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
Destin
address
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 ensure
enough length for Collision
Detection (CD)
6
2
7
Source
address
Frame Check
Sequence
Logical Link Control Sub
-
layer
Destin
address
FCS
Source
address
Type
Destination Service Access Point
(DSAP) 1 octet
Source Service Access Point
(SSAP) 1 octet
Control Field 1 octet
LLC header
Data
P
A
D
IEEE 802.2
More Ethernet Information
http://www.techfest.com/networking/lan/ethernet.htm
http://www.networkmagazine.com/magazine/tutorial/hardware/9602tut.htm
http://telecom.tbi.net/frmlan.html
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