Cisco NCS 2000 Series Network Configuration Guide, Release 10.x.x
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This chapter explains the
network applications and topologies. The chapter also provides
network-level optical performance references.
Note
Unless otherwise specified, "ONS 15454" refers to both ANSI and ETSI
shelf assemblies.
Note
In this chapter, “OPT-BST”
refers to the OPT-BST, OPT-BST-E, OPT-BST-L cards, and to the OPT-AMP-L,
OPT-AMP-C, and OPT-AMP-17-C cards when they are provisioned in OPT-LINE
(optical booster) mode. “OPT-PRE” refers to the OPT-PRE card and to the
OPT-AMP-L, OPT-AMP-C, and OPT-AMP-17-C cards provisioned in OPT-PRE
(preamplifier) mode.
Note
In this chapter, "RAMAN-CTP" refers to the 15454-M-RAMAN-CTP card. "RAMAN-COP" refers to the 15454-M-RAMAN-COP card.
Chapter topics include:
Network Applications
Cisco
NCS Nodes can be provisioned for metro core DWDM network applications.
Metro core networks often include multiple spans and amplifiers, so the optical
signal-to-noise ratio (OSNR) is the limiting factor for channel performance.
Within DWDM
networks, the node uses a communications protocol, called Node Services
Protocol (NSP), to communicate with other nodes. NSP automatically updates
nodes whenever a change in the network occurs. Each
NCS node can identify:
Other
NCS nodes in the network
Different types of DWDM
networks
Whether the DWDM network is
complete or not
Network Topologies
The network topologies
include ring networks, linear networks, mesh networks, interconnected rings and
spurs.
Ring Networks
Ring networks support
any-to-any and mesh traffic topologies.
Any-to-Any Traffic Topology
The any-to-any traffic
topology contains only ROADM nodes with or without optical service channel
(OSC) regeneration or optical amplifier nodes. This topology potentially allows
you to route every wavelength from any source to any destination node inside
the network.
A mesh network can be native
or multiring. In a native mesh network, any combination of four-degree and
eight-degree mesh nodes can work together. Four-degree mesh nodes transmit an
optical signal in four directions, while an eight-degree mesh node transmits an
optical signal in eight directions. The intermediate nodes are ROADM nodes.
In a mesh node, all
wavelengths can be routed through four (four-degree mesh node) to eight
(eight-degree mesh node) different optical line termination ports using a
40-WXC-C, 80-WXC-C, or 40-SMR2-C card without any optical-electrical-optical
(OEO) regeneration. It is possible to combine 40-WSS-C/40-WSS-CE, 40-WXC-C,
40-SMR2-C, and 32WSS cards in the same mesh network without impacting system
performance. For nodes equipped with 32WSS cards, the maximum system capacity
is 32 channels. Terminal sites are connected to the mesh network as a spur.
Figure 2. Mesh Network
In a multiring mesh network,
several rings are connected with four-degree or eight-degree mesh nodes. The
intermediate ROADM nodes are equipped with MMU cards. All wavelengths can be
routed among two or more rings using a 40-WXC-C or 40-SMR2-C card without any
optical-electrical-optical (OEO) regeneration. As in a native mesh network, it
is possible to combine 40-WSS-C/40-WSS-CE, 40-WXC-C, 40-SMR2-C, and 32WSS cards
in the same multiring network without impacting system performance. For nodes
equipped with 32WSS cards, maximum system capacity is limited to 32 channels. A
terminal node is connected to a multiring node as a spur.
Interconnected Rings
The interconnected ring
configuration allows you to connect two different nodes using external ports to
allow traffic flow between different subnets. In the following figure, the main
ring consists of nodes R, R1, and R2 and the tributary ring consists of nodes
r, r1, and r2. It is possible to connect more than one tributary ring to the
main ring at the same point. Node R of the main ring can forward wavelengths to
the node r of the tributary ring and vice-versa.
Figure 3. Interconnected Rings
In the following figure
Node R is a colorless and omni-directional n-degree ROADM node.
Figure 4. Colorless and
Omni-directional n- Degree ROADM Node
Node R can also be a two-degree colorless ROADM node equipped with
80-WXC-C cards as seen in the following figure.
Figure 5. Colorless Two-Degree ROADM
Node
See the section,
Configuring Mesh DWDM Networks
for more information about colorless and omni-directional n-degree ROADM nodes
and two-degree colorless ROADM nodes.
Node r of the tributary
ring is a two-degree ROADM node equipped with 40-SMR1-C, 40-SMR2-C, 40-WSS-C,
or 40-WSS-CE cards. OTS PPCs are provisioned between the EAD ports of the
80-WXC-C card on node R and the EXP or ADD/DROP ports of the 40-SMR1-C,
40-SMR2-C, 40-WSS-C, or 40-WSS-CE cards on node r. All the nodes are managed by
different IP addresses.
Interconnected Ring Scenarios
In the following sections, three interconnected ring scenarios are given:
Scenario A: Interconnect Traffic from Tributary Ring to Main Ring without Local Add/Drop in the Tributary Ring
In scenario A-1, node R is a three-degree colorless and omni-directional ROADM node and node r is a two-degree 40-SMR1-c based
ROADM node. The EAD ports of the 80-WXC-C cards on node R are connected to the ADD/DROP ports of the 40-SMR1-C card on node
r. Traffic from node r can be routed to side A or B of node R. Traffic from side a cannot be added or dropped at node r but
can be routed to side b using the express path.
Figure 6. Interconnected Ring - Scenario A-1
In scenario A-2, node R is a two-degree colorless ROADM node and node r is a two-degree 40-SMR1-C based ROADM node. The EAD
ports of the 80-WXC-C cards on node R are connected to the ADD/DROP ports of the 40-SMR1-C card on node r. Traffic from node
r can be routed to one side of node R. For example, traffic can be routed from side a to side A or from side b to side B.
Traffic from side a cannot be added or dropped at node r but can be routed to side b using the express path.
Figure 7. Interconnected Ring - Scenario A-2
Scenario B: Interconnect Traffic from Tributary Ring to Main Ring with Local Add/Drop in the Tributary Ring
In scenario B-1, node R is a three-degree colorless and omni-directional ROADM node and node r is a hub node with two terminal
sides equipped with 40-SMR1-C or 40-WSS-C cards. The EAD ports of the 80-WXC-C cards on node R are connected to the EXP ports
of the 40-SMR1-C or40-WSS-C card on node r. Traffic from node r can be routed to side A or B of node R. Traffic local to the
tributary ring can be added or dropped at node r. For example, traffic from side a can be dropped at node r but cannot be
routed to side b since the EXP ports are not available.
Figure 8. Interconnected Ring - Scenario B-1
In scenario B-2, node R is a two-degree colorless ROADM node and node r is a hub node with two terminal sides equipped with
40-SMR1-C or 40-WSS-C cards. The EAD ports of the 80-WXC-C cards on node R are connected to the EXP ports of the 40-WSS-C
card on node r. Traffic from node r can be routed to one side of node R. For example, traffic can be routed from side a to
side A or from side b to side B. Traffic local to the tributary ring can be added or dropped at node r. For example, traffic
from side a can be dropped at node r but cannot be routed to side b since the EXP ports are not available.
Figure 9. Interconnected Ring - Scenario B-2
Scenario C: Interconnect Traffic Between Tributary Rings Using the Main Ring
In scenario C-1, nodes R1 and R2 are n-degree colorless and omni-directional ROADM nodes. Node r is a terminal site. The EXP
ports of the 40-SMR-1C card in node r are connected to the EAD ports of the 80-WXC-C card in nodes R1 and R2. Traffic from
node r is routed to side A and B of nodes R1 and R2. Traffic local to the tributary ring can be added or dropped at node r.
Figure 10. Interconnected Ring - Scenario C-1
In scenario C-2, node R is an n-degree colorless and omni-directional ROADM node with 2 omni-directional sides. Nodes r1 and
r2 are hub sites. The ADD/DROP ports of 40-SMR-1-C cards in node r1 and r2 are connected to the EAD ports of 80-WXC-C cards
in node R. Traffic can be routed from node r1 to node r2 through node R. Traffic local to the tributary ring can be added
or dropped at node r1 and r2.
Figure 11. Interconnected Ring - Scenario C-2
Spur Configuration
Remote terminal sites can be connected to the main network using a spur. In a spur configuration, the multiplexer (MUX) and
demultiplexer (DMX) units associated with one of the sides of node R in the main network are moved to the remote terminal
site T. This helps to aggregate traffic from the terminal site. The MUX and DMX units in terminal site T are connected to
node R with a single fibre couple. Node R is a n-degree ROADM node equipped with 40-SMR1-C, 40-SMR2-C, or 80-WXC-C cards.
Traffic from terminal site T can be routed to side A or side B on node R. Amplification on the spur link is not allowed. PSM
is not supported on terminal site T.
Figure 12. Spur
Spur Configuration Scenarios
In the following sections, three spur scenarios are provided:
Scenario A: Spur Configuration without
NCS
Chassis in Remote Terminal T
In the following figure, node
R is a two-degree ROADM node equipped with 40-SMR1-C card. The remote terminal
site T does not have a
NCS
chassis and is not shown in the network map in CTC. The terminal site is built
using passive MUX and DMX units. All OCHNC circuits originating from 40-SMR1-C
on Side A of node R to the remote terminal site are terminated on 40-SMR1-C
ADD/DROP ports.
Figure 13. Scenario A: Spur Without
NCS
Chassis in Remote Terminal T
Scenario B: Spur Configuration with Passive MUX and DMX Units in
Remote Terminal T
In the following figure, node
R is a two-degree ROADM node equipped with 40-SMR1-C card. The terminal site T
is built with a
NCS
chassis equipped with TXP units and passive MUX and DMX units. Terminal site T
is connected to node R on the network map in CTC. All OCHNC circuits
originating from 40-SMR1-C on Side A of node R to the remote site are
terminated on 40-SMR1-C ADD/DROP ports. OCHCC and OCHTRAIL circuits are
supported on the TXP units in terminal site T.
Figure 14. Scenario B: Spur With Passive
MUX and DMX Units in Remote Terminal T
Scenario C: Spur Configuration with Active MUX and DMX Units in
Remote Terminal T
In the following figure, node
R is a two-degree ROADM node equipped with 40-SMR1-C card. The terminal site T
is built with a
NCS
chassis equipped with TXP units and active MUX and DMX units. Terminal site T
is connected to node R on the network map in CTC. DCN extension is supported
between the ADD/DROP ports of 40-SMR1-C and the COM ports of the active MUX and
DMX units. OCHNC circuits are terminated on the CHAN ports of the MUX and DMX
units of terminal site T. OCHCC and OCHTRAIL circuits are supported on the TXP
units in terminal site T.
