Hyoung-Il Lee

A Load Balancing Scheme for Two-Stage Switches Maintaining Packet Sequence

In this paper, we propose a novel load-balancing scheme for two-stage switches which does not disturb the sequence of packets. The proposed scheme uses chamber queues(CQs) in front of the second crossbar fabric as well as VOQs in front of the first crossbar. A chamber queue is composed of N banks each of which can store only one packet destined for each output. The two crossbar fabrics in the proposed switch are configured by a deterministic sequence of N connection patterns as in other two-stage switches. In a time slot, the proposed switch transfers packets from non-empty VOQs to the corresponding empty banks of CQs via the first crossbar, and the packets from CQs are switched to their destinations via the second crossbar. While the proposed scheme is very simple, it can achieve 100% throughput under not only uniform but also non-uniform traffic. Moreover, the simulation results show that the average delay of packets in the proposed two-stage switch is lower than that in the original two-stage switch.

Permutation realizability and fault tolerance property of the inside-out routing algorithm

In this paper, we analyze ways of realizing permutations in a class of 2log/sub 2/N- or (2log/sub 2/N-1)-stage rearrangeable networks. The analysis is based on the newly developed inside-out routing algorithm and we derive the upper and lower bounds on the number of possible realizations of a permutation. It is shown that the algorithm can provide us with comparable degrees of freedom in realizing a given permutation as the well-known looping algorithm, while it can be more generally applied to a class of 2log/sub 2/N- or (2log/sub 2/N-1)-stage rearrangeable networks. In finding a set of complete assignments for the center-stage cycles, alternate realizations of a permutation can be obtained by changing the initial position, changing the assigning direction, or even interchanging the first-level decompositions of the permutation. We also show that these numerable alternate realizations can be utilized to make the networks tolerate some sets of faults, i.e., control faults of SEs including stuck-at-straight and stuck-at-cross. Various cases of single control faults at the center stages and other stages are examined through examples. These new approaches originate from routing outward from center stages to outer stages; therefore, the center stages and two half networks may be treated separately.

A two-stage switch with load balancing scheme maintaining packet sequence

In this letter, we propose a novel load-balancing scheme for two-stage switches, which does not disturb the sequence of packets. The proposed scheme uses chamber queues (CQs) in front of the second crossbar fabric as well as VOQs in front of the first crossbar. While the proposed scheme is very simple, it can achieve 100% throughput under not only uniform but also non-uniform traffic. Moreover, the simulation results show that the average delay of packets in the proposed two-stage switch is lower than that of the original two-stage switch.

Hybrid Optical Transport Network (HOTNET): An Optical Network with Hybrid Switching Technologies for Integrated Services

In this paper, we propose a novel architecture for optical transport networks and its operation scheme guaranteeing the QoS requirements based on real-time traffic measurement. The key concept of the proposed architecture, which we call hybrid optical transport network (HOTNET), is to adopt both optical circuit switching and optical message switching in an optical network. To implement two different switching technologies in a single network, we modify the optical burst switching scheme and merge it into a TDM wavelength routed network. Then, we propose a control framework and an architecture of a switching node for this hybrid switching paradigm. We also discuss a real-time bandwidth provisioning scheme which utilizes the advantages of two respective switching schemes for traffic engineering. Finally, we evaluate the performance of the proposed scheme via computer simulation and the results show that it can guarantee the traffic QoS requirements while maintaining high channel utilization.

A practical approach for statistical matching of output queueing

We study a practical approach to match the performance of an output-queued switch statistically. For this purpose, we propose a novel switching architecture called a multiple input/output-queued (MIOQ) switch that requires no speedup for providing sufficient switching bandwidth. To operate an MIOQ switch in a practical manner, we also propose a multitoken-based arbiter which schedules the switch at a high operation rate and a virtual first-in first-out queueing scheme which guarantees the departure order of cells belonging to the same traffic flow at output. Additionally, we show that the proposed switch can naturally provide asymmetric bandwidth for inputs and outputs, which may be important in dealing with the links with different bandwidth demands. Finally, we compare the performance of an MIOQ switch with that of an output-queued switch and discuss the design criteria to match the performance of an output-queued switch.

