This paper discusses research trends in high-speed LANs, which are leading the way to private networks. It also mentions issues that need to be solved to achieve high-performance seamless networks.

We propose burst based bandwidth reservation method called FRP (Fast Reservation Protocol) in ATM LAN with general topology, and evaluate its performance. In FRP, the bandwidth is allocated on each link on burst basis, not on call basis. This enables an effective use of network resources when it is applied to highly bursty traffic, which can be typically found in data communications. The problem of FRP is that VCs traversing the different number of links experience different blocking probabilities as can be found in the conventional circuit-switching networks. In this paper, we treat a fairness issue in FRP-based ATM local area networks. The Max-Min flow control is adopted as the fair bandwidth allocation method to accomplish the fairness in the throughput. However, the original Max-Min flow control works in a centralized fashion, which is not desirable in the FRP-based ATM LAN. We therefore propose a "semi"-distributed Max-Min flow control suitable to FRP, in which each switch maintains its own local information about bandwidth usage of the connected links. Through simulation experiments, we show that the proposed semi-distributed Max-Min flow control can achieve the fairness among VCs as the original Max-Min flow control when the propagation delays are not large and the number of VCs is not so much.

We propose an architecture of a high-speed internetworking device using central control method. Co-operations of hardware and software is required to realize high relay performance. For the hardware, we have designed an original bus arbitration control method to achieve a high throughput of a data bus. For the software, we have devided a normal relay processing from other processing and built it as a basic function of the monitor. By this method, relay perfomance improves dramatically, because of a multiple effect of the reduction of software overheads and the improvement of cache hit ratio. We have developed the prototype device and confirmed the effects of the proposed method.

Asynchronous Transfer Mode (ATM) is a promised bearer transmission service for high speed multimedia LAN. Recently, high speed multimedia ATM LAN products have been available. Therefore, in order to interconnect them, the multimedia backbone LAN, which has the expandable high throughput over 10Gbps, supporting multicast, multi-QoS, and many interfaces including 622 Mbps, will be widely required. In this paper, the VLSI oriented input and output buffered switch architecture is proposed as the hardware architecture for multimedia backbone switch node. This paper describes that the chip set consisting of four VLSIs, that is, the switch element, the switch access, the distributor/arbiter, and the multiplexer/demultiplexer, can realize the backbone switch core, and the main specifications required to each VLSI are derived.

Both available bit rate (ABR) service and unspecified bit rate (UBR) service with early packet discard (EPD) schemes have been considered for supporting data applications in ATM networks. Since transmission control protocol (TCP) is perhaps the most widely used transport layer protocol in existing data networks, the performance of TCP over ATM using ABR service and UBR service with EPD schemes is of great interest to ATM equipment vendors and service providers. In this paper, we present a simulation study of this interesting issue in a LAN environment using some benchmark network configurations proposed in the ATM Forum. Our simulation results show the following: (1) With UBR service and EPD schemes, TCP suffers significant performance degradation in terms of fairness and requires relatively large switch buffer even with a small number of active virtual connections over a LAN configuration, and (2) for the same set of network configurations and with ABR service using explicit rate feedback schemes, TCP achieves good performance in terms of fairness and link utilization, and requires relatively small switch buffer.

Rate-based congestion control is a promising scheme as data transfer service in ATM networks, and has been standardized in the ATM Forum. To migrate the existing upper layer protocols to ATM networks, however, further investigation is necessary. In particular, when ABR service class is applied to TCP (Transmission Control Protocol), duality of congestion control schemes in different protocol layers, i.e., conventional window-based congestion control in the Transport layer and ratebased congestion control in the ATM layer, may have a unexpected influence on performance. As an alternative approach for supporting TCP protocol, EPD (Early Packet Discard) has been recently proposed, which adds the function to the UBR (Unspecified Bit Rate) service. It does not have a "duality problem" since EPD only discards cells selectively to improve packet-level performance. In this paper, we exhibit performance of TCP protocol over ATM networks by using a simulation technique. We first compare rate-based control of ABR service and EPD applied to UBR service, and show that rate-control achieves better fairness and higher throughput in most circumstances. However, rate-based control requires careful tuning of control parameters to obtain its effectiveness and a duality problem leads to unexpected degradation of TCP-level performance. By the rate-based congestion control, temporal congestion at the switch is quickly relieved by the rate down of the source terminals. However, our simulation explores that if the parameter set of the rate-based congestion control is not appropriately used, the congestion is also recognized at TCP due to packet drops and TCP unnecessarily throttles its window size. To avoid this sort of the problem, we develop the appropriate parameter set suitable to TCP on ABR service, and point out that some modification of TCP may be necessary for further performance improvement.

