Handbook of Local Area Networks, 1998 Edition:Advanced LAN Interconnectivity Issues and Solutions Click Here! Search the site:   ITLibrary ITKnowledge EXPERT SEARCH Programming Languages Databases Security Web Services Network Services Middleware Components Operating Systems User Interfaces Groupware & Collaboration Content Management Productivity Applications Hardware Fun & Games EarthWeb sites Crossnodes Datamation Developer.com DICE EarthWeb.com EarthWeb Direct ERP Hub Gamelan GoCertify.com HTMLGoodies Intranet Journal IT Knowledge IT Library JavaGoodies JARS JavaScripts.com open source IT RoadCoders Y2K Info Previous Table of Contents Next Section 4Advanced LAN Interconnectivity Issues and Solutions Section 4 continues our examination of LAN interconnectivity and related technologies, but shifts the focus to those new and emerging technologies most likely to impact network design over the coming decade. It is technologies such as these that will position LAN managers to be long-term, value-added partners in their respective enterprises. It is no secret that businesses have recently become dependent upon the Internet, and that business use of the Internet is projected to continue to increase sharply. However, today’s Internet is held together by a protocol developed in 1981! Clearly, this protocol, known as IPv4, cannot continue to support the growth indefinitely. Thus, Chapter 4-1, “IPv6: The Next Generation Internet Protocol,” discusses the successor to IPv4, with descriptions of the new protocol’s features, construction, security, and migration plan. Another technology with a long history, and one with a more familiar ring to business and industry, is SNA, once the mainstay of most corporate networks. Despite all the press and attention given to the Internet and its technologies, IBM has not abandoned SNA, nor have business enterprises that continue to retain a significant investment in this technology. Rather than stand still on this technology, the pro-active LAN manager is encouraged to explore ways to exploit LANs and related technologies for the benefit of the SNA world. Chapter 4-2, “SNA Over Frame Relay,” discusses how frame relay can be deployed as a replacement for SDLC as an integral part of IBM’s strategy for integrating SNA and multiprotocol LANs. Historically, one of the impediments of deploying SNA protocols in conjunction with LAN technologies has been the difference in design assumptions regarding quality of service. That is, SNA was designed based on the assumption that leased lines — with service guarantees — would be used; LANs, by contrast, were designed based on the assumption that networking resources were to be shared, leading to the possibility that some data might have to stand in line from time to time, waiting for resources to become available. This design dichotomy has also been a strong impediment to the use of LAN technologies for such timing-sensitive services as voice and real-time video. Things are beginning to change, as discussed in Chapter 4-3, “Priority Frame: Absolute Quality of Service in a Frame Relay Environment,” which explores how quality of service guarantees can be built into frame relay, a service originally designed with LAN interconnectivity in mind. Frame relay has been very well received in the few short years that it has been on the market. Much of its popularity is credited to its inherent simplicity. By contrast, asynchronous transfer mode (ATM) technology has been slow to gain market share, with much of the blame being placed on ATM’s lack of simplicity. However, ATM continues to make significant inroads into the carrier-based wide area network infrastructure. Consequently, while it may never become a dominant player in the LAN market per se, it is expected to become a major consideration for LAN-to-LAN interconnectivity. LAN designers are well advised to become familiar with the technology, its capabilities, and how it can be used to achieve high-performance networking objectives. With this in mind, Chapter 4-4, “InterLAN Switching,” provides yet another look at LAN switching, but from a different angle than that provided in the previous two sections. In this chapter, the focus is on the role that ATM technology will play. In particular, this technology is examined from the perspective of its impact on performance, cost, scalability, and management. Among of the factors that has been an impediment to the use of ATM as an interconnectivity technology is the large gap between affordable T1 services and the not-so-affordable T3 or OC3 service required to access the nearest ATM point of presence in the carrier’s network. This difference becomes particularly acute when the nearest ATM point of presence is a considerable distance away. To help bridge this gap, the ATM Forum has been developing a set of inverse multiplexing standards to allow businesses to use multiple T1s as if they were a single, multimegabit channel to the ATM network. With this technology, network designers have more choices — and much smaller price increments — when looking at high performance LAN-to-LAN connectivity options. This technology is the focus of Chapter 4-5, “Imuxing ATM, Bit by Bit.” As ATM-based LAN-to-LAN connectivity becomes more prevalent, especially if used to support cross-country VLANs, latency and sporadic response times will become more of an issue. Chapter 4-6, “Traffic Control Functions in ATM Networks,” examines the topic of traffic control in the four service classes defined for ATM. Of those four service classes, the one of most concern to LAN managers is called Available Bit Rate (ABR), as this is the class designed specifically for the support of LAN traffic. Chapter 4-7 probes deeper into this area with “A Survey of Congestion Control Schemes for ABR Services in ATM Networks.” This chapter examines several approaches to congestion control for ABR, providing a basis of understanding for network designers and engineers who need to understand the limitations of each approach in order to make better informed decisions about their own enterprise networks. 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