Rizwan Aslam Butt

Improved dynamic bandwidth allocation algorithm for XGPON

Passive optical networks (PONs) require a dynamic bandwidth allocation (DBA) algorithm at the optical line terminal for efficient utilizationofupstreambandwidth among the optical network units (ONUs) as per the quality of service requirements for each traffic class defined by PON standardizing bodies. The GigaPON access network (GIANT) was the first International Telecommunication Union compliant DBAalgorithm, which is further improved by Immediate Allocation with Colorless Grant (IACG) and Efficient Bandwidth Utilization (EBU) algorithms. However, the polling mechanism of IACG and EBU may not report the true bandwidthdemandofONUsduring a service interval. Furthermore, ONU scheduling mechanisms give preference to best effort traffic over the assured traffic during recursive allocation cycles in a service interval, which results in an increase in upstream delays for the assured traffic class. This paper presents an improved bandwidth utilization (IBU) algorithm, which rectifies these deficiencies with a novel polling and scheduling mechanism. Experimental results show that IBU improves the mean of upstream delays of type 2 traffic up to 98%, 93%, and 76% and up to 99%, 92%, and 73% for type 3 traffic compared to the GIANT, IACG, and EBU algorithms, respectively. IBU also shows the least frame loss compared to these state-of-the-art algorithms.

Comprehensive Polling and Scheduling Mechanism for Long Reach Gigabit Passive Optical Network

Abstract Dynamic bandwidth assignment (DBA) schemes for long reach PONs face a suffer from higher upstream channel idle time due to long round trip time (RTT). In ITU PONs, the DBA schemes; Immediate allocation with colorless grant (IACG), Efficient bandwidth utilization (EBU) and GPON redundancy eraser algorithm (GREAL) minimize idle time by sending bandwidth grants to the optical network units (ONUs) every downstream frame (DF). EBU further improves IACG by utilizing unused bandwidth (UBW) of other traffic classes. Sending the grant results every DF requires optical line terminal (OLT) to remember all previous grants sent to ONU during RTT and subtract them from the received queue reports. Since, both IACG and EBU assign the excess bandwidth equally to ONUs. Therefore, the OLT is actually not aware of the complete grant to each traffic class and thus do not subtract these completely from receiving reports. This leads to wastage of bandwidth and higher US delays due to over granting. GREAL resolves this problem by not utilizing the excess bandwidth which also leads to increased US delays. The proposed scheme in this study eliminates this shortcoming by allocating excess bandwidth to each traffic class completely at the OLT. Moreover, the UBW assignment mechanism of EBU is also improved. Simulation results show a 50–85 % reduction in delays of type-2 (T2) and type-3 (T3) traffic classes versus GREAL and IACG and up to 40 % reduction in delays for type-4 (T4) versus EBU.

A Survey of Dynamic Bandwidth Assignment Schemes for TDM-Based Passive Optical Network

Abstract In time division, multiple access (TDMA)-based passive optical network (PONs), a dynamic bandwidth assignment (DBA) is necessary for efficient utilization of the available bandwidth of the upstream link. An efficient DBA scheme can improve the upstream performance of a traffic class of an ONU in two ways. First, it can increase the bandwidth assignment to it by efficiently utilizing the available bandwidth. Secondly, it can reduce the channel and frame idle time by increasing the polling frequency and by assigning extra surplus bandwidth not used by the other ONUs. Many DBA schemes have been reported for both ITU PONs (GPON and XGPON) and IEEE PONs (EPON and 10 G EPON). In this study, we explain the impact of DBA scheme on the upstream performance of PON and then do a thorough survey of both PON standards, categorize the DBA schemes and review them critically. Based on the literature review we also give our opinion on the most suitable DBA scheme for both type PONs on the basis of upstream delays, frame loss and bandwidth utilization efficiency.

On spatially disjoint lightpaths in optical networks

The core network in the information communication technology infrastructure is based on the optical fiber technology. The core network is of prime importance because it connects all the central offices in the wired communication networks and the mobile switching centers in the wireless communication networks. The optical link between two network nodes is a lightpath, which offers very high speed, low loss, lower cost, highly reliable, secure and very high capacity, end-to-end communication over a very long distance. Any damage to a lightpath in the event of a disaster may lead to massive service interruptions and financial losses for the network operators. Therefore, survivable routing in these networks is very important. Generally, the survivability is ensured by having a backup lightpath to keep communication intact because the primary and the backup light paths are always disjoint. However, they may still fail simultaneously in the event of a large-scale disaster, if their separation distance in the physical plane is small. Hence, the spatial distance between the disjoint lightpaths should also be taken into consideration when establishing the lightpaths. Our contributions in this paper are twofold: (1) a routing algorithm is proposed for provisioning a pair of link-disjoint lightpaths between two network nodes such that their minimum spatial distance (while disregarding safe regions) is maximized, and (2) another routing algorithm is proposed for provisioning a pair of link-disjoint lightpaths such that the path weight of the primary lightpath is minimized, subject to the constraint that the backup lightpath has some particular geographical distance from the primary lightpath. Through extensive simulations, we show that our first algorithm can provide maximum survivability against spatial-based simultaneous link failures (due to the maximized spatial distance), whereas the second algorithm can tune the spatial distance between the lightpaths keeping in view the target survivability requirements and the path weight for the primary lightpath.

Processing efficient frame structure for passive optical network (PON)

Abstract The time division multiplexed (TDM) based passive optical networks like GPON/XGPON and EPON/10G-EPON use broadcast mechanism for downstream (DS) communication. This results in any DS frame being received and processed by all optical network units (ONUs), leading to significant processing energy wastage. Specifically, the ITU compliant PONs (GPON/XGPON) frame structure further aggravates this problem due to its inefficient frame structure and synchronous nature which requires sending of DS frames every 125 μs. This frame structure requires an ONU to completely process every DS frame completely, even if it is not destined for it. The bit interleaved PON (Bi-PON) resolves this problem by changing the frame structure to a bit interleaved pattern and introduce a decimator unit that enables an ONU to tune to its concerned bits only. However, due to additional hardware requirement, this solution is not applicable to current ONU architecture. Consequently, this study presents a processing efficient version of GPON frame that helps an ONU to identify an unrelated DS frame at its start and thus discard it without complete processing. A processing efficient strategy for the medium access layer (MAC) processor of an ONU is also presented. The simulation results show a processing energy saving of 88%, 89% and 89.47% with proposed frame structure for a split ratio of 16, 32 and 64 respectively.