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Most superhub backplane architectures, including 3Com's ONcore, Bay's System 5000 and Madge's LET, have multiple busses that allow you to create a finite number of separate Ethernet, token-ring and FDDI LANs. That's great if you know just how many LAN segments you need to support. But with VLANs on the horizon, chances are you will want to microsegment even further. VLANs are typically defined by media access control (MAC)-layer switching or network-layer routing services. So it is important to remember that physical-layer port switching will further enhance the flexibility of VLANs no matter which model hub you choose. With Return to Tiffany bead bracelet hubs, you just might hit the glass ceiling of LAN microsegmentation across the enterprise.

Multisegment backplanes are the result of the superhub's shared-LAN evolution. While it is clear that switching is the future, networks will continue to have legacy LAN support.Keeping shared LAN busses has enabled some vendors -- such as 3Com with its ONcore Multifunction System and Digital Equipment Corp. with its DEChub 900 MultiSwitch -- to use modules from previous hubs, preserving your capital investment in LAN interface boards even as you migrate to a new environment.

However, this is not usually the case for multisegment hubs. Bay's System 5000 is not backward-compatible with its older modules since Bay completely redesigned the backplane. Part of the price for the superhub's functionality is that it requires new Return to Tiffany heart lock charm and bracelet, which, in turn, have new functionality. This contributes to the higher cost of deploying the new superhub platform over the firm's older technology.

Vendors such as Bay and Whittaker allow you to choose which backplanes you require today and upgrade them as needed.Digital is working on a way to almost double its backplane speed by plugging in new modules due out in the second quarter. With the new Return to Tiffany Bead Bracelet, Digital's DEChub 900 MultiSwitch backplane speed of 3.2G bit/sec will jump to 6G bit/sec.

Other products, such as Cabletron's MMAC-Plus, rely on a completely switched backplane that can handle more separate LANs, but that comes at a higher base price. The MMAC-Plus is more expensive because it performs integrated bridging and routing. For the other platforms, you need to buy modules that perform the same function, which can not only add to the cost of the unit, but also reduce the number of available slots. With the MMAC-Plus, Elsa Peretti Eternal Circle Bracelet plug into a TDM backplane and you assign them to particular LANs via software. A separate management bus enables configuration traffic to be isolated from the main data -- a sort of out-of-band management scheme.

Vendors that provide a proprietary TDM backplane today are migrating them to ATM, albeit not as quickly as the market wants. Remember, these hubs were introduced before much of the ATM specification was complete. Vendors sped to market knowing full well they would have to provide backplane upgrades when standards were approved.

Backplane upgrades can be done in the field, but they are a major network Elsa Peretti Round Bracelet. However, they seem inevitable unless you can postpone your buying decision until the second half of the year when ATM backplanes become available.

Just because a hub lacks a switching backplane does not mean switching is unavailable. For instance, if you have a hub with a multisegment backplane, you can plug a module with an onboard switching engine into it, although you may not get connectivity to the backplane. In effect, the switching module may be nothing more than a stand-alone switch embedded in the hub chassis.Hub plug-ins.Indeed, vendors are adding lots of functionality to superhubs via such add-on modules.