Negative Acknowledgement Research Articles

Optimal retrial and timeout strategies for accessing network resources

The notion of timeout (i.e., the maximal time to wait before retrying an action) occurs in many networking contexts. Use of timeouts is encountered especially in large-scale networks, where negative acknowledgments (NACKs) on failures have significantly higher delays than positive acknowledgments (ACKs) and frequently are not employed at all. Selection of a proper timeout involves a tradeoff between waiting too long and loading the network needlessly by waiting too little. The common approach is to set the timeout to a large value, such that, unless the action fails, it is acknowledged within the timeout duration with a high probability. This approach leads to overly long, far from optimal, timeouts. Our quantitative approach has the purpose of computing and studying the optimal timeout strategy. The tradeoff is modeled by introducing a "cost" per unit time (until success) and a "cost" per repeated attempt. The optimal strategy is then defined as one that a selfish user would follow to minimize its expected cost. We discuss various practical interpretations of these costs. We then derive formulas for the optimal timeout values and study some of their fundamental properties. We identify the worthwhile conditions for making parallel attempts from the outset. We also demonstrate a striking property of positive feedback and study the interaction resulting when many users selfishly apply the optimal timeout strategy; we use a noncooperative game model and show that it suffers from an inherent instability problem. Some implications of these results on network design are discussed.

Dominating sets and neighbor elimination-based broadcasting algorithms in wireless networks

In a multihop wireless network, each node has a transmission radius and is able to send a message to all of its neighbors that are located within the radius. In a broadcasting task, a source node sends the same message to all the nodes in the network. In this paper, we propose to significantly reduce or eliminate the communication overhead of a broadcasting task by applying the concept of localized dominating sets. Their maintenance does not require any communication overhead in addition to maintaining positions of neighboring nodes. Retransmissions by only internal nodes in a dominating set is sufficient for reliable broadcasting. Existing dominating sets are improved by using node degrees instead of their ids as primary keys. We also propose to eliminate neighbors that already received the message and rebroadcast only if the list of neighbors that might need the message is nonempty. A retransmission after negative acknowledgements scheme is also described. The important features of the proposed algorithms are their reliability (reaching all nodes in the absence of message collisions), significant rebroadcast savings, and their localized and parameterless behavior. The reduction in communication overhead for the broadcasting task is measured experimentally. Dominating set based broadcasting, enhanced by a neighbor elimination scheme and highest degree key, provides reliable broadcast with /spl les/53 percent of node retransmissions (on random unit graphs with 100 nodes) for all average degrees d. Critical d is around 4, with <48 percent for /spl les/3, /spl les/40 percent for d/spl ges/10, and /spl les/20 percent for d/spl ges/25. The proposed methods are better than existing ones in all considered aspects: reliability, rebroadcast savings, and maintenance communication overhead. In particular, the cluster structure is inefficient for broadcasting because of considerable communication overhead for maintaining the structure and is also inferior in terms of rebroadcast savings.

An Efficient ARQ Protocol for Adaptive Error Control over Time-Varying Channels

This paper investigates a simple and efficient stop-and-wait (SW) automatic repeat-request (ARQ) scheme with adaptive error control. In this scheme, the channel state information (CSI) is extracted by monitoring the contiguous positive acknowledgment (ACK) or negative acknowledgment (NAK) messages. Exploiting this CSI, we adapt the coding strategy to the changes in the channel condition, and thus improve the throughput efficiency. In order to facilitate the throughput analysis and parameters optimization, we model the adaptive system with a Markov chain. Using this analytical model and assuming a static channel, an exact throughput expression for the adaptive ARQ protocol is derived and suboptimal adaptive system parameters are obtained. These design parameters are applied to the adaptive system in a typical time-varying mobile radio channel characterized by Rayleigh multipath fading on top of lognormal shadowing. The throughput performance of the proposed adaptive SW-ARQ scheme in such a time-varying fading channel is evaluated by computer simulation. For slow fading channels, the proposed adaptive system can track the channel variations very well, hence much throughput improvement can be achieved over conventional nonadaptive SW-ARQ schemes for almost all SNR values considered. The simulation results also confirm the applicability of the adaptive system parameters, so-obtained by the throughput analysis in static channel, to a time-varying mobile radio channel.

