Network Working Group G. Fairhurst
Request for Comments: 4947 University of Aberdeen
Category: Informational M.-J. Montpetit
Motorola Connected Home Solutions
Address Resolution Mechanisms for IP Datagrams over MPEG-2 Networks
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright (C) The IETF Trust (2007).
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 Neighbor 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. This document
reviews current methods appropriate to a range of technologies (such
as DVB (Digital Video Broadcasting), ATSC (Advanced Television
Systems Committee), DOCSIS (Data-Over-Cable Service Interface
Specifications), and variants). It also describes the interaction
with well-known protocols for address management including DHCP, ARP,
and the ND protocol.
Table of Contents
1. Introduction ....................................................3
1.1. Bridging and Routing .......................................4
2. Conventions Used in This Document ...............................7
3. Address Resolution Requirements ................................10
3.1. Unicast Support ...........................................12
3.2. Multicast Support .........................................12
4. MPEG-2 Address Resolution ......................................14
4.1. Static Configuration ......................................15
4.1.1. MPEG-2 Cable Networks ..............................15
4.2. MPEG-2 Table-Based Address Resolution .....................16
4.2.1. IP/MAC Notification Table (INT) and Its Usage ......17
4.2.2. Multicast Mapping Table (MMT) and Its Usage ........18
4.2.3. Application Information Table (AIT) and Its Usage ..18
4.2.4. Address Resolution in ATSC .........................19
4.2.5. Comparison of SI/PSI Table Approaches ..............19
4.3. IP-Based Address Resolution for TS Logical Channels .......19
5. Mapping IP Addresses to MAC/NPA Addresses ......................21
5.1. Unidirectional Links Supporting Unidirectional
5.2. Unidirectional Links with Bidirectional Connectivity ......23
5.3. Bidirectional Links .......................................25
5.4. AR Server .................................................26
5.5. DHCP Tuning ...............................................27
5.6. IP Multicast AR ...........................................27
5.6.1. Multicast/Broadcast Addressing for UDLR ............28
6. Link Layer Support .............................................29
6.1. ULE without a Destination MAC/NPA Address (D=1) ...........30
6.2. ULE with a Destination MAC/NPA Address (D=0) ..............31
6.3. MPE without LLC/SNAP Encapsulation ........................31
6.4. MPE with LLC/SNAP Encapsulation ...........................31
6.5. ULE with Bridging Header Extension (D=1) ..................32
6.6. ULE with Bridging Header Extension and NPA Address (D=0) ..32
6.7. MPE with LLC/SNAP & Bridging ..............................33
7. Conclusions ....................................................33
8. Security Considerations ........................................34
9. Acknowledgments ................................................35
10. References ....................................................35
10.1. Normative References .....................................35
10.2. Informative References ...................................36
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 Neighbor Discovery (ND). Such
address resolution complements the higher layer resource discovery
tools that are used to advertise IP sessions. 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
The MPEG-2 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 L2 link supporting IP, 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 AR function. In some AR schemes, the
MPEG-2 TS address space is subdivided into logical contexts known as
Platforms [ETSI-DAT]. Each Platform associates an IP service
provider with a separate context that shares a common MPEG-2 TS
(i.e., uses 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, with any L2 encryption method and any compression
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 arbitrarily
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 a significant path delay (satellite links, use of dial-up
modem return, cellular return, etc.). This higher delay may need to
be accommodated by address resolution protocols that use this
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
that are IP end hosts and end hosts directly connected to bridged LAN
Broadcast Link AR
- - - - - - - - -
1a 2b 2a
----+ R1 +----------+---+ R2 +----
+--------+ MPEG-2 | +--------+
+---+ R3 +----
+---+ R4 +----
Figure 1: A routed MPEG-2 link
Figure 1 shows a routed MPEG-2 link feeding three downstream routers
(R2-R4). AR takes place at the Encapsulator (R1) to identify each
Receiver at Layer 2 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 MPEG-2 link feeding three 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
Layer 2 (R2, etc.). The Encapsulator associates a destination
MAC/NPA address with each bridged PDU sent on an MPEG-2 link. Two
methods are defined by ULE (Unidirectional Lightweight Encapsulation)
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 (B2-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 L2
services (including the use of UDLR (Unidirectional Links)
It is also possible for a bridging Encapsulator (B1) to encapsulate a
PDU with a link-specific header that also 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
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
and 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
- - - - - - - - - - - - - - - -
| MPEG-2 Link AR |
- - - - - - - - -
| | | |
1a x y 2b 2a
+--------+ +----+ +----+ +--------+
----+ R1 +--| B1 +----------+---+ B2 +--+ R2 +----
+--------+ +----+ MPEG-2 | +----+ +--------+
+---+ B3 +--
+---+ B4 +--
Figure 2: A bridged MPEG-2 link
Methods also exist to assign IP addresses to Receivers within a
network (e.g., stateless autoconfiguration [RFC2461], DHCP [RFC2131],
DHCPv6 [RFC3315], and stateless DHCPv6 [RFC3736]). Receivers may
also participate in the remote configuration of the L3 IP addresses
used in connected equipment (e.g., using DHCP-Relay [RFC3046]).
