By adding parity bits during transmitter coding, the Forward Error Correction (FEC) technology enables the receiver to correct bit errors in the bit stream by calculating the parity bits. According to the latest ITU-T Recommendations G.709 and G.975, the STM-16 transmission rate or higher rates are now used in the FED technology to ensure the reliability of data transmission and to significantly extend the communication distance.
FEC is used very early in the extra-long-distance submarine cable systems. With the development of terrestrial optical fiber systems and the increase of single-channel transmission rate, the application of FEC becomes a optimal choice for reducing the required device tolerance and system networking costs.
1.2 FEC Classification
l FEC is also called channel coding which is a type of error control coding. It can be classified into out-of-band FEC and in-band FEC.
p In-band FEC
n In-band FEC as defined in the ITU-T Recommendation G.707 uses certain overhead bytes in SDF frames to carry supervisory elements of FEC codes. (Applicable to SDH systems)
n Advantage: Avoid the dispersion limitation by not increasing the line rate, support interface compatibility, and improve error performance by 1 dB to 2 dB.
n Disadvantage: low error-correcting tolerance.
p Out-of-band FEC
n Out-of-band FEC adopts the OTN FEC scheme and is supported by the ITU-T Recommendations G.975/709. (Widely used in WDM systems)
n Advantage: Support high code redundancy, good error-correcting capability, and high code gains of 5 dB to 6 dB, and allow convenient insertion of FEC overheads without limitation of the SDH frame structure.
n Disadvantage: The inserted overheads cause the increase of line rate. Therefore, modification is required on relevant devices.
l In the definition for OTN architecture in the G.709, the FEC overheads belong to the OTN OTUk layer and the Reed Solomon RS (255, 239) FEC codes are used as standard FEC codes. In consideration of later expansion, other codes can also be used.
Currently, the out-of-band FEC serves as the actual FEC code standard. The FEC types in Recommendations G.975 and G.709 are all out-of-band FEC, and can use RS (255, 239) codes. However, the two FEC types are different. Recommendation G.975 recommends direct FEC encoding/decoding with RS codes for SDH signals, and Recommendation G.709 defines the OTN architecture, in which the FEC overheads are defined as a part of OTN OTUk layer and thus become a standard part of the OTN architecture. In the OTN architecture, columns 3825 to 4080 contain FEC codes.
1.3 Standard Codes Of Out-Of-Band FEC
l Interleaved RS coding supports convenient encoding and decoding, and its coding structure is compatible with binary codes. RS (255, 239) (RS-8 for short) can increase line rate by 7.14%.
l The RS (255, 239) is a type of RS (n, k) coding. The maximum number of corrected burst errors in a single block: r = (n – k)/2. The RS (n, k) supports convenient encoding and decoding and its coding structure is compatible with binary codes. In RS (255, 239) (RS-8 for short), k equals 239. The 239 data bits and 16 parity bits form a packet, and the packet code length n equals 255. With RS-8, the maximum number of corrected burst errors r equals 8 and the line rate increases by 7.14%.
1.4 Out-Of-Band FEC-AFEC
ITU-T Recommendation G.975.1 proposes a powerful FEC method for the high-rate DWDM submarine optical communication systems. This method provides a more powerful error-correcting capability, compared with the RS (255, 239) FEC codes recommended by the Recommendation G.975. The use of this method can improve the transmission performance of the high-rate DWDM submarine optical communication systems.
The powerful FEC method uses cascaded codes in which the long codes are composed of short codes. No unified standards have been established for the powerful FEC method. Different companies develop their own high-gain FEC code types, resulting in poor compatibility between FEC codes. Currently, the OTU boards support adjustable FEC and AFEC to facilitate application and interconnection.
1.5 FEC Summary
The WDM products now use only two out-of-band FEC methods. In terms of coding mode, the two methods are FEC and AFEC, namely, RS coding and AFEC coding. At present, many boards support setting of AFEC and FEC. If compatibility is supported, the two methods can be used.
Talking with FEC use in Huawei transmission product, some cards for long distance use FEC coding, SF64 such us SSND00SF64(out of band STM-64 board), SF16 such as SSN1SF16(out of band STM-16 board), they are all Out of band FEC adopted.
