IPS Request Type Operator Originated

• Lockout of Protection (LO)

Prevents ring wraps anywhere in the ring; if a wrap is present it causes it to drop (note: feature not supported at FCS)

Performs a wrap at the node at which this command was issued and at the adjacent node

Similar to FS but at a lower priority

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Protection Request Hierarchy

Highest Priority

• Lockout of Protection (LO)

i

• Forced Switch (FS)

• Signal Fail (SF)

• Signal Degrade (SD)

• Manual Switch (MS)

1 _..

• Wait to Restore (WTR)

Lowest

Priority

• No Request (IDLE)

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Protection Request Hierarchy

• LO request can co-exist

• Request < SF cannot co-exist with other request

• A node always honors the highest of short path request and self detected request (fault)

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Protection Request Hierarchy

• When there are more request of type < SF the first request to complete the long path signaling takes precedence

• When there exist 2 request of the type < SF on both the inner and outer ring the node chooses the request on the outer ring

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Path Indication

• Short path

Short path IPS packets {Req,Src,Stat,S} are IPS packets sent over the adjacent failed span

Short path IPS packets are never forwarded, it is stripped by the receiving node

A node wraps and unwraps only on the short path request (never on the long path)

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Path Indication

• Long path

Long path IPS packets {Req,Src,Stat,L} are IPS packets sent around the ring

Long path IPS packets are always forwarded

IPS packets are newer wrapped

Long path IPS packets are used to maintain protection hierarchy

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IPS Triggers

• Hard failure • Operator

Protection (LO)

Forced Switch (FS)

Signal Degrade (SD)

Manual Switch (MS)

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^ SONET/SDH Overhead Usage ^

• Loss of Frame (LOF)

A1 and A2 overhead bytes

• Loss of Signal (LOS)

• Alarm Indication Signal (AIS)

• Bit Error Rate (BER)

B2 overhead byte

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IPS States

• Idle

• Pass-through

• Wrapped

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IPS States

• Idle

The node is ready to perform a protection switch; at this state it sends IPS idle packets {0,Self,0,S} to both of the adjacent nodes

• Pass-through

The node enters this state when it receives a long path IPS packet {Req,Src,Stat,L}

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