Aventail is going bigger with its new SSL VPN appliance.Called EX-2500, the device supports up to 2,000 concurrent users and comes with a package of standard features including:* Secure Desktop, which creates a logically separate environment for SSL sessions that can be wiped out afterward.* Aventail Connect, the agent that gives full network layer connectivity to remote users* Aventail Mobile, which grants SSL VPN access to small-screen devices.* Support for native clients for Citrix and Windows Terminal Services.The device has double the session capacity of Avential's original SSL box, the EX-1500, which supported 1,000 users at a time.The development of the Aventail appliance line tells a lot about how the demand for the devices is changing. The EX-1500 was the original device the company offered in 2002 when it expanded beyond being a service provider.But then in 2004, it decided that many potential customers didn't have the need or the financial resources to pay for a 1,000-user device and it came out with the EX-750, which supports just 50 users.Now it seems that demand for SSL VPNs has grown enough to warrant a device that supports very large deployments.Since Aventail is one of the perennial top five among SSL VPN vendors, and one that has been around the longest, its activities can be considered a bellwether of what's going on with the technology. If it thinks customers need larger SSL VPN appliances, that's one more sign of the increasing popularity of SSL VPNs.