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

Oversubscribed Ethernet MDAs

Oversubscribed Ethernet MDAs
The 7750 SR and 7450 ESS support 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/CMA limits the rate at which traffic can enter the MDA/CMA 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/CMA
ensures that traffic is correctly prioritized when the bus from the MDA/CMA 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/CMA 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/CMA uses following
rules:
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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/CMA.
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/CMA.
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/CMA and the Dot1p field ignored.
).
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7750 SR Interface Configuration Guide