Now the IETF has given formal blessing to the CAPWAP working group, which plans to create a standard communications protocol between centralised WLAN switches and "thin" access points, the issues behind it could get thrashed out at last. The standard is being promoted by WLAN vendors, including Airespace and Avaya, and is opposed by others including Aruba Wireless and Cisco. It is still widely referred to as LWAPP, the name under which it was proposed to the IETF. Alan Cohen, vice president of marketing at Airespace, one of the most active supporters of CAPWAP, says it addresses one of the major roadblocks to WLAN adoption: the complexities surrounding security, management and deployment. "Standardisation drives adoption," Cohen says. "LWAPP is essentially USB for WLAN [access points] and network devices. USB allows you to plug a printer, or a CD burner, into a PC and it connects at a very high speed. With USB in place, the issue of how to connect any new device is taken off the table. This encourages people to create. So when HP comes out with a new photo printer, or Apple comes out with the iPod, they just work. The same is true with LWAPP. When you deploy a wireless switch, along with any type of LWAPP-enabled [access point], they will work." But before CAPWAP/LWAPP becomes a ratified IETF standard, it will have to overcome some resistance from Aruba Wireless Networks and Cisco. "It's putting the cart before the horse," says Keerti Melkote, vice president of product management and marketing at Aruba. "Before a protocol is standardised, we must first understand the framework of wireless LANs. What functions belong in the [access point], which ones should reside in the switch? There first needs to be consensus on those points." What CAPWAP does
CAPWAP is a communications protocol for networks that are migrating to "thin" access-point technology. Traditional WLAN products push all traffic handling, authentication, radio frequency management and mobility functions out to individual "fat" access points. The problem is that the access points act in isolation, making it difficult to perform critical functions such as seamless roaming, single sign-on and load balancing. CAPWAP assumes a network configuration that consists of multiple access points connected via Layer 2 (Ethernet) or Layer 3 (IP) to an access router. Today, access routers typically come in the form of WLAN appliances or WLAN switches. The access points are essentially remote RF interfaces that are controlled by the access routers. CAPWAP governs how access points and access routers communicate with each other by defining the following activities:

  • Access point device discovery, information exchange and configurationAccess point certification and software control
  • Packet encapsulation, fragmentation and formatting
  • Communications control and management between access point and wireless system device.
CAPWAP helps WLANs scale
In small deployments, fat access points are fine. But to be enterprise-class, WLANs must support hundreds of users. Distributing control functions out to the access points forces network managers into a tough trade-off: Do they want robust WLANs supporting many users, or do they want a cost-effective solution? In the fat access point world, they can't have both. Which is where LWAPP comes in. With the arrival of WLAN switching start-ups, there has been a trend toward centralised management, security and control based on thin access points connected to the wired network via a WLAN switch (or a gateway or router). By centralising intelligence within a WLAN switch, functions such as security, mobility and quality of service (QoS) can be managed across the entire wireless enterprise. However, as more vendors enter the WLAN switching game, the need has emerged for a standardised way for WLAN switches to communicate with access points. Without such a standard, one of the key benefits of thin access point networking - the ability to build multi-vendor WLANs - is lost. "For enterprises that want to take advantage of new wireless LAN switching architectures, they're left trying to use [SNMP] to communicate with their existing [access points]," says David Passmore, research director at Burton Group. "The problem with SNMP is that many of the features that WLAN switching offers cannot be utilised, such as [radio frequency] management." This leads to relying on one vendor for the switches and access points and abandoning any access points already deployed in the corporation.