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CAPWAP

Control and Provisioning of Wireless Access Points (CAPWAP)Accel was responsible for the Implementation of the CAPWAP protocol on Clients Base Station based on the Open CAPWAP framework.

Client ProfileA high technology and award-winning manufacturer providing end-to-end solutions including access, Backhaul, CPEs, NMS, service provisioning and billing.

Salient Product Features
The CAPWAP protocol transport layer introduces resiliency using a request/response paradigm, where timeouts schedule retransmissions when a response does not follow a certain request. Two types of payload may be managed by this transport protocol:

  • CAPWAP data messages
  • CAPWAP control messages

CAPWAP data messages encapsulate wireless frames forwarded by theWireless Termination Point to the Access Controlleror by the Access Controller to the
Wireless Termination Point.

CAPWAP control messages are CAPWAP management, control or monitoring messages exchanged among Access Controller and Wireless Termination Points.

CAPWAP also defines a discovery protocol for the automatic association of WTPs to the AC.

As soon as the WTP is turned on, it sends a Discovery Request message (Discovery phase). Any AC receiving this request responds with a Discovery Response message. Hence, the WTP selects the AC, if any responded, with which it wants to interact and it establishes a connection without Datagram Transport Layer Security support.

Once the connection has been established, both devices exchange their configurations and capabilities. The WTP is then ready to send and receive CAPWAP messages to/from the AC.

Salient Accel Product Features
The Client wanted to develop a CAPWAP protocol on the Wi-Fi base station so that the Access Controller of the AC vendor will be capable of controlling the Clients Base Stations.

CAPWAP implementation on the Clients Base Station will have the following operations.

  • AC-AP Channel Protocol Operation
  • AP-Device Management Operations
  • Station Management operation

Open CAPWAP implementation available as open source code was used for the development of the CAPWAP.

Following are the specific requirement related to the porting of the Open CAPWAP.

  • Disable DTLS using compilation macro
  • CAPWAP standard elements are not used for managing the AP. Vendor specific extension was used for the implementation
  • The CAPWAP implementation works with both Linux and eCos.

Protocol Requirements
AC-AP Channel Protocol Operation:

AC AP channel protocol operations should support the following.

  • Discovery Operations
  • Join Operations
  • Control Channel Management

Discovery Operation:
The AC Discovery phase allows the AP to determine which ACs areavailable and choose the best AC with which to establish a CAPWAPsession. The Discovery phase occurs when the AP enters the optionalDiscovery state. AnAP does not need to complete the AC Discoveryphase if it uses a pre-configured AC.

Join Operations:
The Join Request message is used by a WTP to request service from an AC after a discovery phase is established to that AC. The Join Response message is
used by the AC to indicate that it will or willnot provide service.

Control Channel Management:
The control channel messages are used by the WTP and AC to maintain a control communication channel.

AP Configuration
Following is the configuration procedure for AP based on CAPWAP

  • AP will create the control channel and will wait for the configuration UDP packet from AC.
  • Once AC gets the configuration packet, it will decode the configuration elements and will save it in the configuration file.
  • It will set the reboot flag to On according to the reboot element value
  • Once the configuration is completed CAPWAP will set the radio On
  • CAPWAP will create the data channel
  • Uses the data channel for further communication

Communication Interfaces
Ethernet will be the communication interface between the AC and AP. CAPWAP protocol uses UDP for the communication above the Ethernet for control channel as well as data channel.

Key Customer Value

  • Different Access Points can be controlled by a Single Access Controller by implementing a standard protocol between the Access Controller and the Access Point.
  • By implementing a Standard CAPWAP protocol compatible with Access Controllers, the Client was able to manufacture specific devices (Access Points) that uses the CAPWAP protocol and thereby increase sales.