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 InterLAN Switching and Virtual LANs A virtual LAN (VLAN) is a logical LAN segment that spans end-station connections attached to different physical LAN segments. Virtual LANs: •  Decrease the costs of moves and changes. •  Enhance performance by eliminating unnecessary broadcasts. •  Increase manageability through placement of mission-critical servers at centralized locations. The concept of extending VLANs over the wide area is just emerging in the industry, using vendor-specific implementations. Passport will support wide area VLANs once these standards are defined. The VLAN concept has also been defined for the ATM environment. In this case, the extension of emulated LANs across the wide area can be accomplished via ATM virtual circuits, providing high-speed, low-latency connectivity. ATM LAN emulation standards define mechanisms to allow a single VLAN to be made up of ATM and Ethernet or Token Ring workstations. In both cases, routing between VLANs can be provided by interLAN switching, providing firewalls and media conversion. Campus Networking via InterLAN Switching Another application area is campus networking, which is presented here as a standalone application, but can be integrated with wide area network consolidation. Campus networks are generally characterized by: •  A layered architecture built on a structured wiring scheme. •  Stackable or chassis LAN hubs in the wiring closet. •  Intermediate concentrators such as multiport bridges (optional). •  LAN backbones based on Token Ring, FDDI, or ATM. •  Some level of redundancy (not shown) at various levels of the architecture in larger sites. This campus environment creates management and control complexity for the network operations staff, particularly because a high degree of redundancy is not economically practical in many cases. More significantly, the ever-increasing application and traffic demands cause risks and difficulties in the expansion of the campus backbone. High-performance switching architectures provide an alternative to meeting the problems associated with highly complex campus networks. A high-performance ATM switching platform combined with cell-based routing and high fanout can support up to 10 ATM OC-3c interfaces, 14 FDDI, 56 Token Ring LANs, or 84 Ethernet LANs as a non-blocking 1.6G-bps campus switch. The operational cost, space, and power requirements are reduced by consolidating multiple multiport bridges and routers onto a single platform. Downtime for software and hardware upgrades can be eliminated because of inherent robustness. For end users, the results are improved application throughput, lower latency, and higher network availability. Further operational benefits can be achieved by integrating the campus, MAN, and WAN environments. Evolution to ATM Networking As public network ATM services become available with competitive price and performance, public network ATM interfaces can be provided on a switched interLAN wherever required. These will support network-to-network communications for all classes of service supported, as well as connectivity to routers and muxes that support standard ATM adaptations (AAL1 for circuit emulation, AAL5 for data). SUMMARY The major challenges associated with LAN networking are performance, scalability, management and cost. In the local environment, users are rapidly moving to switched LAN architectures and ATM. In response to user requirements for LAN interconnectivity across the campus or over an international wide area network, interLAN switching has been developed. An effective ATM enterprise network switch delivers the benefits of switching architectures across the wide area, making network capacity more scalable and simplifying network management. Cell-based routing and switching is the next wave making possible the benefits of ATM-to-LAN interconnection. Previous Table of Contents Next Use of this site is subject certain Terms & Conditions. Copyright (c) 1996-1999 EarthWeb, Inc.. All rights reserved. Reproduction in whole or in part in any form or medium without express written permission of EarthWeb is prohibited. Please read our privacy policy for details.