Johnny W. Wong

The design of teletext broadcast cycles

Abstract Teletext is a one-way picture information system where pages of information are broadcast to all users in a continuous manner. System response time is an important consideration in designing teletext systems. Factors contributing to system response time include transmission speeds, amount of processing required at user terminals, and efficiency of picture encoding procedures. As important is the design of the teletext broadcast cycle, i.e., the order of pages to be broadcast in a cyclic manner. In this paper, we first derive a formula for the mean response time of a given cycle and a lower bound for the mean response time for any cycle. Next we present a design procedure that yields a cycle with mean response time close to the theoretical lower bound. The use of the results of this paper is demonstrated through a numerical example.

On the Optimality of Cyclic Transmission in Teletext Systems

Teletext is a one-way information system where pages of information are broadcast to all users in a continuous manner. System response time is an important consideration in the design of teletext systems. One of the factors contributing to response time is the order in which pages are broadcast. In this paper, we formulate the problem of deciding on the sequence of page transmissions as a Markovian decision process. Using this formulation we show that, from a response time point-of-view, a cyclic order of page transmissions is optimal.

Resource provisioning for cloud computing

In resource provisioning for cloud computing, an important issue is how resources may be allocated to an application mix such that the service level agreements (SLAs) of all applications are met. A performance model with two interactive job classes is used to determine the smallest number of servers required to meet the SLAs of both classes. For each class, the SLA is specified by the relationship: Prob [response time ≤ x] ≥ y. Two server allocation strategies are considered: shared allocation (SA) and dedicated allocation (DA). For the case of FCFS scheduling, analytic results for response time distribution are used to develop a heuristic algorithm that determines an allocation strategy (SA or DA) that requires the smallest number of servers. The effectiveness of this algorithm is evaluated over a range of operating conditions. The performance of SA with non-FCFS scheduling is also investigated. Among the scheduling disciplines considered, a new discipline called probability dependent priority is found to have the best performance in terms of requiring the smallest number of servers.

DQMA and CRMA: new access schemes for Gbit/s LANs and MANs

Distributed-queue multiple-access (DQMA) and cyclic-reservation multiple-access (CRMA) access schemes for gigabit-per-second local and metropolitan area networks are described. These schemes are based on a slotted unidirectional bus structure, with both folded and dual-bus configurations. Like the distributed-queue dual-bus (DQDB) scheme, both the DQMA and the CRMA access schemes achieve full throughput independent of network speed and distance. They have two significant advantages over DQDB. They provide throughput fairness even at high speeds and large distances, where DQDB exhibits dramatic unfairness, and, by allowing reservation of multiple consecutive slots, they make segment labeling unnecessary and facilitate packet reassembly significantly.<<ETX>>

Resource management with virtual paths in ATM networks

A virtual path connection (VPC) is a labelled path which can be used to transport a bundle of virtual channel connections (VCCs) and to manage the resources used by these connections. The virtual network is organized as a collection of VPCs which form a VPC, or logical, overlay network. If the VPCs are permanent or semi-permanent and have reserved capacity, establishing new VCCs requires simple connection admission decisions at the VPC terminators of existing VPCs. This would enable faster connection establishment since transit nodes are not involved in the connection setup. The virtual path concept also allows the possibility of segregating traffic types according to quality of service requirements. However, the extent to which VPC provisioning is able to improve network efficiency is dependent on the resource management decisions that determine the VPC topology and capacity allocations. The article surveys resource management using virtual paths in an ATM network. Of interest are techniques which modify the VPC topology and capacity assignments in order to adapt to changing traffic conditions and possible network failures. The resource management activities employed to facilitate such adaptation can be categorized by the timescale on which they operate. On the shortest timescale are strategies for dynamically making minor changes to the VPC topology or capacity assignments. On a somewhat longer timescale are strategies for making more widespread modifications to the VPC overlay network. This would be appropriate for traffic changes based on time of day and for recovering from network failures. Finally, on an even longer timescale, strategies may be employed to design a general VPC overlay network, to be used at startup or after major network upgrades. Solutions to VPC resource management for each of these timescales are discussed.

A business driven cloud optimization architecture

In this paper, we discuss several facets of optimization in cloud computing, the corresponding challenges and propose an architecture for addressing those challenges. We consider a layered cloud where various cloud layers virtualize parts of the cloud infrastructure. The architecture takes into account different stakeholders in the cloud (infrastructure providers, platform providers, application providers and end users). The architecture supports self-management by automating most of the activities pertaining to optimization: monitoring, analysis and prediction, planning and execution.

Synchronization of distributed simulation using broadcast algorithms

Abstract Simulation, particularly of networks of queues, is an application with a high degree of inherent parallelism, and is of considerable practical interest. We continue the analysis of synchronization methods for distributed simulation, defined by the taxonomy in our previous paper. Specifically, we develop algorithms for time-driven simulation using a network of processors. For most of the synchronization methods considered, each node k of an n-node network simulation cannot proceed directly with its part of a simulation. Rather, it must compute some function B k ( ν 1 , ν 2 , …, ν n ), where ν i is some value which must be obtained from node i . The value of ν i at each node changes as the simulation progresses, and must be broadcast to every other node for the recomputation of the B -functions. In some cases, it is advantageous to compute the B -function in a distributed manner. Broadcast algorithms for such distributed computation are presented. Since the performance of a broadcast algorithm depends on the properties of the inter-process communication facility, we characterize some particular cases and give algorithms for each of them.

A Study of Fairness in Packet-Switching Networks

The use of channel scheduling to improve a measure of fairness in packet-switching networks is investigated. This fairness measure is based on mean end-to-end delays derived from Kleinrocks classical model. The network designer can incorporate any desired relative delay among user classes into this fairness measure. It is found that scheduling is helpful in reallocating delay among user classes and can be used to improve the fairness of a network. It is also shown that a parameterized queueing discipline can be used to further improve fairness. A conservation theorem characterizing the effects of scheduling on overall mean end-to-end delay is established. The results are applicable to both fixed and random routing and are found to be relatively insensitive to fluctuations in traffic.

Analysis of a hybrid token-CSMA/CD protocol for bus networks

Abstract A hybrid control token-CSMA/CD (Carrier Sense Multiple Acess with Collision Detection) protocol for medium access in local-area bus networks is introduced. This protocol is expected to perform as well as the better of the two component protocols at all times. Analytic results for the throughput and mean packet delay of our hybrid protocol are obtained. Numerical results showing the delay-throughput characteristics and comparisons of this protocol with control token and CSMA/CD are presented.

Analysis of a token ring protocol for voice transmission

Abstract For voice transmissions in a local-area network, it is desirable to have a small coefficient of variation for the interdeparture time of voice packets at the destination. This may be achieved by the proper design of the medium access protocol. A token ring protocol with provision for voice traffic is considered. An analytic model is developed to study the performance of this protocol with respect to voice traffic. Numerical results showing the effect of model parameters on interdeparture time are presented.