HUAWEI OptiX OSN 8800 T64/T32 Intelligent Optical Transport Platform. Product Description - part 31
Figure 7-43 Gold services
R4
R1
E
MSP
I
D
F
MSP
C
A
B
MSP
H
G
R2
R3
:ASON NE
:User equipment
Table 7-20 lists the attributes of gold services.
Table 7-20 Attributes of gold services
Attribute
Gold Service
Requirements for creation
Sufficient working resources or non-protection resources are
available between the source node and the sink node.
Multiplex section
l Supports using the working resources of a 1:1 linear multiplex
protection
section protection chain to create gold services.
l Supports using the working resources of a 1+1 linear
multiplex section protection chain to create gold services.
l Supports using the working resources of a 1:N linear
multiplex section protection chain to create gold services.
l Supports using the working resources of a two-fiber
bidirectional multiplex section protection ring to create gold
services.
l Supports using the working resources of a four-fiber
bidirectional multiplex section protection ring to create gold
services.
Protection and restoration
When a fiber is cut for the first time, MS switching is performed
to protect services. When MS switching fails, rerouting is then
triggered to restore services.
323
Attribute
Gold Service
Rerouting
l Supports rerouting lockout.
l Supports rerouting priority.
l Supports three rerouting policies:
- Use existing trails whenever possible
- Do not use existing trails whenever possible
- Best route
Revertive
Supports Automatically Revertive, Non-Revertive, and
Scheduled revertive.
l After the automatically revertive gold service is rerouted, the
service is automatically reverted to the original path if the
fault in the original path is rectified.
l After the scheduled revertive gold service is rerouted, the user
can set the service to be reverted to the original path at a
specific future time (ranging from 10 minutes to 30 days) on
the NMS if the fault in the original path is rectified.
l After the non-revertive gold service is rerouted, the service
is not reverted to the original route after the fault is rectified.
NOTE
The original route is the route before rerouting but may not be the original
route set up when the ASON trail is created.
Preset restoring trail
Supports setting the preset restoring trail.
Service migration
l Supports migration between permanent connections and gold
services.
l Supports migration between gold services and diamond
services.
l Supports migration between gold services and silver services.
l Supports migration between gold services and copper
services.
Service switching
Supports manual switching.
Service optimization
Supports service optimization.
ASON server trail
Supports gold ASON server trails.
Alarms to trigger
R_LOS, R_LOF, B2_EXC, B2_SD, MS_AIS, MS_RDI,
rerouting
AU_AIS, B3_EXC (can be set), B3_SD (can be set)
7.6.6 Silver Services
Silver services, the revertive time is hundreds of milliseconds to several seconds. The silver level
service is suitable for those data or internet services that have low real-time requirement.
Silver services are also called rerouting services. When an LSP failure, the ASON triggers
rerouting to restore the service. If there are not enough resources, service may be interrupted.
324
As shown in Figure 7-44, A-B-G-H-I is a silver service trail. If the fiber between B and G is
cut, the ASON triggers rerouting from A to create a new LSP that does not pass the cut fiber.
Hence, services are protected.
Figure 7-44 A silver service
E
R1
R4
LSP after rerouting
I
D
F
A
C
B
H
G
R2
R3
Original LSP
: ASON NE
: User equipment
Table 7-21 lists the attributes of silver services.
Table 7-21 Attributes of silver services
Attribute
Silver Services
Requirements for creation
Sufficient non-protection resources are available between the
source node and the sink node.
Service restoration
When the original LSP fails, rerouting is triggered to create a
new LSP to restore services.
Rerouting
l Supports rerouting lockout.
l Supports rerouting priority.
l Supports three rerouting policies:
- Use existing trails whenever possible
- Do not use existing trails whenever possible
- Best route
325
Attribute
Silver Services
Revertive
Supports Automatically Revertive, Non-Revertive, and
Scheduled revertive.
l After the automatically revertive silver service is rerouted,
the service is automatically reverted to the original path if the
fault in the original path is rectified.
l After the scheduled revertive silver service is rerouted, the
user can set the service to be reverted to the original path at
a specific future time (ranging from 10 minutes to 30 days)
on the NMS if the fault in the original path is rectified.
l After the non-revertive silver service is rerouted, the service
is not reverted to the original route after the fault is rectified.
