Waiting time and queue length distributions for go-back-N andselective-repeat ARQ protocols

The paper provides a performance analysis of automatic-repeat-request (ARQ) protocols in connection-oriented transmission. Each message arriving at a transmitter is divided into several packets, which are continuously transmitted to a receiver according to go-back-N ARQ or selective-repeat ARQ protocols. Because of connection-oriented transmission, messages are served on a first come first served basis, i.e., transmission of a message is commenced after all packets in the previous message are successfully transmitted. For the two ARQ protocols, the authors derive the probability generating functions of message waiting time and queue length at an arbitrary instant, from which the average performance measures are explicitly obtained     

Information Propagation through Opportunistic Communication in Mobile Social Networks

At present, people can communicate with each other through short range communication technologies (Bluetooth, WiFi, etc.) installed in their smart terminals. Due to limited communication range, communication is opportunistic, and mobile social networks formed by such technologies can be seen as delay tolerant networks (DTN). This paper presents a theoretical framework to evaluate the performance of information propagation in such network based on ODE equations. This framework can evaluate the impact of peoples?? many behaviors. For example, people may not want to help others because of their selfish nature. In addition, peoples who are not interested in the message may not receive the message at all, but they become to be interested in the message later. On the other hand, people may discard the message after they used it. We check the accuracy of our model through simulations based on both synthetic and real motion traces (the average deviation is not bigger than 5.09?%). Numerical results show that peoples?? behaviors really have certain impact on the performance of information propagation. For example, if the selfish level is bigger, some persons cannot obtain message at all. If peoples discard message with bigger probability, above result may also appear.     

Fixed Assignment Access Technique

In this paper, two implementations of the fixed assignment technique are examined for time sharing either a satellite or terrestrial channel among the users of a data communication system. In fixed assignments, the transmission time on the channel is partitioned and permanently assigned to the users. The equations for the user buffer queue length and message delay are obtained for arbitrary allocations. The user allocations, which minimize a system performance measure, are numerically determined for some examples.     

Multiple-access protocols for satellite packet communication networks: A performance comparison

This paper considers satellite packet communication networks with a large population of bursty users and presents an analytic comparison of the throughput versus average message delay trade-off characteristics of multiple-access protocols. The following six multiple-access protocols are examined: 1) slotted ALOHA, 2) reservation-ALOHA, 3) a reservation protocol with a slotted ALOHA reservation channel, 4) a reservation protocol with a TDMA reservation channel, 5) SRUC (Split Reservation Upon Collision), and 6) fixed assigned TDMA. All the protocols are required to ensure that all packets of a message are correctly received in the proper order at the destination. Then, a unified presentation of the delay-throughput performance of the protocols is given by means of an analytical technique called equilibrium point analysis. The throughput versus average message delay tradeoff characteristics are compared taking into account the system stability.     

Cell versus message level performances in ATM networks

The goal of this paper is to provide some insight into the relations that exist between cell level and message level performance guarantees in the context of ATM networks. Cell level guarantees are typically what the network is capable of providing, while message level guarantees are the ones of interest to users. It is, therefore, important to understand how the two are related, and which factors influence this relation. There are many different performance measures that are of importance, and in this paper we try to touch on the (three) most relevant ones. This includes comparing cell and message loss probabilities, average cell and message delays, and cell and message jitter. Specifically, we show that cell and message loss probabilities can exhibit significant differences, which strongly depend on traffic characteristics such as peak rate and burst size, i.e., for a fixed cell loss probability, the message loss probability can greatly vary when peak rate and burst size change. One reason for this sensitivity, is that message loss depends on what happen toall the cells in a message. For delay and jitter, we also find that peak rate and burst size play a role in determining the relation between cell and message performance. However, this sensitivity is not as acute as with losses since message delay and jitter are typically determined by the performance seen by onlyone cell, the last cell in a message. In the paper, we provide quantitative examples that illustrate the range of behaviors and identify the impact of different parameters.This work was done while at the IBM T.J. Watson Research Center.Part of the work was done while visiting the IBM T.J. Watson Research Center.     

