Monday, July 23, 2007 Scalable Adaptive Multicast (SAM) Research Group (RG) Minutes of the Meeting at IETF-69, Chicago, IL (All times are local) John Buford opened the meeting at 0905 with a review of the agenda. Yuji Imai prepared the first presentation, on the subject of XCAST. RG co-chair John Buford presented the slides to the group on his behalf. To investigate XCAST as a way to bootstrap the deployment of SAM protocols, the team has implemented a prototype in a private PlanetLab environment, with the goal of deploying it more widely across the 700 nodes of the open PlanetLab. The development team followed the pattern of VINI [VINI] for the XCAST testbed. In this way, extensions or additional protocols can be deployed alongside XCAST onto PlanetLab "slices" (a collection of virtual machines running on one or more nodes) to form an overlay network. This capability enables experimentation in SAM protocols; interested parties are encouraged to join the mailing list. XCAST implementations are available for FreeBSD and Linux. Beginning at 0915, "SAMTK: A Toolkit for Scalable Adaptive Multicast" was the second presentation, by Nobuo Kawaguchi. Because multicast is not widely used in the "real world", there exists a gap between multicast researchers and real-world applications. SAMTK is intended to help fill this gap. Both multicast researchers and application developers can benefit from the programmer's toolkit, which defines three interfaces: application, group, and protocol. In the current version, group management is performed by specifying group and member URIs manually through a web browser. SAMTK does not yet perform automatic adaptation to system changes; however, the toolkit features an open interface for plugins which can extend functionality. The presentation was followed by a brief demonstration of SAMTK functionality, with components running on several operating systems, including Linux, FreeBSD, OS X, and Windows; source code is available on SourceForge, with more complete documentation to follow. In the current testbed, test traffic is generated with iperf. The SAMTK plugin architecture was further discussed during Q&A following the presentation. Topics included: the interface between plugins and higher layers; the ability of applications to identify and interact with plugins; the use of multiple multicast addressing schemes, and their binding to programming languages; and further testing of the API. Next, starting at 0941, Matthias Waehlisch presented "Hybrid Shared Tree Architecture." As described in the MOBOPTS problem statement, there are several approaches to overcoming the complexities of inter-domain multicast. However, each has its limitations. DHTs impose additional delay; most multicast protocols do not recognize mobility events, and so distribution trees are subject to disruption at such times. Here, we introduce a new concept, the inter-domain multicast gateway, or IMG, as a complement to the hybrid overlay framework [HOMF]. IMG uses Pastry to construct a source-location-independent distributed tree; for this reason, the number of overlay routing hops is algorithmically bounded. An IMG can be located anywhere in the native multicast region; it doesn't have to be at the 'edge' of the region. All IMGs learn about all group memberships. Waehlisch described how multicast traffic is routed across the tree. When there is more than one node in the overlay corresponding to a given prefix, the traffic is forwarded to the closest node according to Pastry. Intermediate nodes simply forward packets down the tree, which is loop-free because packets can only be sent "downward" on the tree. This approach improves reliability by avoiding reliance on rendezvous points. In the fourth presentation, starting at 1000, John Buford described the Hybrid Overlay Multicast Framework. The corresponding I-D [HOMF], which was drafted in response to the SAM RG charter, seeks to enable different multicast schemes to work together in a heterogeneous network. The I-D includes a comparison of native multicast, application layer multicast, and some "hybrid" approaches. P2P overlays have been widely discussed, and many algorithms have been defined, some of which can be interfaced to native multicast. To standardize this interface, we must define protocols for basic overlay operations. One scheme, discussed at some length, involves the use of AMT in conjunction with P2P overlay networks. AMT is preferred where it is deployed, but application layer multicast can be used to reach an AMT region. However, in order to choose among SAM protocols at run time, participating nodes must have topology awareness beyond what is typically available in ALM. Buford described experimentation with several tools, including SSFNet, Oversim, and overlayweaver. During Q&A, the group discussed interactions between mobility and multicast, and between AMT and ALM. Buford concluded by seeking additional comments from the RG on the latest revision of the framework draft. The meeting adjourned at approximately 1045. References [VINI] Bavier, Feamster, Huang, Peterson, Rexford. "In VINI Veritas: Realistic and Controlled Network Experimentation", SIGCOMM 2006. Accessed at http://www.cs.princeton.edu/~jrex/papers/vini.pdf [HOMF] Buford. "Hybrid Overlay Multicast Framework" [Work in Progress]. draft-irtf-sam-hybrid-overlay-framework.