SAM Research Group M. Waehlisch Internet-Draft link-lab & FU Berlin Intended status: Informational T C. Schmidt Expires: January 13, 2011 HAW Hamburg S. Venaas cisco Systems July 12, 2010 A Common API for Transparent Hybrid Multicast draft-waehlisch-sam-common-api-03 Abstract Group communication services exist in a large variety of flavors and technical implementations. Multicast data distribution is most efficiently performed on the lowest available layer, but a varying deployment status of multicast technologies throughout the Internet restricts service binding to runtime. Today, it is difficult to write an application that runs everywhere and at the same time makes use of the most efficient multicast service available in the network. Facing robustness requirements, developers are frequently forced to using a stable, upper layer protocol controlled by the application itself. This document describes a common multicast API that is suitable for transparent communication in underlay and overlay, and grants access to the different multicast flavors. It proposes an abstract naming by multicast URIs and discusses mapping mechanisms between different namespaces and distribution technologies. Additionally, it describes the application of this API for building gateways that interconnect current multicast domains throughout the Internet. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on January 13, 2011. Waehlisch, et al. Expires January 13, 2011 [Page 1] Internet-Draft Common Mcast API July 2010 Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Waehlisch, et al. Expires January 13, 2011 [Page 2] Internet-Draft Common Mcast API July 2010 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. Objectives and Reference Scenarios . . . . . . . . . . . . 6 3.2. Group Communication API & Protocol Stack . . . . . . . . . 7 3.3. Naming and Addressing . . . . . . . . . . . . . . . . . . 9 3.4. Mapping . . . . . . . . . . . . . . . . . . . . . . . . . 10 4. Common Multicast API . . . . . . . . . . . . . . . . . . . . . 11 4.1. Abstract Data Types . . . . . . . . . . . . . . . . . . . 11 4.1.1. Multicast URI . . . . . . . . . . . . . . . . . . . . 11 4.1.2. Interface . . . . . . . . . . . . . . . . . . . . . . 11 4.2. Group Management Calls . . . . . . . . . . . . . . . . . . 12 4.2.1. Create . . . . . . . . . . . . . . . . . . . . . . . . 12 4.2.2. Join . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.2.3. Leave . . . . . . . . . . . . . . . . . . . . . . . . 13 4.2.4. Source Register . . . . . . . . . . . . . . . . . . . 13 4.2.5. Source Deregister . . . . . . . . . . . . . . . . . . 13 4.3. Send and Receive Calls . . . . . . . . . . . . . . . . . . 14 4.3.1. Send . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.3.2. Receive . . . . . . . . . . . . . . . . . . . . . . . 14 4.4. Socket Options . . . . . . . . . . . . . . . . . . . . . . 15 4.4.1. Get Interfaces . . . . . . . . . . . . . . . . . . . . 15 4.4.2. Add Interface . . . . . . . . . . . . . . . . . . . . 15 4.4.3. Delete Interface . . . . . . . . . . . . . . . . . . . 15 4.4.4. Set TTL . . . . . . . . . . . . . . . . . . . . . . . 16 4.5. Service Calls . . . . . . . . . . . . . . . . . . . . . . 16 4.5.1. Group Set . . . . . . . . . . . . . . . . . . . . . . 16 4.5.2. Neighbor Set . . . . . . . . . . . . . . . . . . . . . 16 4.5.3. Designated Host . . . . . . . . . . . . . . . . . . . 17 4.5.4. Update Listener . . . . . . . . . . . . . . . . . . . 17 5. Functional Details . . . . . . . . . . . . . . . . . . . . . . 17 5.1. Mapping . . . . . . . . . . . . . . . . . . . . . . . . . 17 5.2. Namespaces . . . . . . . . . . . . . . . . . . . . . . . . 18 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 7. Security Considerations . . . . . . . . . . . . . . . . . . . 18 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18 9. Informative References . . . . . . . . . . . . . . . . . . . . 18 Appendix A. Practical Example of the API . . . . . . . . . . . . 19 Appendix B. Deployment Use Cases for Hybrid Multicast . . . . . . 20 B.1. DVMRP . . . . . . . . . . . . . . . . . . . . . . . . . . 21 B.2. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . . 21 B.3. PIM-SSM . . . . . . . . . . . . . . . . . . . . . . . . . 22 B.4. BIDIR-PIM . . . . . . . . . . . . . . . . . . . . . . . . 