Novel bandwidth allocation with quota-based excess-distribution algorithm and wavelength assignment in multi-wavelength access network

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Abstract

Dynamic bandwidth allocation (DBA) is of great importance and interest to multichannel passive optical networks (PONs). It plays a crucial role in efficiently and fairly allocating the bandwidth among all users. In this paper, a novel quota-based excess-distribution algorithm which can achieve accurate bandwidth allocation for end-users by using Computational Theory of Perceptions (CTP) has been proposed. To manage resources efficiently, we first present a mathematical model of bandwidth allocation based on matrix theory. Then, the quota-based excess-distribution algorithm is proposed and the excess distribution quota obtained from the algorithm is adjusted in real time and adaptively to further augment the efficiency and fairness of DBA. Thus, the excess distribution becomes more centralized and independent. The proposed algorithm can effectively prevent excess distribution from bandwidth monopolization and over-allocation. Besides, we formulate a wavelength assignment mechanism based on release time to eliminate the idle period and increase the bandwidth utilization of the network. Finally, we conduct detailed simulation experiments to research and analyze the performance in terms of delay, bandwidth utilization and fairness among ONUs. The simulation results demonstrate that at least 8.5% bandwidth utilization improvement and low average delay are achieved compared with other schemes and the fairness index keeps almost constant and is close to 1 in the proposed scheme.

Introduction

Passive optical networks (PONs) have emerged as an attractive broadband access solution to meet the increasing demand of bandwidth from various services [1], [2]. At present, the PONs are mainly based on TDM (time-division-multiplexing) such as EPON and GPON [2]. However, the bandwidth provided for each end-user is limited. The wavelength-division-multiplexing (WDM) technology has extensively been studied in academics and industries as a promising approach to meet huge-bandwidth communication [3], [4]. Due to the large coverage area and easy upgrade, the PON architecture with topology of ring and trees as showed in Fig. 1 is becoming the trend for large-scale passive optical networks [5]. The ring-tree network is comprised of one OLT (optical line terminal), M RNs (remote nodes) and N ONUs (optical network units). All the RNs are connected to the OLT in the ring topology and the ONUs are attached to each RN. Here, Nx (x=1, 2, 3…M) is defined as the number of users connected with the x-th RN. RN consists of circulators, couplers, wavelength blockers (WB) and 1M AWGs (arrayed waveguide gratings). The complex signals for multiple wavelengths are transmitted from one RN to another RN in turn. Specially, the downstream signals are delivered from RN1 to RNM and the upstream signals are delivered from RNM to RN1. The transmission route is realized by the configuration of RN. Here, we take RNM, for example, to explain the operation principle. The OLT is equipped with transmitters and receiver arrays to transmit data or control messages to the ONUs and receive data from the various ONUs. The downstream signals get into RNM through the fiber and they are routed to the coupler1 by circulator 1. Then, the signals are divided into two parts. One part is directly sent to an AWG and a set of them will be de-multiplexed for each ONU. The other part is sent to a WB to enable the wavelengths for other RNs to pass, and they will be sent to the feed fiber through circulator 3 for other RNs׳ downstream transmission. A fast tunable laser with a tuning speed in the range of micrometers and a tuning range of 60 nm is installed in every ONU to enable the ONU to instantly switch from one wavelength to another. Statistical multiplexing can be realized in both wavelength and time domains. In such a multi-wavelength access network based on WDM technology, each user can be assigned one or more wavelengths to meet its bandwidth requirements. The added flexibility and reliability of the network is obvious. However, it also brings challenges to bandwidth management and allocation.

It is known to us that dynamic bandwidth allocation (DBA) mechanism plays a crucial role in producing the best possible results of PONs and it has very important meaning in providing the utmost of network bandwidth utilization as well as high-efficiency network management and operation [6]. Various DBA algorithms have been proposed over the past several years. For multi-wavelength access network, the key design issue of DBA is inter-channel and intra-channel statistical multiplexing. The intra-channel statistical multiplexing has been researched a lot in EPON and GPON [7], [8], [9], [10]. The intra-ONU scheduling schemes such as Deficient Weighted Round Robin (DWRR) [7], fuzzy logic-based algorithm [8], resource reservation method, and Hybrid-Linear method in 10G EPON [9] have been proposed to improve packet loss rate, jitter performance and network throughput. The authors in [10] make use of the excessive bandwidth of lightly loaded ONUs to meet the bandwidth demand of heavily loaded ONUs and they address the idle period problem by using an effective scheduling control mechanism. Most DBA mechanisms are based on the multi-point control protocol (MPCP, IEEE 802.3 ah) and follow the cycle polling principle [11], [12]. Since multi-wavelength access network features multi-granularity (wavelength and time slots), the dynamic bandwidth allocation is carried out in time domain as well as wavelength domain (i.e. inter-channel statistical multiplexing). Reference [13] considered the problem of bandwidth reservation for both dedicated channels and future time slots, and introduced a Time-Wavelength Co-Allocation (TWCA) scheme to effectively improve the overall system throughput and to minimize the transfer latency for data aggregation. A dynamic bandwidth allocation algorithm was proposed for resource reservation and it can cope with temporal traffic overloads by redirecting traffic over uncongested wavelengths [14]. The inter-channel and intra-channel statistical multiplexing has also been discussed a lot in long-reach PON, which is a hot issue recently [15], [16], [17]. For long-reach passive optical networks, a new approach named enhanced inter-thread scheduling (EIS) was proposed in [15], it integrated key features from the existing inter-thread scheduling algorithms. The over-granting problem in long-reach PON was solved by reporting an adjusted timeslot size to the OLT and keeping track of the data that has already been reported earlier under a multi-thread scenario by each ONU [17]. In this way, ONUs only report a timeslot size for which frames can exactly “fit-in” without exceeding the maximum allowed size. In this paper, we take both the inter-channel and intra-channel statistical multiplexing into account. To effectively and fairly allocate bandwidth among end-users, the excess bandwidth distribution is of high importance [18], [19]. Excess distribution can be divided into excess division and excess allocation. Excess division divides excess bandwidth among the overloaded ONUs and redistributes excess credits that are unused by some overloaded ONUs. The taxonomy of excess distribution schemes (including excess division and allocation) was given in [18]. In [19], the OLT allocated the bandwidth to the ONUs in proportion to the weight associated with the excess bandwidth available. The algorithms provided dynamic bandwidth allocation and separate the burden of queue management fairly between the customer and the network. We made comparisons among these excess distributions and proposed a quota-based excess-distribution algorithm to achieve more efficient bandwidth allocation. To avoid delays due to waiting for bandwidth requests from other ONUs, the online scheduling framework is proposed in [20], [21]. The drawback of online scheduling is that the OLT must make bandwidth allocations to each individual ONU without the knowledge of the current bandwidth demands of the other ONUs. Our online DBA scheme overcomes this drawback through an online excess bandwidth distribution mechanism.

