IBM SC30-3865-04 - Manual (Page 44)

A BrNN accomplishes:
v Reduction of the number of network nodes in a large APPN network.
v Hidden branch office topology from the WAN.
v Direct, peer-to-peer communication between defined branches connected to the
same connection network.
v Reduces CP-CP session traffic on the WAN link.
The following are limitations of Branch Extender:
v Network nodes are allowed to connect only over links that a BrNN defines as
uplinks.
v Only end nodes or cascaded BrNNs may be attached to a BrNN downlink.
Border nodes acting as end nodes and DLUR nodes may not be attached to a
BrNN downlink.
v A node cannot connect to a Branch Extender over an uplink and a downlink at
the same time.
v A BrNN can have CP-CP sessions with only one network node at a time.
Extended Border Nodes
Extended Border Nodes (BNs) allow networks with different network IDs to connect
to one another. CP-CP sessions will be established across the network boundaries,
and directory services flows and session establishment will be allowed to span the
interconnected networks. Topology information will not be exchanged across the
network boundary. This allows networks with different network IDs to establish
CP-CP sessions and provides topology isolation between different networks.
In addition to allowing networks with different network IDs to interconnect, BNs
provide a mechanism to subdivide networks with the same network ID into smaller
“topology subnetworks”. This subdivision provides topology isolation between the
two subnetworks while allowing directory services flows and sessions to span the
subnetwork boundaries.
There must be a BN on one side of the subnetwork boundary in order to use this
function. When a BN connects to a non-native NN, the BN looks like an EN to the
non-native NN, even though the BN is actually a NN.
There may be two BNs, one on each side of the boundary, cooperating to perform
this function. When two BNs connect across a subnetwork boundary, the BN will
look like a NN to the non-native BN.
A BN will appear to be the NN server for all non-native resources accessible
through the BN. This allows the existing APPN directory caching and route
calculation functions to work, while enabling the BN to intercept and modify all
Locate and BIND flows which cross an inter-subnetwork TG (ISTG).
BNs implement piece-wise optimal session route calculation. Each subnetwork
calculates its own part of the session’s route selection control vector (RSCV) to the
entry point in the next non-native subnetwork. While the RSCV will be optimal
through the native subnetwork, there is no guarantee that the end-to-end session
path will be optimal.
APPN
14 MRS V3.2 Protocol Config Ref Vol 2