22 Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 23 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24 Waehlisch, et al. Expires January 13, 2011 [Page 3] Internet-Draft Common Mcast API July 2010 1. Introduction Currently, group application programmers need to make a choice of the distribution technology required at runtime. There is no common communication interface that abstracts multicast transmission and subscriptions from the deployment state at runtime. The standard multicast socket options [RFC3493], [RFC3678] are bound to an IP version and do not distinguish between naming and addressing of multicast identifiers. Group communication, however, is commonly implemented in different flavors (e.g., any source vs. source specific mutlicast), on different layers (e.g., IP vs. application layer multicast), and may be based on different technologies on the same tier (e.g., IPv4 vs. IPv6). It is the objective of this document to provide a universal access to group services. Multicast application development should be decoupled of technological deployment throughout the infrastructure. It requires a common multicast API that offers calls to transmit and receive multicast data independent of the supporting layer and the underlying technological details. For inter-technology transmissions, a consistent view on multicast states is needed, as well. This document describes an abstract group communication API and core functions necessary for transparent operations. Specific implementation guidelines with respect to operating systems or programming languages are out-of-scope of this document. In contrast to the standard multicast socket interface, the API introduced in this document abstracts naming from addressing. Using a multicast address in the current socket API predefines the corresponding routing layer. In this specification, the multicast name used for joining a group denotes an application layer data stream that is identified by a multicast URI, independent of a binding to a specific distribution technology. Such a group name can be mapped to variable routing identifiers. The aim of this common API is twofold: o Enable any application programmer to implement group-oriented data communication independent of the underlying delivery mechanisms. In particular, allow for a late binding of group applications to multicast technologies that makes applications efficient, but robust with respect to deployment aspects. o Allow for a flexible namespace support in group addressing, and thereby separate naming and addressing/routing schemes from the application design. This abstraction does not only decouple programs from specific apects of underlying protocols, but may open application design to extend to specifically flavored group Waehlisch, et al. Expires January 13, 2011 [Page 4] Internet-Draft Common Mcast API July 2010 services. Multicast technologies may be of various P2P kinds, IPv4 or IPv6 network layer multicast, or implemented by some other application service. Corresponding namespaces may be IP addresses, overlay hashes, other application layer group identifiers like , or names defined by the applications. This document also proposes and discusses mapping mechanisms between different namespaces and forwarding technologies. Additionally, the multicast API provides internal interfaces to access current multicast states at the host. Multiple multicast protocols may run in parallel on a single host. These protocols may interact to provide a gateway function that bridges data between different domains. The application of this API at gateways operating between current multicast instances throughout the Internet is described, as well. 2. Terminology This document uses the terminology as defined for the multicast protocols [RFC2710],[RFC3376],[RFC3810],[RFC4601],[RFC4604]. In addition, the following terms will be used. Group Address: A Group Address is a routing identifier. It represents a technological identifier and thus reflects the distribution technology in use. Multicast packet forwarding is based on this ID. Group Name: A Group Name is an application identifier that is used by applications to manage (e.g., join/leave and send/receive) a multicast group. The Group Name does not imply any distribution technologies but represents a logical identifier. Multicast Namespace: A Multicast Namespace is a collection of designators (i.e., names or addresses) for groups that share a common syntax. Typical instances of namespaces are IPv4 or IPv6 multicast addresses, overlay group ids, group names defined on the application layer (e.g., SIP or Email), or some human readable strings. Multicast Domain: A Multicast Domain accommodates nodes and routers of a common, single multicast forwarding technology and is bound to a single namespace. Waehlisch, et al. Expires January 13, 2011 [Page 5] Internet-Draft Common Mcast API July 2010 Interface An Interface is a forwarding instance of a distribution technology on a given node. For example, the IP interface 192.168.1.1 at an IPv4 host. Inter-domain Multicast Gateway: An Inter-domain Multicast Gateway (IMG) is an entity that interconnects different multicast domains. Its objective is to forward data between these domains, e.g., between IP layer and overlay multicast. 