EPSR Introduction
©2008 Allied Telesis Inc. All rights reserved.
Software Version 5.2.1
AlliedWare Plus
TM
Operating System Software Reference C613-50003-00 REV E
48.3
Control VLAN
The function of the control VLAN is to monitor the ring domain and maintain its operational
functions. To do this it transmits and monitors operational healthcheck messages using EPSR
healthcheck control frames. The control VLAN carries no user data.
Data VLAN
The data VLAN carries the user data around the ring. Several data VLANs can share a common
control VLAN.
Master node
The master node controls the ring operation. It issues healthcheck messages at regular intervals
from its primary port and monitors their arrival back at its secondary port - after they have
circled the ring. Under normal operating conditions the master node’s secondary port is always
in the blocking state to all data VLAN traffic. This is to prevent data loops forming within the
ring. This port however, operates in the forwarding state for the traffic on the control VLAN.
Loops do not occur on the control VLAN because the control messages stop at the secondary
port, having completed their path around the ring.
Transit nodes
The transit nodes operate as conventional Ethernet bridges, but with the additional capability of
running the EPSR protocol. This protocol requires the transit nodes to forward the healthcheck
messages from the master node, and respond appropriately when a ring fault is detected. The
fault condition procedure is explained in
“Fault Detection and Recovery” on page 48.4
.