Efficient time slot assignment algorithms for TDM hierarchical and nonhierarchical switching systems

Two efficient time slot assignment algorithms, called the two-phase algorithm for the nonhierarchical and the three-phase algorithm for the hierarchical time-division multiplex (TDM) switching systems, are proposed. The simple idea behind these two algorithms is to schedule the traffic on the critical lines/trunks of a traffic matrix first. The time complexities of these two algorithms are found to be O(LN2) and O(LM2), where L is the frame length, N is the switch size, and M is the number of input/output users connected to a hierarchical TDM switch. Unlike conventional algorithms, they are fast, iterative and simple for hardware implementation. Since no backtracking is used, pipelined packet transmission and packet scheduling can be performed for reducing the scheduling complexity of a transmission matrix to O(N2) and O(M2), respectively. Extensive simulations reveal that the two proposed algorithms give close-to-optimal performance under various traffic conditions.published_or_final_versio

On maximizing the throughput of opportunistic multicast in wireless cellular networks with erasure codes

In this paper, we discuss the opportunistic multicast scheduling (OMS) in a wireless network using erasure codes. Originally proposed for channels with erasures such as internet, erasure codes are found useful in wireless multicast to achieve better tradeoff between multiuser diversity and the multicast gain. In this work we investigated how to design an opportunistic multicast scheduling scheme which can efficiently improve the per user throughput capacity in a wireless network using erasure codes. Aiming at maximize the throughput, we proposed a maximal OMS (M-OMS) scheme which is inspired by the unicast maximal opportunistic scheduling. We build a system model and provide theoretical analysis on proposed M-OMS scheme. The proposed scheme shows substantial improvement over existing fixed selection ratio opportunistic multicast scheduling schemes (F-OMS). © 2011 IEEE.published_or_final_versionThe 2011 IEEE International Conference on Communications (ICC 2011), Kyoto, Japan, 5-9 June 2011. In Proceedings of the IEEE ICC, 2011, p. 1-

Super monitor design for fast link failure localization in all-optical networks

Monitoring cycle (m-cycle) based design is cost efficient for fast link failure detection and localization in all-optical networks. An m-cycle is an optical loop-back pre-cross-connection of a supervisory wavelength with a dedicated monitor. Generally, a simple monitor is placed at an arbitrary node of an m-cycle for supervision. In this paper, we propose a novel monitor structure, called super monitor. A super monitor is used to supervise multiple intersecting cycles and placed at the intersection node. For a given set of m-cycles, we use super monitors to replace some (or all) simple monitors that originally locate in the set. Two major advantages of the super monitor are: 1) it has lower hardware cost; 2) the collocation of monitoring devices reduces the management cost simultaneously. Besides, the super monitor does not incur additional bandwidth cost. We formulate an integer linear program (ILP) to solve the problem of monitor placement. Numerical results show that our ILP can efficiently place the monitors with a significantly minimized monitoring cost. © 2011 IEEE.published_or_final_versionThe 2011 IEEE International Conference on Communications (ICC 2011), Kyoto, Japan, 5-9 June 2011. In Proceedings of the IEEE ICC, 2011, p. 1-

A simple adaptive MAC scheduling scheme for bluetooth scatternet

A simple adaptive MAC scheduling algorithm, called Gateway Oriented Scatternet Scheduling (GOSS), is proposed for data exchange in a Bluetooth scatternet. Unlike the existing scheme MDRP (Maximum Distance Rendezvous Point) that has a global superframe schedule shared by all gateways, the schedule used by each gateway is individually determined. Equal partition of the superframe schedule at a gateway to each connected piconet can thus be guaranteed, which enables a more robust performance than MDRP. In addition, GOSS allows a variable sized superframe at each gateway. To maximize its performance, the frame size can be dynamically adjusted according to the scatternet topology and traffic load in every predefined adaptation interval. Simulation results show that even a static GOSS prevails over MDRP. If the adaptation technique is used, further performance enhancement can be found.published_or_final_versio

TCP-Swift: An end-host enhancement scheme for TCP over satellite IP networks

A new transport layer protocol called TCP-Swift is proposed for enhancing the TCP performance over satellite IP networks. TCP-Swift replaces the conventional TCP slow start and fast recovery algorithms by speedy start and speedy recovery. With speedy start, a TCP-Swift sender opens up its congestion window in only two round trip times. This significantly shortens the time needed in probing the network for equilibrium state. With speedy recovery, we can infer the cause of a packet loss by observing the ACK stream received at the sender. If the loss is due to wireless transmission error, the sender's congestion window can be re-opened up more aggressively to fully utilize the available satellite link bandwidth. We show that TCP-Swift outperforms existing TCP schemes by simulations.published_or_final_versio

