Internet Engineering Task Force Gorry Fairhurst
Internet Draft University of Aberdeen
Document: draft-fair-ipdvb-ar-04.txt Marie-Jose Montpetit
Motorola
Hidetaka Izumiyama
Wishnet
Category: Internet Draft Expires October 2005
Address Resolution for IP datagrams over MPEG-2 networks
Status of this Draft
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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) and a specific
Transmission Multiplex The document reviews current methods. It also
describes the interaction with well-known protocols for address
management including DHCP, ARP, and NDP, and provides guidance on
usage.
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Table of Contents
1. Introduction
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 Comparison of SI/PSI table approaches
4.3 IP-based resolution of TS Logical Channels
4.3.1 IP-based multicast resolution of TS Logical Channels
5. Mapping IP addresses to NPA/MAC 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 IP Multicast AR
6. Link Layer Support
6.1 ULE without a destination MAC/NPA address (D=1)
6.2 ULE with a destination NPA/MAC 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
Appendices
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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. It is defined in
specification ISO/IEC 138181 [ISO-MPEG2]. Each Layer-2 frame, known
as a TS Packet, contains a 4 byte header and 188 bytes of 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 using System Information
(SI) Tables [ETSI-SI, ETSI-SI1], or Program Specific Information
(PSI) Tables.
To utilise the MPEG-2 TS as an 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 Address Resolution (AR) [ipdvb-arch]. In some AR
schemes, the MPEG-2 TS address space is sub-divided into logical
contexts known as Platforms. 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) [ipdvb-
arch] to uniquely identify the L2 node within the 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
may need to signal the format of the data being transmitted, for
example, the encapsulation, any L2 encryption method and any
compression scheme [ID-IPDVB-ARCH].
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 address and/or Platform ID. A range of approaches
is described, including Layer-2 methods (utilising MPEG-2 SI
tables), and protocols at the IP level (including the IPv4 Address
Resolution Protocol, ARP [RFC826] and the IPv6 Neighbor Discovery
Protocol, NDP [RFC2461]). Interactions and dependencies between
these methods and the encapsulation methods are described.
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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.
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 in an MPEG-2
Private Section, defined by the ISO MPEG-2 standard.
DVB: Digital Video Broadcast [ETSI-DVB]. A framework and set of
associated standards published by the European Telecommunications
Standards Institute (ETSI) for the transmission of video, audio, and
data, using the ISO MPEG-2 Standard.
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.
INT: Internet/MAC Notification Table. A uni-directional
addressing 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 [DIX]).
MAC Header: The link layer header of the IEEE 802.3 standard [IEEE-
802.3] or Ethernet v2 [DIX]. It consists of a 6B destination
address, 6B source address, and 2B type field (see also NPA, LLC).
MAC: Medium Access and Control of the Ethernet IEEE 802 standard
of protocols (see also NPA).
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
defining an AR table that maps IPv4 multicast addresses to PID
values).
MPE: Multiprotocol Encapsulation [ETSI-DAT; ATSC-DAT; ATSC-DATG]. A
scheme that encapsulates PDUs, forming a DSM-CC Table Section. Each
Section is sent in a series of TS Packets using a single TS Logical
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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. In this document, refers to 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.
PID: Packet Identifier [ISO-MPEG2]. A 13 bit field carried in the
header of TS Packets. This is used to identify the TS Logical
Channel to which a TS Packet belongs [ISO-MPEG2]. The TS Packets
forming the parts of a Table Section, PES, or other Payload Unit
must all carry the same PID value. The all 1s PID value indicates a
Null TS Packet introduced to maintain a constant bit rate of a TS
Multiplex. There is no required relationship between the PID values
used for TS Logical Channels transmitted using different TS
Multiplexes. The all 1s 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.
Private Section: A syntactic structure constructed in accordance
with 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.
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.
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
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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.
to two terrestrial TV transmission cells.
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 signalling.
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) [ID-
ipdvb-arch], 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, plus optional
overhead including an Adaptation Field, encryption details and time
stamp information to synchronise a set of related TS Logical
Channels.
