New error recovery structures for reliable multicasting

Sender-initiated reliable multicast protocols, based on the use of positive acknowledgments (ACKs), lead to an ACK implosion problem at the sender as the number of receivers increases. Briefly, the ACK implosion problem refers to the significant overhead incurred by the sending host due to the processing of ACKs from each receiver. A potential solution to this problem is to shift the burden of providing reliable data transfer to the receivers—thus resulting in a receiver-initiated multicast error control protocol based on the use of negative acknowledgments (NAKs). In this paper we determine the maximum throughputs of the sending and receiving hosts for generic sender-initiated and receiver-initiated protocols. We show that the receiver-initiated error control protocols provide substantially higher throughputs than their sender-initiated counterparts. We further demonstrate that the introduction of random delays prior to generating NAKs coupled with the multicasting of NAKs to all receivers has the potential for an additional substantial increase in the throughput of receiver-initiated error control protocols over sender-initiated protocols.

Sender-initiated reliable multicast protocols based on the use of positive acknowledgments (ACKs) can suffer performance degradation as the number of receivers increases. This degradation is due to the fact that the sender must bear much of the complexity associated with reliable data transfer (e.g., maintaining state information and timers for each of the receivers and responding to receivers' ACKs). A potential solution to this problem is to shift the burden of providing reliable data transfer to the receivers-thus resulting in receiver-initiated multicast error control protocols based on the use of negative acknowledgments (NAKs). We determine the maximum throughputs for generic sender-initiated and receiver-initiated protocols for two classes of applications: (1) one-many applications where one participant sends data to a set of receivers and (2) many-many applications where all participants simultaneously send and receive data to/from each other. We show that a receiver-initiated error control protocol which requires receivers to transmit NAKs point-to-point to the sender provides higher throughput than a sender-initiated counterpart for both classes of applications. We further demonstrate that, in the case of a one many application, replacing point-to-point transfer of NAKs with multicasting of NAKs coupled with a random backoff procedure provides a substantial additional increase in the throughput of a receiver-initiated error control protocol over a sender-initiated protocol. We also find, however, that such a modification leads to a throughput degradation in the case of many-many applications.

We analyze the maximum throughput that known classes of reliable multicast transport protocols can attain. A new taxonomy of reliable multicast transport protocols is introduced based on the premise that the mechanisms used to release data at the source after correct delivery should be decoupled from the mechanisms used to pace the transmission of data and to effect error recovery. Receiver-initiated protocols, which are based entirely on negative acknowledgments (NAKS) sent from the receivers to the sender, have been proposed to avoid the implosion of acknowledgements (ACKS) to the source. However, these protocols are shown to require infinite buffers in order to prevent deadlocks. Two other solutions to the ACK-implosion problem are tree-based protocols and ring-based protocols. The first organize the receivers in a tree and send ACKS along the tree; the latter send ACKS to the sender along a ring of receivers. These two classes of protocols are shown to operate correctly with finite buffers. It is shown that tree-based protocols constitute the most scalable class of all reliable multicast protocols proposed to date.

This document describes the messages and procedures of the Negative- acknowledgment (NACK) Oriented Reliable Multicast (NORM) protocol. This protocol is designed to provide end-to-end reliable transport of bulk data objects or streams over generic IP multicast routing and forwarding services. NORM uses selective, negative acknowledgment mechanism for transport reliability and offers additional protocol mechanisms to allow for operation with minimal a priori coordination among senders and receivers. A congestion control scheme is specified to allow the NORM protocol to fairly share available network bandwidth with other transport protocols such as Transmission Control Protocol (TCP). It is capable of operating with both reciprocal multicast routing among senders and receivers and with asymmetric connectivity (possibly unicast return path) between the senders and receivers. The protocol offers number of features to allow different types of applications or possibly other higher level transport protocols to utilize its service in different ways. The protocol leverages the use of FEC-based repair and other IETF reliable multicast transport (RMT) building blocks in its design. This memo defines an Experimental Protocol for the Internet community.

