HUAWEI OptiX OSN 8800 T64/T32 Intelligent Optical Transport Platform. Product Description - part 27
Permanent connection (PC) is a service connection calculated beforehand and then created
through the NM by issuing a command to NE. A traditional SDH service is a PC.
Switched connection (SC) is a service connection requested by a terminal user (for example, a
router) and is then created in the ASON control plane through signaling.
CAUTION
ASON software only supports SPC. SC is not supported at present.
7.2.10 ASON Network Protection and Restoration
As the transmission network develops, the survivability of the network becomes a key factor in
the design, operation and maintenance of the network. An ASON network must have effective
and flexible protection and restoration schemes.
Difference between Protection and Restoration
Generally, protection involves the capacity pre-allocated among NEs. Simple protection
schemes such as the intra-board 1+1 protection and complex protection schemes such as the
ODUk SPRing protection can be configured. Protection only involves NEs and does not involve
the management system. The protection switching time is short and is generally not more than
50ms. The backup resources, however, cannot be shared in the network.
Generally, restoration involves the usage of any usable capacity among NEs. Even the extra
capacity of low priority can be used for restoration. When a service trail fails, the network
automatically searches for a new route and switches the services from the faulty route. The
algorithm that restores is the same as the algorithm that selects the trail. Restoration requires
spare resources in the network for service rerouting. Service rerouting involves the computation
of routes. Service rerouting involves the computation of routes, route switching, and re-creation
of cross-connections and routes. The service restoration takes a relatively long time.
Protection in an ASON Network
The traditional protection schemes can still be applied in an ASON network. When a fault occurs,
the protection switching is performed by the transport plane. In this case, the protection switching
does not involve the control plane.
Restoration in an ASON Network
In the case of an ASON network, the rerouting scheme is applied to restore services. When an
LSP fails, the source node computes the best trail for service restoration and then uses signaling
to create an LSP. Then, the new trail carries the services. For the non-revertive services, the
original LSP is deleted after the new LSP is created, however, for the revertive services, the
original LSP would not be deleted.
The advantages of rerouting are listed as follows.
l The services can be restored in a fast and automatic manner.
l After the technology for service restoration is applied in an ASON network, less spare
capacity is required when such an ASON network is restored in real time. The bandwidth
279
utilization is increased considerably. Generally, if a network involves more nodes, the
routes are more complicated and less spare resources are required.
l For OCS network, after the technology for service restoration is applied in an ASON
network, only 30% to 60% of spare capacity is required when such an ASON network is
restored in real time compared with the APS protection or a self-healing ring network. The
bandwidth utilization is increased considerably. Generally, if a network involves more
nodes, the routes are more complicated and less spare resources are required.
Service Restoration
The network restoring schemes can be classified into the centralized restoring scheme and
distributed restoring scheme according to the control mechanism. Huawei ASON applies the
distributed restoring scheme.
If the centralized restoring scheme is applied, a central control system is required to control the
entire network in a comprehensive manner. The central control system contains a very large
network database, which stores all the information about all nodes, links and spare resources.
When a link or a node fails, the fault information is reported to the central control system along
other routes. The central control system then computes a route to replace the faulty route
according to the information stored in the database. The central control system then issues control
commands to each node. A route is created to restore the services.
The distributed restoring scheme does not require any central control system. When a link fails,
the nodes at both ends of the faulty link detect the fault and flood this information to the entire
network. When a node fails, the adjacent nodes detect the fault and flood this information to the
entire network. All LSPs that are involved with the faulty link or node then reroute and new
LSPs are created to restore services.
In a WDM ASON network, when a fiber cut occurs, the WDM ASON OCh trail, WDM ASON
ODUk trail, and WDM ASON Client trail can restore separately. You can set the delay time for
the trail recovery. There is, however, no delay by default.
7.3 Automatic Discovery of Topologies and Resources
On an ASON network, link resources, network topologies, and fibers between sites can be
automatically discovered, and then a network map is automatically generated. The ASON
software dynamically obtains the resource status of the wavelength/sub-wavelength services in
real time, including the occupied and idle resources, providing a quick approach to know the
current network capacity.
For any change to network resources and topologies, such as adding/deleting links, changing
link parameters, adding/deleting network nodes, the ASON software may refresh the relevant
information in real time and inform the network management plane. This facilitates the network
expansion and network reconstruction.
