Internet Engineering Task Force Gorry Fairhurst Internet Draft University of Aberdeen Document: draft-fair-ipdvb-ar-03.txt Marie-Jose Montpetit June 2005 Motorola Hidetaka Izumiyama Wishnet Category: Informational Expires June 2005 Address Resolution for IP datagrams over MPEG-2 networks Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress". The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Copyright (C) The Internet Society (2005). 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. Expires June 2005 [page 1] INTERNET DRAFT Address Resolution for IP datagrams over MPEG-2 networks February 2005 Abstract This document describes the current mechanisms to bind IPv4/IPv6 addresses and flows to MPEG-2 Transport Streams (TS)and how these methods interact with well known protocols for address management like DHCP, ARP, NAT and DNS. For MPEG-2 subnetworks like any other IP networks methods are required to signal IPv4/v6 addresses to the link receivers and transmitters; this is known as Address Resolution (AR), or Neighbour Discovery (ND). Although AR is often associated with Ethernet [RFC803], it is essential to the operation of any L2 network. In MPEG-2 networks, an IP address must be associated with a Packet ID (PID) and specific transmission multiplex either statically or via the use of some specific tables. Address resolution complements the higher layer resource discovery tools that are used to advertise IP sessions. In this document the different mechanisms for address resolution for MPEG-2 networking as well as their usage are reviewed. Table of Contents 1. Introduction 2. Convention used in the document 3. Address Resolution Requirement 4. MPEG-2 Address Resolution 5. Mapping IP addresses to NPA/MAC addresses 6. Conclusions and Recommendations 7. Security Considerations 8. Acknowledgements 9. References 10. Author's Addresses 11. IPR Notices 12. Copyright Statements 13. IANA Considerations 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. Expires June 2005 [page 2] INTERNET DRAFT Address Resolution for IP datagrams over MPEG-2 networks February 2005 1. Introduction The MPEG-2 stream is defined in the specification ISO/IEC 138181. It provides a time-division multiplexed (TDM) stream that may contain audio, video and data information. Each frame, known as an MPEG-2 TS Packet, contains 4 bytes of header and 188 bytes of data. The standard also defines the Transport Stream (TS) packet. Each MPEG-2 TS Packet is associated with one Transport Stream (TS) and is identified by a 13 bit Packet ID PID) carried in the MPEG-2 TS Packet header. The standard also defines a MPEG-2 control plane that may be used to transmit control information. For example, specific transmission information is sent to the senders/receivers using System Information (SI) Tables (ETSI-SI, ETSI-SI1], or Program Specific Information (PSI)Tables. The standard also allows Defining tables that can be used to carry IP and PID information about the transported stream. MPEG-2 address resolution assigns IP addresses to particular transmission multiplexes, and within a multiplex to a specific PID. The protocol signals this mapping to the other communicating devices. In some address resolution schemes, this address space is sub-divided into logical contexts known as Platforms or Sections. One use of this sub-division is to associate a separate context with each IP service provider that shares a common MPEG-2 TS (uses the same PID). MPEG-2 Receivers may optionally be assigned a Network Point of Attachment (NPA) 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 address resolution procedure. Finally, address resolution may need to signal the format of the data being transmitted. For example, the encapsulation used or any compression scheme that was used at the sender [ID-IPDVB-ARCH]. This document describes current mechanisms and their usage to signal the TS Multiplex, the PID, and (if used) the MAC address or platform ID associated with each IP address or flow to the network layer at the sender and receiver. As will be seen below this can, for example, be implemented via descriptors sent in MPEG-2 SI tables via one or more new SI tables, or in-band by a protocol using a data channel similarly to the IPv4 Address Resolution Protocol, ARP, or IPv6 Neighbour Discovery (ND) protocol. Expires June 2005 [page 3] INTERNET DRAFT Address Resolution for IP datagrams over MPEG-2 networks February 2005 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 set of framework and associated standards for the transmission of video, audio, and data, using the ISO MPEG-2 standard. DVB: Digital Video Broadcast [ETSI-DVB]. A set of framework and associated standards 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. INT: Internet/MAC Notification Table. A uni-directional addressing resolution mechanism using SI and/or PSI Tables. 