Packet Contention Research Articles

Efficient and fast contention resolution for AWGR based optical data center networks

A packet contention resolution scheme featuring efficient bandwidth utilization (CRSebu) is proposed for arrayed waveguide grating router (AWGR)-based optical data centers (DCNs). Optical bandwidth can be efficiently provided in this proposed scheme to adapt the burst network traffic by flexibly arranging the timeslot and wavelength. Moreover, the CRSebu scheme implements a “Dislocation Pipeline” strategy to prevent the conventional “Request-Grant” scheduling caused extra traffic waiting delay. Experimental investigations prove the CRSebu scheme can completely prevent packet contention and also improves the network performance in terms of packet loss and server-to-server latency due to the high bandwidth utilization. Numerical assessments also validate the excellent scalability of this proposed contention resolution scheme in large-scale AWGR-based DCNs. Compared with the typical OPSquare structure deploying an Optical Flow Control scheme to prevent packet contention, the CRSebu-equipped optical DCN eliminates the retransmission of conflicted packets, which significantly improves the network performance. Experimental investigations prove the proposed CRSebu strategy can completely prevent packet contention. Numerical assessments show that the network deployed with the CRSebu scheme decreases 73.6% packet loss, and 11.9% server-to-server latency compared with the static scheme.

Hybrid Optical-Electrical Data Center Networking: Challenges and Solutions for Bandwidth Resource Optimization

Fast optical switching (FOS) is the most promising technology for data center networks (DCNs) to meet data rate requirements beyond 800 Gb/s, considering its transparent modulation format, low power consumption and dense port integration. However, FOS, leveraging optical packet switching (OPS) technology, is hardly compatible with the electrical switches that are widely used in the current hybrid optical/electrical switching data center networks (Hoe-DCNs). The diversity of topologies and multi-switching granularity increases the risk of service disruption and reduces bandwidth efficiency. Based on the IP-over-OPS system, we propose bandwidth resource optimization techniques with the aid of hybrid polling contention resolution and microsecond-level load balancing in Hoe-DCNs. We first present an optical switching architecture to show its performance characteristics in the context of nanosecond-level FOSs in terms of resource management and setup optimization. Based on the fabricated FOS structure, we discuss the emerging problem of packet contention and introduce a bufferless scheduling solution. The characteristics of load balancing for Hoe-DCN are then investigated and evaluated by simulating Hoe-DCNs. Finally, the numerical results are given and analyzed based on a large-scale DCN testbed.

Flow-Controlled and Clock-Distributed Optical Switch and Control System

Switching the traffic in the optical domain has been considerably investigated as a future-proof solution to overcome the intrinsic bandwidth bottleneck of electrical switches in data center networks (DCNs). However, due to the lack of fast and scalable optical switch control mechanism, the lack of optical buffers for contention resolution, and the complicated implementation of fast clock and data recovery (CDR), the practical deployment of fast optical switches in data centers (DCs) remains a big challenge. In this work, we develop and experimentally demonstrate for the first time a flow-controlled and clock-distributed optical switch and control system, implementing 43.4 ns optical switch configuration time, less than 3.0E-10 packet loss rate resulting from the packet contention, and 3.1 ns fast CDR time. Experimental results confirm that zero buffer overflow caused packet loss and lower than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3~ \boldsymbol {\mu }\text{s}$ </tex-math></inline-formula> server-to-server latency are achieved for network deploying a smaller electrical buffer of 8192 bytes at a traffic load of 0.5. Real servers running the Transmission Control Protocol (TCP) traffic generating and monitoring tools are exploited in this switch and control system as well, validating its capability of running practical DCNs services and applications with full TCP bandwidth.

Nanosecond optical switching and control system for data center networks

Electrical switching based data center networks have an intrinsic bandwidth bottleneck and, require inefficient and power-consuming multi-tier switching layers to cope with the rapid growing traffic in data centers. With the benefits of ultra-large bandwidth, high-efficient cost and power consumption, switching traffic in the optical domain has been investigated to replace the electrical switches inside data center networks. However, the deployment of nanosecond optical switches remains a challenge due to the lack of corresponding nanosecond switch control, the lack of optical buffers for packet contention, and the requirement of nanosecond clock and data recovery. In this work, a nanosecond optical switching and control system has been experimentally demonstrated to enable an optically switched data center network with 43.4 nanosecond switching and control capability and with packet contention resolution as well as 3.1 nanosecond clock and data recovery.

