Technical Documentation

Configuring the JUNOS Software to Enable ATM2 Intelligent Queuing Layer 2 Circuit Transport Mode

On ATM2 IQ PICs only, you can configure Layer 2 circuit cell relay, Layer 2 circuit ATM Adaptation Layer 5 (AAL5), or Layer 2 circuit trunk mode.

Layer 2 circuit cell relay and Layer 2 circuit AAL5 are defined in the Internet draft draft-martini-l2circuit-encap-mpls-04.txt, Encapsulation Methods for Transport of Layer 2 Frames Over IP and MPLS Networks.

Layer 2 circuit trunk mode allows you to send ATM cells over Multiprotocol Label Switching (MPLS) trunking.

The four transport modes are defined as follows:

  • To tunnel IP packets over an ATM backbone, use the default standard AAL5 transport mode.
  • To tunnel a stream of AAL5-encoded ATM segmentation-and-reassembly protocol data units (SAR-PDUs) over an MPLS or IP backbone, use Layer 2 circuit AAL5 transport mode.
  • To tunnel a stream of ATM cells over an MPLS or IP backbone, use Layer 2 circuit cell-relay transport mode.
  • To transport ATM cells over an MPLS core network that is implemented on some other vendor switches, use Layer 2 circuit trunk mode.

    Note: You can transport AAL5-encoded traffic with Layer 2 circuit cell-relay transport mode, because Layer 2 circuit cell-relay transport mode ignores the encoding of the cell data presented to the ingress interface.

When you configure AAL5 mode Layer 2 circuits, the control word carries cell loss priority (CLP) information by default.

By default, ATM2 IQ PICs are in standard AAL5 transport mode. Standard AAL5 allows multiple applications to tunnel the protocol data units of their Layer 2 protocols over an ATM virtual circuit. To configure the Layer 2 circuit transport modes, include the atm-l2circuit-mode statement at the [edit chassis fpc slot-number pic pic-number] hierarchy level:

[edit chassis fpc slot-number pic pic-number]atm-l2circuit-mode (cell | aal5 | trunk trunk);

On a TX Matrix or TX Matrix Plus router, include the atm-l2circuit-mode statement at the [edit chassis lcc number fpc slot-number pic pic-number] hierarchy level:

[edit chassis lcc number fpc slot-number pic pic-number]atm-l2circuit-mode (cell | aal5 | trunk trunk);

aal5 tunnels a stream of AAL5-encoded ATM cells over an IP backbone.

cell tunnels a stream of ATM cells over an IP backbone.

trunk transports ATM cells over an MPLS core network that is implemented on some other vendor switches. Trunk mode can be user-to-network interface (UNI) or network-to-network interface (NNI).

Note: To determine which vendors support Layer 2 circuit trunk mode, contact Juniper Networks customer support.


Published: 2010-04-26