Operation Manual

VigorSwitch G1080 User’s Guide
14
This above diagram shows the Ethernet architecture, LLC sub-layer and MAC sub-layer,
which are responded to the Data Link layer, and transceivers, which are responded to the
Physical layer in OSI model. In this section, we are mainly describing the MAC sub-layer.
L
L
o
o
g
g
i
i
c
c
a
a
l
l
L
L
i
i
n
n
k
k
C
C
o
o
n
n
t
t
r
r
o
o
l
l
(
(
L
L
L
L
C
C
)
)
Data link layer is composed of both the sub-layers of MAC and MAC-client. Here MAC
client may be logical link control or bridge relay entity.
Logical link control supports the interface between the Ethernet MAC and upper layers in
the protocol stack, usually Network layer, which is nothing to do with the nature of the
LAN. So it can operate over other different LAN technology such as Token Ring, FDDI
and so on. Likewise, for the interface to the MAC layer, LLC defines the services with the
interface independent of the medium access technology and with some of the nature of the
medium itself.
The table above 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