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Huawei OptiX BWS 1600G. Technical Description - part 10

4 Networking and System Applications

There is a dedicated APE protocol byte in the overhead frame of the

supervisory signal, which is used to transmit APE related information.

Since an OADM station may exist between the adjustment station and the

monitoring station, all the wavelengths detected in monitoring station may not

be adjusted by V40 or DGE in the adjustment station. As a result, the

wavelengths with APE function activated should be specified by NM.

4.2.4 Clock Transmission

The OptiX BWS 1600G offers a new solution for the transmission of synchronous

clock. Its optical supervisory channel provides three clock transmission channels

operating at 2 Mbit/s.

In each network element, upstream clock can be transparently transmitted, or sent

to local BITS clock receiving equipment, or it can work in the combination of both.

The detailed configuration plan should be designed by the network planning

engineer according to the actual requirements and needs. In network design, not

only the DWDM system but also the local digital synchronous clock network shall

be taken into account.

Clock transmission in an OptiX network is explained in the following example and

Figure 4-7.

Terminal-A is transmitting the clock. Along the East channel, optical amplifier-1

passes the clocks (CLK) channel transparently, i.e. no clock is added or dropped,

while optical amplifier-2 can add or drop one CLK channel to/from the main path.

Terminal-B terminates the East CLK.

Similarly, Terminal-B is transmitting the CLK on West channel. Where at

amplifier-2 the CLK signal channel is dropped locally and meanwhile passed

transparently to the down stream. Optical amplifier-1 can add and drop the one

CLK channel to/from the main path. Finally the CLK is terminated at Terminal-A.

CLK

West

Optical

Terminal-A

Terminal-B

amplifier-1

amplifier-2

East

CLK

Figure 4-7 Schematic diagram of clock transmission

In the OptiX BWS 1600G system, clock transmission can be set to protection mode

or non-protection mode. In clock protection mode, two carrier wavelengths are

used, with 1510 nm for normal channel and 1625 nm for protected channel.

A summary of clock transmission is given below.

In the case that there is no clock being added/dropped at intermediate station,

the system supports 3-channel clock transmission at East and West directions

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4 Networking and System Applications

respectively, no matter in clock protection mode or clock non-protection

mode.

In the case that there is clock being added/dropped at intermediate station, the

intermediate station supports at most 3 clock channels in clock non-protection

mode. The clock channels may come from both East and West directions.

In the case that there is clock being added/dropped at intermediate station, the

intermediate station supports at most 3 clock channels in clock non-protection

mode. The clock channels must come from only one direction (East or West).

4.2.5 Optical Fiber Line Automatic Monitoring

The OptiX BWS 1600G provides the OAMS (Optical fiber line Automatic

Monitoring System) to alert fiber aging, fiber alarm, and locate the fault. The

OAMS realizes the monitoring on the fiber link.

As an embedded system, OAMS is optional depending on the requirement of users.

Monitor and Test

OAMS provides two monitoring modes

On-line (light fiber) monitoring: To monitor and test a working optical fiber (cable).

In this case, the wavelength of test signal is 1310 nm.

Standby fiber (dark fiber) monitoring: To monitor and test a standby optical fiber

(cable). In this case, the wavelength of test signal is 1550 nm.

OAMS provides two test modes

Unidirectional test: To monitor and test a span with unidirectional test signal.

In this case, two adjacent spans share an independent remote test unit (RTU), so the

RTU number is greatly reduced and OAMS cost decreases accordingly.

DWDM node

RTU

OAMS

RTU

Service signal

Test signal

RTU: Remote Test Unit

Figure 4-8 Unidirectional test diagram

Due to the limitation of dynamic test range of the built-in optical time domain

reflectometer (OTDR), the unidirectional test fails when measuring a long span of

much attenuation. Here the monitoring and test can be implemented from both ends

of the span by two OTDR modules.

Bidirectional test: To monitor and test a span with bidirectional test signals.

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4 Networking and System Applications

DWDM node

RTU

OAMS

Service signal

Test signal

RTU: Remote test unit

Figure 4-9 Bidirectional test diagram

In the bidirectional test, configure a RTU module at each end of a span, and the two

RTUs will report their test results to NM for combination, and then the performance

parameter of this span will be obtained by analyzing and processing the test results.

System Architecture

The OAMS structure of online monitoring differs with that of standby fiber

monitoring.

Online monitoring

The RTU shown in Figure 4-8 and Figure 4-9 consists of three boards and their

functions are listed in Table 4-11.

Table 4-11 Introduction of boards in embedded OAMS

Board

Name

Function

FMU

Fiber Measure Unit

It is the core of OAMS to implement the

Board

time-domain reflection measurement of fibers. It

can measure four lines of fibers.

MWA

Measure Wavelength

In online monitoring, it is used to multiplex the

Access Board

service signal of DWDM system with the test

signal.

MWF

Measure Wavelength

In online monitoring, it is used to filter the

Filter Board

wavelength of test signals, to eliminate the effect

to the transmission system. The board is used

only when the service signal and the test signal

are in the same direction.

