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e -server magazine

March 1997: Volume 12, Number 4

Communicating with Sam

LAN Extension

By Sam Johnston

From the questions submitted, the selected issue to be addressed in this issue is:


ur company is currently implementing new enterprise software that is Client/Server based. As a consequence, it appears that we will need to significantly increase the bandwidth necessary to support the wide area connections to our remote branch offices. Our branch offices are located locally, and will require greater than T1 connections. We have started to look for cost effective solutions to obtain the increased bandwidth. One option that has surfaced in talking with the carriers is an Ethernet LAN Extension that provides 10baseT over the WAN, in addition to the LAN. What is your view on these types of offerings? As well, I am a little confused in that I thought that ATM was the only technology that is supported on both wide area and local area networks.


he introduction of the LAN Extension is the latest marketing effort from the carriers to bundle hardware, services and bandwidth into a single package. Despite what they are calling the service, there is no real mystery to the offering. In the case of the Ethernet LAN Extension, although the carrier is offering a 10Mbps service, which is equivalent to a Fractional T3 connection, in reality there is not necessarily 10Mbps of bandwidth available. Bundled in with the bandwidth is the WAN hardware at each of your sites, and Management services relating to this hardware. Therefore, the carrier manages the bandwidth through their switched network. The carrier will support a burst of 10Mbps, but does not continually deliver 10Mbps.

In essence, this is no different than if you were to buy Frame Relay network service from a carrier, and they leased you a router and provided you with monitoring services - the only difference is that LAN Extension bundles all aspects into a single monthly fee per node, so it is difficult for you to assess the cost of each component.

The benefit of the LAN Extension is that it does provide you with more bandwidth, and if it fits your strategy, the carrier will make your life easy by managing the network from the LAN interface outward and eliminating the need to support and manage the corporate WAN with internal resources. However, this service is not without issues. Specific risks include:

In general, in addition to the technology risks identified above, my analysis indicates that these servicew are very expensive relative to the performance they deliver. For maximum cost effectiveness, my recommendation is that unless carrier control of your network fits business strategy, you should buy bandwidth only from the carrier and build a solution around the bandwidth that fits your specific environment, including sizing bandwidth to precisely fit your needs.

Most companies that I talk with are interested in merging voice and video with their data to provide strategic benefits to maximize the cost effectiveness of their communications. To accomplish this today most businesses are utilizing dedicated bandwidth services. As well, the strategic benefit of this approach is that the company is enabled to prioritize their media (voice, video or data) based upon their business requirements across a common backbone. (In contrast to buying a service like LAN extension for your data.)

In your case, ATM on the wide area may be a better solution if the network traffic is growing as quickly as you have described, which leads to your second question. Ethernet was never intended to be a WAN technology, hence, some of the inherent technology issues described above. Conversely, ATM was designed from the beginning to be an end-to-end network solution with a single protocol supporting all media types. As a consequence, my recommendation to clients is to maximize use of current standard WAN technologies until they can justify the leap to ATM.

To summarize, the LAN Extension services are really just bundled marketing programs using traditional technology. Like most marketing programs, it is crucial that you strip away the hype and get a clear view of what you are buying and how it relates to the rest of your network. T < G

Note: Any TUG member wishing to submit a question to Sam can e-mail or forward their typewritten material to the TUG office, or to Intesys. We would be pleased to publish your question and Sam's answer in an upcoming issue of the TUG e-server magazine.