ERP Overview
Configuring ERP
page 11-4
OmniSwitch AOS Release 7 Network Configuration Guide
June 2013
ERP Overview
Ethernet Ring Protection (ERP) is a protection switching mechanism for Ethernet ring topologies, such as
multi-ring and ladder networks. This implementation of ERP is based on the Recommendation
ITU-T G.8032/Y.1344 and uses the ring Automatic Protection Switching (APS) protocol to coordinate the
prevention of network loops within a bridged Ethernet ring.
Loop prevention is achieved by allowing the traffic to flow on all but one of the links within the protected
Ethernet ring. This link is blocked and is referred to as the Ring Protection Link (RPL). When a ring
failure condition occurs, the RPL is unblocked to allow the flow of traffic to continue through the ring.
One designated node within the ring serves as the RPL owner and is responsible for blocking the traffic
over the RPL. When a ring failure condition occurs, the RPL owner is responsible for unblocking the RPL
so that the link can forward traffic to maintain ring connectivity.
The ERPv2 capability supports multi-ring and ladder networks with interconnection nodes,
interconnected shared links, master rings and sub-rings. The following features are also supported:
•
R-APS Virtual Channel
•
Revertive/Non-Revertive modes
A shared link can be a part of one master ring. The sub-rings connected to the interconnection nodes are
open. The sub-rings cannot use shared links.
ERP and ERPv2 Terms
Ring Protection Link (RPL)
and
RB
—
A designated link between two ring nodes that is blocked to
prevent a loop on the ring. RB specifies a blocked RPL.
RPL Owner —
A
node connected to an RPL. This node blocks traffic on the RPL during normal ring
operations and activates the link to forward traffic when a failure condition occurs on another link in the
ring.
RMEPID —
Remote Maintenance End Point identifier.
Link Monitoring
— Ring links are monitored using standard ETH (Ethernet Layer Network)
CC OAM
messages (CFM). Note that for improved convergence times, this implementation also uses Ethernet link
up and link down events.
Signal Fail (SF)
— Signal Fail is declared when a failed link or node is detected.
No Request (NR)
— No Request is declared when there are no outstanding conditions (for example, SF)
on the node.
Ring APS (Automatic Protection Switching) Messages
— Protocol messages defined in Y.1731 and
G.8032 that determine the status of the ring.
ERP Service VLAN
— Ring-wide VLAN used exclusively for transmission of messages, including
R-APS messages for Ethernet Ring Protection.
ERP Protected VLAN —
A VLAN that is added to the ERP ring. ERP determines the forwarding state of
protected VLANs.
FDB
—
The Filtering Database that stores filtered data according to the R-APS messages recieved. This
database also maintains an association table that identifies the master rings for a given sub-ring.