A performance model of deflection routing in multibuffer networkswith nonuniform traffic

Deflection routing can be used in networks whose stations have the same number of input and output links. Fixed length packets arrive synchronously on the station's input links at the beginning of time slots, and each packet is routed via the output link that offers the shortest path to its destination. Since the number of packet buffers at each output link is finite, the simultaneous contention of two packets for the last buffer of a common output link must be resolved by “deflecting” one of the packets to another output link. Thus, the deflection of a packet could result in the packet following a route that is not a shortest path. The potentially unbounded number of routes that a given packet can take makes analyzing the performance of such networks difficult. In particular, there are no analytical models that can analyze multibuffer deflection-routing networks with nonuniform traffic. Using independence assumptions, the authors develop a performance model of deflection routing that allows to estimate accurately and efficiently the mean transport time and throughput in a network that has any given two-connected topology, multiple buffers at each output port, and an arbitrary traffic matrix     

On throughput capacity of large-scale ad hoc networks with realistic buffer constraint

The problem of determining the throughput capacity of an ad hoc network is addressed. Previous studies mainly focused on the infinite buffer scenario, however, in this paper we consider a large-scale ad hoc network with a scalable traffic model, where each node has a buffer of size B packets, and explore its corresponding per node throughput performance. We first model each node as a G/G/1/B queuing system which incorporates the important wireless interference and medium access contention. With the help of this queuing model, we then explore the properties of the throughput upper bound for all scheduling schemes. Based on these properties, we further develop an analytical approach to derive the expressions of per node throughput capacity for the concerned buffer-limited ad hoc network. The results show that the cumulative effect of packet loss due to the per hop buffer overflowing will degrade the throughput performance, and the degradation is inversely proportional to the buffer size. Finally, we provide the specific scheduling schemes which enable the per node throughput to approach its upper bound, under both symmetrical and unsymmetrical network topologies.     

Analysis of a dual-receiver node with high fault tolerance forultrafast OTDM packet-switched shuffle networks

In this paper, we present a high-performance dual-receiver transparent optical node configuration suitable for two-connected multihop transparent optical networks operating at ultrafast bit rates. The steady-state behavior of optical shuffle networks is analyzed with this configuration and a minimum-loss node configuration. Deflection routing is employed as the means for contention resolution. Both analytical results and simulation results are presented on the network performance in terms of network throughput and delay. We also propose modified routing schemes for network fault tolerance. Applying both store-and-forward and deflection routing techniques, the networks can operate without packet loss in the presence of faults     

Routing strategies for maximizing throughput in LEO satellite networks

This paper develops routing and scheduling algorithms for packet transmission in a low Earth orbit satellite network with a limited number of transmitters and buffer space. We consider a packet switching satellite network, where time is slotted and the transmission time of each packet is fixed and equal to one time slot. Packets arrive at each satellite independently with a some probability during each time slot; their destination satellite is uniformly distributed. With a limited number of transmitters and buffer space on-board each satellite, contention for transmission inevitably occurs as multiple packets arrive at a satellite. First, we establish the stability region of the system in terms of the maximum admissible packet arrival rate that can possibly be supported. We then consider three transmission scheduling schemes for resolving these contentions: random packet win, where the winning packet is chosen at random; oldest packet win, where the packet that has traveled the longest distance wins the contention; and shortest hops win (SHW), where the packet closest to its destination wins the contention. We evaluate the performance of each of the schemes in terms of throughput. For a system without a buffer, the SHW scheme attains the highest throughput. However, when even limited buffer space is available, all three schemes achieve about the same throughput performance. Moreover, even with a buffer size of just a few packets the achieved throughput is close to that of the infinite buffer case.     

Deflection routing in slotted self-routing networks with arbitrary topology

A deflection routing scheme for small to medium size future all-optical networks with arbitrary topologies is proposed. The proposed scheme assumes only single-bit all-optical processing and no buffers. The primary output selection and the alternate output choices by a packet at each node are encoded in the packet header in order to reduce the signal processing requirement. Additional features such as priority and time-to-live fields have also been defined. The performance of the deflection routing scheme is studied using the AT&T North America OC-48 optical fiber network topology.     