The embedded OAMS system comprises of FMU, MWA and MWF, as shown in

Figure 4-10.

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4 Networking and System Applications

DWDM

MWF

MWA

MWF

OAMS

FMU

Figure 4-10 Embedded OAMS architecture (online monitoring)

In the Figure 4-10, the DWDM node can be OTM, OLA, OADM, OEQ or REG.

The OTDR module in FMU emits the optical test pulse, and receives, collects,

processes and reports the reflection signal, thus monitoring the running status of the

fiber in real time. FMU can monitor at most four lines of optical fibers.

The coupler on MWA multiplexes the service signal and test signal in one fiber for

transmission. When the test signal and service signal are transmitted in the same

direction, the filter on MWF can filter the test signal at the receive node to eliminate

the effect to the system.

The structure and configuration of OAMS vary with network specifications. The

figure here only shows the OAMS of unidirectional test.

Standby fiber monitoring

Compared with online monitoring, standby fiber monitoring is easier to be

implemented, that is, directly access the test wavelength (1550 nm) into the standby

fiber for test, as shown in Figure 4-11.

DWDM node

Standby

fiber

Figure 4-11 Embedded OAMS architecture (standby fiber monitoring)

The performance monitoring and test to the standby fiber can be achieved by using

FMU board, NE software and NM. The structure and configuration of OAMS vary

with network specifications. Figure 4-11 only shows the OAMS of unidirectional

test.

Configuration Plan

The Raman amplification and optical fiber attenuation will affect the embedded

OAMS to some extent. Table 4-12 lists the OAMS applications with and without

Raman amplification.

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4 Networking and System Applications

Table 4-12 Applications of embedded OAMS

System type

Fiber attenuation

Supported monitoring

With Raman

Standby fiber monitoring

amplification

Without Raman

≤45 dB

Standby fiber monitoring and online monitoring

amplification

>45 dB

Standby fiber monitoring (Note)

Note: The 1310nm test signal is of great attenuation in fiber, resulting in limited monitoring distance,

so the spans more than 45dB are only provided with standby fiber monitoring.

Table 4-13 lists the configuration of OAMS in various system specifications of the

OptiX BWS 1600G under different monitoring modes.

Table 4-13 OAMS configuration specification

Monitoring

System

Span

Monitoring

OTDR

Optical

Test mode

mode

specification

attenuation

signal

dynamic

fiber

(dB)

wavelength

test range

lengthNote1

(nm)

(dB)

(km)

Online

Long

1310

Unidirectional

monitoring

distance

test

transmission

100

Time-shared

bidirectional test

120

Time-shared

bidirectional test

LHP

38-45

138-163

Time-shared

bidirectional test

Standby

Long

1550

Unidirectional

fiber

distance

test

monitoring

transmission

100

Unidirectional

test

120

Time-shared

bidirectional test

LHP

38-45

138-163

Time-shared

bidirectional test

45-56

163-200

Time-shared

bidirectional test

Note1: The optical fiber length is calculated on condition that the attenuation coefficient is 0.275 dB/km.

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4 Networking and System Applications

System Function

On-line monitoring of optical power of fiber link

Query the input and output optical power of the optical fiber link between nodes,

that is, the output optical power of one station and the input optical power of the

next station. Obtain the attenuation over the link between two adjacent nodes

through the NM and compare the result with the pre-set data. Take the difference of

the optical power as the trigger to enable the test. When the difference exceeds the

pre-set value or the threshold set by the user through NM, the OAMS will be

enabled to test the performance of optical fiber link.

Multiple test modes

The system provides two ways to test fibers according to the priority.

On-demand test: Generate through NM manually, select and control a RTU to test a

certain fiber in the monitored optical fiber line.

Periodical test: Conventional test, namely the test is started upon the previously

arranged conditions are satisfied. The equipment will report the result as an event to

NM after the test.

The test requirement of higher priority can stop that of lower priority to start a new

test queue.

Analysis of test events

Besides the test function, the OAMS system also provides analysis of the test result

and then reports the corresponding test curve and event list to NM.

Fiber alarm

The equipment reports alarms depending on the analysis of the test curve. The

alarms fall into three levels.

Critical alarm: Burst of event over 5 dB, including fiber break. The terminal shows

red and gives audible and visible prompt.

Major alarm: The difference between the attenuation of the whole path and the

acceptance value (or original data) is no less than 3 dB; or the attenuation increase

event (new or not) is no less than 2 dB. The terminal shows pink and gives visible

prompt.

Minor alarm: The difference between the attenuation of the whole path and the

acceptance value (or original data) is no less than 1 dB, while less than 3 dB; or the

attenuation increase event (new or not) is no less than 1 dB. This alarm will be

report to NM and recorded as an exception for future query, but will not give

prompt.

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4 Networking and System Applications

Note

Event: The event in OAMS refers to the physical circumstances showing the status

of the optical fiber line during OTDR test. It comprises reflection event and

non-reflection event. The fiber reflection events include connector, mechanical

connection point and optical fiber end, and so on. While the non-reflection events

include optical fiber fusion point, fiber break, bending or macrobend.

