Capwap study notes--first Capwap (i) (EXT)

First knowledge of CAPWAP

2.1 Capwap Introduction

capwap--Control and Provisioning of Wireless Access Points Protocol specification. It consists of two parts: thecapwap protocol and the wireless binding protocol.

The former is a general-purpose tunneling protocol that completes the AP discovery of Basic protocol functions such as AC, regardless of the specific wireless access technology. The latter is a configuration management feature that provides specific and one wireless access technology. In other words, the former prescribes what needs to be done at each stage, and the latter is specific to how these things should be accomplished in various access modes.

The Capwap protocol was released in the 2009 April RFC5415, and the wireless bingding protocol currently only has an RFC with 802.11 access, and was released in 2009 April. the RFC number is 5416.

PS: Drift a bit, incidentally, 802.11,802.15,802.16,802.20, such as the difference between the wireless access mode.

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At present,IEEE802 's wireless network protocol has 802.11,802.15,802.16 and 802.20 and other four categories, the four types of protocol contains a variety of different performance sub-protocol, looks very chaotic appearance ...

The IEEE802.11 system defines a wireless LAN standard (WLAN,Wireless Local Area network), designed for home and enterprise LANs, and is typically confined to a building or a small building group (such as schools, communities, etc.).

IEEE802.15 defines the wireless personal network (WPAN,Wireless Personal area Network), which is mainly used for the automatic interconnection of personal electronic devices and PCs, such devices as mobile phones,MP3 players, Portable media players, digital cameras, handheld computers, and more.

IEEE802.16 is a wide band Wireless access Technology (Broadband Wireless Access,bwa), mainly used for long-distance, high-speed communications environment, defined as the metropolitan Area network (man,< Span lang= "en-us" xml:lang= "en-us" >metropolitan area Network, performance comparable to cable cable, Span lang= Traditional wired technology such as "en-us" xml:lang= "en-us" >dsl, t1 leased line. ieee802.16 includes 802.16 and 802.16a two sub-protocol, the former is 30mbps to 130mbps, while 802.16a transmission distance can reach 50 km, the rate can be achieved 75mbps-see that in the various wireless communication technology, there is no technology can be in the effective range and performance standards are covered ieee802.16a.

IEEE802.20 and 802.16 are similar in characteristics, which have the characteristics of long transmission distance and fast speed. But 802.20 is a mobile broadband access technology (Broadband Wireless access,MBWR), he is more focused on device mobility, such as on high-speed trains, cars can achieve data communication ( 802.16 cannot do this).

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Key features of the CAPWAP protocol:

The AP automatically discovers the AC, the AC authenticates the AP, theAP obtains the software image from the AC, theAP obtains the initial and dynamic configuration from AC, etc. In addition, the system can support local data forwarding and centralized data forwarding.

The thin AP architecture gives AC a complete view of the entire WLAN network, providing the basis for the implementation of business functions such as wireless roaming and wireless resource management.

2.2 Some nouns

¢ Wireless Controller (AC): Network entities, the data layer in the network architecture, the control layer, the management layer, or unite to provide WTP-to-network access services.

¢ Capwap Control channel: A two-way channel, by AC IP address,WTP IP address,AC control port,WTP control port, Transport Layer Protocol (UDP or Udp-lite), which can be used to send and receive Capwap control messages.

¢ Capwap Data channel: A two-way channel, defined by the AC IP address,WTP IP address,AC data port,WTP data port, Transport Layer Protocol (UDP or udp-lite) , you can send and receive CAPWAP data messages on top of this.

¢ Station : A device that contains a wireless interface

¢ Wireless Terminal WTP: physical or network entities that contain an RF antenna and wireless physical layer can transmit and receive data from STA in a wireless access network.

2.3 Capwap's Model

The CAPWAP protocol supports two modes of operation:Split mac and Local Mac.

Split Mac: In split mac mode, all two layers of wireless data and management frames are encapsulated by the Capwap protocol and exchanged between AC and WTP.

As shown in, the wireless frames received from a station are directly encapsulated and then forwarded to AC.  

Local MAC: Native forwarding mode allows data frames to be forwarded with a local bridge or by using a 802.3 frame. In this case, the two-layer wireless management frame has been processed locally in the WTP and then forwarded to AC.

The local forwarding mode is shown, andthe wireless frames transmitted by station are encapsulated into 802.3 data frames and forwarded to AC.

Load type of 2.4 Capwap

The CAPWAP protocol Transport layer transports two types of loads:

¢ Data Messages

Encapsulating and forwarding wireless frames

¢ Control Messages

Manage Management messages exchanged between WTP and AC

Capwap data and control messages are sent based on different UDP ports and can be segmented, so data and control messages can exceed the MTU length.

2.5 Capwap Session creation process

The CAPWAP protocol begins with the discovery phase. Wtps sends a discovery request message, and any AC that receives the request will respond to a discovery response message. Receiving a Discovery response message,WTP chooses an AC to establish a DTLS-based security session. In order to establish a dtls secure connection, theWTP will need a pre-supplied data that will be explained later. The CAPWAP protocol message will be segmented into the maximum length supported by the network.

Once WTP and AC have completed the dtls session setup, the configuration is exchanged between the two to agree on the version information. During this exchange process, theWTP may receive the prescribed settings and then turn on these settings.

The capwap protocol is used to encapsulate The wireless data frames sent between the AC and WTP when the exchange between WTP and AC is completed and the WTP is switched on. If the user data or protocol control data length exceeds The MTU between WTP and AC, the capwap protocol will L2 the layer frame shards . The fragmented Capwap message will be re-formed into the original encapsulation message.

Capwap study notes--first Capwap (i) (EXT)