Figure 15. Scenario C: Spur with Active
MUX and DMX Units in Remote Terminal T
Network Topologies for the OPT-RAMP-C and OPT-RAMP-CE
Cards
The OPT-RAMP-C or OPT-RAMP-CE
card can be equipped in any of the following network topologies:
Open (hubbed) ring network
Multi-hubbed ring network
Closed (meshed) ring network
Any-to-any ring network
Linear network topology
Point-to-point linear network
topology
Multi-ring network
Mesh network
Hybrid network
For more information about the OPT-RAMP-C or OPT-RAMP-CE card, see the chapter, "Provision Optical Amplifier Cards" in the
Cisco NCS 2000 Series Line Card Configuration Guide.
Network Topologies for the PSM Card
The PSM card is supported in the following network topologies:
The PSM card in a channel protection configuration is supported in all network topologies except linear networks as it is
not possible to configure a working and protect path.
The PSM card in a multiplex section protection configuration is supported in linear point-to-point network topologies.
The PSM card in a line protection configuration is supported in the following network topologies:
Linear point-to-point in a single span network (if the OSC card is used).
Linear point-to-point multispan network when a DCN extension is used (on all spans). In this case, the maximum number of span
links can be divided into three according to the DCN extension optical safety requirements.
The PSM card in a standalone configuration is supported in all network topologies.
Optical Performance
This section provides optical
performance information for
NCS DWDM networks. The
performance data is a general guideline based upon the network topology, node
type, client cards, fiber type, number of spans, and number of channels. The
maximum number of nodes that can be in an
NCS DWDM network is 16.
The DWDM topologies and node types that are supported are shown in the
following table.
The automatic power control
(APC) feature performs the following functions:
Maintains constant per
channel power when desired or accidental changes to the number of channels
occur. Constant per channel power increases optical network resilience.
Compensates for optical
network degradation (aging effects).
Simplifies the installation
and upgrade of DWDM optical networks by automatically calculating the amplifier
setpoints.
Note
APC algorithms manage the
optical parameters of the OPT-BST, OPT-PRE, OPT-AMP-17-C, 32DMX, 40-DMX-C,
40-DMX-CE, 40-SMR1-C, 40-SMR2-C,
OPT-AMP-C, OPT-PRE,
OPT-BST-E, OPT-AMP-17C, OPT-EDFA-17, OPT-EDFA-24, 80-WXC-C, 40-WXC-C, 40-WSS,
32-WSS, 40-MUX, 40-DMX, RAMAN-CTP, RAMAN-COP, OPT-RAMP-C, OPT-RAMP-CE, EDRA-1,
EDRA-2, SMR-20, SMR-9, 16-WXC, and PSM cards.
Amplifier software uses a
control gain loop with fast transient suppression to keep the channel power
constant regardless of any changes in the number of channels. Amplifiers
monitor the changes to the input power and change the output power
proportionately according to the calculated gain setpoint. The shelf controller
software emulates the control output power loop to adjust for fiber
degradation. To perform this function, the controller card needs to know the
channel distribution, which is provided by a signaling protocol, and the
expected per channel power, which you can provision. The controller card
compares the actual amplifier output power with the expected amplifier output
power and modifies the setpoints if any discrepancies occur.
APC at the Amplifier Card Level
In constant gain mode, the amplifier power out control loop performs the following input and output power calculations, where
G represents the gain and t represents time.
Pout (t) = G * Pin (t) (mW)
Pout (t) = G + Pin (t) (dB)
In a power-equalized optical system, the total input power is proportional to the number of channels. The amplifier software
compensates for any variation of the input power due to changes in the number of channels carried by the incoming signal.
Amplifier software identifies changes in the read input power in two different instances, t1 and t2, as a change in the traffic
being carried. The letters m and n in the following formula represent two different channel numbers. Pin/ch represents the
input power per channel.
Pin (t1)= nPin/ch
Pin (t2) = mPin/ch
Amplifier software applies the variation in the input power to the output power with a reaction time that is a fraction of
a millisecond. This keeps the power constant on each channel at the output amplifier, even during a channel upgrade or a fiber
cut.
The per channel power and working mode (gain or power) are set by automatic node setup (ANS). The provisioning is conducted
on a per-side basis. A preamplifier or a booster amplifier facing Side i is provisioned using the Side i parameters present in the node database, where i - A, B, C, D, E, F, G, or H.
Starting from the expected per channel power, the amplifiers automatically calculate the gain setpoint after the first channel
is provisioned. An amplifier gain setpoint is calculated in order to make it equal to the loss of the span preceding the amplifier
itself. After the gain is calculated, the setpoint is no longer changed by the amplifier. Amplifier gain is recalculated every
time the number of provisioned channels returns to zero. If you need to force a recalculation of the gain, move the number
of channels back to zero.
APC at the Shelf Controller Layer
Amplifiers are managed
through software to control changes in the input power caused by changes in the
number of channels. The software adjusts the output total power to maintain a
constant per channel power value when the number of input channel changes.
Changes in the network
characteristics have an impact on the amplifier input power. Changes in the
input power are compensated for only by modifying the original calculated gain,
because input power changes imply changes in the span loss. As a consequence,
the gain to span loss established at amplifier start-up is no longer satisfied,
as shown in the following figure.
Figure 16. Using Amplifier Gain
Adjustment to Compensate for System Degradation
In the figure above, Node 1 and Node 2 are
equipped with booster amplifiers and preamplifiers. The input power received at
the preamplifier on Node 2 (Pin2) depends on the total power launched by the
booster amplifier on Node1, Pout1(n) (where n is the number of channels), and
the effect of the span attenuation (L) between the two nodes. Span loss changes
due to aging fiber and components or changes in operating conditions. The power
into Node 2 is given by the following formula:
Pin2 = LPout1(n)
The phase gain of the
preamplifier on Node 2 (GPre-2) is set during provisioning in order to
compensate for the span loss so that the Node 2 preamplifier output power
(Pout-Pre-2) is equal to the original transmitted power, as represented in the
following formula:
Pout-Pre-2 = L x GPre-2 x
Pout1(n)
In cases of system
degradation, the power received at Node 2 decreases due to the change of span
insertion loss (from L to L'). As a consequence of the preamplifier gain
control working mode, the Node 2 preamplifier output power (Pout-Pre-2) also
decreases. The goal of APC at the shelf controller layer is simply to detect if
an amplifier output change is needed because of changes in the number of
channels or to other factors. If factors other than changes in the number of
channels occur, APC provisions a new gain at the Node 2 preamplifier (GPre-2')
to compensate for the new span loss, as shown in the formula:
Generalizing on the above
relationship, APC is able to compensate for system degradation by adjusting
working amplifier gain or variable optical attenuation (VOA) and to eliminate
the difference between the power value read by the photodiodes and the expected
power value. The expected power values are calculated using:
Provisioned per channel power
value
Channel distribution (the
number of express, add, and drop channels in the node)
ASE estimation
Channel distribution is
determined by the sum of the provisioned and failed channels. Information about
provisioned wavelengths is sent to APC on the applicable nodes during circuit
creation. Information about failed channels is collected through a signaling
protocol that monitors alarms on ports in the applicable nodes and distributes
that information to all the other nodes in the network.
ASE calculations purify the
noise from the power level reported from the photodiode. Each amplifier can
compensate for its own noise, but cascaded amplifiers cannot compensate for ASE
generated by preceding nodes. The ASE effect increases when the number of
channels decreases; therefore, a correction factor must be calculated in each
amplifier of the ring to compensate for ASE build-up.
APC is a network-level
feature that is distributed among different nodes. An APC domain is a set of
nodes that is controlled by the same instance of APC at the network level. An
APC domain optically identifies a portion of the network that can be
independently regulated. An optical network can be divided into several
different domains, with the following characteristics:
Every domain is terminated by
two node sides. The node sides terminating domains are:
Terminal node (any type)
ROADM node
Cross-connect (XC)
termination mesh node
Line termination mesh node
APC domains are shown in both
Cisco Transport Controller (CTC) and Transaction Language One (TL1).
In CTC, domains are shown in
the network view and reported as a list of spans. Each span is identified by a
node/side pair, for example:
APC Domain Node_1 Side A,
Node_4 Side B + Span 1: Node_1 Side A, Node_2 Side B + Span 2: Node_2 Side A,
Node_3 Side B + Span 3: Node_3 Side A, Node_4 Side B
APC domains are not refreshed
automatically; instead, they are refreshed using a Refresh button.
Inside a domain, the APC algorithm designates a primary node that is responsible for starting APC hourly or every time a new
circuit is provisioned or removed. Every time the primary node signals APC to start, gain and VOA setpoints are evaluated
on all nodes in the network. If corrections are needed in different nodes, they are always performed sequentially following
the optical paths starting from the primary node.
APC corrects the power level
only if the variation exceeds the hysteresis thresholds of +/– 0.5 dB. Any
power level fluctuation within the threshold range is skipped since it is
considered negligible. Because APC is designed to follow slow time events, it
skips corrections greater than 3 dB. This is the typical total aging margin
that is provisioned during the network design phase. After you provision the
first channel or the amplifiers are turned up for the first time, APC does not
apply the 3 dB rule. In this case, APC corrects all the power differences to
turn up the node.
To avoid large power
fluctuations, APC adjusts power levels incrementally. The maximum power
correction is +/– 0.5 dB. This is applied to each iteration until the optimal
power level is reached. For example, a gain deviation of 2 dB is corrected in
four steps. Each of the four steps requires a complete APC check on every node
in the network. APC can correct up to a maximum of 3 dB on an hourly basis. If
degradation occurs over a longer time period, APC compensates for it by using
all margins that you provision during installation.
If no margin is available,
adjustments cannot be made because setpoints exceed the ranges. APC
communicates the event to CTC, Cisco Transport Manager (CTM), and TL1 through
an APC Fail condition. APC clears the APC fail condition when the setpoints
return to the allowed ranges.
APC can be manually disabled.
In addition, APC automatically disables itself when:
An Hardware Fail (HF) alarm
is raised by any card in any of the domain nodes.
A Mismatch Equipment Alarm
(MEA) is raised by any card in any of the domain nodes.
An Improper Removal
(IMPROPRMVL) alarm is raised by any card in any of the domain nodes.
Gain Degrade (GAIN-HDEG),
Power Degrade (OPWR-HDEG), and Power Fail (PWR-FAIL) alarms are raised by the
output port of any amplifier card in any of the domain nodes.
A VOA degrade or fail alarm
is raised by any of the cards in any of the domain nodes.
The signaling protocol
detects that one of the APC instances in any of the domain nodes is no longer
reachable.
The APC state
(Enable/Disable) is located on every node and can be retrieved by the CTC or
TL1 interface. If an event that disables APC occurs in one of the network
nodes, APC is disabled on all the other nodes and the APC state changes to
DISABLE - INTERNAL. The disabled state is raised only by the node where the
problem occurred to simplify troubleshooting.
APC raises the following
minor, non-service-affecting alarms at the port level in CTC, TL1, and Simple
Network Management Protocol (SNMP):
APC Out of Range—APC cannot
assign a new setpoint for a parameter that is allocated to a port because the
new setpoint exceeds the parameter range.
APC Correction Skipped—APC
skipped a correction to one parameter allocated to a port because the
difference between the expected and current values exceeds the +/– 3 dB
security range.
