The IP multicast model allows scalable and efficient multi-party communication, particularly for groups of large size. However, deployment of IP multicast requires substantial infrastructure modifications and is hampered by a host of unresolved open problems. To circumvent this situation, we have designed and implemented ALMI, an application level group communication middleware, which allows accelerated application deployment and simplified network configuration, without the need of network infrastructure support. ALMI is tailored toward support of multicast groups of relatively small size (several I Os of members) with many to many semantics. Session participants are connected via a vir- tual multicast tree, which consists of unicast connections between end hosts and is formed as a minimum spanning tree (MST) using application-specific performance metric. Using simulation, we show that the performance penalties, introduced by this shift of multicast to end systems, is a relatively small increase in traffic load and that ALMI multicast trees approach the efficiency of IP multicast trees. We have also implemented ALMi as a Java based middleware package and performed experiments over the Internet. Experimental results show that ALMI is able to cope with network dynamics and keep the mul- ticast tree efficient.

Without a doubt, multicast communication---the one-to-manyormany-to-many delivery of data---has become a hot topic. It is of interest in the research community, among standards groups, and to network service providers. For all the attention multicast has received, there are still issues that have not been completely resolved. One result is that protocols are still evolving and some standards are not yet finished. From a deployment perspective, the lackof standards has slowed progress, but efforts to deploymulticast as an experimental service are in fact gaining momentum. The question nowishow long it will be before multicast becomes a true Internet service. The goal of this paper is to describe the past, present, and future of multicast.

Multicast services can be provided either as a basic network service or as an application-layer service. Higher level multicast implementations often provide more sophisticated features, and can provide multicast services, where no network layer support is available. Overlay multicast networks offer an intermediate option, potentially combining the flexibility and advanced features of application layer multicast with the greater efficiency of network layer multicast. Overlay multicast networks play an important role in the Internet. Indeed, since Internet Service Providers have been slow to enable IP multicast in their networks, Internet multicast is only widely available as an overlay service. This paper introduces several routing algorithms that are suitable for overlay multicast networks and evaluates their performance. The algorithms seek to optimize the endto -end delay and the interface bandwidth usage at the routing sites within the overlay network. The interface bandwidth is typically a key resource for an overlay network provider, and needs to be carefully managed in order to maximize the number of sessions that can be served. The simultaneous optimization of both delay and bandwidth is an NP-hard problem. We propose several heuristic algorithms and simulate their performance under various traffic conditions and on various network topologies.

With the growth and acceptance of the Internet, there has been increased interest in maintaining anonymity in the network. This paper presents a new protocol for initiator anonymity called Hordes, which uses forwarding mechanisms similar to those used in previous protocols for sending data, but is the first protocol to make use of the anonymity inherent in multicast routing to receive data. We show this results in shorter transmission latencies and requires less work of the protocol participants, in terms of the messages processed. We also present a comparison of the security and anonymity of Hordes with previous protocols, using the first quantitative definition of anonymity and unlinkability. Our analysis shows that Hordes provides anonymity in a degree similar to that of Crowds and Onion Routing. We find that Onion Routing best maintains anonymity of the three protocols examined, but also that Hordes has numerous performance advantages.

Multicast routing enables efficient data distribution to mul-tiple recipients. However, existing work has concentrated on extending single-domain techniques to wide-area networks, rather than providing mechanisms to realize inter-domain multicast on a global scale in the Internet. We describe an architecture for inter-domain multicast routing that consists of two complementary protocols. The Multicast Address-Set Claim (MASC) protocol forms the basis for a hierarchical address allocation architecture. It dynamically allocates to domains multicast address ranges from which groups initiated in the domain get their mul-tic & addresses. The Border-Gateway Multicast Protocol (BGMP), run by the border routers of a domain, constructs inter-domain bidirectional shared trees, while allowing any existing multicast routing protocol to be used within in-dividual domains. The resulting shared tree for a group is rooted at the domain whose address range covers the group’s address; this domain is typically the group initiator’s do-main. We demonstrate the feasibility and performance of these complementary protocols through simulation.