Synergistic Switch Control Enabled Optical Data Center Networks

Optical switching, which benefits from high bandwidth and low latency, promises to revolutionize data center networks that suffer from a bandwidth bottleneck and hierarchical structure. However, the lack of adaptable and fast optical switch control schemes, the lack of optical buffers for contention resolution, and the high cost of clock and data recovery (CDR) impede the practical deployment of optical switches in data centers. Networking communities have tried to address these challenges from different perspectives. However, the proposed solutions may be interdependent and thus introduce unexpected issues. In this article, a synergistic optical switch control mechanism is proposed to simultaneously solve the aforementioned challenges. The developed label control technique allows for controlling and configuring packet switching within 43.4 ns. The implementation of clock distribution achieves a fast CDR of 3.1 ns at low cost, and the design of an optical flow control protocol prevents packet loss caused by packet contention.

A router architecture with dual input and dual output channels for Networks-on-Chip

Networks-on-Chip (NoCs) are the most viable and scalable solution for connecting thousands of processing cores, and are emerging as the interconnect infrastructure for future Chip-Multiprocessors. Latency and throughput are the primary metrics for on-chip network performance, while chip area and power budgets are increasingly dominated by interconnect networks. Hence, it is critical to achieve higher performance gains at a lower cost. Previous research has proposed a router architecture that forwards packets through idle bidirectional channels to improve network performance, but it introduces significant area and power overheads. In this paper, we propose DIDO: a router architecture with dual input and dual output channels. First, the dual output channels provide extra flexibility for forwarding packets and reduce packet contention. Then, the redesigned input ports and crossbar shorten the pipeline and reduce the crossbar overhead. Finally, the removal of the virtual channel allocator allows DIDO to operate at higher frequencies. Simulation results indicate that DIDO reduces average packet latency by up to 44.8% and improves network throughput by up to 37.8% compared to the baseline router at the same frequency. Synthesis results indicate that the DIDO’s area and power overhead are comparable to the baseline router, while the maximum frequency is boosted by 18%.

Achieving energy efficiency in wireless sensor networks using dynamic channel polling and packet concatenation

There has been a significant interest of researchers to combine different schemes focused on optimizing energy performance while developing a MAC protocol for Wireless Sensor Networks (WSNs). In this paper, we propose to integrate two cross-layer schemes: dynamic channel polling and packet concatenation using a recent asynchronous MAC protocol “Adaptive & Dynamic Polling MAC” (ADPMAC). ADP-MAC dynamically selects the polling interval distribution based on characterization of incoming traffic patterns using Coefficient of variation(CV). Packet Concatenation (PC) refers to combining the individually generated data packets into a single super packet and sending it at the polling instant. Also, the Block Acknowledgement (BA) scheme has been developed for ADP-MAC to work in conjunction with the packet concatenation. The proposed schemes have been implemented in Tiny-OS for Mica2 platform and Avrora emulator has been used for conducting experiments. Simulation results have revealed that the performance both in terms of energy & packet loss improves when ADP-MAC is used in conjunction with the additional features of PC & BA. Furthermore, the proposed scheme has been compared with a state of-art packet concatenation primitive PiP (Packet-in-Packet). It has been observed that ADP-MAC supersedes the performance of PiP in terms of PDR (Packet Delivery Ratio) due to better management of synchronization between source and sink.