UDL: Unidirectional link: A one-way transmission IP over DVB link,
e.g., a broadcast satellite link.
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 [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 MPE [ETSI-DAT,ETSI-DAT1, ATSC-DAT])
and the IETF-defined Ultra Lightweight Encapsulation (ULE) [ID-
ARCH,ID-ULE].
The general IP over MPEG-2 AR requirements are summarized below:
- A scalable and efficient transmission.
- A method to represent the AR information.
- Support for scoping of the addresses.
- Incremental update of clients with AR information.
- Procedures for purging stale client AR information.
- A method to identify the Server sourcing AR information.
- A method to install AR information at the AR server
(unsolicited registration).
- Security associations to authenticate the AR information.
An MPEG-2 Transmission Network may support multiple IP networks.
If this is the case, it is important to recognise the context
(scope) within which an address is resolved, to prevent packets from
one addressed scope leaking into other scopes. 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) 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) Some multicast addresses, (e.g., the scoped multicast
addresses sometimes used in private networks). These are
only valid within an addressed area (examples for IPv4
include; 239/8; 224.0.0/24; 224.0.1/24). Similar cases
exist for some IPv6 multicast addresses.
(iii)Scoped multicast addresses. Forwarding of these addresses
is controlled by the scope associated with the address.
Overlapping address assignments may also occur at L2, where the same
NPA/MAC address is used to identify multiple receivers [ID-IPDVB-
ARCH]:
(i) An NPA unicast address must be unique within the addressed
area. The IEEE assigned MAC addresses used in Ethernet LANs are
Globally unique. If the NPA addresses are not globally unique,
an NPA address must only be re-used by receivers in
different addressed (scoped) areas.
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(ii) The NPA broadcast address (all 1 MAC address). Traffic
with this address should be confined to one addressed area.
(iii) IP and other protocols may view sets of MAC multicast
addresses as link-local, and may produce unexpected results if
frames with these address are distributed across several
private networks.
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. 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 may be required at two levels. At the
upper level, the AR procedure needs to associate an IP address with
a specific NPA/MAC address. 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.
The same unicast IP address may be associated with more than one TS
Logical Channel within the same scope [DVB-DAT]. These may have
different content, but there is also the possibility of a Receiver
receiving duplicated copies of packets.
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 one level in associating a
specific L2 address with am IP Group Destination Address (section
5). In IPv4 and IPv6 over Ethernet, this association is normally a
direct mapping, and this is the default method also specified in
both ULE [ID-IPDVB-ULE] and in 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
(PID value) 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. For example, schemes that may
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be easily implemented in hardware would be beneficial, since these
may relieve the drivers and operating systems from discarding
unwanted multicast traffic.
There are specific issues concerning IPv4 and IPv6 multicast over
MPEG-2 Transmission Networks:
(i) Mapping IP multicast groups to the underlying MPEG-2 TS
Logical Channel (PID) and the MPEG-2 TS Multiplex.
(ii) Provide signalling information to allow a receiver to
locate an IP multicast flow within an MPEG-2 TS Multiplex.
(iii) Determining group membership (e.g. utilising IGMP/MLD).
Methods are required to identify the scope of an address when an
MPEG-2 transmission network supports several logical IP network and
carries groups within different multicast scopes.
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 end hosts act as senders to
contribute IP packets with the same IP Group Destination Address in
the ASM address range.
Another different 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 also known as Simulcasting [DVB-DAT]). In this
case, at the IP level, the host/router may be unaware of this
duplication and it needs to be detected by other means.
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4. MPEG-2 Address Resolution
In this section, current MPEG-2 address resolution mechanisms are
reviewed.
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 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. Section or MAC
filtering may be used to differentiate subnetworks.
4.1.1 MPEG-2 Cable Networks
Cable networks use a different transmission schemes for downstream,
(headend to cable modem/STB) and upstream (cablemodem/STB to
headend) transmission.
The information is sent (on the downstream) to the STBs as
IP/Ethernet packets encapsulated in MPEG-2 TS Packets sent on a
single well-known TS Logical Channel (PID); there is no use of
inband 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 in cable networks for IP traffic was proprietary,
and did not usually employ a table-based address resolution method.