Technical issues for 40G transport such as sensitivity, chromatic dispersion(CD) and polarization dispersion(PD) have been solved, enabling commercial deployment of 40G technology.
Most of the technical challenges associated with 40G DWDM are already widely understood, as challenges from the 10G world taken to more demanding levels. In some cases, the tighter tolerances associated with driving a 40G pulse of light down a narrow fiber requires a different response than 10G. As the following pages explain, all technical challenges have been successfully met.
- OSNR Sensitivity
40G signals occupy four times the bandwidth of signals with 10G line rates. Therefore, an optical receiver suitable for 40G utilizes a four times larger pass band. The broader pass band collects four times the optical noise of a standard 10G receiver. This explains why 40G receivers are inherently much more sensitive to optical noise and require a four times (or 6 dB) higher optical signal to noise ratio (OSNR).
Countermeasures: Enhanced forward error correction (EFEC) filters out errors that occur during transmission and reduces the sensitivity to optical noise. While only high performance 10G line cards take advantage of this technology, it is a must for 40G line cards. Furthermore, alternative modulation formats reduce the required optical bandwidth and therefore also the sensitivity to optical noise.
- Chromatic Dispersion
Compensation of chromatic dispersion was also an issue during the introduction of 10G in the late nineties. Since then dispersion compensation modules have been developed that guarantee the proper compensation of chromatic dispersion. Now, when moving from 10G signals to 40G signals, the sensitivity against chromatic dispersion increases by a factor of 16. This leads to issues with NRZ modulation, the standard for 10G DWDM. While 10G NRZ signals tolerate up to 1000 ps/nm chromatic dispersion with an acceptable penalty, 40G NRZ signals can tolerate only about 60 ps/nm. This is just too low for any practical use of 40G.
Countermeasures: New modulation formats help to reduce the influence of dispersion and so make 40G transmission feasible. In addition the dispersion compensation scheme along the line can be optimized to facilitate robust transmission of 10G as well as 40G traffic. In addition, tunable dispersion compensation modules can adjust the chromatic dispersion at the receiver site.
- Polarization Mode Dispersion
Polarization mode dispersion (PMD) is the most critical impairment for 40G transport.
Alternative modulation formats and PMD compensation enable 40G transmission on most installed fibres.
Polarization Mode Dispersion (PMD) is inherent to DWDM transmission systems and occurs when the two different polarizations of the transmitted light signal propagate with slightly different velocities through the fiber (see Figure 2). This effect can be caused by production related fiber imperfections or geometrical asymmetries as well as by mechanical stress, temperature drifts or fiber movements. Also, most of the optical components of the DWDM system itself contribute slightly to the PMD of the transmission system. While affecting a small number of 10G lines, PMD is a major limiting factor for 40G, and can restrict the
distance over which light can be transmitted over a fiber. The following guidelines apply:
- High PMD (possibly > 0.5ps/km1/2) must be assumed for fiber manufactured before 1995. Older fiber was produced with more significant imperfections than today, and was also laid in the ground and routed around corners with more stress than is now acceptable. In addition, splices connecting fibers were of a lower quality standard. For these reasons, fiber installed prior to 1995 is generally considered to be of an unknown quantity for PMD, and not suitable for 40G transmission.
- For modern fibers (manufactured since 1995), PMD is usually within acceptable limits (< 0.2ps/km1/2) for 40G transmission. Some level of PMD can be expected in 10-20% of these newer fibers, with longer transmission lengths more likely to be affected.
- For fiber laid in the ground today, PMD is usually negligible (< 0.1ps/km1/2). Fiber manufacturers are now aware of the problems caused by minute asymmetries and have modified their processes accordingly. Fiber is also laid in the ground with more care and awareness of PMD than previously.
- Air fiber is particularly vulnerable to PMD, with stresses likely when fiber moves in the wind and during switching in the high voltage network. For this reason, air fiber – even when manufactured recently – is of questionable use for transporting 40G.
So how severe a problem is PMD for 40G transport? A studyfound that 69% of the company’s fiber can be used for 40G transmissionup to 600 km without mitigating measures such as PMD compensation.
