基于移动IP的WLAN和GPRS互通

在GPRS中扩展了用户描述信息表以及SGSN和GGSN处理消息的算法,在移动IP中扩展了注册请求消息;在移动IP的基础上实现了GPRS和WLAN的互通,给出了GPRS的Gi接口和WLAN互通的网络体系结构和相应的数据传输协议栈,实现了GPRS和WLAN互通切换时基于AAA认证服务器的移动IP节点认证及注册、通信节点和移动节点间的数据传送。     

Applications of machine learning approach on multi-queue message scheduling

Due to limited resource contentions and deadline constraints, messages on the controller area network (CAN) are competing for service from the common resources. This problem can be resolved by assigning priorities to different message classes to satisfy time-critical applications. Actually, because of the fluctuation of network traffic or an inefficient use of resources, these static or dynamic priority policies may not guarantee flexibility for different kinds of messages in real-time scheduling. Consequently, the message transmission which cannot comply with the timing requirements or deadlines may deteriorate system performance significantly. In this paper, we have proposed a controller-plant model, where the plant is analogous to a message queue pool (MQP) and the message scheduling controller (MSC) is responsible to dispatch resources for queued messages according to the feedback information from the MQP. The message scheduling controller, which is realized by the radial basis function (RBF) network, is designed with machine learning algorithm to compensate the variations in plant dynamics. The MSC with the novel hybrid learning schemes can ensure a low and stable message waiting time variance (or a uniform distribution of waiting time) and lower transmission failures. A significant emphasis of the MSC is the variable structure of the RBF model to accommodate to complex scheduling situations. Simulation experiments have shown that several variants of the MSC significantly improve overall system performance over the static scheduling strategies and the dynamic earliest-deadline first (EDF) algorithms under a wide range of workload characteristics and execution environments.     

Network access protocol for hard real-time communication systems

Distributed hard real-time systems are characterized by communication messages associated with timing constraints, typically in the form of deadlines. A message should be received at the destination before its deadline expires. Carrier sense multiple access with collision detection (CSMA/CD) appears to be one of the most common communication network access schemes that can be used in distributed hard real-time systems. In this paper, we propose a new real-time network access protocol which is based on the CSMA/CD scheme. The protocol classifies the messages into two classes as ‘critical’ and ‘noncritical’ messages. The messages close to their deadlines are considered to be critical. A critical message is given the right to access the network by preempting a noncritical message in transmission. Extensive simulation experiments have been conducted to evaluate the performance of the protocol. It is shown that the protocol can provide considerable improvement over the virtual time CSMA/CD protocol proposed for hard real-time communication by Zhao et al.¹.     

G/M/1 queue study of buffer behavior in the decoding system of computer communication

This paper deals with the buffer behavior at the decoding center of a computer communication system in which the messages are in the Huffman code of English text. It is assumed that the arrival of messages has an arbitrary distribution, with the message lengths having negative exponential distribution. The situation is well described by the G/M/1 model of queue theory. The waiting time model is simulated on the EC-1030 computer, assuming the HP2100A computer is the decoding machine. The simulation results are used for estimation of buffer size in a character-oriented system and block-oriented system for a very low overflow probability.     

A tandem queue with general bulk service and servers' “vacation”

This paper analyses two queueing models consisting of two units I and II connected in series, separated by a finite buffer of size N. In both models, unit I has only one exponential server capable of serving customers one at a time and unit II consist of c parallel exponential servers, each of them serving customers in groups according to general bulk service rules. When the queue length in front of unit II is less than the minimum of batch size, the free servers take a vacation. On return from vacation, if the queue length is less than the minimum, they leave for another vacation in the first model, whereas in the second model they wait in the system until they get the minimum number of customers and then start servicing. The steady-state probability vector of the number of customers waiting and receiving service in unit I and waiting in the buffer is obtained for both the models, using the modified matrix geometric method. Numerical results are also presented.     