3. Overview 3.1. Objectives and Reference Scenarios The default use case addressed in this document targets at applications that participate in a group by using some common identifier taken from some common namespace. This group name is typically learned at runtime from user interaction like the selection of an IPTV channel, from dynamic session negotiations like in the Session Initiation Protocol (SIP), but may as well have been predefined for an application as a common group name. Technology- specific system functions then transparently map the group name to group addresses such that o programmers are enabled to process group names in their programs without the need to consider technological mappings to designated deployments in target domains; o applications are enabled to identify packets that belong to a logically named group, independent of the interface technology used for sending and receiving packets. The latter shall also hold for multicast gateways. This document refers to a reference scenario that covers the following two hybrid deployment cases displayed in Figure 1: 1. Multicast domains running the same multicast technology but remaining isolated, possibly only connected by network layer unicast. 2. Multicast domains running different multicast technologies, but hosting nodes that are members of the same multicast group. Waehlisch, et al. Expires January 13, 2011 [Page 6] Internet-Draft Common Mcast API July 2010 +-------+ +-------+ | Member| | Member| | Foo | | G | +-------+ +-------+ \ / *** *** *** *** * ** ** ** * * * * MCast Tec A * * * * ** ** ** * *** *** *** *** +-------+ +-------+ | | Member| | Member| +-------+ | G | | Foo | | IMG | +-------+ +-------+ +-------+ | | | *** *** *** *** *** *** *** *** * ** ** ** * * ** ** ** * * * +-------+ * * * MCast Tec A * --| IMG |-- * MCast Tec B * +-------+ * * +-------+ * * - | Member| * ** ** ** * * ** ** ** * | G | *** *** *** *** *** *** *** *** +-------+ Figure 1: Reference scenarios for hybrid multicast, interconnecting group members from isolated homogeneous and heterogeneous domains. It is assumed throughout the document that the domain composition, as well as the node attachement to a specific technology remain unchanged during a multicast session. 3.2. Group Communication API & Protocol Stack The group communication API consists of four parts. Two parts combine the essential communication functions, while the remaining two offer optional extensions for an enhanced management: Group Management Calls provide the minimal API to instantiate a multicast socket and manage group membership. Send/Receive Calls provide the minimal API send and receive multicast data in a technology-transparent fashion. Waehlisch, et al. Expires January 13, 2011 [Page 7] Internet-Draft Common Mcast API July 2010 Socket Options provide extension calls for the configuration of the multicast socket, i.e., setting path length and associated interfaces explicitly. Service Calls provide extension calls that grant access to internal multicast states of an interface such as the multicast groups under subscription. Multicast applications that use the common API require assistance by a group communication stack. This protocol stack serves two needs: o It provides system-level support to transfer the abstract functions of the common API, including namespace support, into protocol operations at interfaces. o It bridges data distribution between different multicast technologies. The general procedure to initiate multicast communication in this setting proceeds as follows: 1. An application opens an abstract multicast socket. 2. The application subscribes/leaves/sends to a group using a logical group identifier. 3. An intrinsic function of the stack maps the logical group ID (Group Name) to a technical group ID (Group Address). This function may make use of deployment-specific knowledge such as available technologies and unused group addresses in its domain. 4. Packet distribution proceeds to and from one or several multicast-enabled interfaces. The multicast socket describes a group communication channel composed of one or multiple interfaces. A socket may be created without explicit interface association by the application, which leaves the choice of the underlying forwarding technology to the group communication stack. However, an application may also bind the socket to one or multiple dedicated interfaces, which predefines the forwarding technology and the namespace(s) of the Group Address(es). Applications are not required to maintain mapping states for Group Addresses. The group communication stack accounts for the mapping of the Group Name to the Group Address(es) and vice versa. Multicast data passed to the application will be augmented by the corresponding Group Name. Multiple multicast subscriptions thus can be conducted on a single multicast socket without the need for Group Name encoding Waehlisch, et al. Expires January 13, 2011 [Page 8] Internet-Draft Common Mcast API July 2010 at the application side. Hosts may support several multicast protocols. The group communication stack discovers available multicast-enabled communication interfaces. It provides a minimal hybrid function that bridges data between different interfaces and multicast domains. Details of service discovery are out-of-scope of this document. The