The benefits of a new technology rollout aren’t always easy to quantify. Take security products. It’s impossible to know all the costs that are averted because an enterprise buys a product or service that provides some kind of protection from destructive threats. That doesn’t mean the ROI isn’t there, just that it requires some faith to accept.

That isn’t the case with WAN optimization gear. The people who buy the gear (and the vendors that sell it) are lucky to be able to compare some before and after metrics. Buyers can quantify how much time employees aren’t wasting on slow downloads, for example, and they can put a dollar amount on the bandwidth upgrade they didn’t have to make.

Maybe that’s why investors seem to be so attracted to the market. Lately there has been a string of funding doled out to vendors -- veterans and start-ups alike. Here are some deals that caught my eye over the last couple of quarters:

* Apparent Networks secured $13.6 million in financing in a second funding round announced in July. Bain Capital Ventures and JMI Equity led the round, which included investments from Business Development Bank of Canada and Aden Investments. The company’s AppCritical software is designed to measure and diagnose network performance problems that could impact voice, video and data applications.

* Certeon in July announced it raised $15 million in its second round of funding. RRE Ventures led the round, which included investments from Sigma Partners, Globespan Capital, Dow Employees' Pension Plan and Union Carbide Employees' Pension Plan. Certeon offers its S-Series application acceleration appliances as well as Application Acceleration Blueprints designed to speed specific enterprise applications such as Microsoft’s Office and SharePoint and EMC’s Documentum and eRoom.

* Coghead in March announced $8 million in a second round of funding. American Capital Strategies led the round with participation from SAP Ventures and El Dorado Ventures. The start-up offers a Web-based application creation and delivery service.

* Exinda Networks secured $6 million in its first round of funding, which was announced in April and led by OpenView Venture Partners. Exinda’s WAN optimization appliances tackle application acceleration and traffic shaping, and the company offers a hosted software for centrally managing its gear.

Ann Bednarz is associate news editor at Network World.