2. USAGE CONSIDERATIONS › 2.2 General Analysis Considerations › 2.2.2 SNA Overview › 2.2.2.1 SNA Terminology › 2.2.2.1.1 SNA Network Addressing

2.2.2.1.1 SNA Network Addressing

Names and addresses are assigned during system generation to
identify network resources to end-users and the path control
network.  Two levels of addressing are used by the path
control network:

o Network Addresses - used to route messages between subareas
  and between NAUs in subarea nodes

o Local Addresses - used to route messages between subareas
  and peripheral nodes, and between NAUs in peripheral nodes


NETWORK ADDRESSES

Network addresses uniquely identify NAUs (SSCPs, LUs, PUs,
links, and so on).  Network addresses are made up of two
parts:  the subarea address and the element address.

Subarea addresses contain the subarea number of the subarea
Node.  The subarea number is user-assigned at system
definition.

Element addresses are unique only within a subarea.  They are
assigned during system generation, network reconfiguration,
activation of switched resources, or initiation of parallel
LU-LU sessions.

Extended addressing uses a 23-bit address field for the
network address.  The extended address is divided into 8 bits
for the subarea address and 15 bits for the element address.
Previous addressing schemes used a total of 16 bits for the
network address with a user-selected length for the subarea
portion.


LOCAL ADDRESSES

Local addresses uniquely identify NAUs within a peripheral
node.  These addresses are used only to identify resources
within a peripheral node and are not the same as the element
addresses discussed above.

Network addresses are translated to local addresses by the
boundary function, which resides in the subarea node.  Thus,
the boundary function insulates the peripheral node from
network address changes resulting from reconfigurations.

NETWORK NAMES

End-users avoid having to know network addresses by referring
to NAUs by symbolic names.  These names are translated into
addresses for the path control network by directory services
in the SSCP.  The use of network names insulates the end-user
from address changes in the network.


SNA NETWORK INTERCONNECTION (SNI)

SNA network interconnection allows end-users in two separate
SNA networks to communicate with each other without requiring
unique addresses of network names in both networks.  The
interconnection is effected by a gateway consisting of a
gateway node and at least one gateway SSCP.  Network
addresses are translated by the gateway node and network
names are translated by the gateway SSCP.  To ensure that
addresses and names are unique among interconnected
networks, gateways prefix them with a network identifier.
The network identifiers are uniquely assigned during system
generation.

The CA MICS Network Analyzer Option distinguishes between
interconnected networks by retaining the network name in a
common data element, NETWRKID.  For the CA MICS files derived
from NPM data, NETWRKID may be set to the value of the NPM
data field PLUNETID.  An additional network identifier,
SLUNETID, is carried in the CA MICS NPM User Activity File.
The Network Identifier Exit Routine, SNTNIDRT, is explained
in Section 7.3.4.