For 10G transmission, the figure climbs to 89%.
Countermeasures: Regenerating the optical signal using shorter optical paths is one possibility, but results in additional equipment costs and additional operational and maintenance effort. A far more affordable solution is to reduce the sensitivity of the 40G transmission system, either by using alternative modulation formats which are less susceptible to polarization effects or by integrating PMD compensation mechanisms into the WDM system. Compared to alternative modulation formats with still limited PMD tolerance, PMD compensation techniques can completely cancel the effect of PMD up to much higher values.
In summary, PMD is a challenge to be respected, but definitely not feared. Network operators with a modern fiber plant should not expect major problems or significant extra costs.
- Modulation Formats: What Works for 40G?
The NRZ (Non-return to zero) modulation format is the standard format for optical signal transmission up to 10G. However, NRZ lacks the necessary dispersion tolerance to accommodate 40G, making it unsuitable for this higher transmission rate. Accordingly, the DWDM industry is now moving away from NRZ and is looking for new alternative modulation formats for 40G applications. From a physical point of view, NRZ is a very basic modulation technique where light is simply switched on and off to encode the binary information onto the transmitted light. In addition to this so-called amplitude modulation, the phase or frequency of the transmitted light can also be modulated, with the various combinations of these elements resulting in a wide variety of possible modulation schemes.
Choosing a modulation scheme which best fits all requirements is a technological challenge. The modulation format has to not only improve performance for 40G transmission, it also has to be ready for commercial deployment and support interworking of the new 40G lines with 10G in the same DWDM system. Currently, two possible modulation methods, CS-RZ and duo-binary, are commercially available. Two others, DPSK and DQPSK, are under development.
4.1 CS-RZ (Carrier Suppressed Return to Zero)
CS-RZ modulation utilizes a return to zero modulation. It also engineers the phase of the optical signal in a way that the average optical signal power is reduced by one half. Therefore, the 40G signal is much less sensitive to fiber nonlinear effects and provides higher robustness against transmission impairments. It further provides improved OSNR performance and slightly improved dispersion tolerance compared to NRZ. However, CS-RZ has a fundamental limitation: it can’t operate on a 50 GHz grid necesary to support 80 channel DWDM systems. This limits its use to DWDM systems operating on a 100 GHz grid used to carry 40 channels.
The traditional NRZ modulation format is not suited for 40G transmission. Duo-binary modulation offers seemless integration of 40G technology into existing 10G networks
Duo-binary modulation (also called Phase Shaped Binary Transmission, or PSBT) also engineers the phase of the optical signal and reduces the average optical signal power by one half compared to standard NRZ signals. However, due to the phase coding, the optical bandwidth of the signal is also reduced significantly. This leads to some major advantages for the transmission of 40G. First, the CD tolerance increases from 60 ps/nm to approximately 160 ps/nm. Second, the PMD tolerance increases.
Third, 40G channels utilizing the duo-binary modulation format can be operated over a 50 GHz grid, which is standard for DWDM backbone networks. A DWDM system using duo-binary for 40G modulation even supports any combination of 10G/40G wavelengths without the need for wavelength sub-bands (not possible with other modulation formats).
4.3 DPSK and DQPSK
In contrast to amplitude modulation techniques such as NRZ and duobinary, DPSK (Differential Phase Shifted Keying) and DQPSK (Differential Quadruple Phase Shifted Keying) code the bit information directly into the phase of the optical light without touching the amplitude. This technique provides a 3dB higher OSNR sensitivity and higher transmission tolerance against system impairments. In particular, DQPSK, due to the fact that it reduces the line rate by 50% while keeping the full data rate,
provides significantly enhanced tolerance against chromatic dispersion and PMD. In contrast to DPSK, DQPSK can operate over a 50 GHz spacing, which is mandatory for DWDM backbones. However, phase coding techniques require much more complex and technically sophisticated transponders and receivers compared to amplitude modulation, driving up costs for 40G equipment. Furthermore, a lack of mature components for DPSK/DQPSK makes a commercial deployment unlikely in the near
future. When they become available, these formats will likely replace today’s modulation technology – unless, of course, another modulation format emerges in the meantime Based on these facts, For example, when DPSK is ready for commercial use, administrators can simply plug in the new transponder. It’s an advantage of having a DWDM solution that is future proof, both in terms of capacity and performance.
