3Com CoreBuilder 7000, Operation Manual

Page: 64 / 264

64 C
HAPTER
3: E-IISP P
ROTOCOL
Figure 14
Alternate Routes in an ATM Network
Alternate routes are desirable for the following reasons:
Dividing the load between nodes over several links reduces congestion
(see next section)
If one link fails, an alternate link can be used.
If the node cannot be found or accessed via a link, it can be searched
through another link after
crankback.
Rules for Creating Alternate Routes
The following rules apply when you plan alternate routes:
It is helpful to carefully draw all the network nodes and their
connections to have a general overview of the entire network.
When creating alternate routes within the same tree, connect to an
ancestor, not to another branch.
Keep the E-IISP routing algorithm in mind as described in “E-IISP
Hierarchical Routing Algorithm” on page 60.
Eliminate infinite loops by configuring the Hop Count Limit to be one
more than the number of hops in the longest path through the graph
(the Hop Count Limit is 7 for most hierarchial networks).
Consider all possible ups and downs through the trees with each
alternate route.
Create alternate routes with “equal” matches so that the calls are
distributed.
ATM NETWORK
B1*
A*
B*
1
2
3
1
2
3