Analysis and Implementation for Traffic-Aware Channel Assignment and Contention Scheme in LoRa-Based IoT Networks

Internet of Things (IoT) is a promising technology attracting huge attentions in recent years, allowing an excessive number of connections between sensors and devices. Different from conventional human-oriented applications, long range (LoRa) developed in IoT facilitates massive simultaneous sensor data transmissions for the low-power wide-area network (LPWAN), where massive LoRa devices perform packet contention and backoff mechanisms to access opportunity for uplink data transfer. Therefore, it is compellingly imperative to take into account the fluctuation of different channel qualities and various traffic-buffer types for the optimum contention policy, which are not considered in open literatures. In this article, we propose a traffic-aware channel and backoff window size allocation (TCBA) scheme to improve network capacity and latency. Moreover, a statistical latency-aware network model is designed to derive the closed forms of the optimum packet transmission probability and maximum number of LoRa devices supported. The performance results validate that the theoretical analysis approaches the simulated one. Moreover, in both simulated and experimental results, our proposed TCBA scheme is capable of supporting massive LoRa connections achieving the highest throughput and the lowest end-to-end latency compared to other schemes in existing literatures.

Experimental Assessments of SDN-Enabled Optical Polling Flow Control for Contention Resolution in Optical DCNs

Due to the lack of optical buffer, high packer loss caused by packet contention is one of the main challenges for the optical switching data centers (DCs). Flow control (FC) protocol employing electrical buffers at the top of racks (ToRs) and exploiting packet retransmission mechanism in case of contention has been extensively investigated to decrease the packet loss in optical DCs. However, the packet retransmission and the head-of-line (HOL) blocking in electrical buffers at substantial load traffic introduce extra latency and buffer-overflow that still cause packet loss. To overcome these issues, a novel contention resolution technique based on a software-defined networking (SDN) enabled optical polling flow control is proposed and experimentally assessed in this article. Experimental assessments show that the proposed contention resolution scheme achieves zero packet loss and 7.4 μs latency performance at the load of 0.4. In addition, we numerically modelled and investigated the scalability of the proposed contention resolution technique in a large scale DCN based on the experimental parameters. Results prove the excellent scalability performance of OPFC scheme, in which the packet loss increases from 2.1E-3 to 9.02E-3 and the average latency increases 5.17 μs at the load of 0.5 as the OPFC based network scales from 4 to 40960 servers.

Optical combinational circuit for contention detection circuit in all optical router

This paper presented an optical combinational circuit based on nonlinearities of semiconductor optical amplifier (SOA) and its associated configuration. The associated circuits used are semiconductor optical amplifier - Mach Zehnder Interferometer (SOA-MZI) and semiconductor optical amplifier plus dispersion compensation fiber (SOA + DCF) for packet contention detection. The optical combinational circuits include the optical adder connected in 2 × 2 optical node for the optical packet management. All nodes have capability of decisions and processing of incoming optical signals at 1.25 Gbps. The system performance has been evaluated and optimized by varying the SOA parameters. The proposed optical combinational circuit is also suitable for network with 3 × 3 optical node. The proposed optical combinational circuit can be verified at 10 Gbps for the next generation broadband optical network.

Hybrid and optical packet switching supporting different service classes in data center network

Optical packet switching is a prominent technology proposing not only a reduction in the energy consumption by the elimination of numerous optical–electrical–optical conversions in electronic switches, but also a decrease in network latencies due to the cut-through nature of packet transmission. However, it is adversely affected by packet contention, preventing its deployment. Solutions have been proposed to tackle the problem: addition of shared electronic buffers to optical switches (then called hybrid opto-electronic switches), customization of TCP protocols, and use of different service classes of packets with distinct switching criteria. In the context of data center networks, we investigate a combination of said solutions and show that the hybrid switch, compared to the optical switch, boosts the performance of the data center network. Furthermore, we show that introducing a “Reliable” service class improves performance for this class not only in the case of the hybrid switch, but also brings the optical switch to performance levels comparable to that of the hybrid switch, all the while keeping other classes’ performance on the same level.