extended multicast functions can be implemented by a middleware as visualized in Figure 2. *-------* *-------* | App 1 | | App 2 | *-------* *-------* | | *---------------------* ---| | Middleware | | *---------------------* | | | | *---------* | | | Overlay | | \ Group Communication *---------* | / Stack | | | | | | *---------------------* | | Underlay | | *---------------------* ---| Figure 2: A middleware for offering uniform access to multicast in underlay and overlay 3.3. Naming and Addressing Applications use Group Names to identify groups. Names can uniquely determine a group in a global communication context and hide technological deployment for data distribution from the application. In contrast, multicast forwarding operates on Group Addresses. Even though both identifiers may be identical in symbols, they carry different meanings. They may also belong to different namespaces. The namespace of a Group Address reflects a routing technology, while the namespace of a Group Name represents the context in which the application operates. URIs [RFC3986] are a common way to represent namespace-specific identifiers in applications. Throughout this document, any kind of Group Name follows a URI notation with the syntax defined in Section 4.1.1. Examples are, ip://224.1.2.3:5000, and sip://news@cnn.com. Waehlisch, et al. Expires January 13, 2011 [Page 9] Internet-Draft Common Mcast API July 2010 An implementation of the group communication middleware can provide convenience functions that detect the namespace of a Group Name and use it to optimize service instantiation. In practice, such a library would provide support for high-level data types to the application, similar to the current socket API (e.g., InetAddress in Java). Using this data type could implicitly determine the namespace. Details of automatic identifcation is out-of-scope of this document. A multicast socket (IPv4/v6 interface) can be used by multiple logical multicast IDs from different namespaces (IPv4-group address, IPv6-group address). 3.4. Mapping Group Names require a mapping to Group Addresses prior to service instantiation at an Interface. Similarly, a mapping is needed at gateways to translate between Group Addresses from different namespaces. Some namespaces facilitate a canonical transformation to default address spaces. For example, ip://224.1.2.3:5000 has an obvious correspondance to 224.1.2.3 in the IPv4 multicast address space. Note that in this example the multicast URI can be completely recovered from any data packet received from this group. However, mapping in general can be more complex and need not be invertible. Mapping functions can be stateless in some contexts, but may require states in others. The application of such functions depends on the cardinality of the namespaces, the structure of address spaces, and possible address collisions. For example, it is not obvious how to map a large identifier space (e.g., IPv6) to a smaller, collision-prone set like IPv4. Two (or more) Multicast Addresses from different namespaces may belong to a. the same logical group (i.e., same Multicast Name) b. different multicast channels (i.e., different technical IDs). This decision can be solved based on invertible mappings. However, the application of such functions depends on the cardinality of the namespaces and thus does not hold in general. It is not obvious how to map a large identifier space (e.g., IPv6) to a smaller set (e.g., IPv4). A mapping can be realized by embedding smaller in larger namespaces or selecting an arbitrary, unused ID in the target space. The relation between logical and technical ID is stored based on a Waehlisch, et al. Expires January 13, 2011 [Page 10] Internet-Draft Common Mcast API July 2010 mapping service (e.g., DHT). The middleware thus queries the mapping service first, and creates a new technical group ID only if there is no identifier available for the namespace in use. The Group Name is associated with one or more Group Addresses, which belong to different namespaces. Depending on the scope of the mapping service, it ensures a consistent use of the technical ID in a local or global domain. All group members subscribe to the same Group Name within the same namespace. 4. Common Multicast API 4.1. Abstract Data Types 4.1.1. Multicast URI Multicast Names and Multicast Addresses follow an URI scheme that defines a subset of the generic URI specified in [RFC3986] and is compliant with the guidelines in [RFC4395]. The multicast URI is defined as follows: scheme "://" group "@" instantiation ":" port "/" sec-credentials The parts of the URI are defined as follows: scheme referes to the specification of the assigned identifier [RFC3986] which takes the role of the namespace. group identifies the group uniquely within the namespace given in scheme. instantiation identifies the entitiy that generates the instance of the group (e.g., a SIP domain or a source in SSM) using the namespace given in scheme. port identifies a specific application at an instance of a group. sec-credentials used to implement security credentials (e.g., to authorize a multicast group access). 