CoS on Circuit Emulation ATM MICs Overview

The following class-of-service features are supported on Circuit Emulation ATM MICs:

• Traffic shaping and scheduling—Traffic shaping determines the maximum amount of traffic that can be transmitted on an interface.

  You can configure three different categories of ATM service: constant bit rate (cbr), non-real-time variable bit rate (nrvbr), and real-time variable bit rate (rtvbr). The service category works in conjunction with ATM cell parameters peak-rate, sustained-rate, and max burst-size to impose traffic shaping, transmit rate, shaping rate, and default excess rate for an ATM queue.

  Beginning with Junos OS Release 14.2, for an ATM MIC with SFP (MIC-3D-8OC3-2OC12-ATM), you can configure CBR bandwidth speeds up to 622 Mbps (OC12 speed) per virtual circuit (VC). To enable each VC on an ATM MIC with SFP to support up to line rate traffic in OC12 mode, define both of the following parameters in the traffic shaping and scheduling profile:

  • Configure cbr as the ATM service category (atm-service) .

  • Configure up to a maximum of 1,412,829 cells per second (cps) as the ATM peak cell rate (peak-rate) .

  To set the OC12 per-VC port speed for an ATM MIC with SFP, configure the oc12-stm4 port speed option for the desired port.

  Note:

  When you configure up to OC12 CBR bandwidth speed per VC on an ATM MIC with SFP, the actual Layer 3 payload throughput you obtain depends on the ATM encapsulation type and IP packet size that you use. The Layer 3 payload rate is the maximum Layer 3 (IP) payload throughput achieved for a given Layer 2 traffic rate.

• Policing—Policing, or rate limiting, enables you to limit the amount of traffic that passes into or out of the interface. It works with firewall filters to thwart denial-of-service (DoS) attacks.

  Networks police traffic by limiting the input or output transmission rate of a class of traffic on the basis of user-defined criteria. The ATM policer controls the maximum rate of traffic sent from or received on the interface on which it is applied.

  To apply limits to the traffic flow, configure the cdvt and peak-rate parameters within the policer. Define the policing-action parameter as discard, discard-tag, and count to set a consequence for the packets that exceed these limits. The consequence is usually a higher loss priority so that if the packets encounter downstream congestion, they are discarded first.