100Base-T/IEEE 802.12/packet switching

Three LAN technologies look set to satisfy the ever-increasing demand for LAN bandwidth. Two of these technologies are 100 Mb/s shared-medium LANs: 100Base-T (aka IEEE 802.3 Fast Ethernet) and IEEE 802.12 (aka 100VG-AnyLAN or 100VG). The third technology is packet switching, which is really an extension of existing LAN bridge technology, but offers excellent performance gains at very low cost. The authors describe the three technologies and provide a comparison between the two 100 Mb/s LANs. Also presented are results that compare the measured performance of 100 Mb/s shared-medium LANs with switched LANs     

The Design of the IEEE 802.12 Coding Scheme

In 1995, the IEEE approved the 802.12 standard for data transmission at 100-Mbit/s using the Demand Priority Network Access protocol. 100 VG-AnyLAN products conforming to this standard offered an upgrade path for Ethernet and token ring networks, without requiring new building wiring. A key factor in the approval of the 802.12 standard was the demonstrated error detection properties of its coding scheme. In particular, the coding scheme allows the detection of error bursts affecting encoded data carried on four parallel conductors, using nothing more than the standard IEEE 32-bit cyclic redundancy check applied to the unencoded data. Although these error detection properties were presented for verification as part of the standards process, for many years commercial considerations prevented public disclosure of how the code was actually found. These considerations no longer apply, and, in this paper, we explain in detail the design principles of the code, combining geometrical insight, linear algebra, combinatorial reasoning, and computer search.     

100 Mb/s data transmission on UTP and STP cabling for demandpriority networks

There have been considerable advances towards higher speed (100 Mb/s) workgroup LANs which support the existing UTP and STP structured cabling utilized by 10 BASE-T and token ring LANs. The paper describes the transmission techniques used by an IEEE 802.12 demand priority network with UTP and STP structured cabling. The UTP transmission scheme supports categories 3-5 UTP (i.e. voice-grade and data-grade) using a 5B6B block coded binary signalling scheme on four pairs. This binary signalling scheme is shown to provide better immunity against crosstalk and external (impulse) noise than multilevel signalling schemes. The STP scheme combines the strengths of the 5B6B block code with signalling technology similar to existing SDDI links     

Low-latency mobile IP handoff for infrastructure-mode wireless LANs

The increasing popularity of IEEE 802.11-based wireless local area networks (LANs) lends them credibility as a viable alternative to third-generation (3G) wireless technologies. Even though wireless LANs support much higher channel bandwidth than 3G networks, their network-layer handoff latency is still too high to be usable for interactive multimedia applications such as voice over IP or video streaming. Specifically, the peculiarities of commercially available IEEE 802.11b wireless LAN hardware prevent existing mobile Internet protocol (IP) implementations from achieving subsecond Mobile IP handoff latency when the wireless LANs are operating in the infrastructure mode, which is also the prevailing operating mode used in most deployed IEEE 802.11b LANs. In this paper, we propose a low-latency mobile IP handoff scheme that can reduce the handoff latency of infrastructure-mode wireless LANs to less than 100 ms, the fastest known handoff performance for such networks. The proposed scheme overcomes the inability of mobility software to sense the signal strengths of multiple-access points when operating in an infrastructure-mode wireless LAN. It expedites link-layer handoff detection and speeds up network-layer handoff by replaying cached foreign agent advertisements. The proposed scheme strictly adheres to the mobile IP standard specification, and does not require any modifications to existing mobile IP implementations. That is, the proposed mechanism is completely transparent to the existing mobile IP software installed on mobile nodes and wired nodes. As a demonstration of this technology, we show how this low-latency handoff scheme together with a wireless LAN bandwidth guarantee mechanism supports undisrupted playback of remote video streams on mobile stations that are traveling across wireless LAN segments.     

100BASE-T2: a new standard for 100 Mb/s Ethernet transmission overvoice-grade cables

100BASE-T2 is a new physical-layer specification for IEEE 802.3 LANs operating at 100 Mb/s (“Fast Ethernet”). It enables users of the prevailing 10BASE-T Ethernet LAN technology to upgrade their networks from 10 to 100 Mb/s performance while retaining an existing voice-grade cabling infrastructure. 100BASE-T2 transceivers will operate over two pairs in unshielded twisted-pair cables corresponding to EIA/TIA category 3 (UTP-3), as minimally required for 10BASE-T. In a four-pair UTP-3 cable, simultaneous operation of two 100BASE-T2 links, or one 100BASE-T2 and one 10BASE-T link, is permitted. Since voice-grade cables exhibit more signal attenuation and significantly higher crosstalk coupling between adjacent pairs than data-grade cables, sophisticated digital signal processing techniques are needed to achieve reliable duplex 100 Mb/s transmission over two pairs. The 100BASE-T2 standard defines dual-duplex baseband transmission at a modulation rate of 25 Mbaud. During each modulation interval, a four-bit data nibble or Ethernet-specific control information is encoded into a pair of quinary signals. These signals are transmitted simultaneously on the two wire pairs in both signaling directions. In the receivers, adaptive digital filters are required for echo and NEXT cancellation, equalization, and interference suppression     

