The Demand Priority MAC protocol

A new technology needs to offer more than just 100 Mb/s. To succeed in the LAN marketplace, a new LAN technology must be very cost competitive with the established LANs, such as Ethernet and Token Ring, while also providing backwards compatibility with existing network software. We describe a new 100-Mb/s LAN technology that has these characteristics This technology is being defined as an open standard within the IEEE Project 802.12 Demand Priority group. Two important objectives were established for this LAN technology: first, it should be able to use the unshielded twisted pair (UTP) wiring found in a large number of installations and, in particular, to use the same wiring as defined for use in 1OBase-T. This objective was later extended to encompass support for the shielded twisted pair (STP) used for IEEE 802.5. This will enable the majority of current LAN users to benefit from their enormous investment in cable plant. The second objective was that the network should support new applications, such as video conferencing and remote training, while also providing backwards compatibility with the massive installed software base. Both objectives have been met. The Demand Priority MAC protocol currently being standardized in IEEE 802.12, offers substantial benefits over the CSMA/CD protocol of IEEE 802.3. By preserving both the current wiring infrastructure and investment in software, and by using the very simple Demand Priority MAC protocol, 100 Mb/s LANs could soon be as low-cost as 10Base-T is today     

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     

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.     

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.     

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     

A 622 Mb/s LAN/WAN gateway and experiences with wide area ATMnetworking

The use of similar technology in local and wide area networks enables geographically distributed high-performance applications. Key elements in achieving high performance are the appropriate use of traffic control and the development of efficient gateways between LANs and WANs. Even though the basic technology used on both sides of a gateway may be similar, the operational aspects of these elements are significantly different. A gateway has been developed and implemented not only to support communications between an ATM LAN and WAN at 622 Mb/s, but also to provide a platform for conducting network control and traffic research. In addition, the performance of the MAGIC WAN was evaluated, and bottlenecks were identified and analyzed. Techniques were developed and implemented, specifically ATM cell-level pacing, to eliminate these bottlenecks. Throughput performance close to the theoretical maximum was demonstrated. This article describes experiences with ATM over a WAN and how the gateway was developed, implemented, and evaluated. The results included show how high-speed LAN/WAN internetworking can be achieved and applied in many environments as appropriate control techniques and interfaces become ubiquitous     

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.     

New high-rate wireless LAN standards

After the IEEE 802.11 standardization group established the first wireless LAN, several efforts were started to increase data rates and also to use other bands. This article describes the new wireless LAN standards developed by IEEE 802.11, ETSI BRAN, and MMAC. The new standards are targeting data rates up to 11 Mb/s in the 2.4 GHz band and up to 54 Mb/s in the 5 GHz band     

Topological design of interconnected LAN/MAN networks

The authors describe a methodology for designing interconnected LAN/MAN networks with the objective of minimizing the average network delay. They consider IEEE 802 standard LANs interconnected by transparent bridges. These bridges are required to form a spanning tree topology. The authors propose a simulated annealing-based algorithm for designing minimum delay spanning tree topologies. In order to measure the quality of the solutions, a lower bound for the average network delay is found. The algorithm is extended to design the overall LAN/MAN topology consisting of a MAN or high-speed data service interconnecting several clusters of bridged LANs. Comparison with the lower bound and several other measures show that the solutions are not very far from the global minimum     

Standardization efforts for wireless LANs

The Digital European Cordless Telecommunications (DECT) draft standard, which is the only wireless local area network (LAN) standard close to the 1-Mb/s data rate is briefly described. Active standards groups and their activities are reviewed. The work of the IEEE working groups for wireless LANs is examined     

Mobility using IEEE 802.21 in a heterogeneous IEEE 802.16/802.11-based, IMT-advanced (4g) network

Industry is defining a new generation of mobile wireless technologies, called in cellular terminology "fourth generation" or "4G." This article shows that a system combining extensions of two radio access technologies, IEEE 802.11 and IEEE 802.16, meets the ITU-R's "IMT-Advanced" or 4G requirements. The extensions are 802.16 m (100 Mb/s, 250 km/h) and 802.11VHT (1 Gb/s, low velocity). The focus of this article is to show how IEEE 802.21 (the emerging IEEE standard for media-independent handover services) supports ";seamless"; mobility between these two radio access technologies. This mobility integrates the two radio access technologies into one system. We conclude that an 802.11VHT + 802.16 m + 802.21 system is likely to be proposed to the ITU-R for IMT- Advanced 4G.     

Recent advances and evolution of WLAN and WMAN standards [guest editorial]

Standardization of wireless technologies is a continuous process, and even established standards are updated and modified in response to changes in the technology and the marketplace. One such example is the successful IEEE 802.11 standard for wireless local area networks (WLANs), which was originally designed for 1 and 2 Mb/s traffic, and is now being upgraded to support 600 Mb/s in 802.11n and being considered as a high-throughput (up to 1 Gb/s) wireless interface for the nomadic scenarios of the next generation of wireless systems. Similarly, enhancements to the IEEE 802.16 standard for wireless metropolitan area networks (WMANs) are being considered to develop a mobile air interface with support for up to 100 Mb/s in high mobility scenarios. This continuous evolution of the IEEE 802.11 WLAN and 802.16 WMAN standards is made possible with new innovation and contribution from both academia and industry. Given the rapid growth of these technologies, it is important to understand what new application scenarios have triggered the recent developments within WLAN and WMAN standards, how they are evolving, the technological challenges they face, and the opportunities for both the industry and research communities. In this issue, from a large number of submissions, we have selected five key articles for inclusion, which provide the reader with ongoing developments in these standards, technology roadmaps, current research challenges, and comprehensive evolution of these technologies, as well as deployment experience and application requirements.     