APC Disabled—APC is disabled,
either by a user or internal action.
After the error condition is
cleared, the signaling protocol enables APC on the network and the APC DISABLE
- INTERNAL condition is cleared. Because APC is required after channel
provisioning to compensate for ASE effects, all optical channel network
connection (OCHNC) and optical channel client connection (OCHCC) circuits that
you provision during the disabled APC state are kept in the Out-of-Service and
Autonomous, Automatic In-Service (OOS-AU,AINS) (ANSI) or
Unlocked-disabled,automaticInService (ETSI) service state until APC is enabled.
OCHNCs and OCHCCs automatically go into the In-Service and Normal (IS-NR)
(ANSI) or Unlocked-enabled (ETSI) service state only after APC is enabled.
APC in a Raman Node with Post-Amplifiers
After the Raman gain is calculated and the Raman and OSC links are turned up, APC performs the following sequence of events:
The line amplifier that is downstream of the OPT-RAMP-C or OPT-RAMP-CE card is the first card that the APC regulates. The
line amplifier is configured as OPT-PRE in ROADM nodes or as OPT-LINE in OLA nodes.
After Automatic Power Reduction (APR) is implemented, the working mode of the line amplifier is forced to Control Power and
remains in the same mode until all the node regulations are complete. This ensures that the calculation of the Gain setpoint
is accurate during Raman node internal regulations. The amplifier signal output power is regulated using the Power (LINE-TX
port) setpoint.
The APC changes the Gain setpoint of the embedded EDFA to reach the value that is equal to Power (DC-TX port) value multiplied
by the number of active channels.
The APC can set the Gain setpoint of the embedded EDFA (GEDFA) in the following ranges:
OPT-RAMP-C 10 dB < GEDFA < 18 dB
OPT-RAMP-CE 7 dB < GEDFA < 13 dB
The internal VOA is set to 0 dB on the DC-TX port. The VOA attenuation is set to zero because the actual DCU insertion loss
is unknown until the optical payload is transmitted to the card. Therefore a proper attenuation setpoint cannot be estimated.
When the attenuation value is set to 0 dB, it ensures that the system turns up in any circumstance.
After the GEDFA is set, APC regulates the power on the VOA (DC-TX port) of the OPT-RAMP-C or OPT-RAMP-CE card to match the
target Power (COM-TX port) value, and accounts for the actual DCU loss.
After Steps 2 and 3 are completed, the optical power received on the line amplifier that is downstream of the OPT-RAMP-C or
OPT-RAMP-CE card becomes fully regulated and stable. The Raman tilt and GEDFA tilt are fixed. The APC regulates the value
of the Total Power on the LINE-TX port of the line amplifier and accounts for the ASE noise contribution.
After the value of the total power on the line amplifier becomes a stable value, APC stops the regulations and the automatic
gain calculation procedure is completed on the line amplifier card. The TCC checks if the gain setpoint is within range and
eventually changes the working mode of the OPT-RAMP-C or OPT-RAMP-CE card to Gain Control mode.
Note
If the value of the Raman Total Power was manually provisioned or set by ANS instead of the Raman installation wizard, a fiber
cut recovery procedure is automatically performed, before APC regulation.
APC in a Raman Node without Post-Amplifiers
After the Raman gain is calculated and the Raman and OSC links are turned up, APC performs the following sequence of events:
The APC adjusts the VOA attenuation of the OPT-RAMP-C or OPT-RAMP-CE card if the Total Power (LINE-TX port) does not match
the expected value that is equal to the maximum power multiplied by the number of active channels. The VOA attenuation value
on the OPT-RAMP-C or OPT-RAMP-CE cards is set to 15 dB. This value ensures that the system turns up in any circumstance.
If a short span is used, the embedded EDFA in the downstream node receives excessive input power and is unable to maintain
proper per channel power value on its output port as the number of channels increase. The APC detects output power saturation
on the EDFA of the downstream node and increases the value of the VOA attenuation on the upstream node thereby reducing the
Power (LINE-TX port) value.
Managing APC
The APC status is indicated by
four APC states shown in the node view status area:
Enabled—APC is enabled.
Disabled—APC was disabled
manually by a user.
Disable - Internal—APC has
been automatically disabled for an internal cause.
Not Applicable—The node is
provisioned to Not DWDM, which does not support APC.
You can view the APC
information and disable and enable APC manually on the Maintenance >
DWDM > APC tab.
Caution
When APC is disabled, aging
compensation is not applied and circuits cannot be activated. Do not disable
APC unless it is required for specific maintenance or troubleshooting tasks.
Always enable APC as soon as the tasks are completed.
The APC subtab provides the following
information:
Position—The slot number,
card, and port for which APC information is shown.
Last Modification—Date and
time APC parameter setpoints were last modified.
Parameter—The parameter that
APC last modified.
Last Check—Date and time APC
parameter setpoints were last verified.
Side—The side where the APC
information for the card and port is shown.
State—The APC state.
A wrong use of maintenance
procedures (for example, the procedures to be applied in case of fiber cut
repair) can lead the system to raise the APC Correction Skipped alarm. The APC
Correction Skipped alarm strongly limits network management (for example, a new
circuit cannot be turned into IS). The Force APC Correction button helps to
restore normal conditions by clearing the APC Correction Skipped alarm.
The Force APC Correction
button must be used under the Cisco TAC surveillance since its misuse can lead
to traffic loss.
The Force APC Correction
button is available in the
Card View >
Maintenance >
APC tab pane in CTC for
the following cards:
OPT-PRE
OPT-BST-E
OPT-BST
OPT-AMP-C
OPT-AMP-17C
OPT-EDFA-17
OPT-EDFA-24
40-SMR1-C
40-SMR2-C
This feature is not available
for the TL1 interface.
The APC Gain Limit Check can be enabled or disabled for amplifiers in the Card View > Maintenance > APC tab in or through TL1. The gain check is performed automatically every hour or whenever APC runs. The default value of gain
limit check is Disabled.
The GAIN-NEAR-LIMIT alarm is raised when APC regulates an amplifier gain and its value reaches +2 or ‐2 dB, within the minimum
and maximum gain range. For more information, see the GAIN-NEAR-LIMIT alarm.
Power Side Monitoring
DWDM nodes allow you to view
bar graphs of the input and output spectrum on each optical side of the node in
the Maintenance > DWDM > Side Power Monitoring tab. When you place the
mouse over each wavelength in the bar chart, the power level, wavelength, and
wavelength type are displayed. This feature is available on nodes that are
installed with cards with Optical Channel Monitoring (OCM) capability.
The Side Power Monitoring
panel is divided into Optical Side
X subtabs, where
X is the optical side.
The number of subtabs is equal to the number of optical sides in the node. Each
subtab displays two bar graphs.
The IN bar graph displays the
optical spectrum at the input port (LINE-RX) of the side in the direction from
the fiber to the node provided the OCM functionality is available on this port
else the graph displays the aggregate signal spectral distribution on the first
port in the signal flow (indicated in the title of the bar chart) that is
downstream of the LINE-RX port where an OCM measurement is available (For
example, in node using a booster and a 40-SMR1-C card, the measurement is done
on the EXP port of the 40-SMR1-C card).
The OUT bar graph displays
the optical spectrum at the output port (LINE-TX) of the side in the direction
from the node to the fiber provided the OCM functionality is available on this
port else the graph displays the aggregate signal spectral distribution on the
first port (indicated in the title of the bar chart) that is upstream of the
LINE-TX port where an OCM measurement is available.
Note
Depending on the side layout,
the LINE-TX port (output) and the LINE-RX port (input) of the card facing the
fiber cannot measure the optical spectrum in a reliable manner if the OCM
functionality is not available on these ports.
When you place the mouse over
each wavelength in the bar chart, the power level, wavelength, and the
wavelength type (local ADD/DROP or EXPRESS) are displayed as a ScreenTip.
IN graph: The Screen Tip
displays the destination side of each wavelength. The wavelength is either
dropped locally or expressed to another side.
OUT graph: The Screen Tip
displays the source side of each wavelength. The wavelength is either added
locally or expressed from another side.
Span Loss Verification
Span loss measurements can be
performed from the Maintenance > DWDM > WDM Span Check tab. The CTC span
check compares the far-end OSC power with the near-end OSC power. A Span Loss
Out of Range condition is raised when the measured span loss is higher than the
maximum expected span loss. It is also raised when the measured span loss is
lower than the minimum expected span loss and the difference between the
minimum and maximum span loss values is greater than 1 dB. The minimum and
maximum expected span loss values are calculated by Cisco TransportPlanner for
the network and imported into CTC. However, you can manually change the minimum
and expected span loss values.
CTC span loss measurements
provide a quick span loss check and are useful whenever changes to the network
occur, for example after you install equipment or repair a broken fiber. CTC
span loss measurement resolutions are:
+/– 1.5 dB for measured span
losses between 0 and 25 dB
+/– 2.5 dB for measured span
losses between 25 and 38 dB
For span loss
measurements with higher resolutions, an optical time domain reflectometer
(OTDR) must be used.
Span Loss Measurements on Raman Links
Span loss measurement when Raman amplification is active is less accurate than a standard link as it is based on a mathematical
formula that uses the Raman noise and Raman gain.
Span loss on a Raman link is measured in the following states:
Automatically during Raman link setup (without Raman amplification)
Automatically during fiber cut restore (without Raman amplification)
Periodically or upon request (with Raman amplification)
CTC reports three values in the Maintenance > DWDM > WDM Span Check tab:
Current Span Measure with Raman—Estimated span loss with Raman pump turned ON.
Wizard Span Measure with Raman Off—Span loss with Raman pump turned OFF, during Raman installation.
Last Span Measure with Raman—Span loss after a fiber cut restoration procedure.
Measurements are performed automatically on an hourly basis.
A Span Loss Out of Range condition is raised under the following conditions:
Span loss is greater than the maximum expected span loss + resolution
Span loss is less than the minimum expected span loss – resolution
The minimum and maximum expected span loss values are calculated by Cisco Transport Planner for the network and imported into
CTC. However, you can manually change the minimum and maximum expected span loss values.
Note
During Raman installation using a wizard, the Span Loss Out of Range alarm is not raised when the out of range condition is
raised. In such a case, the wizard fails and an error message is displayed, and the span is not tuned.
CTC span loss measurements provide a quick span loss check and are useful whenever changes to the network occur, for example
after you install equipment or repair a broken fiber. CTC span loss measurement resolutions are:
+/– 1.5 dB for span loss measurements between 0 and 26 dB
+/– 2.0 dB for span loss measurements between 26 and 31 dB
+/– 3.0 dB for span loss measurements between 31 and 34 dB
+/– 4.0 dB for span loss measurements between 34 and 36 dB
Network Optical Safety
If a fiber break occurs on
the network, automatic laser shutdown (ALS) automatically shuts down the OSCM
and OSC-CSM OSC laser output power and the optical amplifiers contained in the
OPT-BST, OPT-BST-E,
OPT-AMP-C,
OPT-AMP-17-C, OPT-RAMP-C, OPT-RAMP-CE, EDRA-1-26, EDRA-1-35, EDRA-2-26,
EDRA-2-35, 40-SMR1-C, and 40-SMR2-C cards, and the TX VOA in the protect path
of the PSM card (in line protection configuration only). (Instead, the PSM
active path will use optical safety mechanism implemented by the booster
amplifier or OSC-CSM card that are mandatory in the line protection
configuration.)
