802.17cProtected Inter-Ring Connection

Rafi Ram - Corrigent SystemsJanuary 2007

2

PGM State Machine

BothActive

MateDown

SelfDown

HoldOff

myICF

down

myICF

down

1

mate ICF downor mate stationnot in topology 2

my ICF down

my ICF up

1

mate ICF downor mate stationnot in topology

2

Hold-Offtimer

expired3

1

mateICF up2

Start

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

7

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

9

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

10

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)

11

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

12

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 station’s 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)

13

Data Frame Format with ICTttl

baseControl

da

sa

ttlBase

extendedControl

hec

payload

fcs

protocolType

destSI

srcSI

Basic Data Frame Format

ttl

baseControl

da

sa

ttlBase

extendedControl

hec

payload

fcs

protocolType

destSI

srcSI

daExtended

saExtended

Extended Data Frame Format

"ict" & "ef" bits set to 1"ict" bit set to 1

14

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

15

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

16

Interconnection Frame Forwarding

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

17

Flooding

A B C D E F G

H I J K M

a

m

MC A m a

MC A m a

A RPR

A PGI=201

a A SI(I)

MC A m a

0 SI(I)

18

Unicast Forwarding

A B C D E F G

H I J K M

a

m

A M a m

a m

A M a m

A RPR

M PGI=101

A PGI=201

M RPR

m M SI(C)

SI(I)

A M

SI(C)

a A SI(I)

0

0