Increasingly, there is a need for context-aware networking. For example, in multimedia networks with heterogeneous end equipment, if two or more communicating nodes do not have the same application-layer interface, the network should be aware of the "context" of the communication in order to select an appropriate converter through which to route connections. In this paper, we motivate the need for logical connections, where a logical connection consists of one or more network-layer connections routed through application-layer resources, such as bridges and/or format/rate converters. We then describe the application-aware routing protocol (AARP) for managing logical connections.

This paper proposes algorithms for handoff, location, and connection management in a wireless asynchronous transfer mode (ATM) local-area network (LAN). Fast handoffs while maintaining cell sequence and quality-of-service (QoS) guarantees are achieved by distributing switching functionality to base stations, and using a networking scheme based on provisioned virtual trees. A new distributed location management scheme using a minimal registration procedure and broadcasts on wired links is proposed for this LAN. The detailed signaling procedures that support the algorithms for mobility and connection management are described. Finally, an implementation of these procedures and an analysis of the measured data is presented. Measurements of service times obtained from this implementation indicate that over 100 calls/s. can be handled by each node in 50-node network with a high-percentage of mobiles (75%) relative to fixed endpoints. This is comparable to current wired ATM switch call handling throughputs, in spite of the fact that these nodes perform additional handoff and location management functions. The data also indicates handoff latency times of 1.3 ms. This validates our proposal for maintaining cell sequence while performing handoffs.

In a wireless packet (e.g., ATM) network that supports an integrated mix of multimedia traffic, a large variety of mobiles with different service rates will need to be accommodated efficiently in a bandwidth-on-demand fair-sharing manner. We propose and study multi-code CDMA (MC-CDMA) with distributed-queueing request update multiple access (DQRUMA) for multi-rate wireless packet networks. The network incorporates MC-CDMA (a flexible multiplexing scheme for providing multi-rate packet transmissions) and DQRUMA (an efficient demand-assignment multiple access protocol for wireless access and scheduling) to form a unified bandwidth-on-demand fair-sharing platform for multi-rate wireless services. A slot-by-slot packet transmit scheduling policy provides the possibility of slot-by-slot allocation of pseudo-noise (PN) codes (primary codes) and optimal power levels to the mobiles involved in packet transmissions. Also, a maximum capacity power allocation (MCPA) criterion is derived to exploit the subcode concatenation property of the MC-CDMA transmission. Simulation results show that the system provides close to ideal-access performance for multi-rate mobiles, both with homogeneous traffic characteristics and with a mix of heterogeneous traffic characteristics.

This paper presents a Wireless Virtual Local Area Network (WVLAN) to support mobility in IP-over-ATM networks.Mobility is handled by a joint ATM-layer handoff for insession mobility and MAC-layer handoff for inter-session mobility, such that the effects of mobility are localized and transparent to the higher-layer protocols.Different functions, such Address Resolution Protocol (ARP), mobile location, and ATM connection admission are combined to reduce front-end delay for connectionless packet transmission in connection-oriented ATM networks.The proposed WVLAN, through the use of ATM technology, provides a scalable wireless virtual LAN solution for IP mobile hosts.

Multi-code direct-sequence code division multiple access (MC-CDMA) has been proposed as a flexible multiple access scheme for wireless packet networks that support a large variety of mobiles with different and even time-varying rates. However, the interference model typically used with conventional DS-CDMA cellular systems - a large number of low-power mobiles uniformly distributed in cells - may not hold. In MC-CDMA cellular systems, it is possible for a high-rate mobile, perhaps near the boundary of a cell, to have all the codes for high-rate transmission - therefore transmitting at high power and causing significant interference to the neighboring cell. In this study, we analyze the effects of MC-CDMA intercell interference on the reverse link (i.e., mobile to cell site) and investigate a maximum capacity power allocation (MCPA) criterion that exploits the sub-code concatenation property of MC-CDMA transmission. When the transmission rate is high, power control with MCPA criterion can significantly reduce reverse-link MC-CDMA intercell interference. However, with only four codes per mobile (e.g., as in IS-95), the reduction in intercell interference is less than 1 dB.

The use of two resource-sharing techniques for congestion control in a backbone asynchronous transfer mode (ATM) network consisting of ATM cross-connects interconnected with high-speed optical links such as 2.4-Gb/s OC-48c fibers is studied. Memory sharing allows an optimal shared use of buffer space in an ATM switch fabric. Channel (or line) sharing, on the other hand, takes advantage of spare line capacity in the system to permit temporary increases in the output rates of the congested output ports. Fundamental bounds on delay-throughput performance and buffer requirements for specific cell loss rates are presented, and two practical application scenarios, representing line protection arrangements with and without service access capabilities, are introduced.>

