OSI/TS Configuration and Management Manual

Managing a Transport Connection
OSI/TS Configuration and Management Manual—424831-001
6-6
Successful Connection Initiation
The number of fields in the variable part of the CR-TPDU varies according to the class
and configuration.
Successful Connection Initiation
After sending a CR-TPDU, OSI/TS cannot complete connection establishment and enter
the data-transfer phase until it receives a valid CC-TPDU from the remote transport peer
entity. This TPDU contains response values for connection parameters that OSI/TS
requested in the CR-TPDU. If any response values are different from the requested
values, OSI/TS makes adjustments to the transport connection parameters before
entering the data-transfer phase.
On receiving a valid CC-TPDU, OSI/TS evaluates the following parameters:
Initial credit
DST-REF
Protocol class
Expedited data
TPDU size
These parameters are discussed in the following subsections.
Initial Credit
If the CC-TPDU contains a value that is less than the value sent in the CR-TPDU,
OSI/TS uses the lesser value. The protocol does not permit a greater value in the
CC-TPDU.
DST-REF
The destination reference is an internal reference assigned by the remote transport entity.
OSI/TS places this value in the SRC-REF field of all outgoing DT-TPDUs. The remote
transport entity uses this field to associate protocol data units with connection endpoints.
Protocol Class
If the CC-TPDU contains a lower-numbered class than is configured as the alternate
class for the subdevice, OSI/TS uses the lower number. Table 6-4 lists the valid
responses.
Table 6-4. Valid Protocol Class Responses in CC-TPDU
Class Proposed by
OSI/TS in CR-TPDU
Class Contained in
Response in CC-TPDU
00
1 1 0
2 2 0
3 3 2 1 0
4 4 3 2 1 0