FastQueue：一种高性能的磁盘队列存储管理机制

High reliability is the primary requirement for messaging system. Messaging system always utilizes disk queue to temporarily store message to be delivered. Experiments show that Disk queue I/O is the primary performance bottleneck in the messaging system. In this paper we present a high performance disk queue storage management mechanism-FastQueue. The FastQueue utilizes a large file to serve as disk queue to reduce file manage overhead, in which adjacent messages are stored in adjacent disk block. Several messages are written to disk queue in a one large write by Lazy Gathering Write. Several adjacent messages are read into buffer in a one read by Sequential Grouping Prcfetch. The Lazy Gathering Write and Sequential Grouping Prefetch policies take full advantage of the disk bandwidth. Experiment shows that performance of the FastQueue is more than an order of magnitude higher than that of traditional disk queue.     

DNS解析正常情况下使用TSTDNS命令测得主机地址却为“NULL”的案例分析

维护中发现国际漫入用户无法使用GPRS业务,经在SGSN上进行DNS解析,发现测试得到的地址有时正常,有时显示为空。通过LMT查看SGSN9810设备告警,发现测试主机地址为空时,SGSN上有大量“GTP—C隧道路径断”的告警,对端IP为“212．129．65．225”与“212．129．65．233”。而测试主机地址正常时却没有上述两个IP的告警。对比告警与国外漫游用户正常使用GPKS业务时所要完成的信令流程以及所涉及的IP地址和路由通达情况等,基本可以确定国内SGSN与国外运营商GGSN之间的Gn接口路由中断导致漫游用户和移动网络之间无法完成“PDP上下文激活”流程,造成国外漫游用户无法使用GPRS业务。经了解,国外运营商为优化数据流量,对部分国际漫出路由进行调整。     

稀疏机会网络中基于固定中继节点与消息相关性的缓存管理策略

针对稀疏机会网络中固定中继节点和移动节点间的相遇频率以及缓存资源的差异性问题,在多副本路由协议中,提出一种结合固定中继节点重要性和消息相关性的缓存管理策略。该策略通过交互固定节点和移动节点的接触信息和消息队列信息,减少固定中继节点缓存中冗余消息的数量,从而合理地利用固定中继节点的缓存资源。仿真结果表明,所提的缓存管理策略能够在保证消息传输成功率的基础上提高固定中继节点缓存空间的利用率。     

Analysis of a finite buffer queue with different scheduling and push-out schemes

A queueing system M₁, M₂/G₁, G₂/1/N with different scheduling and push-out scheme is analyzed in this paper. This work is motivated by the study of the performance of an output link of ATM switches with traffic of two classes with different priorities. However, the queueing model developed in this paper is more general than that of the output link of ATM switches with two-class priority traffic. General service time distributions are allowed for classes 1 and 2 and a general service discipline function, ₁(i, j), is introduced where ₁(i, j) is the probability that a class 1 packet will be served, given that there are i class 1 and j class 2 packets waiting for service. An exact solution is obtained for the loss probabilities for classes 1 and 2, the queue length distribution and the mean waiting time for class 1. The queue length distribution and the mean waiting time for class 2 are calculated approximately. It is shown that the approximation is an upper bound and the error due to the approximation is very small when the loss probability of class 2 is small (e.g., less than 0.01).     

Dynamic Prediction based Multi Queue (DPMQ) drop policy for probabilistic routing protocols of delay tolerant network

Two most important issues should be considered to achieve data delivery in DTN networking: routing protocols for the network and intelligent buffer management policy for everyone node in the network. The routing scheme decides which messages should be forwarded when nodes meet, and the buffer management policy determines which message is purged when the buffer overflows in a node. This study proposes a buffer management policy named as Dynamic Prediction based Multi Queue (DPMQ) for probabilistic routing protocols. It works by classification of local buffer into three queues of messages, which are DCTL, HPTL and LPTL. The simulation results have proven that the DPMQ performs well as compared to DLA, DOA, MOFO, LIFO, LEPR and LIFO in terms of reducing the message relay, message drop, hop counts average and overhead while rising in the delivery probability.     