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). MPE: Multiprotocol Encapsulation [ETSI-DAT, ETSI-DAT1]. A scheme that encapsulates Ethernet frames or IP Packets, creating a DSM-CC Section. The Section will be sent in a series of TS Packets over a TS Logical Channel. MPEG-2: A set of standards specified by the Motion Picture Experts Group (MPEG), and standardized by the International Standards Organisation (ISO/IEC 113818-1) [ISO-MPEG2], and ITU-T (in H.220). NPA: Network Point of Attachment. Addresses primarily used for station (receiver) identification within a local network (e.g. IEEE MAC address). 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. Expires June 2005 [page 4] INTERNET DRAFT Address Resolution for IP datagrams over MPEG-2 networks February 2005 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. RECEIVER (in the UDL context): A router or a host that has receive only connectivity to a UDL. SI TABLE: Service Information Table. In this document, the term is used to describe any table used to convey information about the service carried in a TS Multiplex (e.g. [ISO-MPEG]). SI tables are carried in MPEG-2 private sections. TS: Transport Stream [ISO-MPEG], a method of transmission at the MPEG-2 level using TS Packets; it represents level 2 of the ISO/OSI reference model. See also TS Logical Channel and TS Multiplex. TS LOGICAL CHANNEL: Transport Stream Logical Channel. In this document, this term identifies a channel at the MPEG-2 level [ISO- MPEG2]. It 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). According to MPEG-2, some TS Logical Channels are reserved for specific signalling. Other standards (e.g., ATSC, DVB) also reserve specific TS Logical Channels. 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. Expires June 2005 [page 5] INTERNET DRAFT Address Resolution for IP datagrams over MPEG-2 networks February 2005 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. 3. Address Resolution Requirements The general IP over MPEG-2 AR requirements are summarized below; These requirements are generic, enable the usage of network layer protocols and will be used to evaluate existing approaches: - Use SI tables for non-static allocation to promote AR scaling. - Provide mechanisms to install AR information at the server (unsolicited registration). - Provide incremental table updates or purging of stale information. - Support address scoping. - Provide security associations to authenticate the AR information. The MPEG IP address resolution is independent of encapsulation and supports existing IP over MPEG-2 (e.g., MPE [ETSI-DAT, ETSI-DAT1]) and also any IETF encapsulation that may be defined [ID-IPDVB-ARCH]. A 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. (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. IP packets with these addresses must not be allowed to travel outside their intended scope, and may cause unexpected behaviour if allowed to do so. Expires June 2005 [page 6] INTERNET DRAFT Address Resolution for IP datagrams over MPEG-2 networks February 2005 In addition, overlapping address assignments can arise when using Level 2 Network Point of Attachment (NPA) addresses [ID-IPDVB- ARCH]: (i) The NPA address must be unique within the addressed area. IEEE MAC addresses used in Ethernet LANs are globally unique. If the NPA addresses are not globally unique, the same NPA address may be re-used by receivers in different addressed areas. (ii) The NPA broadcast address (all 1 MAC address). Traffic with this address should be confined to one addressed area. (iii) Other non-IP protocols may also view sets of MAC multicast addresses as link-local, and may produce unexpected results if distributed across several private networks. 3.1 Unicast Support Reception of unicast packets destined for another addressed area may lead to an increase in the rate of received packets by systems connected via the network. IP end hosts normally filter received unicast IP packets based on their assigned IP address. 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 acts as an IP router, the receipt of such packet may lead to unexpected protocol behaviour. This also provides a security vulnerability since arbitrary packets may be passed to the IP layer. 3.2 Multicast Support 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). Appropriate procedures need to be specified to identify 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. Another different case arises when a receiver may potentially receive more than one copy of the same packet. In some cases, these may be sent in different TS Logical Channels, or even different TS Multiplexes. In this case, at the IP level, the host/router may be unaware of this duplication. Expires June 2005 [page 7] INTERNET DRAFT Address Resolution for IP datagrams over MPEG-2 networks February 2005 The primary goal of multicast support will be efficient filtering of IP-multicast packets by the receiver, and the mapping of IPv4 and IPv6 multicast addresses onto the associated PID value and TS Multiplex. The design should 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 be easily implemented in hardware would be beneficial, since these may relieve the drivers and operating systems from discarding unwanted multicast traffic. 4. MPEG-2 Address Resolution In this section, current MPEG-2 address resolution mechanisms are reviewed. 