Optimization of the Scheduler for the Non-Blocking High-Capacity Router

The sequential greedy scheduling (SGS) is a scalable maximal matching algorithm that provides non-blocking in an Internet router with input buffers and a cross-bar. In this paper, we will present the FPGA design of the SGS scheduler. We have optimized scheduler components, and we will prove their correct functioning. The scheduler optimization significantly reduces the worst-case packet delay through the router.     

Two phase load balanced routing using OSPF

The Internet traffic is growing, and its nature changes because of new applications. Multimedia applications require bandwidth reservations that were not needed initially when the file transfers dominated the Internet. P2P applications are making traffic patterns impossible to predict, and the traffic loads generated at nodes need to be routed regardless of the traffic pattern. When the guaranteed node traffic loads are known, bandwidth reservations can be made simple as will be explained in the paper. The shortest path routing (SPR) protocols used on the Internet today do not maximize the guaranteed node traffic loads, and do not provide scalable and fast bandwidth reservations. Load balancing can improve the network throughput for arbitrary traffic pattern. In this paper we analyze and implement a routing protocol that is based on load balancing and a commonly used shortest path routing protocol, and is, consequently, termed as LB-SPR. LB-SPR is optimized for an arbitrary traffic pattern, i.e. it does not assume a particular traffic matrix. Optimization assumes only the weights assigned to the network nodes according to their estimated demands. It will be shown that the optimized routing achieves the throughputs which are significantly higher than those provided by the currently used SPR protocols, such as OSPF or RIP. Importantly, LB-SPR calculates the guaranteed traffic loads and so allows fast autonomic bandwidth reservations which are the key for the successful support of triple-play applications, including video and audio applications that require high QoS. An actual modification of the TCP/IP stack that includes LBSPR is also described. Using the signaling mechanisms of the OSPF protocol, the information needed to perform the routing optimization is automatically distributed among the network nodes whenever the network topology changes. The LB-SPR implementation is validated on a sample network using a popular virtualization tool - Xen.     

Design of the Switching Controller for the High-Capacity Non-Blocking Internet Router

The sequential greedy scheduling (SGS) algorithm is a scalable maximal matching algorithm. This algorithm was conceptually proposed and well received since it provides non-blocking in an Internet router with input buffers and a cross-bar, unlike other existing implementations. In this paper, we implent a new design of the SGS algorithm, and determine its exact behaviour, performance and QoS that it provides. We examine different design options and measure the performance of their implementations in terms of their scalability and speed. It will be shown that multiple scheduler modules of a terabit Internet router can be implemented on a low-cost field-programmable gate-array (FPGA) device, and that the processing can be performed within the desired time slot duration. Proper functioning of the implemented scheduler was confirmed through thorough software and hardware testing.      

A demand-assignment algorithm based on a Markov modulated chain prediction model for satellite bandwidth allocation

This article deals with the problem of the design of a control-based demand-assignment algorithm for a satellite access network using a Markov modulated chain traffic prediction model. The objective is to guarantee a target Quality of Service (QoS) to Internet traffic, while efficiently exploiting the air interface. The proposed algorithm is in charge of dynamically partitioning the uplink bandwidth capacity in a satellite spotbeam among the in-progress connections. Such partition is performed aiming at matching the QoS requirements of each connection and maximizing the satellite bandwidth exploitation. A closed-loop Control Theory approach is adopted to efficiently tackle the problem of the delay between bandwidth requests and bandwidth assignments, while minimizing the signaling overhead caused by control messages. The algorithm efficiently copes with both the satellite propagation delay and the delays inherent in the periodic nature of the bandwidth request mechanism. The proposed demand-assignment algorithm and Markov chain traffic prediction model are shown to improve the overall satellite network performance through extensive simulation experiments.     

