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EPSR Introduction
©2008 Allied Telesis Inc. All rights reserved.
48.2 AlliedWare Plus
TM
Operating System Software Reference C613-50003-00 REV E Software Version 5.2.1
Introduction
Ethernet Protection Switching Ring (EPSR) is a protection system that prevents loops within
Ethernet ring based topologies. EPSR offers a rapid detection and recovery time (in the order
of 50 ms, depending on configuration) if a link or node fails. This rapid recovery time makes
EPSR a more effective alternative to spanning tree options when using ring-based topologies to
create high speed resilient layer two networks.
Ring Components and Operation
EPSR operates only on ring-based topologies. An EPSR ring comprises a series of nodes
(Ethernet bridges) connected end to end. The figure below shows a basic ring configuration. A
ring comprises one master node and a number of transit nodes. Each node connects to the ring
via two ports. On the master node one port is configured to be the primary port and the
other, the secondary port.
Figure 48-1: Simple EPSR ring configuration
EPSR instances
and domains
Each physical EPSR ring contains one or more EPSR instances. An EPSR instance can be thought
of as a component of an EPSR ring existing on a single node. A set of instances across the
whole ring is called a “domain.” Therefore a ring whose individual nodes each have two
instances results in a two domain ring. Each instance contains a control VLAN and a number of
data VLANs.
The EPSR control VLAN and its associated data VLANs form a Ring Domain. Although a
physical ring can have more than one domain, each domain must operate as a separate logical
group of VLANs and must have its own master node. This means that several domains may
share the same physical network, but must operate as logically separate VLAN groups.
Data
VL
AN
_2
Data
VLA
N_
1
Contr
ol V
LAN
Master
Node
Transit
Node
1
Transit
Node
4
Transit
Node
2
Data VLAN_1
Control VLAN
Primary Port
Transit
Node
3
EPSR 1.eps
Control VLAN
Data VLAN_2
P
S
Secondary Port
Control VLAN “forwarding”
Data VLAN “forwarding”
End User Ports
End User Ports
End User Ports
End User Ports
End User Ports
Data VLAN_2
Control VLAN “forwarding”
Data VLAN“blocked”
P S
Data VLAN_1