The remainder of this 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
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
on issues that would need to be considered to supply IP-based address
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 8-bits.
B: Byte. Groups of bytes are represented in Internet byte order.
DSM-CC: Digital Storage Media Command and Control [ISO-DSMCC]. A
format for the 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
bidirectional IPv4/IPv6 service employing low-cost Receivers
DVB-S: Digital Video Broadcast for Satellite [ETSI-DVBS].
Encapsulator: A network device that receives PDUs and formats these
into Payload Units (known here as SNDUs) for output as a stream of TS
Feed Router: The router delivering the IP service over a
INT: Internet/MAC Notification Table. A unidirectional address
resolution mechanism using SI and/or PSI Tables.
L2: Layer 2, the link layer.
L3: Layer 3, the IP network layer.
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 (Logical Link Control)).
MHP: Multimedia Home Platform. An integrated MPEG-2 multimedia
Receiver, that may (in some cases) support IPv4/IPv6 services
MMT: Multicast Mapping Table (proprietary extension to DVB-RCS
[ETSI-RCS] defining an AR table that maps IPv4 multicast addresses to
MPE: Multiprotocol Encapsulation [ETSI-DAT], [ATSC-A90]. 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
MPEG-2: A set of standards specified by the Motion Picture Experts
Group (MPEG), and standardized by the International Standards
Organization (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
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 (Program Map Table). 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. A PID value of all ones 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 and ATSC, have
defined sets of table structures using the private_section structure.
A Private Section is transmitted as a sequence of TS Packets using a
TS Logical Channel. A TS Logical Channel may carry sections from
more than one set of tables.
PSI: Program Specific Information [ISO-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
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
Table Section: A Payload Unit carrying all or a part of an SI or PSI
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 and DVB) also reserve specific PID
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.
ULE: Unidirectional Lightweight Encapsulation. 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].
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], [ATSC-A90]) 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 mechanisms to authenticate the AR information to
protect against 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 minimize 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 recognize 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; and 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] and [RFC2375].
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 (a L2 address of all
ones). Traffic with this address should be confined to one
(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
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
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 to allow a Receiver
to associate an IPv4 or IPv6 multicast address with a specific TS
Logical Channel and the corresponding TS Multiplex [RFC4259]. This
association needs to permit a large number of active multicast
groups, and should minimize 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
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 (Any-Source
Multicast) 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.
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], Layered Coding Transport (LCT)
[RFC3451], and Wave and Equation Based Rate Control (WEBRC)
[RFC3738]). The current set of active addresses may be determined
dynamically via a multicast group membership protocol (e.g., Internet
Group Management Protocol (IGMP) [RFC3376] and Multicast Listener
Discovery (MLD) [RFC3810]), via multicast routing (e.g., Protocol
Independent Multicast (PIM) [RFC4601]) and/or other means (e.g.,
[RFC3819] and [RFC4605]), however each active address requires a
binding by the AR method. Therefore, there are 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
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 [ISO-MPEG2] identifies the
existence and format of a Stream, using a combination of two PSI
tables: the Program Association Table (PAT) and entries in the
program element loop of a Program 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 program. 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.
A pre-defined set of IP addresses may be used within an 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 optimize
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 specialization 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)
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], and
[RFC3256]. Issues in deployment of IPv6 are described in [RFC4779].
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 each
Receiver [ETSI-SI], [ETSI-SI1]. This scheme reflects the complexity
of delivering and coordinating 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 that allows an MPEG-2 Receiver to
identify the appropriate PID and the multiplex associated with a
specific IP address include:
(i) IP/MAC Notification Table (INT) in the DVB Data standard
[ETSI-DAT]. This provides unidirectional 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) is an MPEG-2 Table employed by
some DVB-RCS systems to provide unidirectional 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
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. The use of this method is specified for Multiprotocol
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 by 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, for 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
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
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
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
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
corresponding PID values [MMT]. This table allows a DVB-RCS Forward
Link Subsystem (FLSS) to specify the mapping of IPv4 and IPv6
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 specified by
the SatLabs Forum [MMT] and is not currently a part of the DVB-RCS
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-A54A] 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,
and 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.