Reliable Multicast in Multi-Access Wireless LANs

Multicast is an efficient paradigm for transmitting data from a sender to a group of receivers. In this paper, we focus on multicast in single channel multi-access wireless local area networks (LANs) comprising several small cells. In such a system, a receiver cannot correctly receive a packet if two or more packets are sent to it at the same time, because the ackets "collide". Therefore, one has to ensure that only one node sends at a time. We look at two important issues.First, we consider the problem of the sender acquiring the multi-access channel for multicast transmission. Second, for reliable multicast in each cell of the wireless LAN, we examine ARQ-based approaches. The second issue is important because the wireless link error rates can be very high. We present a new approach to overcome the problem of feedback collision in single channel multi-access wireless LANs, both for the purpose of acquiring the channel and for reliability. Our approach involves the election of one of the multicast group members (receivers) as a "leader" or representative for the purpose of sending feedback to the sender. For reliable multicast, on erroneous reception of a packet, the leader does not send an acknowledgment, prompting a retransmission. On erroneous reception of the packet at receivers other than the leader, our protocol allows negative acknowledgments from these receivers to collide with the acknowledgment from the leader,thus destroying the acknowledgment and prompting the sender to retransmit the packet. Using analytical models, we demonstrate that the leader-based protocol exhibits higher throughput in comparison to two other protocols which use traditional delayed feedback-based probabilistic methods. Last, we present a simple scheme for leader election.

Hybrid ARQ and optimal signal—to—interference ratio assignment for high—quality data transmission in DS—CDMA

AbstractCombined error correction and detection techniques, or hybrid automatic—repeat—request (ARQ) schemes with negative acknowledgment are considered for highly reliable reverse link data transmission in direct sequence code division multiple access (DS—CDMA) personal communication systems. The proposed selective repeat hybrid ARQ scheme employs an inner convolutional code for error correction and an outer shortened BCH code for error detection. Each negative acknowledgment message contains all packet sequence numbers that have been detected in error, and it is both error—correction and error—detection encoded. Accepted packet error rate and throughput are derived as a function of the error correction encoded frame error rate. An optimum signal—to—interference ratio (SIR) assignment maximizing the system's capacity is also found. A comprehensive simulation is conducted to evaluate performance of the data transmission system. Analysis and simulations show that by applying the proposed type I hybrid ARQ scheme with properly selected system parameters, virtually error free and highly efficient data transmission in CDMA personal communication systems is possible.

Precise and fast error tracking for error-resilient transmission of H.263 video

A precise error tracking scheme for robust transmission of real-time H.263 video is presented. By utilizing a feedback channel, the decoder reports the addresses of corrupted blocks induced by transmission errors back to the encoder. With these negative acknowledgments, the encoder can precisely calculate and track the propagated errors by examining the backward motion dependency for each pixel in the current encoding frame. With this precise tracking, the error-propagation effects can be terminated completely by INTRA refreshing the affected macroblocks. In addition, by utilizing the four-corner tracking approximation and the linear motion model, a fast algorithm is also developed to further reduce the computation and memory requirements. The simulations show that both schemes yield significant video quality improvements in error-prone environments. The advantages of the low memory requirement and the low computation complexity are particularly suitable for real time implementation.

Scalable reliable multicast using multiple multicast channels

We examine an approach for providing reliable, scalable multicast communication, involving the use of multiple multicast channels for reducing receiver processing costs and reducing network bandwidth consumption in a multicast session. In this approach a single multicast channel is used for the original transmission of packets. Retransmissions of packets are done on separate multicast channels, which receivers dynamically join and leave. We first show that protocols using an infinite number of multicast channels incur much less processing overhead at the receivers compared to protocols that use only a single multicast channel. This is due to the fact that receivers do not receive retransmissions of packets they have already received correctly. Next, we derive the number of unwanted redundant packets at a receiver due to using only a finite number of multicast channels, for a specific negative acknowledgment (NAK)-based protocol. We then explore the minimum number of multicast channels required to keep the cost of processing unwanted packets to a sufficiently low value. For an application consisting of a single sender transmitting reliably to many receivers we find that only a small number of multicast channels are required for a wide range of system parameters. In the case of an application where all participants simultaneously act as both senders and receivers a moderate number of multicast channels is needed. Finally, we present two mechanisms for implementing multiple multicast channels, one using multiple IP multicast groups and the other using additional router support for selective packet forwarding. We discuss the impact of both mechanisms on performance in terms of end-host and network resources.

Error-resilient video transmission using long-term memory motion-compensated prediction

Long-term memory prediction extends the spatial displacement vector utilized in hybrid video coding by a variable time delay, permitting the use of more than one reference frame for motion compensation. This extension leads to improved rate-distortion performance. However, motion compensation in combination with transmission errors leads to temporal error propagation that occurs when the reference frames at the coder and decoder differ. In this paper, we present a framework that incorporates an estimated error into rate-constrained motion estimation and mode decision. Experimental results with a Rayleigh fading channel show that long-term memory prediction significantly outperforms the single-frame prediction H.263-based anchor. When a feedback channel is available, the decoder can inform the encoder about successful or unsuccessful transmission events by sending positive (ACK) or negative (NACK) acknowledgments. This information is utilized for updating the error estimates at the encoder. Similar concepts, such as the ACK and NACK mode known from the H.263 standard, are unified into a general framework providing superior transmission performance.