The authors propose a single way to dramatically improve the performance of input-queued ATM packet switches beyond the 82% saturation point obtained in previous work. The method is an extension of the independent output-port schedulers technique and is based on the notion of recycled time slots, i.e. reusing time slots normally wasted due to scheduling conflicts. In contrast to previous results, the technique yields a throughput improvement from 65% to 92% without speedup, trunking, or complicated hardware. If input grouping with a group size of four is also employed, then the method can yield up to 95% throughput.>

The problem of designing a large high-performance, broadband packet of ATM (asynchronous transfer mode) switch is discussed. Ways to construct arbitrarily large switches out of modest-size packet switches without sacrificing overall delay/throughput performance are presented. A growable switch architecture is presented that is based on three key principles: a generalized knockout principle exploits the statistical behaviour of packet arrivals and thereby reduces the interconnect complexity, output queuing yields the best possible delay/throughput performance, and distributed intelligence in routing packets through the interconnect fabric eliminates internal path conflicts. Features of the architecture include the guarantee of first-in-first-out packet sequence, broadcast and multicast capabilities, and compatibility with variable-length packets, which avoids the need for packet-size standardization. As a broadband ISDN example, a 2048*2048 configuration with building blocks of 42*16 packet switch modules and 128*128 interconnect modules, both of which fall within existing hardware capabilities, is presented.>

An optical cross-connect switch using the star-coupler-based frequency-division-multiplex technique are discussed. Two specific tunable receivers have been implanted. The first is a heterodyne receiver with a tunable laser as the local oscillator (LO) and the second is a tunable filter followed by a direct-detection receiver. In the heterodyne receiver, the tunable LO was a monolithic three-section multiple-quantum-well distributed Bragg laser capable of a 1000-GHz tuning range. Receiver sensitivity was measured to be -38 dBm at 1 Gb/s (BER=10/sup -10/). The power margin in the system substantiated feasibility for a 400*400 switch. In the tunable-filter receiver, the tunable filter is a tunable two-stage optical fiber Fabry-Perot filter design consisting of a narrowband filter followed by a wideband filter. The tuning of the filters is computer controlled, and the combined filter has a tuning range of 15000 GHz with a finesse of approximately=5170. Therefore, it is capable of covering over 1000 channels of 2.9 GHz each.>

The knockout switch is a packet-switch architecture recently proposed for high-performance packet networks. In addition to providing point-to-point connections among user pairs, a packet network must often support multicast and broadcast capabilities. Multicast connections differ from point-to-point connections in that each packet is addressed to a number of destinations. Two specific approaches using the knockout switch to provide a practical and efficient means for multicast services under both light and heavy traffic conditions are proposed. The first involves packet duplication and is more suitable for light traffic loads. The second uses a fast address comparison technique and is capable of handling larger loads. In both cases, the knockout principle is utilized to yield the best delay-throughput performance, guarantee the first-in first-out packet sequence, and provide for a simple, modular implementation.>

A high-performance packet switch is discussed which uses a photonic interconnect fabric to route very-wideband data packets from input to output. Packet contention is accomplished using a much slower electronic controller, based on the knockout principle operating in parallel with the optical interconnect. Specifically, the use of a wavelength-division-multiplex fabric whereby high-speed (2-4 Gb/s) packets are regenerated before modulating a single-frequency laser at each switch input. The optical signals from various inputs are summed in a star coupler and then broadcast to the different coupler outputs. Each coupler is equipped with a small number (L) of tunable receivers arranged in a parallel manner, each preceded by a power splitter so that up to L simultaneous packets can be received by each output. The L packets so received are stored in an L-input one-output first-in first-out (FIFO) buffer so that the FIFO packet sequence is always guaranteed. Not only does this architecture achieve the best delay-throughput performance, but, remarkably, modularity is such that the optical complexity grows linearly with the number of switch ports./.>

A three-tiered digital switching hierarchy is considered in which traffic from remote users is grouped, concentrated into time-multiplexed lines, and then transmitted to a central location for interconnection by a central space division switch. While the configuration provides efficient sharing of both transmission and switching resources, the TDM (time-division multiplexing) assignment problem for a conventional time-space-time (T-S-T) switch can become quite formidable due to the various hierarchical constraints. A time-slot assignment strategy is proposed that circumvents this problem by temporarily storing the incoming traffic at the central switch. Unlike the traditional T-S-T approach, the in-bound and out-bound assignments are entirely decoupled, which greatly simplifies the assignment process and produces a fast circuit switching capability. Necessary and sufficient conditions governing the assignability of traffic to the three-tiered switching system are stated and proved, and a block diagram of the proposed switching architecture is presented.>

