802.17c
Protected Inter-Ring Connection
Rafi Ram - Corrigent Systems
January 2007
802.17c Proposed Requirements
• Backwards compatible with non-802.17c stations
• Support rings interconnect through dual-station
homing
• Provide sub 50msec protection
• Allow for hash based load balancing using both
stations
• The load balancing shall allow unicast forwarding
(prevent persistent flooding)
• Support for local tributary interfaces in
interconnecting stations
• Prevent loops in normal and protection states, and
during the transient process between the states
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802.17c Proposed Requirements (cont’)
• Support both point-to-point and multi-point-tomulti-point services
• Support network topology of collector ring with
multiple subtending rings
• Support for efficient selective MAC table flush
• Attend the MAC table scalability issue
• Provide maintenance commands (e.g. manual
switch-over)
• Allow implementation of interconnecting station
as two separate stations with back-to-back
connections
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Network Topology of Collector
Ring with Subtending Rings
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Suggested Solution
• Backwards compatible with non-802.17c stations
• Transparent for non-interconnecting stations
• Minimal overhead of provisioning, protocol
messages, database and state-machines
• The basic suggestion resolve all proposed
requirements (with the exception of static MAC
entries)
• An additional enhancement can be suggested to
addresses the MAC table scalability issue
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Definitions
• Stations A & B are members of
a protection group (PG) for
interconnect in ring 1 with ring 2
• Stations A & B are members of
a (different) protection group
for interconnect in ring 1 with
ring 3
• Each protection group is
provisioned with a ring wide
unique identifying index – PGI
• One of the stations in a PG is
provisioned as the “0” member,
and the other as the “1”
member
Ring 1
Ring 2
Station
Station
A
B
Ring 3
Station
Station
C
D
PGM = protection
group member
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Provisioning Example
• PGI 101 is provisioned in ring
1 for interconnect with ring 2
• station A is provisioned in ring
1 as PGI member 101.0
• station B is provisioned in ring
1 as PGI member 101.1
• PGI 102 is provisioned in ring
1 for interconnect with ring 3
• station A is provisioned in ring
1 as PGI member 102.0
• station B is provisioned in ring
1 as PGI member 102.1
Ring 1
Ring 2
Station
Station
A
B
Ring 3
Station
Station
C
D
There is no need to
provision stations A & B
as PG in ring 2 or 3
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Frame Forwarding
• The forwarding of frames between the rings through
the interconnect shall be based on the switching
method implemented by the station client (layer 2 or
layer 3)
• For example, in case of layer 2 switching :
– MAC table learning shall be done in the interconnecting station on frames forwarded between
the rings
– Multicast and broadcast shall be forwarded
though interconnect
– Unicast frames with relevant matching entries in
the MAC table shall also be forwarded though the
interconnect
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Load Balancing
• To allow for load balancing, the protection group
members shall use hash function to distribute the
inter-connecting traffic between them
• The hash function should be flow based
• For example, if both inter-connecting member
stations are active then :
– the “0” member station shall not forward (discard)
frames with odd hash result
– the “1” member station shall not forward frames
with even hash result
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PGM Status Message
• Protection group member status messages are
used to advertises the state of the interconnect
functionality to the mate PG member
• The PGM status message is a broadcast frame.
The message can be a new control type or a
new OAM type
• The frame shall contains multiple entries, an
entry per protection group that the station
participates
• A message entry consists of the PG index, “0” or
“1” configuration and interconnect functionality
state
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