Table 2. Feature History Table
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Feature Name
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Release Information
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Feature Description
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SR-TE Delay Normalization for OSPF
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Release 7.3.1
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This feature extends the current Delay Normalization feature to support OSPF.
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Performance measurement (PM) measures various link characteristics like packet loss and delay. Such characteristics can be
used by IS-IS as a metric for Flexible Algorithm computation. Low latency routing using dynamic delay measurement is one of
the primary use cases for Flexible Algorithm technology.
Delay is measured in microseconds. If delay values are taken as measured and used as link metrics during the IS-IS topology
computation, some valid ECMP paths might be unused because of the negligible difference in the link delay.
The Delay Normalization feature computes a normalized delay value and uses the normalized value instead. This value is advertised
and used as a metric during the Flexible Algorithm computation.
The normalization is performed when the delay is received from the delay measurement component. When the next value is received,
it is normalized and compared to the previous saved normalized value. If the values are different, then the LSP generation
is triggered.
The following formula is used to calculate the normalized value:
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Dm – measured Delay
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Int – configured normalized Interval
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Off – configured normalized Offset (must be less than the normalized interval Int)
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Dn – normalized Delay
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a = Dm / Int (rounded down)
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b = a * Int + Off
If the measured delay (Dm) is less than or equal to b, then the normalized delay (Dn) is equal to b. Otherwise, Dn is b + Int.
Example
The following example shows a low-latency service. The intent is to avoid high-latency links (1-6, 5-2). Links 1-2 and 5-6
are both low-latency links. The measured latency is not equal, but the difference is insignificant.
We can normalize the measured latency before it is advertised and used by IS-IS. Consider a scenario with the following:
The measured delays will be normalized as follows:
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Dm = 29
a = 29 / 10 = 2 (2.9, rounded down to 2)
b = 2 * 10 + 3 = 23
In this case, Dm (29) is greater than b (23); so Dn is equal to b+I (23 + 10) = 33
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Dm = 31
a = 31 / 10 = 3 (3.1, rounded down to 3)
b = 3 * 10 + 3 = 33
In this case, Dm (31) is less than b (33); so Dn is b = 33
The link delay between 1-2 and 5-6 is normalized to 33.
Configuration
Delay normalization is disabled by default. To enable and configure delay normalization, use the delay normalize interval
interval [offset
offset] command.
IS-IS Configuration
router isis 1
interface GigEth 0/0/0/0
delay normalize interval 10 offset 3
address-family ipv4 unicast
metric 77
OSPF Configuration
router ospf 1
area 0
interface GigabitEthernet0/0/0/0
delay normalize interval 10 offset 3
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