Huawei OptiX BWS 1600G. Technical Description - part 19
A Measures in DWDM Network Designing
A.3 Optical Signal-to-Noise Ratio
Noise Generation Principle
The optical amplifier also generates the light signals with broad bandwidth, called
amplified spontaneous emission (ASE). In a transmission system with several
cascaded EDFAs, like original signals, ASE noise of the optical amplifier can be
attenuated and amplified. As the entered ASE noise is amplified in each optical
amplifier and is overlapped on the ASE generated by the optical amplifier, the total
ASE noise power is increased in proportion to the number of optical amplifiers. The
noise power might be more than the signal power.
ASE noise spectrum distribution varies with the system length. When ASE noise
from the first optical amplifier is sent to the second optical amplifier, the gain
distribution of the second optical amplifier will cause ASE noise due to gain
saturation, which will cause gain distribution change. Similarly, the valid gain
distribution of the third optical amplifier will also be changed. This effect will be
transmitted to the next optical amplifier towards downstream. Even the
implementation of narrow-band filter cannot avoid this noise, because the noise
exists in the same band in which the original signal exists.
The optical signal-to-noise ratio (OSNR) is defined as:
OSNR =signal optical power per channel/noise optical power per channel
Transmission Restriction
ASE noise accumulation affects the system’s OSNR, because the receiving signal
OSNR deterioration is mainly related to ASE beat noises. Beat noises are increased
linearly with the increase of optical amplifier number. Therefore, the error rate is
deteriorated together with the increase of optical amplifier number. In addition,
noises are accumulated as exponentially with the gain range of amplifiers.
As a result of optical amplifier gain, ASE noise spectrum with the accumulation of
ASE noises from multiple optical amplifiers will have a wavelength peak caused by
the spontaneous emission effect. It should be noted that in a closed full optical loop
network system equivalent to innumerable optical amplifiers are cascaded, ASE
noises will be infinitely accumulated. In the system with narrow band filters, the
ASE accumulation will be reduced due to the filter, but the in-band ASE will be
increased with the increase of optical amplifiers. Therefore, OSNR will be smaller
for more optical amplifiers.
Consideration of OSNR in DWDM Network Design
(Note: This section contains additional information. You may skip this section).
For different network applications, the OSNR requirements are more or less similar,
as given in Table A-1.
A-3
A Measures in DWDM Network Designing
Table A-1 Recommended OSNR values for different spans
Amplifier cascade type
OSNR (dB)
5 × 20 dB system (5 × 72 km)
20
2 × 24 dB system (2 × 87 km)
20
1 × 28 dB system (1 × 101 km)
20
OSNR is an important factor of DWDM system error performance. For a DWDM
system with multiple cascaded line optical amplifiers, the optical power of noises
are mainly controlled by the ASE noises of the amplifiers.
In the actual DWDM system, the different EDFA gain might cause different output
power per channel and different EDFA noise coefficient. Therefore, in designing,
OSNR of the worst channel should be considered to stretch the working limits.
A.4 Other Effects
The above three factors should be considered in DWDM networking. In addition,
many other factors might affect system performance, such as SBS (Stimulated
Brillouin Scattering), SRS (Stimulated Raman Scattering), SPM (Self Phase
Modulation), XPM (ex-Phase Modulation), FWM (Four-Wave Mixing), PMD
(Polarized Mode Dispersion) and PDL (Polarisation Dependent Loss). The effect of
these parameters on the system is not significant and is not considered in network
designing. But in case of some unusual system response, these parameters should
be checked carefully.
A-4
B Technology Introduction
B
Technology Introduction
B.1 FEC
The optical wavelength conversion units have forward error correction (FEC)
function or Enhanced FEC (EFEC ) function.
In fact, the FEC technology is the error correction technology. The OTU adopts
Reed-Solomon Coding. It can correct eight byte errors at most in any location per
255 bytes, and has a fairly powerful capability of error correction. Due to
redundancy codes added, the digital rate is increased. The FEC employed in the
OptiX BWS 1600G is in compliance with the ITU-T G.709 or G.975 and supports
the processing of overhead as stated in the ITU-T G.709.
The EFEC technology, compared with FEC, adopts much more predominant
encoding/decoding technology. Two-degree encoding/decoding can evenly
distribute the burst error code, and enable much more powerful error correction
capability.
