.

The generally accepted approach to these challenges is to provide a core network capability that has adequate switching capacity and throughput capability to support the combined traffic of the campus. To this core are attached edge switches to which are then connected the departmental LANs, application servers, storage appliances and other systems.

So a wide range of edge environments are interconnected through a high-speed, high capacity core, which is, in turn, connected to the outside world. This concept is illustrated in highly schematic form here.

In today's technology marketplace, there are competing approaches to many aspects of networking and systems deployment. For CANs, the most commonly used approaches today include Ethernet (and it's emerging variants called high-speed Ethernet and Gigabit Ethernet) and Asynchronous Transfer Mode (ATM).

Ethernet is the most ubiquitous network access method in use today. It accounts for the majority of LAN deployments and is used in many intranet environments as well. Because of its wide distribution and popularity, Ethernet technology has been seen by some as the best alternative for future CAN deployments too. In an effort to make Ethernet meet the needs of campus environments, new variations of it have been under development and are finding their way into general use. These offer greater throughput capabilities than traditional Ethernet.

But, Ethernet isn't the only network access method and while suitable for LANs, it has difficulty integrating with other network technologies in heterogeneous environments. Further, traditional Ethernet LANs do not scale well, encountering significant problems as the number of nodes increases. More importantly though, Ethernet based networks, by virtue of their design and that of the protocols they employ, cannot provide guaranteed Quality of Service (QoS) as required by applications such as real-time video and audio transmission. Given the state of the efforts to correct the limitations to reliable QoS on Ethernet based campus networks, ATM has also been considered for the core of many  campuses and has been found to be a much better alternative.

The campus area networking equipment to be used on a campus must have the capability to support multiple OC-3 and multiple OC-12 connections to provide for quality desktop conferencing and other information streams defined in this document. For the IVN requirements, PPP , UNI 3.1 or 4.0, NNI, PNNI, Frame-Relay, and FUNI, must be supported and must be configurable for all of the physical interfaces listed as CAN requirements.

Having selected a basic design concept and core technology for a campus, it is necessary to focus on how such an approach can be implemented. The first step in this process is the determination of core design. This is critical because, as stated, the core must be capable of carrying and switching the full campus load, must provide for the high availability requirement and must be scalable to meet future needs.

While network switching equipment with fully redundant internal components, automatic fail over capability and hot swappable components are available and are certainly suggested here, the placement of a single switching complex will still leave significant exposure in the event of fire or other disaster. Further, a single large switching unit would, by definition, be less scalable than multiple smaller units. Based on estimated loading requirements computed from raw user counts in the campus buildings and increased for anticipated growth, the use of three general purpose core ATM switches is a design that will accommodate current needs well and will scale extensively over time in a very flexible way.

The ATM network equipment could be deployed as shown in the figure here. The core network buildings could have an ATM Backbone Switch and an Intelligent Routing Switch. To these main components one could attach Stackable Ethernet Switches that provide 10/100 Mbit/s connectivity to the desktop. Of course, desktop equipment equipped with ATM attachment capabilities may connect directly to the core switches as appropriate. Buildings on the edge could be equipped with ATM Workgroup Switches and Stackable Ethernet Switches. Multiple edge buildings connect to each core switch via OC-3 ATM.