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 and 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
The AR mechanism does not require interpretation of L2 tables;
this is an advantage especially in the growing market share for
home network and audio/video networked entities.
An IP-based protocol can provide a common method across
different network scenarios for both IP to MAC address mappings
and mapping to TS Logical Channels (PID value associated with a
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).
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, Operations and Management (OAM),
mobility, configuration control, etc., that combine AR with
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 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 a 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 are desirable
(e.g., where a range of source/destination addresses are matched to a
single entry). It can also be beneficial to use methods that permit
a range of IP addresses to be mapped to a set of TS Logical Channels
(e.g., a hashing technique similar to the mapping of IP Group
Destination Addresses to Ethernet MAC addresses [RFC1112] [RFC2464]).
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
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
neighbor/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 bidirectional 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) [RFC4346]. 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
The ND protocol uses a set of IP multicast addresses. In large
networks, many multicast addresses are used, but each client
typically only listens to a restricted set of group destination
addresses and little traffic is usually sent in each group.
Therefore, Layer 2 AR for MPEG-2 Networks must support this in a
A large number of ND messages may cause a large demand for performing
asymmetric operations. The base ND protocol 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 the ND protocol [RFC2461] can
introduce interoperability problems (e.g., a failure to resolve when
the link RTT (round-trip time) exceed 3 seconds) and performance
degradation (duplicate ND messages with a link RTT > 1 second) when
used in networks where 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. In addition, SEND does not require the configuration
of per-host keys and can coexist with the use of both SEND and
insecure ND on the same link.
The ND Protocol is also used by IPv6 systems to perform other
functions beyond address resolution, including Router Solicitation /
Advertisement, Duplicate Address Detection (DAD), Neighbor
Unreachability Detection (NUD), and Redirect. These functions are
useful for hosts, even when address resolution is not required.
5.1. Unidirectional Links Supporting Unidirectional Connectivity
MPEG-2 Networks may provide a Unidirectional 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
| MPEG-2 |
| Receiver |
Figure 3: Unidirectional connectivity
The ARP and ND protocols require bidirectional L2/L3 connectivity.
They do not provide an appropriate method to resolve the remote
(destination) address in a unidirectional 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.
5.2. Unidirectional Links with Bidirectional Connectivity
Bidirectional connectivity may be realized using a unidirectional
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
+-----------+ | |
+--<<--+ MPEG-2 |
Return | Receiver |
Figure 4: Bidirectional connectivity
The Unidirectional 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 unidirectional routing from the
IP and upper layer protocols by providing a L2 tunnelling mechanism
that emulates a bidirectional 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 unidirectional links employ wireless technology for the
forward (Feed) link, 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 minimize the volume and frequency of control
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
(i) A Feed Router needs a Receiver MAC/NPA address.
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 recognizes 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 encapsulation format also permits
packets to be sent without specifying a MAC/NPA address, where
this is desirable (Section 6.1 and 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
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 the 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.
5.3. Bidirectional Links
Bidirectional 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/server processing 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 optimization 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 the system state within a middle-box device. This
resembles a classic man-in-the-middle security attack; interactions
with SEND are described in [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.
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
5.5. DHCP Tuning
DHCP [RFC2131] and DHCPv6 [RFC3315] may be used over MPEG-2 Networks
with bidirectional connectivity. 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 the allocation of network addresses to systems.
The configuration of DHCP Servers and DHCP Clients should take into
account the local link round trip delay (possibly including the
additional delay from bridging, e.g., using UDLR). A large number of
clients can make 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 an 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 the 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 [ETSI-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
The L2 group addressing method specified in [RFC1112] and [RFC2464]
can result in more than one IP destination address being mapped 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. Therefore, senders may 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 an 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, RFC 3077 notes that a
Receiver needs to be configured with appropriate filter rules to
ensure that 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, re-
broadcast 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 [RFC4605]), 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 encapsulation formats also do not include an MAC/NPA source
address (Table 1). 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 (bootstrap protocol)
[RFC951], DHCP [RFC2131] and ND [RFC2461]), where the source at L3
can not be determined at the 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.
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 summarizes the options for
both MPE ([ETSI-DAT], [ATSC-A90]) and ULE [RFC4326] encapsulations.
[RFC4840] describes issues and concerns that may arise when a link
can support multiple encapsulations. In particular, it identifies
problems that arise when end hosts that belong to the same IP network
employ different incompatible encapsulation methods. An Encapsulator
must therefore use only one method (e.g., ULE or MPE) to support a
single IP network (i.e., set of IPv4 systems sharing the same subnet
broadcast address or same IPv6 prefix). All Receivers in an IP
network must receive all IP packets that use a broadcast (directed to
all systems in the IP network) or a local-scope multicast address
(Section 3). Packets with these addresses are used by many IP-based
protocols including service discovery, IP AR, and routing protocols.
