s are identified using an address called a Data Link Connection Identifier, or DLCI (pronounced "delsie"). At any given endpoint, the customer's router can support multiple DLCIs, and each DLCI can be assigned varying bandwidths based upon the requirements of the device/application on the router port associated with that DLCI. In Figure 7-3, the customer has purchased a T1 circuit to connect his router to the frame-relay network. The router is connected to a videoconferenc- ing unit at 384 Kbps, a frame-relay-capable PBX at 768 Kbps, and a data circuit for Internet access at 512 Kbps. Note that the aggregate band- width assigned to these devices exceeds the actual bandwidth of the access line by 128 Kbps (1,664-1,536). Under normal circumstances this would not be possible, but frame relay assumes that the traffic that it will normally be transporting is bursty by nature. If the assumption is correct (and it usually is), there is very little likelihood that all three devices will burst at the same instant in time. As a consequence, the cir- cuit's operating capacity can actually be "overbooked," a process known as oversubscription. Most service providers allow as much as 200 percent oversubscription, something customers clearly benefit from, provided the circuit is designed properly. This means that the salesperson must care- fully assess the nature of the traffic that the customer will be sending over the link and ensure that enough bandwidth is allocated to support the requirements of the various devices that will be sharing access to the link. Failure to do SO can result in an underengineered facility that will not meet the customer's throughput requirements. This is a critical com- ponent of the service delivery formula. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Transport Technologies Chapter 7 The throughput level, that is, the ban