7.3.1 Auto-Discovery of ASON NEs
In the ASON network, the OSPF protocol discovers ASON NEs automatically by sending the
protocol packets.
After discovering the neighbor NEs, the OSPF protocol floods the information about the
neighbor NEs to other NEs. In the end, every ASON NE in the domain has the information about
all ASON NEs in the entire ASON domain.
280
l When an ASON NE is added to an ASON network, other NEs are able to automatically
discover the new NE by using the OSPF protocol.
l When an ASON NE is removed from an ASON network (for example, power off the NE,
remove the SCC board, or shut down the physical channel), other NEs are able to
automatically detect the missing of this NE.
As shown in Figure 7-21, if two ASON NEs are added, the source topology on the U2000 is
automatically updated in real time.
Figure 7-21 TE link automatic discovery
R1
R4
New NE
R2
R3
:ASON NE
:User equipment
7.3.2 Auto-Discovery of Control Links
The ASON network automatically discovers the control links through the OSPF-TE protocol.
When the fiber connection (including the inter-station fiber automatically discovered and the
intra-station fiber manually configured) is complete in an ASON network, each ASON NE uses
the OSPF protocol to discover the control links and then floods the information about its own
control links to the entire network. See Figure 7-22. As a result, each NE obtains the information
of the control links in the entire network and also obtains the information about the network-
wide control topology. The following figure shows the details. Each ASON NE then computes
the shortest route to any ASON NE and writes these routes into the route forwarding table, which
is used for the signaling RSVP to transmit and receive packets.
281
Figure 7-22 Auto-discovery of control links
ASON Domain
When the fiber connection in the entire network is complete, ASON NEs automatically discover
the network-wide control topology and report the topology information to the management
system. See Figure 7-23.
Figure 7-23 Management of control topology
R1
R4
R2
R3
:ASON NE
: User equipment
282
7.3.3 Auto-Discovery of TE Links
The ASON network spreads the TE links to the entire network through the OSPF-TE protocol.
After an ASON NE creates a control channel between neighboring NEs through LMP, the TE
link verification can be started. Each ASON NE floods its own TE links to the entire network
through OSPF-TE. Each NE then gets the network-wide TE links, that is, the network-wide
resource topology.
ASON software detects change in the resource topology in real time, including the deletion and
addition of links, and the change in the link parameters, and then reports the change to U2000,
which performs a real-time refresh.
As shown in Figure 7-24, if one TE link is cut, the NM updates the resource topology displayed
on the NM in real time.
Figure 7-24 TE link auto-discovery
R4
R1
R2
R3
:ASON NE
:User Equipment
7.4 Creation and Deletion of the ASON Trail
The RSVP-TE signaling is needed during the process of creation, deletion, change and rerouting
of the ASON trail.
7.4.1 Creation of an LSP
The creation of an ASON trail is the creation of an LSP.
283
As shown in the Figure 7-25, create a bidirectional based on the wavelength services from NE1
to NE3.
Figure 7-25 Creation of an LSP
1 A bi-directional service is to
be created from NE1 to NE3
NE 2
7
4
3
NE 1
5
R2
6
R1
NE 3
2 Compute the route
from NE1 to NE3
The process of LSP creation is as follows:
1.
Select the basic information such as service level on the NM, and click the source and sink
nodes that are NE1 and NE3. Respectively select the WDM-side optical interfaces of the
corresponding OTU boards and set the constraint condition of the route according to the
actual use. After confirming the information, the NM issues a command for service creation
to source node NE1.
2.
NE1 invokes the CSPF algorithm to compute the most suitable service route according to
the control topology and service topology, which are obtained by the OSPF-TE through
convergence. For example, such a service route is NE1-NE2-NE3.
3.
NE1 uses the RSVP-TE signaling protocol to transmit a message to NE2 according to the
service route. NE1 requests NE2 to reserve resources and create a cross-connection.
4.
NE2 uses the RSVP-TE signaling protocol to transmit a message to NE3. NE2 requests
NE3 to reserve resources and create a cross-connection.
5.
After NE3 creates the cross-connection, NE3 provides feedback message to NE2.
6.
NE2 provides a feedback message to NE1.
7.
NE1 receives the feedback message and stores the related information. NE2 then reports
the successful creation of the LSP to the management system.