4.1 Static configuration. The static mapping option (IP addresses or flows statically mapped to 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 is the scheme used by the well known DOCSIS protocol in cable modems. This results in all IP traffic to be placed into the specified TS stream. Section or MAC filtering may be used to differentiate subnetworks. 4.2 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 PIDs. 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 stream associated with multimedia TV. Because of its historical usage, there is no direct support for IP mechanisms for identification of the TS multiplex and PID in use for a particular IP address. It is also important to highlight that a PID value is unidirectional and does not define a virtual channel in the ATM sense. Expires June 2005 [page 8] INTERNET DRAFT Address Resolution for IP datagrams over MPEG-2 networks February 2005 A TS multiplex may provide PID information for IP services by integrating additional information into the existing MPEG-2 tables, or to define additional tables specific to the IP service. This has a dual advantage: (i) IP specific information can be obtained directly. (ii) The mechanism uses an already standardised mechanism. Examples of current implementations of systems for allowing a MPEG-2 receiver to identify the appropriate PID and multiplex used to transmit traffic to a specific IP address include: (i) IP/MAC Notification Table (INT) in the DVB Data standard [ETS_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 is DVB standardised and more general purpose. It supports both IPv4 and IPv6 and can be used in combination with the other tables. It is the favoured choice of some members of the DVB community for address management and is briefly described below. 4.2.1 IP/MAC Notification Table (INT) and its usage The INT provides a mechanism for carrying information about the location of IP/MAC flows within DVB networks. An IP/MAC Platform represents a set of IP/MAC streams and/or receiver devices. Such a Platform may span several transport streams within one or multiple DVB networks and represents a single IP network with a harmonized address space (i.e. one without address conflicts). The IP/MAC Platform concept allows for the coexistence of several non-harmonized IP/MAC address spaces on the same DVB network. The INT allows "subnets" and fully specified single destination addresses to make signalling bandwidth efficient and flexible as required. The "subnet mask" (also for IPv6) can be given in full form or in slash notation (e.g. /127), this supports IPv6 prefixes. Multicast addresses can be given with or without source (address or range), although if source address is given then only the slash notation can be used for prefixes/subnets. Expires June 2005 [page 9] INTERNET DRAFT Address Resolution for IP datagrams over MPEG-2 networks February 2005 In addition to identification and security descriptors the following descriptors are used for address binding in INT tables: (i) target_MAC_address_descriptor: The descriptor used to describe a single or group of MAC addresses (and their mask). (ii) target_MAC_address_range_descriptor: May be used to setup filters. (iii) target_IP_address_descriptor: The descriptor describing a single or group of IPv4 unicast or multicast addresses (and their mask). (iv) target_IP_slash_descriptor: Allows definition and announcement of an IPv4 subnet. (v) target_IP_source_slash_descriptor: Uses source and destination addresses to target a single or group of devices; could be used to define flows. (vi) IP/MAC stream_location_descriptor: This descriptor directly locates the 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 In addition, the ISP_access_mode_descriptor allows definition if the access to the ISP is done via an alternative non-DVB network (hence another address is necessary). The INT provides a set of descriptors to manage addressing in a DVB network. Its drawbacks are that while the IP/MAC concept is general enough there is still a need to manage the addressing (and the traffic) at the PID level. It currently is defined only for Multi-Protocol Encapsulation (MPE) and would need extension to support other schemes. In addition the use of a centralized management prevents the implementation of a more dynamic scheme. 4.2.2 Multicast Mapping Table (MMT) and its usage The Multicast Mapping Table (MMT) is an example employing an MPEG-2 level control table to communicate a set of multicast addresses and their associated PID value. This table allows a DVB-RCS Forward Link Subsystem (FLSS) to specify the mapping and Return Channel Satellite Terminals (RCSTs) to determine the PID values are being used by the traffic that need to be received. The MMT is not currently a part of the DVB-RCS specification. Expires June 2005 [page 10] INTERNET DRAFT Address Resolution for IP datagrams over MPEG-2 networks February 2005 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 each MHP Receiver monitors to receive a variety of control information. The AIT is a DSMCC format table that provides information about data broadcasts, the required activation state of applications carried by a broadcast stream, etc. This information allows the broadcaster to request that the receiver change the activation state of an application, and to direct applications to receive specific multicast packet flows (using IPv4 or IPv6 routing descriptors. In MHP, AR is not seen as specific function, but a part of a wider configuration and control function. 