A 100 Mb/s multi-LAN crosspoint chip set for cable management

A multi-LAN, 0 dB insertion loss, analog crosspoint switch chip-set is described which forms the heart of a new LAN cable management product. The chip-set is capable of switching FDDI (TP-PMD), ethernet, token ring, and half-duplex protocols through a matrix of 108×108 differential cross-connects, for services using 100 m of unshielded twisted pair cabling and data rates of up to 100 Mb/s, using commercial CMOS and BiCMOS technologies. Using this chip set, it is possible to construct the largest 0 dB insertion-loss programmable analog crosspoint (108×108), operating at 100 Mb/s, currently available     

Next generation local area networks

Many people now consider the local area network (LAN) to which their desktop personal computer (PC) is attached to be more important to them than the telephone network, resulting in a drive to increase both the performance and the reliability of LANs. This paper examines the key drivers for new LAN technologies, summarising LAN developments over previous years. It then looks at possible options for future LANs, which will need to evolve to meet changing traffic patterns brought about by widespread use of intranets and multimedia applications. This encompasses both new technologies such as Gigabit Ethernet, and new architectures such as virtual LANs (VLANs), multi-protocol over ATM (MPOA) and multi-protocol over LANs (MPOL).     

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。     

Telephone wiring: a conduit for networking standards

The author discusses emerging standards for local area networks (LANs) on unshielded copper wires that are expected to make it cheaper and easier for computers to communicate in offices, factories, and laboratories. He describes two twisted-pair standards developed by the IEEE 802.3 working group, one, already approved, designed for data transmission at 1 Mb/s, the other at 10 Mb/s. The official designation of the 1 Mb/s network is 1BASE5, but it is known as StarLAN after the AT&T network from which it is adapted     

ATM local area networks: a survey of requirements, architectures,and standards

There is increasing interest in deploying ATM technology in local or campus networks. ATM is an ideal technology to overcome many of the limitations of today's LAN technologies. This article focuses on the application of ATM in the LAN environment to interconnect high-end host computers, and on the interworking of ATM-based LANs with legacy LANs. The authors introduce ATM LAN requirements, followed by a discussion of possible ATM LAN architectures to support these requirements. The article then covers current standards and their relation to the possible architectures, and concludes with a discussion of current ATM LAN issues and directions     

Fiber optic LANs for the manufacturing environment

The physical layer requirements for local area networks (LANs) that satisfy the set of environmental requirements unique to factory automation applications are discussed. In many cases these requirements are best met with fiber-optic LANs compatible with the IEEE 802.3 (CSMA/CD) or 802.4 (token bus) network standards. Implementation of a passive fiber-optic star-coupler-based LAN is presented in terms of two simple fiber-optic system design rules. A number of applications of the passive star-coupler-technology LAN are briefly described to highlight the benefits of fiber optics as a data communication medium     

Wideband local access: wireless LAN and wireless ATM

An overview of the status of wideband wireless local access technologies is provided. Service scenarios and availability of the market and products for wireless LAN and wireless ATM technologies are discussed. Similarities among IEEE 802.11 and HIPERLAN standards for wireless LANs and the developing prototypes for wireless ATM are evaluated. An update on the status of the available unlicensed bands in the United States as well as the status of the wideband wireless projects in the European Community and Japan are presented     

Efficient multicasting and broadcasting in layer 2 provider backbone networks

Ethernet has grown from its roots in LANs to contend in previously unchartered territory of MANs and WANs. A slew of projects underway in the IEEE 802 standards bodies plan to groom Ethernet with carrier grade features like high availability, fault management, and resiliency thus far found only in other circuit-switched technologies. These include, among others, IEEE 802.1ag (connectivity fault management), IEEE 802.1ad (provider bridges), and IEEE 802.1ah (provider backbone bridges). IEEE 802.1ah addresses the service and MAC address scalability of provider backbone bridges. Since Ethernet has been architected and designed for a shared medium, it inherently handles broadcast and multicast traffic very efficiently, unlike layer 3 technologies, where multicasting and broadcasting rely on using multiple point-to-point connections. With IEEE 802.1ah, Ethernet would be able to provide millions of service instances in a provider backbone network. While flooding of frames in a LAN may provide for good multicasting, flooding of data in a MAN or WAN could mean huge bandwidth wastages, especially when the remote peers are geographically distant, and the traffic is not necessarily destined to any of its local ports of the peers. In this article we explore technologies to Address efficient multicasting in provider backbone networks. We also consider extending this technology to address unknown unicast floods and efficient proxy of customer multicast frames.