4.1.2. Interface The interface denotes the layer and instance on which the corresponding call will be effective. In agreement with [RFC3493] we identify an interface by an identifier, which is a positive integer Waehlisch, et al. Expires January 13, 2011 [Page 11] Internet-Draft Common Mcast API July 2010 starting at 1. Properties of an interface are stored in the following struct: struct if_prop { unsigned int if_index; /* 1, 2, ... */ char *if_name; /* "eth0", "eth1:1", "lo", ... */ char *if_addr; /* "1.2.3.4", "abc123" ... */ char *if_tech; /* "ip", "overlay", ... */ }; The following function retrieves all available interfaces from the system: struct if_prop *if_prop(void); It extends the functions for Interface Identfication in [RFC3493] (cf., Section 4). 4.2. Group Management Calls 4.2.1. Create The create call initiates a multicast socket and provides the application programmer with a corresponding handle. If no interfaces will be assigned based on the call, the default interface will be selected and associated with the socket. The call may return an error code in the case of failures, e.g., due to a non-operational middleware. int createMSocket(uint32_t *if); The if argument denotes a list of interfaces that will be associated with the multicast socket. This parameter is optional. On success a multicast socket identifier is returned, otherwise NULL. 4.2.2. Join The join call initiates a group subscription. Depending on the interfaces that are associated with the socket, this may result in an IGMP/MLD report or overlay subscription. int join(int s, const uri group_name); The s argument identifies the multicast socket. The group_name argument identifies the group. Waehlisch, et al. Expires January 13, 2011 [Page 12] Internet-Draft Common Mcast API July 2010 On success the value 0 is returned, otherwise -1. 4.2.3. Leave The leave call results in an unsubscription for the given Group Name. int leave(int s, const uri group_name); The s argument identifies the multicast socket. The group_name identifies the group. On success the value 0 is returned, otherwise -1. 4.2.4. Source Register The srcRegister call allows sources to register for a Group Name. This may be helpful for the creation of sub-overlays, for example. This call is optional. int srcRegister(int s, const uri group_name, uint_t num_ifs, uint_t *ifs); The s argument identifies the multicast socket. The group_name argument identifies the multicast group to which a source sends data. The num_ifs argument holds the number of elements in the ifs array. The ifs argument points to the list of interfaces for which the source registration failed. If num_ifs was 0 on output, a NULL pointer is returned. If source registration succeeded for all interfaces associated with the socket, the value 0 is returned, otherwise -1. 4.2.5. Source Deregister The srcDeregister indicates that a source does no longer intend to send data to the multicast group. int srcDeregister(int s, const uri group_name, uint_t num_ifs, uint_t *ifs); The s argument identifies the multicast socket. The group_name argument identifies the multicast group to which a Waehlisch, et al. Expires January 13, 2011 [Page 13] Internet-Draft Common Mcast API July 2010 source stops sending multicast data. The num_ifs argument holds the number of elements in the ifs array. The ifs argument points to the list of interfaces for which the source deregistration failed. If num_ifs was 0 on output, a NULL pointer is returned. If source deregistration succeeded for all interfaces associated with the socket, the value 0 is returned, otherwise -1. 4.3. Send and Receive Calls 4.3.1. Send The send call passes multicast data for a Multicast Name from the application to the multicast socket. int send(int s, const uri group_name, size_t msg_len, const void *buf); The s argument identifies the multicast socket. The group_name argument identifies the group to which data will be sent. The msg_len argument holds the length of the message to be sent. The buf argument passes the multicast data to the multicast socket. On success the value 0 is returned, otherwise -1. 4.3.2. Receive The receive call passes multicast data and the corresponding Group Name to the application. int receive(int s, const uri group_name, size_t msg_len, msg *msg_buf); The s argument identifies the multicast socket. The group_name argument identifies the subscribed multicast group. The msg_len argument holds the length of the received message. The msg_buf argument points to the payload of the received multicast data. Waehlisch, et al. Expires January 13, 2011 [Page 14] Internet-Draft Common Mcast API July 2010 On success the value 0 is returned, otherwise -1. 4.4. Socket Options The following calls configure an existing multicast socket. 