Wavetek ANT-20, Руководство по эксплуатации

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Broadband Analyzer/Generator ANT-20/ANT-20E
O-38 Operation
6 Defining Virtual Channels
VI: ATM Test Control
6.1 Overview
Virtual channel
The term “virtual channel” is central to ATM technology. A virtual channel is basically
characterized by
•
The type of virtual connection: switched (SVC) or permanent (PVC)
•
The direction: unidirectional or bi-directional
•
The virtual channel number (VPI/VCI) for permanent virtual connections or the ATM address
for switched virtual connections
•
The traffic contract which is basically defined by the “Conformance Definition”, the “Traffic
Descriptor” and the “Quality of Service” class
•
The AAL type
•
For a measurement task it is usually also necessary to assign the channel to a traffic source
which is defined by the source type and the source parameters.
As can be seen, a large number of parameters are used to fully define a virtual channel. The
“Channel Editor” tool in the “ATM Test Control” VI has been provided to keep operations
involving virtual channels as simple as possible.
The “Channel Editor” allows you to define, modify and copy channels. Each channel definition
can be assigned a user-defined name.
Database
A channel database is included in the “Channel Editor”. This database is used to exchange
channel definitions between applications and instruments.
One database is available per instrument. When a channel is used in an application, a copy of
the channel is saved with the application. Each time the application is loaded, the instrument
checks that the copy is identical to the channel definition in the database, or if the channel is still
present in the database. If differences are found, the “Channel Import” dialog is displayed. This
allows you to remove any inconsistencies between the application and the database. As a copy
of each channel used is present in the application, the channels will automatically be exported
when an application is exported to another instrument. These channels can be included into the
database of the other instrument when the application is started there for the first time.
6.2 The “Channel Editor” dialog
The Channel Editor is used to define virtual channels and save them in a database. Push
buttons and a list box in the dialog window header are used for defining and handling the
channels. When first used, the list contains a range of default virtual channels for the usual
types of traffic (CBR, VBR, etc.). These channels can be saved under a new name and edited
individually.
Access to the various parameter groups is by means of index cards.