Issues and approaches on extending Ethernet beyond LANs

Currently, LAN technology is predominantly Ethernet-based and offers packet-optimized switched technology. With more than 90 percent of Internet traffic originating from Ethernet-based LANs, efforts are underway to extend Ethernet beyond LANs into MANs and further into WANs. However, native Ethernet protocols need extensions or support from other technologies in order to succeed as MAN technology in terms of scalability, QoS, resiliency, OAM, and so on. The two emerging trends to carry Ethernet traffic across the MAN can be classified into native Ethernet (IEEE) protocol extensions, and encapsulation by another transportation technology such as MPLS networks. The goal is to offer new and challenging services such as virtual private LAN service, also known as transparent LAN service (TLS). This article presents a comprehensive overview of the required extensions/support of the Ethernet with an emphasis on the emerging provider bridge technology.     

Does the IEEE 802.11 MAC protocol work well in multihop wireless adhoc networks?

The IEEE 802.11 MAC protocol is the standard for wireless LANs; it is widely used in testbeds and simulations for wireless multihop ad hoc networks. However, this protocol was not designed for multihop networks. Although it can support some ad hoc network architecture, it is not intended to support the wireless mobile ad hoc network, in which multihop connectivity is one of the most prominent features. In this article we focus on the following question: can the IEEE 802.11 MAC protocol function well in multihop networks? By presenting several serious problems encountered in an IEEE 802.11-based multihop network and revealing the in-depth cause of these problems, we conclude that the current version of this wireless LAN protocol does not function well in multihop ad hoc networks. We thus doubt whether the WaveLAN-based system is workable as a mobile ad hoc testbed     

Enhancing the performance of medium access control for WLANs with multi-beam access point

Wireless LANs with multi-beam directional antennas have received intensive attention lately due to the potential gain in throughput performance. However, when the multi-beam directional antennas are introduced in this system, the ever popular contention-based medium access control protocol such as IEEE 802.11 MAC is no longer effective, and many challenging problems, such as beam-synchronization problem, beam-overlapping problem, mobility and receiver blocking problem (deafness problem), need to be resolved. In this paper, we propose a novel MAC protocol to carefully address these problems. In addition to improving communication efficiency, we also consider the backward compatibility in our design, whereby an IEEE 802.11 terminal can transparently access a multi-beam access point. Furthermore, we present an analytical model to evaluate the performance of multi-beam wireless LANs. Extensive simulation studies are used to validate the analytical model and show that our scheme can significantly improve the throughput performance     

QoS Routing for Mesh-Based Wireless LANs

Wireless LANs with their increased data rate become an attractive technology for connecting mobile users to the Internet. Efficient deployment of wireless LANs will require the ability to extend the wireless LANs coverage without the need to deploy a very large number of access points. Mesh-based wireless LANs are an attractive solution to this problem. These networks extend wireless LAN coverage by using each node in the network as a router, resulting in a multihop topology. In this paper we introduce a novel routing algorithm, wireless mesh routing (WMR), that provides quality-of-service (QoS) support and accounts for the characteristics of both infrastructure-based wireless LANs and ad hoc networks. The algorithm is validated using the OPNET modeler. The simulation results show that the mesh network using WMR protocol can provide QoS support and react dynamically to the network status changes with low control overheads. Using the proposed software architecture the proposed routing protocol can be implemented with any MAC protocol, resulting in easy implementation in existing wireless nodes.     

