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e -server magazine

January 1996: Volume 11, Number 3

Communicating with Sam

Switched Virtual Networks

By Sam Johnston

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


recently heard that IBM has announced a new networking strategy called SVN. What exactly is SVN, and what will the implication be on any investments I am making in my network in 1996?


BM's recently announced SVN strategy, or "Switched Virtual Networks", is really IBM's variation on what ATM will look like in the market place. All of the major networking companies have developed their visions of ATM, (for examples, Cisco "Fusion", and Newbridge "VIVID".)

ATM, and indeed all of the strategies that have been announced, are complex. ATM is high speed networking, providing 155 Mbps to the work station on demand, and enhancing the speed of data movement via fixed-length with headers to indicate the destination and data type, enabling prioritization and reducing congestion.

The IBM SVN strategy is essentially a network centric world in which the use of switches and routing -- not necessarily routers -- is the backbone. The key difference between the IBM SVN and other ATM strategies is that it places routing at the work station rather than out in the network. This is a subtle, but important point. Placing routing at the workstation on the adapter card makes the PC like a telephone - (dial an address, and the device on which it is dialed is able to directly tell the network a destination address that it recognizes.) Leaving the routing in the network is like the old party line operator - (pick up the phone, dial the local operator, provide the operator with a number, and then the operator attempts to establish a communications link.) Given that the goal of ATM, and indeed the reason for being, is to merge all forms of communication (data, voice, image, video) over a single pipe with phone system speed and quality of service, it is my judgment that the IBM strategy is likely the long-term outlook for ATM. In fact many of IBM's competitors have signed interoperability agreements with IBM in recognition that the SVN is very compliant with the standard's forum.

Your 1996 investments can be very well protected, provided that you invest based on an understanding of ATM. This is based on two factors. First, the initial place that ATM and SVN will impact in the network is the LAN, and specifically the Campus environment. With the explosion in applications and needs at the work station, most organizations are facing congestion in the LAN, and need to add capacity. A LAN switch is the most effective means to add capacity to the existing LAN infrastructure, and the IBM LAN switches can be integrated with existing hubs (and topologies) and can later be upgraded to accommodate ATM. Secondly, as routing is important to ATM, the longevity of the routers you buy today will be driven by your own migration strategy. This point is further enhanced by the fact that ATM is currently only fully resolved in the LAN and Campus, and not on the WAN. Routing and routers will in the near future continue to be crucial to wide area communications.

In the end, the IBM SVN strategy is more about how you can get to ATM -- and "can" is the operative word -- and you may decide to adopt only portions of ATM. 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/400 e-server magazine.