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5 Protection

Protection

5.1 Power protection

5.1.1 DC Input Protection

The power supply system supports two -48 V/-60 V DC power inputs for mutual

backup. Therefore, the equipment keeps running normally in case either of the two

DC inputs is faulty.

5.1.2 Secondary Power Protection

Non OTU boards adopt two power modules for 1+1 power hot backup, to avoid

system breakdown by the damage of one power module.

5.1.3 Centralised Power Protection for OTUs

The system uses power backup unit (PBU) to provide centralised power protection

for the secondary power of all OTUs on each subrack, including:

+3.3 V power supply of the OTU

+5 V power supply of the OTU

-5.2 V power supply of the OTU

When detecting the power of the OTU fails (under/over-voltage), the system

switches to the PBU for power supply in 600μs. The PBU can supply power for two

OTUs at the same time.

The PBU is inserted in slot 1, providing power backup for all OTUs in the subrack,

as shown in Figure 5-1.

5-1

5 Protection

Secondary power backup

Figure 5-1 Centralised power protection for OTUs

5.2 Service Protection

5.2.1 1+1 Line Protection

The OptiX BWS 1600G provides protection for the lines at the optical layer

through the dual-fed signal selection function of the OLP01. The protection

mechanism is shown in Figure 5-2.

Station A

Station B

Station C

Working path

Protected path

Protectected path

Figure 5-2 1+1 line protection

As shown in Figure 5-2, two optical fibres in an optical cable are used as a

bidirectional working path, and other two optical fibres from the other optical cable

are used as the protection path. Normally, the working path carries the traffic. In

case of any anomaly on the working path, for example, the working optical cable is

broken or the performance becomes deteriorated, the traffic will automatically

switch to the protection path through the OLP01.

Moreover, the protection path is monitored in real time. When any problem occurs

on the protection path, the equipment can detect the fault and handle it in time.

Therefore, with the help of the OLP01, the DWDM equipment protects the

transmission line on the optical layer level, improving the network performance.

5.2.2 Optical Channel Protection

1+1 Optical Channel Protection

In a ring network, each wavelength can adopt optical channel protection, as shown

in Figure 5-3.

5-2

5 Protection

λn

Nomal

Protection

λn

Working wavelength

Protection wavelength

Fiber cut

Figure 5-3 Schematic diagram of optical channel protection

The advantages of optical channel protection are fast switching and no need for

protection switching protocol.

Inter-OTU 1+1 optical channel protection

For a protected wavelength, the SCS board at the transmit end separates the

incoming client side services into two channels, and sends them to the working

OTU and protection OTU. Another SCS board at the receive end combines the

services from the working OTU and the protection OTU, and sends them to the

client side. Figure 5-4 shows the mechanism.

Protection channel

Working channel

λn

West

East

West/Protection

East/Working

OTU

SCS

Add

Drop

Figure 5-4 Inter-OTU 1+1 optical channel protection

In normal conditions, the services on the working channel will be received and

further processed, while the services in the protection channel will be terminated.

That is, optical signals are output from the working channel at the receive end and

the client side optical transmitter of the protection channel is shut down.

If the LOS alarm is detected on the working channel, the services on the protection

channel will be received and processed while the services on the working channel

will be terminated. That is, optical signals are output from the protection channel

and the client-side optical transmitter at the receive end is shut down.

You can select protection or non-protection for every service channel. If protection

is required, the number of OTU boards should be doubled and a certain number of

SCS boards are required. See Chapter 11 "Protection Units" in OptiX BWS 1600G

Backbone DWDM Optical Transmission Hardware Description for details on the

SCS.

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5 Protection

This optical channel protection is usually used in ring networks.

Note

To realise 1+1 optical channel protection, it is required to set channel protection

pair on the NM.

Client-side optical channel protection

Client-side protection is only applicable to OTUs with convergence function, such

as LDG, FDG, TMX, TMXS, LOG and LOGS.

The SCS can split or couple two optical signals. As shown in Figure 5-5, after

receiving two client optical signals, the SCS splits each signal into two channels

and then sends them to the working and protection OTUs. After convergence and

wavelength conversion, the signals are sent to the line for transmission.

When a client signal received by the working OTU is faulty, only this signal is

switched. No switching is performed on the WDM side. That is, the working OTU

in the opposite end will shut down the client-side transmitting laser corresponding

to this failed channel and the protection OTU in the opposite end will turn on the

corresponding client-side transmitting laser. Other normal signals are still

transmitted through the working OTU.

The client-side protection can be seen as a subset of 1+1 OTU inter-board

protection. When protection switching occurs, only part of client-side services are

switched to the protection OTU, no need for switching all services.

Protection

Working

channel

Protection

Working

OTU

SCS

Client-side

equipment

Figure 5-5 Client-side optical channel protection

Inter-subrack 1+1 optical channel protection

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