Ethernet Standards IEEE802.3

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