3Com CoreBuilder 9000, User Manual

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310 C
HAPTER
10: ATM N
ETWORK
B
ASICS
ATM Layers
As in the OSI (Open Systems Interconnection) model, ATM has levels that
divide the functions of ATM.
Figure 5 shows the OSI and ATM models, side by side. Note that the ATM
layers do not exactly match the OSI layers.
Figure 5 OSI and ATM Layers
Physical Layer The physical layer in ATM defines the mapping of cells, much in the same
way that the traditional OSI Physical Layer handles bits, defining physical
media characteristics, line coding, and framing. The ATM physical layer
transmits and receives ATM cell streams over a physical medium. It also
checks the integrity of the bits being transferred over a physical medium,
and makes sure that they are error-free. For more information see
“Physical Layer Interfaces” on page 435.
ATM Layer The ATM layer defines how the network carries the cells between users.
ATM A daptation Layer
ATM Layer
Physical Layer
Netw ork Layer
Data Link Layer
Physical Layer
Transport Layer
ATM Layers OSI Layers