Masayoshi Nabeshima

Performance Evaluation of MulTCP in High-Speed Wide Area Networks

SUMMARY It is reported that TCP does not perform well in highspeed wide area networks. Because MulTCP behaves like the aggregate of N TCP flows, MulTCP can be used to achieve throughputs of 1 Gbps or more. However, no performance evaluation of MulTCP in high-speed wide area networks has been published. Computer simulations are used to evaluate the performance of MulTCP. The results clarify that synchronized packet losses greatly impact the performance of MulTCP.

Performance Evaluation and Comparison of Transport Protocols for Fast Long-Distance Networks

It is well known that TCP does not fully utilize the available bandwidth in fast long-distance networks. To solve this scalability problem, several high speed transport protocols have been proposed. They include Highspeed TCP (HS-TCP), Scalable TCP (S-TCP), Binary increase control TCP (BIC-TCP), and H-TCP. These protocols increase (decrease) their window size more aggressively (slowly) compared to standard TCP (STD-TCP). This paper aims at evaluating and comparing these high speed transport protocols through computer simulations. We select six metrics that are important for high speed protocols; scalability, buffer requirement, TCP friendliness, TCP compatibility, RTT fairness, and responsiveness. Simulation scenarios are carefully designed to investigate the performance of these protocols in terms of the metrics. Results clarify that each high speed protocol successfully solves the problem of STD-TCP. In terms of the buffer requirement, S-TCP and BIC-TCP have better performance. For TCP friendliness and compatibility, HS-TCP and H-TCP offer better performance. For RTT fairness, BIC-TCP and H-TCP are superior. For responsiveness, HS-TCP and H-TCP are preferred. However, H-TCP achieves a high degree of fairness at the expense of the link utilization. Thus, we understand that all the proposed high speed transport protocols have their own shortcomings. Thus, much more research is needed on high speed transport protocols.

The i-QOCF (iterative quasi-oldest-cell-first) algorithm for input-queued ATM switches

This paper proposes a new scheduling algorithm for input-queued ATM switches, called the iterative quasi-oldest-cell-first (i-QOCF) algorithm. In i-QOCF, each input port and each output port maintains its own list. The length of the list can be N,2/spl times/N,...,B/spl times/N, where B is the size of the buffer that queues cells destined for an output port. The list maintained by an input port contains the identifiers of those output ports to which that input port will send a cell. The list maintained by an output port contains the identifiers of input ports which have a cell destined for that output port. We show the performance of i-QOCF and results in which we compare i-QOCF with i-OCF in terms of cell delay time. We find that an input-queued ATM switch with i-QOCF and virtual output queue (VOQ) can achieve 100% throughput for independent arrival processes. The 3-QOCF is enough to achieve convergence during one cell time. If we use a 3-QOCF in which the list length is 3/spl times/N, then its cell delay time performance is almost the same as that of a 4-OCF.

New scheduling mechanisms which efficiently utilize policing for GFR service

This paper proposes new scheduling mechanisms for meeting fairness criteria which are not met by conventional scheduling mechanisms such as weighted round robin (WRR). These proposed mechanisms utilize the arrival of untagged cells at an ATM switch not only for a frame drop policy but also for deciding which VC cell is eligible to be serviced. The guaranteed frame rate (GFR) service using the proposed mechanisms can provide the users with bandwidth allocation which meets several fairness criteria.

Scalable-distributed-arbitration ATM switch supporting multiple QoS classes

This paper proposes a multi-QoS scalable-distributed-arbitration (MSDA) ATM switch that supports both the high-priority class and the low-priority class under the head-of-line-priority discipline. It has a crosspoint buffer and a transit buffer, each consisting of a high-priority buffer and a low-priority buffer. Arbitration is executed between the crosspoint buffer and the transit buffer in a distributed manner. The MSDA switch extends the advantage of our previously proposed single-QoS scalable-distributed-arbitration (SSDA) switch. It is expandable while permitting high output-line speeds due to the distributed arbitration. The SSDA switch has a problem when its delay-time-based cell selection mechanism is applied to the low-priority class due to the limitation of the number of bits for the delay measure in the cell overhead. We solved this problem by introducing a distributed-ring-arbiter-based cell selection mechanism at each crosspoint for the low-priority class. The low-priority transit buffer at each crosspoint has virtual queues in accordance with the upper input ports. Cells for the low-priority class are selected by distributed ring arbitration among the low-priority crosspoint buffer and the virtual queues at the low-priority transit buffer. Simulations confirm that the MSDA switch ensures fairness in terms of delay time for the high-priority class, while it ensures fairness in terms of throughput for the low-priority class.

New transfer methods for client-server traffic in ATM networks

This paper presents new transfer schemes for client-server traffic over ATM networks, with the objective of achieving a bounded transmission time of about one second for as many connection requests as possible. We evaluate via simulations the performance of these new schemes in terms of network utilization, cell loss ratio, and transmission time. The simulation results show that these schemes provide effective means of supporting client-server traffic with quasi-real time requirements.