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1, There are two reasons may cause this problem, NMS problem or equipment problem.
2, Check other packet service board PEG8 on NMS, it can show these two RMON items, and check other PEX1 boards, it can not show these two RMON items.
3, Check the product document of this version, it shows that the current version support “port untilization” and “port bandwidth utilization” items.
4, Use command :pm-get-curdata:pmall,0xff,0,0,”” to check from equipment, also can not show the above to items.1, Send all these information to RnD, after RnD locate, it is a software bug that all the current V2R11 versions do not support these two RMON items.
1,From R12C00 and its later versions, there will have PORT_TX_BW_UTILIZATION and PORT_RX_BW_UTILIZATION, they show Tx and Rx width untilization.
2,For these two problem items, RnD will release new versions to solve it, then will optimize this case.
Firstly, Eth service is running on MSTP link with virtual concatenation. And it’s configured with LCAS.
Customer complains the link interrupts occasionally for a short time.Alarm FCS_ERR,ALM_GFP_dLFD report at the same time. The issue happens 8 times in one month.
Topology as attached. Version of equipment and boards as below:
Base on the alarm FCS_ERR,ALM_GFP_dLFD, we first check the configuration at both ends if the capsulation protocal is the same;
Then check the transmission link performance, at the faulty point there is no corresponding bit error or optical power alarm;
After replace the Ethernet boards the issue still exist;
Collect the information for R&D analysis, we found the time delay of virtual concatenation on different paths is different, and it’s beyond the limitatioin of delay range.
So we try to configure the service on the same physical path. Finally the issue resolved.
If the time delay of virtual concatenation is too much, some package can’t be framed when transmitted.But the FCS function can correct the bit error, so there is no obvious alarm. After accumulation, the bit error will be out of the limitaion and report FCS_ERRSolution: Put all service into one SDH path to avoid the the delay of Virtual concatenation.
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GSCC is a system control and communication board with part number 03020DCM. The GSCC is available in 4 functional versions: N1GSCC, N3GSCC, N4GSCC, N6GSCC. The functions provided by the functional versions are different.
NE are unmanaged and traffic is down.
This NE only have one GSCC,and Original GSCC can not use for some problem,so Customer replace the GSCC with a new one,then did the NMS download,but download failed.To make matters worse,they upload NE configuration to NMS after download failed.so configuration data on NMS and NE had been lost.1.Configuration data on NMS and NE had been lost.and didn’t find any NE database backup.
there was only NMS script and NMS mo.
2.Restored NMS configuration by importing script.
3.Got the reason for failure to download,Original GSCC software version was V100R009,but new GSCC software version was V100R006.the version was too low.
4.Upgraded new GSCC to R9 version,then download from NMS.New GSCC board version was too low,some logic boards were not supported on this version.
Upgraded new GSCC version the same as NE.Then download from NMS.
when we replace board of NE,new board should have the same version as old one.
SCC replacement,please refer to Guide as follows:
OSN3500 and OSN7500,Replacement Guide for the GSCC Boards on the NG-SDH Equipment
OSN1500 and OSN2500 and3500Ⅱ,Optix OSN1500_2500_3500Ⅱ CXL Board Upgrade Guide
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The OptiX OSN3500 incorporates an intelligent optical transmission platform and core optical transmission system to schedule and transmit services of different types and granularities. Combined with other Huawei equipment, the OptiX OSN3500 supports various networking applications, such as pure packet mode, hybrid networking (packet and TDM mode overlay networking), and pure TDM mode.
- Confirm that extension cable is connected from main to extension subrack.
- Remove the J9 jumper from AUX card.
- Undo the XCE cables from extension subrack side.
- Adding the extension sub rack cards manually by right click and add.
The root cause for this case may for:
- subrack not power up.
- XCE cards is faulty.
- XCE cables are faulty.
- U2000\ SW problem.
- Extension ethernet cable not exist.
- Remove the J9 jumper from AUX card.
- Undo the XCE cables from extension subrack side.- If you facing problem in extension subrack cards adding, remove J9 jumper from AUX card, then Undo the XCE cables and add the cards manually.