Systems that fail to receive these packets can suffer connectivity
failure or incorrect behaviour (e.g., they may be unable to
participate in IP-based discovery, configuration, routing, and
announcement protocols). Consistent delivery can be ensured by
transmitting link-local multicast or broadcast packets using the same
Stream that is used for unicast packets directed to this network. A
Receiver could simultaneously use more than one L2 AR mechanism.
This presents a potential conflict when the Receiver receives two
different bindings for the same identifier. When multiple systems
advertise AR bindings for the same identifiers (e.g., Encapsulators),
they must ensure that the advertised information is consistent.
Conflicts may also arise when L2 protocols duplicate the functions of
IP-based AR mechanisms.
In ULE, the bridging format may be used in combination with the
normal mode to address packets to a Receiver (all ULE Receivers are
required to implement both methods). Frames carrying IP packets
using the ULE Bridging mode, that have a destination address
corresponding to the MAC address of the Receiver and have an IP
address corresponding to a Receiver interface, will be delivered to
the IP stack of the Receiver. All bridged IP multicast and broadcast
frames will also be copied to the IP stack of the Receiver.
Receivers must filter (discard) frames that are received with a
source address that matches an address of the Receiver itself
[802.1D]. It must also prevent forwarding frames already sent on a
connected network. For each network interface, it must therefore
filter received frames where the frame source address matches a
unicast destination address associated with a different network
| | 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 with LLC/SNAP&Bridging | 38 | x | x | x |
Table 1: L2 Support and Overhead (x =supported, - =not supported)
The remainder of the section describes IETF-specified AR methods for
use with these encapsulation formats. Most of these methods rely on
bidirectional communications (see Sections 5.1, 5.2, and 5.3 for a
discussion of this).
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 at a Receiver that have no connectivity
to other networks). Since there is no MAC/NPA address in the SNDU,
ARP and the ND protocol are not required for AR.
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.
Even when not used for AR, the ND protocol may still be required to
support DAD, and other IPv6 network-layer functions. This protocol
uses a block of IPv6 multicast addresses, which need to be carried by
the L2 network. However, since this encapsulation format does not
provide a MAC source address, there are topologies (e.g., Section
5.6.1) where a system can not differentiate DAD packets that were
originally sent by itself and were re-broadcast, from those that may
have been sent by another system with the same L3 address.
Therefore, DAD can not be used with this encapsulation format in
topologies where this L2 forwarding may occur.
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 uses a block of IPv6 multicast addresses, which need to be
carried by the L2 network. However, since this encapsulation format
does not provide a MAC source address, there are topologies (e.g.,
Section 5.6.1) where a system can not differentiate DAD packets that
were originally sent by itself and were re-broadcast, from those that
may have been sent by another system with the same L3 address.
Therefore, DAD can not be used with this encapsulation format in
topologies where this L2 forwarding may occur.
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 (Sub-Network Access Protocol) format of MPE provides an
EtherType field and therefore may support ARP [RFC826]. There is no
specification to define how this is performed. No MAC source address
is present in the SNDU, although the protocol communicates the source
MAC address in the ARP record payload of any query messages that it
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 IPv6 ND protocol is supported. The protocol uses a
block of IPv6 multicast addresses, which need to be carried by the L2
network. However, since this encapsulation format does not provide a
MAC source address, there are topologies (e.g., Section 5.6.1) where
a system can not differentiate DAD packets that were originally sent
by itself and were re-broadcast, from those that may have been sent
by another system with the same L3 address. Therefore, DAD can not
be used with this encapsulation format in topologies where this L2
forwarding may occur.
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
precede this Extension, 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
configured MAC destination address filter. ARP and ND messages may
be carried within a PDU that is bridged by this encapsulation format.
Where the topology may result in subsequent reception of re-
broadcast copies of multicast frames that were originally sent by a
Receiver (e.g., Section 5.6.1), the system must discard frames that
are received with a source address that it used in frames sent from
the same interface [802.1D]. This prevents duplication on the
bridged network (e.g., this would otherwise invoke DAD).
