Slide 1

Load sharing in PBB-TE

Zehavit Alon

IEEE Interim Meeting May 2008

Slide 2

Definitions

• BSI - Backbone service instance (identified by I-SID)

• TESI – TE service instance (identified by TE-SID which corresponds to a series of 3-tuples <ESP-MAC DA, ESP-MAC SA, ESP-VID>

• TEPG – TE Protection Group

• Preferred TESI - A configuration option that specifies the preferred path for a BSI

• Alternate TESI - A configuration option that specifies the alternate path for a BSI in the event of a failure of its preferred TESI

• Protection switching - Quote from the introduction of G.8031 - “Protection switching is a fully allocated survivability mechanism. It is fully allocated in the sense that the route and bandwidth of the protection entity is reserved for a selected working entity. It provides a fast and simple survivability mechanism.”

Slide 3

Protection Switching Models

Each BSI in a TESI is protected against a single failure by the other TESI that belongs to the TEPG.

1:1 w/o load sharing N×(M:1) with load sharing

Each BSI in a TESI is protected against a single failure by one of the other N-1 TESIs that belong to the TEPG.

One of the N TESIs in a TEPG can serve as the preferred TESI for a BSI and one of the remaining (N-1) TESIs can serve as the alternate TESI for that BSI.

All the BSIs in the TEPG are carried by one of the TESIs in the TEPG.

BSIs are carried by different TESIs that belong to the TEPG.

The TEPG is composed of 2 TESIs. The TEPG is composed of N TESIs. (N > 1, M < N-1)

One TESI in the TEPG is defined as the working TESI and the other is defined as the protection TESI.

When the working TESI fails, all the BSIs that are carried by it are switched to the protecting TESI.

When a TESI fails, each BSI that is carried by it is switched to one of the remaining TESIs (its alternate TESI).

Slide 4

1:1 without load sharing

I-LA

N

4 TESIs 2 TEPG12 BSI

Each BSI is mapped to the TEPG

Slide 5

N×(M:1) with load sharing

I-LA

N

4 TESIs 1 TEPG12 BSIs

Each BSI is mapped to the TEPG and is configured with the preferred and alternate TESIs

Each BSIs from the failed TESI is moved to a different TESI

Slide 6

Comparison between the 2 modelsFunctionality

1:1 w/o load sharingN×(M:1) with load sharingProtection per TESIWhen a TESI fails, all the traffic carried by it (all the BSIs) is switched to the second TESI.

To activate protection switching, the node only needs to determine the protection entity in the TEPG.

Protection per BSIWhen a TESI fails, each BSI is switched to its alternate TESI

To activate protection switching, the alternate TESI of each BSI must be determined by the node.

Revertive functionality is performed per TESI

None or complicated revertive functionality, Per TESI? Per BSI?

LoP is determined None or complicated LoP. Per TESI? Per BSI?

Slide 7

Comparison between the 2 modelsManagement and Operation

1:1 w/o load sharingN×(M:1) with load sharingManual and Force switch to protection/working Supports the requirements defined by Josef in ay-roese-APS-protocol-1107-v01[1].pdf in November 2007

Support Manual and Force switch to TESI. A Manual switch per TESI The BSIs are switched to several TESIs.No straightforward support of the requirements defined by Josef in ay-roese-APS-protocol-1107-v01[1].pdf in November 2007

I-LA

N

Manual Switch of TESI

Manual Switch back of BSIManual Switch back of BSIManual Switch back of BSI

I-LA

N

Manual Switch to protection

Manual Switch to working

Slide 8

Comparison between the 2 modelsManagement and Operation

1:1 w/o load sharingN×(M:1) with load sharing

Configuration of:• TESIs • Protection Groups • BSI mapping to Protection Group

Configuration of:• TESIs• Protection Groups• BSIs mapping to Protection Group• BSI preferred and alternate TESI

Coordination of:• TESI’s configuration (revertive, protection and working)• Protection Groups configuration• BSI mapping to Protection Group

Coordination of:• Protection Groups configuration• BSIs mapping to Protection Group• BSI configuration to preferred and alternate TESIs

Slide 9

Comparison between the 2 models Management and Operation (cont’d)

1:1 w/o load sharingN×(M:1) with load sharingIn transport networks, TESIs and TEPGs constitute the infrastructure that is pre-provisioned before services are mapped to it.

It is straight forward to map BSIs to the infrastructure.

It is difficult to efficiently determine which TESI should protect each BSI and to calculate the amount of BW that should be reserved per TESI when provisioning the infrastructure.

The TEPG structure and state indicate the exact paths where traffic traverses.

The TEPG’s structure and state are insufficient for indicating traffic paths. The TESI’s state is also insufficient, since the failure status of a TESI does not indicate the other TESIs over which its BSIs are carried. The state of each BSI should be determined.

Slide 10

Comparison between the 2 modelsResource utilization

1:1 w/o load sharingN×(M:1) with load sharing

The BW required to protect all the BSIs in the TEPG is 2 x ΣBW(BSI).The BW of the protection TESI and the working TESI must be identical to ensure that each BSI is protected against a single failure of the TESI. The BW of each TESI is Σ(BW(BSI).

CAC can be performed easily when BSIs are assigned to a PG. This prevents assignment of BSI to the TEPG when the TESI is fully booked.

The BW needed to protect all the BSI is the TEPG 2 x ΣBW(BSI) The BW of each TESI in the protection group must be the sum of the BW of all the BSIs mapped to it (preferred and alternate) This ensures that each BSI is protected against a single failure. The BW of each TESI is Σ(BW(BSI-preferred)+Σ(BW(BSI-alternate).

