3Com CoreBuilder 7000, Руководство по эксплуатации

Страница: 65 / 264

E-IISP Hierarchical Routing Algorithm 65
Routing Table
As the routing algorithm establishes the internal connections, it also
establishes a routing table. For each connection it establishes, the
algorithm stores alternate links that it might have used instead of the one
it did use. This table can be used either for load balancing (see next
section) or for establishing an alternate connection after crankback.
Table 18 shows a typical routing table.
Load Balancing
As mentioned in the previous section, one reason for providing alternate
routes is to divide or balance the load between the alternate links. Load
balancing ensures that calls are distributed equally among the available
links between source and destination nodes.
The CoreBuilder 7000 family ATM switch is designed to automatically
distribute calls equally over alternate links provided that these links have
the appropriate addressing.
The routing algorithm distinguishes between different types of address
matching among the NNI neighbors: exact match, best match, and partial
match (see “E-IISP Hierarchic Routing Algorithm” on page 125). If two or
more NNI neighbors have the same match type, the CoreBuilder 7000
family ATM switch uses its routing table to assign a connection to each of
the links in a round robin algorithm; the first connection to the first link,
the second connection to the second link, and so on. In this way, the calls
are distributed and the load is balanced.
To effect load balancing, the addressing of the alternate routes needs to
be planned with the match types in mind. For example, in the network of
Figure 14, link-1 and link-2 are used for load balancing since they both
have the same match type (exact match); link-3 is not used because it is
the only one with its type (best match).
Table 18
Routing Table
Connection # Current Link Optional Link(s)
1 1 2 3
2 2 3 1
3 3 2 1
4 1 2 3