Verilink 9000 Series (34-00271) Product Manual - Manual (Page 255)

X.25 Channel List 233
PVC
Channel
Number
A PVC (permanent virtual circuit) is used when an address needs to always be
assigned to the same LCN (logical channel number). A PVC is conceptually like a
leased line. It always connects the user to the same destination. This eliminates the
ability to use the connect command in host switching. When assigning LCNs
(channel numbers) to PVCs, it is necessary to start at 1 and increment the LCN by
one for each additional PVC.
VC
Sub-Address
When using VCs (virtual channels), a subaddress is usually assigned to the
terminal address. The subaddress must be digits only and can be from one to three
positions. This is necessary since some terminal addresses may contain characters
and these are illegal in the X.25 addressing scheme. All entries in the channel list
must have unique subaddresses. When connecting to another TXPORT unit, the
channel list at each end must be identical, otherwise an address conversion may
take place. The subaddress is appended to both the called and calling address in
the call request packet.
Subaddresses must start in the first position of the field. For example: [12 ] is valid
and [ 12] is not valid.
Using VCs without subaddressing: In some instances, using VCs without
appending the subaddress to the address is desired. A typical application would be
when connecting to a non-TXPORT unit that has address pooling defined on it. In
this case, the receiving unit would expect the same calling (local) address from
each device and would then internally assign an individual station. If this is
desired, leave the sub-address field blank. This defines the channel as a VC but the
subaddress is null and it is not appended to either the called (access) or calling
(local) address.
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