mistake noted by George Kinal
   * Comments on various issues received from Rupert Goodrings
   * Comments on various issues received from Martin Striemerling
   * Comments on DAD and UDLR from Tina Strauf
   * Comments on DAD and MAC addresses from Bernhard Collini-Nocker
   * English fixed.
   * Title change (inserted methods)

   WG-05 (following WGLC)
   * Fixed security issues noted by George Gross
   * Added text on Mobility, topology changes with AR cache.

   * To be consistent with RFC4326, NPA = ULA address indicated by the
   D-bit, whereas MAC means IEEE-style address. I've reworked the text
   to make this clearer. Also made all "NPA/MAC" into "MAC/NPA".

   * Added notes on AR caches when used in mobile/ST topology changes.

   * Also note a mistake to section (iii) which was confusing about L2
   multicast addresses, this now reads:
   "  (iii) IP and other protocols may view sets of L3 multicast
           addresses as link-local. This may produce unexpected results
           if frames with the corresponding multicast L2 addresses are
           distributed to systems in a different L3 network or
           multicast scope (see sections 3.2 and 5.6)"

   * Section 2, Added:
   MAC Address: A 6 byte link layer address of the format described by
   the Ethernet IEEE 802 standard (see also NPA).

   * Section 3, Revised bullet into two points:
   A scalable architecture that may support large numbers of systems
   within the MPEG-2 network [RFC4259].
   A method for transmission of AR information from an AR Server to
   clients that minimise the transmission cost (link local multicast,
   is preferable to subnet broadcast).

   * Section 3, changed context to scope
   * Section 4.3. Revised wording on T Stream v. TS Logical Channel.
   * Section 5.4. 2nd para, added (mapping the IP address to the L2
   address)
   * Added:
   The default parameters specified in RFC 2461 for the ND protocol can
   introduce interoperability problems (e.g. a failure to resolve when
   the link RTT exceed 3 seconds) and performance degradation
   (duplicate ND messages with a link RTT > 1 second) when used in
   networks were the link RTT is significantly larger than experienced
   by Ethernet LANs. Tuning of the protocol parameters (e.g.
   RTR_SOLICITATION_INTERVAL) is therefore recommended when using
   network links with appreciable delay (Section 6.3.2 of [RFC2461]).
    [>>> NOTE to RFC Editor: End of appendix]

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