Development of the DECbridge 500 Product

Bridges only forward The DECbridge 500 product traffic destined for other connects Ethernet/802.3 LANs; local traffic is local area networks (LANs) confined to its home LAN. to fiber distributed One important function of data interface (FDDI) bridges is the ability, LANs and is, therefore, under network management a fundamental element of control, to block traffic an extended LAN. Developers of selected protocol types of this product encountered or traffic from specific many technical hurdles. The sources. Restricting higher data rate and token unnecessary traffic, ring topology inherent especially multicast or in the FDDI technology broadcast, significantly impose several demands improves the utilization of on any bridging product LAN bandwidth. connected to an FDDI LAN. In this paper we first The differences in formats discuss the role of the and size of frames on the DECbridge 500 product two types of LANs introduce in an FDDI and Ethernet further requirements. The /802.3 extended LAN and development team met these outline the design of the requirements and delivered bridge. We then describe a high-performance product the operation of the bridge that provides seamless by tracing the flow of integration of both LAN LAN traffic through it. types. This description gives Introduction insight into many of Bridges are essential to the complex tasks that a the creation of extended bridge must perform to local area networks (LANs) connect two dissimilar because they provide LANs. Key points of the transparent forwarding development methodology are of traffic between adjacent also presented. LANs.[1] Traffic may be forwarded to or from individual destinations, to groups of destinations (multicast), or to all destinations (broadcast). Digital Technical Journal Vol. 3 No. 2 Spring 1991 1 Development of the DECbridge 500 Product DECbridge 500 Design requirements. File servers Considerations and other common resources The DECbridge 500 device may also be part of the serves as the point of local FDDI LAN. Here, the connection between a new role of the DECbridge 500 family of LAN products product is to provide a based on the fiber path from the local work distributed data interface group to other parts of the (FDDI) technology and a extended LAN via Ethernet large installed base of /802.3 LANs. Ethernet/802.3 LANs. The DECbridge 500 product must meet the requirements of both LANs to provide a smooth migration path for Digital's customers. Note that Ethernet and 802.3 have media access control (MAC) frame formats that may be used on the same 10-megabit (Mb)-persecond LAN. Throughout this paper, the expression Ethernet/802.3 is used to identify such LANs and to distinguish them from 100Mb-per-second FDDI LANs. The terms Ethernet, 802.3, and FDDI are used when discussing the specific MAC frame formats.