The Maintenance > ALS tab
in CTC card view provide the following ALS management options for OSCM,
OSC-CSM, OPT-BST, OPT-BST-E,
OPT-AMP-C,
OPT-AMP-17-C, OPT-RAMP-C, OPT-RAMP-CE, EDRA-1-26, EDRA-1-35, EDRA-2-26,
EDRA-2-35, 40-SMR1-C, 40-SMR2-C, and PSM (on the protect path, only in line
protection configuration) cards:
Disable—ALS is off. The OSC
laser transmitter and optical amplifiers are not automatically shut down when a
traffic outage loss of signal (LOS) occurs.
Auto Restart—ALS is on. The
OSC laser transmitter and optical amplifiers automatically shut down when
traffic outages (LOS) occur. It automatically restarts when the conditions that
caused the outage are resolved. Auto Restart is the default ALS provisioning
for OSCM, OSC-CSM, OPT-BST, OPT-BST-E,
OPT-AMP-C,
OPT-AMP-17-C, OPT-RAMP-C, OPT-RAMP-CE, EDRA-1-26, EDRA-1-35, EDRA-2-26,
EDRA-2-35, 40-SMR1-C, 40-SMR2-C, and PSM (on the protect path, only in line
protection configuration) cards.
Manual Restart—ALS is on. The
OSC laser transmitter and optical amplifiers automatically shut down when
traffic outages (LOS) occur. However, the laser must be manually restarted when
conditions that caused the outage are resolved.
Manual Restart for
Test—Manually restarts the OSC laser transmitter and optical amplifiers for
testing.
OSRI
When Optical Safety Remote Interlock (OSRI) is set to ON, the laser is turned off. If OSRI is set to OFF, the laser is turned on using the ALS mode that is configured. The OSRI is supported on OSCM, OSC-CSM, TNCx, OPT-PRE, OPT-BST,
OPT-BST-E, OPT-AMP-C, OPT-AMP-17-C, OPT-EDFA-17, OPT-EDFA-24, RAMAN-CTP, RAMAN-COP, OPT-RAMP-C, OPT-RAMP-CE, EDRA-1-26, EDRA-1-35,
EDRA-2-26, EDRA-2-35, 40-SMR1-C, 40-SMR2-C, and PSM cards.
Automatic Laser Shutdown
When ALS is enabled on OPT-BST, OPT-BST-E, OPT-EDFA-17, OPT-EDFA-24, RAMAN-CTP, RAMAN-COP, SMR-20, SMR-9, OPT-AMP-C, OPT-AMP-17-C,
OPT-RAMP-C, OPT-RAMP-CE, EDRA-1-26, EDRA-1-35, EDRA-2-26, EDRA-2-35, 40-SMR1-C, 40-SMR2-C, PSM (on the protect path, only
in line protection configuration), OSCM, OSC-CSM, TNC, TNCE, and TNCS/TNCS-O cards, a network safety mechanism will occur in the event of a system failure. ALS provisioning is also provided on the transponder
(TXP) and muxponder (MXP) cards. However, if a network uses ALS-enabled OPT-BST, OPT-BST-E, OPT-AMP-C, OPT-AMP-17-C, OPT-RAMP-C,
OPT-RAMP-CE, EDRA-1-26, EDRA-1-35, EDRA-2-26, EDRA-2-35, 40-SMR1-C, 40-SMR2-C, PSM (on the protect path, only in line protection
configuration), OSCM, and OSC-CSM cards, ALS does not need to be enabled on the TXP cards or MXP cards. ALS is disabled on
TXP and MXP cards by default and the network optical safety is not impacted.
If TXP and MXP cards are
connected directly to each other without passing through a DWDM layer, ALS
should be enabled on them. The ALS protocol goes into effect when a fiber is
cut, enabling some degree of network point-to-point bidirectional traffic
management between the cards.
If ALS is disabled on the
OPT-BST, OPT-BST-E,
OPT-AMP-C, OPT-AMP-17-C, OPT-RAMP-C,
OPT-RAMP-CE, 40-SMR1-C, 40-SMR2-C, PSM (on the protect path, only in line
protection configuration), OSCM, and OSC-CSM cards (the DWDM network), ALS can
be enabled on the TXP and MXP cards to provide laser management in the event of
a fiber break in the network between the cards.
Automatic Power Reduction
Automatic power reduction
(APR) is controlled by the software and is not user configurable. During
amplifier restart after a system failure, the amplifier (OPT-BST, for example)
operates in pulse mode and an APR level is activated so that the Hazard Level 1
power limit is not exceeded. This is done to ensure personnel safety.
When a system failure occurs
(cut fiber or equipment failure, for example) and ALS Auto Restart is enabled,
a sequence of events is placed in motion to shut down the amplifier laser
power, then automatically restart the amplifier after the system problem is
corrected. As soon as a loss of optical payload and OSC is detected at the far
end, the far-end amplifier shuts down. The near-end amplifier then shuts down
because it detects a loss of payload and the OSC shuts down due to the far-end
amplifier shutdown. At this point, the near end attempts to establish
communication to the far end using the OSC laser transmitter. To do this, the
OSC emits a two-second pulse at very low power (maximum of 0 dBm) and waits for
a similar two-second pulse in response from the far-end OSC laser transmitter.
If no response is received within 100 seconds, the near end tries again. This
process continues until the near end receives a two-second response pulse from
the far end, indicating the system failure is corrected and full continuity in
the fiber between the two ends exists.
After the OSC communication
is established, the near-end amplifier is configured by the software to operate
in pulse mode at a reduced power level. It emits a nine-second laser pulse with
an automatic power reduction to +8 dBm. (For 40-SMR1-C and 40-SMR2-C cards, the
pulse is not +8 dBm but it is the per channel power setpoint.) This level
assures that Hazard Level 1 is not exceeded, for personnel safety, even though
the establishment of successful OSC communication is assurance that any broken
fiber is fixed. If the far-end amplifier responds with a nine-second pulse
within 100 seconds, both amplifiers are changed from pulse mode at reduced
power to normal operating power mode.
For a direct connection
between TXP or MXP cards, when ALS Auto Restart is enabled and the connections
do not pass through a DWDM layer, a similar process takes place. However,
because the connections do not go through any amplifier or OSC cards, the TXP
or MXP cards attempt to establish communication directly between themselves
after a system failure. This is done using a two-second restart pulse, in a
manner similar to that previously described between OSCs at the DWDM layer. The
power emitted during the pulse is below Hazard Level 1.
APR is also implemented on
the PSM card (on the protect path, only in line protection configuration). In
the PSM line protection configuration, when a system failure occurs on the
working path (cut fiber or equipment failure, for example), the ALS and APR
mechanisms are implemented by the booster amplifier or the OSC-CSM card.
Alternately, when a system failure occurs on the protect path, and ALS Auto
Restart is enabled on the PSM card, a sequence of events is placed in motion to
shut down the TX VOA on the protect path, and then automatically restart it
after the system failure is corrected. During protect path restart, the TX VOA
on the protect path operates in pulse mode and limits the power to maximum
+8 dBm so that the Hazard Level 1 power limit is not exceeded on protect TX
path.
When ALS is disabled, the
warning Statement 1056 is applicable.
Warning
Invisible laser radiation could be emitted from the end of the unterminated fiber cable or connector. Do not stare into the
beam directly with optical instruments. Viewing the laser output with certain optical instruments (for example, eye loupes,
magnifiers, and microscopes) within a distance of 100 mm could pose an eye hazard. Statement 1056
Note
If you must disable ALS,
verify that all fibers are installed in a restricted location. Enable ALS
immediately after finishing the maintenance or installation process.
Note
For the line amplifier to
start up automatically, disable the ALS on the terminal node that is
unidirectional.
Network Optical Safety on OPT-RAMP-C, OPT-RAMP-CE, EDRA-1-xx,
and EDRA-2-xx Cards
Optical safety on the
OPT-RAMP-C, OPT-RAMP-CE, EDRA-1-xx, and EDRA-2-xx cards is implemented in the
RAMAN-TX and COM-TX ports. RAMAN-TX will report safety settings associated to
the Raman pump while the COM-TX port will report safety settings associated
with the embedded EDFA.
RAMAN-TX Settings on Raman Pump
The Raman pump is
automatically turned off as soon as the LOS alarm is detected on the LINE-RX
port. The Raman pump is automatically turned on at APR power every 100 secs for
a duration of 9 seconds at a pulse power of at 8 dBm, as soon as the LINE-RX
port is set to IS-NR/unlocked-enabled.
Note
Optical safety cannot be
disabled on the OPT-RAMP-C , OPT-RAMP-CE, EDRA-1-xx, and EDRA-2-xx cards.
Optical safety cannot be disabled on OSCM cards when connected to a OPT-RAMP-C
or OPT-RAMP-CE card.
The system periodically
verifies if the signal power is present on the LINE-RX port. If signal power is
present, the following occurs:
Pulse duration is extended.
Raman pumps are turned on at
APR power, if the laser was shut down.
The Raman power is then moved
to setpoint if power is detected for more than 10 seconds on OPT-RAMP-C and
OPT-RAMP-CE cards (15 seconds on EDRA-1-xx and EDRA-2-xx cards). During
Automatic Laser Restart (ALR) the safety is enabled. The laser is automatically
shut down if LOS is detected on the receiving fiber. In general Raman pump
turns on only when Raman signals are detected. However, the Raman pump can be
configured to turn on to full power even when OSC power is detected for more
than 9 seconds on OSC-RX port on OPT-RAMP-C and OPT-RAMP-CE cards.
COM-TX Safety Setting on EDFA (OPT-RAMP-C and
OPT-RAMP-CE)
EDFA is shutdown
automatically under the following conditions:
The Raman pumps shut down.
An LOS-P alarm is detected on
the COM-RX port.
If EDFA was shut down because
of Raman pump shut down, the EDFA restarts by automatically turning on the EDFA
lasers as soon as the Raman loop is closed.
Pulse duration: 9 seconds
Pulse power: 8 dB (maximum
APR power foreseen by safety regulation)
Exit condition: Received
power detected on the DC-RX port at the end of APR pulse. If power is detected
on DC-RX (so DCU is connected) EDFA moves to set-point; otherwise, it keeps 9
dB as the output power at restart
EDFA moves to the power
setpoint when power is detected on the DC-RX port.
If EDFA was shutdown because
of an LOS-P alarm. The EDFA restarts by automatically turning on the EDFA laser
as soon as an LOS-P alarm on the COM-RX port is cleared, and the Raman loop is
closed.
