LAN Topology Design and Cabling



LAN Topology Design and Cabling

LAN Design and Cabling

Local area networks (LANs) have become pervasive in their application to business, government, and academic data communications. In the United States alone, by 1993 there were over three million tANs installed. This paper describes how advances in structured cabling systems and electronics concentrated in the wiring closet have enabled the evolution of tANs toward a dedicated bandwidth model. Due to the growing number of users, LANs are required to provide increased data capacity and Improved management capabilities. These user requirements are being met by increased functions in the electronic wiring closet that include fault isolation, remote network management, increased aggregate bandwidth, and virtual LAN capabilities (Murphy, 2008).

The choice of a star topology for the cabling standard was easily made. Figure 1 shows a star cabling distribution for a LAN. The choice of the star topology was natural to those accustomed to the traditional practices of the telephony industry. The benefits of a star topology had also become obvious to those in the data transmission sector who had more recently gained painful experiences in the operation and maintenance of LANs that had been cabled by direct runs between stations (Denzel, 2007).

Direct cable runs between stations offered shorter cables that delivered stronger signals and resulted in lower initial installation costs because less cable was needed. This was the initial installation practice for Ethernet LANs and IBM's early R-Loop system. However, early dissatisfying experiences in problem identification, isolation, and correction in direct-wired systems prepared the industry for quick acceptance of a star-wired topology. With star wiring, telecommunications wiring closets offered key locations for almost all of the testing necessary to locate and correct a system fault that might have affected hundreds of stations. Not only was the testing made easier, much more importantly, it was made immensely faster. The availability of the network was increased by being able to correct a fault and return the network to operation in less time (Boudec, 2007).

Port switching is the ability to remotely change the LAN segment to which a workstation is attached. A port switching hub contains multiple high-speed buses where each bus is a separate LAN segment. Via a network manager it is possible to define the attachment of each workstation to a specific LAN segment within the hub. Without port switching, to change the LAN segment to which a workstation is attached would require a manual cabling change in a wiring closet. Thus, port switching can save labor costs for reconfiguring users. Port switching can also be used to localize traffic to individual segments and to isolate stations for troubleshooting.

Source routing bridges filter traffic by a special Routing Information Field (RIF) inserted into a LAN frame by a sending station. The RIF immediately follows the source address field in a LAN frame and is defined in the IEEE 802.5 token-ring standard. The contents to be placed in the RIF are typically determined via a discovery process initiated by the sending ...