Legacy Protocols Research Articles

MAC for Networks with Multipacket Reception Capability and Spatially Distributed Nodes

The physical layer of future wireless networks will be based on novel radio technologies such as UWB and MIMO. One of the important capabilities of such technologies is the ability to capture a few packets simultaneously. This capability has the potential to improve the performance of the MAC layer. However, we show that in networks with spatially distributed nodes, reusing backoff mechanisms originally designed for narrow-band systems (e.g., CSMA/CA) is inefficient. It is well known that when networks with spatially distributed nodes operate with such MAC protocols, the channel may be captured by nodes that are near the destination, leading to unfairness. We show that when the physical layer enables multipacket reception, the negative implications of reusing the legacy protocols include not only such unfairness, but also a significant throughput reduction. We present alternative backoff mechanisms and evaluate their performance via Markovian analysis, approximations, and simulation. We show that our alternative backoff mechanisms can improve both overall throughput and fairness.

유비쿼터스 센서 네트워크의 매체 접근 제어 기법에 대한 개선 방안

we present more efficient method of a medium access for real-time ubiquitous sensor networks. Proposed MAC protocol is like the randomized CSMA/CA protocol, but unlike previous legacy protocols, it does not use a time-varying contention window from which a node randomly picks a transmission slot. To reduce the latency for the delivery of event reports from sensor nodes, we carefully decide to select a fixed-size contention window with non-uniform probability distribution of transmitting in each slot. We show that the proposed method can offer up to several times latency reduction compared to legacy of IEEE 802.11 as the size of the sensor network scales up to 256 nodes using a widely-used network simulation package, NS-2. We finally show that proposed MAC scheme comes close to meet bounds on the best latency being achieved by a decentralized CSMA-based MAC protocol for real-time ubiquitous sensor networks which is sensitive to latency.

Large-Scale Network Parameter Configuration Using an On-Line Simulation Framework

As the Internet infrastructure grows to support a variety of services, its legacy protocols are being overloaded with new functions such as traffic engineering. Today, operators engineer such capabilities through clever, but <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">manual</i> parameter tuning. In this paper, we propose a back-end support tool for large-scale parameter configuration that is based on efficient parameter state space search techniques and on-line simulation. The framework is useful when the network protocol performance is sensitive to its parameter settings, and its performance can be reasonably modeled in simulation. In particular, our system imports the network topology, relevant protocol models and latest monitored traffic patterns into a simulation that runs on-line in a network operations center (NOC). Each simulation evaluates the network performance for a <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">particular</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">setting</i> of protocol parameters. We propose an efficient large-dimensional parameter state space search technique called ldquorecursive random search (RRS).rdquo Each sample point chosen by RRS results in a single simulation. An important feature of this framework is its <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">flexibility</i> : it allows arbitrary choices in terms of the simulation engines used (e.g., ns-2, SSFnet), network protocols to be simulated (e.g., OSPF, BGP), and in the specification of the optimization objectives. We demonstrate the flexibility and relevance of this framework in three scenarios: joint tuning of the RED buffer management parameters at multiple bottlenecks, traffic engineering using OSPF link weight tuning, and outbound load-balancing of traffic at peering/transit points using BGP LOCAL_PREF parameter.

Capacity Estimation of IEEE 802.11e WLAN

Today’s IEEE 802.11 WLAN is an excellent solution for the broadband wireless networking. However, it lacks the capability to support real time services such as voice and video. IEEE 802.11e is an upcoming QoS enhanced standard supported by the IEEE working group. IEEE 802.11e protocol provides a level of service differentiation by statically associating different QoS parameters for pre-defined traffic classes. This paper describes the new QoS features of 802.11e protocol. The performance of 802.11e will be investigated and compared with legacy protocol through computer simulation. Additionally, the 802.11e WLAN capacity will be presented in different scenarios.

A novel MAC mechanism to resolve 802.11 performance anomaly

In the 802.11b networks, the guarantee of an equal long-run channel access probability causes performance anomaly in a multi-rate wireless cell. Much interest has been involved in this issue and many effective mechanisms have been proposed. The usual MAC layer solutions include the initial contention window adaptation, the maximum transfer unit size adaptation and the packet bursting. In this paper, we propose a novel approach which introduces a new parameter called the transmission probability p(subscript t) to the legacy protocol. By adjusting p(subscript t) according to the transmission rate, the proposed scheme can solve the performance anomaly problem cleanly. Throughput analysis and performance evaluation show that our scheme achieves significant improvement in the aggregate throughput and the fairness.

Smooth and efficient real-time video transport in the presence of wireless errors

In this article we study a smooth and efficient transport protocol for real-time video over wireless networks. The proposed scheme, named the video transport protocol (VTP), has a new and unique end-to-end rate control mechanism that aims to avoid drastic rate fluctuations while maintaining friendliness to legacy protocols. VTP is also equipped with an achieved rate estimation scheme and a loss discrimination algorithm, both end-to-end, to cope with random errors in wireless networks efficiently. We show by analysis that VTP preserves most of the convergence properties of AIMD and converges to its fair share fast. VTP is compared to two recent TCP friendly rate control (TFRC) extensions, namely TFRC Wireless and MULTFRC, in wired-cum-wireless scenarios in Ns-2. Results show that VTP excels in all tested scenarios in terms of smoothness, fairness, and opportunistic friendliness. VTP is also implemented to work with a video camera and an H.263 video codec as part of our hybrid testbed, where its good performance as a transport layer protocol is confirmed by measurement results.

