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Backbone

Currently backbone technologies consist of backbone routers, fiber distributed data interface (FDDI) bridge/routers, or connection to a variety of WAN networks such as frame relay, integrated services digital network (ISDN), X.25, or dedicated circuits. At this level in the infrastructure, enterprises will either continue to use these technologies, or they will begin to deploy ATM switches.

In cases where backbone routers are still used, the routers must continue to offer connections to virtually every type of LAN and every type of WAN service. They must also become faster. In cases where ATM is introduced, the ATM switches will offer a wide variety of WAN interfaces and will need routing hubs to connect to traditional LAN-based desktop devices, servers, and other resources.

Hubs

Hubs are evolving to the point where they will support more LAN standards (e.g., 100M-bps or 1G-bps Ethernet) and mix internetworking and repeating functions. Such hubs can allow different speed devices to connect to them, provide dedicated LAN support to individual stations, provide increased segmentation to reduce traffic on individual LAN segments, and allow connections to ATM backbone services.

A true enterprise hub must support a continuum of solutions, from simple 10-BaseT to dedicated bandwidth-to-a-port to routed segments within the hub. Network managers can then choose the appropriate solution for each user.

ATM

ATM is an exciting new technology for many reasons. First, ATM provides high-speed data switching that is faster than all but the fastest standards-compliant LAN today. Second, ATM can be used for both local and wide area communications, offering the possibility of a single technology from carrier to desktop. Finally, ATM can provide fixed bit-rate services that will support applications demanding it.

ATM holds considerable promise for use within the enterprise network infrastructure as a:

  Carrier service.
  Local switching service.
  Direct device connectivity service.

ATM switches are already being deployed as local switching devices. During the time that ATM is employed primarily as a backbone switching service, existing LAN devices will require LAN physical connectivity and support for routing. Traditional backbone routers may be substantially replaced by ATM switches at sites that choose ATM technology. At these sites, routing hubs may be necessary to fulfill this function.

THE HUB OF THE FUTURE: THE ROUTING HUB

Hubs designed to meet future networking requirements need to provide support for a variety of media, and they must be able to interconnect heterogeneous LAN segments running at different speeds. Some of the characteristics of such routing hubs are described next.

LAN Types

The hub connects to local stations through a variety of LAN types, including 10M-bps Ethernet, 4M-bps and 16M-bps Token Ring, FDDI, 100M-bps Ethernet, and 1G-bps Ethernet Each of these connections may operate over a variety of physical interfaces, including both fiber and copper.

Segmentation

As more users share a single network segment, the utilization of that segment increases, eventually creating a bottleneck. Network administrators may reduce this utilization by breaking a single segment up into multiple segments and by breaking up the user community sharing that segment into smaller communities. Each smaller community would have its users and the resources they use most often connected on a new, smaller segment. The segments are then connected to each other using standard internetworking technology as implemented in a bridge or router.

Today, network segmentation is configured using standalone routers; increasingly, however, this segmentation will be configured inside the hub. One of the advantages of this approach is that it preserves investment in the existing network infrastructure while effectively allowing more enterprise bandwidth.


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