Proprietary methods continue to be used in some cases where STBs
require interaction. In this case, equipment at the headend may act
as gateways between the cablemodem/STB and the Internet. These
gateways receive L2 information and allocate an IP address.
DOCSIS utilises DHCP for IP client configuration. The Cable Modem
Terminal System (CMTS) provides a DHCP server that allocates IP
addresses to DOCSIS cable modems and STBs. The MPEG-2 Transmission
Network provides a L2 bridged network to the cable modem. This
usually acts as a DHCP relay for IP devices [RFC2131, RFC3256].
Issues in deployment of IPv6 are described in [ID-V6OPS-DEPLOY].
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4.2 MPEG-2 Table-Based Address Resolution
The information about the set of MPEG-2 TS streams carried over a TS
Multiplex can be distributed via tables that are assigned a specific
and well-known set of PID values. This design requires access to and
processing of the SI Table information [ETSI-SI, ETSI-SI1]. This
scheme reflects the complexity of delivering and co-ordinating the
various TS associated with multimedia TV. A TS Multiplex may provide
AR information for IP services by integrating additional information
into the existing MPEG-2 tables or by transmitting additional SI
Tables 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 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 MPEG-2 TS.
The MMT and AIT are used for specific applications. The INT [DVB-
DAT] is a more general DVB standard, 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 mechanism for carrying information about the
location of IP/L2 flows within a DVB network. The INT defines the
concept of a Platform_ID, which may identify the addressing scope
for a set of IP/L2 streams and/or Receivers. A Platform may span
several transport streams within one or multiple DVB multiplexes and
represents a single IP network with a harmonized address space (i.e.
addressing scope). This allows for the coexistence of several non-
harmonized IP/MAC address spaces on the same DVB network.
The INT allows both fully-specified IP addresses and prefix matching
to reduce the size of table (and hence enhance signalling
efficiency). An IPv4/IPv6 "subnet mask" may be given in full form or
in 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.
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In addition to identification and security descriptors, the
following descriptors are defined for address binding in INT tables:
(i) target_MAC_address_descriptor: The descriptor used to
describe a single or set of MAC addresses (and their mask).
(ii) target_MAC_address_range_descriptor: May be used to set
filters.
(iii) target_IP_address_descriptor: The 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: This descriptor 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.
The INT provides a set of descriptors to specify addressing in a DVB
network. One key benefit is that the approach follows the MPEG-2
signaling methods and is integrated with the other signalling
information. This allows the INT to operate in the presence of
(re)multiplexors [ipdvb-arch] and refer to PID values that are
carried within a number of different TS Multiplexes. This makes it
well-suited to a Broadcast TV Scenario [ipdvb-arch].
The principle drawbacks are that while the INT, there is a need for
a Gateway to introduce associated PSI/SI MPEG-2 control information.
This control information also needs to be processed at the receiver
below the IP layer, and 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. The
method is currently defined only for Multi-Protocol Encapsulation
(MPE) and would need extension to support other schemes.
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4.2.2 Multicast Mapping Table (MMT) and its usage
The Multicast Mapping Table (MMT) is an MPEG-2 level control table
to that associates a set of multicast addresses with the
corresponding PID values. This table allows a DVB-RCS Forward Link
Subsystem (FLSS) to specify the mapping of IPv4 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 currently a part of the DVB-RCS
specification.
4.2.3 Application Information Table (AIT) and its usage
The DVB Multimedia Home Platform (MHP) specification does not define
a specific AR function. However, the MHP Standard specifies an
Application Information Table (AIT) that allows MHP Receivers to
receive a variety of control information. The AIT uses a DSMCC
format 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 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 all have 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, encourage the development of 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 resolution of TS Logical Channels
As MPEG-2 transmission networks evolve to become multiservice
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, transmission using IP packets could
also be used for address resolution. The advantages of using a
IP-based address resolution for TS streams 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.
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(ii) Uniformity:
An IP-based protocol can provide a common method across
different network scenarios for IP/MAC address mappings to TS
Logical Channels (PID Values).
