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The table 3-1 is the format of LLC PDU. It comprises four fields, DSAP, SSAP, Control, and
Information. The DSAP address field identifies the one or more service access points, in which the I/G bit
indicates it is individual or group address. If all bit of DSAP is 1s, it’s a global address. The SSAP address
field identifies the specific services indicated by C/R bit (command or response). The DSAP and SSAP
pair with some reserved values indicates some well-known services listed in the table below.
0xAAAA SNAP
0xE0E0 Novell
IPX
0xF0F0 NetBios
0xFEFE
IOS network layer PDU
0xFFFF
Novell IPX 802.3 RAW packet
0x4242 STP
BPDU
0x0606 IP
0x9898 ARP
Table 3-2
LLC type 1 connectionless service, LLC type 2 connection-oriented service and LLC type 3
acknowledge connection-less service. There are three types of LLC frame for all classes of service. In Fig
3-2, it shows the format of Service Access Point (SAP). Please refer to IEEE802.2 for more details.
Table 3-1 LLC Format