Tree-based reliable multicast protocols provide scalability by distributing error-recovery tasks among several repair nodes. These repair nodes integrate the status information of several receiver nodes and perform local error recovery for these nodes using the data stored in their buffers. We propose a buffer management scheme that uses both positive and negative acknowledgments to manage these buffers in an efficient manner. Under our scheme, receiver nodes send negative acknowledgments to repair nodes to request packet retransmissions. At infrequent intervals, they also send positive acknowledgements to indicate which packets can be safely discarded from the buffer of their repair node. Our scheme reduces delay in error recovery, because the packets requested from the repair nodes are always available in their buffers. It achieves this goal without increasing the server workload because (a) each receiver node only sends infrequent positive acknowledgments and (b) their sending times are randomized among all the receiver nodes. We also show how our scheme can be extended to provide full flow control and eliminate buffer overflows.

In current IEEE 802.11 WLAN, the unicast provides a reliable way of communication thanks to the use of acknowledgement feedbacks. As to the multicast, it suffers from unreliability and inefficiency. Recently many protocols have been designed for 802.11 such as Leader Based Protocol (LBP), to provide a reliable multicast transport. Yet no optimal solution has been proposed. In this paper we present Reliable PLCP-based Multicast Protocol (RPMP), a new reliable multicast protocol as an extension to the 802.11g and 802.11a. RPMP achieves reliability through the use of Negative Acknowledgements (NAK). We reduce the transmission overhead of our protocol, compared to other NAK-based proposals, by adding one additional OFDM symbol in the Physical Layer Convergence Procedure (PLCP) header of the multicast frame instead of using additional control frames. Further we show, based on our simulation results that the delivery ratio of RPMP remains at 100% in a lossy channel when it falls down to 50% with the standard. We also show that the efficiency of RPMP is much more enhanced than that of LBP.

Feedback implosion is one of the crucial issues related to the scalability of reliable multicast protocols. Generally speaking, in timer-based solutions, when a receiver needs to send feedback, it multicasts the feedback to all receivers early enough, hence suppressing others from returning feedback in response to the same event. In this paper we present an effective end-to-end negative acknowledgment (NACK) control algorithm which could solve the problem caused by correlative packet loss and independent packet loss among receivers.

Multicast in wireless sensor networks (WSNs) is an efficient way to spread the same data to multiple sensor nodes. It becomes more effective due to the broadcast nature of wireless link, where a message transmitted from one source is inherently received by all one-hop receivers, and therefore, there is no need to transmit the message one by one. Reliable multicast in WSNs is desirable for critical tasks like code updation and query based data collection. The erroneous nature of wireless medium coupled with limited resource of sensor nodes, makes the design of reliable multicast protocol a challenging task. In this work, we propose a time division multiple access (TDMA) based energy aware media access and control (TEA-MAC) protocol for reliable multicast in WSNs. The TDMA eliminates collisions, overhearing and idle listening, which are the main sources of reliability degradation and energy consumption. Furthermore, the proposed protocol is parametric in the sense that it can be used to trade-off reliability with energy and delay as per the requirement of the underlying applications. The performance of TEA-MAC has been evaluated by simulating it using Castalia network simulator. Simulation results show that TEA-MAC is able to considerably improve the performance of multicast communication in WSNs.

A reliable multicast protocol enables a process to multicast a message to a group of processes in a way that ensures that all honest destination-group members receive the same message, even if some group members and the multicast initiator are maliciously faulty. Reliable multicast has been shown to be useful for building multiparty cryptographic protocols and secure distributed services. We present a high-throughput reliable multicast protocol that tolerates the malicious behavior of up to fewer than one-third of the group members. Our protocol achieves high-throughput using a novel technique for chaining multicasts, whereby the cost of ensuring agreement on each multicast message is amortized over many multicasts. This is coupled with a novel flow-control mechanism that yields low multicast latency.