DTN中基于二分散发和等待路由的自适应拥塞控制策略

针对二分散发和等待路由中报文被转发的特点,提出节点首先通过应答交换机制丢弃已被递交到信宿节点的报文,来减少网络中冗余报文的传输;当节点缓存完全占用又需存储新报文时,执行拥塞检测和拥塞避免操作,遍历缓存,找到缓存中拷贝数最小的报文将其丢弃（若此报文正在被传输则丢弃拷贝数次小的报文）直至有足够的缓存空间存储新接收到的报文。通过大量仿真实验及相关数据的分析与比较,说明该拥塞策略能显著提高递交率,减小开销,并对拥塞状况有更好的自适应能力。     

A model of periodic acknowledgement

We study a problem abstracted from modeling a multicast protocol. In our model, messages generated by a single source are simultaneously forwarded to a set of receivers where they are independently processed. We assume a state-dependent message arrival rate and memoryless service time distributions. The receivers may process messages at different average rates. Messages processed by all receivers are periodically acknowledged and cleared from the system. Due to finite buffer space, the total number of non-acknowledged messages in the system is limited. Our focus in this paper is on the number of messages cleared at acknowledgement time.

The problem under consideration bears resemblance to a fork/join process with heterogeneous servers, used in the study of multiprocessing computer systems. Our model includes the additional features of finite buffer space and delayed periodic departure of completed jobs. Even without these features, the resulting type of queuing model has no known closed-form solution in the general case of more than two servers. Because the arrival processes to the servers are correlated, the model is difficult to decompose. We propose a relatively simple decomposition technique and a fixed-point iteration scheme. In our approach, we consider each receiver (server) in isolation, and we account for the influence of other receivers through the probability that a given number of messages can be cleared at acknowledgement time. We derive elementary differential equations for the number of messages processed by a receiver. These equations involve the conditional probability of the number of messages not yet processed given the number of messages waiting to be cleared. We compute an approximate solution using the conditional probability obtained from a model with exponentially distributed acknowledgement periods. Our numerical results for the average number of messages cleared at acknowledgment time are typically within a few percent of simulation midpoints.     

Performance analysis of double buffer technique (DBT) model for mobility support in wireless IP networks

Existing mobility support models in cellular communications misinterpret mobility loss in cellular networks as congestion loss, thus it degrades the performance by invoking unnecessary congestion control action. In this paper, we investigated the performance of Double Buffer Technique (DBT) model for mobility support in wireless IP networks. The DBT model uses the END message and the TQRS timer to maintain the packet sequence and decrease the load on the new foreign agent when the timer expires, respectively. Also, the protocol showed improved performance degradation caused by the handover of the mobile terminal. In order to demonstrate the superiority of our scheme over the existing ones, we used the following performance metrics: packet out-of-sequence, cell loss ratio, bandwidth overhead, and suitability for real-time services. The numerical results obtained revealed that the buffer size, the waiting time, and the packet loss probabilities in the model were suitable to the wireless IP environment.     

基于密度和距离的多跳广播转发节点选择方案

多数车联网VANET(Vehicular Ad Hoc Network)的安全应用均采用多跳广播方式分发安全消息。现已提出了许多的多跳广播转发节点选择方案,但它们以减少转发节点数为目的。为此,提出基于密度和距离的多跳广播转发节点选择方案DDBFS(Density-Distance based multi-hop Broadcast Forwarder Selection scheme),记为DDBFS。DDBFS方案主要解决两个问题：密集区域的冗余广播和稀疏区域的高的传输时延。在提出的DDBFS方案中,节点在决策是否转播接收的消息前,依据距离和网络密度设置定时器,一旦定时完毕,且在定时期间,没有其他节点转发该消息,该节点就成为下一跳转发节点。仿真结果表明,与现有的方案相比,提出的DDBFS协议在重播次数和传输时延性能得到显著提高。在密集区域,消息重播次数下降了约57%,在稀疏区域,传输时延缩短了约82%。     

Closed Bernoulli Production Lines: Analysis, Continuous Improvement, and Leanness

In closed production lines, each part is placed on a carrier at the input of the first machine and is removed from the carrier at the output of the last machine. The first machine is starved if no carriers are available, and the last machine is blocked if the empty carrier buffer is full. The number of carriers in the system is S and the capacity of the empty carrier buffer is N ₀. Under the assumption that the machines obey the Bernoulli reliability model, this paper provides methods for determining if a pair (N ₀, S) impedes the open line performance and, if it does, develops techniques for improvement with respect to S and N ₀. In addition, bottlenecks in closed lines are discussed, and an approach to selecting the smallest N ₀ and S, which result in no impediment, is described.     