(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 a part of the IP network layer, simplifying
support for AAA, policy, OAM, mobility, configuration control,
etc. that combine AR with security.
Drawbacks of an IP-based method include:
One drawback of IP-based AR is that this method can not operate
over an MPEG-2 Transmission Network that uses remultiplexors
[ipdvb-arch] to modify the PID values of the TS Logical
Channels during the multiplexing operation. This makes the
method unsuitable for use in deployed broadcast TV networks
[ipdvb-arch].
IP-based methods can also introduce concerns about the
integrity of the information and authentication of the sender
[ipdvb-arch] (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 devices from the larger Internet creating
virtual MPEG2 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.
4.3.1 IP-based multicast resolution of TS Logical Channels
AR resolution must also be performed to associate the IP multicast
Group Destination Address with an MPEG-2 layer TS Logical Channel
(PID) and TS Multiplex. Solutions have been described in 4.2 to
perform this below the IP layer using MPEG-2 Tables. Such methods
currently perform a direct mapping (where a single address or set of
addresses are associated with a specific PID value).
There is an opportunity to define an IP-level method that could use
an IP multicast protocol over a well-known IP multicast address.
Scalability is an important feature of any multicast AR protocol,
methods that employ prefix matching (e.g. where a range of
source/destination addresses are matched to a single entry are
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desirable), but so also are methods that allow a range of addresses
to mapped to a set of TS Logical Channels (similar to the mapping of
IP Group Destination Addresses to Ethernet MAC addresses).
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5. Mapping IP addresses to NPA/MAC addresses
This section reviews IETF protocols that may be used to assign and
manage the mapping of IP addresses to/from NPA/MAC addresses.
IP Encapsulation Gateways may require AR information to select an
appropriate MAC/NPA address in the SNDU header [ipdvb-arch] (see
also section 6). The information to complete this header may be
taken directly from a neighbour/arp cache, or may require the
Gateway to retrieve the information using an AR protocol. The way in
which this information is collected will depend upon whether the
Gateway functions as a Router (at L3) or a Bridge (at L2).
Two IETF-defined protocols for mapping IP addresses to NPA/MAC
addresses are ARP [RFC-ARP] and NDP [RFC-ND] for IPv4 and IPv6
respectively. Both protocols are normally used in a bi-directional
mode, although both also permit unsolicited transmission of
mappings. The mapping defined in [RFC2464] may result in use of a
large number of L2 MAC addresses.
ARP requires support for L2 broadcast packets.
<< inputs requested on ARP scalability to large receiver groups >>
<< inputs requested on ARP security for wireless networks >>
<< inputs requested on ARP scoping when supporting multiple ISPs >>
The NDP uses a set of IP multicast addresses. In large networks,
many multicast addresses are likely to be used, although little
traffic is likely to be sent in each group. The AR multicast
mechanism therefore needs to be able to support this in a scalable
manner (see section XXX).
<< inputs requested on NDP scalability to large receiver groups >>
<< inputs requested on NDP security for wireless networks >>
<< inputs requested on NDP scoping when supporting multiple ISPs >>
5.1 Uni-directional links supporting uni-directional connectivity
Most MPEG-2 Transmission Networks 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 are more commonly used for IP multicast content
distribution.
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,-----.
MPEG-2 uplink /MPEG-2 \
*##################( Network )
# \ /
+----*------+ `--.--'
| Network | |
| Provider + v MPEG-2 downlink
+-----------+ |
+-----v------+
| MPEG-2 |
| Receiver |
+------------+
Figure XX: Uni-directional connectivity
Although ARP and NDP may both operate in an unsolicited/promiscuous
mode where they advertise information to the remote nodes, this does
not provide an appropriate method to resolve the remote
(destination) address in a uni-directional environment. To perform
this task, these protocols require bi-directional L2/L3
connectivity.
<< inputs required on receiver address assignment in this case >>
5.2 Uni-directional links with bi-directional connectivity
Bi-directional connectivity may be realised using a pair of uni-
directional 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. It also often exhibits asymmetric network capacity
[RFC-ASYM].
,-----.
