Forum

Currently, I'm trying to understand the relationship of WLAN - Ethernet II - 802.3 protocols in a network.

My Questions:

1. How do we send TCP/IP in a 802.3 frame? My understanding is that we have to incorporate the 802.3 LLC layer. The DSAP and SSAP in the LLC layer will provide information of the type of data inside the Information field of the LLC layer. Is this correct? Can we specify DSAP to tell that the information field inside the LLC is a TCP/IP packet? OR Do we need to use Ethernet-SNAP for the LLC layer before putting the TCP/IP?

2. What is the difference and the significance of DSAP, SSAP, and Ethernet Type field inside LLC layer? My understanding is that the DSAP and SSAP is used for specifying the receiving and the sending network layer process respectively. What does it mean by network layer process? The actual application? The process ID of the applications?

3. According to what I understand, DSAP and SSAP value will be the same. But if they are the same, why do we need them both? (obviously, there must be cases when the two values are different). Can someone give me an example when the two values are not the same?

4. The Access Point and the WNIC will automatically convert the 802.11 frame into either 802.3 or Ethernet II frame. How does the WNIC knows what kind of frame type should it convert the 802.11 frame into?

5. I did some packet capturing on my wireless network with wireshark. Why is most of the packet that I see is Ethernet II? I thought the 802.3 is the de facto standard?

6. Who wraps the IP datagram with MAC layer? My understanding is that the MAC layer added by the network card controller (OSI Layer 2). How does this work? Does the OS tell the NIC (through the Driver) the destination MAC and the type of packet to the NIC? And the the NIC will placed the same information to the IP datagram?

Help will be GREATLY appreciated.