25/05/2007 IEEE 802.17 RPRWG Yan Wang

Multiple Links Failure Protection in Protected Inter-Ring Connection

May 2007 Interim Meeting

Geneva Switzerland

zhaisuping@huawei.comyanw@huawei.com

Huawei Technologies

25/05/2007 IEEE 802.17 RPRWG Yan Wang

Interconnected node failure• When one interconnected node fails, the other

interconnected node shall take over all the inter-ring traffic forwarding.

• The node failure may be of the following situations The whole node failure One ring component failure The forwarding component failure

C2 R4

R3R1

R2

C1

C2 R4

R3R1

R2

C1

Ri ng 1

Ri ng 2

Ri ng 1

Ri ng 2

Ri ng 1

Ri ng 2

25/05/2007 IEEE 802.17 RPRWG Yan Wang

Multiple links failure• From the node C2 viewpoint, scenario (a) can be equal to

an interconnected node failure (one ring component failure).

• In this case, the same protection action shall be taken just like the node C1 failure.

• Scenario (b) can be protected by two interconnected nodes forwarding.

• Scenario (a) can be regarded as a specific case of scenario (b). The mechanism for scenario (b) can also be used by scenario (a).

(b)

C2 R4

R3R1

R2

C1

C2 R4

R3R1

R2

C1

(a)

25/05/2007 IEEE 802.17 RPRWG Yan Wang

Multiple links failure protection

• C2 is selected to forward the inter-ring traffic.• Two links failure makes R1 can’t communicate

with C2, inter-ring traffic from R1 fails. • Protection is achieved by both inter-ring nodes

C1 and C2 forwarding all inter-ring traffic.

C2 R4

R3R1

R2

C1

C2 R4

R3R1

R2

C1

C2 R4

R3R1

R2

C1

25/05/2007 IEEE 802.17 RPRWG Yan Wang

The problem of transient loop

• After link defect recovers, there are transient loop, because the two interconnected nodes C1 and C2 both are still in forwarding status.

C2 R4

R3R1

R2

C1

C2 R4

R3R1

R2

C1

25/05/2007 IEEE 802.17 RPRWG Yan Wang

Transient loop prevention

• When nodes R1 and R2 find the link recovers, they shouldn’t switch to normal status immediately.

• Timer mechanism– They keep in protected status until their

timers expire.– Before the timers expire, the correlative

interconnected node C1 shall know the reversion and stop forwarding.

• Notification mechanism– They keep in protected status until the

correlative interconnected node C1 stops forwarding and notifies them.

C2 R4

R3R1

R2

C1

C2 R4

R3R1

R2

C1

C2 R4

R3R1

R2

C1

25/05/2007 IEEE 802.17 RPRWG Yan Wang

Performance consideration

• In the dual-interconnected rings that there are 8-10 nodes on each ring– The two links failure protection time can be

less than 50ms– During reversion, there is a transient

interruption for some traffic because of the loop prevention mechanism.

– The interruption time can be less than 50ms– The interruption time depends on

The interconnected nodes’ processing capability The number of nodes on the ring

25/05/2007 IEEE 802.17 RPRWG Yan Wang

Benefits vs. Shortages

• Benefits– Enhanced inter-ring traffic protection ability.– Better utilization of the dual interconnected

nodes.

• Shortages– New mechanism to prevent transient loop during

reversion. – Possibility of modifying the non-interconnected

nodes.