Pulse duration: 9 seconds
Pulse power: 8 dB (maximum
APR power foreseen by safety regulation)
Exit condition: Received
power detected on the LINE-RX port at the end of the APR pulse
All users must be properly
trained on laser safety hazards in accordance with IEC 60825-2, or ANSI Z136.1.
Fiber Cut Scenarios
In the following paragraphs,
ALS scenarios are given:
Scenario 1: Fiber Cut in Nodes Using OPT-BST/OPT-BST-E
Cards
The following figure shows
nodes using OPT-BST/OPT-BST-E cards with a fiber cut between them.
Figure 17. Nodes Using OPT-BST/OPT-BST-E
Cards
Two photodiodes at Node B monitor the received signal strength for the optical payload and OSC signals. When the fiber is
cut, an LOS is detected at both of the photodiodes. The AND function then indicates an overall LOS condition, which causes
the OPT-BST/OPT-BST-E transmitter, OPT-PRE transmitter, and OSCM lasers to shut down. This in turn leads to an LOS for both
the optical payload and OSC at Node A, which causes Node A to turn off the OSCM, OPT-PRE transmitter, and OPT-BST/OPT-BST-E
transmitter lasers. For more information on alarms, see the Cisco NCS 2000 Series Troubleshooting Guide. The sequence of events after a fiber cut is as follows (refer to the numbered circles in the figure above):
Fiber is cut.
The Node B power monitoring
photodiode detects a Loss of Incoming Payload (LOS-P) on the OPT-BST/OPT-BST-E
card.
On the OPT-BST/OPT-BST-E
card, the simultaneous LOS-O and LOS-P detection triggers a command to shut
down the amplifier. CTC reports an LOS alarm (loss of continuity), while LOS-O
and LOS-P are demoted.
The OPT-BST/OPT-BST-E card
amplifier is shut down within one second.
The OSCM laser is shut down.
The OPT-PRE card
automatically shuts down due to a loss of incoming optical power.
The Node A power monitoring
photodiode detects a LOS-O on the OPT-BST/OPT-BST-E card and the OSCM card
detects a LOS (OC3) at the SONET layer.
The Node A power monitoring
photodiode detects a LOS-P on the OPT-BST/OPT-BST-E card.
On the OPT-BST/OPT-BST-E, the
simultaneous LOS-O and LOS-P detection triggers a command to shut down the
amplifier. CTC reports an LOS alarm (loss of continuity), while LOS-O and LOS-P
are demoted.
The OPT-BST/OPT-BST-E card
amplifier is shut down within one second.
The OSCM laser is shut down.
The Node A OPT-PRE card
automatically shuts down due to a loss of incoming optical power.
When the fiber is repaired,
either an automatic or manual restart at the Node A OPT-BST/OPT-BST-E
transmitter or at the Node B OPT-BST/OPT-BST-E transmitter is required. A
system that has been shut down is reactivated through the use of a restart
pulse. The pulse is used to signal that the optical path has been restored and
transmission can begin. For example, when the far end, Node B, receives a
pulse, it signals to the Node B OPT-BST/OPT-BST-E transmitter to begin
transmitting an optical signal. The OPT-BST/OPT-BST-E receiver at Node A
receives that signal and signals the Node A OPT-BST/OPT-BST-E transmitter to
resume transmitting.
Note
During a laser restart pulse,
APR ensures that the laser power does not exceed Class 1 limits. See the
section,
“Automatic
Power Reduction” for more information about APR.
Scenario 2: Fiber Cut in Nodes Using OSC-CSM Cards
The following figure shows
nodes using OSC-CSM cards with a fiber cut between them.
Figure 18. Nodes Using OSC-CSM
Cards
Two photodiodes at the Node B OSC-CSM card monitor the received signal strength for the received optical payload and OSC signals.
When the fiber is cut, LOS is detected at both of the photodiodes. The AND function then indicates an overall LOS condition,
which causes the Node B OSC laser to shut down and the optical switch to block traffic. This in turn leads to LOS for both
the optical payload and OSC signals at Node A, which causes Node A to turn off the OSC laser and the optical switch to block
outgoing traffic. For more information on alarms, see the Cisco NCS 2000 Series Troubleshooting Guide. The sequence of events after a fiber cut is as follows (refer to the numbered circles in the figure above):
Fiber is cut.
The Node B power monitoring
photodiode detects a LOS-P on the OSC-CSM card.
On the OSC-CSM, the
simultaneous LOS-O and LOS-P detection triggers a change in the position of the
optical switch. CTC reports a LOS alarm (loss of continuity), while LOS-O and
LOS-P are demoted.
The optical switch blocks
outgoing traffic.
The OSC laser is shut down.
The Node A power monitoring
photodiode detects a LOS-O on the OSC-CSM card.
The Node A power monitoring
photodiode detects a LOS-P on the OSC-CSM card.
On the OSC-CSM, the
simultaneous LOS-O and LOS-P detection triggers a change in the position of the
optical switch. CTC reports a LOS alarm (loss of continuity), while LOS-O and
LOS-P are demoted.
The OSC laser is shut down.
The optical switch blocks
outgoing traffic.
When the fiber is repaired,
either an automatic or manual restart at the Node A OSC-CSM card OSC or at the
Node B OSC-CSM card OSC is required. A system that has been shut down is
reactivated through the use of a restart pulse. The pulse indicates the optical
path is restored and transmission can begin. For example, when the far-end Node
B receives a pulse, it signals to the Node B OSC to begin transmitting its
optical signal and for the optical switch to pass incoming traffic. The OSC-CSM
at Node A then receives the signal and tells the Node A OSC to resume
transmitting and for the optical switch to pass incoming traffic.
Scenario 4: Fiber Cut in Nodes Using
OPT-AMP-C, OPT-AMP-17-C (OPT-LINE Mode),
40-SMR1-C, or 40-SMR2-C Cards
The following figure shows
nodes using
OPT-AMP-C, OPT-AMP-17-C (in OPT-LINE mode),
40-SMR1-C, or 40-SMR2-C cards with a fiber cut between them.
Note
A generic reference to the
OPT-AMP card refers to the
OPT-AMP-17-C,
OPT-AMP-C, 40-SMR1-C, or 40-SMR2-C cards.
Figure 19. Nodes Using OPT-AMP
Cards
Two photodiodes at Node B monitor the received signal strength for the optical payload and OSC signals. When the fiber is
cut, an LOS is detected at both of the photodiodes. The AND function then indicates an overall LOS condition, which causes
the OPT-AMP card amplifier transmitter and OSCM card OSC lasers to shut down. This in turn leads to an LOS for both the optical
payload and OSC at Node A, which causes Node A to turn off the OSCM card OSC and OPT-AMP card amplifier lasers. For more information
on alarms, see the Cisco NCS 2000 Series Troubleshooting Guide. The sequence of events after a fiber cut is as follows (refer to the numbered circles in the figure above):
Fiber is cut.
The Node B power monitoring
photodiode detects an LOS-P on the OPT-AMP card.
On the OPT-AMP card, the
simultaneous LOS-O and LOS-P detection triggers a command to shut down the
amplifier. CTC reports an LOS alarm (loss of continuity), while LOS-O and LOS-P
are demoted.
The OPT-AMP card amplifier is
shut down within one second.
The OSCM card laser is shut
down.
The Node A power monitoring
photodiode detects an LOS-O on the OPT-AMP card and the OSCM card detects an
LOS (OC3) at the SONET layer.
The Node A power monitoring
photodiode detects an LOS-P on the OPT-AMP card.
On the OPT-AMP card, the
simultaneous LOS-O and LOS-P detection triggers a command to shut down the
amplifier. CTC reports an LOS alarm (loss of continuity), while LOS-O and LOS-P
are demoted.
The OPT-AMP card amplifier is
shut down within one second.
The OSCM card laser is shut
down.
When the fiber is repaired,
either an automatic or manual restart at the Node A OPT-AMP card transmitter or
at the Node B OPT-AMP card transmitter is required. A system that has been shut
down is reactivated through the use of a restart pulse. The pulse indicates
that the optical path is restored and transmission can begin. For example, when
the far end, Node B, receives a pulse, it signals to the Node B OPT-AMP card
transmitter to begin transmitting an optical signal. The OPT-AMP card receiver
at Node A receives that signal and signals the Node A OPT-AMP card transmitter
to resume transmitting.
Note
During a laser restart pulse,
APR ensures that the laser power does not exceed Class 1 limits. See the
section,
“Automatic
Power Reduction” for more information about APR.
Scenario 5: Fiber Cut in Nodes Using DCN Extension
The following figure shows a
fiber cut scenario for nodes that do not have OSC connectivity. In the
scenario, references to the OPT-BST cards refers to the OPT-BST,
OPT-BST-E, OPT-AMP-C,
OPT-AMP-17-C, 40-SMR1-C, and 40-SMR2-C cards when provisioned in OPT-LINE mode.
Figure 20. Fiber Cut With DCN
Extension
Two photodiodes at Node B monitor the received signal strength for the optical payload. When the fiber is cut, an LOS is detected
on the channel photodiode while the other one never gets a signal because the OSC is not present. The AND function then indicates
an overall LOS condition, which causes the OPT-BST amplifier transmitter to shut down. This in turn leads to a LOS for the
optical payload at Node A, which causes Node A to turn off the OPT-BST amplifier lasers. For more information on alarms,
see the Cisco NCS 2000 Series Troubleshooting Guide.
The sequence of events after
a fiber cut is as follows (refer to the numbered circles in the figure above):
Fiber is cut.
The Node B power monitoring
photodiode detects an LOS on the OPT-BST card.
On the OPT-BST card, the LOS
detection triggers a command to shut down the amplifier.
The OPT-BST card amplifier is
shut down within one second.
The Node A power monitoring
photodiode detects a LOS on the OPT-BST card.
On the OPT-BST, the LOS
detection triggers a command to shut down the amplifier.
The OPT-BST card amplifier is
shut down within one second.
When the fiber is repaired, a
manual restart with 9 sec restart pulse time (MANUAL RESTART) is required at
the Node A OPT-BST transmitter and at the Node B OPT-BST transmitter. A system
that has been shut down is reactivated through the use of a 9 sec restart
pulse. The pulse indicates that the optical path is restored and transmission
can begin.
For example, when the far
end, Node B, receives a pulse, it signals to the Node B OPT-BST transmitter to
begin transmitting an optical signal. The OPT-BST receiver at Node A receives
that signal and signals the Node A OPT-BST transmitter to resume transmitting.
Note
During a laser restart pulse,
APR ensures that the laser power does not exceed Class 1 limits. See the
section,
“Automatic
Power Reduction” for more information about APR.
Scenario 6: Fiber Cut in Nodes Using OPT-RAMP-C or OPT-RAMP-CE
Cards
The following figure shows a
fiber cut scenario for nodes using OPT-RAMP-C or OPT-RAMP-CE cards.
