Local Area Network Protocol Research Articles

Infrastructure-based MAC in wireless mobile ad-hoc networks

The IEEE 802.11 standard is the most popular Medium Access Control (MAC) protocol for wireless local area networks. However, in an ad-hoc environment, the Point Coordination Function (PCF), defined in the standard, cannot be readily used. This is due to the fact that there is no central authority to act as a Point Coordinator (PC). Peer-to-peer ad-hoc mode in the IEEE 802.11 standard only implements the Distributed Coordination Function (DCF). In this paper, an efficient and on-the-fly infrastructure is created using our proposed Mobile Point Coordinator (MPC) protocol. Based on this protocol, we also develop an efficient MAC protocol, namely MPC–MAC. Our MAC protocol extends the IEEE 802.11 standard for use in multi-hop wireless ad-hoc networks implementing both the DCF and PCF modes of operation. The goal, and also the challenge, is to achieve QoS delivery and priority access for real-time traffic in ad-hoc wireless environments while maintaining backward compatibility with the IEEE 802.11 standard. The performance of MPC–MAC is compared to the IEEE 802.11 DCF-based MAC without MPC. Simulation experiments show that in all cases the use of PCF benefits real-time packets by decreasing the average delay and the discard ratio. However, this may come at the expense of increasing the average delay for non-real-time data. On the other hand, the discard ratio for both real-time and non-real-time packets improves with the use of PCF. Therefore, our MPC–MAC outperforms the standard DCF IEEE 802.11 MAC protocol in multi-hop ad-hoc environments.

Performance evaluation of a new multiaccess protocol for local area networks

A new self-adaptive protocol for broadcast networks, capable of operating efficiently under bursty traffic conditions and allowing stations to transmit packets of variable length, is introduced. Fixed-assignment protocols such as TDMA have known drawbacks, which are resolved by learning protocols such as LTDMA. However, the fact that LTDMA uses fixed-sized timeslots can result in network equipment overloading as well as wasted timeslots and reduced channel usage. The proposed Variable Packet Length/LTDMA protocol is tested by using real LAN traffic traces and it is proved that it successfully resolves the above issues and achieves a high throughput-delay performance when operating under realistic traffic conditions.

Performance evaluation of a new multiaccess protocol for local area networks

A new self-adaptive protocol for broadcast networks, capable of operating efficiently under bursty traffic conditions and allowing stations to transmit packets of variable length, is introduced. Fixed-assignment protocols such as TDMA have known drawbacks, which are resolved by learning protocols such as LTDMA. However, the fact that LTDMA uses fixed-sized timeslots can result in network equipment overloading as well as wasted timeslots and reduced channel usage. The proposed Variable Packet Length/LTDMA protocol is tested by using real LAN traffic traces and it is proved that it successfully resolves the above issues and achieves a high throughput-delay performance when operating under realistic traffic conditions.

On the impact of IEEE 802.11 MAC on traffic characteristics

IEEE 802.11 medium access control (MAC) is gaining widespread popularity as a layer-2 protocol for wireless local-area networks. While efforts have been made previously to evaluate the performance of various protocols in wireless networks and to evaluate the capacity of wireless networks, very little is understood or known about the traffic characteristics of wireless networks. In this paper, we address this issue and first develop an analytic model to characterize the interarrival time distribution of traffic in wireless networks with fixed base stations or ad hoc networks using the 802.11 MAC. Our analytic model and supporting simulation results show that the 802.11 MAC can induce pacing in the traffic and the resulting interarrival times are best characterized by a multimodal distribution. This is a sharp departure from behavior in wired networks and can significantly alter the second order characteristics of the traffic, which forms the second part of our study. Through simulations, we show that while the traffic patterns at the individual sources are more consistent with long-range dependence and self-similarity, in contrast to wired networks, the aggregate traffic is not self-similar. The aggregate traffic is better classified as a multifractal process and we conjecture that the various peaks of the multimodal interarrival time distribution have a direct contribution to the differing scaling exponents at various timescales.

