Alcatel-Lucent 7750 SR OS Interface Configuration Manual page 208

Configuring Ports
1. ATM interface bundle characteristics enforced over the link. Note that when a link is removed
from an IMA bundle, the link's ATM characteristics are reset to ATM interface defaults.
2. No services can be configured on the member link itself.
After the primary member has been added each additional member added to the group will only be
accepted if it matches the configuration of the IMA group. ATM interface characteristics are not
part of this verification as they are overwritten/reset to defaults when a link is added to/removed
from an IMA bundle.
Upon addition to an IMA group, each added member gets automatically assigned an IMA link Id.
IMA link Ids are in range from 0 to 7 and stay constant as long as the router does not reboot.
When configuring IMA bundles, consider the following guidelines:
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IMA bundles should contain at least two members.
A maximum of eight members can be included in an IMA bundle.
IMA links can only be aggregated into a bundle within a single MDA.
IMA group maximum bandwidth and minimum link settings allows, by default, for
oversubscription of shaped services; however when that occurs scheduling of traffic over
an IMA group ATM interface degrades to round-robin between shaped services, therefore
to preserve full ATM TM even during a member link failure, it is recommended that
maximum bandwidth is set to minimum links.
When configuring the red differential delay for IMA groups on ASAP MDAs, the value
configured is converted into acceptable frame sequence number delay on a link since
delay is granular to IMA frame sequence number difference. For E1 channels (receiving
frame time 27ms), configured values map to the enforced values as follows: 0 ms maps to
0 frame sequence number difference (27ms delay), 1-27 ms maps to 1 frame sequence
number difference (54 ms delay), 28 - 50 ms maps to 2 frame sequence number difference
(81 ms delay). Similarly, for DS1 channels (receiving frame time 35 ms), configured
values map to enforced values as follows: 0 ms maps to 0 frame sequence number
difference (35 ms delay), 1-35 ms maps to 1 frame sequence number difference (70 ms
delay), 36 - 50 ms maps to 2 frame sequence number difference (105 ms delay).
When a channel is deleted from an IMA group it is recommended that a deletion takes
place at the far end first when the far end supports graceful deletion to ensure no cell loss
takes place on the 7750 RX end of the channel. When a channel is deleted on the 7750 end
first, a small data loss will take place on the 7750 RX side (depending on the time required
for the far end to deactivate its TX on the link being deleted).
When no member links are configured on an IMA group, the speed of an E1 channel will
be used to compute the maximum IMA group bandwidth that may be allocated to shaped
services.
The shutdown command for IMA groups sets the IMA group state to "Blocking". This
makes the group operationally down but will not bring down the individual IMA links.
Services configured on the IMA group will go operationally down as well.
7750 SR OS Interface Configuration Guide