Figure 21. Nodes Using OPT-RAMP-C or
OPT-RAMP-CE Cards
The sequence of events after
a fiber cut is as follows (refer to the numbered circles in the figure above):
Fiber is cut in the direction
of Node A to Node B.
No alarms are initially
detected on Node B. The Raman pumps are still in ON state and continue to pump
power on to the broken fiber. The residual Raman noise propagated towards the
LINE-RX port keeps the embedded EDFA active. The LOS alarm is not raised on the
DC-TX port because the EDFA continues to transmit minimum output power to the
line amplifier that it is connected to.
On Node A, the OPT-RAMP-C card no longer receives the Raman remnant pump signal on the LINE-TX port. The RAMAN-RX port detects
an LOS-R alarm on the OPT-RAMP-C or OPT-RAMP-CE card. The OSCM card that is connected to the OPT-RAMP-C card detects OSC failure
and raises a LOS alarm at the OC-3 level. For the LOS-R troubleshooting procedures, see the Cisco NCS 2000 Series Troubleshooting Guide.
On the OPT-RAMP-C or
OPT-RAMP-CE card, the LOS-R alarm triggers a command to shut down the Raman
pump on Node A.
On Node A, the LOS alarm on
the OSCM card causes a laser TX shutdown because ALS is always enabled on the
OSCM card. This results in the OPT-RAMP-C or OPT-RAMP-CE card raising the LOS-O
alarm on the OSC-RX port.
Because the Raman pump on
Node A is shutdown, the RAMAN-RX port detects an LOS-R alarm on Node B.
The LOS-R alarm triggers a
command to shut down the Raman pump on Node B.
The embedded EDFA on Node B
no longer receives residual power Raman noise. An LOS alarm is detected on the
input port of the EDFA that causes the embedded EDFA to shut down.
The LINE-RX port of the line
amplifier on Node B that receives the payload signal from the embedded EDFA of
the OPT-RAMP-C card detects an LOS alarm.
The LOS alarm triggers an ALS
and causes the line amplifier to shut down.
The COM-RX port of the
OPT-RAMP-C card on Node B and consequently the LINE-TX port that is connected
to Node A through the safe fiber, no longer receive power.
Because the OSCM card on Node
A is in the ALS condition, there is no OSC signal on the LINE-TX port of the
OSCM card on Node B that raises an LOS alarm.
The LOS alarm on the OSCM
card causes a laser TX shutdown that raises an LOS-O alarm on the OSC-RX port
of the OPT-RAMP-C card on Node B. The simultaneous presence of an LOS-O alarm
on the OSC-RX port and an LOS-R alarm on the RAMAN-RX port of the OPT-RAMP-C
card can be interpreted as a fiber cut and an LOS alarm is generated on the
LINE-RX port.
On Node A, the LINE-RX port
of the OPT-RAMP-C card detects an LOS alarm because the C-band payload is
absent and triggers a command to shut down the embedded EDFA.
The line amplifier that
receives the payload signal from the embedded EDFA of the OPT-RAMP-C card
detects an LOS alarm on its LINE-RX port and causes the line amplifier to shut
down. The C-band power is no longer transmitted to the COM-RX port of the
OPT-RAMP-C card and subsequently to the LINE-TX port that connected to the
broken fiber.
An Automatic Laser Restart
(ALR) on the Raman pump is detected when the fiber is restored. This turns both
the Raman pumps to ON state, on both the nodes. When the power on the Raman
pump is restored, it turns on the embedded EDFA also. The booster amplifiers on
both Node A and Node B detect power on the LINE-RX port. This restarts the
booster amplifier.
Once the active TCC of the
Raman node detects a stable condition, the link is automatically revaluated.
The TCC initiates a fiber restoration procedure as described in the section,
Fiber
Cut Recovery in Nodes Using OPT-RAMP-C or OPT-RAMP-CE Cards. The
procedure takes a maximum of one or two minutes and causes a temporary
transient condition on C-band signals.
Scenario 7: Fiber Cut in Optical Line Amplifier Nodes Using OPT-RAMP-C or OPT-RAMP-CE Cards
In the following sections, fiber cut scenarios for three node layouts are given:
Scenario 7A—Node Equipped With OPT-RAMP-C or OPT-RAMP-CE Cards
on Side A and Side B.
The following figure shows a
fiber cut scenario for a node equipped with OPT-RAMP-C or OPT-RAMP-CE cards on
Side A and Side B.
Figure 22. Nodes Using OPT-RAMP-C or
OPT-RAMP-CE Cards on Side A and B
The sequence of events after
a fiber cut is as follows (refer to the numbered circles in the figure above):
The fiber that is connected
to the LINE-TX port of the OPT-RAMP-C or OPT-RAMP-CE card on Side A of Node A
is cut. The Raman link goes down.
The RAMAN-RX port detects an LOS-R alarm on the OPT-RAMP-C or OPT-RAMP-CE card on Side A. For LOS-R troubleshooting procedures,
see the Cisco NCS 2000 Series Troubleshooting Guide.
On the OPT-RAMP-C or
OPT-RAMP-CE card, the LOS-R alarm triggers a command to shut down the Raman
pump on Side A.
No power is detected by the
embedded EDFA on the LINE-RX port of the OPT-RAMP-C or OPT-RAMP-CE card on Side
A.
The embedded EDFA of the
OPT-RAMP-C or OPT-RAMP-CE card on Side A is automatically shutdown.
An LOS-P alarm is detected on
the COM-RX port of the OPT-RAMP-C or OPT-RAMP-CE card on Side B of Node A.
The LOS-P alarm triggers an
ALS of the embedded EDFA of the OPT-RAMP-C or OPT-RAMP-CE card on Side B.
No C-band power is
transmitted out of the COM-TX port of the OPT-RAMP-C or OPT-RAMP-CE card on
Side B, to the COM-RX port and subsequently to the LINE-TX port of the
OPT-RAMP-C or OPT-RAMP-CE card on Side A that is connected to the broken fiber.
Scenario 7B—Node Equipped With OPT-RAMP-C or OPT-RAMP-CE and
Booster Cards on Side A and OPT-RAMP-C or OPT-RAMP-CE Cards on Side B.
Scenario 1—Fiber cut on the
LINE-TX port of the OPT-RAMP-C or OPT-RAMP-CE card on Side A.
Figure 23. Nodes Using OPT-RAMP-C or
OPT-RAMP-CE and Booster Cards on Side A and OPT-RAMP-CE Cards on Side B -
Scenario 1
The sequence of events after
a fiber cut is as follows (refer to the numbered circles in the figure above):
The fiber that is connected
to the LINE-TX port of the OPT-RAMP-C or OPT-RAMP-CE card on Side A of Node A
is cut.The Raman link goes down.
The RAMAN-RX port detects an LOS-R alarm on the OPT-RAMP-C or OPT-RAMP-CE card. For LOS-R troubleshooting procedures, see
the Cisco NCS 2000 Series Troubleshooting Guide.
On the OPT-RAMP-C or
OPT-RAMP-CE card, the LOS-R alarm triggers a command to shut down the Raman
pump on Side A.
No power is detected by the
embedded EDFA on the LINE-RX port of the OPT-RAMP-C or OPT-RAMP-CE card on Side
A.
The embedded EDFA of the
OPT-RAMP-C or OPT-RAMP-CE card on Side A is automatically shutdown.
An LOS alarm is detected on
the downstream line amplifier on Side A of Node A since it no longer receives
the optical payload from the embedded EDFA of the OPT-RAMP-C or OPT-RAMP-CE
card.
The ALS mechanism causes the
line amplifier to shut down.
The C-band power is no longer
transmitted out of the line amplifier to the COM-RX port and subsequently to
the LINE-TX port of the OPT-RAMP-C or OPT-RAMP-CE card that is connected to the
broken fiber.
Scenario 2—Fiber cut on the
LINE-TX port of the OPT-RAMP-C or OPT-RAMP-CE card on Side B.
Figure 24. Nodes Using OPT-RAMP-C or
OPT-RAMP-CE and Booster Cards on Side A and OPT-RAMP-CE Cards on Side B -
Scenario 2
The sequence of events after
a fiber cut is as follows (refer to the numbered circles in the figure above):
The fiber that is connected
to the LINE-TX port of the OPT-RAMP-C or OPT-RAMP-CE card on Side B of Node A
is cut.
An LOS-R alarm is detected on
the OPT-RAMP-C or OPT-RAMP-CE card on Side B because it no longer receives the
Raman remnant signal from Node B.
On the OPT-RAMP-C or
OPT-RAMP-CE card, the LOS-R alarm triggers a command to shut down the Raman
pump on Side B.
The embedded EDFA of the
OPT-RAMP-C or OPT-RAMP-CE card on Side B no longer receives residual Raman
power and causes it to shut down.
A very low C-band signal
reaches the OPT-RAMP-C or OPT-RAMP-CE card on Side A. An LOS-P alarm is
detected on the COM-RX port of the OPT-RAMP-C or OPT-RAMP-CE card on Side A.
The embedded EDFA of the
OPT-RAMP-C or OPT-RAMP-CE card on Side A is automatically shutdown.
The C-band power is no longer
transmitted to the line amplifier through the DC-TX port of the OPT-RAMP-C or
OPT-RAMP-CE card on Side A, to the COM-RX port and subsequently to the LINE-TX
port of the OPT-RAMP-C or OPT-RAMP-CE card on Side B that is connected to the
broken fiber.
Scenario 7C—Node Equipped With OPT-RAMP-C or OPT-RAMP-CE and
Booster Cards on Side A and OSC-CSM Cards on Side B.
Scenario 1—Fiber cut on the
LINE-TX port of the OPT-RAMP-C or OPT-RAMP-CE card on Side A.
Figure 25. Nodes Using OPT-RAMP-C or
OPT-RAMP-CE and Booster Cards on Side A and OSC-CSM Cards on Side B - Scenario
1
The sequence of events after
a fiber cut is as follows (refer to the numbered circles in figure above):
The fiber that is connected
to the LINE-TX port of the OPT-RAMP-C or OPT-RAMP-CE card on Side A of Node A
is cut. The Raman link goes down.
The RAMAN-RX port detects an
LOS-R alarm on the OPT-RAMP-C or OPT-RAMP-CE card.
On the OPT-RAMP-C or
OPT-RAMP-CE card, the LOS-R alarm triggers a command to shut down the Raman
pump on Side A.
No power is detected by the
embedded EDFA on the LINE-RX port of the OPT-RAMP-C or OPT-RAMP-CE card on Side
A.
The embedded EDFA of the
OPT-RAMP-C or OPT-RAMP-CE card on Side A is automatically shutdown.
An LOS alarm is detected on
the downstream line amplifier on Side A of Node A because it no longer receives
the optical payload from the embedded EDFA of the OPT-RAMP-C or OPT-RAMP-CE
card.
The ALS mechanism causes the
line amplifier to shut down.
The C-band power is no longer
transmitted out of the line amplifier to the COM-RX port and subsequently to
the LINE-TX port of the OPT-RAMP-C or OPT-RAMP-CE card that is connected to the
broken fiber on Side A.