Measurements of a wireless link in an industrial environment using an IEEE 802.11-compliant physical layer

The design and simulation of coding schemes, medium access control (MAC), and link-layer protocols for future industrial wireless local area networks can be supported by some understanding of the statistical properties of the bit error patterns delivered by a wireless link (which is an ensemble of transmitter, channel, receiver, modems). The authors present results of bit error measurements taken with an IEEE 802.11-compliant radio modem in an industrial environment. In addition to reporting the most important results, they draw some conclusions for the design of MAC and link-layer protocols. Furthermore, they show that the popular Gilbert/Elliot model and a modified version of it are a useful tool for simulating bit errors on a wireless link, despite their simplicity and failure to match certain measured statistics.

TRAP: a high performance protocol for wireless local area networks

The fixed number of available random addresses for randomly addressed polling (RAP) poses a significant problem in terms of scalability in case of many active stations. In such cases, the protocol's performance is significantly degraded. In this paper, we propose a TDMA-based randomly addressed polling (TRAP) protocol. The protocol employs a variable-length TDMA-based contention stage with the length based on the number of active stations. At the beginning of each polling cycle, the base station invites all active mobile stations to register their intention to transmit via transmission of a short pulse. The base station uses the aggregate received pulse in order to obtain an estimate of the number of contending stations and schedules the contention stage to comprise an adequate number of time slots for these stations to successfully register their intention to transmit. Then it transmits a READY message carrying the number of time slots P. Each mobile station calculates a random address in the interval [0… P−1], transmits its registration request in the respective time slot and then the base station polls according to the received random addresses. Simulation results are presented that reveal the superiority of TRAP against the RAP protocol in case of medium and high offered loads. Furthermore, the implementation of the proposed protocol is much simpler than that of CDMA-based versions of RAP, since no extra hardware is needed for the orthogonal reception of the random addresses.

How to develop a low cost, in-house distance learning center for continuing medical education. Part I.

Continuing medical education is essential to improve the quality of health care. Residential courses are expensive for small hospitals but videoconferencing is an economical alternative. Models of distance learning centers are described along with an explanation of INTERNET basics and the use of INTERNET protocol for local area networks (INTRANET). Hardware, software and other technology required and the advantages and disadvantages of different communication methods are reported.

A Software Implementation Technique for Simulation of Ethernet Local Area Networks

A software system designed for simulating Ethernet, Fast Ethernet, and Gigabit Ethernet local area networks (LAN) is described. Implementation-specific features of programs simulating the operation of switch-based full-duplex and half-duplex networks are considered. A subsystem for simulating the stochastic behavior of programs based on full-duplex LAN protocols is described.

An efficient polling MAC for wireless LANs

Polling schemes are an important class of medium access control (MAC) protocols for wireless local area networks (WLANs). A major drawback of these schemes is their inefficiency when only a small number of mobile stations have packets to transmit. This inefficiency is due to the polling of mobile stations with no packets to transmit, which delays the transmissions of mobile stations with packets. In this paper, we suggest a new polling MAC which exploits the capture phenomena and enables simultaneous polling and transmissions of information packets. Mathematical analysis and simulation results show that the new MAC overcomes the above inefficiency considerably, and thus it is more efficient in the sense that it enables higher throughput and a lower access delay. For example, we show scenarios in which the average access delay is reduced by about 30% and the throughput increases by 66%-75%.

Performance analysis of the IEEE 802.11 distributed coordination function

The IEEE has standardized the 802.11 protocol for wireless local area networks. The primary medium access control (MAC) technique of 802.11 is called the distributed coordination function (DCF). The DCF is a carrier sense multiple access with collision avoidance (CSMA/CA) scheme with binary slotted exponential backoff. This paper provides a simple, but nevertheless extremely accurate, analytical model to compute the 802.11 DCF throughput, in the assumption of finite number of terminals and ideal channel conditions. The proposed analysis applies to both the packet transmission schemes employed by DCF, namely, the basic access and the RTS/CTS access mechanisms. In addition, it also applies to a combination of the two schemes, in which packets longer than a given threshold are transmitted according to the RTS/CTS mechanism. By means of the proposed model, we provide an extensive throughput performance evaluation of both access mechanisms of the 802.11 protocol.