6.6. ULE with Bridging Header Extension and NPA Address (D=0)
The combination of an 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. Where the topology may result in the
subsequent reception of re-broadcast copies of multicast frames, that
were originally sent by a Receiver (e.g., Section 5.6.1), the system
must discard frames that are received with a source address that it
used in frames sent from the same interface [802.1D]. This prevents
duplication on the bridged network (e.g., this would otherwise invoke
6.7. MPE with 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. There is currently no formal description
of the Receiver processing for this encapsulation format. 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. Where the topology may result in a
subsequent reception of re-broadcast copies of multicast frames, that
were originally sent by a Receiver (e.g., Section 5.6.1), the system
must discard frames that are received with a source address that it
used in frames sent from the same interface [802.1D]. This prevents
duplication on the bridged network (e.g., this would otherwise invoke
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, and 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
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 unauthorized 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 [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 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
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 (summarized in "Experiments with RFC 3077",
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),
[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 Organization (ISO), 2000.
[RFC826] Plummer, D., "Ethernet Address Resolution Protocol: Or
Converting Network Protocol Addresses to 48.bit
Ethernet Address for Transmission on Ethernet
Hardware", STD 37, RFC 826, November 1982.
[RFC1112] Deering, S., "Host extensions for IP multicasting", STD
5, RFC 1112, August 1989.
[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December
[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.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3736] Droms, R., "Stateless Dynamic Host Configuration
Protocol (DHCP) Service for IPv6", RFC 3736, April
[RFC4326] Fairhurst, G. and B. Collini-Nocker, "Unidirectional
Lightweight Encapsulation (ULE) for Transmission of IP
Datagrams over an MPEG-2 Transport Stream (TS)", RFC
4326, December 2005.
10.2. Informative References
[802.1D] IEEE 802.1D, "IEEE Standard for Local and Metropolitan
Area Networks: Media Access Control (MAC) Bridges",
[802.3] 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 Computer
Society, (also ISO/IEC 8802-3), 2002.
[ATSC] A/53C, "ATSC Digital Television Standard", Advanced
Television Systems Committee (ATSC), Doc. A/53C, 2004.
[ATSC-A54A] 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.
[ETSI-DVBS] EN 301 421,"Digital Video Broadcasting (DVB);
Modulation and Coding for DBS satellite systems at
11/12 GHz", European Telecommunications Standards
[ETSI-RCS] EN 301 790, "Digital Video Broadcasting (DVB);
Interaction channel for satellite distribution
Systems", European Telecommunications Standards
[ETSI-SI1] TR 101 162, "Digital Video Broadcasting (DVB);
Allocation of Service Information (SI) codes for DVB
systems", European Telecommunications Standards
[IPDVB-SEC] H. Cruickshank, S. Iyengar, L. Duquerroy, P. Pillai,
"Security requirements for the Unidirectional
Lightweight Encapsulation (ULE) protocol", Work in
Progress, May 2007.
[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
Organization (ISO), 2002.
[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 Organization (ISO), 1998.
[MMT] "SatLabs System Recommendations, Part 1, General
Specifications", Version 2.0, SatLabs Forum, 2006.
[RFC951] Croft, W. and J. Gilmore, "Bootstrap Protocol", RFC
951, September 1985.
[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
[RFC3451] Luby, M., Gemmell, J., Vicisano, L., Rizzo, L.,
Handley, M., and J. Crowcroft, "Layered Coding
Transport (LCT) Building Block", RFC 3451, December
[RFC3569] Bhattacharyya, S., "An Overview of Source-Specific
Multicast (SSM)", RFC 3569, July 2003.
[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.
[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
[RFC4259] Weis, B., "The Use of RSA/SHA-1 Signatures within
Encapsulating Security Payload (ESP) and Authentication
Header (AH)", RFC 4359, January 2006.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer
Security (TLS) Protocol Version 1.1", RFC 4346, April
[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor
Discovery Proxies (ND Proxy)", RFC 4389, April 2006.
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August
[RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick,
"Internet Group Management Protocol (IGMP) / Multicast
Listener Discovery (MLD)-Based Multicast Forwarding
("IGMP/MLD Proxying")", RFC 4605, August 2006.
[RFC4779] Asadullah, S., Ahmed, A., Popoviciu, C., Savola, P.,
and J. Palet, "ISP IPv6 Deployment Scenarios in
Broadband Access Networks", RFC 4779, January 2007.
[RFC4840] Aboba, B., Davies, E., and D. Thaler, "Multiple
Encapsulation Methods Considered Harmful", RFC 4840,
[SCTE-1] "IP Multicast for Digital MPEG Networks", SCTE DVS
311r6, March 2002.
[SP-ND] Daley, G., "Securing Proxy Neighbour Discovery Problem
Statement", Work in Progress, February 2005.
Department of Engineering
University of Aberdeen
Aberdeen, AB24 3UE
Motorola Connected Home Solutions
55 Hayden Avenue, 3rd Floor
Lexington, Massachusetts 02421
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