Adaptation as a premise for perceptual-based multimedia communications

The vision of a new generation of network communication architectures, which deliver a Quality of Service based on intelligent decisions about the interactions that typically take place in a multimedia scenario, encourages researchers to look at novel ways of matching user-level requirements with parameters characterising underlying network performance. In this paper, we suggest an integrated architecture that makes use of the objective-technical information provided by the designer and the Quality of Perception metric for intelligent decision making in the construction of user-centred adaptable communication protocols. This approach, based on the Analytic Hierarchy Process, incorporates not only classical Quality of Service considerations, but indeed, user preferences as well, and opens the possibility for the suggested protocols to dynamically adapt based on a changing operating environment. Results show that the proposed approach does provide an enhanced user multimedia experience when compared with legacy communication protocols.

Software download enabling terminal reconfigurability

We present a software download algorithm that enables download of configuration software, via different media, to mobile terminals. The proposed signalling protocol and the message sequence have been described in detail; Downloading software through any media has basically the same set of requirements i.e. download initiation, client capability negotiation, download channel capacity, user/provider mutual authentication procedures and error-free software delivery, installation, authorisation and billing have to be negotiated. Procedures that provide implementations of these algorithms have been incorporated in the proposed download signalling protocol. Also, all message parameters to be passed for the full information exchange between client and server have been described, and a prototype implementation based on a distributed object platform (JavaRmi-corba) is presented and described. Software download signalling within the prototype usesCorba (OrbixWeb) as the signalling platform. The hop connection between remote peers (client and server) is handled by two proxies communicating via the orb. These proxies are generated from interfaces defined inIdl . For download however, Java-Rmi has been used as the transport mechanism. Finally, the signalling and download delay behaviour of the proposed architecture is presented. It is shown that an overhead of 0.35–0.45 seconds due to signalling exchange is independent of the file size to be downloaded for file sizes in the range 100–200 kB. The behaviour shows a flat delay duration of ~240ms for files sizes below 100 kB and a linearly increasing duration for files sizes beyond. A size of 200 kBytes can be regarded as the break-even point after which the signalling (and marshalling) overheads ofRmi start to become more efficient and the duration starts to depend on the file sizes rather than the overheads of the transport mechanism. Legacy protocol stack implementations such asGsm for example, have sizes in the region of 200–300 kBytes. Such file sizes are within the range considered and beyond the break even point, and therefore the download mechanism developed provides a suitable platform for reconfiguration software download in terms of procedural delay.

User-Centric Communication Protocols and Architecture for the Web

When viewing a multimedia document on the web, 2 parameters comprise the user perception of the document: user satisfaction/enjoyment of the document and user assimilation/understanding of the information contained in the document. Existing communication architectures and protocols do not cater to the user's experience with multimedia. In this article we present a communication architecture based on microprotocols that adapt so as to maintain user perception even as the quality of the multimedia presentation degrades due to network congestion. We compare our protocols with 2 legacy protocols by testing real users for perception as the quality of the multimedia presentation deteriorates. Our results show that despite the overheads for adaptation, our protocol performed the best from a user's perspective. Our research shows that not only is it desirable but feasible to tailor communication architectures and protocols to the benefit of the user.

Design and implementation of efficient communication abstractions on the Virtual Interface Architecture: Stream sockets and RPC experience

AbstractThe emergence and standardization of system area networks (SANs) has provided distributed applications with a medium for high‐bandwidth, low‐latency communication. Standard user‐level networking architecture such as the Virtual Interface (VI) Architecture enables distributed applications to perform low overhead communication over SANs. The VI Architecture significantly reduces system processing overheads and provides each consumer process with a protected, directly accessible interface to the network hardware. Developing distributed applications using low‐level primitives provided by user‐level networking architecture like the VI Architecture is complex and requires significant effort.This paper describes how high‐level communication paradigms like stream sockets and remote procedure call (RPC) can be efficiently built over the VI Architecture. To evaluate performance benefits for standard client–server and multi‐threaded environments, our focus is on off‐the‐shelf sockets and RPC interfaces and commercially available VI Architecture‐based SANs. The key design techniques developed in this paper include credit‐based flow control, decentralized user‐level protocol processing, caching of pinned communication buffers, and deferred processing of completed send operations.In the experimental evaluation, the one‐way bandwidth achieved by stream sockets over VI Architecture was three to four times better than the bandwidth achieved by running legacy protocols over the same interconnect. On the same SAN, high‐performance stream sockets and RPC over VI Architecture achieve significantly better (between 2× and 3× less) latency than conventional stream sockets and RPC over standard networking protocols in a Windows NT™ 4.0 environment. Furthermore, our high‐performance RPC transparently improved the network performance of the distributed component object model (DCOM) by a factor of two to three. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Frame Relay to ATM interworking

Frame Relay is a well-established technology that has attracted a large number of customers world-wide. It is typically used to interconnect large, multi-site company local area networks (LANs). These data connections are usually at low to medium speeds. Asynchronous transfer mode (ATM) is a newer, broadband technology that is capable of very high speed LAN interconnection. In addition, it is arguably an ideal transport medium for legacy protocols such as Frame Relay.This paper describes the data transport features of each technology and discusses how ATM may be used to interconnect existing Frame Relay networks, and how an ATM user may exchange data with a Frame Relay user.