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10.What are the key advantages and disadvantages among routed and switched backbones?
computers are moved (or support dynamic addressing). Switched backbones Performance is improved. With the traditional backbone network, the backbone circuit was shared among many LANs; each had to take turns sending messages. With the collapsed backbone, each connection into the switch is a separate point-to-point circuit. The switch enables simultaneous access, so that several LANs can send messages to other LANs at the same time. Throughput is increased significantly, often by 200% to 600%, depending upon the number of attached LANs and the traffic pattern. Since there are far fewer networking devices in the network, this reduces costs and greatly simplifies network management. All the key backbone devices are in the same physical location, and all traffic must flow through the switch. If something goes wrong or if new cabling is needed, it can all be done in one place. Software reconfiguration replaces hardware reconfiguration. Because data link layer addresses are used to move packets, there is more broadcast traffic flowing through the network and it is harder to isolate and separately manage the individually attached LANs. Layer 3 switches can use the network layer address, so future collapsed backbones built with layer 3 will not suffer from this problem. Collapsed backbones use more cable, and the cable must be run longer distances, which often means that fiber optic cables must be used. If the switch fails, so does the entire backbone network. If the reliability of the switch has the same reliability as the reliability of the routers, then there is less chance of an failure (because there are fewer devices to fail). For most organizations, the relatively minor disadvantages of cable requirements and impacts of potential switch failure are outweighed by the benefits offered by collapsed backbones. 11.Compare and contrast rack-based and chassis-switch based switched backbones. The rack-based collapsed backbonehas the advantage of placing all network equipment in one place for easy maintenance and upgrade, but does require more cable. In most cases, the cost of the cable itself is only a small part of the overall cost to install the network, so the cost is greatly outweighed by the simplicity of maintenance and the flexibility it provides for future upgrades. The room containing the rack of equipment is sometimes called the main distribution facility(MDF) or central distribution facility(CDF). The cables from all computers and devices in the area served by the MDF (often hundreds of cables) are run into the MDF room.