无线局域网MAC层信道利用效率分析

基于IEEE802·11g的WLAN的标称速率高达54Mb/s,而实际数据传输速率只有20Mb/s左右。从成帧效率、信道共享效率和冲突避免效率的角度对IEEE802·11g的MAC层信道利用效率进行了分析,得出这种基于CSMA/CA机制的MAC层信道利用效率较低。实测结果验证了分析结论的有效性。     

High-performance architectures for IP-based multihop 802.11 networks

The concept of a forwarding node, which receives packets from upstream nodes and then transmits these packets to downstream nodes, is a key element of any multihop network, wired or wireless. While high-speed IP router architectures have been extensively studied for wired networks, the concept of a "wireless IP router" has not been addressed so far. We examine the limitations of the IEEE 802.11 MAC protocol in supporting a low-latency and high-throughput IP datapath comprising multiple wireless LAN hops. We first propose a wireless IP forwarding architecture that uses MPLS with modifications to 802.11 MAC to significantly improve packet forwarding efficiency. We then study further enhancements to 802.11 MAC that improve system throughput by allowing a larger number of concurrent packet transmissions in multihop 802.11-based IP networks. With 802.11 poised to be the dominant technology for wireless LANs, we believe a combined approach to MAC, packet forwarding, and transport layer protocols is needed to make high-performance multihop 802.11 networks practically viable.     

Improving goodput in IEEE 802.11 wireless LANs by using variable size and variable rate (VSVR) schemes

In IEEE 802.11 wireless LANs, channel quality, network load, as well as the protocol itself are time‐varying, limiting the goodput performance improvement in wireless LANs. Therefore, it becomes critical to dynamically adjust parameters of MAC and PHY layers according to variations of channel quality. In this paper, we propose variable frame size and variable data rate schemes for goodput enhancement. We first propose two optimal frame size predictors: a goodput regulator to maintain the committed goodput for non‐greedy applications and an optimal frame size predictor for maximizing the goodput for greedy applications. Then, we propose a data rate drafting scheme and develop a variable size and variable rate (VSVR) scheme for further goodput improvement. Our extensive simulation results show that the proposed VSVR algorithm can double the channel goodput of current implementations. Moreover, the proposed scheme can be easily integrated with the current implementations of the wireless LAN MAC protocol. Copyright © 2004 John Wiley & Sons, Ltd.     

Next-generation 100-gigabit metro ethernet (100 GbME) using multiwavelength optical rings

This paper investigates the challenges for developing the current local area network (LAN)-based Ethernet protocol into a technology for future network architectures that is capable of satisfying dynamic traffic demands with hard service guarantees using high-bit-rate channels (80...100 Gb/s). The objective is to combine high-speed optical transmission and physical interfaces (PHY) with a medium access control (MAC) protocol, designed to meet the service guarantees in future metropolitan-area networks (MANs). Ethernet is an ideal candidate for the extension into the MAN as it allows seamless compatibility with the majority of existing LANs. The proposed extension of the MAC protocol focuses on backward compatibility as well as on the exploitation of the wavelength domain for routing of variable traffic demands. The high bit rates envisaged will easily exhaust the capacity of a single optical fiber in the C band and will require network algorithms optimizing the reuse of wavelength resources. To investigate this, four different static and dynamic optical architectures were studied that potentially offer advantages over current link-based designs. Both analytical and numerical modeling techniques were applied to quantify and compare the network performance for all architectures in terms of achievable throughput, delay, and the number of required wavelengths and to investigate the impact of nonuniform traffic demands. The results show that significant resource savings can be achieved by using end-to-end dynamic lightpath allocation, but at the expense of high delay.     

Design of an access mechanism for a high speed distributed wirelessLAN

The medium used by indoor wireless LANs is a shared, scarce resource. Hence, efficient use of this medium is important, which in turn requires an efficient MAC protocol. Moreover, next generation wireless LANs will have to support data rates from 10 to 100 Mbits/s. At these data rates, turnaround times in half-duplex radios are a large overhead. This makes the current wireless standards inefficient. However, busy-tone solutions can get around this problem. In spite of their better performance, the busy-tone protocols are not widely used because of the hardware cost, i.e., the requirement of two transceivers-one each for the data and feedback channel. A novel wireless transceiver architecture which mitigates this hardware cost by overlaying the data channel and the feedback channel in the same frequency band is designed. It is shown that this transceiver can be built with current technology. Based on this wireless transceiver, a new MAC protocol called wireless collision detect (WCD) is proposed. This protocol uses a carrier detect signal to decrease the collision probability and receiver initiated feedback to handle hidden nodes. We derive a mathematical expression for the throughput of the protocol. The simulation results match the analysis. At 100 Mbits/s, WCD achieves 77% efficiency with 192 byte packets. For this scenario, the throughput of the IEEE 802.11 MAC protocol and RI-BTMA is 3% and 52%, respectively     