Configuration Trait
The service configuration of the ASON WDM products has the following traits:
l Support the end-to-end bidirectional services of wavelength level based on the OCh trail.
The source and sink of the services must be the WDM-side optical interfaces of the OTU
board.
284
l Supports the end-to-end bidirectional services on the level of ODUk. That is, after you
specify the source/sink node, source/sink slot, source/sink port, source/sink channel ID,
service level, rate, and protection attributes, a sub-wavelength LSP is created automatically.
l The ODUk SPRing protection configuration can be added or deleted on the ASON ODUk
sub-wavelength service. The span ID, however, cannot be bound with the ASON service.
l Only notice the source and sink of the services but not the intermediate trail in the
configuration of the end-to-end wavelength services.
l Users can set the explicit node, link, the excluded node and link to restrict the service route.
l During route calculation, the ASON software considers the fiber distance, number of node
hops and available bandwidth according to the weights and user cost set by the users to
choose the best route.
7.4.2 Deletion of an LSP
The deletion of an LSP is the deletion of an ASON trail.
As shown in the Figure 7-26, the bidirectional service from NE1 to NE3 is deleted.
Figure 7-26 Deletion of an LSP
1 Delete a service
from NE1 to NE3
NE 2
6
3
2
NE 1
R2
4
5
R1
NE 3
The process for deleting an LSP is described as follows.
1.
The management system issues a command to NE1. The requirement is that a bidirectional
service from NE1 to NE3 has to be deleted.
2.
NE1 deletes the resources used by the LSP and uses the RSVP-TE signaling to transmit a
message to NE2.
3.
After receiving the message from NE1, NE2 deletes the resources used by the LSP and
uses the RSVP-TE signaling to transmit a message to NE3.
4.
After receiving the message from NE2, NE3 deletes the resources used by the LSP and
provides feedback message to NE2.
5.
NE2 provides a feedback message to NE1.
285
6.
NE1 receives the feedback message and stores the related information. NE2 then reports
the successful deletion of the LSP to the management system.
7.4.3 Rerouting of an LSP
After the trigger conditions of rerouting is detected, for the non-revertive services, a new LSP
is created and the original LSP is deleted, while for the revertive services, the original LSP would
be reserved.
Trigger Conditions of Rerouting
For the WDM service of the OTN networking, Table 7-4 lists the trigger conditions of LSP
rerouting.
Table 7-4 Trigger conditions of rerouting
Event
Alarms That Trigger Rerouting
Type
SF
The trigger conditions of optical-layer service rerouting include the following
alarms of the FIU board:
FIU: BD_STATUS, MUT_LOS
The trigger conditions of electrical-layer service rerouting include the following
alarms of the OTU board:
ODUk_PM_AIS, ODUk_PM_OCI, ODUk_PM_LCK, ODUk_PM_SSF
OTUk_AIS, OTUk_LOF, OTUk_LOM.
SD
The trigger conditions of electrical-layer service rerouting include the following
electrical-layer service alarms of the OTU board:
ODUk_PM_DEG, ODUk_PM_EXC
OTUk_DEG, OTUk_EXC
NOTE
When the BIP detection is of the burst mode, the ODUk_PM_DEG or OTUk_DEG alarm
is reported. When the BIP detection is of the Poisson mode, the ODUk_PM_DEG,
OTUk_DEG, ODUk_PM_EXC or OTUk_EXC alarm is reported.
NOTE
The default state of SD conditions is Disabled. Hence, SD conditions can serve as the
trigger conditions of service rerouting only when the state of SD conditions is set to
Enabled.
NOTE
For details of the above alarms, refer to the Alarms and Performance Events Reference.
For the SDH service of the OCS networking the following alarms trigger the LSP rerouting:
R_LOS, R_LOF, B2_EXC, B2_SD, MS_AIS, MS_RDI, B3_EXC, B3_SD and AU_AIS.
Rerouting Process
When an LSP fails, the faulty LSP sends a rerouting request to the control plane to create a new
LSP. After receiving the request, the source node re-computes the route and allocates resources
286
for the new LSP. Then, the source node starts the creation of the new LSP. For details on the
process of creating the LSP, refer to 7.4.1 Creation of an LSP.
For a non-revertive service, after the new LSP is created, the original LSP is deleted. For details
on the process of deleting the LSP, refer to 7.4.2 Deletion of an LSP.