A Production-Efficiency Oriented Approach for Evaluating The Performance of a Local Area Network

Network technology plays a vital role in integrating manufacturing facilities and controlling production information flows. A computer-integrated manufacturing (CIM) system with different production characteristics, e.g., production throughput rate and the amount of process infonnation, should be facilitated with a network protocol that meets the individual CIM system's requirements. PEO-NET, a Production-Efficiency-Oriented Network Evaluation Tool, is developed in this paper which adopts network efficiency (Esys), an improved practical perfonnance evaluation index, as the decision criteria while determining the installation suitability of the tentative network protocol. In order to achieve greater portability and flexibility, PEO-NET is designed with three replaceable modules: 1) the CIM system configuration module for defining the configuration of a CIM system as well as its production requirements, 2) the industrial network protocol simulation module for predicting the production communication behavior under different network protocols, and 3) the network perfonnance analysis module for generating the network efficiency significance decision table. Simulations are also perfonned to demonstrate how PEO-NET is facilitated as a decision support tool for selecting a feasible network protocol for both job shop and flow shop production environment with two major LAN (Local Area Network) protocols: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) and Token Passing Bus, respectively.

IEEE 802.11-saturation throughput analysis

To satisfy the emerging need of wireless data communications, the IEEE is currently standardizing the 802.11 protocol for wireless local area networks. This standard adopts a CSMA/CA medium access control protocol with exponential backoff. We present a simple analytical model to compute the saturation throughput performance in the presence of a finite number of terminals and in the assumption of ideal channel conditions. The model applies to both basic and request-to-send/clear-to-send (RTS/CTS) access mechanisms. Comparison with simulation results shows that the model is extremely accurate in predicting the system throughput.

A concurrent network architecture for cost-efficient parallel computing using workstation clusters

Within the past few years, workstation clusters have gained an increasing importance as platforms for parallel high-performance simulation problems. In contrast to the specialized and cost-intensive interconnection network of distributed memory multiprocessor systems, workstation clusters utilize local area networks (LANs) and common communication protocols. Therefore, the cost-efficiency of workstation clusters for parallel tasks is high while the communication performance is limited compared to parallel computer systems. To improve the communication performance of clusters, new protocols can be applied as well as specialized interconnection networks. On one hand, these solutions decrease the cost-efficiency of clusters, while on the other hand the performance of local area networks is increasing because of new technologies such as FastEthernet, GigaEthernet or ATM. In this contribution, we propose increasing the communication performance of clusters through the concurrent network architecture (CNA) with multi-channel communication systems. Through the use of parallel and independent LANs, the communication performance of a cluster can be improved while maintaining the cost-efficiency of the wide-spread LAN technology and protocols. This paper gives an overview of the CNA, the requirements of an implementation and a performance evaluation of a CNA workstation cluster.

A load adaptive bandwidth allocation method for high-speed LANs

Recently, Local Area Networks (LANs) have been a basic technology for information exchange between high-speed peripheral devices and multimedia communication facilities. Furthermore, they are considered a fundamental element (domain) of internetworking to construct high-tech information processing systems. Therefore, it is highly desirable to develop a new LAN protocol supporting super high-speed multimedia communications and preparing an easy interconnection methodology for LANs. In this paper, we propose an adaptive bandwidth allocation (ABA) method which promises a high bandwidth utilization rate and adequate fairness for dual ring LAN topology. The communication protocol using this method not only realizes a gigabit LAN but also can support the multimedia communications. Performance evaluation via simulations shows that the ABA protocol has better characteristics than the MetaRing method. © 1998 Scripta Technica. Electron Comm Jpn Pt 1, 81(1): 41–49, 1998

An adaptive wireless local area network protocol that improves throughput via adaptive control of direct sequence spread spectrum parameters

We develop and analyze an elegant, opportunistic medium access control (MAC) protocol based on the proposed MAC standard for wireless local area networks (WLAN)---IEEE 802.11. Our adaptation of 802.11 is called CATER (Code Adapts To Enhance Reliability) and allows communicating stations to reconfigure their transceivers to use a longer pseudo-noise (PN) code when retransmissions are unsuccessful over a degraded channel. Results show that our protocol continues to function, permitting up to 14 percent normalized aggregate throughput, at times when IEEE 802.11 fails. In addition, throughput experiences only a small decrease due to protocol overhead during periods when stations experience a good channel with few bit errors.

