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.
ASON
- 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 SDH network is the transport plane. It transmits and multiplexes 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 services. 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.
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 a new LSP to transmit the service. After creating a new 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 of LSP. Then you need to set rerouting lockout.
Rerouting Priority
There are 8 levels of rerouting priority. Level 1 is the highest, and its resource cannot be occupied by other levels whenever. The working path of level 2 cannot be occupied, but the temp resource used by rerouting can be occupied by level 1 service. Level 3 to level 8 services resources can be occupied by the higher level.
When a node or link fails, all the LSPs that are affected by the one-time fault and can be rerouted are restored in the sequence based on the priority levels. That is, the high-priority LSPs are restored first. When the backup network resources are insufficient, the high-priority LSPs can empty the restoring resources of the rerouted low-priority and low-and-delayed-priority LSPs.
NOTE: One-time fault: indicates the collection of faults that occur within the time period (shorter than period T) after a fault occurs. Period T is the "one-time fault delay time".
For the SDH ASON trail, the relationships between priorities and SLA is listed in the following table.
SLA |
Supported Priority |
|---|---|
Diamond |
1,2 |
Gold |
1,2 |
Silver |
1,2,3,4,5,6,7,8 |
Copper |
1,2,3,4,5,6,7,8 |
Iron |
Not Supported |
The ASON NE with the version prior than GCP V100R007C03 cannot supported eight priority levels, the relationship between old version and new version ASON NE is listed in the following table.
Priority of ASON NE with GCP V100R007C03 or prior version |
Priority of ASON NE with GCP V100R007C03 or later version |
|---|---|
High |
1 |
Low |
2 |
Low and Delay |
3 |
Rerouting Policy
- Use existing trails whenever possible: During rerouting, the route of the new LSP overlaps the original route whenever possible.
- Do not use existing trails whenever possible: During rerouting, the route of the new LSP is separated from the original route whenever possible.
- No Rerouting constraint: During rerouting, the best route is computed for the new LSP.
- Use simulated section restoration: There are several TE links between two nodes, but the service only passes one of the links. When a fiber cut occurs in the link that carries the service, the service can first be switched to one of the other available TE links between the two nodes.
Crankback Mechanism
The Crankback mechanism during rerouting, optimization, and creation of the 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.