Demonstration of SDN-Enabled Hybrid Polling Algorithm for Packet Contention Resolution in Optical Data Center Network

We propose and experimentally demonstrate a Software-Defined Network (SDN) enabled Hybrid Polling Algorithm for packet Contention Resolution (HPACR) in optical Data Center Network (DCN) based on Fast Optical Switches (FOS). Fast Semiconductor Optical Amplifier (SOA)-based buffer-less FOS with nanoseconds reconfiguration time are employed for interconnecting Top-Of-the Racks (TORs) switches with distributed flow control. Under the realistic 10 Gb/s server traffic, the network performance of the DCN employing the proposed HPACR algorithm is experimentally assessed. Results show that the HPACR increases 13.6% throughput at the high load of 1.0 and decreases the 75% contention ratio for the load >0.5 with respect to the traditional packet contention resolution methods. Based on the experimental parameters, a simulation platform is built to numerically evaluate the HPACR performance of DCN with 64 TORs connecting 1280 servers. The results show that HPACR improves the system performance by increasing the throughput by 5% compared with existing algorithms, reducing the TOR-to-TOR latency by 18.5%, and decreasing the packet loss by 14.1% at the load of 1.

Construction of Subexponential-Size Optical Priority Queues With Switches and Fiber Delay Lines

All-optical switching has been considered as a natural choice to keep pace with growing fiber link capacity. One key research issue of all-optical switching is the design of optical buffers for packet contention resolution. One of the most general buffering schemes is optical priority queue, where every packet is associated with a unique priority upon its arrival and departs the queue in order of priority, and the packet with the lowest priority is always dropped when a new packet arrives but the buffer is full. In this paper, we focus on the feedback construction of an optical priority queue with a single $\boldsymbol{(M+2)\times (M+2)}$ optical crossbar Switch and $\boldsymbol{M}$ fiber Delay Lines (SDL) connecting $\boldsymbol{M}$ inputs and $\boldsymbol{M}$ outputs of the switch. We propose a novel construction of an optical priority queue with buffer $\boldsymbol{2^{\Theta(\sqrt{M})}}$, which improves substantially over all previous constructions that only have buffers of $\boldsymbol{O(M^c)}$ size for constant integer $\boldsymbol{c}$. The key ideas behind our construction include (i) the use of first in first out multiplexers, which admit efficient SDL constructions, for feeding back packets to the switch instead of fiber delay lines, and (ii) the use of a routing policy that is similar to self-routing, where each packet entering the switch is routed to some multiplexer mainly determined by the current ranking of its priority.

Gathering data with packet-in-packet in wireless sensor networks

In many wireless sensor network (WSN) mission-critical applications, a collector, e.g., a drone acting as a data sink, is required to gather data from all the source nodes in the area of interest. It is, thus, an all-to-one scenario. Data from each node (e.g., local temperature or its binary status) normally only consists of several bytes. Furthermore, often, data collection is expected to be done as fast as possible, especially for mission-critical applications or applications where a battery-powered sink is used (e.g., a drone). Thus, it is preferred that there is no preparation phase for the network to schedule or establish any routes in advance. Concurrent transmission (CT), a novel communication paradigm, has been shown to effectively achieve reliable and energy-efficient flooding in low-power wireless networks. With multiple nodes exploiting a receive-and-forward scheme, this technique requires no routing and works effectively in flooding-based networks, i.e., in one-to-many scenarios. Hence, CT-based communication is a good choice for fast data collection. However, a kind of global scheduling is essential for data collection in CT-based WSNs, in order to globally schedule a node that initiates a flooding in the network. In this article, to comply with the requirements of the aforementioned data collection application, we propose Packet-in-Packet (PiP), an energy-efficient paradigm requiring no global scheduling for timely data collection in low-power WSNs. PiP builds on concurrent transmissions and uses a packet concatenation capability to gather single-hop information in a best-effort manner. PiP does not require any pre-scheduling of traffic in the network, and thereby significantly reducing collection time. We compare PiP with a number of state-of-the-art protocols by extensive experiments in two testbeds, FlockLab and Indriya, respectively. Experimental results show that PiP achieves high reliability and low latency in all the scenarios in the real-world testbeds. Specifically, when the transmission power of nodes is set to 0 dBm, PiP takes only 287 ms (at least 1.8 × faster than the state-of-the-art protocols) to complete a 26-to-one data collection in FlockLab and 965 ms (1.1 × faster than a state-of-the-art protocol LWB) to complete a 42-to-one collection in Indriya, respectively.

