Figure 4-2 Separation of high-speed videodata traffic from PSTN network.
Particularly in the U.S., operators of the PSTN network offer a wide range of value-added voice services such as custom calling features call waiting, call forwarding, etc., Centrex and EKTS features for business customers. Implementation of such features for ATM networks will take enormous
amount of time and effort. Hence the availability of such calling features for voice service is an important factor in maintaining the current PSTN network for sometime into the future. However, there is no doubt that we will reach a crossover point when ATM networks can provide these
sophisticated voice services cost effectively.
The manufacturers of the traditional PSTN equipment already are considering various approaches to prolong the life cycle of their equipment. These approaches involve integration of ATM capability into their equipment or providing adjunct ATM capability for handling high bandwidth data and video
traffic.
III. Data Networks
At present, the data networks public or private are segmented into various sub-networks such as Frame-Relay, SMDS, SNA, X.25, etc. This segmentation can be attributed to the development of several data transport technologies to address very specific needs. In most cases, these sub-
networks are not compatible. Hence, internetworking between these networks is not possible or very costly.
Due to globalization of business and increasing dependence on information and computing, a need to interconnect these sub-networks has arisen
Initially, LAN technologies such as Token-Ring and various Ethernet-based technologies were designed to operate in isolation in a particular business and university campus environment. In other words, a LAN would be dedicated to a particular workgroup, which tightly interact within the workgroup
with little or no interaction with other workgroups. For example, a workgroup may represent a single department in a corporation or university campus. A LAN would then provide a medium to share information among the members of the workgroup.
Figure 4-3 A Typical LAN FDDI Backbone.
Figure 4-4 Typical LAN ATM Backbone.
The need to access global information resources and to share that information on a global basis are the cornerstones of the information age. As a result, it became necessary to interconnect these isolated LANs. As an internetworking technology, ATM will play a critical role in interconnecting these LAN
clusters as part of a campus, MAN Metropolitan Area Network, WAN, InternetIntranet, PNVPN Private NetworkVirtual Private Network application.
We next look at the internetworking application scenarios for the ATM technology in the context of LAN-based networks. We first look at the business campus setting. In this case, various LAN clusters based on the same or different LAN technologies are interconnected, typically via an FDDI Fiber
Distributed Data Interface-based LAN backbone ring as shown in Figure 4-3. As the bandwidth demand increases beyond 100 Mbps for the LAN backbone network, ATM is expected to replace the currently used FDDI technology as illustrated in Figure 4-4. As the ATM workgroup switches
become more affordable it is expected that ATM will also be used as a LAN application to connect LAN users.
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