Atm Layer; Atm Cell Structure - 3Com CoreBuilder 9000 User Manual

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PPENDIX ROTOCOLS AND

ATM Layer

ATM Cell Structure

Table 71 ATM Cell Header Fields
Field Full Field Name
GFC Generic Flow Control
VPI/VCI Virtual Path Identifier/
Virtual Channel Identifier
(continued)
I
NTERFACES
This section presents the structure of the ATM cell and ATM layer.
The ATM cell is defined as 48 bytes of payload and 5 bytes of header
information totaling 53 bytes. The header contains enough information
to allow the network to forward each cell to its proper destination. The
cell header also provides the network with the ability to implement
congestion control and traffic management mechanisms.
Figure 32 and Table 71 present the structure of the ATM cell.
Figure 32 Layout of the ATM Cell
The ATM cell header consists of the fields listed in Table 71.
:
Description
This field has local significance only and provides standardized local
functions (such as flow control) on the customer site. The value encoded
in the GFC is not carried end-to-end and may be overwritten by ATM
switches. It protects the header of the ATM cell, in addition to being used
for cell delineation. This defines where cells begin in a stream of cells, for
example, on the SONET interface
The VPI/VCI value allows the network to associate a given cell with a given
virtual channel connection, so it can be routed to the correct destination.
The VPI/VCI is only meaningful in the context of the given network
interface (UNI or NNI).
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