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Private switch
ATM Cell Structure
Header
Figure 11-1 shows ATM network UNIs and NNIs.
Private switch
Private switch
Figure 11-1 ATM Network UNIs and NNIs
One of the challenges in defining ATM was to determine a structure that
could efficiently handle any type of traffic. Because ATM must carry voice,
data, and video traffic simultaneously, the structure must accommodate a
variety of bit rates and support bursty communications. ATM supports these
needs by formatting all information into small fixed-length units called cells.
Each ATM cell comprises two parts: a 5-byte header and a 48-byte
information field (payload).
Figure 11-2 shows the structure of the UNI ATM cell. The header contains the
information necessary to deliver the cell to its destination. For networking
purposes, only the header is significant. The NNI header eliminates the
generic flow control (GFC) field, extending the virtual path identifier (VPI)
field. This allows the NNI to support a much greater number of virtual paths.
Public switch
Public switch
Public switch
Public switch
About ATM
11-3
Private UNI
Public UNI
Private NNI
Public NNI
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