4.4.1. Get Interfaces The getInterface call returns an array of all available multicast communication interfaces associated with the multicast socket. int getInterfaces(int s, uint_t num_ifs, uint_t *ifs); The s argument identifies the multicast socket. The num_ifs argument holds the number of interfaces in the ifs list. The ifs argument points to an array of interface identifiers. On success the value 0 or lager is returned, otherwise -1. 4.4.2. Add Interface The addInterface call adds a distribution channel to the socket. This may be an overlay or underlay interface, e.g., IPv6 or DHT. Multiple interfaces of the same technology may be associated with the socket. int addInterface(int s, uint32_t if); The s and if arguments identify a multicast socket and interface, respectively. On success the value 0 is returned, otherwise -1. 4.4.3. Delete Interface The delnterface call removes the interface if from the multicast socket. int delInterface(int s, uint32_t if); The s and if arguments identify a multicast socket and interface, respectively. On success the value 0 is returned, otherwise -1. Waehlisch, et al. Expires January 13, 2011 [Page 15] Internet-Draft Common Mcast API July 2010 4.4.4. Set TTL The setTTL call configures the maximum hop count for the socket a multicast message is allowed to traverse. int setTTL(int s, int h); The s and h arguments identify a multicast socket and the maximum hop count, respectively. On success the value 0 is returned, otherwise -1. 4.5. Service Calls 4.5.1. Group Set This groupSet call returns all registered multicast groups. The information can be provided by group management or routing protocols. The return values distinguish between sender and listener states. int groupSet(uint32_t if, uint_t *num_groups, struct groupSet *groupSet); struct groupSet { uri group_name; /* registered multicast group */ int type; /* 0 = listener state, 1 = sender state */ The if argument identifies the interface for which states are maintained. The num_groups argument holds number of groups in the groupSet array. The groupSet argument points to an array group states. On success the value 0 is returned, otherwise -1. 4.5.2. Neighbor Set The neighborSet function can be invoked to get the set of multicast routing neighbors. int neighborSet(uint32_t if, uint_t *num_groups, const uri *group_name); The if argument identifies the interface to which neighbors are attached. The num_groups argument holds the number of addresses in the Waehlisch, et al. Expires January 13, 2011 [Page 16] Internet-Draft Common Mcast API July 2010 group_name array. The group_name argument points to a list of multicast neighbors on a successfull return. On success the value 0 is returned, otherwise -1. 4.5.3. Designated Host The designatedHost function returns if the host has the role of a designated forwarder or querier, or not. Such an information is provided by almost all multicast protocols to handle packet duplication, if multiple multicast instances serve on the same subnet. int designatedHost(const uri *group_name); The group_name argument points to the group for which the host may attain the role of designated forwarder. The function returns 1 if the host is a designated forwarder or querier, otherwise 0. The return value -1 indicates an error. 4.5.4. Update Listener The updateListener function is invoked to inform a group service about a change of listener states for a group. This is the result of receiver new subscriptions or leaves. The group service may call groupSet to get updated information. const uri *updateListener(); On success the updateListener function points to the Group Name that experienced state change, otherwise NULL. 5. Functional Details In this section, we describe the functional details of the API and the middleware. TODO 5.1. Mapping Group Name to Group Address, SSM/ASM TODO Waehlisch, et al. Expires January 13, 2011 [Page 17] Internet-Draft Common Mcast API July 2010 5.2. Namespaces 6. IANA Considerations This document makes no request of IANA. 7. Security Considerations This draft does neither introduce additional messages nor novel protocol operations. TODO 8. Acknowledgements We would like to thank the HAMcast-team, Dominik Charousset, Gabriel Hege, Fabian Holler, Alexander Knauf, Sebastian Meiling, and Sebastian Woelke, at the HAW Hamburg for fruitful discussions. This work is partially supported by the German Federal Ministry of Education and Research within the HAMcast project, which is part of G-Lab. 9. Informative References [I-D.ietf-mboned-auto-multicast] Thaler, D., Talwar, M., Aggarwal, A., Vicisano, L., and T. Pusateri, "Automatic IP Multicast Without Explicit Tunnels (AMT)", draft-ietf-mboned-auto-multicast-10 (work in progress), March 2010. [RFC1075] Waitzman, D., Partridge, C., and S. Deering, "Distance Vector Multicast Routing Protocol", RFC 1075, November 1988. