Container Interfaces Overview
Container interfaces provide the following features:
- APS on SONET links are supported using container infrastructure.
- Container physical interfaces and logical interfaces remain up on switchover.
- APS parameters are auto-copied from the container interface to the member links.
 | Note: Paired groups and true unidirectional APS are not currently supported. |
Container interfaces features are described in the following sections:
- Understanding Traditional APS Concept
- Container Interfaces Concept
- APS Support for Container-Based Interfaces
- Autocopy of APS Parameters
Understanding Traditional APS Concept
Traditional APS is configured on two independent physical SONET interfaces: one configured as the working circuit and the other as the protect circuit (see Figure 1). The circuit, named Circuit X in the figure, is the link between the two SONET interfaces.
Figure 1: APS Interface
Traditional APS uses routing protocols that run on each individual SONET interface (since circuit is an abstract construct, instead of being an actual interface). When the working link goes down, the APS infrastructure brings up the protect link and its underlying logical interfaces, and brings down the working link and its underlying logical interfaces, causing the routing protocols to reconverge. This consumes time and leads to traffic loss even though the APS infrastructure has performed the switch quickly.
Container Interfaces Concept
To solve this problem, the JUNOS Software provides a soft interface construct called a container interface (see Figure 2).
Figure 2: Container Interface
The container interface allows routing protocols to run on the logical interfaces associated with a virtual container interface instead of on the physical SONET interfaces. When APS switches the underlying physical link based on a fault condition, the container interface remains up, and the logical interface on the container interface does not flap. The routing protocols remain unaware of the APS switching.
APS Support for Container-Based Interfaces
With the container interface, APS is configured on the container interface itself. Individual member SONET links are either marked as primary (corresponding to the working circuit) or standby (corresponding to the protect circuit) in the configuration. No circuit or group name is specified in the container interface model; physical SONET links are put in an APS group by linking them to a single container interface. APS parameters are specified at the container interface level, and are propagated to the individual SONET links by the APS daemon.
Autocopy of APS Parameters
Typical applications require copying APS parameters from the working circuit to the protect circuit, since most of the parameters must be the same for both circuits. This is automatically done in the container interface. APS parameters are specified only once under the container physical interface configuration, and are internally copied over to the individual physical SONET links.