The FEC function can improve the OSNR budget of the DWDM transmission
system and increase the transmission distance. In addition, the FEC function can
reduce bit error rate in line transmission, and alleviate the effects on the signal
transmission quality caused by the aging components or deterioration of fibre
performance, thereby improving the communication quality of the DWDM
transmission network.
B-1
B Technology Introduction
B.2 SuperWDM
Introduction
SuperWDM is a transmission solution provided by Huawei DWDM products for
long-haul application. Super CRZ encoding is the core technology for SuperWDM
solution. It inherits all the features of RZ encoding and is enhanced with a unique
phase modulation capability. Therefore, the Super CRZ encoding is capable of
effectively suppressing the non-linear effects in transmission and improving the
noise tolerance capability.
With the SuperWDM technology, the OptiX BWS 1600G achieves ultra long haul
transmission in the absence of Raman amplification. Compared with NRZ
encoding, Super CRZ encoding widens its spectrum thus effectively suppressing
the non-linear effects in ultra long haul transmission. As a result, the linear
transmission distance of the DWDM system without REG is greatly extended to
2000 km.
Features
Improve the optical noise tolerance capability, increasing the receiver’s
OSNR tolerance by 3 dB (compared with NRZ encoding).
Effectively reduce the non-linear effects due to its adequate spectrum width
and special phase modulation technology.
Improve the transmission performance due to excellent clock jitter
performance and higher extinction ratio.
The application of SuperWDM technology in the system requires excellent
dispersion management.
B-2
B Technology Introduction
B.3 Raman Amplification
The Raman amplifier is an important application of stimulated Raman scattering
(SRS). Quartz fibre has a very broad SRS gain spectrum. It has a broad peak near
the frequency of 13 THz. If a weak signal and a strong pump light are transmitted in
the fibre simultaneously, and their frequency difference is within the range of
Raman gain spectrum, the weak signal beam can be amplified. The gain spectrum
of the fibre Raman amplifier is shown in the Figure B-1.
Pump light
Gain
13THz(70 nm-100 nm)
30nm
Figure B-1 Raman amplifier gain spectrum
The fibre Raman amplifier is always used with the EDFA amplifier at the receive
end. It adopts distributed amplification mechanism for extra long haul and extra
long span applications, as shown in Figure B-2.
Raman amplifier
Signal light
EDFA
EDFA
Pump light
Pump light
Laser
Fiber
Transmitting end
Coupler
Receiving end
Figure B-2 Raman amplification application in OptiX BWS 1600G system
Usually the optical fibre Raman amplifier is used at the receive end of DWDM
system to amplify optical signals. Mainly composed of pumping lasers, the Raman
amplifier works in a way of counter pumping.
Note
Counter pumping means the pump light is injected at the fibre end and the direction
is opposite to the main signals. This kind of pumping achieves a big phase
difference between the main signals and the pump light. And the Raman pump
power vibration is leveled in the direction opposite to signal transmission, thus
effectively suppressing the noise created by the pump.
B-3
C Glossary
C
Glossary
This document defines the following terms:
Numerics
3R
Regenerating, Reshaping and Retiming.
A
ADM
Add/Drop Multiplexing. Network elements that provide access to all, or some
subset of the constituent signals contained within an STM-N signal. The
constituent signals are added to (inserted), and/or dropped from (extracted) the
STM-N signal as it passed through the ADM.
Administrator
A user who has access rights to all the Management Domains of the EMLCore
product. He has access to the whole network and to all the management
functionalities.
Agent
Agent is used to describe the entity that represents certain attributes and behaviour
of a resource. The agent allows interaction between various resources and
management and control functions. More than one agent may represent a resource.
Alarm boolean value
The value to alarm, which set to define, simplify and manipulate logical function
based on statements which are true or false.
Attenuator
A passive component that produces a controlled signal attenuation in an optical
fiber transmission line.
B
Bandwidth
The highest frequency that can be transmitted by an analog system. Also, the
information-carrying capacity of a system (especially for digital systems).
C
Chain network
Type of network that all network nodes are connected one after one to be in series.
CRZ
Chirped Return to Zero.
C-1
C Glossary
D
DCC
Data Communication Channel. Within an STM-N signal there are two DCC
channels, comprising bytes D1-D3, giving a 192 kbit/s channel, and bytes D4-D12,
giving a 576 kbit/s channel. D1-D3 (DCCR) are accessible by all SDH NEs
whereas D4-D12 (DCCM), not being part of the regenerator section overhead, are
not accessible at regenerators.
DCF
Data Communication Function.