NOTE
The original route is the route before rerouting but may not be the original
route set up when the ASON trail is created.
Preset restoring trail
Supports setting the preset restoring trail.
Shared mesh restoration
Supports setting the shared mesh restoration trial for revertive
trail
silver trials.
Service migration
l Supports migration between permanent connections and
silver services.
l Supports migration between diamond services and silver
services.
l Supports migration between gold services and silver
services.
l Supports migration between silver services and copper
services.
Service optimization
Supports service optimization.
Service association
Supports service association.
ASON server trail
Supports silver ASON server trails.
Alarms to trigger rerouting
R_LOS, R_LOF, B2_EXC, B2_SD, MS_AIS, MS_RDI,
AU_AIS, B3_EXC (can be set), B3_SD (can be set)
7.6.7 Copper Services
The copper services are seldom used. Generally, temporary services, such as the abrupt services
in holidays, are configured as copper services.
Copper services are also called non-protection services. If an LSP fails, services do not reroute
and are interrupted. Table 7-22 lists the attributes of copper services.
326
Table 7-22 Attributes of copper services
Attribute
Silver Service
Requirements for
Sufficient non-protection resources are available between the source
creation
node and the sink node.
Service restoration
Does not support rerouting.
Service migration
l Supports migration between copper services and traditional
services.
l Supports migration between copper services and diamond services.
l Supports migration between copper services and gold services.
l Supports migration between copper services and silver services.
Service
Supports service optimization.
optimization
Service association
Supports service association.
ASON server trail
Supports ASON server trails.
7.6.8 Iron Services
The iron services are also seldom used. Generally, temporary services are configured as iron
services. For example, when service volume soars, during holidays, the services can be
configured as iron services to fully use the bandwidth resources.
An iron service is also called a preemptable service. Iron services apply non-protection resources
or protection resources of the TE link to create LSPs. When an LSP fails, services are interrupted
and rerouting is not triggered.
l When the iron service uses the protection resources of the TE link, if the MS switching
occurs, the iron service is preempted and the service is interrupted. After the MS is
recovered, the iron service is restored. The interruption, preemption and restoration of the
iron service are all reported to the U2000.
l When the iron service uses the non-protection resources, if the network resources are
insufficient, the iron service may be preempted by the rerouted silver service or diamond
service. Thus, the service is interrupted.
Table 7-23 lists the attributes of iron service.
Table 7-23 Attributes of iron services
Attribute
Iron Service
Requirements
Sufficient protection resources or non-protection resources are available
for creation
between the source node and the sink node.
327
Attribute
Iron Service
Multiplex
To create iron services, the following resources can be used:
section
l Protection resources of 1:1 linear MSP
protection
l Protection resources of 1:N linear MSP
l Protection resources of two-fiber bidirectional MSP
l Protection resources of four-fiber bidirectional MSP
Service
Does not support rerouting.
restoration
Service
Supports migration between iron services and extra permanent
migration
connections.
Service
Supports service optimization.
optimization
7.6.9 Tunnels
Tunnels are mainly used to carry VC-12 or VC-3 services. Tunnels are also called as ASON
server trails.
When lower order services are to be created, first create a VC-4 tunnel. The protection level for
the tunnel can be diamond, gold, silver or copper. Then, use the management system to complete
the configuration of the lower order service. See Figure 7-45.
Figure 7-45 Tunnel
VC-4 tunnel
VC-12 service
R4
R1
R3
R2
: ASON NE
ASON domain
: User equipment
The configuration of a tunnel is different from that of the above-mentioned service types. Its
cross-connection from the tributary board to the line board can only be configured manually. As
shown in Figure 7-46, there is a tunnel between NE1 and NE2 which can be a diamond ASON
328
server trail, a gold ASON server trail, silver ASON server trail or copper ASON server trail.
During service creation, the ASON automatically chooses the line boards of NE1 and NE2 and
the timeslots of the line boards.
After creating tunnels, you must manually create and delete the lower order cross-connection
from the tributary board to the line board. During rerouting or optimization of the tunnels,
however, the cross-connections at the source and sink nodes automatically switch to the new
ports.
NOTE
In addition, the end-to-end tunnel and lower order service can be created.
Figure 7-46 Lower cross-connection
VC-12
ASON server trail
VC-12
VC-4
NE1
NE2
Cross-
connection
VC-12
Tributary unit Line unit
Table 7-24 lists the attributes of tunnels.
