SAM J. Buford, Panasonic Internet Draft S. Kadadi, Motorola Expires: June 30, 2007 December 31, 2006 SAM Problem Statement draft-irtf-sam-problem-statement-01.txt 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 BCP 79. 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/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on June 30, 2007. Copyright Notice Copyright (C) The Internet Society (2006). All Rights Reserved. Abstract We describe the generally expected behavior of a scalable and adaptive multicast architecture, leaving further details to separate documents on requirements and the SAM design space. This document is Buford Expires June 30, 2007 [Page 1] Internet-Draft SAM Problem Statement December 30, 2006 a starting point for discussions of feasibility, priority, and deployability. Conventions used in this document In examples, "C:" and "S:" indicate lines sent by the client and server respectively. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 [1]. Table of Contents 1. Introduction...................................................2 2. Heterogeneous Multicast Infrastructure.........................3 2.1. Varying Infrastructure by Network Region..................3 2.2. Regional Transitions......................................4 3. Quality of Service.............................................4 3.1. Native QOS, No Native Multicast...........................4 3.2. Other Combinations........................................5 4. Mobility.......................................................5 4.1. Multicast Service Selection...............................6 4.2. Transitions between ALM and Native Multicast..............7 4.3. Other Considerations......................................7 5. Security Considerations........................................7 6. Conclusions....................................................8 7. References.....................................................8 7.1. Normative References......................................8 7.2. Informative References....................................8 Author's Addresses................................................8 Intellectual Property Statement...................................9 Disclaimer of Validity............................................9 Copyright Statement...............................................9 Acknowledgment....................................................9 1. Introduction The concept of scalable adaptive multicast includes both scaling properties and adaptability properties. Scalability is intended to cover: o large group size o large numbers of small groups Buford Expires June 30, 2007 [Page 2] Internet-Draft SAM Problem Statement December 30, 2006 o rate of group membership change o admission control for QoS o use with network layer QoS mechanisms o varying degrees of reliability o trees connect nodes over global internet Adaptability includes o use of different control mechanisms for different multicast trees depending on initial application parameters or application class o changing multicast tree structure depending on changes in application requirements, network conditions, and membership o use of different control mechanisms and tree structure in different regions of network depending on native multicast support, network characteristics, and node behavior The following sections describe some adaptation scenarios. After the base scenarios are elaborated, then scenarios for scalability and dynamic adaptation should be added. 2. Heterogeneous Multicast Infrastructure 2.1. Varying Infrastructure by Network Region Regions A, B, C are disjoint areas of the network with some type of native multicast support. Region Z is all other areas of the network with no native multicast support. Region Z may be partitioned by A, B, and/or C. A multicast connection between nodes in A, B, C, and Z is needed. In each region A, B, C, the respective native multicast mechanism is used. Multicast topology choices include: o Multicast applications see an end-to-end multicast application layer which is mapped to a native layer transparently in the regions that it is available. The overlay’s group management mechansisms hold for all nodes, and are mapped transparently to the native layer mechanisms in the appropriate regions. All nodes have addresses in the overlay. Buford Expires June 30, 2007 [Page 3] Internet-Draft SAM Problem Statement December 30, 2006 o Multicast applications see an end-to-end native multicast, where nodes in region Z connect to native regions using tunnels. The native group management mechanisms hold for all nodes. Homogeneous sub-case: regions A, B, C may use the same native multicast protocol. 2.2. Regional Transitions A node in a new region D joins the multicast tree. Region D has native support. What is the minimum number of nodes in a region needed for native support to be used in that part of the tree? 3. Quality of Service 3.1. Native QOS, No Native Multicast Each endpoint in the multicast tree specifies QOS constraints such as bandwidth, delay, and jitter for a given source. Multicast join includes admission control step for the selected QOS mechanism. This means that the join decision combines both multicast tree considerations (eg., best metrics) and an admission control decision. Paths to different endpoints from a given source might have different QOS constraints. A given multicast tree may mix QOS delivery and best effort delivery to different receivers. Available IP QOS mechanisms include Intserv, Diffserv, and MPLS. Assume all regions of network have interoperable native QOS mechanism. Assume all receivers have homogenous capabilities. The topology of the overlay is not assumed to be isomorphic to available QOS paths. The overlay must be sophisticated enough to determine what paths are available and arrange its tree construction and routing behaviour accordingly. In order to enforce QOS, a measurement mechanism is needed. The scalability of the measurement, feedback and policing mechanism is an important issue. RTP is such a measurement and feedback protocol for UDP. A source might adapt its bit rate and quality depending on feedback from receivers. There might be graceful degradation mechanisms such as multi-description coding over different multicast paths. This behavior is application dependent. Buford Expires June 30, 2007 [Page 4] Internet-Draft SAM Problem Statement December 30, 2006 3.2. Other Combinations Heterogeneous QOS refers to either 1) portions of the network where no QOS mechanism exists at native level, or 2) receivers which have heterogeneous capabilities. These combinations need further elaboration. o Native QOS with Regional Native Multicast o Heterogeneous QOS, No Native Multicast o Heterogeneous QOS, Regional Native Multicast 4. Mobility We assume mobile nodes use Mobile IP (MIP), and that regions of the network that mobile nodes operate in are MIP enabled. Any node in the multicast tree may be mobile, and we consider source node mobility as a special case. A mobile node’s home address (HoA) is associated with its overlay address (if this is an overlay) or group multicast address. As the node moves to another network, multicast messages are routed to it via the home