Scalable feedback for large groups

We investigate the scalability of feedback in multicast communication and propose a new method of probabilistic feedback based on exponentially distributed timers. By analysis and simulation for up to 10/sup 6/ receivers, we show that feedback implosion is avoided while feedback latency is low. The mechanism is robust against the loss of feedback messages and works well in case of homogeneous and heterogeneous delays. We apply the feedback mechanism to reliable multicast and compare it to existing timer-based feedback schemes. Our mechanism achieves lower negative acknowledgment character (NAK) latency for the same performance in terms of NAK suppression. No topological information of the network is used, and data delivery is the only support required from the network. The mechanism adapts to a dynamic number of receivers and leads to a stable performance for implosion avoidance and feedback latency.

A comparison of reliable multicast protocols

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.

Total acknowledgements (extended abstract)

End-to-end data transport protocols have two main functions: error recovery and congestion control. The information required by the sender to perform these functions is provided by acknowledgements (ACKs) from the receiver. The Internet transport protocol, TCP/IP, uses cumulative acknowledgements (CACKs), which provide a robust but minimal mechanism for error recovery which is inadequate for heterogeneous networks with random loss. Furthermore, TCP's congestion control mechanism is based on counting ACKs, and is therefore vulnerable to loss of ACKs on the reverse path, particularly when the latter may be slower than the forward path, as in asymmetric networks. The contributions of this paper are as follows:(a) We show that a simple enhancement of CACK provides sufficient information for end-to-end congestion control . We term this ACK format total ACKs (TACKs).(b) We devise a novel ACK format that uses TACKs for congestion control, and negative ACKs (NACKs) for efficient error recovery. Typically, the main concern with NACKs is that of robustness to ACK loss, and we address this using an implementation that provides enough redundancy to provide such robustness.(c) We use the TACK+NACK acknowledgement format as the basis for a new transport protocol that provides efficient error recovery and dynamic congestion control. The protocol provides large performance gains over TCP in an environment with random loss, and is robust against loss of ACKs in the reverse path. In particular, the protocol gives high throughput upto a designed level of random loss, independent of the bandwidth-delay product. This is in contrast to TCP, whose throughput deteriorates drastically if the random loss probability is higher than the inverse square of the bandwidth-delay product.

Asymptotic behavior of global recovery in SRM

The development and deployment of a large-scale, wide-area multicast infrastructure in the Internet has enabled a new family of multi-party, collaborative applications. Several of these applications, such as multimedia slide shows, shared whiteboards, and large-scale multi-player games, require reliable multicast transport, yet the underlying multicast infrastructure provides only a best-effort delivery service. A difficult challenge in the design of efficient protocols that provide reliable service on top of the best-effort multicast service is to maintain acceptable performance as the protocol scales to very large session sizes distributed across the wide area. The Scalable, Reliable Multicast (SRM) protocol [6] is a receiver-driven scheme based on negative acknowledgments (NACKs) reliable multicast protocol that uses randomized timers to limit the amount of protocol overhead in the face of large multicast groups, but the behavior of SRM at extremely large scales is not well-understood.In this paper, we use analysis and simulation to investigate the scaling behavior of global loss recovery in SRM. We study the protocol's control-traffic overhead as a function of group size for various topologies and protocol parameters, on a set of simple, representative topologies --- the cone (a variant of a clique), the linear chain, and the binary tree. We find that this overhead, as a function of group size, depends strongly on the topology: for the cone, it is always linear; for the chain, it is between constant and logarithmic; and for the tree, it is between constant and linear.

An evaluation of flow control in group communication

Group communication services have been successfully used to construct applications with high availability, dependability, and real-time responsiveness requirements. Flow control techniques enable group members to manage their local buffers, which they use to temporarily store multicast updates. Despite buffer overflow being one of the main causes of process failures, flow control has not been studied much in the literature. We study different flow control techniques used in some of the group communication services and present two generic flow control techniques: a conservative and an optimistic technique. All existing flow control techniques for group communication can be classified as either conservative or optimistic. We then present discrete event simulation results that compare the effect of these two generic flow control techniques on the performance of two, different atomic multicast protocols, a positive acknowledgment protocol and a negative acknowledgment protocol, under several different operating conditions. Based on the study of differed existing flow control techniques for group communication and the results obtained from the simulation experiment, we provide some design guidelines for the design and implementation of a suitable flow control technique for a given group communication service.