Hybrid wavelength conversion with dynamic pump-wavelength selection for synchronous optical packet switching

Abstract In this paper, we propose and study the performance of two conversion schemes for optical packet switch (OPS) with the objective of reducing packet contention, and hence, improving the overall packet loss ratio (PLR). In both schemes, conversion is performed in two layers. The first layer contains a dedicated wavelength converter (WC) for each input wavelength, while the second conversion layer consists of a dynamic pump-wavelength selection (DPS) of parametric wavelength converters (PWCs) shared in a Feed-Back fashion. The first scheme uses non-circular WCs (NCWCs) with DPS of chained PWCs (called LDPSC, for short). In the LDPSC scheme, an incoming packet is accepted only if it could be assigned to its required output using only the NCWCs in the first layer or more than one PWCs in a chained fashion in the second layer; otherwise it will be dropped. The second scheme uses circular wavelength conversion (CWCs) with DPS of PWCs without chaining (named CDPS, for short). In the CDPS scheme, an incoming packet is accepted only if it can be assigned to its required output using only CWCs in the first layer or only one of the PWCs in the second layer; otherwise it will be dropped. For each of the two schemes, a matching algorithm along with a Dynamic pump conversion (DPC) algorithm is presented. The performances of the proposed schemes are compared to two conventional schemes; namely, the DPSC scheme that uses a shared pool of DPS of chained PWCs, and the LDPS scheme that uses a dedicated NCWC for each input wavelength and a shared pool of DPS of PWCs without chaining. Simulation results show that, the new CDPS scheme achieves the same performance (in terms of PLR) of the LDPS scheme, while reducing the required number of PWCs by more than 44 % and 57 % for conversion distances (that is the maximum number of wavelengths adjacent to any input wavelength on any one of its sides), d = 1 and 2; respectively. Moreover, using conversion distance d = 1 , the new LDPSC scheme reduces the PLR compared to the LDPS scheme by up to 85 % and 22 % for traffic loads, 0.5 and 1; respectively. In addition, for d = 1 , the new LDPSC scheme reduces the PLR compared to the DPSC scheme by up to 99.8 % and 30 % for traffic loads, 0.5 and 1; respectively.

On the Capacity of Smart Grid Wireless Backhaul With Delay Guarantee and Packet Concatenation

In future smart grids, low channel efficiency due to small data payloads and the delay guarantee of many near-real-time applications would become two important issues. In this paper, we propose to employ a deadline-ordered scheduler with packet concatenation and apply admission control (AC) to resolve these two issues. In order to execute the AC mechanism, the delay bounds in the home area network and the neighborhood area network and the affine arrival curves for modeling the flows injecting into the concentrator are derived using network calculus. The performance of this novel design is illustrated via analytical and simulation results. In addition, the robust header compression protocol is adopted as a benchmark to evaluate the performance with the packet concatenation method. It is shown that the proposed scheduler with packet concatenation significantly improves the capacity of the smart grid wireless backhaul, and our AC mechanism provides a reliable estimate of the capacity.

Synchronous optical packet switch architecture with tunable single and multi-channels wavelength converters

Abstract In this paper, we propose a bufferless synchronous optical packet switch (OPS) architecture named the Limited-range wavelength conversion with Dynamic Pump-wavelength Selection (LDPS) architecture. LDPS is equipped with a dedicated limited-range wavelength converters (LRWCs, and a shared pool of parametric wavelength converters (PWCs) with dynamic pump-wavelength selection (DPS). The adoption of hybrid conversion types in the proposed architecture aims at improving the packet loss rate (PLR) compared to conventional architecture with single conversion types, while reducing (or at least maintaining) the conversion distance ( d ) of used wavelength converters. Packet contention in the proposed architecture is resolved using the first available algorithm (FAA) and the dynamic pump-wavelength selection algorithm (DPSA). The performance of the proposed architecture is compared to two well-known conventional architectures; namely, the LRWC architecture that uses dedicated LRWCS for each input wavelength, and the DPS architecture that uses a shared pool of dynamic pump-wavelength converters (PWCs). Simulation results show that, for the same value of d , the new architecture reduces the PLR compared to the LRWC architecture by up to 40 % and 99.7 % for traffic loads, 0.5 and 1; respectively. In addition, for d = 1 , the new architecture reduces the PLR compared to the DPS architecture by up to 10 % and 99.3 % for traffic loads, 0.5 and 1; respectively.

