In the case of distributed backbones, all buildings on a site or the individual floor distributors of a building are connected in series. The series connection of the backbone means that only a few interconnecting cables are required between the individual distribution centers.
Since in a distributed backbone all cables are looped through from distribution center to distribution center, the cables can no longer be used to implement multiple parallel LANs and multiple LAN technologies such as Ethernet, Token Ring or FDDI at the floor level. In a distributed backbone, the available bandwidth is shared by all connected devices. The maximum data throughput of distributed backbones, i.e., the sum of all cross- subnet data streams, is determined by the capacity of the backbone LAN. This means that sufficient reserves must be planned in to avoid bottlenecks. In the event of a fault, for example if a distributor or a link fails, all downstream equipment is affected.
Distributed backbones are set up via a fast backbone LAN (Ethernet or FDDI) and bridges or routers in hubs, each of which connects different buildings or floors. The principle of load separation and fault containment through segmentation applies. The bridges or routers in turn connect all hubs of the individual LAN segments to the backbone.
One area of application for distributed backbones is concepts with central servers (e.g., file storage, mail servers, central databases) in larger sites with multiple buildings, where users from all buildings need to access the servers. These are then to be connected to the backbone, whereby all access is equal from all connected subnets.
Another application is the operation of terminal networks that are served via central hosts in the data center and/or departmental computers. Here, too, users may access the central computer from all buildings at a site.