Intelligent Dynamical Buffer Scheduling Mechanism for Intermittently Connected Mobile Network

According to the store-carry-forward packet transmission method, nodes can communicate with each other in intermittently connected mobile network flexibly. As can be seen, the successful transmission of packets is assisted by multiple copies injected into the network. Therefore, the limited buffer should be utilized reasonably in this situation. In this paper, an adaptive buffer scheduling mechanism is proposed with the aid of packet transmission status estimation. According to the activity degree of node and the number of packet copies, the status of packet transmission in the network can be evaluated. Furthermore, with the estimated outcome of packet redundancy, the packets in the buffer are scheduled dynamically. Numerical results show that the activity degree can be estimated accurately, especially when the networks become larger. The number of packet copies can be proved that it follows normal distribution. Compared with other buffer scheduling mechanisms, our mechanism displays better performance, e.g., the packet delivery probability is enhanced by 21–50 %, and the latency is reduced by 15–23 %.     

Packet loss and delay performance of feedback and feed-forwardarrayed-waveguide gratings-based optical packet switches with WDMinputs-outputs

This paper analyzes the packet loss and delay performance of an arrayed-waveguide-grating-based (AWG) optical packet switch developed within the EPSRC-funded project WASPNET (wavelength switched packet network). Two node designs are proposed based on feedback and feed-forward strategies, using sharing among multiple wavelengths to assist in contention resolution. The feedback configuration allows packet priority routing at the expense of using a larger AWG. An analytical framework has been established to compute the packet loss probability and delay under Bernoulli traffic, justified by simulation. A packet loss probability of less than 10^-9 was obtained with a buffer depth per wavelength of 10 for a switch size of 16 inputs-outputs, four wavelengths per input at a uniform Bernoulli traffic load of 0.8 per wavelength. The mean delay is less than 0.5 timeslots at the same buffer depth per wavelength     

Deflection routing in IP optical networks

This paper deals with optical packet switching in a full-IP transport network scenario. Given the technological limits of accomplishing packet buffering in the optical domain, deflection routing is here explored as an alternative technique for resolving packet contentions without buffering packets. Two different network topologies have been considered here, that is a regular six-node network with different connectivity factors and the classical NSF network. A limited amount of optical buffering is considered in the switching nodes that performs both input queuing and shared queuing of packets to be switched. The performance improvements that can be obtained by deflection routing have been evaluated considering different methods for choosing the alternative paths where to deflect packets that cannot be transmitted onto the shortest path to the addressed destination.     

On protective buffer policies

Studies buffering policies which provide different loss priorities to packets/cells, while preserving packet ordering (space priority disciplines). These policies are motivated by the possible presence, within the same connection, of packets with different loss probability requirements or guarantees, e.g., voice and video coders or rate control mechanisms. The main contribution of the paper is the identification and evaluation of buffering policies which preserve packet ordering and guarantee high priority packets performance (loss probability), irrespective of the traffic intensity and arrival patterns of low priority packets. Such policies are termed protective policies. The need for such policies arises from the difficulty to accurately characterize and size low priority traffic, which can generate large and unpredictable traffic variations over short periods of time. The authors review previously proposed buffer admission policies and determine if they satisfy such “protection” requirements. Furthermore, they also identify and design new policies, which for a given level of protection maximize low priority throughput     

BER-based Power Scheduling in Wireless Sensor Networks

In wireless sensor networks, there are many information exchanges between different terminals. In order to guarantee a good level of Quality of Service (QoS), the source node should be smart enough to pick a stable and good quality communication route in order to avoid any unnecessary packet loss. Due to the error-prone links in a wireless network, it is very likely that the transmitted packets over consecutive links may get corrupted or even lost. It is known that retransmissions will increase the overhead in the network, which in turns increase the total energy consumption during data transmission. In this paper, we focus on the Bit Error Rate (BER) during packet transmission and propose a power scheduling scheme to reduce the total energy consumption in the routing. Our approach controls the transmission power of each transmitter to achieve the minimum energy consumption for successful packet transmission. Considering the limited bandwidth resource, we also plan the multihop route while considering the BER and network load at the same time. The simulation results show that our approach can reduce the total energy consumption during data transmission.     