4.2.4 Comparison of table based approaches All tables 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. 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. Two IETF-defined protocols for mapping IP addresses to NPA/MAC addresses are ARP and ND for IPv4 and IPv6 respectively. Both protocols are normally used in a bi-directional mode, although both also permit unsolicited transmission of mappings, which could potentially be used in a uni-directional environment. The use of ARP does not raise specific issues with the MPEG-2 Table-based AR for MPEG-2 Transmission Network Virtual Logical Channels, since ARP uses only broadcast and unicast addresses. The use of ND requires a multicast mapping of the set of addresses used by ND to one or more MPEG-2 Transmission Network Virtual Logical Channels. <<< Some text is required to describe operational experience >>> Expires June 2005 [page 11] INTERNET DRAFT Address Resolution for IP datagrams over MPEG-2 networks February 2005 5.1 Link Layer Support This section considers two layer 2 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 | +------------------------------+--------+-------+-------+------+ |a. ULE without dst MAC address| 8 | - | - | x | |b. ULE with dst MAC address | 14 | - | x | x | |c. MPE without LLC/SNAP | 16 | - | x | - | |d. MPE with LLC/SNAP | 24 | - | x | x | |e. ULE with Bridging extension| 22 | x | x | x | |f. ULE with Bridging & NPA | 28 | x | x | x | |g. MPE+LLC/SNAP+Bridging | 38 | x | x | x | +------------------------------+--------+-------+-------+------+ Table of L2 support and overhead (x=supported, -=not supported) a. ULE with no dst MAC/NPA address << to be written>> b. ULE with dst MAC/NPA address The IPv4 Address Resolution Protocol (ARP) [RFC826] uses an IANA-assigned EtherType and is supported with ULE [IP-IPDVB-ULE]. The ND protocol of IPv6 [RFC2461] may be used. << More info on use of ND is required, noting that in one form of header there is no MAC src address>> c. MPE without LLC/SNAP MPE does not provide an IANA-assigned EtherType and therefore can not support the Address Resolution Protocol (ARP) [RFC826]. The ND protocol of IPv6 [RFC2461] may be used. << More info on use of ND is required, noting that in one form of header there is no MAC src address>> Expires June 2005 [page 12] INTERNET DRAFT Address Resolution for IP datagrams over MPEG-2 networks February 2005 d. MPE with LLC/SNAP 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. In its simplest form, no MAC source address is present in the L2 frame. LLC/SNAP format MPE frames may optionally carry and IEEE bridging header [LLC]. This header supplies both a MAC source and destination address, at the expense of larger encapsulation overhead. The ND protocol of IPv6 [RFC2461] may be used. << More info on the use of ND is required, noting that in one form of header there is no MAC src address>> 5.2 Impact on Network Protocols when using Bi-directional Transmission <<< Other real implementation experience is requested: >>> <<< Please send any experience to ipdvb list >>> <<< text on DHCP, L2TP, PPoE, etc to be added by other volunteers >>> 5.3 Impact on Network Protocols when using Uni-directional Transmission The IP over DVB link is basically a Uni-Directional broadcast (UDL). ARP and ND do not work in their normal form over such links, because these protocols assume the bi-directional layer 2 connectivity. The UDL receiver cannot send any response to a querier over the UDL link. To solve this, we propose to use the UDLR (RFC3077)link layer tunneling mechanism. UDLR emulates the UDL as a bi-directional broadcast type link at the datalink layer. The uni-directional functionality is hidden to IP and upper layer protocols. This section introduces how to use UDLR link layer tunneling mechanisms to use ARP and ND on Uni-Directional DVB links and shows the results of the evaluation of the combinations of UDLR and various IP over DVB encapsulation protocols. <<< Will be completed later, inputs required from WG >>> Expires June 2005 [page 13] INTERNET DRAFT Address Resolution for IP datagrams over MPEG-2 networks February 2005 5.4 Cable Networks Cable networks use different transmission schemes for the upstream and downstream transmission. They do not usually employ table based approaches for address resolution. Until the deployment of DOCSIS and EuroDOCSIS most address resolution schemes in cable networks for IP traffic have been proprietary and are still used for some STB requiring interaction. In last case it is the role of specific headend equipment to act as gateways between cable set-top boxes and the Internet. These gateways receive STB layer 2 information and