Oversubscribed Ethernet Mdas; Rate Limiting; Packet Classification And Scheduling - Alcatel-Lucent 7750 SR OS Interface Configuration Manual

Oversubscribed Ethernet MDAs

The 7750 SR supports oversubscribed Ethernet MDAs. These have more bandwidth towards the
user than the 10 Gbps capacity between the MDA and IOM.
A traffic management function is implemented on the MDA to control the data entering the IOM.
This function consists of two parts:
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Rate Limiting

The oversubscribed MDA limits the rate at which traffic can enter the MDA on a per port basis. If
a port exceeds its configured limits then the excess traffic will be discarded, and 802.3x flow
control frames (pause frames) are generated.

Packet Classification and Scheduling

The classification and scheduling function implemented on the oversubscribed MDA ensures that
traffic is correctly prioritized when the bus from the MDA to the IOM is overcommitted. This
could occur if the policing parameters configured are such that the sum of the traffic being
admitted into the MDA is greater than 10 Gbps.
The classification function uses the bits set in the DSCP or dot1p fields of the customer packets to
perform classification. It can also identify locally addressed traffic arriving on network ports as
Network Control packets. This classification on the oversubscribed MDA uses following rules:
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7750 SR OS Interface Configuration Guide
Rate limiting
Packet classification and scheduling
If the service QoS policy for the SAP (port or VLAN) uses the default classification
policy, all traffic will be classified as Best Effort (
If the service QoS policy for the SAP contains a dot1p classification, the dot1p field in the
customer packets is used for classification on the MDA.
If the service QoS policy for the SAP contains a DSCP classification, the DSCP field in
the customer packets is used for classification on the MDA.
If a mix of dot1p and DSCP classification definitions are present in the service QoS policy
then the field used to perform classification will be the type used for the highest priority
definition. For example, if High Priority 1 is the highest priority definition and it specifies
that the DSCP field should be used, then the DSCP field will be used for classification on
the MDA and the dot1p field ignored.
Interface Configuration
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