METANET: principles of an arbitrary topology LAN

The MetaNet is a scalable local area network (LAN) architecture with an arbitrary topology and a switch at each node (i.e., a switch based LAN). Its design provides on one hand a service in which any node can try to transmit asynchronously in a bursty manner without reservation as much as it can (as in traditional LAN), and on the other hand the network access and flow control ensure the following properties: (1) no packet loss due to congestion, (2) fair access to the network, (3) no deadlocks, and (4) self-routing with broadcast. The switching over this network requires only a (5) single buffer per input link. The MetaNet is asynchronous, distributed, and designed for transmission of fixed size cells or variable size packets. It can be viewed as a “general-topology buffer-insertion architecture with fairness,” thus generalizing the MetaRing architecture     

Adaptive per hop differentiation for end-to-end delay assurance in multihop wireless networks

As the rapid growth of smart hand-held devices, multihop wireless access networks have a lot of potential applications in a variety of fields in civilian and military environments. Many of these applications, such as realtime audio/video streaming, will require some form of end-to-end QoS assurance. In this paper, we present an adaptive per hop differentiation (APHD) scheme towards achieving end-to-end delay assurance in multihop wireless networks. Our scheme is based on EDCA technique which is proposed in 802.11e draft. In EDCA, data packets of different priorities will use different MAC contention parameter set, which translate into different delays. Our APHD scheme extends the capability of EDCA into multihop environment by taking end-to-end delay requirement into consideration at each intermediate hop. Following a cross-layer design approach, APHD is aimed to be a distributed and localized technique. Individual nodes keep track of the channel state independently without any intercommunication overhead. Data packets carry end-to-end delay requirement along with other important information in the packet header. At an intermediate node, based on data packet’s end-to-end requirement, its accumulative delay so far, and the current node’s channel status, APHD smartly adjusts data packet’s priority level in order to satisfy its end-to-end delay requirement. Simulation results show that APHD scheme can provide excellent end-to-end delay assurance while achieving much higher network utilization, compared to a pure EDCA scheme.     

Sharp approximate models of deflection routing in mesh networks

Deflection routing is a simple, decentralized, and adaptive method for routing data packets in communication networks. The focus of this work is on deflection routing in the Manhattan street network (a two-dimensional directed mesh), although the analytic approach should apply to any regular network. Two approximate performance models that give sharp estimates of the steady-state throughput and the average packet delay for packets admitted to the network are presented. The results of extensive simulation experiments are reported, which corroborate the models' predictions. The results show that deflection routing is very effective. Two measures of the merit of a network for deflection routing are its diameter and its deflection index. Networks are presented whose diameter and deflection index are near the optimal values     

CL-MAC: A Cross-Layer MAC protocol for heterogeneous Wireless Sensor Networks

In duty cycled MAC protocols, multi-packet, multi-flow and multi-hop traffic patterns experience significant latencies, which are partially due to duty cycling. Several cross-layer routing/MAC schemes have been proposed to mitigate this latency. However, they utilize routing information from a single flow and/or a single packet perspective, thus limiting their adaptation to varying traffic loads and patterns. In this paper, we propose a novel Cross-Layer MAC protocol (CL-MAC) for WSNs, to efficiently handle multi-packet, multi-hop and multi-flow traffic patterns while adapting to a wide range of traffic loads. CL-MAC’s scheduling is based on a unique structure of flow setup packets that efficiently utilize routing information to transmit multiple data packets over multiple multi-hop flows. Unlike other MAC protocols, supporting construction of multi-hop flows, CL-MAC considers all pending packets in the routing layer buffer and all flow setup requests from neighbors, when setting up a flow. This allows CL-MAC to make more informed scheduling decisions, reflecting the current network status, and dynamically optimize its scheduling mechanism accordingly. We evaluate CL-MAC through extensive ns-2 simulations and compare its performance to the state of the art, over various networks and for a wide variety of traffic loads and patterns. In all our experiments, CL-MAC substantially reduces end-to-end latency, increases delivery ratio while reducing the average energy consumed per packet delivered.     

New nodal design for high throughput data vortex optical interconnection network

This paper proposes a new three input nodal structure within the data vortex packet switched interconnection network. With additional optical switches, the modified architecture allows for two input packets in addition to a buffered packet to be processed simultaneously within a routing node. A much higher degree of parallel processing is allowed in comparison to previously proposed enhanced buffer node with two input processing or the original network node with single input processing. Unlike the previous contention prevention mechanism, the new network operates by introducing the packet blocking within the node if no exit path is available. This eliminates the traffic control signaling and the strict timing alignment associated with the routing paths which simplifies the overall network implementation. This study shows that both data throughput and the latency performance are improved significantly within the new network. The study compares the three input node with the two input node as well as the original single input data vortex node. Due to additional switch count and nodal cost, networks that support the same I/O ports and of the same cost are compared for a fair comparison. The limitation introduced by the blocking rate is also addressed. The study has shown that under reasonable traffic and network condition, the blocking rate can be kept very low without introducing complex controls and management for dropped packets. As previous architectures require operation under saturation point, the proposed architecture should also operate at reasonable level of network redundancy to avoid excessive packet drop. This study provides guidance and criteria on the proposed three input network design and operation for feasible applications. The proposed network provides an attractive alternative to the previous architectures for higher throughput and lower latency performance.     

