Basic Concepts of ASON

The basic concepts related to the ASON are the three planes, label switched path (LSP) and rerouting.

As shown in Figure 1, the ASON has three planes: the control plane, the transport plane, and the management plane.

Figure 1 Three planes of the ASON

ASON

ASON is a new generation optical network that has the following features:

Customers launch a service request dynamically.
Routes are selected automatically.
Signaling controls the creation and removal of connections.
Network connections are automatically and dynamically completed.
Switching and transmission are integrated into one system.

Control Plane

The control plane consists of a group of communication entities. It is responsible for the calling control and connection control, including automatic setting up, releasing, monitoring, and maintaining connections. The control plane automatically restores the failed connections through signaling exchange.

Transport Plane

The traditional WDM network is the transport plane. It transmits optical signals, configures cross-connection and protection switching for optical signals, and guarantees the reliability of all optical signals.

Management Plane

The management plane is a complement to the control plane. It maintains the transport plane, the control plane and the whole system. It can configure end to end service. Its functions include performance management, fault management, configuration management and security management.

LSP

Label switched path (LSP) is the path ASON services pass through. In an ASON, to create ASON services is to create LSPs. On Web LCT, LSP is also called ASON Trail.

WDM ASON Trail

WDM ASON Trail is classified into WDM ASON OCh Trail and WDM ASON ODUk (k = 0, 1, 2, 3, 4) Trail. See Figure 2.

NOTE:

OptiX OSN 8800 series support WDM ASON ODU0 Trail.

The WDM ASON OCh trail can be created when there are sufficient OCh TE link resources.
The WDM ASON ODUk trail can be created when there are sufficient TE link resources where the payload type is ODUk.

Figure 2 WDM ASON Trail

Rerouting

Rerouting is a means of resuming services. When an LSP is disconnected, the source node queries and finds the best route to resume services. Then, the initial node creates an LSP to transmit the service. After creating an LSP, the source node deletes the original LSP.

NOTICE:

After a revertive service reroutes, the original LSP is not deleted.

NOTE:

For more information on service restoration, refer to ASON Network Protection and Restoration.

Rerouting Lockout

In some cases, rerouting is not required after failure in LSP. Then you need to set rerouting lockout.

Rerouting Policy

Diamond and silver services all support the following four rerouting polices:

Use existing trails whenever possible

During rerouting, the route of the new LSP overlaps the original route whenever possible. This policy helps save network resources. When bandwidth resources are insufficient, the service is more likely to reroute successfully.
Do not use existing trails whenever possible

During rerouting, the route of the new LSP is separated from the original route whenever possible. This policy is applicable to a network with sufficient link resources.
No rerouting constraint

During rerouting, the no rerouting constraint is computed for the new LSP. Whether the new or old route resources are utilized again is not considered. This policy chooses a route with the minimum cost as the new route after rerouting according to network conditions.
Use simulated section restoration

During rerouting, the services must reuse the original routes without involving faulty spans. End-to-end rerouting is enabled only when rerouting on the faulty spans fails, and thus service route can be controlled and managed more easily.
Use preset restoration

During rerouting, only the preset restoration trail can be used to restore the ASON service.

Crankback Mechanism

The crankback mechanism during rerouting, optimization, and creation of the wavelength/sub-wavelength LSP is supported.

It takes a certain time to spread network routing information. When rerouting is performed, the source node may use the outdated network status information to calculate the trail. Therefore, the selected route may be unavailable, resulting in a rerouting failure.

The ASON software supports the crankback rerouting mechanism. When setting up connections according to the calculated trail, the ASON software informs the source node of the information related to the faulty network nodes or links if the connection setup process is baffled due to insufficient network resources or network faults. In this case, the source node recalculates a trail that meets the constraint conditions but does not traverse the obstacle node and then establishes the connections for the calculated trail. This effectively restores a service by means of rerouting.