Technology Description
In order to understand fully how the network shown in Figure 13.1 works, we must
start with some basics. In spite of their ubiquity, the knowledge of exactly how bridges
work is somewhat scarce, so a semi-historical introduction is in order.
The original DEC/Intel/Xerox Ethernet was standardized by IEEE Std 802.3, Carrier
Sense Multiple Access/Collision Detection (CSMA/CD) Ethernet. The original Ethernet
provided users with access to a local area network (LAN) consisting of a single largediameter
coaxial trunk cable (usually bright yellow), with ???taps??? (or medium attachment
units) through which stations could connect to the cable. Every data frame transmitted
by any station was seen by every other station attached to the trunk cable.
Figure 13.1 Metro Ethernet implemented with IEEE 802.1 bridges
802.1ah MAC-in-MAC
Provider backbone bridge
cloud
A
802.1ah MAC-in-MAC
Provider backbone bridge
cloud
B
802.1ad Q-in-Q
Provider bridge
cloud
C2
802.1ad Q-in-Q
Provider bridge
cloud
H
802.1ad Q-in-Q
Provider bridge
cloud
G
802.1ad Q-in-Q
Provider bridge
cloud
F
802.1ad Q-in-Q
Provider bridge
cloud
E
802.
Pages:
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847