WDM packet routing for high-capacity data networks

We present experimental and numerical studies of a novel packet-switch architecture, the data vortex, designed for large-scale photonic interconnections. The selfrouting multihop packet switch efficiently scales to large port counts (>10 k) while maintaining low latencies, a narrow latency distribution, and high throughput. To facilitate optical implementation, the data-vortex architecture employs a novel hierarchical topology, traffic control, and synchronous timing that act to reduce the necessary routing logic operations and buffering. As a result of this architecture, all routing decisions for the data packets are based on a single logic operation at each node. The routing is further simplified by the employment of wavelength division multiplexing (WDM)-encoded header bits, which enable packet-header processing by simple wavelength filtering. The packet payload remains in the optical domain as it propagates through the data-vortex switch fabric, exploiting the transparency and high bandwidths achievable in fiber optic transmission. In this paper, we discuss numerical simulations of the data-vortex performance and report results from an experimental investigation of multihop WDM packet routing in a recirculating test bed     

规则全光分组网络中偏射路由算法的分析

就在ShuffleNet和Manhattan Street Network两种规则网络中使用偏射路由算法后的网络性能以及允许一个时隙插入多个数据包对该算法的影响进行了分析。结果说明，偏射路由算法不仅能使网络得到较高的性能，而且发挥了网状网具有迂回路由的能力。当采用允许插入多个数据包的策略时，网络的吞吐量和平均跳转次数都有小幅度的增加。     

Performance of hypercube routing schemes with or without buffering

Considers two different hypercube routing schemes, which are called the simple and the priority schemes. The authors evaluate the throughput of both the unbuffered and the buffered version of these schemes for random multiple node-to-node communications. The results obtained are approximate, but very accurate as simulations indicate, and are given in particularly interesting forms. They find that little buffer space (between one and three packets per link) is necessary to achieve throughput close to that of the infinite buffer case. They also consider two deflection routing schemes, called the simple nonwasting deflection and the priority nonwasting deflection schemes. They evaluate their throughput-using simulations, and compare them to the priority scheme     

Distortion-Driven Video Streaming over Multihop Wireless Networks with Path Diversity

Multihop networks provide a flexible infrastructure that is based on a mixture of existing access points and stations interconnected via wireless links. These networks present some unique challenges for video streaming applications due to the inherent infrastructure unreliability. In this paper, we address the problem of robust video streaming in multihop networks by relying on delay- constrained and distortion-aware scheduling, path diversity, and retransmission of important video packets over multiple links to maximize the received video quality at the destination node. To provide an analytical study of this streaming problem, we focus on an elementary multihop network topology that enables path diversity, which we term "elementary cell." Our analysis is considering several cross-layer parameters at the physical and medium access control (MAC) layers, as well as application-layer parameters such as the expected distortion reduction of each video packet and the packet scheduling via an overlay network infrastructure. In addition, we study the optimal deployment of path diversity in order to cope with link failures. The analysis is validated in each case by simulation results with the elementary cell topology, as well as with a larger multihop network topology. Based on the derived results, we are able to establish the benefits of using path diversity in video streaming over multihop networks, as well as to identify the cases where path diversity does not lead to performance improvements.     

Quality of service for packet telephony over mobile ad hoc networks

IP telephony over mobile ad hoc networks is a topic of emerging interest in the research arena as one of the paths toward the fixed-mobile convergence in telecommunications networks. To investigate the performance characteristics of this service, we propose a complete system architecture, which includes a MAC protocol, a routing protocol, and the treatment of voice packets. The telephone system is analyzed in the case of point-to-point calls inside the ad hoc network, and the end-to-end performance is assessed in terms of the percentage of blocked and dropped calls, packet loss and packet delay. The analysis takes into account network scalability by investigating how; the size of the multihop ad hoc network impacts the quality of service. Moreover, the synthetic mean opinion score of the telephone service is evaluated according to the ITU-T E-model.