Alcatel-Lucent 7710 SR SONET, Configuration Manual

Page: 23 / 496

Interface Configuration
7710 SR OS Interface Configuration Guide Page 23
Oversubscribed Ethernet MDAs
The 7710 SR supports oversubscribed Ethernet MDAs/CMAs. These have more bandwidth
towards the user than the 5.4 Gbps capacity between the MDA/CMA and CFM.
A traffic management function is implemented on the MDA/CMA to control the data entering the
CFM. This function consists of two parts:
• Rate limiting
• Packet classification and scheduling
Rate Limiting
The oversubscribed CMA limits the rate at which traffic can enter the 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 CMA ensures that
traffic is correctly prioritized when the bus from the CMA to the CFM is overcommitted. This
could occur if the policing parameters configured are such that the sum of the traffic being
admitted into the 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 CMA uses following rules:
• If the service QoS policy for the SAP (port or VLAN) uses the default classification
policy, all traffic will be classified as Best Effort (
be
).
• 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 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 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 CMA and the Dot1p field ignored.