Multicast (multipoint) distribution of video is an important component of many existing and future networked services. Today's Internet lacks support for quality of service (QoS) assurance which makes the transmission of real-time traffic (such as video) challenging. In addition, the heterogeneity of the Internet's transmission resources and end-systems makes it extremely difficult, if not impossible, to agree on acceptable traffic characteristics among multiple receivers of the same video stream. In this paper we survey techniques that have been proposed for transmitting video in this environment. These techniques generally involve adaptation of the video traffic carried over the network to match receiver requirements and network conditions. In addition to their applicability to the near-term capabilities of the Internet, they also are of relevance to a future, QoS-aware Internet environment because of the inevitable inaccuracies in traffic and resource reservation specifica...

In secure group communications, users of a group share a common group key. A key server sends the group key to authorized new users as well as performs group rekeying for group users whenever the key changes. In this paper, we investigate scalability issues of reliable group rekeying, and provide a performance analysis of our group key management system (called keygem) based upon the use of key trees. Instead of rekeying after each join or leave, we use periodic batch rekeying to improve scalability and alleviate out-of-sync problems among rekey messages as well as between rekey and data messages. Our analyses show that batch rekeying can achieve large performance gains. We then investigate reliable multicast of rekey messages using proactive FEC. We observe that rekey transport has an eventual reliability and a soft real-time requirement, and that the rekey workload has a sparseness property, that is, each group user only needs to receive a small fraction of the packets that carry a rekey message sent by the key server.

We derive estimators and bounds that drive probabilistic polling algorithms for the estimation of the session size, r, of any potentially large scale multicast session. We base our analysis upon a mapping of polling mechanisms to the problem of estimating the parameter r of the binomial (r, p) distribution. From the binomial model, we derive an inter- val estimator for r, and we characterize the tradeoff between the estimator 's quality and its overhead in a manner readily matched to application requirements. We derive other estimators and bounds that enable applications to treat as a tunable parameter the confidence that they will not exceed their overhead limits. We also suggest revised estimators and other improvements for the mechanisms proposed by Bolot, Turletti, and Wakeman [1], and Nonnenmacher and Biersack [2], [3], [4].

This paper focuses on the scalability of distributed protocols, in group communication systems, providing some form of guaranteed reliability. Examples include the virtual synchrony protocols for reliable group communication [1], scalable reliable multicast (SRM) [2], and reliable multicast transport protocol (RMTP) [3]. We argue that the usual architecture for supporting reliability exposes mechanisms of this sort to serious scalability problems

We present the design and specification of a protocol for scalable and reliable group rekeying together with performance evaluation results. The protocol is based upon the use of key trees for secure groups and periodic batch rekeying. At the beginning of each rekey interval, the key server sends a rekey message to all users consisting of encrypted new keys (encryptions, in short) carried in a sequence of packets. We present a scheme for identifying keys, encryptions, and users, and a key assignment algorithm that ensures that the encryptions needed by a user are in the same packet. Our protocol provides reliable delivery of new keys to all users eventually. It also attempts to deliver new keys to all users with a high probability by the end of the rekey interval. For each rekey message, the protocol runs in two steps: a multicast step followed by a unicast step. Proactive forward error correction (FEC) multicast is used to reduce delivery latency. Our experiments show that a small FEC block size can be used to reduce encoding time at the server without increasing server bandwidth overhead. Early transition to unicast, after at most two multicast rounds, further reduces the worst-case delivery latency as well as user bandwidth requirement. The key server adaptively adjusts the proactivity factor based upon past feedback information; our experiments show that the number of NACKs after a multicast round can be effectively controlled around a target number. Throughout the protocol design, we strive to minimize processing and bandwidth requirements for both the key server and users.

We examine the impact of the loss recovery mechanism on the performance of a reliable multicast protocol. Approaches for loss recovery in reliable multicast can be divided into two major classes: centralized (source-based) recovery and distributed recovery. For both classes we consider the state of the art: For centralized recovery, an integrated transport layer scheme using parity multicast for error recovery (hybrid ARQ type 2) as well as timer-based feedback suppression. For distributed recovery, a scheme with local data multicast retransmission and feedback processing in a local neighborhood. We also evaluate the benefits of combining the two approaches into distributed error recovery with local retransmissions using a type 2 hybrid ARQ scheme. The schemes are evaluated for up to 10 receivers under different loss scenarios with respect to network bandwidth usage and completion time of a reliable transfer. We show that using distributed error recovery with type 2 hybrid ARQ gives best performance in terms of bandwidth and latency. For networks, where local retransmission is not possible, we show that a centralized protocol based on type 2 hybrid ARQ comes close to the performance of a protocol with local retransmissions.

This paper addresses the efficient multicast dissemination of bulk data from a single server to numerous clients. The challenge is complex: a client may commence reception at arbitrary times, should receive as Httle "extra" data as possible until it can reconstruct the entire content, and should have flexibility in choosing the data rate. From the network perspective, the data rate over any link should be as close as possible to the maximum singie-downstream-cHent subscription rate. Also, the solution should scale to huge ties and numerous subscribers, and should withstand changing network conditions and packet loss. Finally, it should be friendly to other traffic. For any base client-subscription rate and integer factors thereof, we jointly achieve all these goals in a near-optimal way while using standard ("any k of N") block erasure-correcting codes. Scalability in file size is attained by breaking the fie into equisized groups of equisized blocks and separately encoding each group. The other properties are attained by a unique openloop layered multicast transmission schedule. Each client merely subscribes to one or more standard multicast groups. The need to use special, non-standard and possibly proprietary codes that scale well is thus obviated.

This work presents a thorough investigation of the structure of multicast trees cut from the Internet and power-law topologies. Based on both generated topologies and real Internet data, we characterize the structure of such trees and show that they obey the rank-degree power law; that most high degree tree nodes are concentrated in a low diameter neighborhood; and that the sub-tree size also obeys a power law.

We present a new reliable multicast protocol, called ARM for Adaptive Reliable Multicast. Our protocol integrates ARQ and FEC techniques. The objectives of ARM are (1) reduce the message overhead due to NACK requests, (2) reduce the amount of data transmission, and (3) reduce the time it takes for all receivers to receive the data intact (without loss). During data transmission, the sender periodically informs the receivers of the number of packets that are yet to be transmitted. Based on this information, each receiver predicts whether this amount is enough to recover its losses. Only if it is not enough, that the receiver requests the sender to encode additional redundant packets. Using ns simulations, we show the superiority of our hybrid ARQ-FEC protocol over the wellknown Scalable Reliable Multicast (SRM) protocol. 1 Introduction An increasing number of distributed applications involve one sender transmitting data to many recipients concurrently. Examples include distributed gam...

Existing reliable transport protocols for periodic information dissemination ignore application semantics while attempting to be 100% reliable. "Application Level Framing" (ALF) suggests that taking application semantics into account when designing transport protocols can result in performance that is highly optimized for the network. We apply this principle in designing a policy-based TUNAble quasi-reliable multicast protocol (TUNA) for periodic information dissemination. Specifically, TUNA is not constrained to guarantee full reliability, but allows the receiving application to selectively request retransmissions of lost portions of the data stream, based on user-level policies. TUNA uses statistical properties of the data stream to adaptively guide receivers in dynamically altering their reliability policies. This is particularly well matched for satellite systems, where end node to satellite bandwidth is limited, especially when shared by large community of end nodes. Our simulatio...