Load sharing in PBB-TE

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Load sharing in PBB-TE

• Zehavit Alon
• IEEE Interim Meeting May 2008

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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
  ltESP-MAC DA, ESP-MAC SA, ESP-VIDgt
• 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.

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Protection Switching Models
11 w/o load sharing
N(M1) with load sharing
The TEPG is composed of 2 TESIs.
The TEPG is composed of N TESIs. (N gt 1, M lt N-1)
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.
One TESI in the TEPG is defined as the working
TESI and the other is defined as the protection
TESI.
Each BSI in a TESI is protected against a single
failure by the other TESI that belongs to the
TEPG.
Each BSI in a TESI is protected against a single
failure by one of the other N-1 TESIs that belong
to the TEPG.
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.
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).
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11 without load sharing
Each BSI is mapped to the TEPG
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N(M1) with load sharing
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
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Comparison between the 2 modelsFunctionality
11 w/o load sharing N(M1) with load sharing
Protection per TESI When 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 BSI When 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?
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Comparison between the 2 modelsManagement and
Operation
11 w/o load sharing N(M1) with load sharing
Manual and Force switch to protection/working Supports the requirements defined by Josef in ay-roese-APS-protocol-1107-v011.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-v011.pdf in November 2007
Manual Switch to working
Manual Switch back of BSI
Manual Switch back of BSI
Manual Switch back of BSI
I-LAN
I-LAN
Manual Switch of TESI
Manual Switch to protection
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Comparison between the 2 modelsManagement and
Operation
11 w/o load sharing N(M1) 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 TESIs 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
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Comparison between the 2 models Management and
Operation (contd)
11 w/o load sharing N(M1) with load sharing
In 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 TEPGs structure and state are insufficient for indicating traffic paths. The TESIs 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.
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Comparison between the 2 modelsResource
utilization
11 w/o load sharing N(M1) with load sharing
The BW required to protect all the BSIs in the TEPG is 2 x SBW(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 S(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 SBW(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 S(BW(BSI-preferred)S(BW(BSI-alternate). Configuration of the preferred and alternate TESIs is a complex procedure.
I-LAN
No Available BW in the alternate TESI
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Comparison between the 2 modelsSignaling (future
functionality)
11 w/o load sharing N(M1) 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-v021.pdf in March 2008 It will be very difficult to support the requirements defined by Hiroshi in ay-ohta-ps-requirements-0308-v021.pdf in March 2008
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Comparison between the 2 modelsGeneral
11 w/o load sharing N(M1) with load sharing
11 path protection switching capable of load sharing is in the scope of the PAR NOT defined in the scope of the PAR
50G
50G
50G
50G
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Comparison between the 2 modelsGeneral (contd)
11 w/o load sharing N(M1) with load sharing
Bridge implementation State machine per TEPG Bridge implementation State machine per TESI Different from the 11 state machine State machine per BSI MANY state machines
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Motivation for load sharing

• BW saving
• BUT
• 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 11 protection switching.
• Good utilization of network resources
• BUT
• The assignment of BSIs to TESIs is static rather
  than dynamic and is configured in the same way as
  for 11 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

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Conclusions

• The N(M1) path protection with load sharing
  model
• Does not add any useful functionality that cannot
  be easily achieved using the 11 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 bridges 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 11 and N(M1) models.
  Therefore, it does not comply with the PAR that
  states 11 path protection switching capable
  of load sharing.

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Recommendation

• Comply with the scope of the PAR by including 11
  path protection switching only, providing the
  load sharing capability by means of the 11 path
  protection mechanism
• Remove support for the N(M1) load sharing model
  from the current project

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Thank You

• zehavit.alon_at_nsn.com

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Backup slides
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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(M1) 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(M1) load sharing can be achieved by defining
  several 11 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.

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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 (12.19.2.1.3e6)
• 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 11 protection
  the bandwidth reserved for protection is 100 of
  the working bandwidth. Using 11 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.

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Configuration and Management

• The configuration and management of N(M1) is
  much more complicated than 11 and includes
  additional configuration commands.
• Assuming we have 12 BSIs and we want to use 4
  different paths, we need to configure
• N(M1) 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
• 11 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.