Configuration of the preferred and alternate TESIs is a complex procedure.

I-LA

N

70%100%

100%

100%

No Available BW in the alternate TESI

Slide 11

Comparison between the 2 modelsSignaling (future functionality)

1:1 w/o load sharingN×(M:1) with load sharing

Future signaling option for coordination of configuration and operator requests will be available per TESI

Depending on the information, signaling option for coordination will be per TESI or BSI. For example the following need to be signaled per BSI: mismatch, switch back, lockout of protection.

If APS signaling, as defined in G.8031, is adopted , it will run on the protection entity.

APS signaling will not be an option, since there is no protection entity.

Can support the signaling requirements defined by Hiroshi in ay-ohta-ps-requirements-0308-v02[1].pdf in March 2008

It will be very difficult to support the requirements defined by Hiroshi in ay-ohta-ps-requirements-0308-v02[1].pdf in March 2008

Slide 12

Comparison between the 2 modelsGeneral

1:1 w/o load sharingN×(M:1) with load sharing

1:1 path protection switching capable of load sharing is in the scope of the PAR

NOT defined in the scope of the PAR

50G

50G50G

50G

Slide 13

Comparison between the 2 modelsGeneral (cont’d)

1:1 w/o load sharingN×(M:1) with load sharingBridge implementation:

• State machine per TEPG

Bridge implementation:

• State machine per TESI – Different from the 1:1 state machine

• State machine per BSI–MANY state machines…

Slide 14

Motivation for load sharing

• BW savingBUT

To provide protection switching, each BSI must have a pre-provisioned backup path. To provide protection for X BW, prior allocation of 2X BW is required as in 1:1 protection switching.

• Good utilization of network resourcesBUT

The assignment of BSIs to TESIs is static rather than dynamic and is configured in the same way as for 1:1 protection switching.

• Better utilization of network resources and links BUT

The same functionality can be achieved in both modes. ▪ Define 4 TESIs of 50G BW consisting of 2 TEPGs, instead of 1 TEPG with

2 TESIs of 100G each▪ Distribute traffic between links (instead of LAG) by sharing the TEPGs

among the links instead of distributing the TESIs of a single TEPG

Slide 15

Conclusions

• The N×(M:1) path protection with load sharing model – Does not add any useful functionality that cannot be easily achieved

using the 1:1 model– Adds complexity to management and operation– Adds complexity to calculate the resources needed for each TESI in a

TEPG to guarantee protection– Will be difficult to synchronize between the edges– Adds complexity in the bridge’s internal implementation– Not in the scope of PAR

• The draft covers 2 solutions with completely different mechanisms, different state machines, different capabilities, and different methods of operation for the 1:1 and N×(M:1) models. Therefore, it does not comply with the PAR that states: “1:1 path protection switching capable of load sharing”.

Slide 16

Recommendation

• Comply with the scope of the PAR by including 1:1 path protection switching only, providing the load sharing capability by means of the 1:1 path protection mechanism

• Remove support for the N×(M:1) load sharing model from the current project

Slide 17

Thank You

zehavit.alon@nsn.com

Slide 18

Backup slides

Slide 19

Protection Switching

• Protection switching is defined as guarantied if the resources needed to carry traffic of failed resource are pre-alocated. I.e. each TESI must have enough BW to carry all the BSI that are mapped to it (preferred and alternate)

– The assumption that N×(M:1) load sharing will save bandwidth is incorrect since all the traffic of a failed TESI must have a protection path. Similarly, the assumption that only a single TESI of a protection group may fail is incorrect.

• N×(M:1) load sharing can be achieved by defining several 1:1 TESIs with load sharing. Operating such a system is straightforward.

• Since assigning a BSI to a TESI is static rather than dynamic, traffic characteristics at a given moment (heavy or moderate) do not influence this operation.

Slide 20

Manual switch

• Force switch, as defined in 26.10.5.1.3 : “A Boolean flag associated with a particular TESI indicating the presence of an administrative command to make this TE service instance available while all the other TE service instances in the protection group (12.19.1.2.2) unavailable. Its value is controlled by an administrator action (12.19.2.1.3:e6)”

– In this case, each TESI must be able to carry all traffic from all the other TESIs, i.e NX, in contrary to what is explained in annex M that claims that “Using conventional 1:1 protection the bandwidth reserved for protection is 100% of the working bandwidth. Using 1:1 protection with load sharing the bandwidth reserved for protection can be significantly reduced”

• On the other hand, if the command is as defined in http://www.ieee802.org/1/files/public/docs2008/ay-mack-crane-load-sharing-protection-0308.pdf i.e remove traffic from a selected entity. In order to switch back to the original mapping it is necessary to locate all the switched BSIs and switch each of them back. This cannot be done per TESI since the TESI does not recognize the preferred TESI of each of the BSIs that are in the alternate TESI.

Slide 21

Configuration and Management

• The configuration and management of N×(M:1) is much more complicated than 1:1 and includes additional configuration commands.

• Assuming we have 12 BSIs and we want to use 4 different paths, we need to configure:

– N×(M:1) model ▪ 4 TESIs ▪ 1 protection group ▪ 12 BSI attachments to the protection group ▪ 24 (12 * 2) preferred and alternate TESI selection per BSI▪ 40 commands

– 1:1 model ▪ 8 TESIs ▪ 4 protection groups▪ 12 BSI attachments to the protection groups▪ 24 commands

• The configuration complexity increases the likelihood of inconsistency between the TESI edges.