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APPN on the router uses a set of default TG characteristics for each port (or DLSw
port). These defaults, defined by the
default TG characteristics
parameter apply to
all the TGs for link stations defined on a port unless they are overridden for a
particular link station by the
modify TG characteristics
parameter.
These default TG characteristics are also used for dynamic link stations established
when an adjacent node requests a connection with the router network node, but
does not have a predefined link station definition on the router network node. The
Service any node
parameter must be enabled.
You can change the following parameters using the router talk 6> interface as well
as the Configuration Program:
time cost
byte cost
user-defined TG characteristics1-3
effective capacity
propagation delay
security
Calculating APPN Routes Using TG Characteristics
The APPN route calculation function uses a COS definition for TGs which is a table
containing rows of TG characteristic ranges. Each row defines a given range for
each of the eight TG characteristics and the corresponding TG weight for that row.
APPN starts at the top of the table and continues down the table until all eight of
the TG characteristic parameter values fit within the ranges given for that row.
APPN then assigns the weight of that row as the TG weight for that link. There is
also a COS definition for nodes that calculates a node’s weight. The route
calculation function continues until it has found the path with the least combined
weight of TGs and nodes. This is the least weight route.
As an example of how TG characteristics are used to influence the selection of a
route through an APPN network node, suppose that a route from network node
router A to network node router D can pass through either network node router B or
router C. In this example, router A defines serial port PPP connections to both
router B and router C. However, the connection from router A to router B is a
64-Kbps link, while the connection from router A to router C is a slower-speed
19.2-Kbps link.
To ensure that the higher-speed connection from router A to router B is viewed as
the more desirable path for routing APPN interactive traffic, the effective capacity
TG characteristic for the link station associated with this path would be modified. In
this case, the default value for effective capacity is X'38', which correctly represents
a link speed of approximately 19.2-Kbps. However, the effective capacity would be
changed to X'45' to properly represent the 64-Kbps link. Since the effective capacity
for the TG from router A to router B is now X'45', this path is assigned a lower
weight in the COS file for interactive traffic. Consequently, the connection from
router A to router B is represented as more desirable than the connection from
router A to router C.
You can also change the TG characteristics if you purposefully want to favor certain
TGs for route selection. In addition to the five architected TG characteristics, there
APPN
Chapter 1. APPN 37