Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of broadband equipment maker Calix (NYSE: CALX) fell as far as 12.1% in average-volume morning trading.

So what: Fears of economic trouble in Europe are hurting infrastructure stocks with trans-Atlantic exposure today, including a heavy toll on long-haul networking specialists: Alcatel-Lucent (NYSE: ALU) and Oclaro (Nasdaq: OCLR) saw double-digit declines, Ciena (Nasdaq: CIEN) dropped by 9%, and Finisar (Nasdaq: FNSR) fell as much as 6.4%.

Now what: Calix is mainly an American operator today, counting Verizon (NYSE: VZ) and Frontier Communications (NYSE: FTR) among its largest customers. But the company is fighting for market share in Europe, the Caribbean, and other new markets, so a lack of network infrastructure investments in Europe puts a huge crimp in Calix's growth prospects. The short-term implications of these market conditions may be severe, but a long-term investor should see nothing but a huge buy-in opportunity at this point. For more on long-distance networking stocks and the enormous opportunity in front of them, click here to read a totally free special report on the industry.