SSN1SXCSA is a Super Cross-connect and Synchronous Timing Board(Without Extension Host) with Part Number 03030DKF.
N3PSXCSA is an OSN 3500-200G TDM and 100G Packet Switching and Synchronous Timing Board with Part Number 03021ARY. The Version Description of SSN3PSXCSA is available in the following functional versions: N3PSXCSA, N1PSXCS and N2PSXCSA. The N1PSXCS and N2PSXCSA are discontinued.
Site engineer upgrde from R8C02SPC200 to R12COOSPC102+SPH103 smoothly, accordingly, upgrde the N1SXSCA board to N3PSXCSA. But it is failed when site engineer deleted the N1SXSCA board to replace N3PSXCSA. The error code(38667) of snap is following:
1, Query the cross-connection board DPS status, we found that there are no DPS relationship in cross-coonection.
2, insert the old cross-connection board and GSCC board to rollabck, and feedback the collecting data in full mode to HQ analyze.1, after analyze, expert find that the software has one bug, the software will create two DPSmanager after upgrde from R8/R10 to R12C00 and all sub-version. But it cannot create new DPS protection group when delete the original cross-connection board. So the DPS proection group is invalid. Then the substitution of cross-connection was failed. 1, The site running GSCC were two N1GSCC. the version is R8C02SPC200.And two SSN3PSXCSA.( the versoin can be R11 or R12).
2,The new GSCC is two N6GSCC(R12C00SPC102+SPH103),let site engineer degrade one N6GSCC to R11C00SPC300.( it is convenient to rollback)
3,Two SSN1SCXSA run in site NE.
4,Replace the standby N1GSCC to N6GSCC(R11C00SPC300 version).
5,Synchronize the databse from master to standby GSCC using DC tools.
6,Switch GSCC, let the N6GSCC to be master GSCC.
7,Pull out standby GSCC(N1GSCC), and backup databse using NMS.
8,Check the NE has no abnormal status, pull out the N1SXSCA, and insert SSN3PSXCSA, and configure as SSN2PSXCSA.(in R11C00 version and all sub-version just support configuring as SSN2PSXCSA)
9,After about 5 minutes, trigger cross-connection switching.
10,Replace current standby cross-connection board N1SXSCA to SSN2PSXCSA.
11,Upgrde master N6GSCC to V200R12C00SPC102+SPH103 version.
12,After master N6GSCC one line , insert another N6GSCC(V200R12C00SPC102+SPH103) in standby slot.
13,Replace current standby cross-connection board from SSN2PSXCSA to SSN3PSXCSA.(after R12 version and all sub-version just support configuring as SSN3PSXCSA)
14,Trigger cross-connection board switching.
15, Replace current standby cross-connection board from SSN2PSXCSA to SSN3PSXCSA.
16, Soft reset standby cross-connection board.
17, After the standby cross-connection board online, soft reset master cross-connection board.
18, After master cross-connection board online, upgrde all NE using stimulation pakge. And here, please eliminate GSCC because the two N6GSCC have already upgrded.Becuase it can save the time of upgrding N6GSCC.
1, Upgrade from R8/R10 to R12C00 and sub-version, and replace the cross-connection board, we have to first upgrde to R11C00 and sub version( suggest to use R11C00SPC300), the upgrde guidancewill be modified in supporting website.
2, If upgrade failed using above solution becuase some abnormal cause, we can insert the original N1GSCC and SSN1SXCSA board to rollback.
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The SSND00EFS411 is a 4-port 10M/100M Fast Ethernet Processing Board with LAN Switch. Part Number: 03020KHU. Compatibility: OSN7500, OSN 3500, OSN 2500, OSN 1500. SSND00EFS411 is available in three functional versions, namely, N1, N2 and N3. The difference between the three versions is their different maximum uplink bandwidths. The N1EFS4 and N2EFS4 are discontinued.
Some customer added N2EFS4 board recently to slot #4 of osn3500. Board software versions is not match with NE Software version. Customer tried to update EFS4 board software using V100R008C02SPC200
package by DataCenter, but Data Center do not recongnize slot 4 EFS4 board. See Load Package menu screenshot- board #4 is missing.