A comparison of protocols for a meteor-burst channel based ontime-varying channel model

The performance of a meteor-burst (MB) communication system using three different protocols is examined. The protocols were chosen to study the relative advantages of using a simple stop-and-wait automatic repeat request (ARQ) scheme as well as the ability to sense the presence of a channel. It was found that for long messages, the use of the ARQ scheme gave significant performance improvement; however, when the message length was on the order of the average burst length, the use of the ARQ scheme was not helpful. For packet sizes on the order of the average burst length, it was found that the ability to sense the presence of the channel gave about a 20% reduction in the time necessary to complete a message, but for much shorter packet sizes, the channel probing was not needed. The model used to analyze these systems takes into account the time-varying signal-to-noise ratio (SNR) present in a MB channel. The performance predicted by this model is compared to a less sophisticated constant SNR (signal-to-noise) model and its is found that the author's model predicted significantly more optimistic performance     

Performance analysis of CSMA/CD‐PS systems

Recently, the interest in wireless LANs has been increasing. For wireless LANs, light and simple terminals are desirable, and random access protocols such as CSMA and CDMA are preferable. In order to improve the performance of these protocols, some variations have been proposed. Among them is the CSMA/CD‐PS (Carrier Sense Multiple Access with Collision Detection and Packet Segmentation) protocol, in which a message to be transmitted is divided into several packet segments separated by short intervals to enable sensing the channel state. In this paper we analyze the performance of CSMA/CD‐PS systems and derive the Laplace–Stieltjes transform (LST) of the probability distribution function (PDF) of the message interdeparture time and that of the PDF of the message response time. We note that the analysis of the LSTs of the PDFs of performance measures is important, because in communication systems, the output process of each sub‐system may form the input process to another one and that in order to evaluate the performance of communication systems more accurately, we need the stochastic characteristics of relevant output processes. Through LSTs, we can calculate not only averages but also higher moments of performance measures such as coefficients of variation. As for the analysis, we first define the state of the system and observe it at those epochs just after the end of successful/unsuccessful message transmissions. Then we derive the state transition probability matrix and obtain the state probability distribution. Secondly we analyze the interdeparture time and response time distribution of the system to obtain their LSTs. We also present some numerical results for the channel utilization, the average and the coefficient of variation of the interdeparture time, and the average and the coefficient of variation of the message response time. This revised version was published online in June 2006 with corrections to the Cover Date.     

An Analysis of One Direction of Window Mechanism

A queuing model is presented for the analysis of one direction of window mechanism as used in numerous data communication control procedures e.g., X.25, HDLC and SDLC. Two models of message length are considered viz. fixed length and exponential distribution. A novel approach is used to determine an effective service time to account for possible inserted idle time while waiting for the window to reopen. A set of delay characteristics is determined for different window sizes. A minor modification of the frame format is suggested to improve on the performance of the window mechanism.     

轮询多址通信系统门限服务策略研究

从两方面对离散时间情况下轮询多址通信门限排队服务系统进行了研究。改进了系统服务策略，运用嵌入式马尔可夫链理论和多维概率母函数的方法，得到了改进后系统查询时间点处的平均排队队长和信息分组平均时延理论解析式，仿真结果表明分析方法有效且系统性能较之原系统得到提高；采用一种简化的近似算法，得到了轮询周期内平均队长的理论解析式，理论计算与仿真结果有较好的一致性。     

Analysis of packet loss in transport layer over ATM networks

In asynchronous transfer mode (ATM) networks, when cells are lost due to congestion, packets containing the lost cells should be retransmitted in the transport layer, which manages the end-to-end communication. The probability that a packet contains at least one lost cell depends on the packet length. It is thus very likely that the performance of the end-to-end communication is influenced by the packet length. In this paper, we analyse packet loss probability and the achievable maximum throughput when a block of data is divided into packets of fixed size and the lost packets are retransmitted based on the selective repeat automatic repeat request (ARQ). Through this analysis, we examine the effect of packet length and peak cell transmission rate on the performance measures mentioned above. © 1997 John Wiley & Sons, Ltd.     

