3Com 3C780 User Guide - Page 28
FDDI Technology
UPC - 662705029917
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1-2 Overview The management module is based on the Motorola® 68EC020 processor, which provides the following: s 256 KB of nonvolatile RAM s 1 MB of local RAM s 512 KB of EPROM s 1 MB of flash memory s 128 KB of RAM for frame buffer and descriptors This guide is intended for network installers and operators who are familiar with FDDI technology and experienced in installing hubs. The next section contains a brief summary of FDDI technology; it is intended as an overview only. (For detailed information about FDDI architecture and its functionality, 3Com recommends that you secure the FDDI self-paced study course, Understanding FDDI, 3CS-360, available through 3Com Education Services.) FDDI Technology FDDI technology is an American National Standards Institute (ANSI) standard that supports data transfer rates of 100 million bits per second (100 Mbps). Advancements in fiber technology allow modulated beams of light to be carried in dual counter-rotating token rings made of glass fiber-optic cable. The FDDI standard now includes the definition of other types of cabling media, including shielded twisted pair (STP) and unshielded twisted pair (UTP). FDDI provides for up to 500 nodes operating over tens of kilometers. The maximum network length is 100 km. FDDI's dual-ring architecture provides a high level of reliability and fault tolerance. Under normal operation one of the rings, called the primary ring or the trunk ring, carries data traffic. The other ring, called the secondary ring, is generally used for automatic recovery in the event of a break in the primary ring. If a fault occurs, as shown in Figure 1-1, the dual attached stations on either side of the fault detect and automatically bypass it. This ring reconfiguration is known as a ring wrap.