A cell switching WDM broadcast LAN with bandwidth guarantee andfair access

This paper presents the design of a cell-switching wavelength division multiplexing (WDM) local area network (LAN), which constitutes a key component of a next-generation internet (NGI) consortium project recently funded by DARPA. An important goal of the NGI project is to support bandwidth-on-demand services with quality-of-service (QOS) guarantee over WDM networks. As a first step toward this goal, we have developed several fast scheduling algorithms for flexible bandwidth reservations and fair sharing of unreserved bandwidth in a WDM broadcast network with fast-tunable transceivers. Unlike circuit-based bandwidth reservation schemes that impose a fixed schedule precomputed on setup, our scheme deals with bursty traffic by allocating network resources dynamically using very efficient algorithms. Our algorithms are based on a new concept of computing maximal weighted matchings, which is a generalization of maximal matchings on unweighted graphs. We prove that our algorithms can support total reserved bandwidth of up to 50% of the network capacity, and in that case constant delay bounds are also established. Simulations show that our algorithms can in practice support much higher reserved bandwidth-up to 90% of network capacity, and with much better delay bounds, even for burst traffic. In addition to the bandwidth guarantee, the unreserved bandwidth can be shared fairly among the users using our fair access algorithms with case to 100% network utilization in simulations     

Fast Switching and Fair Control of Congested Flow in Broadband Networks

A new switching architecture is proposed based on the tradeoffs of modern VLSI technology-inexpensive memory and 2-dimensional layout structures. Today, it is economically feasible to preallocate buffer space individually to each virtual circuit in every node, so that "congestion" ceases to have negative effects. On the contrary, when some low-priority circuits offer more traffic than the network can carry, full utilization of the link bandwidth is achieved. In this context, the allocation of bandwidth can be done automatically and in a "fair" way, if packets are multiplexed by circularly scanning all virtual circuits and transmitting one packet from each "ready" circuit. This multiplexing algorithm equally distributes all the available link BW to all the VC's that can use it (other than equal distribution is also possible), while it also guarantees an upper bound for the total packet delay through noncongested VC's (VC's that use less than their share of BW). We present methods for hardware implementation of such fast circular scans, and propose a structure for the switching nodes of such networks, consisting of a cross-bar arrangement like a systolic array that performs merge sorting. It is ideally suited for physical layout on printed-circuit boards or with wafer-scale integration.     

联合能耗与负载均衡的虚拟网络映射方法

为解决弹性光网络中虚拟网络映射时能耗严重、资源分配不均的问题,该文提出一种联合能耗与负载均衡的虚拟网络映射（PC-LB-VONE）方法.在虚拟节点映射时,选择相邻链路长度短、光节点计算资源多与相邻链路带宽资源多的光节点映射.在虚拟链路映射时,提出一种基于极大团的候选光路资源匹配度单路径映射策略.当单路径映射失败时,设计基于链路负载均值的多路径映射策略.仿真结果表明,所提方法能在减少弹性光网络能耗的同时均衡网络负载.     

A pipeline-based approach for maximal-sized matching scheduling ininput-buffered switches

This letter proposes an innovative pipeline-based maximal-sized matching scheduling approach, called PMM, for input-buffered switches. It dramatically relaxes the timing constraint for arbitration with a maximal matching scheme. In the PMM approach, arbitration operates in a pipelined manner. Each subscheduler is allowed to take more than one time slot for its matching. Every time slot, one of them provides the matching result. The subscheduler can adopt a pre-existing efficient round-robin-based maximal matching algorithm. We show that PMM provides 100% throughput under uniform traffic since it preserves a desynchronization effect of the round-robin pointers as in the preexisting algorithm. In addition, PMM maintains fairness for best-effort traffic due to the round-robin-based arbitration     

Analytical Evaluation of PHM Convergence

The parallel hierarchical matching (PHM) algorithm is a distributed maximal size matching scheduler for virtual output-queued switches. In a previous letter, we formulated an upper bound on the maximum number of iterations PHM requires to achieve a maximal size matching in any traffic scenario. In this letter, we follow an analytical approach to find the average number of iterations for PHM to achieve a maximal size matching under diverse traffic models. The estimated number of iterations is$O(log_2N)$, as in the case of iSLIP-like algorithms.     

Deficit round-robin scheduling for input-queued switches

We address the problem of fair scheduling of packets in Internet routers with input-queued switches. The goal is to ensure that packets of different flows leave a router in proportion to their reservations under heavy traffic. First, we examine the problem when fair queuing is applied only at output link of a router, and verify that this approach is ineffective. Second, we propose a flow-based iterative deficit-round-robin (iDRR) fair scheduling algorithm for the crossbar switch that supports fair bandwidth distribution among flows, and achieves asymptotically 100% throughput under uniform traffic. Since the flow-based algorithm is hard to implement in hardware, we finally propose a port-based version of iDRR (called iPDRR) and describe its hardware implementation.     