In this paper, an algorithm which aims at achieving inter-channel and intra-channel statistical multiplexing in multi-wavelength access network has been proposed. To manage resources efficiently, we present a mathematical model of bandwidth allocation based on matrix theory. The traditional REPORT-GATE mechanism based on MPCP is adopted to carry out the bandwidth allocation. On the basis of Limited with Excess Distribution [18], a novel excess bandwidth distribution algorithm which is based on quota distribution by using Computational Theory of Perceptions (CTP) [22], [23] is proposed to augment the limited grant-sizing scheme and to improve statistical multiplexing of both inter-channel and intra-channel. The proposed algorithm is centralized and it is carried out by OLT. It can achieve high bandwidth utilization and make fair allocation inter ONUs. On the other hand, the excess bandwidth distribution gets more bandwidth for each ONU and achieves low average delay intra ONUs. This quota-based excess-distribution algorithm adaptively adjusts the excess distribution quota assign to each ONU by using the gradient searching method. The excess distribution quota obtained from the algorithm can be adjusted in real time and can decrease the bandwidth waste and ensure the fairness of DBA. Thus, the excess distribution becomes more centralized and independent. Furthermore, the problem of bandwidth monopolization and over-allocation is resolved in our scheme. Besides, we formulate a wavelength assignment mechanism based on release time to eliminate the idle period and increase the bandwidth utilization of the network. Our simulation result demonstrates the effectiveness of our proposed scheme in terms of bandwidth utilization, delay and fairness. The simulation results demonstrate that at least 8.5% bandwidth utilization improvement and low average delay are achieved compared with other schemes and the fairness index keeps almost constant and is close to 1 in the proposed scheme.

Section snippets

Mathematical model of bandwidth allocation

A mathematical model of bandwidth allocation based on matrix theory is proposed to efficiently utilize the bandwidth resources in multi-wavelength access network.

We suppose that there are m wavelengths and n ONUs (optical network units) in the access network (m<n). To specify the relationship between the ONUs and wavelengths, matrix E is introduced as follows:E=[e11e12e1ne21e22e2nem1em2emn]m×nHere, eij=1/0 indicates the i-th wavelength is/is not employed by the j-th ONU.

The traditional

Quota-based excess-distribution algorithm

The bandwidth allocation here is carried out on the basis of Limited mechanism to prevent ONUs from monopolizing the link bandwidth, which is mentioned in Section 2. In this section, we combined the Limited bandwidth allocation with excess distribution to augment the limited grant-sizing scheme and to improve statistical multiplexing of both inter-channel and intra-channel. Moreover, a novel excess bandwidth distribution algorithm is proposed. The proposed algorithm adaptively adjusts the

Wavelength assignment

As mentioned above, we defined n×m matrixes to indicate the allocation of bandwidth for every ONU (n) over every wavelength (m). These matrixes (especially matrix E) indicate whether the i-th wavelength is employed by the j-th ONU or not (namely: eij=1/0). And they make it possible that the ONUs can choose any wavelength to transmit (the corresponding value is eij=1). But they did not solve the problem when to allocate the ONUs on the wavelengths. Thus, in this section, we formulated the

Analysis and simulation

In this section we study the performance of the dynamic bandwidth allocation scheme with the quota-based excess-distribution and the wavelength assignment proposed in this paper. A multi-wavelength access network event-driven simulator was developed in C++. The network system was equipped with 64 ONUs and 4 wavelength channels. The access link data rate from users to an ONU is 100 Mb/s and the wavelength access capacity R=1 Gbps. The guard time Tg=1 μs and the cycle time Tcycle=2 ms. The distance

Conclusion

A novel bandwidth allocation with quota-based excess distribution algorithm and wavelength assignment in multi-wavelength access network was proposed in this paper. We presented a mathematical model of bandwidth allocation based on matrix theory to efficiently manage the bandwidth resources in the network. Specially, a novel quota-based excess-distribution algorithm which could achieve accurate bandwidth allocation for end-users by using CTP was proposed. The excess distribution quota obtained

Acknowledgment

This work is supported by the Programs of Natural Science Foundation of China (Nos. 61132004 and 61275073), the Shanghai Science and Technology Development Funds (Nos. 11511502500 and 11510500500), the Shanghai Leading Academic Discipline Project and STCSM (Nos. S30108 and 08DZ2231100).

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