Information Technology Reference
In-Depth Information
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T491 Polling Interval
—The time period between status polls.
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N491 Error Threshold
—If the number of messages defined by N491 is missing out of a
total number of messages defined by N492, a communication failure is reported.
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N492 Event Threshold
—The number of attempted messages in conjunction with the
N491 threshold, to determine a communication failure.
ILMI supports ES address registration. ES address registration allows ESs to automatically be
assigned an AESA without operator intervention.
As specified in the UNI 4.0 specification, the Private ATM Address Structure consists of multiple
fields. Two of these fields, the end system identifier (ESI) and the selector (SEL) fields form the
user part and are supplied by the user-side IME.
All other fields form a network prefix for ATM addresses that typically have the same value for
all ATM addresses on the same ATM UNI. The network side of the UNI supplies the value of
the network prefix. An ATM address for an ES on the user side of a Private UNI is obtained by
appending values for the ESI and SEL fields to the network prefix for that UNI.
IISP
IISP is a static routing protocol for ATM. IISP allows a UNI signaling request to be routed
across multiple switches based on static routes. However, IISP does not support QoS. IISP is
useful where PNNI is not supported.
IISP requires the configuration of static routes. Use the following rules for configuring IISP:
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IISP static routes must avoid routing loops.
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Each switch is given an ATM address.
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A route can have a primary path and a secondary path.
In each switch a routing table is configured that contains the address prefixes that are reachable
through each interface on the switch.
When UNI signaling is enabled, the switch arbitrarily takes the role of a UNI user on the
network side.
Figure 5-26 shows an ATM network with UNI signaling enabled for IISP.
When the switch receives a signaling request, the switch matches the destination ATM address
with the table entry with the longest prefix match. Each ATM switch that receives the connection
setup message selects the next outgoing interface to which to forward the setup message. This
process is less efficient than PNNI source routing.
The ability to crank back and compute an alternate route when congestion or connection failure
occurs is not inherent in IISP. However, redundant or alternate paths can be configured.
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