Table 7-24 Attributes of tunnels
Attribute
Gold Tunnel
Silver Tunnel
Copper Tunnel
Requirement
Same as gold services
Same as silver services
Same as copper
s for creation
services
Service
Same as gold services
Same as silver services
Does not support
restoration
rerouting
Rerouting
l Supports rerouting
l Supports rerouting
Does not support
lockout.
lockout.
rerouting
l Supports rerouting
l Supports rerouting
priority.
priority.
Revertive
Supported
Supported
Not supported
Pre-
Supported
Supported
Not supported
configuratio
n of restoring
route
Service
Not supported
Supported
Supported
association
329
Attribute
Gold Tunnel
Silver Tunnel
Copper Tunnel
Service
l Supports migration between tunnel services and permanent connections.
migration
l Supports migration between silver tunnels and copper tunnels.
l Supports migration between gold tunnels and silver tunnels.
l Supports migration between gold tunnels and copper tunnels.
Service
Supports service optimization.
optimization
Tunnel level
VC-4
7.6.10 Shared Mesh Restoration Trail
On the OCS network, in the case of a revertive silver service, a restoration trail can be reserved.
In the case of rerouting, the silver service reroutes to the reserved restoration trail. Such a
restoration trail is called a shared mesh restoration trail.
When a service configured with the shared mesh restoration trail reroutes, the service uses the
resources on this trail with priority. If all resources on the shared mesh restoration trail are usable,
these resources are used for service restoration. If only partial resources on the shared mesh
restoration trail are usable, these resources are used with priority for computation of a restoration
trail. The other resources may be faulty or used by other services that share the trail.
As shown in Figure 7-47, the shared mesh restoration trail for two revertive silver services share
the TE link and timeslots between G and H. When the revertive silver service 1 (A-B-C) reroutes,
the service directly reroutes to the shared mesh restoration trail 1 (A-G-H-C). When the revertive
silver service 2 (D-E-F) reroutes, the service directly reroutes to the shared mesh restoration trail
2 (D-G-H-F). If both silver services reroute, only one of them can reroute to the shared mesh
restoration trail, for the two restoration trails share the TE link and timeslots between G and H.
Figure 7-47 Shared mesh restoration trail
Revertive silver service 1
A
B
C
Share MESH
restoration trail 1
G
H
Share MESH
restoration trail 2
D
E
F
Revertive silver service 2
330
Features of the Shared Mesh Restoration Trail
The shared mesh restoration trail has the following features.
l Only the revertive silver service can be configured with the shared mesh restoration trail.
l A shared mesh restoration trail cannot be set to concatenation services at different levels.
l For a silver service configured with the shared mesh restoration trail, the revertive attribute
cannot be changed.
l The resources on a shared mesh restoration trail can only be the unprotected resources of
TE links.
l For a silver service configured with the shared mesh restoration trail, do not set the preset
restoration trail.
Differences Between Shared Mesh Restoration Trail and Preset Restoration Trail
The shared mesh restoration trail and the preset restoration trail have the following differences.
l For a preset restoration trail, only route information of the trail is recorded and no resources
are actually reserved. In this way, the resources for a preset restoration trail may be used
by other services. When the service reroutes, the preset restoration trail cannot be used.
l For a shared mesh restoration trail, resources are actually reserved. The reserved resources
cannot be used by other services. In this way, services can be restored with the best effort.
In addition, to increase the resource utilization, the shared mesh restoration trails for
different services can share some resources.
NOTE
The preset restoration trail and the shared mesh restoration trail adopt different restoration mechanisms
and thus cannot be used at the same time.
7.6.11 Crankback Mechanism
The Crankback mechanism during rerouting, optimization, and creation of the wavelength/sub-
wavelength LSP is supported.
It takes a certain time to spread network routing information. When rerouting is performed, the
source node may use the outdated network status information to calculate the trail. Therefore,
the selected route may be unavailable, resulting in a rerouting failure.
The ASON software supports the Crankback rerouting mechanism. When setting up connections
according to the calculated trail, the ASON software informs the source node of the information
related to the faulty network nodes or links if the connection setup process is baffled due to
insufficient network resources or network faults. In this case, the source node recalculates a trail
that meets the constraint conditions but does not traverse the obstacle node and then establishes
the connections for the calculated trail. This effectively restores a service by means of rerouting.