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast Listener Discovery (MLD) for IPv6", RFC 2710, October 1999. [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. Thyagarajan, "Internet Group Management Protocol, Version 3", RFC 3376, October 2002. Waehlisch, et al. Expires January 13, 2011 [Page 18] Internet-Draft Common Mcast API July 2010 [RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W. Stevens, "Basic Socket Interface Extensions for IPv6", RFC 3493, February 2003. [RFC3678] Thaler, D., Fenner, B., and B. Quinn, "Socket Interface Extensions for Multicast Source Filters", RFC 3678, January 2004. [RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery Version 2 (MLDv2) for IPv6", RFC 3810, June 2004. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. [RFC4395] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and Registration Procedures for New URI Schemes", BCP 35, RFC 4395, February 2006. [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", RFC 4601, August 2006. [RFC4604] Holbrook, H., Cain, B., and B. Haberman, "Using Internet Group Management Protocol Version 3 (IGMPv3) and Multicast Listener Discovery Protocol Version 2 (MLDv2) for Source- Specific Multicast", RFC 4604, August 2006. [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, "Bidirectional Protocol Independent Multicast (BIDIR- PIM)", RFC 5015, October 2007. Appendix A. Practical Example of the API Waehlisch, et al. Expires January 13, 2011 [Page 19] Internet-Draft Common Mcast API July 2010 -- Application above middleware: //Initialize multicast socket; //the middleware selects all available interfaces MulticastSocket m = new MulticastSocket(); m.join(URI("ipv4://224.1.2.3:5000")); m.join(URI("ipv6://[FF02:0:0:0:0:0:0:3]:6000")); m.join(URI("sip://news@cnn.com")); -- Middleware: join(URI mcAddress) { //Select interfaces in use for all this.interfaces { switch (interface.type) { case "ipv6": //... map logical ID to routing address Inet6Address rtAddressIPv6 = new Inet6Address(); mapNametoAddress(mcAddress,rtAddressIPv6); interface.join(rtAddressIPv6); case "ipv4": //... map logical ID to routing address Inet4Address rtAddressIPv4 = new Inet4Address(); mapNametoAddress(mcAddress,rtAddressIPv4); interface.join(rtAddressIPv4); case "sip": //... map logical ID to routing address SIPAddress rtAddressSIP = new SIPAddress(); mapNametoAddress(mcAddress,rtAddressSIP); interface.join(rtAddressSIP); case "dht": //... map logical ID to routing address DHTAddress rtAddressDHT = new DHTAddress(); mapNametoAddress(mcAddress,rtAddressDHT); interface.join(rtAddressDHT); //... } } } Appendix B. Deployment Use Cases for Hybrid Multicast This section describes the application of the defined API to implement an IMG. Waehlisch, et al. Expires January 13, 2011 [Page 20] Internet-Draft Common Mcast API July 2010 B.1. DVMRP The following procedure describes a transparent mapping of a DVMRP- based any source multicast service to another many-to-many multicast technology. An arbitrary DVMRP [RFC1075] router will not be informed about new receivers, but will learn about new sources immediately. The concept of DVMRP does not provide any central multicast instance. Thus, the IMG can be placed anywhere inside the multicast region, but requires a DVMRP neighbor connectivity. The group communication stack used by the IMG is enhanced by a DVMRP implementation. New sources in the underlay will be advertised based on the DVMRP flooding mechanism and received by the IMG. Based on this the updateSender() call is triggered. The relay agent initiates a corresponding join in the native network and forwards the received source data towards the overlay routing protocol. Depending on the group states, the data will be distributed to overlay peers. DVMRP establishes source specific multicast trees. Therefore, a graft message is only visible for DVMRP routers on the path from the new receiver subnet to the source, but in general not for an IMG. To overcome this problem, data of multicast senders will be flooded in the overlay as well as in the underlay. Hence, an IMG has to initiate an all-group join to the overlay using the namespace extension of the API. Each IMG is initially required to forward the received overlay data to the underlay, independent of native multicast receivers. Subsequent prunes may limit unwanted data distribution thereafter. B.2. PIM-SM The following procedure describes a transparent mapping of a PIM-SM- based any source multicast service to another many-to-many multicast technology. The Protocol Independent Multicast Sparse Mode (PIM-SM) [RFC4601] establishes rendezvous points (RP). These entities receive listener and source subscriptions of a domain. To be continuously updated, an IMG has to be co-located with a RP. Whenever PIM register messages are received, the IMG must signal internally a new multicast source using updateSender(). Subsequently, the IMG joins the group and a shared tree between the RP and the sources will be established, which may change to a source specific tree after a sufficient number of data has been delivered. Source traffic will be forwarded