The Economics and Performance of Satellite Packet Switching

The economics and performance of packet-switched satellite systems operating in a broadcast mode are studied and compared to landline-based systems similar to the ARPANET. The fixed-packet length inefficiencies and the satellite channel utilization of the satellite systems are presented as functions of the message length distribution, the number of earth stations, the average message delay, and the average number of messages generated at each earth station. Some of the economic factors in the design of packetswitched satellite networks are discussed, including hardware costs as a function of technology and system performance. Satellite network configurations with or without backhaul facilities are compared and it is concluded that configurations using backhaul facilities consisting of two 30 mile private leased lines (each 50 kbits/s) are more expensive. Parameters and estimated costs of satellite system configurations are presented and an engineering estimate of the cost function for satellite packet-switched networks is derived and presented in the form of long range average cost curves. Economies of scale with respect to network traffic and diseconomies of scale with respect to the number of network earth stations are found to be present.     

Performance Evaluation of a Cell Reassembly Mechanism with Individual Buffering in an ATM Switching System

We present a performance evaluation model of cell reassembly mechanism in an ATM switching system. An ATM switching system may be designed so that communications between processors of its control part can be performed via its switching network rather than a separate inter-processor communications network. In such a system, there should be interface to convert inter-processor communication traffic from message format to cell format and vice versa, that is, mechanisms to perform the segmentation and reassembly sublayer. In this paper, we employ a continuous-time Markov chain for the performance evaluation model of cell reassembly mechanism with individual buffering, judicially defining the states of the mechanism. Performance measures such as message loss probability and average reassembly delay are obtained in closed forms. Some numerical illustrations are given for the performance analysis and dimensioning of the cell reassembly mechanism.     

IEEE 802.11 protocol: design and performance evaluation of anadaptive backoff mechanism

In WLANs, the medium access control (MAC) protocol is the main element that determines the efficiency of sharing the limited communication bandwidth of the wireless channel. The fraction of channel bandwidth used by successfully transmitted messages gives a good indication of the protocol efficiency, and its maximum value is referred to as protocol capacity. In a previous paper we have derived the theoretical limit of the IEEE 802.11 MAC protocol capacity. In addition, we showed that if a station has an exact knowledge of the network status, it is possible to tune its backoff algorithm to achieve a protocol capacity very close to its theoretical bound. Unfortunately, in a real case, a station does not have an exact knowledge of the network and load configurations (i.e., number of active stations and length of the message transmitted on the channel) but it can only estimate it. In this work we analytically study the performance of the IEEE 802.11 protocol with a dynamically tuned backoff based on the estimation of the network status. Results obtained indicate that under stationary traffic and network configurations (i.e., constant average message length and fixed number of active stations), the capacity of the enhanced protocol approaches the theoretical limits in all the configurations analyzed. In addition, by exploiting the analytical model, we investigate the protocol performance in transient conditions (i.e., when the number of active stations sharply changes)     

Spread spectrum image steganography

We present a new method of digital steganography, entitled spread spectrum image steganography (SSIS). Steganography, which means "covered writing" in Greek, is the science of communicating in a hidden manner. Following a discussion of steganographic communication theory and review of existing techniques, the new method, SSIS, is introduced. This system hides and recovers a message of substantial length within digital imagery while maintaining the original image size and dynamic range. The hidden message can be recovered using appropriate keys without any knowledge of the original image. Image restoration, error-control coding, and techniques similar to spread spectrum are described, and the performance of the system is illustrated. A message embedded by this method can be in the form of text, imagery, or any other digital signal. Applications for such a data-hiding scheme include in-band captioning, covert communication, image tamperproofing, authentication, embedded control, and revision tracking.     

Cooperative communication for safety message dissemination in unsaturated networks with varying contention windows

Safety message dissemination is crucial in vehicular ad hoc networks (VANETs) for road safety applications. Vehicles regularly transmit safety messages to surrounding vehicles to prevent road accidents. However, changing vehicle mobility and density can cause unstable network conditions in VANETs, making it inappropriate to use a fixed contention window (CW) for different network densities. It has been proposed a 1-D Markov model under unsaturation conditions to analyze the performance of the system with varying CWs under changing vehicle densities. Additionally, it introduces the use of cooperative communication (CoC) to relay failed safety messages. In CoC, two control packets, namely, negative acknowledge (NACK) and enable to cooperate (ETC), are utilized. The proposed analytical model named cooperative communication for safety message dissemination (CoC-SMD) is used to calculate throughput and average packet delay for varying CW and different packet size. The simulation confirms the validity of the analytical results and show significant improvement in the metrics through the use of varying CW sizes and CoC compared with existing techniques.     