Multicast scheduling in feedback-based two-stage switch

Proceedings of the IEEE Workshop on High Performance Switching and Routing, 2009, p. 28-33Scalability is of paramount importance in high-speed switch design. Two limiting factors are the complexity of switch fabric and the need for a sophisticated central scheduler. In this paper, we focus on designing a scalable multicast switch. Given the fact that the majority traffic on the Internet is unicast, a cost-effective solution is to adopt a unicast switch fabric for handling both unicast and multicast traffic. Unlike existing approaches, we choose to base our multicast switch design on the load-balanced two-stage switch architecture because it does not require a central scheduler, and its unicast switch fabric only needs to realize N switch configurations. Specifically, we adopt the feedback-based two-stage switch architecture [10], because it elegantly solves the notorious packet mis-sequencing problem, and yet renders an excellent throughput-delay performance. By slightly modifying the operation of the original feedback-based two-stage switch, a simple distributed multicast scheduling algorithm is proposed. Simulation results show that with packet duplication at both input ports and middle-stage ports, the proposed multicast scheduling algorithm significantly cuts down the average packet delay and delay variation among different copies of the same multicast packet. Keywords-Feedback-based two-stage switch, scalable multicast switch, load-balanced switch. © 2009 IEEE.published_or_final_versio

Minimizing internal speedup for performance guaranteed optical packet switches

Providing QoS guarantee for Internet services is very important It evokes the issue that packet switches should provide guaranteed performance (i.e. 100% throughput with bounded worst-case delay). Optical switching technology is widely considered as an excellent solution for packet switches in future networks. However, to achieve guaranteed performance in optical packet switches, an internal speedup is required due to the existence of reconfiguration overhead. How to reduce the internal speedup is the main concern for making these switches practical In this paper, we first derive the internal speedup S as a function of the number of switch configurations N S and the reconfiguration overhead δ, or S=f(N S,δ). We show that the recently proposed ADJUST algorithm is flawed. Based on the internal speedup function we derived, a new algorithm (ADAPTIVE), with time complexity of O((λ-l)N 2logN), is proposed to minimize S. © 2004 IEEE.published_or_final_versio

Scheduling optical packet switches with minimum number of configurations

In order to achieve the minimum traffic delay in a performance guaranteed optical packet switch (OPS) with reconfiguration overhead, the switch fabric has to use the minimum number of configurations (i.e. N configurations where N is the switch size) for traffic scheduling. This requires a very high speedup in the switch fabric to compensate for the loss in scheduling efficiency. The high speedup requirement makes the idea of using N configurations (to schedule the traffic) impractical under current technology. In this paper, we propose a new scheduling algorithm called α i-SCALE to lower the speedup required. Compared with the existing MIN algorithm [5], α i- SCALE succeeds in pushing the speedup bound (i.e. worst-case speedup requirement) to a much lower level. For example, when N=200, the speedup bound required to compensate the loss in scheduling efficiency is 30.75 for MIN, whereas 23.45 is sufficient for our α i-SCALE. © 2005 IEEE.published_or_final_versio

D-LQF: An efficient distributed scheduling algorithm for input-queued switches

Due to the massive use of parallel and distributed operations of inputs and outputs, iterative scheduling algorithms are attractive in finding a maximal size matching for an input-queued switch. For constructing a large high-speed switch, a distributed multi-chip implementation of an iterative scheduling algorithm should be followed. Since different chips may locate on different switch linecards and linecards can be separated by tens of meters, the propagation delay between chips/linecards is non-negligible. This calls for a pipelined implementation of a single-iteration scheduling algorithm. In this paper, an efficient, pipelined single-iteration algorithm called Distributed Longest Queue First (D-LQF) is proposed. In D-LQF, exhaustive service policy is adopted for reusing the matched input-output pairs in the previous time slot. To avoid incorrectly granting an empty VOQ from transmission (caused by inter-chip latency), each output keeps track of the lengths of all VOQs destined to it. As compared with other single-iteration scheduling algorithms, extensive simulation results show that D-LQF provides the best delay-throughput performance. © 2011 IEEE.published_or_final_versionThe 2011 IEEE International Conference on Communications (ICC 2011), Kyoto, Japan, 5-9 June 2011. In Proceedings of the IEEE ICC, 2011, p. 1-

A new phase for screening redundant broadcast nodes in source-independent broadcasting protocols

Following the distributed approach, source-independent broadcasting protocols select a subset of nodes in a network as broadcasting nodes to cover the entire network. The selection of broadcasting nodes is performed prior to actual message transmission. These broadcasting nodes collectively form a connected dominating set or CDS. Aiming at finding a minimum CDS, existing source-independent broadcasting protocols consist of two phases. In this paper, we propose to add a third phase to eliminate unnecessary nodes in a CDS while ensuring all remaining nodes are still connected. We call it the redundant node screening phase. This paper shows that this new phase is a very important element that has been ignored by existing source-independent broadcasting protocols. When applying the new phase on existing broadcasting protocols, the savings in terms of number of nodes in the CDS could be as high as 21% in a 1000m x 1000m network of 20 nodes. © 2011 IEEE.published_or_final_versionThe 2011 IEEE International Conference on Communications (ICC 2011), Kyoto, Japan, 5-9 June 2011. In Proceedings of the IEEE ICC, 2011, p. 1-