Scenario 2—Fiber cut on the
LINE-RX port of the OSC-CSM card on Side B.
Figure 26. Nodes Using OPT-RAMP-C or
OPT-RAMP-CE and Booster Cards on Side A and OSC-CSM Cards on Side B - Scenario
2
The sequence of events after
a fiber cut is as follows (refer to the numbered circles in the figure above):
The fiber that is connected
to the LINE-RX port of the OSC-CSM card on Side B of Node A is cut.
An LOS alarm is detected on
the OSC-CSM card on Side B because it no longer receives the OSC signal.
The power is shut down by
means of a 1x1 optical switch in the OSC-CSM card.
Note
During a laser restart pulse,
APR ensures that the laser power does not exceed Class 1 limits. For more
information about APR, see the section,
“Automatic Power
Reduction”.
Scenario 8: Fiber Cut in Nodes Using EDRA-1-xx or EDRA-2xx Cards
The following figure shows a fiber cut scenario for nodes using EDRA-2-xx cards.
Figure 27. Nodes Using EDRA-2-xx Cards
The sequence of events after a fiber cut is as follows (refer to the numbered circles in the figure above):
Note
The shutdown procedure happens in less than 500 ms.
Procedure
Step 1
Fiber is cut.
Step 2
No alarms are initially detected on Node B. The Raman pump is still in ON state and continue to pump power on to the broken
fiber.
Step 3
On Node A, the EDRA card no longer receives the Raman remnant pump signal on the LINE-TX port. The RAMAN-RX port detects an
LOS-R alarm on the EDRA card.
Step 4
On the EDRA card, the LOS-R alarm triggers a command to shut down the Raman pump on Node A.
Step 5
The C-band optical switch is opened on Node A to stop C-band signals in to the cut fiber.
Step 6
The EDFA is shut off on Node A.
Step 7
The Raman pump on Node A is shutdown, the RAMAN-RX port detects an LOS-R alarm on Node B. Due to the open switch on Node A,
a LOS-P alarm is also raised on Node B. The LOS-R and LOS-P alarms causes the EDRA card to raise a LOS alarm that is shown
to the user.
Step 8
The LOS-R alarm triggers a command to shut down the Raman pump on Node B.
Step 9
The C-band optical switch is opened on Node B to stop C-band signals in to the fiber.
Step 10
The EDFA is shut off on Node B.
Step 11
Node A also detects the loss of C-Band and raises a LOS-P alarm. The LOS-R and LOS-P alarms causes the EDRA card to raise
a LOS alarm that is shown to the user.
After fiber recovery, a complete calibration is re-run on the EDRA cards.
Fiber Cut Recovery in Nodes Using OPT-RAMP-C or OPT-RAMP-CE Cards
A fiber cut recovery procedure is automatically performed after the OCH channels are restored to measure the actual Raman
gain on the span.
Node A sends a message through OSC or DCN to Node B to be ready for Raman Gain measurement.
The TCC configures the Raman pumps on Node A to operate at APR power (+8 dBm). In this state, no Raman amplification is generated
on the input fiber of Node A and a reliable span loss measurement is performed. The Raman pumps must not be shut down completely
to avoid an improper fiber cut event.
Node B acknowledges the message and reports the value of the Raman power received on the channel to Node A.
On Node A, the TCC configures the line amplifiers in power control mode and APR state (+8 dBm). The C-band power received
with Raman pumps in OFF state is recorded.
The TCC turns the Raman pumps to full power maintaining the Raman ratio calculated by the Raman installation wizard. The Raman
total power is adjusted, so that the Raman gain setpoint is reached. The actual Raman gain is calculated using the C-band
power values.
When the Raman gain setpoint is reached, the value of the Power field gets updated and the status of the Fiber Cut Recovery
field changes to “Executed” in CTC.
If the provisioned Raman gain setpoint is not reached by setting the Raman total power to the maximum value of 450 mW, the
procedure stops and the RAMAN-G-NOT-REACHED alarm is raised on the OPT-RAMP-C or OPT-RAMP-CE card.
EDRA Card Start Up
and Fiber Link Turn Up
The local and remote
nodes, equipped with EDRA cards, must follow this sequence to start the card
and complete the Raman link turnup.
After a fiber cut,
the Raman pumps are in OFF state, the C-band optical switch is open, and there
is no C-band signal on the spans. The restart procedure begins only when the
RAMAN and LINE ports are in service and OSRI is OFF.
The restart
procedure:
Ensures span
continuity between the local and remote node before transmitting high power
signals.
Verifies that
the span connected to the LINE-RX port is capable of sustaining the high-power
Raman signals.
Verifies length
of the span connected to the LINE-RX port is not short. If the span is short,
the remote EDRA card may get damaged, if local Raman pumps reach operative
power.
The restart
procedure is implemented by these measures:
Span continuity
is checked-If the ALS Auto restart is enabled on the EDRA cards, the Raman
pumps operate in pulse mode at a reduced power level. If ALS manual restart is
set, a single pulse is generated on user request. An acknowledgment mechanism
is used between the peer EDRA modules to verify span continuity.
The Raman
pumps of the local node emit a nine-second laser pulse into the fiber with an
automatic power reduction to +8 dBm.This level assures that Hazard Level 1
power limit is not exceeded. This is done for personnel safety.
The local
node waits for a similar nine-second pulse in response from the remote node.
If the
remote node detects a valid signal on the RAMAN-RX port, it responds with a
nine-second laser pulse.
If no
response is received within 100 seconds, the local node tries again. This
process continues until the local node receives a nine-second response pulse
from the remote node.
The duration
of the laser pulse is checked. If the signal is detected on the RAMAN-RX for at
least 12 seconds, link continuity is verified, indicating that a broken fiber,
if any, is fixed.
Note
If the
RAMAN-RX port detects a drop in the power below the threshold value before 12
seconds have elapsed, the procedure to check span continuity is restarted.
The Raman
pumps on the local and remote nodes are changed from pulse mode at reduced
power to normal operating power mode.
The C-band
optical switch is closed and the EDFA 2 module (if present) is enabled.
Excessive back
reflection is checked- If a malfunctioning, open, or dirty connector is present
in the optical path near LINE-RX port, it may break down with high pump
operative power causing excessive back-reflection. To avoid this event, during
the APR phase, the Raman power entering the EDRA card on the LINE-RX port is
measured. The back-reflection mechanism checks the ratio between the
back-reflected power and the transmitted power. If the ratio is above a
pre-defined value, it indicates the presence of a problematic connector. The
APR pulse is immediately stopped and a Raman Laser Shutdown (RLS) alarm is
raised on the RAMAN-TX port.
A check for short spans is performed-A span loss assessment is performed on the remote node. When the photodiode on the RAMAN-RX
port of the remote node receives an APR pulse of x dBm, the span loss is x+ 8dBm. If the value of x is greater than the pre-defined threshold, the photodiode on the LINE-RX port of the remote node may get damaged when the
Raman pump reaches operative power. To prevent damage, the remote node does not acknowledge the signal coming from the local
node. This cancels the restart procedure and the Raman pump never reaches operative power. A SPAN-TOO-SHORT alarm is raised
on LINE-TX port. The span continuity check is performed. This implements an automatic recovery from the check failure.
ARPC tuning-The
characteristics of the span may have changed. The ARPC procedure is run and the
total power of Raman pumps is changed to match the Raman gain value that was
present before the fiber cut. If the original Raman gain is reached, the ARPC
attribute value changes to “success”.
The Raman span is now ready for traffic provisioning.
Network Optical Safety on RAMAN-CTP and RAMAN-COP Cards
Bidirectional optical safety mechanisms for Raman and C-band signals have been independently implemented. The Raman pump laser
shutdown and restart is managed by the RAMAN-CTP card. The RAMAN-COP card is controlled by the RAMAN-CTP card using two backplane
wires. The RAMAN-COP card can be absent in some node configurations.
The C-band signal shutdown and restart is managed by an MSTP card, such as 40-SMR1-C, 40-SMR-2C, OPT-EDFA-17, or OPT-EDFA-24.
The optical safety mechanism on the RAMAN-CTP and RAMAN-COP cards is managed by:
DFB signal (1568.77 nm) and detection of DFB related signals—The RAMAN-CTP card on the local node transmits a DFB signal and
waits for a similar response from the remote side. If a valid DFB signal is not detected, the RAMAN-CTP card switches off
its transmitting DFB laser that causes a loss of DFB signal on the remote RAMAN-CTP card which in turn switches off its DFB
laser. Both the RAMAN-CTP cards must turn off the DFB signals, when a fiber cut occurs.
Raman pump laser back reflection mechanism on the RAMAN-CTP and RAMAN-COP cards—This mechanism uses the ratio between the
back-reflected optical power and the total output Raman pump power to reduce the output power when patchcords are removed.
If excessive back-reflection occurs, a Raman Laser Shutdown (RLS) alarm is raised on the RAMAN port where the failure is detected.
Photodiode (P8) on the RAMAN-CTP card—The photodiode (P8) detects the Raman pump power transmitted by the RAMAN-COP card and
is used to check for optical continuity between the RAMAN-CTP and RAMAN-COP cards. The RAMAN-COP card is shut down if the
cards get disconnected.
Network-Level Gain—Tilt Management of Optical Amplifiers
The ability to control and
adjust per channel optical power equalization is a principal feature of DWDM
metro core network applications. A critical parameter to assure optical
spectrum equalization throughout the DWDM system is the gain flatness of
erbium-doped fiber amplifiers (EDFAs).
Two items, gain tilt and gain
ripple, are factors in the power equalization of optical amplifier cards such
as the OPT-BST and OPT-PRE. The following figure shows a graph of the amplifier
output power spectrum and how it is affected by gain tilt and gain ripple.
Figure 28. Effect of Gain Ripple and
Gain Tilt on Amplifier Output Power
Gain ripple and gain tilt are
defined as follows:
Gain ripple is random and
depends on the spectral shape of the amplifier optical components.
Gain tilt is systematic and
depends on the gain setpoint (Gstp) of the optical amplifier, which is a
mathematical function F(Gstp) that relates to the internal amplifier design.
Gain tilt is the only contribution to the power
spectrum disequalization that can be compensated at the card level. A VOA
internal to the amplifier can be used to compensate for gain tilt.
An optical spectrum analyzer
(OSA) is used to acquire the output power spectrum of an amplifier. The OSA
shows the peak-to-peak difference between the maximum and minimum power levels,
and takes into account the contributions of both gain tilt and gain ripple.
Note
Peak-to-peak power
acquisition using an OSA cannot be used to measure the gain tilt, because gain
ripple itself is a component of the actual measurement.
Gain Tilt Control at the Card Level
In the following figure ,
OPT-BST and OPT-PRE amplifier cards have a flat output (gain tilt = 0 dB) for
only a specific gain value (Gdesign), based on the internal optical design.
Figure 29. Flat Gain (Gain Tilt = 0
dB)
If the working gain setpoint
of the amplifier is different from Gdesign, the output spectrum begins to
suffer a gain tilt variation.
