Load sharing in PBB-TE
Zehavit Alon
IEEE Interim Meeting May 2008
Slide 1
Definitions
• BSI - Backbone service instance (identified by I-SID)
• TESI – TE service instance (identified by TE-SID which corresponds to a
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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 2
Protection Switching Models
1:1 w/o load sharing
N×(M:1) with load sharing
The TEPG is composed of 2 TESIs.
The TEPG is composed of N TESIs.
One TESI in the TEPG is defined as the
working TESI and the other is defined as
the protection TESI.
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.
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).
Slide 3
(N > 1, M < N-1)
1:1 without load sharing
Each BSI is mapped to the TEPG
I-LAN
12 BSI
Slide 4
4 TESIs
2 TEPG
N×(M:1) with load sharing
Each BSI is mapped to the TEPG and is configured
with the preferred and alternate TESIs
I-LAN
12 BSIs
Each BSIs from the failed TESI is
moved to a different TESI
Slide 5
4 TESIs
1 TEPG
Comparison between the 2 models
Functionality
1:1 w/o load sharing
N×(M:1) with load sharing
Protection per TESI
Protection per BSI
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.
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
LoP is determined
None or complicated revertive
functionality, Per TESI? Per BSI?
None or complicated LoP. Per TESI?
Per BSI?
Slide 6
Comparison between the 2 models
Management and Operation
Manual and Force switch to
protection/working
Supports the requirements defined by Josef in
ay-roese-APS-protocol-1107-v01[1].pdf in November
2007
I-LAN
Manual Switch to working
N×(M:1) with load sharing
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
Manual Switch back of BSI
I-LAN
1:1 w/o load sharing
Manual Switch of TESI
Slide 7
Manual Switch to protection
Comparison between the 2 models
Management and Operation
1:1 w/o load sharing
N×(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 8
Comparison between the 2 models
Management and Operation (cont’d)
1:1 w/o load sharing
N×(M:1) 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.
The TEPG structure and state
indicate the exact paths where traffic
traverses.
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.
Slide 9
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.
Comparison between the 2 models
Resource utilization
1:1 w/o load sharing
N×(M:1) with load sharing
The BW required to protect all the
BSIs in the TEPG is 2 x ΣBW(BSI).
The BW needed to protect all the
BSI is the TEPG 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 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-LAN
100%
70%
100%
100%
Slide 10
No Available BW in the
alternate TESI
Comparison between the 2 models
Signaling (future functionality)
1:1 w/o load sharing
Future signaling option for
coordination of configuration and
operator requests will be available
per TESI
N×(M:1) with load sharing
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
APS signaling will not be an option,
G.8031, is adopted , it will run on the since there is no protection entity.
protection entity.
Can support the signaling
It will be very difficult to support the
requirements defined by Hiroshi in
requirements defined by Hiroshi in
ay-ohta-ps-requirements-0308ay-ohta-ps-requirements-0308v02[1].pdf in March 2008
v02[1].pdf in March 2008
Slide 11
Comparison between the 2 models
General
1:1 w/o load sharing
1:1 path protection switching
capable of load sharing is in the
scope of the PAR
50G
50G
Slide 12
N×(M:1) with load sharing
NOT defined in the scope of the
PAR
50G
50G
Comparison between the 2 models
General (cont’d)
1:1 w/o load sharing
Bridge implementation:
• State machine per TEPG
N×(M:1) with load sharing
Bridge implementation:
• State machine per TESI
– Different from the 1:1 state machine
• State machine per BSI
– MANY state machines…
Slide 13
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 1:1 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 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 14
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 15
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 16
Thank You
[email protected]
Slide 17
Backup slides
Slide 18
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 19
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-loadsharing-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 20
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.
Slide 21