7.6.12 Network Traffic Engineering
An ASON network has one network traffic engineering policies, that is, network traffic
equilibrium, so as to make network resources distributed in the best state. In addition, various
restraint conditions for route selection are developed. In this manner, network resources are
properly used.
331
Network Traffic Equilibrium
Due to manual planning of services on a traditional network, it is difficult for the traditional
network to achieve traffic equilibrium on the entire network. The introduction of ASON features
makes the network resources automatically adjusted. With the traffic engineering algorithm, the
resources of the entire network can be automatically and evenly allocated, which avoids
congestion and improves network security and operability.
On an ASON network, the traffic of each trail is equalized, and thus the situation where the
traffic of certain trails is large but certain trails are idle can be avoided.
The ASON computes a best route according to the CSPF algorithm. If there are many services
between two nodes, there may be several services sharing a same route. The traffic equilibrium
function is used to avoid this situation. As shown in Figure 7-48, there are many silver services
between R2 and R4. To make the network more safe and reliable, the ASON allocates them to
different routes such as A-D-E-I, A-B-C-F-I and A-B-G-H-I as evenly as possible. In this
manner, network security and stability are enhanced.
Figure 7-48 Traffic equilibrium
R4
R1
E
I
D
F
C
A
B
H
G
R2
R3
: ASON NE
: User equipment
Route Selection Policy
With traffic engineering, Huawei ASON equipment develops various constraint conditions on
the control plane for route selection based on the WDM/OTN ASON network. The constraint
conditions for route selection are as follows:
l Constraint conditions for network resources (explicit node, explicit link, explicit
wavelength, and explicit channel)
l Constraint conditions for exclusion of network resources (excluded node and excluded link)
l Strict route and number of nodes (hops) that a service traverses
l Fiber length of a service, load balancing, SRLG, and associated services
l Combination of the preceding constraint conditions
332
The constraint conditions for the ASON wavelength or sub-wavelength services are mainly
reflected in the trail cost. The trail cost includes the following factors:
l Link bandwidth occupancy
l Link length
l Number of nodes (hops) that a service traverses
During service route computation, you should consider the preceding factors of the trail cost
(the function of setting the weight of each factor is provided), and thus you can select the route
with the minimum trail cost. In this manner, the traffic is equalized and the network resources
are properly used.
Customized Link Cost
The ASON software supports the customized link cost. Hence, users can adjust the link cost and
select the expected link according to actual situations. After the customized link cost is
introduced, the trail with the lowest cost is selected according to the integrated cost of a link
during service creation or rerouting.
The customized link cost is used to describe the customized link attributes. By using the
customized link cost, users can assign different meanings to a link. The examples are as follows:
l Link age
The cost of a link ascends with the age of the link. When computing a trail, the ASON
software is more likely to select a new trail.
l Link price
The cost of a link ascends with the price of the link. When computing a trail, the ASON
software is more likely to select a cheap trail.
l Link interruption rate
The cost of a link ascends with the link interruption rate. When computing a trail, the ASON
software is more likely to select a trail with a low link interruption rate.
The customized link cost can be queried, and a change of the customized link cost on a node
can be flooded to all nodes on the entire network. In this manner, all nodes on the network
acknowledge the customized link cost information, which can be used as a basis of computing.
Shared Risk Link Group
On an ASON network, a shared risk link group (SRLG) needs to be set when a group of optical
fibers are in one cable.
SRLG represents the shared risk link group. Fibers in the same optical cable have the same risk.
That is, when the cable is cut, all fibers are cut. Hence, an ASON service should not be rerouted
to another link that has the same risk.
Hence, an SRLG needs to be correctly set for the links sharing the same risk on a network so as
to avoid the situation where an LSP after rerouting of ASON services traverses a link that has
the same risk as that of the faulty link. In this manner, the service restoration time during ASON
service rerouting is shortened. You can change the SRLG attribute.
When an electrical-layer service selects its trail, the electrical-layer link inherits the SRLG
information of the links involved in its electrical server layer and the SRLG information of the
links involved in its optical server layer. As a result, during rerouting, the electrical-layer service
follows the principle of separating SRLGs as possible.
333