Steady-state analysis of rate-controlled data transport in ATM Local Area Networks

This paper presents a steady-state analysis of rate-based flow control operating with the regular window mechanism of the transport protocol in ATM local area network (LAN) or local high-speed network environments. The rate control schemes are divided into single-threshold and two-threshold cases. By applying Norton's theorem for queuing model simplification and deriving a computation algorithm, the analytical results for steady-state performance of these schemes are found to be computationally efficient and yield accurate approximations. In the numerical results, the rate control schemes have been shown to have significant effects in reducing congestion levels at the receiving entity as well as in the high-speed networks. We also conclude that the two-threshold rate control scheme can be more effective in alleviating network congestion conditions than single-threshold control, while keeping the control overhead (in terms of the rate adjustment frequency) at a low level, provided that threshold values are selected appropriately. The total throughput could be affected, but only in a limited fashion.

Robustness of real-time local area network protocols

This paper proposes a formal definition of the robustness property which, we believe, developers of future real-time local area network (LAN) protocols must aim to realize. As demonstrations of the utility of this definition, the TDMA (time division with multiple access) protocol and the carrier sense multiple access with deterministic collision resolution (CSMA/DCR) protocol are analyzed for their robustness. CSMA/DCR is one of the few major real-time bus LAN protocols, striking a good balance between the CSMA/CD protocol with weakly predictable timing behavior, and the TDMA protocol that has a tightly bounded worst-case delay but is inflexible. We show that the ordinary CSMA/DCR and other LAN protocols, which are relatively weak in regularity and predictability of shared media access patterns, are not very robust in that the protocols lose their real-time delivery properties when various types of faults occur.

Design and performance evaluation of a MAC protocol for wireless local area networks

We propose and analyze, from a performance viewpoint, a Medium Access Control (MAC) protocol for Wireless Local Area Networks (WLANs). The protocol, named Prioritized-Access with Centralized-Control (PACC), supports integrated traffics by guaranteeing an almost complete utilization of network resources. The proposed protocol combines random access for signalling, with collision-free access to the transmission channel. The transmission channel is assumed to be slotted, with slots grouped into frames. Access to transmission slots is controlled by a centralized scheduler which manages a multiclass queue containing the users' requests to access the transmission channel. Three classes of users are assumed: voice traffic (voice), data traffic with real-time constraints (high-priority data), and classical data traffic (low-priority data). A priority mechanism ensures that speech users have the highest priority in accessing the idle slots, since speech packets have a more demanding delay constraint. The remaining channel bandwidth is shared fairly among the high-priority data terminals. The low-priority data terminals use the slots left empty by the other classes. Specifically, access to transmission slots is controlled by the centralized scheduler by managing a transmission cycle for each class of terminals. The voice-terminals cycle has a constant length equal to one frame, while the lengths of the data-terminals cycles are random variables which depend on the number of active voice and data terminals. In this paper we show that the proposed scheme can support the same maximum number of voice terminals as an ideal scheduler, while guaranteeing an almost complete utilization of network capacity. In addition, via a performance analysis, we verify that by limiting the number of real-time data terminals in the network this class of traffic can be statistically guaranteed access delays in the order of 200--300 msec. Hence, the QoS the network gives to the real-time data terminals makes this service suitable for real-time applications such as alarms or low bit rate video.

Implementation of a MAC-layer protocol (GIT-CSMA/CD) for industrial LAN's and its experimental performance

This paper describes the pilot implementation of a local area network by using a hybrid medium access control (MAC) layer protocol, called group implicit token-carrier sense multiple access with collision detection (GIT-CSMA/CD) developed for hard real-time industrial local area networks (LANs). This protocol outperforms standard CSMA/CD and token-passing protocols, as well as other hybrid protocols, in terms of mean and maximum packet delays versus throughput. Also, GIT-CSMA/CD offers bounded packet delay and a great degree of adaptation to the varying requirements imposed by the user applications. A seven-node pilot network was set up and its experimental performance evaluated. The implementation of the network node is based on the existing microcontroller technology (INTEL 80C3152 Communication Controller) and field programmable gate array (FPGA) logic (XILINX XC3190). The measurements carried out in real time on a 1-Mb/s LAN yielded reproducible results. The comparison between the experimental and the simulation results showed excellent agreement.

A performance evaluation method that uses simple network management protocol for radio local area networks

AbstractLocal area network (LAN) is used widely at present, and the radio LAN also is utilized worldwide in practice. This paper focuses on the performance evaluation of the radio LAN in actual operation. It is shown that the method based on simple network management protocol (SNMP) is useful.