Ultra-High-Capacity Optical Packet Switching Networks with Coherent Polarization Division Multiplexing QPSK/16QAM Modulation Formats

Optical packet switching (OPS) networks and its subsystems, like the burst-mode receiver, are an essential technology currently used in passive optical networks (PONs). Moreover, OPS may play a fundamental role on future hybrid optical circuit switching (OCS)/OPS networks and datacenter networks. This paper focuses on two fundamental subsystems of packetized optical networks: the digital coherent burst-mode receiver and the electro-optical switch. We describe and experimentally characterize a novel digital coherent burst-mode receiver that makes uses of the Stokes parametrization to rapidly estimate the state of polarization (SOP) and optimize the equalizer convergence time. This burst-mode receiver is suitable for optical packetized networks that make use of advanced modulation formats such as quadrature amplitude modulation (QAM). We study the suitability of (Pb,La)(Zr,La)O3 (PLZT) optical switches for amplitude-variable coherent polarization division multiplexing (PDM) 16QAM modulation format and demonstrate a switching capacity of 10.24 Tb/s/port. We demonstrate a full 2 × 2 OPS node with a control plane capable of solving packet contention by means of packet dropping or buffering with a switching capacity of 10.24 Tb/s/port. Finally, we demonstrate the operation of the 2 × 2 OPS node with a record capacity of 12.8 Tb/s/port plus 100 km of dispersion-compensated fiber transmission.

OPSquare: A Flat DCN Architecture Based on Flow-Controlled Optical Packet Switches

Aiming at solving the scaling issues of bandwidth and latency in current hierarchical data center network (DCN) architectures, we propose and investigate a novel optical flat DCN architecture in which the number of interconnected ToRs scales as the square of the optical packet switches&#x2019; (OPS) port count (OPSquare). The proposed flat DCN architecture consists of two parallel inter- and intra-cluster networks that are built on a single-hop OPS with nanosecond time and wavelength switching for efficient statistical multiplexing operations. Fast optical flow control is implemented for solving packet contentions that may occur at the buffer-less optical switches. The performance of OPSquare DCN in terms of scalability, packet loss, latency, and throughput is assessed by a numerical simulation employing OMNeT++ under realistic data center (DC) traffic. The results report a server-to-server latency of less than 2 &#x03BC;s (including packet retransmission), a packet loss &lt;10&#x2212;5 at a load of 0.4, and a DC size of 10,240 servers with a ToR buffer size equal to 50 KB for all traffic patterns. Moreover, the cost and power consumption of the OPSquare DCN have been studied and compared with fat-tree DCN based on electrical switches and H-LION connected by an arrayed wave guide grating router (AWGR). The results indicate 23.8% and 39% cost and power savings, respectively, for the OPSquare DCN supporting 160,000 servers with respect to the fat-tree DCN. The OPSquare has a cost saving of 56% compared with H-LION for a 160,000-server DCN.

Putting Sensor Data to the Service of the Smart Grid: From the Substation to the AMI

One of the requirements of a smart grid (SG) is making the electrical network and its subsystems aware of their condition. The deployment of various sensing devices plays an essential part in achieving this goal. Nevertheless, data generated by this deployment needs to be well managed so that it can be leveraged for operational improvement. Data aggregation is perceived as an important technique for managing data in the SG in general, and in its Advanced Metering Infrastructure (AMI) in particular. Indeed, data aggregation techniques have been used in order to reduce communication overhead in SG networks. However, in order to fully take advantage of the aggregation process, some level of intelligence should be introduced at concentrator nodes to make the network more responsive to local conditions. Moreover, by using a more meaningful aggregation technique, entities can be accurately informed of any disturbance. This paper contributes an agent-based approach for data and energy management in an SG. It also proposes CoDA, a correlation-based data aggregation technique designed for the AMI. CoDA employs fuzzy logic to evaluate the correlation between several messages received from Smart Meters (SMs). Analysis and simulation results show the benefits of the proposed approach w.r.t. both packet concatenation and no aggregation approaches.