Tree-based reliable multicast protocols are well-known for being scalable for one-to-many sessions, but their behaviour in terms of throughput and bandwidth requirements has not been identifed for many-to-many sessions. In this paper, existing tree-based reliable multicast protocols are categorised into four classes according to their feedback/retransmission mechanisms. Analysing and comparing them using a new spatial multicast loss model that considers the correlation of packet loss events can yield realistic analysis results. The analysis reveals that for many-to-many sessions, tree-based protocols with unicast NACK, unicast retransmission, and periodic polling are most scalable with respect to throughput and network bandwidth for practical session sizes. The result is contrary to the one-to-many case and it is shown that the reason is that reducing the sender's processing time is a key factor for scaling one-to-many reliable multicast, whereas reducing the receiver's processing time is far more important factor for scalability of many-to-many reliable multicasts.

Even though tree-based reliable multicast protocols are known to be most scalable for one-to-many sessions, there is still an open question whether these protocols are also scalable for many-to-many sessions. In this paper, we analyze and compare two promising multicast protocols - the receiver-initiated protocol with NACK suppression and the tree-based protocol - using a new spatial loss model. The proposed model considers the correlation of packet loss events for more realistic analysis unlike the previous work. The analysis results show that the tree-based protocol achieves much higher throughput than the receiver-initiated protocol for a many-to-many session as the number of participants in the session becomes larger.

In this paper we examine the impact of widely spread multicast groups on the performance of reliable multicast protocols. In a brief analysis we show that transmission cost for reliable multicast increases rapidly with the distance between retransmitting and receiving hosts. Since this distance is not considered by existing protocols, which are based on retransmissions originated at the sender or receiver, the performance often is rather poor and a new error recovery concept has to be developed. Our approach. the Scalable and Reliable Multicast Transport protocol (SRMT), allows retransmissions by extended multicast routers to limit the path length for error recovery. Moreover, the retransmission load can be further reduced by an XOR combination of packets. SRMT is defined as an overlay network model and therefore can be applied to any existing multicast protocol.

Multicasting plays an important role in internet networks. Supporting wavelength division multiplexed (WDM) multicasting in an IP over WDM network poses interesting problems because some WDM switches may be incapable of switching an incoming signal to more than one output interface. Although some multicast applications, such as audio/video conferencing can tolerate packet error or loss, other applications such as one-to-many file transfer and military applications do not. Hence, an inevitable need for reliable multicasting arises. The reliable multicast protocol ensures the eventual delivery of multicast data to all multicast group members. The reliable multicast is receiver initiated NACK-based and it makes use of feedback suppression in order to avoid NACK and retransmission implosion. The loss recovery burden is distributed over the multicast group members in order to reduce recovery latency and end-to-end delay. The proposed protocol is evaluated in terms of performance metrics for an IP/WDM optical network which will be the candidate for the next generation internet networks.

This paper introduces a reliable multicast transport protocol RCCMP (reliable congestion controlled multicast protocol) that has been designed to be simple, scalable, reliable and TCP-friendly. The congestion control is a central part of the protocol, where the feedback of the worst receiver is used to control a transmission window in a TCP-like fashion. The scalability issue is addressed with an exponential timers scheme, that is also used to estimate the number of receivers involved in the communication. The protocol neither needs support from network elements nor maintains state information dependent of the number of receivers. The paper presents a number of simulation results on its performance. Besides, some design choices are evaluated.

Forward error correction (FEC) has been proposed as a technique for implementing efficient reliable multicast (RM). However, FEC incurs costs in encode/decode delay and implementation complexity. How much benefit is provided relative to these costs and how dependent is the benefit on the specific RM protocol? In this paper, we evaluate the benefits of FEC for RM, considering both proactive and reactive use with three RM recovery techniques: duplicate avoidance, limited scope multicast and subcast. Our simulation-based results indicate that FEC provides little benefit for an efficient RM protocol like OTERS and introduces extra delay for multi-point streaming data applications.