A hub-hub-spoke model is ideal for companies with overseas and/or regional traffic flows. Say manufacturer based in the United States has a multilingual, multinational network based in England into which all European Union countries are tied. Orders and consolidation information are relayed to U.S. systems for stock replenishment in the British central warehouse. A much smaller long-haul communications pipe is necessary between the British and U.S. sites--hence, the hub-hub-spoke model. Because the England-to-United States link is the most expensive, long-haul communications are minimized and special requirements (multilingual) are handled at the second hub.
[Lesson learned] Know before you go; look before you leap. We worked with a company that had outgrown its single building and decided to move the engineering/development group to a new site a couple of miles away. T1 lines were ordered, with bandwidth allocated based on an IT manager's gut feeling rather than on usage statistics. Day 1 was a nightmare: The bandwidth allocated was inadequate, and the engineering teams were rightly upset. Business came to a halt. The network team should have been allowed to monitor LAN traffic from the groups involved to determine the bandwidth necessary to maintain service levels across the WAN. Amazingly, the manager chalked it up to "working out the bugs" and wasn't disciplined. We would have considered that a career-altering decision.
[Lesson learned] Rush, and you'll go nowhere fast. One company was in such a hurry to complete its systems conversion, it chose dial-on-demand ISDN lines rather than wait for leased lines. Routers were set to establish connections on an as-needed basis. After implementation, the central network staff failed to monitor outgoing connections, and some keep-alive traffic caused unnecessary connections to be established every five minutes. When the bill arrived, it exceeded all estimates. In the rush to "get things done," costly router-programming oversights were made. Even worse, they weren't caught until flags went up in accounting.
Don't forget backup facilities when you're performing capacity planning for new lines or adding capacity to existing lines. And don't assume anything: If you're using a single carrier to provide both your primary and backup communications, get full disclosure on the circuits behind the scenes.
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