In order to compensate for
the absolute value of the increase of the spectrum tilt, the OPT-BST and
OPT-PRE cards automatically adjust the attenuation of the VOA to maintain a
flat power profile at the output, as shown in the following figure.
Figure 30. Effect of VOA Attenuation on
Gain Tilt
The VOA attenuator automatic
regulation guarantees (within limits) a zero tilt condition in the EDFA for a
wide range of possible gain setpoint values.
The following table shows the
flat output gain range limits for the OPT-BST and OPT-PRE cards, as well as the
maximum (worst case) values of gain tilt and gain ripple expected in the
specific gain range.
Table 2. Flat Output Gain Range
Limits
Amplifier Card Type
Flat Output
Gain Range
Gain Tilt (Maximum)
Gain Ripple (Maximum)
OPT-BST
G < 20 dB
0.5 dB
1.5 dB
OPT-PRE
G < 21 dB
0.5 dB
1.5 dB
OPT-BST-E
8 to 23
0.5 dB
1.8 dB
OPT-AMP-C
12 to 24
0.5 dB
1.2 dB
OPT-AMP-17C
0.5 dB
1.5 dB
OPT-EDFA-17
5 to 17
0.5 dB
1.2 dB
OPT-EDFA-24
12 to 24
0.5 dB
1.2 dB
40-SMR1-C
5 to 21
0.5 dB
1.2 dB
40-SMR2-C (EDFA-1)
5 to 21
0.5 dB
1.2 dB
40-SMR2-C (EDFA-2)
13 to 17
0.5 dB
1.2 dB
If the operating gain value
is outside of the range, the EDFA introduces a tilt contribution for which the
card itself cannot directly compensate. This condition is managed in different
ways, depending the amplifier card type:
OPT-BST—The OPT-BST amplifier
is, by design, not allowed to work outside the zero tilt range. Cisco
TransportPlanner network designs use the OPT-BST amplifier card only when the
gain is less than or equal to 20 dB.
OPT-PRE—Cisco
TransportPlanner allows network designs even if the operating gain value is
equal to or greater than 21 dB. In this case, a system-level tilt compensation
strategy is adopted by the DWDM system. A more detailed explanation is given in
the section,
System Level Gain Tilt
Control.
System Level Gain Tilt Control
System level gain tilt control for OPT-PRE cards is achievable with two main scenarios:
Without an ROADM node
With an ROADM node
System Gain Tilt Compensation Without ROADM Nodes
When an OPT-PRE card along a specific line direction (Side A-to-Side B or Side B-to-Side A) is working outside the flat output
gain range (G > 21 dB), the unregulated tilt is compensated for in spans that are not connected to ROADM nodes by configuring
an equal but opposite tilt on one or more of the amplifiers in the downstream direction. The number of downstream amplifiers
involved depends on the amount of tilt compensation needed and the gain setpoint of the amplifiers that are involved.
Figure 31. System Tilt Compensation Without an ROADM Node
The proper Tilt Reference value is calculated by Cisco TransportPlanner and inserted in the Installation Parameter List imported
during the node turn-up process. For both OPT-PRE and OPT-BST cards, the provisionable Gain Tilt Reference range is between
–3 dB and +3 dB.
During the ANS procedure, the Tilt value for the OPT-BST or OPT-PRE card is provisioned by the controller card. The provisioned
Tilt Reference Value is reported in the CTC OPT-PRE or OPT-BST card view > Provisioning > Opt. Ampli. Line > Parameters >
Tilt Reference tab.
System Gain Tilt Compensation With ROADM Nodes
When a ROADM node is present in the network, as shown in the following figure, a per channel dynamic gain equalization can
be performed. Both gain tilt and gain ripple are completely compensated using the following techniques:
Implementing the per channel VOAs present inside the 32WSS card
Operating in Power Control Mode with the specific power setpoint designed by Cisco TransportPlanner
Figure 32. System Tilt Compensation With an ROADM Node
Optical Data Rate Derivations
This section discusses the derivation of several data rates commonly used in optical networking.
OC-192/STM-64 Data Rate (9.95328 Gbps)
The SONET OC-1 rate is 51.84 Mbps. This rate results from a standard SONET frame, which consists of 9 rows of 90 columns of
8-bit bytes (810 bytes total). The transmission rate is 8000 frames per second (125 microseconds per frame). This works out
to 51.84 Mbps, as follows:
(9) x (90 bytes/frame) x (8 bits/byte) x (8000 frames/sec) = 51.84 Mbps
OC-192 is 192 x 51.84 Mbps = 9953.28 Mbps = 9.95328 Gbps
STM-64 is an SDH rate that is equivalent to the SONET OC-192 data rate.
10GE Data Rate (10.3125 Gbps)
10.3125 Gbps is the standard 10 Gbps Ethernet LAN rate. The reason the rate is higher than 10.000 Gbps is due to the 64-bit
to 66-bit data encoding. The result is 10 Gbps x 66/64 = 10.3125 Gbps. The reason for 64-bit to 66-bit encoding is to ensure
that there are adequate data transitions to ensure proper operation of a clock and data recovery circuit at the far end. Additionally,
the encoding assures a data stream that is DC balanced.
10G FC Data Rate (10.51875 Gbps)
The Fibre Channel rate is based on the OC-192 rate of 9.95328 Gbps, with the addition of 64-bit to 66-bit encoding and WAN
Interconnect Sublayer (WIS) overhead bytes.
The rate is derived from the basic 9.95328 Gbps OC-192 rate. First, it has the 64-bit to 66-bit encoding added, which brings
it to the 10.3125 Gbps rate (10 Gbps x 66/64 = 10.3125 Gbps). Beyond that, the WIS overhead is added, which is an additional
two percent on top of the 10.3125 Gbps. This yields:
10.3125 Gbps x 0.02 = 0.20625 Gbps
10.3125 Gbps + 0.20625 Gbps = 10.51875 Gbps
ITU-T G.709 Optical Data Rates
To understand optical
networking data rates, an understanding of the ITU-T G.709 frame structure is
needed.
Figure 33. ITU-T G.709 Frame
Structure
Each of the sub-rows in the
figure above contains 255 bytes. Sixteen are interleaved horizontally
(16 x 255 = 4080). This is repeated four times to make up the complete ITU-T
G.709 frame.
The Reed Solomon (RS)
(255,239) designation indicates the forward error correction (FEC) bytes. There
are 16 FEC, or parity, bytes. The ITU-T G.709 protocol uses one overhead byte
and 238 data bytes to compute 16 parity bytes to form 255 byte blocks—the RS
(255,239) algorithm. Interleaving the information provides two key advantages.
First, the encoding rate of each stream is reduced relative to the line
transmission rate and, second, it reduces the sensitivity to bursts of error.
The interleaving combined with the inherent correction strength of the RS
(255,239) algorithm enables the correction of transmission bursts of up to 128
consecutive errored bytes. As a result, the ITU-T G.709 contiguous burst error
correcting capability is enhanced 16 times above the capacity of the
RS(255,239) algorithm by itself.
ITU-T G.709 defines the
Optical Transport Unit 2 (OTU2) rate as 10.70923 Gbps. ITU-T G.709 defines
three line rates:
2,666,057.143 kbps—Optical
Transport Unit 1 (OTU1)
10,709,225.316 kbps—Optical
Transport Unit 2 (OTU2)
43,018,413.559 kbps—Optical
Transport Unit 3 (OTU3)
The OTU2 rate is higher than
OC-192 because the OTU2 has to carry overhead and FEC bytes in its frame; the
bits must be sent faster to carry the payload information at the OC-192 rate.
The ITU-T G.709 frame has two
parts. Two are similar to a SDH/SONET frame:
Overhead area for operation,
administration, and maintenance functions
Payload area for customer
data
In addition, the ITU-T G.709
frame also includes FEC bytes.
OC-192 Packaged Into OTU2 G.709 Frame Data Rate (10.70923 Gbps)
In this case, an OC-192 frame is being transported over a OTU2 G.709 frame, which adds the benefit of FEC. The OC-192 data
rate (9.95328 Gbps) must increase in order to transport more bytes (OC-192 plus ITU-T G.709 overhead plus ITU-T G.709 FEC
bytes) in the same amount of time. In an OTU2 transmission, 237 of the 255 bytes are OC-192 payload. This means the resultant
data rate is:
9.95328 x 255/237 = 10.70923 Gbps
10GE Packaged Into OTU2 G.709 Frame Data Rate (Nonstandard 11.0957 Gbps)
Encapsulating Ethernet data into an OTU2 G.709 frame is considered nonstandard. The goal is to add the benefit of ITU-T G.709
encapsulation to achieve better burst error performance. However, this means adding overhead and FEC bytes, so more bytes
must be transmitted in the same amount of time, so the data rate must increase. The new date rate is:
10.3215 x 255/237 = 11.0957 Gbps
10G FC Packaged Into OTU2 G.709 Frame Data Rate (Nonstandard 11.31764 Gbps)
Encapsulating Fibre Channel in an OTU2 frame is considered nonstandard. The rate is higher than the 10.51875 rate because
OTU2 includes FEC bytes. The bits must run at a faster rate so that the payload is provided at the standard Fibre Channel
rate. The rate is:
10.51875 x 255/237 = 11.31764 Gbps
Wavelength Drifted Channel Automatic Shutdown
The wavelength drifted
channel automatic shutdown feature detects wavelength instability or wavelength
drift on the source port of the card connected to an MSTP multiplexer. The
channel photodiode or optical channel monitor (OCM) associated with a variable
optical attenuator (VOA) is used to detect the power fluctuation.
The wavelength drifted
channel automatic shutdown feature is supported on 40-SMR1-C, 40-SMR2-C,
80-WXC-C, 40-WXC-C, and 40-WSS-C cards. The 40-SMR1-C, 40-SMR2-C, and 80-WXC-C
cards have the OCM devices connected to the ADD port, which detect the power
fluctuation. The 40-WSS-C and 40-WXC-C cards do not detect the power
fluctuation on their ADD ports because the Add photodiode is located before the
filtering stage. The different ports on each card detect the power fluctuation.
The following table lists the ports on which the power fluctuation is detected.
Table 3. Detection of Power
Fluctuation
Card
Port
Circuit
40-SMR1-C , 40-SMR2-C
LINE-TX
ADD/DROP, EXP/PT
80-WXC-C
COM/EAD/AD
ADD/DROP EXP/PT
40-WXC-C
COM-TX
ADD/DROP EXP/PT
40-WSS-C
CHAN-RX
ADD/DROP
PT
PT
When the card exceeds the
OPT-PWR-DEG-LOW threshold value 16 times in 24 hours, the WVL-DRIFT-CHAN-OFF
alarm is raised. When the WVL-DRIFT-CHAN-OFF alarm is raised, the VOA
associated to that port is moved to the automatic VOA shutdown (AVS) state,
which shuts down the channel.
For more information on the severity level of the conditions and procedure to clear the alarms, see the Cisco NCS 2000 Series Troubleshooting Guide.