MPEG-2 uplink /MPEG-2 \
*##################( Network )
# \ /
+----*------+ `--.--'
| Network | |
| Provider +-<-+ v MPEG-2 downlink
+-----------+ | |
| +-----v------+
+--<<--+ MPEG-2 |
uplink | Receiver |
+------------+
Figure XX: Bi-directional connectivity
The Uni-Directional Link Routing, UDLR [RFC3077] protocol may be
used to overcome the routing issues associated with asymmetric
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routing. UDLR provides a L2 tunnelling mechanism that emulates a bi-
directional broadcast link at L2. The uni-directional routing is
hidden from IP and upper layer protocols.
This section introduces how to use UDLR link layer tunnelling
mechanisms to use ARP and ND on Uni-Directional DVB links.
<<< Will be completed later, inputs required from WG >>>
5.3 Bi-directional links
Bi-directional IP networks can be and are constructed by a
combination of two MPEG-2 transmission links. 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.
<<< text on DHCP, L2TP, PPoE, etc to be added by
other volunteers >>>
5.4 IP Multicast AR
This section describes the case where the destination network layer
address is an IP multicast Group Destination Address.
In MPE [DVB-DAT], the mapping of IP multicast addresses to MAC/NPA
addresses follows normal practice for IEEE MAC Addresses when using
IPv4 and IPv6. (A variant of DVB (DVB-H) uses a modified MAC header
[DVB_DAT]).
In ULE [ID-IPDVB-ULE], 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, it follows the mapping
of MPE and many other L2 link technologies.
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6. Link Layer Support
This section considers layer 2 support for address resolution. It
considers two issues that need to be considered. One is the code-
point to be used at L2 and the other is the efficiency of
encapsulation for transmission to utilise the AR method. The table
below summarises the options for both MPE and ULE 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 of 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 NPA/MAC
address is not present in the encapsulated frame. This mode may be
used with both IPv4 and IPv6. When this mode is used, the Receiver
is expected to perform network-layer filtering of packets based on
their IP destination address. Encapsulation Gateways must ensure
that packets are associated with a TS Logical Channel (PID value)
that uniquely identifies the intended recipient [IP-IPDVB-ULE]. This
requires careful consideration of the network topology when used as
a link between IP routers (a simple case where this is permitted is
the connection of stub networks).
Since there is no MAC/NPA address in the SNDU, ARP and NDP are not
required.
Note, since IPv6 systems can (and usually do) automatically
configure their IPv6 network address based upon a local MAC address,
the IP driver at the Receiver may still need to access the MAC/NPA
address of the receiving interface.
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6.2 ULE with a destination NPA/MAC address (D=0)
The IPv4 Address Resolution Protocol (ARP) [RFC826] uses an IANA-
assigned EtherType and may be used over a link that supports ULE
[IP-IPDVB-ULE]. Although no MAC source address is present in the
SNDU, the protocol still communicates the source MAC address in the
ARP record payload of any query messages that it generates.
The ND protocol of IPv6 [RFC2461] may be used.NDP does not require
specification of a MAC source address, although this is required for
a node to participate in Duplicate Address Detection (DAD).
<< More info on use of ND is required, also on usage of DAD and
SEND>>
6.3 MPE without LLC/SNAP Encapsulation
This is the default (and sometimes only) mode specified by most MPE
Encapsulation Gateways.
MPE does not provide an IANA-assigned EtherType 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 NDP.
6.4 MPE with LLC/SNAP Encapsulation
The LLC/SNAP format of MPE provides an IANA-assigned EtherType and
therefore may support the Address Resolution Protocol (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 ND protocol of IPv6 [RFC2461] may be used with The LLC/SNAP
format of MPE. NDP does not require specification of a MAC source
address, although this is required for a node to participate in
Duplicate Address Detection (DAD).
<< More info on use of ND is required, also on usage of DAD and
SEND>>
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
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the ULE SNDU as that used for an NPA destination address. The
Receiver may optionally be configured so that MAC destination
address value is identical to the Receiver NPA address.
At the Encapsulation Gateway, the ULE NPA/MAC 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 messages may be carried within a PDU that is bridged by this
encapsulation format.
