OSI/TS Configuration and Management Manual

Managing a Transport Connection
OSI/TS Configuration and Management Manual—424831-001
6-3
Requesting a Connection
Requesting a Connection
After receiving a T-CONNECT service primitive over a connection-oriented
subnetwork, OSI/TS determines whether a connection is already open to the same NSAP
for this transport entity. If a connection exists, it is used, unless the transport connection
currently assigned to it does not allow multiplexing. If no connection exists, OSI/TS
requests one.
No subnetwork connection is required in a connectionless environment.
Building the CR-TPDU
OSI/TS uses the subnetwork connection to send a CR-TPDU to the remote peer entity.
The CR-TPDU contains protocol-negotiation parameters; it can optionally contain user
data. All parameters and data must fit into a single TPDU. Figure 6-1
illustrates the
structure of a CR-TPDU.
The following subsections explain the parameters in Figure 6-1
. Some parameters are
subject to change, based on the content of the CC-TPDU these are indicated below.
Length Indicator (Octet 1)
The length indicator specifies the length of the CR-TPDU in octets.
TPDU Code (Octet 2)
TPDU:type code in CR-TPDU
The TPDU code indicates the type of TPDU.
Initial Credit (Octet 2)
The initial credit parameter determines the size of the flow-control window in classes 2,
3, and 4. OSI/TS sets the initial credit to the configured value when constructing a CR-
Figure 6-1. CR-TPDU Structure
601CDT .CDD
Length Indicator
Octet 1
Octet 2
Octets 3-4
Octets 5-6
Variable
Length
Fields
Octet 7
TPDU Code Initial Credit
DST-REF
SRC-REF
Protocol Class Options
Variable Part
User Data (TSDU)