Ethernet(802.3), WLAN(802.11) 구분

면접준비하면서 나의 무지가 어마무시하다는걸 절실히 깨닫고 있다. ㅠㅠ

Ethernet vs. WLAN[1]

Ethernet is a (set of) data-link layer (layer 2) protocol(s), known as 802.3, that runs over various physical (layer 1) media.

WLAN is also a (set of) data-link layer (layer 2) protocol(s) known as 802.11 that runs over the Wi-Fi physical media (layer 1) using radio signals rather than electrical signals through a cable.

Wireless Frames vs. Ethernet Frames[2]

wireless frame 는 MTU가 2346 bytes, ethernet frame 는 MTU가 1500bytes 이다. 

이렇게 차이가 나는 이유는 Access Point에서 wireless frame을 ethernet frame으로 변경해준다. 이로 인해 wireless frame에는 fragmentation을 위한 fragment Number field가 포함되어 있다. 즉 AP에서 알려주는 sequence number로 볼 수 있다.

infrastructure를 살펴보면 AP는 wired network에 연결되어 있다.

잘 알다시피 standard ethernet frame은 위와 같이 MAC addresses, the MAC address of the sending device and the MAC address of the receiving device 로 구성되어 있다.

 A wireless frame, however, has to take into account that the MAC address of the device that sent the frame may not be the last MAC address the frame “saw” and might not be the first MAC address the frame has to return to.  For example, if a wireless client is behind a wireless repeater, then frames coming from that client will need the MAC address of that repeater in addition to the actual source and destination address.  A wireless frame can have up to 4 MAC addresses.

Types of Frames - While all wireless frames have pretty much the same kind of header, what happens from then on depends a lot on what kind of frame it is. 

Wireless networks use 3 types of frames.  Management frames are used for beacons, probes, disassociations, and pretty much anything else that pertains to the AP and client associations.  Control frames pretty much have to do with preparing to send data and then acknowledging that data has been received.  These include the frames that are used to request to send and are mostly used when the AP has taken control of the medium, specifying when it is a station’s turn to send data.  Data frames are exactly what they sound like…they contain data.

reference

[1] http://stackoverflow.com/questions/11875470/what-is-the-relationship-between-the-wifi-and-ethernet-protocols

[2]http://redwarrior77.wordpress.com/2008/12/31/wireless-frames-vs-ethernet-frames/