Avaya M770 Manual Do Utilizador
Appendix F
Routing and Signalling Concepts
304
Avaya M770 ATM Switch User’s Guide
All setup requests, travel on reserved channel 0/5 (VPI=0, VCI=5 on root virtual
port 0), but the ATM switch will assign an incoming and outgoing VPI and VCI on a
particular port, for the connection through the switch. Therefore, an ATM virtual
circuit is a sequence of switch VPI/VCI translations.
The value of the VPI and VCI within a particular ATM cell header will change as the
ATM cell is switched through the ATM network. In a single switch configuration a
cell’s VPI and VCI are translated only once, but in a multiple switch environment a
cell’s VPI and VCI may be translated many times. VPI and VCI values are assigned
symmetrically, that is, the same values are reserved in both directions across a link.
This means that all virtual circuits are inherently bi-directional. This does not imply
that SVC traffic must be sent in both directions; it can be either bi-directional or
uni-directional. With point-to-multipoint virtual circuits, data is only sent from the
root (source) to the leaves (destination parties).
port 0), but the ATM switch will assign an incoming and outgoing VPI and VCI on a
particular port, for the connection through the switch. Therefore, an ATM virtual
circuit is a sequence of switch VPI/VCI translations.
The value of the VPI and VCI within a particular ATM cell header will change as the
ATM cell is switched through the ATM network. In a single switch configuration a
cell’s VPI and VCI are translated only once, but in a multiple switch environment a
cell’s VPI and VCI may be translated many times. VPI and VCI values are assigned
symmetrically, that is, the same values are reserved in both directions across a link.
This means that all virtual circuits are inherently bi-directional. This does not imply
that SVC traffic must be sent in both directions; it can be either bi-directional or
uni-directional. With point-to-multipoint virtual circuits, data is only sent from the
root (source) to the leaves (destination parties).
Note:
On a given link, VPI/VCI identifiers are assigned in both directions of a
circuit. However if a circuit is uni-directional, one of these will not be used.
Note:
A cell’s VPI and VCI are of local significance only. They identify the cell as
being associated with a particular virtual circuit through a single link.
When the M770 ATM Switch receives a cell, it examines the ATM cell header to
determine the VPI/VCI on which the cell was transmitted. Using this information,
the M770 ATM Switch determines the destination port and appropriate VPI/VCI
for the transmission of the ATM cell.
For example, in a single switch environment the switch can be configured such that
a cell received on port A with VPI.VCI=0.35 is switched to port B with
VPI.VCI=0.72. The translation from input port VPI and VCI to output port VPI and
VCI is carried out by the switch hardware.
determine the VPI/VCI on which the cell was transmitted. Using this information,
the M770 ATM Switch determines the destination port and appropriate VPI/VCI
for the transmission of the ATM cell.
For example, in a single switch environment the switch can be configured such that
a cell received on port A with VPI.VCI=0.35 is switched to port B with
VPI.VCI=0.72. The translation from input port VPI and VCI to output port VPI and
VCI is carried out by the switch hardware.