DCN
Data Communication Network. A communication network within a TMN or
between TMNs which supports the data communication function (DCF).
Distributed service
The transmitting services are distributed between each neighboring nodes
connected over a ring network.
DVB-ASI
Digital Video Broadcasting-Asynchronous Serial Interface.
DWDM
Dense Wavelength Division Multiplexing. DWDM technology utilizes the
characteristics of broad bandwidth and low attenuation of single mode optical fiber,
employs multiple wavelengths with spacing of 100GHz or 50GHz as carriers, and
allows multiple channels to transmit simultaneously in the same fiber.
E
ECC
Embedded Control Channel. An ECC provides a logical operations channel
between SDH NEs, utilizing a data communications channel (DCC) as its physical
layer.
EDFA
Erbium-Doped Fiber Amplifier. Optical fiber doped with the rare earth element
erbium, which can amplify at 1530 to 1610 nm when pumped by an external light
source.
ESC
Electric Supervisory Channel. It owns the same function with OSC to realize the
communication among all the nodes and transmit the monitoring data in the optical
transmission network. The difference is monitoring data of ESC is introduced into
DCC service overhead and is transmitted with service signals.
ESCON
Enterprise System Connection.
Ethernet
A data link level protocol comprising the OSI model's bottom two layers. It is a
broadcast networking technology that can use several different physical media,
including twisted pair cable and coaxial cable. Ethernet usually uses CSMA/CD.
TCP/IP is commonly used with Ethernet networks.
Extinction ratio
The extinction ratio (EX) is defined as:
EX = 10 log10 (A/B)
where
A is the average optical power level at the centre of the logical "1"; and
B is the average optical power level at the centre of the logical "0".
Eye pattern
A graphic presentation formed by the superimposition of the waveforms of all
possible pulse sequences.
C-2
C Glossary
F
FC
Fiber Channel. A standard for transmitting signals at 100 Mbit/s to 4.25Gbit/s over
fiber or (at slow speeds) copper.
FDDI
Fiber Distributed Data Interface. A standard for a 100-Mbit/s fiber-optic local-area
network.
FE
Fast Ethernet.
FEC
Forward Error Correction. A method to detect and correct certain error conditions
with redundant coding.
FICON
Fiber Connection.
G
Gain spectrum-shape
The technology to keep the gain into being a basically fixed value.
pre-tilt
GE
Gigabit Ethernet.
I
Insertion loss
It is the reduction in optical power between an input and output port of a passive
component in decibels. It is defined as:
⎛
P
⎞
out
IL
= −10 log⎜
⎟
⎝
P
⎠
in
where:
P
in
is the optical power launched into the input port and Pout the optical
power received from the output port.
IPA
Intelligent Power Adjustment. The system controls and adjusts automatically the
optical power in the transmission link in order to be against the situations like as
fiber is broken, the performance of equipments trend to be inferior or the connector
is not plugged well. Also the maintenance engineers are not hurt by the laser being
sent out from the slice of broken fiber.
Isolation
A non-reciprocal optical device intended to suppress backward reflections along an
optical fibre transmission line while having minimum insertion loss in the forward
direction.
J
Jitter
Variations in a short waveform caused by voltage fluctuations.
Jitter transfer
This is the relationship between jitter applied at the input port and the jitter
appearing at the output port.
C-3
C Glossary
L
Laser
One of the wide range of devices that generates light by that principle. Laser light is
directional, covers a narrow range of wavelengths, and is more coherent than
ordinary light. Semiconductor diode lasers are the used light source in fiber-optic
system.
LCN
Local Communication Network.
M
MAN
Metropolitan Area Network. An IEEE-approved network that supports high speeds
over a metropolitan area.
Mean launched power
The average power of a pseudo-random data sequence coupled into the fiber by the
transmitter.
MF
Mediation Function. In telecommunications network management, a function that
routes or acts on information passing between network elements and network
operations.
N
NE
Network Element. A stand-alone physical entity that supports at least network
element functions and may also support operations system function or mediation
functions. It contains managed objects, a message communication function and a
management applications function.
NEF
Network Element Function. A function block which represents the
telecommunication functions and communicates with the TMN OSF function
block for the purpose of being monitored and/or controlled.
NM
Network Management. Any aspect of monitoring or controlling a network,
including all administration details.
Noise figure
The specification to scale the random signal in the system presenting in addition to
any wanted signal.
