802.17c Protected Inter-Ring Connection

1
802.17cProtected Inter-Ring Connection

• Rafi Ram - Corrigent Systems
• January 2007

2
PGM State Machine
ICF Inter-Connect Functionality
3
Frame Filtering

• A protection group member station shall transmits
  and receives data frames through the ring
  interconnection according to its state
• State Mate Down forward all frames
• State Both Active forward frames with even or
  odd hash result (depending if it is the 0 or
  1 member)
• Otherwise (Self Down or Hold-Off), do not
  forward any frame

4
Transmission of OAM_SAS_Notify

• A protection group member shall transmit a
  selective OAM_SAS_Notify frame when
• Its local interconnect functionality changes
  state from up to down
• Its state changes from Mate Down (to Both
  Active or Self Down)
• Note According to 802.17b, after a topology
  change (e.g. station down), each station
  performs selective MAC table flush

5
Transmission of PGM Status Messages

• Every protection group member periodically
  broadcasts a PGM status message
• In addition, a protection group member shall
  also generate a message when its state changes
  from or to Self Down state

6
Hold-Off State

• The purpose of the Hold-Off state is guarantee
  that there shall be no loops when an
  interconnection functionality is restored
• The time period of the Hold-Off timer shall be
  set according to the worst case transit delay
  through the ring

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Removing a PG Member Provisioning

• When an active PG membership provisioning is
  removed, the station must transmit a PGM status
  message with down state, so the mate would know
  it no longer should expect PGM status messages

8
Detection of Miss-Configuration

• When a protection group member receives a PGM
  message with the same 0/1 provisioning as
  itself, it could assert an appropriate
  miss-configuration alarm

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Removing the Need for the 0/1 Provisioning

• A station can detect if it is the 0 or 1
  member according to the RPR MAC address
• If its RPR MAC address is lower than its mate it
  is the 0 member, otherwise the 1 member
• This removes a potential miss-configuration of
  the 0/1 provisioning
• A conflict may arise if PG are provisioned on
  both sides (rings) of the interconnect, and a
  certain station is 0 on one ring but 1 on the
  other

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Hashing based on MAC Address

• Performing the hash function on the users MAC
  address might be problematic
• Loss of connectivity ARP packets might be
  forwarded though a different interconnect station
  then the unicast traffic that will follow the ARP
• Persistent flooding A specific flow might be
  forwarded though different interconnect stations
  in each direction (A-to-Z and Z-to-A)

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Enhancement for MAC Table Scalability

• Suggested enhancement main concept
• Allow the interconnecting stations to do
  forwarding based on the RPR MAC addresses and not
  the users MAC addresses
• The size of the MAC table is proportional to the
  total number of stations in the interconnected
  nodes and not the total number of users
• The suggested enhancement resemble the concept of
  MAC-in-MAC

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MAC Table Scalability Suggestion Details

• Each station on a ring is assigned with a unique
  index (SI), a number in the range 1 to 255
• A stations SI value does not change if other
  stations are added or removed from the ring
• A frame which is forwarded between
  inter-connected rings is tagged with ICT
  (inter-connect tags)
• The inter-connect tag consists the destination
  interconnect SI and the source interconnect SI
• A bit in the extendedControl indicates if the
  frame is tagged (similar to the ef bit)

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Data Frame Format with ICT
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Assignment of RPR DA/SA and ICT for Interconnect
flows

• The RPR DA is the MAC address of the destination
  (off-ring) station
• The RPR SA is the MAC address of the source
  (off-ring) station
• The destSI is the SI of the station that should
  do the interconnect. A value of 0 indicates
  that it is not known if interconnection is
  required
• The srcSI is the SI of the station that did the
  interconnect. A value of 0 indicates that frame
  did not originate from interconnect station

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MAC Table Learning

• The interconnect stations learn only the RPR MAC
  address of the frames they forward
• The stations connected to the users learn the
  users MAC addresses and their association to RPR
  MAC addresses and indication if the RPR stations
  are on the local ring or through interconnect
  station

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Interconnection Frame Forwarding

• A station receiving a frame with its SI in the
  destSI (in the ICT) shall forward the frame
  through the interconnection

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Flooding
H
I
J
K
M
MC
A
m
a
A PGI201

0
SI(I)
m
a A SI(I)

MC
A
m
a
MC
A
m
a
A RPR

a
A
B
C
D
E
F
G
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Unicast Forwarding
H
I
J
K
M
A PGI201
M RPR
A
M
a
m
SI(I)
0
m
a A SI(I)

a
m
A
M
m M SI(C)

A RPR
M PGI101
a
A
M
a
m
SI(C)
0
A
B
C
D
E
F
G