Multiple access control with intelligent bandwidth allocation forwireless ATM networks

Two major challenges pertaining to wireless asynchronous transfer mode (ATM) networks are the design of multiple access control (MAC), and dynamic bandwidth allocation. While the former draws more attention, the latter has been considered nontrivial and remains mostly unresolved. We propose a new intelligent multiple access control system (IMACS) which includes a versatile MAC scheme augmented with dynamic bandwidth allocation, for wireless ATM networks. IMACS supports four types of traffic-CBR, VBR, ABR, and signaling control (SCR). It aims to efficiently satisfy their diverse quality-of-service (QoS) requirements while retaining maximal network throughput. IMACS is composed of three components: multiple access controller (MACER), traffic estimator/predictor (TEP), and intelligent bandwidth allocator (IBA). MACER employs a hybrid-mode TDMA scheme, in which its contention access is based on a new dynamic-tree-splitting (DTS) collision resolution algorithm parameterized by an optimal splitting depth (SD). TEP performs periodic estimation and on-line prediction of ABR self-similar traffic characteristics based on wavelet analysis and a neural-fuzzy technique. IBA is responsible for static bandwidth allocation for CBR/VBR traffic following a closed-form formula. In cooperation with TEP, IBA governs dynamic bandwidth allocation for ABR/SCR traffic through determining the optimal SD. The optimal SDs under various traffic conditions are postulated via experimental results, and then off-line constructed using a back propagation neural network (BPNN), being used on-line by IBA. Consequently, with dynamic bandwidth allocation, IMACS offers various QoS guarantees and maximizes network throughput irrelevant to traffic variation     

PCA算法在P2P加密流量识别中的研究与应用

传统的应用层协议识别方法均从改进匹配算法的角度来提高识别率,但是随着P2P协议的发展,其特征呈现多维化的趋势,算法复杂度也随之提高。鉴于此,在对P2P流量的多维特征进行分析并提取后,采用主成分分析(PCA)算法将提取到的特征降维处理,并通过实验证明了该方法在网络流量识别上的可行性和有效性。     

Adaptive Counting Rule for Cooperative Spectrum Sensing Under Correlated Environments

We propose in this paper a dual-antenna-array (with transmitter antenna array and receiver antenna array) architecture, where the antenna elements are divided into several antenna element sets and each traffic channel is transmitted over an antenna element set, to realize the multiple traffic channels set up by a user. A SINR feedback based algorithm, which can regulate the transmission rate by iteratively adjusting the power on each traffic channel, is proposed to execute the rate control for the proposed dual-antenna-array architecture under cochannel interference. It is shown that the proposed algorithm can make the throughput meet the throughput requirement or achieve the weighted bandwidth sharing for certain fairness. In addition, we further propose a traffic channel configuration algorithm to help the SINR feedback based algorithm find the optimal traffic channel configuration that can meet the throughput requirement for each traffic channel or results in the maximal total throughput for each user.     

Resource assignment for integrated services in wireless ATM networks

The task of supporting integrated multirate multimedia traffic in a bandwidth-poor wireless environment poses a significant challenge for network designers. In this paper we propose a novel bandwidth allocation strategy which partitions the available bandwidth amongst the different traffic classes in a manner that ensures quality-of-service guarantees for digital video while minimizing the maximum blocking probability for voice and data connections. At the connection level, near-optimum utilization of the reserved bandwidth for video traffic is achieved through an intra-frame statistical multiplexing algorithm, while at the system level the delicate task of partitioning the bandwidth between voice, video and data is accomplished by developing an efficient algorithm which uses traffic parameters consisting only of the aggregate traffic load and the total available bandwidth. The algorithm, built on non-trivial mathematical results is robust, easy to implement and has a geometric rate of convergence which ensures that the partitioning points are found quickly. These properties make it well suited for practical implementations, even for cases where changes in the aggregate traffic loads cause bandwidth allocations to be recomputed frequently. © 1998 John Wiley & Sons, Ltd.     