The NDP messages may be carried within an IPv6 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 NPA/MAC address).
At the Encapsulation Gateway, the ULE NPA/MAC 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.
An ARP message may be carried within a PDU that is bridged by this
encapsulation format.
An NDP message may be carried within an IPv6 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. This 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 Encapsulation Gateway, the MPE
MAC destination address is determined by a L2 forwarding decision.
As in other L2 LANs, the Receiver may choose to filter received
frames based on a configured MAC destination address filter.
At the Encapsulation Gateway, the MPE MAC destination address is
determined by a L2 forwarding decision. Received frames may be
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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.
An ARP message may be carried within a PDU that is bridged by this
encapsulation format.
An NDP message may be carried within an IPv6 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 has described addressing and address resolution issues
concerning the use of IP protocols over MPEG-2 transmission
networks. A number of specific IETF protocols are discussed along
with their expected behaviour over MPEG-2 transmission networks and
recommendations for usage.
In current MPEG-2 networks, a static binding may be configured for
IP addresses and PIDs (as in some cable networks). This information
may also be provided by the Gateway/Multiplexor and carried in
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, defined their usage and provided
information to identify what would be needed to improve their
support for IP protocols.
8. Security Considerations
The normal security issues relating to the use of wireless links for
transport Internet traffic should be considered. Readers are also
referred to the known security issues associated with ARP [RFC826]
and ND [RFC-ND].
9. Acknowledgments
The authors wish to thank Rod Walsh, Jun Takei, Michael Mercurio and
the ipdvb WG members for their inputs. The authors would also like
to acknowledge the support of the European Space Agency. The authors
also thank Martin Stiemerling, for contributions of scenarios and
configuration, and Hidetaka Izumiyama for his contributions on UDLR
issues.
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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. http://www.etsi/org/
[ETSI-MHP] ETSI TS 101 812, "Digital Video Broadcasting (DVB);
Multimedia Home Platform (MHP) Specification", v1.2.1, European
Telecommunications Standards Institute (ETSI), June 2002.
http://www.etsi/org/
[ETSI-SI] ETSI EN 300 468: "Digital Video Broadcasting (DVB);
Specification for Service Information (SI) in DVB systems".
[ISO-DSMCC] ISO/IEC IS 13818-6 "Information technology -- Generic
coding of moving pictures and associated audio information -- Part
6: Extensions for DSM-CC is a full software implementation",
International Standards Organisation (ISO).
[ISO-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), IETF. August 1989.
[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.
[RFC3077] Duros, E., Dabbous, W., Izumiyama, H., Fujii, N., and Y.
Zhang, "A Link-Layer Tunneling Mechanism for Unidirectional Links",
RFC 3077, March 2001.
10.2 Informative References
[ATSC] A/53C, "ATSC Digital Television Standard", Advanced
Television Systems Committee (ATSC), Doc. A/53C, 2004.
[DOCSIS]>>> Missing Reference <<<
[ETSI-SI1] ETSI TR 101 162: "Digital Video Broadcasting (DVB);
Allocation of Service Information (SI) codes for DVB systems".
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[ID-IPDVB-ARCH] Montpetit, M.J., Fairhurst, G., Clausen, H.D.,
Collini-Nocker, B., and H. Linder, "Architecture for IP transport
over MPEG-2 Networks", Internet Draft, draft-ipdvb-arch-00.txt,
February 2005, Work in Progress, IPDVB WG.
[ID-IPDVB-ULE] Fairhurst, G., Collini-Nocker, B. "Ultra Lightweight
Encapsulation (ULE) for transmission of IP datagrams over an MPEG-2
Transport Stream", February 2005, Work in Progress, IPDVB WG.
[ID-V6OPS-DEPLOY] Asadullah, S., Ahmed, A., Popoviciu, C.,
"ISP IPv6 Deployment Scenarios in Broadband Access Networks"
draft-ietf-v6ops-bb-deployment-scenarios-00.txt, Work in Progress,
IPDVB WG
[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.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.
