OSI/TS Configuration and Management Manual

OSI Transport Services
OSI/TS Configuration and Management Manual—424831-001
5-9
Addressing
the transport connection to a new network connection and performs the resequencing
procedure.
Addressing
TPDUs are sent through a network service access point (NSAP). NSAP addresses are
globally defined by the authority responsible for the network addressing domain. See
Section 2, Background Information About Addressing
for a detailed explanation of
addresses.
The NSAP address must be mapped to the subnetwork address at which the end system
or intermediate system is attached to the subnetwork. Subnetwork point of attachment
(SNPA) addresses are locally assigned
they are used by the subnetwork software to convey data to a destination on the same
subnetwork. (Note that a subnetwork address can specify either a final or an
intermediate destination.)
On an X.25 subnetwork, subnetwork addresses are identical to DTE addresses. On a
LAN, subnetwork addresses are mapped directly to the addresses used by the Data Link
Layer protocol.
The OSI/TS subsystem supports the configuration of NSAP addresses and subnetwork
addresses for each transport connection. These addresses are stored in the configuration
for each subdevice.
Address Sharing
Address sharing allows multiple addresses on the same physical connection. Figure 5-1
illustrates a possible OSI/TS configuration with five transport addresses sharing a single
line (either an X.25 DTE address or a LAN station address).