OSI/TS Configuration and Management Manual

OSI Transport Services
OSI/TS Configuration and Management Manual—424831-001
5-11
Called/Calling and SRC-REF/DST-REF Addresses
Address Sharing for LANs
For LANs, all transport connections by default share the same TLAM (for D-series and
pre-G06 releases, or PAM, for G06 and above releases) port (LAN station address). The
possible levels of multiplexing are as follows:
•
NSAP address
The NSAP address provides the first level of address sharing. With this option,
several NSAPs can share the same LAN station address.
•
TSEL
TSELs can share the same NSAPs so that two or more transport logical addresses
can share the same network address.
Called/Calling and SRC-REF/DST-REF Addresses
The T-CONNECT service primitives that the OSI/TS subsystem exchanges with an
application include several parameters, two of which are the calling address and the
called address. The TPDUs that OSI/TS exchanges with a remote transport peer include
SRC-REF and DST-REF parameters.
The called and calling addresses are absolute in the sense that they have the same
meaning at both ends of the connection. The called address is the transport service
access point selector (TSEL) of the responding transport entity. The calling address is
the TSEL of the initiating transport entity.
SRC-REF refers to the source of the TPDU, and DST-REF refers to the destination. The
SRC-REF and DST-REF are relative in the sense that their values can differ at the two
ends of the connection. The transport entities assign values to these parameters, then
use these values to refer to the connection for as long as it exists. The reference
numbers are arbitrary they are not related to the addresses of the transport entities.
When the connection terminates, the reference number is reused as described under
Section , Frozen Connection Identifier References
earlier in this section.
The initiating transport entity assigns a value to the SRC-REF parameter in the
CR-TPDU and sets the DST-REF parameter to 0. The responding entity inserts the
incoming SRC-REF value into the DST-REF parameter of the CC-TPDU and assigns a
value to SRC-REF. DT-TPDUs sent by the initiator contain the responder's SRC-REF in
the DST-REF parameter.
DT-TPDUs sent by the responder contain the initiator's SRC-REF in the DST-REF
parameter. Figure 5-2
illustrates the relationship between SRC-REF and DST-REF.