Riverbed Networks is upgrading its WAN acceleration appliance software to help customers keep corporate files available to remote workers if WAN connections fail.

Riverbed's Steelhead appliances placed at either end of wide-area connections already use a variety of means to speed up performance on those links but can now serve files locally even if the connection between branch sites and central servers is broken.

Similar to capabilities announced recently by Tacit Networks , Riverbed's new Proxy File Services feature in Steelhead 2.0 software lets customers designate which files should remain accessible during outages and how extensive the access should be.

For example, a file can be designated for read-only access, read/write access or no access in the event of a WAN failure. This capability defaults to a global-access setting, which means files can be accessed only directly from the server storing them. Local storage mode places a copy of a file on a local Steelhead device where it can be accessed and altered. Broadcast mode places a file on multiple Steelheads but allows users to only read them, the company says.

"It's not an all-or-nothing proposition," says Steve Duplessie, an analyst with Enterprise Strategy Group. If all files were stored at the local server and had to be updated periodically, that could clog the WAN links that the Riverbed boxes were installed to keep free, he says. "It's going to take up some space. This [feature] helps to fine-tune the wire."

For architectural/engineering firm Blakely, Johnson & Ghusn in Reno, Nev., the local file serving not only protects against WAN outages but speeds general file access, says Ron Maxwell, IT manager for the firm, which has removed file servers from its Las Vegas branch office in an effort to reduce confusion among different versions of files. "Instead of going across the WAN to the main office and grab files and bring them back, they'll go to a local file server," he says.

Riverbed is also adding TCP acceleration to the device, improving performance across IP networks by making less-pronounced reductions in sending speed when lines become congested and by returning to full speed more quickly when congestion clears, making effective throughput subject to less dramatic and prolonged swings. Duplessie says TCP acceleration is already implemented by competing vendors such as Tacit, Swan Labs and Juniper.

Steelhead 2.0 adds acceleration for Microsoft SQL traffic over and above TCP acceleration. Many protocols require many back-and-forth transactions that can result in delay. By having local Steelhead machines respond as if they were the remote database, some of these transactions don't have to cross the WAN, improving response time.

Riverbed also is introducing the Steelhead 2510 and 3510. Both are based on existing Steelhead hardware but have software that supports larger WAN links and more simultaneous TCP sessions than current models. The 2510 supports 6M bit/sec WAN links and 1,500 TCP sessions and costs $24,000. The 3510 supports 20M bit/sec WAN links and 2,400 TCP sessions and costs $39,000. Both are available.