FALB:一种FC协议链路聚合算法

链路聚合是一种通过将多条物理链路捆绑成一条逻辑链路来增加带宽的常用技术,但是在基于光纤通道（fibre channel,FC）协议的交换网络中,随着转发流量区域的不断集中,传统静态链路聚合算法存在负载均衡性差、可靠性低的问题。因此提出了一种基于FC协议的动态负载均衡（flow adaptive load balancing, FALB）链路聚合算法,可以实现对流量的动态自适应匹配以及断链可重连保护机制。结果表明,该算法机制相较于静态负载均衡的算法设计,可以将有效带宽比最终收敛到 95%以上,有效提升聚合链路的负载均衡特性和可靠性。     

End-to-end bandwidth allocation scheme for voice traffic support over MANETs

Multimedia and real-time applications require bandwidth guarantees, which can be achieved by resource reservation. However, bandwidth reservation in ad-hoc networks is a very challenging task due to the instability of radio channels, node mobility and lack of coordination between mobile nodes. Most proposed reservation protocols focus on point-to-point reservations, and only a few work has been done to propose an efficient end-to-end reservation scheme. In this paper, we propose a reservation scheme called End-to-end reservation scheme for voice and data traffic support (EERV). The basic component of our protocol is a handshake mechanism which has the role to establish point-to-point reservations, and to ensure consistency of reservations between neighbor nodes. Both data and voice sources are allowed to establish reservations with priority given to voice sources. This reservation scheme is extended to support the reservation and release of resources along a path in cooperation with the routing layer. Our reservation scheme is based on DSR, a well-known reactive routing protocol. Mobility of nodes and node failure cause frequent reservation breakages resulting in significant performance degradation. In order to resolve this issue we propose a reservation loss detection and reservation recovery mechanisms. We achieved intensive simulations to evaluate the performance of our protocol. Simulation results show the effectiveness of this protocol.     

On the isochronous paths selection problem in an interconnected WDMnetwork

In this paper, a new wavelength division multiplexing (WDM) interconnection architecture for supporting both isochronous and asynchronous traffic is proposed. Based on this architecture, the problem of allocating an isochronous bandwidth is investigated. We show that given a set of established isochronous connections and a set of new isochronous requests, the problem of using a minimal amount of an isochronous bandwidth to serve this isochronous traffic, including the established connections and new requests, is NP-hard. On the other hand, given a limited isochronous bandwidth, the goal is to establish a maximal number of isochronous connections. An efficient isochronous paths selection algorithm, based on the concept of paths merging and splitting, is also proposed for this problem. The proposed algorithm is evaluated by simulation. Simulation results show that for a limited isochronous bandwidth, the proposed algorithm can achieve high performance in terms of isochronous slots utilization, call blocking rate, and the number of successfully established isochronous connections     

All-optical WDM multi-rings with differentiated QoS

This article considers all-optical WDM networks based on a slotted multichannel ring topology, where nodes are equipped with one fixed-wavelength receiver and one wavelength-tunable transmitter; and shows how to design very effective MAC protocols that provide packet-mode transport to multiple information flows with different QoS requirements. As an example, we describe SR3, a collision-free slotted MAC protocol which combines a packet scheduling strategy (called SRR), a fairness control algorithm (called MMR); and a reservation mechanism. SRR achieves an efficient exploitation of the available bandwidth, MMR guarantees fair throughput access to each node, and SR3, by permitting slot reservations, leads to tighter control on access delays, and can thus effectively support traffic classes with different QoS requirements     

Flexible bandwidth allocation in high-capacity packet switches

This paper introduces a protocol for scheduling of packets in high-capacity switches, termed weighted sequential greedy scheduling (WSGS). WSGS is a simple, greedy algorithm that uses credits to reserve bandwidth for input-output pairs. By using a pipeline technique, WSGS implemented by the current technology readily supports a switching capacity exceeding 1 Tb/s. Admission control is straightforward, allowing bandwidth reservations on a submillisecond time scale. Namely, the central controller readily determines if the newly requested bandwidth can be assigned to the given input-output pair. We have shown that a newly requested bandwidth should be assigned if both the input and output have enough capacity, which requires checking of only two inequalities. Therefore, WSGS is well suited for switching in data networks where sessions might require high bit rates and last for a short time. The WSGS allows bandwidth reservations with fine granularity, e.g., bandwidth can be reserved for individual web sessions, video streams, etc     

The development of a simplified cross-bar mixer operating at Ka-band

Many receivers operating at millimetre wavelengths utilise a frequency downconverter as their first stage. A rugged, low-conversion loss and simplified cross-bar mixer operating at the atmospheric window centered at 33 GHz was designed, developed and tested as a forerunner to mixers operating at atmospheric windows centred at higher frequencies. The cross-bar mixer exhibits a conversion loss of less than 5 dB over a bandwidth of 2 GHz. Design and optimisation procedures of the mixer are outlined.