Technical Documentation

Option: Configuring Layer 2 Circuit Trunk Mode on ATM2 IQ Interfaces

When you configure Layer 2 circuits on CE-facing ATM2 IQ interfaces in a PE router that connects to some vendors’ ATM switches, you can create a trunk. The trunk bundles several ATM cell streams into one LSP, preserves the cell loss priority (CLP) and class-of-service (CoS) information of the cells within the experimental (EXP) bits of the MPLS header, and provides network-to-network interface (NNI) or user-to-network interface (UNI) information within a proprietary header. A physical interface supports a total of 32 logical trunks in NNI mode and 8 logical trunks when you use the UNI option. To configure a trunk, include the trunk statement at the [edit chassis fpc fpc-slot pic pic-slot atm-l2circuit-mode] hierarchy level, select NNI or UNI mode with the nni or uni statement, and specify a number of bits in the ATM header that will carry an identifier with the id-width statement. You can choose a value from 1 through 8 for the identifier width.

[edit]chassis {fpc fpc-slot {pic pic-clot {atm-l2circuit-mode {trunk {(nni | uni) {id-width number;}}}}}}

You can also configure several trunk options at the [edit interfaces at-fpc/pic/port unit unit-number] hierarchy level:

  • To specify an ATM interface as the control channel for a Layer 2 circuit trunk, include the control-channel statement at the [edit interfaces at-fpc/pic/port unit unit-number] hierarchy level.
  • To specify a trunk identifier, include the trunk-id statement at the [edit interfaces at-fpc/pic/port unit unit-number] hierarchy level. Trunk ID values range from 0 through 31.
  • To configure the amount of bandwidth reserved for the trunk, include the trunk-bandwidth statement at the [edit interfaces at-fpc/pic/port unit unit-number] hierarchy level and specify a value from 1,000,000 bps (1 Mbps) through 542,526,792 bps.
  • To apply a CoS scheduler map to the trunk, include the atm-scheduler-map statement at the [edit interfaces at-fpc/pic/port unit unit-number] hierarchy level. This statement must reference an ATM2 IQ interface-based scheduler map at the [edit interfaces at-fpc/pic/port atm-options scheduler-maps map-name] hierarchy level.
    interfaces {at-fpc/pic/port {atm-options {pic-type atm2;scheduler-maps {map-name {...}}unit unit-number {atm-scheduler-map map-name;control-channel;trunk-id id-number;trunk-bandwidth bandwidth;}}}}

You can configure a variety of CoS-related statements for an ATM2 IQ interface-based scheduler map. To select the CoS mode used for virtual circuits, include the vc-cos-mode statement at the [edit interfaces at-fpc/pic/port atm-options scheduler-maps map-name] hierarchy level. To specify forwarding class settings, include the priority, transmit-weight, and epd-threshold statements at the [edit interfaces at-fpc/pic/port atm-options scheduler-maps map-name forwarding-class class-name] hierarchy level. For more information about CoS, see the JUNOS Class of Service Configuration Guide.

[edit]interfaces {at-fpc/pic/port {atm-options {pic-type atm2;scheduler-maps {map-name {vc-cos-mode (alternate | strict);forwarding-class class-name {priority (high | low);transmit-weight (cells number-of-cells | percent percentage);epd-threshold plp0-threshold plp1 plp1-threshold;}}}}}}

Published: 2010-04-15