A Load Balancing Scheme for Birkhoff-von Neumann Input-Queued Switches

In this paper, we propose a novel load-balancing scheme for the Birkhoff-von Neumann input-queued (BvN-IQ) switch, which we call the cyclic exchange. According to the cyclic exchange scheme, in each time slot each linecard transfers a cell from its non-empty VOQ to the empty VOQ of another linecard which is destined for the same output. In order to guarantee the cell sequence in this procedure, we propose a simple rule of selecting the cells to be transferred for load balancing, and prove the sequence guarantee by the proposed rule. Since the cyclic exchange is performed locally between two linecards, its communication and computation overhead is not too heavy to implement. To be specific, the communication overhead of the proposed scheme is the transmission of N bits and its computation overhead corresponds to a priority encoder with a fixed highest priority. The simulation results show that the proposed scheme achieves 100% throughput asymptotically and shorter delay than the two-stage switch.

Analysis model of multiple input-queued switches with PIM scheduling algorithm

In this letter, we propose a new analysis model of multiple input-queued switches that use the parallel iterative matching (PIM) scheduling algorithm under i.i.d Bernoulli traffic. Compared to the previous analysis models, our approach incurs very low computational complexity while maintaining good accuracy by employing a simple queueing model. Specifically, we model an input queue of the switch as a synchronous Geom/Geom/1/B queue with a service rate which is directly obtained from a PIM scheduling algorithm. We perform the simulation and verify the accuracy of our model.

A high performance ATM switch based on the augmented composite banyan network

In this paper, we propose a new high performance ATM switch architecture based on a high connectivity multipath multistage interconnection network called augmented composite banyan network (ACBN). The ACBN is created by adding a link to each switching element of the composite banyan network, which is a multipath network with at least two disjoint paths and was originally proposed in Seo and Feng (1995). The switch performance is studied under uniform and full load conditions. The analysis and simulation results show that the proposed switch can achieve a required cell loss probability using fewer stages than previously reported switches.

The Augmented Composite Banyan Network

A new multipath multistage interconnection network called the Augmented Composite Banyan Network (ACBN) is proposed. The ACBN is created by adding a link to each SE of the Composite Banyan Network (CBN), which is a multipath network with at least two disjoint paths and was originally proposed in (Seo and Feng, 1995). Therefore, the basic building blocks in the ACBN are 4/spl times/4 SEs with log/sub 2/N stages. The ACBN inherits the favorable features of the CBN such as regularity, symmetry and easy rerouting capability under faults and conflicts. The ACBN also has an efficient and fast control algorithm that can easily generate a primary routing tag and alternative routing tags as in the CBN. A major improvement of the ACBN over the CBN is the higher connectivity with four disjoint paths between any source and destination pair. Moreover the ACBN can generate alternative routing tags in a much simpler way i.e., by a simple binary operation not by the conversion table as in the CBN. To compare the ACBN with other networks in connectivity, we introduce the definition of a degree of connectivity as a new connectivity measure function. The comparison results show that due to high connectivity the ACBN can resolve more random connection requests than other networks by using only a small amount of additional hardware.

Design and analysis of an ATM switch based on a distributed network: weaved GSN

We design a new high performance ATM switch architecture based on a distributed network with O(N) hardware complexity. Considering various performance parameters such as average hop distance, adoptability of self routing, and flexibility on the number of nodes, we choose the generalized shuffle network (GSN) as a building block for the ATM switch design. To improve the throughput of the switch, a layering strategy called weaved GSN (WGSN) is adopted in our switch design. The performance of WGSN is studied under uniform and full load conditions through analytic modeling and simulation. The analysis and simulation results show that the proposed switch has better throughput and cell loss performance when compared with other banyan-based switch architectures known so far.