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In search of greater bandwidth.

If you have a LAN environment that is beginning to crack under an astronomical increase in user demand, you are not alone. Most organizations have already begun to evaluate and implement solutions that increase bandwidth.

But high-speed network alternatives that offer reliability, scalability, and manageability are numerous, and it can be difficult to determine which technology to implement and when. Solutions include switching/VLANs, ATM, 100Base-T, 100VG-AnyLAN, FDDI, Fast Ethernet, and more.

In many cases, switching and virtual LAN (VLAN) technology is the best way to increase bandwidth. Switching is a technology that forwards packets between users on different LAN segments based on a look-up table.

A LAN switch interconnects any number of LAN segments that would otherwise share the same collision domain and (in the case of Ethernet) occupy a single 10 Mb/s pipe. The switch provides each segment with its own 10 Mb/s pipe.

Switching creates multiple collision domains, reducing the amount of contention on a network. When conversations occur between different collision domains, each conversation receives a 10 Mb/s pipe. (See Figure 1.)


Switching initially operated at Layer 2 of the OSI Model, which meant frames moved through the switch based on media access control (MAC)-layer address, similar to the way bridges functioned.

Switching has become very attractive for two primary reasons: cost and supportability. Switching solutions reduce costs in several ways. Because switches allow desktop devices to continue using their current interfaces and cabling infrastructures, existing investments are protected.

Switching also minimizes change. This in turn reduces downtime and eliminates the need to retrain the support staff. Also, migration issues are not as complex as they would be with, for example, ATM. The reduction in complexity minimizes the time to implement.

Switching solutions also work well in conjunction with technologies such as ATM, FDDI, 100Base-T, and 100VG, enabling implementation of new technologies in a phased approach. This can minimize costs by reducing the number of network interface cards (NICs) upgraded.

At the same time, a phased approach to switching can maximize throughput by increasing bandwidth where it is needed, at the server. Switching can, and in most cases should, be implemented in conjunction with these technologies to offer a solution that is cost-effective and focuses the high-speed connections where they are needed most.

The per-port cost of implementing switching hubs continues to decrease dramatically. This has promoted the use of switches to create private LANs, in which each user has his or her own segment. or collision domain. This progression helps to resolve the problem that switch configurations encounter in legacy shared-media LAN environments.

Before switching, shared-media LANs were the norm. This approach bogged down communication, as users shared the same collision domain and, hence, vied for the same bandwidth. As user dependency on the network grew--along with use of bandwidth-hungry applications--a more efficient means of communicating became necessary. Enter switching.

But switching was not a panacea. During the initial deployment of switches into shared-media LANs, many organizations found no increase in performance at all. Data flows between clients and servers were largely misunderstood, and users reported discouraging results.

In a shared-media environment, multiple source collision domains communicating with the same destination or one source collision domain communicating with many destinations--negates the entire switching advantage, because of the way switching works. (See Figure 2.)


VLANs offer the ability to manage network adds, moves, and changes from a single, central management station instead of sending a technician to physically locate and alter connection points at the desktop and wiring closet. This saves time, resources and money. It also eliminates the cabling and topology problems that can occur as a result of physically altering the network.

There are, however, issues associated with implementing VLANs. The major concern is standardization. Because the standards for virtual LANs are still in development, any full-scale deployment of a VLAN solution at this time is risky.

Most vendors claim that when a standard is formalized, they will retrofit their components to comply at no cost. However, what will the cost be to your organization in terms of downtime or retraining?

As you begin to plan for and implement these solutions, the best approach is a phased one. 10Base-T switching can be implemented at minimal cost, with minimal disruptions.

Select a high-speed technology to complement your organization's switching environment, and upgrade key servers to a 100 Mb/s technology. VLANs can be used to simplify adds/moves/ changes and control broadcast traffic.

When considering widespread deployment of these many technologies, consider these issues: management of the environment, standardization changes to the technologies, and effect on the existing environment.

As always, when developing a strategy to offer greater bandwidth, choose a solution and technologies based on their ability to address your organization's specific objectives and not simply on technical merit. Determine whether the need you are addressing is tactical or strategic (see box), and set your expectations accordingly.


When developing a switching/VLAN solution to enhance bandwidth, it is essential to identify tactical vs. strategic business issues. Each requires its own kind of solution.

There are tactical issues within every organization. These are problems that must be dealt with today, and the solutions that address these issues provide an instant resolution to a problem area but not necessarily a long-term return on investment.

An example would be a group of 10 engineering users in a organization who need to transfer large amounts of information (CAD files) very rapidly amongst themselves. In the past, these users worked on projects independently of each other. They used the network only for Lotus Notes access, e-mail, and network printing.

The organization has just landed a large contract that requires these engineers to work as a team. The problem is that the engineers are on a 10 Mb/s Ethernet subnet with other non-engineering users; the concern is that the new project, as well as the other users, will be crippled by the lack of network bandwidth.

The first step is to understand 1) the type(s) of access the engineers need, and 2) bandwidth requirements.

A solution may be to implement a single switch with a 100 Mb/s port for the engineering users. The switch would essentially replace the existing 10Base-T hub. The other users could continue 10Base-T access either through the newly implemented switch or through the existing hub. The engineers would be the only ones affected by the change.

Access to any other services would continue at 10 Mb/s, as the rest of the network would remain unchanged. The bottom line: bandwidth would be increased and collisions reduced. This solution is tactical because it deals with an immediate need without necessarily addressing any long-term direction or requirement.

Strategic issues deal with the long term. An example of this would be a call-center application.

Initially, the organization's 300 customer service reps will only access the product data base. Within a year, however, they will need access to virtually all other key servers throughout the organization, as well as to full-motion video clips, CAD product drawings, and large documentation files.

Access to all information is time-sensitive, because customers dislike hanging on the phone. Reliability, speed, and integration with legacy applications are essential.

Because of the critical nature of the application and the expected transaction rates, a switching environment using 100 Mb/s connections to the desktop would seem appropriate.
COPYRIGHT 1997 Nelson Publishing
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Copyright 1997 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Technology Information; includes related article on strategic vs. tactical switching solutions; switching and virtual LAN technology
Author:Federico, Gary V.
Publication:Communications News
Date:Feb 1, 1997
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