A control mechanism to prevent correlated message arrivals fromdegrading Signaling No. 7 network performance

Signaling System No. 7 (SS7) is designed to provide a connectionless transfer of signaling messages of reasonable length. Customers having access to user signaling bearer capabilities as specified in the ANSI T1.623 and CCITT Q.931 standards can send bursts of correlated messages (e.g., by doing a file transfer that results in the segmentation of a block of data into a number of consecutive signaling messages) through SS7 networks. These message bursts with short interarrival times could have an adverse impact on the delay performance of the SS7 networks. A control mechanism, credit manager, is investigated in this paper to regulate incoming traffic to the SS7 network by imposing appropriate time separation between messages when the incoming stream is too bursty. The credit manager has a credit bank where credits accrue at a fixed rate up to a prespecified credit bank capacity. This paper presents simulation results showing delay performance of the SS7 ISUP and TCAP message traffic with a range of correlated message traffic, and control parameters of the credit manager (i.e., credit generation rate and bank capacity) are determined that ensure the traffic entering the SS7 network is acceptable. The results show that control parameters can be set so that for any incoming traffic stream there is no detrimental impact on the SS7 ISUP and TCAP message delay, and the credit manager accepts a wide range of traffic patterns without causing significant delay     

一种新型稀疏Ad Hoc网络消息签名方案

针对稀疏Ad Hoc网络的易断易延时特性,采用基于身份的密码体制和椭圆曲线双线性对,提出一种新的稀疏Ad Hoc网络消息签名方案,并对方案的安全性和性能进行了分析。该方案可以解决第三方密钥托管带来的签名伪造问题,限制稀疏Ad Hoc网络中节点私钥泄密带来的伪造消息签名的影响,在保证安全性的前提下,有效减少密钥长度、签名长度与签名的计算量,降低了对网络通信带宽和节点存储、计算能力的要求,符合稀疏Ad Hoc网络的签名需求。     

Cellular communication schemes using generalized fixed channel assignment and collision type request channels

Schemes for accessing the message channels of base stations in a cellular communication system are considered. Detailed analysis is given for a fixed channel assignment scheme with collision type request channels. The probability Pfthat a request fails to secure a message channel is considered as a performance criterion. That fraction of bandwidth allocated to request channels, which minimizes the failure probability Pf, is determined as well as the optimum Pf. Both are plotted as a function of bandwidth utilization S. Sensitivity of system performance to various parameters is considered. A new fixed channel assignment (FCA) scheme, in which a user can be served by any of the nearest k base stations, has been considered and compared with the standard (k = 1) FCA scheme. A mixed scheme with two message types has also been considered. One message type can be served by any of the nearest three base stations but the other type can be served only by the nearest.     

Design Tradeoffs for Local Access Systems in Computer Networks

A computer-aided design tool has been developed to study the hardware/software structure of various types of data switching systems used in the local loop distribution of computer communication networks. A simulation package is used to evaluate the performance parameters (such as the system throughput, average message delay, and probability of data loss) of local access systems under different input traffic conditions. Two types of traffic commonly used in teleprocessing applications are considered: the inquiry/response mode and the file transfer mode. Design tradeoffs for a line concentrator and a message interswitch are discussed and their performance is compared. The message interswitch permits a number of low-speed terminals to share communication lines and also to gain access to local common resources such as line printers, databases, and optical character readers.     

MTAODV:一种新的高速公路场景下VANET路由协议

在高速公路场景中,针对车辆间通信特性,在AODV的基础上提出了一种基于应用消息类型的改进路由协议(MTAODV).其核心思想是在路由建立过程中充分考虑VANET中应用消息的类型,从而减小路由请求洪泛范围,降低网络开销.仿真实验结果表明,与AODV协议相比,MTAODV协议能够有效地提高分组递交率,降低了路由开销,改善了分组时延和抖动.