IEEE 802.16安全机制的研究与实现

分析并讨论了IEEE 802.16标准的安全机制,指出了其安全缺陷和最新标准的相关安全改进工作。在安全机制分析的基础上,设计了802.16d标准安全系统的软件架构,并在Linux平台下以可动态加载的内核模块形式实现了其安全子层协议栈。通过仿真MAC层及PHY层的功能,对安全子层软件实现进行了性能验证及兼容性测试。结果表明,该系统完全实现了IEEE 802.16d标准的设计目标。     

A Centralized MAC-Level Admission Control Algorithm for Traffic Stream Services in IEEE 802.11e Wireless LANs

The admission control algorithm that can be performed at the MAC (Medium Access Control) layer in a real-time is proposed for the decision for accepting or rejecting the requests for adding traffic streams to an IEEE 802.11e wireless LAN (Local Area Network). In numerical examples, we apply the proposed admission control algorithm to VOIP (Voice Over Internet Protocol) traffic streams, and obtain the maximum numbers of VOIP traffic streams that can be admitted to IEEE 802.11a/e, IEEE 802.11b/e and IEEE 802.11g/e wireless LANs for various delay requirements.     

EPON中点到点LAN和共享LAN的仿真技术

IEEE802.3ahEFM工作组正在研究以太网无源光网络（EPON），文章首先介绍了两种方法，分别将EPON仿真成若干个点到点局域网（LAN）的集合和仿真成共享LAN，然后主要介绍了在媒体接入控制（MAC）控制层中使用ULSLE模块的方法，利用ULSLE模块，可以在一个共享LAN仿真中提供点到点的通信能力。     

The evolution of 5GHz WLAN toward higher throughputs

A standardization effort has started within the IEEE 802.11 working group to define the next generation of 802.11 wireless LANs. This article illustrates how throughput achieved above the MAC layer of 5 GHz WLANs can be increased from an existing 30 Mb/s maximum with 802.11a/g to rates exceeding 90 Mb/s. After a brief review of ongoing WLAN standardization activities, the support of a higher physical-layer bit rate by various standardized MAC protocols (802.11, 802.11e, and HIPERLAN/2) is discussed, showing the PHY and MAC layers must be considered jointly in order to achieve a significant throughput increase. Various physical layer techniques are compared in terms of performance and complexity. In particular, simulations show that by relying on MAC layers with good efficiency like 802.11e and HIPERLAN/2, a combination of space-time block coding with a possibility of channel bundling could bring a peak throughput increase from 30 to 90 Mb/s as well as a significant cell range increase.     

Design and implementation of an all-CMOS 802.11a wireless LAN chipset

The tremendous growth in wireless LANs has generated interest in technologies that provide higher data rates and greater system capacities. The IEEE 802.11a standard, based on coded OFDM modulation, provides nearly five times the data rate and at least 20 times the overall system capacity compared to the incumbent 802.11b wireless LAN systems. This article describes the design challenges and circuit implementation of a two-chip set that forms a complete 802.11a solution in 0.25 /spl mu/m CMOS technology. Wherever possible, sophisticated digital signal processing techniques are used to compensate for possible analog impairments associated with integrating RF circuitry in a CMOS technology. The analog portion of the chip set implements a 5 GHz transceiver comprising all the necessary RF and analog circuits of the 802.11a standard integrated on a single chip. Some features of this IC include 22 dBm peak transmitted power, 8 dB overall receive-chain noise figure, and -112 dBc/Hz synthesizer phase noise at 1 MHz frequency offset. The digital portion of the chip set, the baseband and MAC processor, contains dual ADCs/DACs and all the digital circuits for synchronization, detection, and 802.11 MAC layer data processing. This IC delivers up to 54 Mb/s in a 20 MHz channel according to the 802.11a standard, and includes proprietary modes supporting up to 108 Mb/s in a 40 MHz channel.     

Performance Analysis for a New Medium Access Control Protocol in Wireless LANs

One fundamental issue in high-speed wireless local area networks (LANs) is to develop efficient medium access control (MAC) protocols. In this paper, we focus on the performance improvement in both MAC layer and transport layer by using a novel medium access control protocol for high-speed wireless LANs deploying carrier sense multiple access/collision avoidance (CSMA/CA). We first present a recently proposed distributed contention-based MAC protocol utilizing a Fast Collision Resolution (FCR) algorithm and show that the proposed FCR algorithm provides high throughput and low latency while improving the fairness performance. The performance of the FCR algorithm is compared with that of the IEEE 802.11 MAC algorithm via extensive simulation studies on both MAC layer and transport layer. The results show that the FCR algorithm achieves a significantly higher efficiency than the IEEE 802.11 MAC and can significantly improve transport layer performance.