802.17c Protected InterRing Connection

1
802.17cProtected Inter-Ring Connection

• Rafi Ram - Corrigent Systems
• July 2007

2
PIRC Suggestion Highlights

• Stations A B are members of a protection group
  (PG) for interconnect between two rings
• Station A and station B are protection group
  members (PGM)
• One of the interconnected rings shall be
  provisioned as the primary ring and the other
  as secondary ring
• The station on the secondary ring with the lower
  MAC address is designated as the 0 member, and
  the other as the 1 member

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Network Diagram

• Stations A C are peer stations
• Stations B D are peer stations
• Stations A B are mate stations
• Stations C D are mate stations

• Stations A B are protection group members on
  the primary ring
• Station A is the 0 member and station B is the
  1 member
• Stations C D are protection group members on
  the secondary ring
• Station C is the 0 member and station D is the
  1 member

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Station-OK State Variable

• Station-OK (adminStatusUP) AND
  (mateVisableTRUE) AND

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Peer Stations Communication

• Peer stations exchange messages which are also
  used as keep-alive
• The messages consist the following information
  (per protection group)
• Station-OK state variable
• Peer keep-alive timer expired
• The peer messages are sent
• periodically
• after a protection event
• after change of admin-status
• after peer keep-alive timer expires

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Self-OK State Variable

• Self-OK (my_Station-OKTRUE) AND
  (my_KA_Timer_ExpiredFALSE) AND
  (peer_Station-OKTRUE) AND (peer_KA_Timer_Expired
  FALSE)

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Mate Stations Communication

• Mate stations exchange messages which are also
  used as keep-alive
• Mate stations exchange the value of the Self-OK
  state variable (per protection group)
• The mate messages are sent
• periodically
• after a protection event
• after change Self-OK state variable value
• The messages could be new control type or new OAM
  type

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PIRC Stations Communication
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Mate-OK State Variable

• Mate-OK (mateVisableTRUE) AND(mate_Self-OK
  TRUE) AND (mate_KA_Timer_ExpiredFALSE)

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PGM State Machine
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MAC Table Flush

• 802.17b When an interconnecting station no
  longer appears in the topology, the MAC entries
  associated with that stations are deleted
• When a PIRC station it sends SAS_Group_Notify
  message when
• it changes PG state to FWD-None
• it changes PG state from FWD-All to FWD-mine

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myFlow(frame) Function

• The function could be used to implementation of
  the load-balancing functionality
• On of the possible implementations of the myFlow
  function could be
• myFlow(frame) (hashing(frame) modulo 2)
  member-type
• The hashing could be on the service class and/or
  VLAN
• member-type equals to 0 if the station is the 0
  member, and equals to 1 if the station is the 1
  member

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PIRC Sublayer Logic on the Path Client ? MAC as
State Table
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PIRC Sublayer Logic on the Path Client ? MAC as
Pseudo-Code

• if (MAC is on primary ring)
• forward frame
• else
• if (((PG state is fwd-mine) and
  myFlow(frame)) or (PG state is fwd-all)) then
• forward frame
• else
• discard frame

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PIRC Sublayer Logic on the Path MAC ? Client as
State Table
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PIRC Sublayer Logic on the Path MAC ? Client as
Pseudo-Code

• if (MAC is on primary ring)
• if ((PG state is fwd-all) and (RPR SA is the
  mate MAC address))
• discard frame
• else
• forward frame
• else
• if (RPR SA is the mate MAC address)
• discard frame
• else
• if (((PG state is fwd-mine) and
  myFlow(frame)) or (PG state is fwd-all)) then
• forward frame
• else
• discard frame

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Local Tributaries at PIRC Stations

• According to the suggested algorithm, if the PIRC
  station are isolated on the primary ring, then
  their local tributaries are also disconnected
• Complicating the algorithm to allow forwarding
  through the secondary ring is not critical
  because
• isolation on the primary ring is a DUAL failure
• if the primary ring has isolation, the local
  tributaries at the PIRC stations are usually not
  the biggest problem