Last week, we broached the subject of high availability in branch-office sites - a notion that might seem oxymoronic in today's networked environment.Branch-office routers, after all, are rapidly becoming commodities in a market fraught with fierce price competition (Adtran, for example, offers a basic IP WAN router for under a grand). In this milieu, adding high-availability features that will boost the price tags of these devices isn't a top vendor priority.Similarly, enterprises growing more distributed need to outfit more locations with network equipment and WAN circuits. Keeping capital investments and recurring service fees at bay is a serious budgetary goal.The flip side of the argument, though, is that the greater the number of distributed sites, the higher the number of employees who would be left in the productivity lurch if their access links or CPE die. So simplistically speaking, the larger the percentage of remote users, the more important high-availability routing features in remote offices become.Like the age-old security question, though, figuring out how much redundancy to build into a particular site isn't quite this black-and-white an exercise. You have to calculate the cost per minute (or per hour or per day) of a particular site being cut off from resources at the data center. Then, you must determine whether that cost is greater than the price of a back-up router plus monthly recurring charges for a second access link.In some cases, the cost of downtime would be, as MasterCard would say, "priceless." Depending on the function and size of a branch site, damage to the business caused by an outage there may transcend lost productivity for X number of minutes or an interrupted e-commerce transaction. A lost customer - or customers - could have long-ranging, high-cost ramifications.We talked to several branch-office router makers, including Adtran, Alcatel, Cisco and Quick Eagle, which all make provisions for WAN circuit backup or dual-homing in their low-end routers. Their high-availability features range from dial backup (PSTN and ISDN) to full-link redundancy, load balancing, and hot-standby "virtual router" failover capabilities between primary and back-up routers, should you choose to invest in redundant CPE.Next week, we'll take a look specifically at what high-availability features are available from the branch-office router vendors, the protocols and technologies involved, and the basic considerations associated with them.