Allied Telesis RAPIER I - Manual (Page 200)

2 Software Reference
Introduction to Ethernet Protection
Switching Ring (EPSR)
Ethernet Protection Switching Ring (EPSR) is a protection system employed to
prevent 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 based 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.
Figure 1-1 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 1-1: 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, will result in a two
domain ring. Each instance contains a control VLAN and a number of data
VLANs. EPSR instances are created using the
create epsr command on
page 1-17 .
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