BID BD-Name BD-TYPE PCB
4 SSN3EFS4-B2 0x602b 0
PCB Version : SSN5EFS001 VER.A
BIOS Version : 2.02
ExtBIOS Version : 2.03
Software Version : 2.61
Logic Version : (U130)130
2. check version matching table, it should be 2.51.
|1500、2500、3500、7500||Realized in R9.In case the NE software is of the R9 or a later version, the logical board can be configured as SSN1EFS4、SSN2EFS4、SSN3EFS4. In case the NE software is of a version earlier than R9, the logical board can be configured as SSN1EFS4、SSN2EFS4.|
4. due to this board is realized in R9, its software not in the package of V1R8, but at EXT file.
OptiX OSN 1500_2500_3500_7500 V100R008C02SPC200 Software_VPKG_20130221.zip
OptiX OSN 3500 V100R008C02SPC200 Software EXT_20130221.zip
5. after confirm there is the board software in EXT file, using board level loading upgrade board successfully.due to no N3EFS4 board software in software VPKG , DC cannot find it. need use board level loading and find the software in EXT file.
need use board level loading and find the software in EXT file.
before upgrade should check each board physical type first.
and check Board Version Replacement in version matching table, confirm need find the board software in general package file or EXT file.
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All the Node B should be aggregated through RTN with MSTP+equipment at aggregation site and then integrated with RNC through two active/standby switch followed by protected Tx path. Also MSTP node should be aggregated with MSTP+ at RNC Station which carrying EoS service to integrate Node B. Please see the following basic network architecture as per requirement.
According to the customer requirement network architecture and connection diagram is given bellow. Here we developed MPLS network with 1:1 MPLS Tunnel Protection. MSTP+nodes are configured as E-Line via PW service at aggregation site and VPLS service at RNC station.VRRP Heart Bit of master/slave switch should be pass through MSTP+equipment.Link protection achieved between MSTP+and MSTP node by configuring LAG at MSTP+and DLAG at MSTP+end.
For an example,4 interfaces f two different PEG8 Boards(port 1-2 and port 3-4) are configured as UNI interfaces of VPLS service. Port1 and Port4 are connected to the corresponding Master and Slave Switch and configured Admin VRRP VLAN to pass VRRP Heart Bit from Master to Slave Switch. Port 2 and Port 3 are connected with two different EGS4 Boards of MSTP equipment and configured LAG(as static,load non-sharing & non-revertive mode) at MSTP+and DLAG at MSTP node.
1. 1:1APSTunnelProtectionconfiguredtoutilizebandwidthofprotectionpathforotheraggregated service carryingMSTP+nodeduringnonfailurecasesofworkingtunnel.
3. Using different UNI interfaces (in above example port 1/4 and port 2/3) from different PEG8 board under same VPLS services to achieve board level protection.
4. In case of MSTP+and MSTP inter connection,LAG and DLAG protection scheme adapted instead of BPS at MSTPtoavoidunnecessaryalarmreportedatprotectionpathinterfaceofMSTP+node i.e ETH Link Down (as MSTP+doesn’t support BPS protection scheme).
5. Finally service provisioning becomes more convenient to integrate new Node B by only adding VLAN sat UNIinterfacesofVPLSserviceandalsosimplifyconfigurationprocesstoaddnumberaggregatedPW services by adding their respective PWID sand VLANs.
At first Master and Slave switch was directly connected with each other to pass VRRP Hear Bit. When we interconnect MSTP+with both Switch through two UNI interfaces of VPLS service, it became loop as both UNI interface flow the same service VLAN and also same VLAN passed between Master & Slave Switch(as all the interfaces configured as layer two). Please find the following diagram for reference.
To avoid loop generation problem we passed the VRRP Heart Bit through MSTP+i.e. through UNI Interfaces(port 1&4) of VPLS Service and configured Admin VRRP VLAN at both UNI inter faces which used to trace the path status and to change the state(master/backup)of Switch.
After completion of MPLS Network Configuration through MSTP+equipment as described above, following test has been per formed before going to put live traffic.And now the 3G services through MPLS Network are running perfectly and soundly.
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