In this paper, we present, QoSMIC, a multicast protocol for the Internet that supports QoS-sensitive routing, and minimizes the importance of a priori configuration decisions (such ascore selection). The protocol is resource-efficient, robust, exible, and scalable. In addition, our protocol is provably loop-free. Our protocol starts with a resources-saving tree (Shared Tree) and individual receivers switch to a QoS-competitive tree (Source-Based Tree) when necessary. In both trees, the new destination is able to choose the most promising among several paths. An innovation is that we use dynamic routing information without relying on a link state exchange protocol to provide it. Our protocol limits the effect of preconfiguration decisions drastically, by separating the management from the data transfer functions; administrative routers are not necessarily part of the tree. This separation increases the robustness, and flexibility of the protocol. Furthermore, QoSMIC is able to adapt dynamically to the conditions of the network. The QoSMIC protocol introduces several new ideas that make it more exible than other protocols proposed to date. In fact, many of the other protocols, (such asYAM, PIM-SM, BGMP, CBT) can be seen as special cases of QoSMIC. This paper presents the motivation behind, and the design of QoSMIC, and provides both analytical and experimental results to support our claims.

Clusters of identical intermediate servers are often created to improve availability and robustness in many domains. The use of proxy servers for the WWW and of Rendezvous Points in multicast routing are two such situations. However, this approach can be inefficient if identical requests are received and processed by multiple servers. We present an analysis of this problem, and develop a method called the Highest Random Weight (HRW) Mapping that eliminates these difficulties. Given an object name and a set of servers, HRW maps a request to a server using the object name, rather than any a priori knowledge of server states. Since HRW always maps a given object name to the same server within a given cluster, it may be used locally at client sites to achieve consensus on objectserver mappings. We present an analysis of HRW and validate it with simulation results showing that it gives faster service times than traditional request allocation schemes such as round-robin or least-loaded, and...

Internet telephony offers the opportunity to design a global multimedia communications system that may eventually replace the existing telephony infrastructure. We describe the upper-layer protocol components that are specific to Internet telephony services: the Real-Time Transport Protocol (RTP) to carry voice and video data, and the Session Initiation Protocol (SIP) for signaling. We also mention some complementary protocols, including the Real Time Streaming Protocol (RTSP) for control of streaming media, and the Wide Area Service Discovery Protocol (WASRV) for location of telephony gateways. 1

Proposals for multicast security that have been published so far are complex, often require trust in network components or are inefficient. In this paper we propose a series of novel approaches for achieving scalable security in IP multicast, providing privacy and authentication on a group-wide basis. They can be employed to efficiently secure multi-party applications where members of highly dynamic groups of arbitrary size may participate. Supporting dynamic groups implies that newly joining members must not be able to understand past group communications, and that leaving members may not follow future communications. Key changes are required for all group members when a leave or join occurs, which poses a problem if groups are large. The algorithms presented here require no trust in third parties, support either centralized or fully distributed management of keying material, and have low complexity (O(log N) or less). This grants scalability even for large groups. Keywords: Secure multicasting, tree-based key distribution, multicast key distribution schemes, distributed key management 1

In this paper, we propose a Two-tier Overlay Multicast Architecture (TOMA) to provide scalable and e#cient multicast support for various group communication applications. In TOMA, Multicast Service Overlay Network (MSON) is advocated as the backbone service domain, while end users in the access domains form a number of small clusters, in which an application-layer multicast protocol is used for the communication between the clustered end users. TOMA is able to provide e#cient resource utilization with less control overhead, especially for large-scale applications. It also alleviates the state scalability problem and simplifies multicast tree construction and maintenance when there are large numbers of groups in the networks. Simulation studies are conducted and the results demonstrate the promising performance of TOMA.