10.3 Un-cited references (to be used or removed in final edit):
[RFC1122] B. Braden, ed., "Requirements for Internet Hosts -
Communication Layers", RFC 1122.
http://www.atsc.org/standards/Code_Point_Registry.pdf
[ID-MMUSIC-IMG] Y. Nomura, R. Walsh, J-P. Luoma, J. Ott, H.
Schulzrinne, "Protocol Requirements for Internet Media Guides",
Internet Draft, draft-ietf-mmusic-img-req-07.txt, June 2004, Work
in Progress, MMUSIC WG.
[ATSC-DAT] A/90, "ATSC Data Broadcast Standard", Advanced Television
Systems Committee (ATSC), Doc. A/090, 2000.
[ATSC-DATG] A/91, "Recommended Practice: Implementation Guidelines
for the ATSC Data Broadcast Standard", Advanced Television Systems
Committee (ATSC),Doc. A/91, 2001.
[ATSC-A92] A/92 "Delivery of IP Multicast Sessions over ATSC Data
Broadcast", Advanced Television Systems Committee (ATSC),
Doc. A/92, 2002.
[ATSC-G] A/54A, "Guide to the use of the ATSC Digital Television
Standard", Advanced Television Systems Committee (ATSC),
Doc. A/54A, 2003.
[ATSC-PSIP-TC] A/65B, "Program and System Information Protocol for
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Terrestrial Broadcast and Cable", Advanced Television Systems
Committee (ATSC), Doc. A/65B, 2003.
[ETSI-DAT1] EN 101 202, "Implementation Guide for Data", v1.2.1,
European Telecommunications Standards Institute (ETSI), May 2003.
http://www.etsi/org/
11. Authors' Addresses
Godred Fairhurst
Department of Engineering
University of Aberdeen
Aberdeen, AB24 3UE
UK
Email: gorry@erg.abdn.ac.uk
Web: http://www.erg.abdn.ac.uk/users/gorry
Marie-Jose Montpetit
MJMontpetit.com
Email: marie@mjmontpetit.com
Hidetaka Izumiyama
President CEO, Wishnet Inc.
5-15-5-001 Shirokanedai, Minato-ku
Tokyo, 108-0071, Japan
Email: izu@wishnet.co.jp
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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
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 (2004). 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
NOT KNOWN AT THIS TIME.
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APPENDICES
[>>> NOTE to RFC Editor: Please remove this appendix prior to
publication]
APPENDIX A: 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.
[>>> NOTE to RFC Editor: End of appendix]
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APPENDIX B: Candidate IP-based L2 AR Protocols
This appendix contains a list of candidate protocols for "above IP"
AR. None of these protocols currently support the AR methods
required for MPEG-2 Transmission Networks. Specifically they do not
all support:
(i) Resolution of Addresses to TS Logical Channels
(ii) Resolution of multiple addresses in a single AR update message
(table-based).
(iii) Multicast transport.
Candidate protocols include:
ARP <extension required>
- IPv4 only.
- No table support <could be added>
- Support for versioning within current implementations not clear.
- Broadcast mode has drawbacks.
- No obvious support for scoping to multiple addressing domains.
ND <extension required>
- IPv6 only.
- No table support <could be added>
- Use multicast address.
- No obvious support for scoping to multiple addressing domains.
DTCP [RFC3077] <extension required>
- IPv4 and IPv6.
- Table support seems natural.
- Uses multicast address.
- Need to consider scoping for multiple addressing domains.
- Not really an IP AR protocol
- Already used on some (UDLR) links - and this new use seems
complementary.
AR/IP <new protocol required>
- IPv4 and IPv6.
- Based on UDP or at network-layer.
- Could use multicast address.
- Table support possible.
- New protocol format.
- Could add scoping for multiple addressing domains.
XML/foo/IP <new protocol required>
- IPv4 and IPv6.
- Based on UDP or at network-layer or an XML transport (which?).
- Could use multicast address.
- Table support seems natural.
- New protocol format.
- Could add scoping for multiple addressing domains.
- Extensible/flexible to other configuration data (if required).
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- Compression of XML required to achieve efficiency comparable with
other methods.
<<<<
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