Geneva, 28 May 2010

802.1Qay PBB-TE Protection Switching Overview

Panagiotis SaltsidisEricsson

Joint ITU-T/IEEE Workshop on The Future of Ethernet Transport

(Geneva, 28 May 2010)

What is PBB-TE?

Provider Backbone Bridges – Traffic Engineering is the latest development in a series of ongoing efforts to enable support for advanced connectivity service offerings by a network of Bridges. It corresponds to a set of functions that enable support for full traffic engineering of paths in a bridged network. PBB-TE disables the MSTP control plane for a subset of VLANs, using instead either the management plane or another (possibly external) control plane to populate filtering database table entries of related bridges

BEB

BEB

BCBBCB

BCBBCB

Provisioned Control

Customer

Network

Customer

Network

CustomerNetwork

CustomerNetwork

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The main design principle is based on a building blocks model where the added functionality is mainly confined at the external interfaces associated with a specific service demand. The same network is able to offer PBB-TE services (Traffic Engineered Service Instances – TESIs), Provider Backbone Bridged services (B-VLANs) and Provider Bridged services (S-VLANs).

Services in a Bridged Network

TESI

B-VLAN1

I-SID1

BEB

S1S2

S1S2

S3

S3S4

S5

S6

S4

S5S6

S4

S5

S6

I-SID3

S7S8

S7

S8

S7

S8

S-VLAN1

S9

S9

BEB

BEB

BEB

BEB

I-SID2

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UNI

S1

S2

S3

S4

S5

S6

S7

S8

B-VID1

I-SID1

TESI

UNI

I-SID2

I-SID3

S9 S-VID1

IEEE802.1Qay – Summary

Enables construction of point-to-point and point-to-multipoint traffic engineered paths (TESIs) by splitting of the VID space between distributed spanning tree protocols and provisioned control.Supports discard of frames with unknown destination addresses and disables learning for B-VIDs under provisioned control.Supports the operation of Continuity Check, Loopback, and Linktrace protocols on point-to-point and point-to-multipoint TESIs.Supports 1:1 protection switching capable of load sharing for point-to-point TESIs.Provides required extension to SNMP management by SMIv2 MIB modules

TESI Definitions

Ethernet Switched Path (ESP): A provisioned traffic engineered unidirectional connectivity path among two or more Customer Backbone Ports (CBPs) that extends over a PBBN. An Ethernet Switched Path is point-to-point or point-to-multipoint.point-to-point TE service instance: A TE service instance supported by two point-to-point ESPs where the ESPs’ endpoints have the same Customer Backbone Port (CBP) MAC addresses.point-to-multipoint TE service instance: A TE service instance supported by a set of ESPs that comprises one point-to-multipoint ESP from the root to n leaves plus a point-to-point ESP from each of the leaves to the root.

802.1Qay - Protection

PBB-TE provides end-to-end linear protection for point-to-point TESIs, where a dedicated protection point-to-point TESI is established for one particular working point-to-point TESI, and the traffic is automatically switched from the working TESI to the protection TESI when a failure occurs on the working entity. Failure is detected by the operation of the Continuity Check protocolSwitching is achieved by changing the Backbone Service Instance table B-VID entries on the Customer Backbone Ports associated with the TESI MEPs.

IEEE802.1Qay – PS State Machines

The local protection commands and protection behavior specified by IEEE802.Qay follow the architectural model used in ITU-T Recommendation G.8031.The priorities associated with the various requests in IEEE802.1Qay are in general alignment with the corresponding priorities in ITU-T G.8031 and the corresponding state machine operation in IEEE802.Qay is in alignment to the state transition tables in G.8031. The only differences in the state machine operation are related to the inclusion of the MStoWorking request which is referred by protection switching documents in ITU-T (e.g., G870) but has been dropped by G.8031 and that the precedence of p.SF and FS are inverted since G.8031 relies on an APS protocol to be running on the protection path.

G.8031/IEEE802.1Qaydifferences

The protected entity is different. G.8031 protection applies to point-to-point VLAN based Ethernet Subnetwork Connections.IEEE802.1Qay protection applies to a point-to-point TESI in a traffic engineered region.

The protection scope is different. G.8031 supports linear 1+1 and linear 1:1 protection switching architectures. IEEE802.1Qay is required to support 1:1 path protection capable of load sharing.

G.8031 specifies an in-band Automatic Protection Switching (APS) protocol, whereas signaling in IEEE802.1Qay is provided by CCM flags.

There are a few specific differences regarding the externally observable protection switching behavior. In particular, in IEEE802.1Qay:

The Hold-off function is applied to all SF indications,A Manual Switch request is supported to switch traffic to the working entity,A Force Switch has precedence over an SF-P,The receiver combines traffic from both the working and protected entities,An SF results from any of the following defects: xconCCMdefect, errorCCMdefect, someRMEPCCMdefect, someRDIdefect.

TE Protection Groupsand load sharing

The protection switching mechanism is capable of load sharing as the TE service instances that are assigned to a TE protection group can be re-used in a number of TE protection groups enabling a list of I-SIDs to be distributed among a set of interdependent TE protection groups. A set of interdependent TE protection groups forms a coordinated protection group.Protection switching requests to interdependent TE protection groups must be coordinated for an operator to manage the TESIs in a coherent manner and to avoid potentially competing requests for each TESI.

Protection Group

Working TESI

Protection TESI

Coordinated PGs

PG_A TESI_1 TESI_2 {PG_A, PG_C}

PG_B TESI_3 TESI_4

PG_C TESI_2 TESI_1 {PG_A, PG_C}

Backbone Service Instance

Protection Group

I-SID_1 PG_A

I-SID_2 No PG

I-SID_3 PG_C

I-SID_4 PG_B

I-SID_5 PG_B

Traffic Field in the CCM flags

TESI MEPs make use of the Traffic Field in the CCM Flags Field in order to identify traffic misalignments on point-to-point TESIs

RDI

CCM Interval Traffic Field

The bit is set whenever the BSI instance table associated to the TESI MEP has an I-SID entry for the monitored TESI

Mismatch Defects

Mismatch Defects are detected whenever Differences in the Traffic fields of transmitted and received CCMssimultaneous settings of the RDI and Traffic fields

are reported for a specified period of time

802.1Qay – PS operation summary

IEEE802.1Qay follows the architectural model used in ITU-T Recommendation G.8031 and the state machine operation is similar to the state transition tables in G.8031. The main differences are due to the different requirements associated with PBB-TE

TESIs are provided in a network domain that is under the overall control of an external agent with high levels of management/control requirementsThe PBB-TE PS operation is capable of load sharing