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Unformatted text preview: Cisco Router Handbook Sackett $70.00 0-07-058098-7 Backward Forward Chapter: 1 | 2 | 3 | 4 | 5 | 6 _________________________________________________________________ Chapter Five Frame Relay Network Design Frame relay is based on a packet-switched data network. The differential of frame relay to previous packet-switched networks like X.25 is that frame relay switches a frame versus a packet. Frame relay has considerable low overhead and its speed through the network is in part to not insuring delivery of data. Frame relay as a WAN network solution grew due to the low cost for acceptable performance as compared to leased-line WAN solutions. An optimal frame relay network design is based on the following: * Balancing the cost savings of using a public network with the business performance requirements. * A scalable WAN design founded in a manageable environment. * Utilizes a hierarchical design. Main concerns for implementing a frame relay design is the ability of the design to scale to not only topology growth but to traffic growth. Components for creating a scalable frame relay network designs are: * The adherence to the three-layer router model of core, distribution and access layers. * Overall hierarchical design * Implementing various mesh topology design * Addressing protocol broadcast issues * Addressing performance concerns Meeting these guidelines results in providing a scalable, high-availability and low cost frame relay network design. 1. Hierarchical Design of Frame Relay Internetworks Frame relay design is based on permanent virtual connections (PVCs). A PVC is identified using a Data Connection Link Identifier (DLCI) number. Multiple PVCs are possible over a single physical communication link. Using this ability, a single link can communicate with multiple locations. This function is shown in Figure 5.1 where router R1 using two PVCs communicates with two other routers over the public frame relay network. A PVC can be assigned a bandwidth. The total bandwidth of all defined PVCs can equal the actual bandwidth of the physical communication link. In a sense, frame relay acts as a time-division multiplexer (TDM) over a public network. Due to the nature of frame relay services through PVCs, hierarchical designs are more logical than physical in definition. Each PVC may be guaranteed a bandwidth parameters called committed information rate (CIR) and excessive burst limits (Be). The CIR is an agreement with the frame relay provider for a minimum throughput for the PVC. The excessive burst limit is an agreement with the frame relay provider for the available for use by the PVC over and above the PVC bandwidth to the maximum available on the physical link. These two variables greatly influence the cost and therefore the design of the frame relay network. 1. Scalability Scalability is achieved in frame relay network design through the implementation of a hierarchy. Using a hierarchy enables incremental growth. The hierarchical approach however, must followincremental growth....
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- Spring '11
- Router, routing protocol, Frame Relay