allocate IP addresses; there is no use of inband tables. The information is sent (on the downstream) to the STBs as IP/Ethernet encapsulated as MPEG frames on a well known PID. DOCSIS uses only one PID. On the upstream, traffic is handled just like any Ethernet frames and not as IP/Ethernet over MPEG-2. While this approach is widespread, other roprietary schemes are still used. In the DOCSIS world, Cable Modem Terminal Systems (CMTSs) act as DHCP servers and allocate IP addresses to DOCSIS modems and STBs. DOCSIS acts as an Ethernet bridge between the Cable Modem and the CMTS. The CMTS transparently proxies DHCP requests on behalf of a DHCP server on the network. The DHCP option is "giadd" (Gateway Internet Address)also called a "helper address", which is usually the address of a real DHCP server. From the point of view of modems and attached devices, it appears that the CMTS (default gateway/router)is also the DHCP server. Expires June 2005 [page 14] INTERNET DRAFT Address Resolution for IP datagrams over MPEG-2 networks February 2005 6. Conclusions and Recommendations This document has examined 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, the bindings between IP addresses and PIDs can be done statically (such as in the cable networks) or carried in tables such at the standard AIT in MHP, the IP Notification Tables (INT) of DVB and the DVB-RCS Multicast Mapping Tables (MMT). This document has reviewed the status of these current address resolution mechanisms in MPEG-2 networks, defined their usage and proved information to identify what would be needed to improve their conformity to standard IP practices. Limitations of the current methods include the dynamics of the table refresh support for IP scoping of addresses, a generic access method for ARP and ND using the ULE encapsulation and the lack of a universal and generic table access methodology. 7. 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. Consideration will be given to those methods that will ensure that usage of MPEG-2 network resources will be restricted to IP addresses that are not a threat to those resources or other resources in the Internet. 8. Acknowledgments The authors wish to thank Rod Walsh, Jun Takei, Alexander Adolf, Michael Mercurio and the ipdvb WG members for their inputs. The authors would also like to acknowledge the support of the European Space Agency. Expires June 2005 [page 15] INTERNET DRAFT Address Resolution for IP datagrams over MPEG-2 networks February 2005 9. References 9.1 Normative References [ATSC] A/53C, "ATSC Digital Television Standard", Advanced Television Systems Committee (ATSC), Doc. A/53C, 2004. [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 Terrestrial Broadcast and Cable", Advanced Television Systems Committee (ATSC), Doc. A/65B, 2003. [ETSI-DAT] EN 301 192, "Specifications for Data Broadcasting", v1.3.1, European Telecommunications Standards Institute (ETSI), May 2003. http://www.etsi/org/ [ETSI-DAT1] EN 101 202, "Implementation Guide for Data", v1.2.1, 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". [ETSI-SI1] ETSI TR 101 162: "Digital Video Broadcasting (DVB); Allocation of Service Information (SI) codes for DVB systems". Expires June 2005 [page 16] INTERNET DRAFT Address Resolution for IP datagrams over MPEG-2 networks February 2005 [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-MMUSIC-IMG] Y. Nomura, R. Walsh, J-P. Luoma, J. Ott, H. Schulzrinne, "Protocol Requirements for Internet Media Guides", nternet Draft, draft-ietf-mmusic-img-req-07.txt, June 2004, Work in Progress,MMUSIC WG. [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). [RFC826] Plummer, D. "An Ethernet Address Resolution Protocol", RFC 826, IETF, November 1982. [RFC1122] B. Braden, ed., "Requirements for Internet Hosts - Communication Layers", RFC 1122. [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", RFC2464, IETF December 1998. 9.2 Informative References [ETSI-DAT] EN 301 192 Specifications for Data Broadcasting, European Telecommunications Standards Institute (ETSI). [ETSI-DVBC] EN 300 800 Digital Video Broadcasting (DVB); DVB interaction channel for Cable TV distribution systems (CATV), European Telecommunications Standards Institute (ETSI). [ISO-MPEG] ISO/IEC DIS 13818-1:2000 "Information technology ? Generic coding of moving pictures and associated audio information: Systems", International Standards Organisation (ISO). [ETSI-DAT] EN 301 192 Specifications for Data Broadcasting, European Telecommunications Standards Institute (ETSI). http://www.atsc.org/standards/Code_Point_Registry.pdf Expires June 2005 [page 17] INTERNET DRAFT Address Resolution for IP datagrams over MPEG-2 networks February 2005 10. Authors' Addresses Godred Fairhurst Department of Engineering University of Aberdeen Aberdeen, AB24 3UE UK Email: gorry@erg.abdn.ac.uk Web: http://www.erg.abdn.ac.uk/users/gorry 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 11. 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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. 13. IANA Considerations NOT KNOWN AT THIS TIME. Expires June 2005 [page 19]