2-3 Routing Hubs and ATM
GEORGE CONANT
Internetworking functions, specifically routing functions, are poised to play a crucial role in the design of enterprise networks that are implemented using intelligent wiring hubs. One reason is that mixed-speed devices such as 10M-bps and 100M-bps Ethernet connected to the same hub cannot be connected through simple repeating hardware; they must be connected through an internetworking function. Second, asynchronous transfer mode (ATM) switches will reduce the need for backbone routers, resulting in a migration of the routing functions in the network into intelligent wiring hubs.
TRENDS IN NETWORKING
At the start of the 1980sthe decade of the LANLANs were developed in research facilities but were not widely deployed. By the middle of the decade, local area networks had become widely deployed but, in the case of Ethernet, they were deployed as shared linear cabling systems with attached stations. By the late 1980s, structured wiring, similar in topology to phone wiring, was considered the preferred method of deployment for one simple reason: It was less expensive to install and easier to maintain.
The wiring hub evolved as the wiring closet device to which end stations were connected in a star topology. Increasingly, these end stations were connected to a backbone router through a LAN connection. This topology is depicted in Exhibit 2-3-1. Hubs deployed were basically multiport repeaters. The repeating functions were implemented in hardware. The role of software in these hubs was primarily for network management.
Exhibit 2-3-1. Typical LAN Topology
Now, however, several application trends are causing significant changes in the communications infrastructure and the technology employed in todays (and tomorrows) enterprise networks.
More Powerful Graphical Applications
The adoption of graphical user interfaces (GUIs) has allowed users to bring in-house many functions that previously would have been handled by outside agencies. A prime example is the boom in desktop publishing.
Paralleling these developments, computing engines have become much faster, an advancement that in turn has enabled more complex applications such as color image editing to run on desktop platforms. The files that are generated by these activities are much larger than those generated by simple character-based applications.
More Bandwidth Required
More users are organized into logical work groups sharing files on common file servers. These users are working on compound documents and printing larger images on high-resolution printers. As a result, network segments within the enterprise are reaching their maximum capacities and causing increasingly unacceptable delays for users.
Video and Voice Application Support
Increasingly, the desktop is the point at which traditional data communications applications are merging with new video and voice applications. E-mail, voice mail, and desktop videoconferencing are just a few of the technologies currently established or emerging. As an example, newer Apple Macintosh computers come equipped with microphones and digital sampling software, and Microsoft Word now ships with standard voice annotation software.
Although these developments are also driving the need for more bandwidth, not all users will require 155M bps, 100M bps, or even dedicated 10M bps to their desktop. Many users will be satisfied by shared access to 10M bpsprovided only a limited number of users are sharing that bandwidth.
Network planners should be attempting to design the underlying network infrastructure (i.e., hubs and wiring) to support greater bandwidth with minimum disruption as needs demand. This means hubs and wiring must support mixed-speed networks. In these mixed-speed networks, routing or bridging must be integrated into the hub.
ADMINISTRATIVE ISSUES
Network administrators must also implement solutions that address issues of flexibility, preservation of current investments, and heterogeneous environments.
Flexibility
When networks were smaller, administrators could place users physically close to their resources because repeating technology could tie them together. Today, workgroups sharing common resources may be physically separated from each other as well as their resources. Some users may share network resources with other users and other users may need dedicated resources. Administrators need to allow ready access to some resources and restricted access to other resources for a constantly changing topology of users, servers, host systems, and other devices.
Staged Technology Introduction
Network infrastructures are growing so large that is impossible for network administrators to introduce new technologies overnight. Budgetary restrictions also limit the changes that can be made quickly. Network administrators must introduce changes slowly and preserve as much investment in the existing infrastructure as possible.
Management of Heterogeneous Environments
As networks have evolved over the past 10 years, two issues have come to the forefront: remote manageability and multivendor management systems.
As networks grow physically larger and more complex, managing devices locally is no longer feasible. Remote manageability is key to quickly resolving network problems and reducing the cost of management personnel. Although open multivendor network management platforms are becoming available and hardware vendors are quickly incorporating standards such as Simple Network Management Protocol (SNMP) and Remote Network Monitoring Protocol (RMON), network managers have been left handicapped in a heterogeneous environment by the proprietary management systems that were designed to serve the homogeneous network.
KEY TECHNOLOGY CHANGES
Exhibit 2-3-2 summarizes the changes in backbone, hub, and end station technologies that are going to define future enterprise networks. These changes are following two paths: ATM and backbone routers.
Exhibit 2-3-2. Technological Changes within the Enterprise Network
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