Ethernet Standards IEEE802.3 Data Link Layer contains two sub-layers:
Media Access Control (MAC) Logical Link Control (LLC)
Four generic Ethernet frame standards of IEEE 802.3 Ethernet 802.3 (Raw) (No LLC information, supports IPX/SPX only) Ethernet 802.2 (contains LLC header, supports IPX/SPX and FTAM) Ethernet II (no LLC header, uses Type instead of Length, supports
IPX/SPX, TCP/IP) Ethernet SNAP (with extended LLC capacities, support TCP/IP,
IPX/SPX, AppleTalk Phase 2)
Network Layer
Physical Layer
LLC Sub-Layer
MAC Sub-Layer
Ethernet Standards
Not all frame types can support all traffic variants. For example, NetWare IPX/SPX packets are usually transmitted by 802.3 (Raw) frames. In fact, the 802.3 (Raw) frame type can only support IPX/SPX traffic. When TCP traffic is generated, the Ethernet II frame is often used. Some desktop LAN analyzers will employ Sub-Network Access Protocol (SNAP) frames.
Ethernet/IEEE 802.3 Frame
Destinaddress FCS
Preamble (for synchronization) (01010…0111)
Type (Ethernet II, TCP/IP - 0800H, IPX - 8138H)Length (IEEE 802.3)If the value > 0x05-DC (decimal 1500), then Ethernet II
Logical Link Control data
6 46 - 1500 octets 4
IEEE 802.2 LLC standard for access to higher layers.PAD may be added to ensureenough length for CollisionDetection (CD)
6 27
Sourceaddress
Frame CheckSequence
Logical Link Control Sub-layer
Destinaddress FCS
Sourceaddress
Type
Destination Service Access Point (DSAP) 1 octet
Source Service Access Point (SSAP) 1 octet
Control Field 1 octet
LLC header
DataPAD
IEEE 802.2
More Ethernet Information
http://www.techfest.com/networking/lan/ethernet.htmhttp://www.networkmagazine.com/magazine/tutorial/hardware/9602tut.htmhttp://telecom.tbi.net/frmlan.html
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