to the RP based on the IMG join, even if there are no further receivers in the native multicast domain. Designated routers of a PIM-domain send receiver subscriptions towards the PIM-SM RP. The reception of such Waehlisch, et al. Expires January 13, 2011 [Page 21] Internet-Draft Common Mcast API July 2010 messages invokes the updateListener() call at the IMG, which initiates a join towards the overlay routing protocol. Overlay multicast data arriving at the IMG will then transparently be forwarded in the underlay network and distributed through the RP instance. B.3. PIM-SSM The following procedure describes a transparent mapping of a PIM-SSM- based source specific multicast service to another one-to-many multicast technology. PIM Source Specific Multicast (PIM-SSM) is defined as part of PIM-SM and admits source specific joins (S,G) according to the source specific host group model [RFC4604]. A multicast distribution tree can be established without the assistance of a rendezvous point. Sources are not advertised within a PIM-SSM domain. Consequently, an IMG cannot anticipate the local join inside a sender domain and deliver a priori the multicast data to the overlay instance. If an IMG of a receiver domain initiates a group subscription via the overlay routing protocol, relaying multicast data fails, as data are not available at the overlay instance. The IMG instance of the receiver domain, thus, has to locate the IMG instance of the source domain to trigger the corresponding join. In the sense of PIM-SSM, the signaling should not be flooded in underlay and overlay. One solution could be to intercept the subscription at both, source and receiver sites: To monitor multicast receiver subscriptions (updateListener()) in the underlay, the IMG is placed on path towards the source, e.g., at a domain border router. This router intercepts join messages and extracts the unicast source address S, initializing an IMG specific join to S via regular unicast. Multicast data arriving at the IMG of the sender domain can be distributed via the overlay. Discovering the IMG of a multicast sender domain may be implemented analogously to AMT [I-D.ietf-mboned-auto-multicast] by anycast. Consequently, the source address S of the group (S,G) should be built based on an anycast prefix. The corresponding IMG anycast address for a source domain is then derived from the prefix of S. B.4. BIDIR-PIM The following procedure describes a transparent mapping of a BIDIR- PIM-based any source multicast service to another many-to-many multicast technology. Bidirectional PIM [RFC5015] is a variant of PIM-SM. In contrast to Waehlisch, et al. Expires January 13, 2011 [Page 22] Internet-Draft Common Mcast API July 2010 PIM-SM, the protocol pre-establishes bidirectional shared trees per group, connecting multicast sources and receivers. The rendezvous points are virtualized in BIDIR-PIM as an address to identify on-tree directions (up and down). However, routers with the best link towards the (virtualized) rendezvous point address are selected as designated forwarders for a link-local domain and represent the actual distribution tree. The IMG is to be placed at the RP-link, where the rendezvous point address is located. As source data in either cases will be transmitted to the rendezvous point address, the BIDIR-PIM instance of the IMG receives the data and can internally signal new senders towards the stack via updateSender(). The first receiver subscription for a new group within a BIDIR-PIM domain needs to be transmitted to the RP to establish the first branching point. Using the updateListener() invocation, an IMG will thereby be informed about group requests from its domain, which are then delegated to the overlay. Appendix C. Change Log The following changes have been made from draft-waehlisch-sam-common-api-02 1. Rename init() in createSocket(). 2. Cleanup code in "Practical Example of the API". 3. Editoral improvements. The following changes have been made from draft-waehlisch-sam-common-api-01 1. Document restructured to clarify the realm of document overview and specific contributions s.a. naming and addressing. 2. A clear separation of naming and addressing was drawn. Multicast URIs have been introduced. 3. Clarified and adapted the API calls. 4. Introduced Socket Option calls. 5. Deployment use cases moved to an appendix. 6. Simple programming example added. 7. Many editorial improvements. Waehlisch, et al. Expires January 13, 2011 [Page 23] Internet-Draft Common Mcast API July 2010 Authors' Addresses Matthias Waehlisch link-lab & FU Berlin Hoenower Str. 35 Berlin 10318 Germany Email: mw@link-lab.net URI: http://www.inf.fu-berlin.de/~waehl Thomas C. Schmidt HAW Hamburg Berliner Tor 7 Hamburg 20099 Germany Email: schmidt@informatik.haw-hamburg.de URI: http://inet.cpt.haw-hamburg.de/members/schmidt Stig Venaas cisco Systems Tasman Drive San Jose, CA 95134 USA Email: stig@cisco.com Waehlisch, et al. Expires January 13, 2011 [Page 24]