The Knockout Switch is a new packet switch architecture recently proposed for high-speed local and metropolitan area networks, multiprocessor interconnects, and local or toll switches for integrated traffic loads. We describe an approach to extend the original Knockout Switch to work with variable-length packets. This new architecture employs an input broadcast bus arrangement to achieve complete interconnection of the inputs and outputs. Consequently, there is no congestion in the switch fabric other than the unavoidable conflict of multiple simultaneous packets destined for the same output. It is with this output contention that the Knockout principle is fully utilized to efficiently concentrate and store contending packets while maintaining the first-in first-out discipline of the packet sequence; and yet the fabric speed required is no more than the input/output line speeds, Under these design goals, no switch can yield better delay/ throughout performance. These are the most important attributes that have been preserved in the current proposal from the original Knockout Switch. For anN \times Nswitch configuration, the variable-length packet Knockout Switch consists ofNinput broadcast buses, and anN:Lconcentrator (L \ll N) and a shared buffer for each output. The design of each subsystem is discussed with emphasis on possible VLSI realization. Using today's technology, we should be able to implement the proposed switch with both input/output lines and internal hardware operating at 50 Mbits/s. The dimension of the switch (N \times N) can grow modularly from say 32 × 32 to 1024 × 1024, rendering a total throughput in the range of tens of gigabits per second. Future upgrading of the line interfaces to much higher speed without modification to the internal switch hardware is also possible with a modest restriction on the minimum length of new packets.

We consider the traffic handling capability of a new switching architecture which generalizes upon the structure of a traditional time multiplex switching system. For the traditional approach, lowbandwidth end users are formed into groups, each of which shares a single high bandwidth time-division multiplexed (TDM) line into the central time multiplex switch. Each user synchronously generates packets of data in preassigned time slots at a rate consistent with its offered traffic, and the feeder for the TDM line serving a group of users merely time multiplexes the arriving packets prior to routing by the central switch; analogously, each output port of the switch feeds a demultiplexer which routes the packets to the appropriate user within its group. The generalized approach permits each user group to share some multitude of TDM lines interconnecting that group with the central switch, and the group multiplexers and demultiplexers are replaced by switches which route packets from users to TDM lines (and vice versa). For this structure, we derive a set of necessary and sufficient conditions on the user-touser offered traffic such that a valid, nonconflicting TDM assignment of packets-to-time slots exists. These conditions reveal that the constraints imposed by the three-tiered switching hierarchy do not limit the useable capacity of the switch. Consequently, with no loss of traffic bearing efficiency, it is possible to reduce the number of multiplexers used to serve the end-user population, achieve greater trunking efficiency since small user groups served by one TDM line are replaced by larger groups serving multiple lines, and modularly grow the system by adding TDM lines to each group commensurate with the traffic offered by that group. As a byproduct, it is shown that such a system designed to switch low-speed circuits of some particular data rate can, with no hardware change, switch circuits at lower rates (subrate switching). These conclusions have important ramifications for the design of terrestrial and satellite-based switching systems.

We describe an experimental system for demonstrating time-compression multiplexing (TCM) of two NTSC color television signals in a satellite channel of 36 MHz. The system employs digital processing to derive line or field differentials from each picture. The television signals are then converted into interleaved lines (or fields) of unimpaired baseband video and companded line (or field) differentials. These signal components are finally time compressed and multiplexed into a combined signal for single-carrier FM transmission. With 4.5-m earth stations, the field-differential technique offers extremely good transmission quality suitable for TV distribution to cable head-ends (weighted signal-to-noise ratio, WSNR ≈ 51.5 dB), while the line-differential method provides a slightly lower WSNR ( ≈ 49 dB). We recommend the field-differential approach because of its superior overall picture quality. For larger receive stations (7m), higher picture quality (WSNR ≈ 56 dB) could be obtained. If 10-m earth stations are employed, the received video performance is practically indistinguishable from the corresponding one in the one-television-per-transponder case, and we infer that three pictures can indeed be sent with a graceful degradation as previously suggested. By choosing the parameters properly, the current TCM system can be optimized for a wide variety of applications with higher channel capacity.

Intermodulation (IM) effects were recently observed in communications satellites where the source of nonlinearity was traced back to passive and normally linear components. This phenomenon is sometimes called passive intermodulation (PIM) and can cause serious interference to the ultrasensitive receiver on board the spacecraft. One interesting and important aspect of the PIM study is to find the order and type of IM products causing interference in an arbitrary satellite receive band. It is shown that the problem can be reduced by the use of number theory to a Diophantine optimization problem. Two types of tree searches are formulated and proposed as viable approaches. Some additional bounds for the equal-spacing case and an iterative technique for the unequal-spacing case are described. Finally, we show, by means of an example, that the proposed techniques offer a practical method of solving the order and type prediction problem.

Higher picture quality and better link utilization can be obtained using time compression multiplexing of color television signals in satellite channels instead of the conventional approach of frequency-division multiplexing. A time compression/expansion technique based on chirp transforms is proposed for such an application. The real-time chirp transform needed is realizable by surface acoustic wave devices. The processing itself introduces truncation distortion on the signal, but the distortion can be controlled to a negligible level by proper design of the chirp filter. Preliminary results are encouraging and indicate that the method is promising for future applications.