agent (HA). In addition to increased latency, node mobility can impact robustness of multicast delivery due to loss of connectivity during mobility transitions. Some link layer solutions may mitigate or eliminate connectivity loss, but may require sending packets to both old and new care-of addresses during the transition. If the node uses its care-of address (CoA) in the overlay or multicast tree, then any mobility transition will be disruptive, causing a leave-join sequence. Forwarding of packets can be through the home agent. If the source address is the care-of address, these might be rejected by nodes expecting packets only from overlay-registered addresses. In general, mobile node transitions to another network lead to lost packets during the transition, and downstream nodes in the tree will also be disconnected. Possibile solutions are bi-casting the packets to both old and new CoA, or buffering packets at the HA or old or new anchored points. If the overlay is aware that the node is mobile, then it could construct a mesh rather than tree to connect to. The mesh might provide redundant paths to the mobile node’s children in the tree. Buford Expires June 30, 2007 [Page 5] Internet-Draft SAM Problem Statement December 30, 2006 The overlay might use knowledge about node movement to make a set of target anchor points prejoin the multicast group/service so that the handoff delay can be reduced. Solutions similar to low latency handoffs/Fast MIPv6 (prereg) could be used. There can be different scenarios depending on whether all nodes in multicast tree are mobile or a subset of nodes. 4.1. Multicast Service Selection As the node moves from one network to another network, it can get multicast service in the new network in three ways: 1) from the new foreign network, 2) from the home network via a tunnel, 3) from the old foreign network via a tunnel, if the transition was from one foreign network to another. The selection may depend on what is available in the new foreign network and which of the three mechanisms was used in the previous foreign network. 1. Multicast service to/from the new foreign network o In the case of native multicast, this means that the new foreign network has a multicast router which the mobile node uses. The mobile node can use the new IP address (obtained in the new network). This causes a leave-join sequence. If the router in the new network is not already a part the multicast tree, there will be additional delay to join the multicast tree in the foreign network. The mobile node uses either the CoA as the source address of control messages or its HoA. 2. Multicast service via home network o Multicast packets are tunneled to/from the mobile node by the HA. The mobile node uses HoA for multicast control messages. No need to join/leave the multicast group during handoff. The transmission path is not optimal. o If the tunnel end-point is not a mobile node, this may result in duplicate packets. Consider the case where packets of the same multicast group are tunneled to the new network. This means two HAs are tunneling packets for the same multicast group to the same foreign network. Possible solutions to this are: 1) applications in mobile node takes care of duplicate packets, 2) multicast packets are sent to mobile node as unicast packets (e.g., Mobile IPv4 uses this solution). 3. Multicast service from old foreign network Buford Expires June 30, 2007 [Page 6] Internet-Draft SAM Problem Statement December 30, 2006 o The mobile node gets the packets from its old multicast service anchor point until it registers/joins new multicast service anchor point in new network. Once it starts getting packets from new anchor point, it leaves its old anchor point. This means that packets are tunneled from the old foreign network until the mobile node gets multicast service from the new foreign network. o There is minimal packet loss. There may be duplicate packets during the transition. A leave and join sequence results. 4.2. Transitions between ALM and Native Multicast Transitions of mobile nodes between heterogeneous multicast networks (say, from a native multicast region to OL/ALM multicast region or vice versa) need to be considered. 4.3. Other Considerations o Multicast source mobility: Mobile source nodes may have more impact than other cases, and overlay tree/mesh may be reorganized when the multicast source moves to a new network. There may be solutions specific to source node mobility that may not scale to mobile nodes in general. o Scalability of advertisement mechanisms. Multicast advertisements are also multicast packets with well known multicast group address and port number. If mobile nodes which are in the foreign network want to know about multicast services in home network, these advertisement packets should be sent to foreign network. The home agent can tunnel packets to the foreign network, but it can increase the load on the HA. o Network topology supported by the access network. 5. Security Considerations [RESC2006] surveys the security issues specific to overlay networks which include: o Correctness of routing due to malicious nodes acting individually or collectively o Node impersonation due to lack of secure routing and identity o Fairness enforcement since each node acts autonomously, it can chose to limit its resource contribution to the operation of the overlay Buford Expires June 30, 2007 [Page 7] Internet-Draft SAM Problem Statement December 30, 2006 o Denial of service (DOS) o Using overlays for launching DDoS attacks [ROSS2006] SAM will not solve the overlay security problems, but should work with overlays that provide security mechanisms. 6. Conclusions Using this discussion with the separately developed SAM Design Space, we will be able to enumerate those ares of the problem space for which solutions exist and those which are open problems. This will suggest the steps by which the SAM Framework is designed. 7. References 7.1. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 7.2. Informative References [MUR2006] E. Muramoto, Y. Imai, N. Kawaguchi. Requirements for Scalable Adaptive Multicast Framework in Non-GIG Networks. November 2006. Internet Draft draft-muramoto-irtf-sam- generic-require-01.txt, work in progress. [RESC2006] E. Rescorla. Introduction to Distributed Hash Tables. IETF-65 Technical Plenary, March 2006. www3.ietf.org/proceedings/06mar/slides/plenaryt-2.pdf [ROSS2006] K. Ross. Exploiting P2P Systems for DDOS Attacks. IETF 65 P2PRG CORE Subgroup. www.cs.uml.edu/~buford/irtf- p2prg/ietf65/ietf65-irtf-p2prg-core-ddos.pdf Author's Addresses John Buford Panasonic Princeton Laboratory rd 2 Research Way, 3 Floor Princeton, NJ 08540, USA Email: buford@research.panasonic.com Shivanand Kadadi Motorola Bangalore India Email: a22063@motorola.com Buford Expires June 30, 2007 [Page 8] Internet-Draft SAM Problem Statement December 30, 2006 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. 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Please address the information to the IETF at ietf-ipr@ietf.org 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. Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. 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