7.4.4 Change of an LSP
The change of an LSP is to improve an ASON trail.
The process for the change of an LSP is as follows.
1.
The management system issues the command to the source node to change the LSP. After
receiving the request, the source node starts creating a new LSP. Refer to 7.4.1 Creation
of an LSP.
2.
After the new LSP is created, the source node and the destination node start to switch the
cross-connection from the original LSP to the new LSP.
3.
After the switching, the source node starts the process for the deletion of the original LSP.
Refer to 7.4.2 Deletion of an LSP.
7.5 OTN ASON Feature
The OptiX OSN WDM series products of Huawei can provide the OTN ASON function after
the ASON software is loaded.
7.5.1 End-to-End Service Configuration
The ASON network supports end-to-end service configuration, which is very convenient.
The ASON supports both WDM permanent connections and end-to-end ASON services. To
configure an ASON service, you only need to specify its source node, sink node, and protection
level. Service routing and cross-connection at intermediate nodes are all automatically
completed by the network. You can also set explicit node, excluded node, explicit link and
excluded link to constrain the service routing.
For example, consider the configuration of an ASON service between A and I in Figure 7-27.
The network automatically finds the A-D-E-I route and configures cross-connection at nodes A,
D, E and I. Although there is more than one route from A to I, the network calculates the best
route according to the configured algorithm. It is assumed that A-D-E-I is the best route.
The service is created as follows:
l Choose the bandwidth granularity.
l Choose the server level.
l Choose the source node.
l Choose the sink node.
l According to the service bandwidth and existing network resources, the ASON software
computes a proper service trail through the routing protocol.
l The ASON software sets up end-to-end service connections between sites through the
RSVP-TE signaling protocol.
287
Figure 7-27 End-to-end service configuration
R1
R4
E
I
D
F
C
A
B
H
G
R2
R3
:ASON NE
:User Equipment
The system support optical-layer ASON services that cross electrical regeneration NEs,
including:
l Creation, reroute, and optimization of SLA services, and wavelength-tunable ASON
services crossing electrical regeneration NEs.
l Conversion of crossing electrical regenerator service from static wavelength services to
ASON wavelength services and the vice versa.
l Pre-calculation of the optical-layer ASON services when the services cross electrical
regeneration NEs, including the creation, optimization, and restoration trail preset of SLA
services.
NOTE
The end-to-end wavelengths of the ASON services that cross the electrical regeneration NEs must be the
same.
The regeneration mode of the electrical regeneration NEs that the ASON services cross must be in the
transparent transmission mode and cannot be in the electrical cross-connect back-to-back mode.
7.5.2 Mesh Networking Protection and Restoration
The ASON provides mesh networking protection to enhance service survivability and network
security.
As a main networking mode of ASON, mesh features high flexibility and scalability. Compared
with the traditional WDM network, this networking mode also provides more than one recovery
route for each services so it can best utilize the network resources and enhance the network
security.
On a mesh network, to make the interrupted services available, you can immediately restore the
services through the rerouting mechanism in addition to the traditional protection scheme such
as 1+1 protection and shared protection scheme such as ODUk SPRing. That is, the mesh
network can support traditional protection schemes, the services that can be dynamically
288
restored, and service restoration mechanisms in case of protection failures. In this manner,
services are not interrupted only if the resources are available.
As shown in Figure 7-28, when the C-G link fails, to restore the service, the network calculates
another route from D to H and creates a new LSP to transmit the service.
Figure 7-28 Trail restoration
Recovery route
R4
R1
E
I
D
F
C
A
B
H
G
R2
R3
:ASON NE
:User Equipment
NOTE
In the case of the optical-layer ASON, a wavelength service must be in a channel from end to end. Hence,
the restoration trail with the same channel as that of the original trail may not be found during rerouting.
In this case, the ASON software supports the wavelength tunable function during rerouting. If an end-to-
end restoration trail with the same channel as that of the original trail cannot be found (for example, the
channel in a span is used), the ASON software will try to find another end-to-end restoration trail with
another channel so that the services can be restored to the greatest extent. Note that this function is available
only when the OTU board supports the wavelength tunable function.
7.5.3 SLA Classification of Services
The ASON network can provide services of different QoS to different clients.
The service level agreement (SLA) is used to classify services according to the service protection,
as listed in Table 7-5.
289