Transition Networks
S4224 Web User Guide
33558 Rev. C
Page 207 of 669
EPS Instance Configuration
If configured, the possible Protection Types are:
1+1 Unidirectional, no APS communication.
1+1 Unidirectional with APS communication.
1+1 Bidirectional with APS communication.
1:1 Bidirectional with APS communication.
Protection Type
Select Unidirectional or Bidirectional protection mode:
Unidirectional
: EPS in the two ends can select traffic from different working/protecting flow. This is
only possible in case of 1+1 protection.
Bidirectional
: EPS in the two ends is selecting traffic from the same working/protecting flow. This
requires APS enabled. This is mandatory for 1:1 protection.
APS
Check or uncheck the checkbox to enable or disable Automatic Protection Switching (the APS protocol).
This is mandatory for 1:1 protection. Check the checkbox to enable the automatic protection switching
APS protocol and linear protection switching mechanisms for point-to-point VLAN-based ETH SNC (Sub
Network Connection) in Ethernet transport networks per Rec. ITU-T G.8031/Y.1342 (11/2009).
Bidirectional switching always requires APS communication. The only switching type that does not require
APS communication is 1+1 unidirectional switching.
Revertive
Check or uncheck the checkbox to enable or disable Revertive mode. The revertive switching to working
flow can be enabled or disabled here.
Revertive mode
: traffic is restored to the working entities after a switch reason has cleared. In the case
of clearing a command (e.g., Forced Switch), this happens immediately. In the case of clearing of a
defect, this generally happens after the expiry of a “Wait to Restore” timer, which is used to avoid
chattering of selectors in the case of intermittent defects.
Operationally, in revertive mode, in conditions where working traffic is being received via the protection
entity, if local protection switching requests have been previously active and now become inactive, a local
WTR state is entered. Since this state now represents the highest priority local request, it is indicated on
the transmitted “Request/State” information and maintains the switch. This state normally times out and
becomes a NR state after the WTR timer has expired. The WTR timer is deactivated earlier if any local
request of higher priority pre-empts this state.
Note that for the decision of whether or not to enter the WTR state, only local requests are considered.
A switch to the protection entity may be maintained by a local WTR state or by a remote request (WTR or
other) received via the “Request/State” information. Therefore, in a case where a bidirectional failure for a
working entity has occurred and subsequent repair has taken place, the bidirectional reversion back to
the working entity does not take place until both WTR timers at both ends have expired.
Non-revertive mode
: normal traffic is allowed to remain on the protection entity even after a switch
reason has cleared. This is generally accomplished by replacing the previous switch request with a “Do
not Revert (DNR)” request, which is low priority.
1+1 protection is often provisioned as non-revertive; the protection is fully dedicated in any case, and this
avoids a second “glitch” in the traffic. However there may be reasons to provision this to be revertive (e.g.,
so that the traffic uses the “short” path except during failure conditions. Certain operator policies also
dictate revertive operation even for 1+1).
1:1 protection is usually revertive. It is possible to define the protocol in a way that would permit non-
revertive operation for 1:1 protection; however, since the working transport entity is typically more