A polynomial factorization approach to the discrete time GI/G/1/(N) queue size distribution

The queue of a single server is considered with independent and identically distributed interarrivai and service times and an infinite (GI/G/1) or finite (GI/G/1/N) waiting room. The queue discipline is non-preemptive and independent of the service times.

A discrete time version of the system is analyzed, using a two-component state model at the arrival and departure instants of customers. The equilibrium equations are solved by a polynomial factorization method. The steady state distribution of the queue size is then represented as a linear combination of geometrical series, whose parameters are evaluated by closed formulae depending on the roots of a characteristic polynomial.

Considering modified boundary constraints, systems with finite waiting room or with an exceptional first service in each busy period are included.     

Impact of Network Dynamics on User's Video Quality: Analytical Framework and QoS Provision

We develop an analytical framework to investigate the impacts of network dynamics on the user perceived video quality. Our investigation stands from the end user's perspective by analyzing the receiver playout buffer. In specific, we model the playback buffer at the receiver by a G/G/1/? and G/G/1/N queue, respectively, with arbitrary patterns of packet arrival and playback. We then examine the transient queue length of the buffer using the diffusion approximation. We obtain the closed-form expressions of the video quality in terms of the start-up delay, fluency of video playback and packet loss, and represent them by the network statistics, i.e., the average network throughput and delay jitter. Based on the analytical framework, we propose adaptive playout buffer management schemes to optimally manage the threshold of video playback towards the maximal user utility, according to different quality-of-service requirements of end users. The proposed framework is validated by extensive simulations.     

CAN控制系统的时延分析及混合算法

在车载控制器局域网络(CAN)总线的通信中,消息之间的碰撞及低优先级消息的等待时延过长严重影响了通信的稳定性和实时性。通过对CAN控制系统中的消息时延分析,确定排队等待时间是影响通信的关键因素,结合改进的共享时钟算法和动态ID序列算法,提出一种共享ID序列混合算法。将节点消息按ID序列发送,减少消息在同一时刻碰撞,消除消息的排队等待时延,从而提高网络的实时性和稳定性。仿真结果表明,该算法能够避免消息的碰撞,增强消息的确定性,有效改善网络性能。     

DTN中基于生命游戏的拥塞控制策略

为了应对容迟网络中拓扑结构剧烈变化、节点间连接频繁中断等问题,报文通常采用“存储—携带—转发”的方式进行传输：节点将报文存储在缓存中,携带报文直到遇到合适的机会才将报文转发给其他节点.因为缓存有限,这样的传输方式会使节点缓存溢出,导致拥塞的发生.在容迟网络环境下提出一种基于生命游戏的拥塞控制策略(game of life based congestion control strategy in delay tolerant networks, GLCCS),并将其应用于Epidemic路由方式.GLCCS借鉴生命游戏的演化思想,依据邻居节点中持有特定报文的节点比例来决定节点本地缓存中相应报文的操作.同时还提出了基于全网信息的报文排队机制和丢弃策略,依据传递或者丢弃一个报文对整个网络投递成功率的影响,计算出报文的效用值,按照效用值对缓存中报文进行排队和丢弃.在机会网络模拟器ONE中对仿真移动模型和真实运动轨迹进行模拟,实验结果表明,GLCCS与其他拥塞控制策略相比提高了投递成功率,减小了网络时延、丢包率以及负载比率.     

Traffic analysis of a buffered digital data acquisition system

A digital data acquisition system is analyzed under the traffic standpoint. This system receives a random stream of digital messages, accumulates them in an electronic buffer storage and unloads them on a magnetic tape. The system is representable as a single waiting line, the service mechanism of which is ruled by the characteristics of the cascaded functional blocks. Queueing theory methods are applied to determine the queue length distribution under stationary conditions as a function of the system parameters; this, conversely, provides some criteria for the selection of the values of the parameters, necessary to achieve a given statistical behavior. The expected message loss due to temporary system saturation is also computed.