The benefits of ATM techniques have been widely recognized and many organizations envisage the introduction of ATM techniques into their telecommunication networks. The ATM benefits can, however, be fully exploited only after effective network resource management techniques have been developed. This paper focuses on CBR-VP management techniques. The ATM transport network architecture and VP roles are summarized. Next, the issues of VP accommodation design are described. The point is how to create a design that accommodates cell loss and cell delay jitter, both of which depend on various network parameters and conditions. For this purpose, analytical procedures based on an M/D/1 queueing model are adopted. The approximation method is shown to be very effective in practical use through computer analysis. The method guarantees conservative QOSs. Finally, the proposed method is applied to several design examples to illustrate VP management issues. The proposed method will enable ATM techniques to be introduced to our telecommunication networks by the mid-1990's.

This paper proposes a half-chip offset QPSK (Quadrature Phase Shift Keying) modulation CDMA (Code Division Multiple Access) scheme to allow the simple differential detection while realizing a compact spectrum in nonlinear channels for wireless LAN systems. The experimental results show the proposed scheme achieves excellent Pe (probability of error) performances in ACI (adjacent channel interference) and CCI (co-channel interference) environments. Moreover, by employing time diversity and high-coding-gain FEC (Forward Error Correction), the half-chip offset QPSK-CDMA scheme realizes an improvement of 3.0 dB (in terms of Eb/No at a Pe of 10⁵) in Rician fading environments with a Doppler frequency fD of 10 Hz and a delay spread of 40 nsec.

This paper proposes a new digitized group modulator for radio base station transmitters of multi-carrier TDMA. This group modulator can flexibly set carrier spacing and features a simple construction as a result of employing the Simple Fractional Sampling technique. A group modulator LSI was designed and built using 0.5-µm BiCMOS technology, and a π/4-shifted QPSK group modulator was constructed using this LSI. Experiments confirm that the modulator simultaneously generates multiple carriers in a wide bandwidth without the need for precise adjustment and there is little difference between each of the carriers in terms of BER performance. Moreover, experiments confirm that the group modulator's burst-output (frequency hopping) performance is excellent.

Subcarrier multiplexing (SCM) transmission over optical fiber for microcelluler mobile communication systems has been actively studied. However, as increasing the number of channels, intermodulation distortion (IMD) becomes the intrinsic problem. On the other hand, coherence multiplexed (CM) system for broad-band access communications has been developed and may find wide spread application because of its simplicity and flexibility. However the interference noise produced by the mixing of different optical channels at a photodetector is the serious problem. Therefore, on the down link for fiber optic microcell systems, it is attractive to consider the combination of SCM and CM: coherence multiplexed/subcarrier multiplexing (CM/SCM). In this hybrid scheme, since each optical channel is modulated by M microwave subcarriers, the bandwidth allocation is very flexible. In addition, the same microwave subcarrier frequency may be used among the different optical channels, because the optical channels are uncorrelated each other. We derive the received carrier-to-noise ratio (ONR) characteristics of CM/SCM system with optical amplifier as preamplifier or in-line amplifier for the optical down link from central station to base stations. The system performance of CM/SCM system is compared with those of coherent SCM (C-SCM) and CM systems from the viewpoint of the maximum number of base stations to be admitted. It is shown that the performance of CM/SCN system is superior to those of C-SCM and CM systems when optical power at the input to in-line amplifier is limited. CM system has good performance when preamplifier gain and optical power are large, and C-SCM system is the best when in-line amplifier is used.

This letter studies the Peak Cell Rate (PCR) policing of ATM connections that consist of multiple cell flow components. It is shown that the conventional methods proposed for policing the aggregate flow do not use the network's resources efficiently. This letter proposes a simple and efficient UPC (Usage Parameter Control) mechanism based on a tandem leaky bucket for multi-component ATM connections. The results show that network resource requirements can be minimized, with reasonable hardware complexity.

In ths letter, we suggest a collision resolution algorithm when the packet length is random, and analyze its throughput and delay performance. Here, three different packet length distributions and two feedback schemes (ternary and binary success/failure feedback) are considered.

The reception level of a round-trip signal from a VSAT (Very Small Aperture Terminal) was monitored continuously for three years starting October 1991.For these experimental measurements, a commercial satellite channel (up-link 14GHz/downlink 12GHz, bandwidth 100kHz) was used and rainfall was measured simultaneously. Data gathering time interval of 2 seconds was adopted to elucidate very rapid variation and lower percentage statistics. In this paper, attenuation due to rainfall is shown using the data obtained in this three-year period. It is shown that so far, the measured rain attenuation agrees very well with the values estimated using the CCIR model, and limits the range where the cumulative time exceeds 0.01%, even for our VSAT system in Tagajo, Miyagi Prefecture, Japan.