O
OCP
Optical Channel Protection. With the way to back up the working optical channel,
it supports primary channel with multiple wavelengths and standby one in order to
be against the situation that there is any fault in the primary channel.
OLP
Optical Line Protection. With the way to back up the working link, it supports
primary optical transmitting link with multiple wavelengths and standby one in
order to be against the situation that there is any fault in the primary link.
Optical amplifier
A device or subsystem in which optical signals can be amplified by means of the
stimulated emission taking place in an suitable active medium. In this active
medium a population inversion, needed to advantage stimulated emission with
respect to absorption, is achieved and maintained by means of a suitable pumping
system.
Optical channel
C-4
C Glossary
Optical demultiplexer
A device which performs the inverse operation of a wavelength multiplexer, where
the input is an optical signal comprising two or more wavelength ranges and the
output of each port is a different preselected wavelength range.
Optical multiplexer
A branching device with two or more input ports and one output port where the
light in each input port is restricted to a preselected wavelength range and the
output is the combination of the light from the input ports.
Optical return loss
It is the fraction of input power that is returned from the input port of a passive
component. It is defined as:
RL = -10 log (Pr / Pi)
where :
Pi is optical power launched into the input port and Pr the optical power received
back from the same input port.
OS
Operations System. A physical block which performs operations systems functions
(OSFs).
OSC
Optical Supervisory Channel. It realizes the communication among the nodes in the
optical transmission network and transmits the monitoring data in the certain
channel (the wavelength of the working channel for it is 1510nm and that of the
corresponding protection one is 1625nm).
OSNCP
Optical Sub-Network Connection Protection.
OSNR
Optical Signal-to-Noise Ratio. Ratio of the amplitude of the transmitted optical
signal to the noise on the received signal.
P
PDH
Plesiochronous Digital Hierarchy. It is the first multiplexing hierarchy used in
digital transmission systems. The base frequency was 64Kbit/s, multiplexed up to
2048, 8448, 34,368 and 139,264 kbit/s. There was more than one standard system
and it varied between Europe, the US and Japan.
PIN
A semiconductor detector with an intrinsic (i) region separating the p- and n-doped
regions. It has fast linear response and is used in fiber-optic receivers.
Polarization
The maximum variation of loss due to a variation of the state of polarization of the
dependence loss
input signal at nominal operating conditions.
Q
QA
Q Adapter. A physical block that is characterized by a contained Q adapter function
block and which connects NE-like or OS-like physical entities with non-TMN
compatible interfaces (at m reference points) to Q interfaces.
QoS
Quality of Service. The collective effect of service performances, which determine
the degree of satisfaction of a user of the service.
C-5
C Glossary
R
Reflection coefficient
The difference between the amount of light incident and the amount that is
reflected back from a surface.
Regenerator
A receiver-transmitter pair that detector and amplifiers a weak signal for
retransmission through another length of fiber.
ROADM
Reconfigurable Optical Add/Drop Multiplexer. A device that can block or pass
through any wavelength channel carrying the multiplexing signals so as to
implement the reconfiguration of the corresponding wavelength in the main optical
path. Therefore, it can configure flexibly and dynamically the wavelength resource
among each node in the network under the situation not to impact the running of the
working channel.
S
SDH
Synchronous Digital Hierarchy. A hierarchical set of digital transport structures,
standardized for the transport of suitably adapted payloads over physical
transmission networks.
Self-healing
Establishment of a replacement connection by network without the NMC function.
When a connection failure occurs the replacement connection is found by the
network elements and rerouted depending on network resources available at that
time.
Service protection
The measures to make sure the service transmitting not to be damaged or corrupted.
Side mode
The ratio of the largest peak of the total source spectrum to the second largest peak.
suppression ratio
Splitter
A device that divides incident light into two separate beams.
Star network
Network of several nodes where each terminal is linked individually to a central
node.
STM
Synchronous Transport Module. It is the information structure used to support
section layer connections in the SDH. It consists of information payload and SOH
information fields organized in a block frame structure. The information is suitably
conditioned for serial transmission on the selected media at a rate which is
synchronized to the network.
Sub-wavelength
One of the several wavelengths carrying service signal on the client side of OTU
board.
SuperWDM
A technical solution can extend effectively the transmitting distance of DWDM
system with the application of Super CRZ encoding and the advanced phase
modulation capability.
T
Telecom management
The entity which provides the means used to transport and process information
network
related to management functions for the telecommunications network.
U
Unit management
Designates the management functions performed on units assembled in a network.
layer
C-6