Design, analysis, and evaluation of an improved scheme for ATM burst-level admission control

Fast reservation protocols (FRP) have been under consideration for burst-level admission control and block transfer in both ATM LAN and WAN. In this paper we propose a modification to the FRP and the FRP/IT (Immediate Transmission). The resulting protocols, named MFRP (Modified FRP) and MFRP/IT (Modified FRP/IT), are based on bandwidth negotiation between the source and a fast server at the network. Initially, the source requests a desired rate and an acceptable minimum rate. If the network can support at least the minimum rate, it sends an acknowledgment with a granted rate, otherwise a negative acknowledgment is sent. The new mechanism thus uses one extra parameter in both the request and the acknowledgment, but requires no more complicated control mechanism at the network server than the original FRP and FRP/IT protocols. We present mathematical analysis of the new scheme in terms of blocking probability, delay, and wasted bandwidth in unsuccessful multipoint requests. Using computer simulation, the performance of the new protocols are also evaluated and compared with existing protocols: the original FRP, the Adaptive FRP (AFRP), and the FRP/IT. The simulation environment includes both single-stage and multi-stage ATM LAN and WAN for single-rate and multi-rate traffic streams. Simulation results show that the new protocols significantly reduce blocking probability, and, as a result, improve network throughput and message delay; which agrees with what the analysis suggests. Applications of the proposed schemes to block transfer in ATM networks and traffic control in wireless ATM networks are also discussed.

Scalable reliable multicast using multiple multicast groups

We examine an approach for providing reliable, scalable multicast communication, using multiple multicast groups for reducing receiver processing costs in a multicast session. In this approach a single multicast group is used for the original transmission of packets. Retransmissions of packets are done to separate multicast groups, which receivers dynamically join or leave. We first show that by using an infinite number of multicast groups, processing overhead at the receivers are substantially reduced. Next, we show that, for a specific negative acknowledgment (NAK)-based protocol, most of this reduction can be obtained by using only a small number of multicast groups for a wide range of system parameters. Finally, we present a local filtering scheme for minimizing join/leave signaling when multiple multicast groups are used.

A comparison of sender-initiated and receiver-initiated reliable multicast 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.

Standard compatible extension of H.263 for robust video transmission in mobile environments

In this paper we address the problem of robust video transmission in error prone environments. The approach is compatible with the ITU-T video coding standard H.263. Fading situations in mobile networks are tolerated and the image quality degradation due to spatio-temporal error propagation is minimized utilizing a feedback channel between transmitter and receiver carrying acknowledgment information. In a first step, corrupted group of blocks (GOB's) are concealed to avoid annoying artifacts caused by decoding of an erroneous bit stream. The GOB and the corresponding frame number are reported to the transmitter via the back channel. The encoder evaluates the negative acknowledgments and reconstructs the spatial and temporal error propagation. A low complexity algorithm for real-time reconstruction of spatio-temporal error propagation is described in detail. Rapid error recovery is achieved by INTRA refreshing image regions (macroblocks) bearing visible distortion. The feedback channel method does not introduce additional delay and is particularly relevant for real-time conversational services in mobile networks. Experimental results with bursty bit error sequences simulating a Digital European Cordless Telephony (DECT) channel are presented with different combinations of forward error correction (FEC), automatic repeat on request (ARQ), and the proposed error compensation technique, Compared to the case where FEC and ARQ are used for error correction, a gain of up to 3 dB peak signal-to-noise ratio (PSNR) is observed if error compensation is employed additionally.

Reliability considerations of a selective-repeat ARQ policy for a data communication system

This paper considers the following selective-repeat ARQ (automatic-repeat-request) policy which is mainly used in a data communication system: We transmit a block of data successively to a receiver. A negative (NAK) or positive (ACK) acknowledgement is returned from a receiver, depending on whether errors of data have occurred or not. When we have received NAK, we retransmit the erroneous block, otherwise we continue to send new blocks waiting for transmission. The expected numbers of ACK's and retransmitted blocks and the mean time until the first successive N + 1 NAK's are derived. Using these results, the optimal numbers N ∗ which minimize the mean time per successful blocks and the mean loss time in the mean time are discussed.

A comparison of sender-initiated and receiver-initiated reliable multicast protocols

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.

Trans: a reliable broadcast protocol

Trans is a novel reliable broadcast protocol for the data-link layer of the ISO protocol hierarchy. The protocol exploits the broadcast nature of the physical communication media typically used in local-area networks. A combination of positive and negative acknowledgment strategies with transitivity of positive acknowledgments provides reliable operation without requiring a separate acknowledgment from every recipient of a message frame. Trans achieves reliable communication despite a noisy communication medium and processor fail-stop, omission and timing faults. Multicast, rather than fully broadcast, communication is readily obtained by operating several subnetworks over the same local-area network or, alternatively, by including a destination address list in the header of each broadcast frame.