Calculating resistance for adjacent connections

Table 1 summarizes how JES2 calculates path resistance for adjacent connections. The parameters that the JES2 path manager uses to calculate resistance varies depending on the connection type as follows:

Table 1. Resistance calculation for adjacent connections
Connection type	Partial resistance from local definitions	Partial resistance from non-local definitions (Unless SENTREST=IGNORE is specified on the NODE (nnnn) statement.)
Dynamic SNA Connection to JES2	NJEDEF RESTNODE + APPL or NODE REST	NJEDEF RESTNODE + APPL or NODE REST
Dynamic TCP/IP Connection to JES2	NJEDEF RESTNODE + SOCKET or NODE REST	NJEDEF RESTNODE + SOCKET or NODE REST
Dynamic BSC Connection to JES2	NJEDEF RESTNODE + LINE REST	NJEDEF RESTNODE + LINE REST
Dynamic Connection to JES3 or POWER® Node	NJEDEF RESTNODE + LINE, APPL or NODE REST	0
Dynamic Connection to VM or System i®	NJEDEF RESTNODE + LINE, APPL or NODE REST	200
Static Connection	CONNECT REST= value (overrides any dynamic resistance as previously described)

Use the following formula to calculate the resistance of a connection to an adjacent node without a CONNECT statement:

Figure 1. Formula for Calculating the Resistance of Adjacent Nodes.

From Node A    R = RLa + RWa + NCCIREST

From Node B    R = RLb + RWb + NCCIREST


KEY:

 R        - represents total resistance
 RLx      - represents the resistance of the line (BSC) or session (SNA)
 RWx      - represents the resistance through the node
 NCCIREST - represents the partial resistance sent by the other node

Note:

NCCIREST consists of the combined resistance of the line plus the JES2 workload as determined by the node at the other end of the connection.
Neither node can control the line or workload resistance specified by the other node. For ways of limiting the impact of another node's resistance, see Path selection considerations.
Two nodes must first exchange their partial resistance values to establish the total resistance of a connection. The partial resistance is the sum of the resistance of the line plus the resistance caused by workload as determined by each node. The exchange occurs as follows:
1. The node that initiates the connection sends its partial resistance to the other node using an NCC I (initial signon) record.
2. The other node returns its partial resistance using an NCC J (response signon) record.
3. If path manager is active, the total resistance of the connection is sent back and forth in the NCC K (reset) and the NCC L (concurrence) records, respectively.

For example, when defining the 3-node connection shown in Figure 2, an installation would base the resistance of the BSC connection between NEWYORK and BOSTON using line 3 using these variables:

Variable: Description
RLa: Represents the resistance of the line as evaluated by the installation manager at node “a” (NEWYORK in the following example). This is the value specified on NODE A's REST= parameter on the LINE(3) statement.
RLb: Represents the resistance of the line as evaluated by the installation manager at node “b” (BOSTON in the following example). This is the value specified on NODE B's REST= parameter on the LINE(3) statement.
RWa: Represents the resistance because of workload on JES2 as evaluated by the installation manager at node “a”. This is the value specified on NODE A's RESTNODE= parameter on the NJEDEF statement.
RWb: Represents the resistance because of workload on JES2 as evaluated by the installation manager at node “b”. This is the value specified on NODE B's RESTNODE= parameter on the NJEDEF statement.

Figure 2. Path Resistance Values

For the SNA connection in Figure 2, the resistance between NEWYORK1 and WASHDC2 (using line 1) is calculated with the following variables:

Variable: Description
RLa: Represents the resistance of the session as evaluated by the installation manager at node “a” (NEWYORK1 in the previous example). This is the value specified on the REST= parameter of NEWYORK1's APPL(WASHDC2) initialization statement. If APPL(WASHDC2) is omitted, resistance is obtained from the REST= parameter in the NODE(nnnn) initialization statement for WASHDC2.
RLb: Represents the resistance of the session as evaluated by the installation manager at node “b” (WASHDC2 in the previous example). This is the value specified on the REST= parameter of WASHDC2's APPL(NEWYORK1) initialization statement. If APPL(NEWYORK1) is omitted, resistance is obtained from the REST= parameter in the NODE(nnnn) initialization statement for NEWYORK1.
RWa: Represents the resistance because of workload on JES2 as evaluated by the installation manager at node “a”. This is the value specified on NODE A's RESTNODE= parameter on the NJEDEF statement.
RWb: Represents the resistance because of workload on JES2 as evaluated by the installation manager at node “b”. This is the value specified on NODE B's RESTNODE= parameter on the NJEDEF statement.

Using values from Figure 2, you would calculate the total resistance for these connections as follows:

NEWYORK1 to WASHDC2 (line 1):      R = 20 + 20 + 50 + 50 = 140
WASHDC2 to BOSTON3  (line 2):      R = 20 + 20 + 50 + 50 = 140
NEWYORK1 to BOSTON3 (line 3):      R = 100 + 100 + 50 + 50 = 300

If parallel lines with different resistance values connect two nodes (for example, lines 2 and 5 in Figure 2), JES2 uses the lower resistance value when determining the best path.

You can use the SENTREST= parameter on the NODE(nnnn) initialization statement to ignore the partial resistance sent by another node (in the NCC I and NCC J records). SENTREST= allows you to specify whether another node's resistance should be added to the local node's to determine resistance at the local node. If you specify SENTREST=IGNORE, the local node ignores the resistance sent from the connecting node. This value allows the local node to control the resistance sent during sign on processing. You can specify SENTREST=IGNORE for only non-path manager nodes.

For example, if NEWYORK1 in Figure 2 were a VM node, BOSTON3 can maintain a local resistance of the NEWYORK1-to-BOSTON3 connection of 150 by refusing to accept the partial resistance from NEWYORK1.