JDSU

In my last post, I discussed the MoCA throughput performance over loss and how robust it is under ideal test conditions. It showed pretty consistent performance up to 60 dB of loss. Even at 70 dB of loss it was still providing ~45 Mbps throughput.

It is important to understand that a MoCA signal can take two different paths when it is going through a splitter backward:

1. Output port to output port isolation path
2. Output port to input port, then the signal reflects back to input to output port

The diagram below shows the 23 dB loss between output port to output port.

The next diagram shows only an 8 dB loss between two ports, because the signal bounces off the input port. In this example, the signal detects an opening and, therefore, reflects back.

Due to the interaction of both signals, the loss through the splitter somewhat unpredictable. The diagram below shows a more realistic case with a simple two-way splitter architecture, which illustrates the complexity of the loss between A and B, because of the standing wave that the reflective signal causes at the ground block. Because of the large peak and valley of the standing wave, the performance of MoCA varies significantly compared with the ideal case shown in the previous post, indicating that the throughput becomes affected at around 54 dB. Also note the huge cliff effect of the MoCA performance. In other words, by adding an additional 5 dB of loss (for a total of 60 dB loss), MoCA will no longer work at all. This is important to note, because another splitter in line could affect MoCA performance causing it to go from working perfectly to not working at all.

Fiber connectors are widely known as the weakest points in an optical network. The more connections there are in a network, the greater the potential for problems caused by improper handling during installation, operation, expansion, and maintenance. Follow the simple inspection process below to ensure fiber end faces are clean prior to mating connectors.

• Step 1—Optical Fiber Inspection: Use a probe microscope to inspect the fiber. If the fiber is dirty, go to step 2. If the fiber is clean, go ahead and connect.
• Step 2—Optical Fiber Cleaning: If the fiber is dirty, use a proper cleaning tool (like the JDSU CleanBlast fiber end face cleaning system) to clean the fiber end face.
• Step 3—Re-inspect: Use a probe microscope to re-inspect and confirm the fiber is clean. If the fiber is still dirty, go back to Step 2. If the fiber is clean, go ahead and connect.

Inspect Before You Connect Process

For more information, check out the white paper, Fiber-Handling Essentials for Next-Generation Networks at www.jdsu.com/inspect

Regarding MPEG monitoring and MPEG analysis, several people have asked me how to correlate MPEG problems using the JDSU PathTrak™ Video Monitoring and the RSAM RF probes. Because an RF probe scans, it is impossible to see all of the problems all of the time, making “scan snapshots” ineffective for localizing problems. MPEG problems are often generated in a headend that serves multiple hubs or secondary headends; therefore, problems show up downstream in multiple locations. In this case, exporting the event log to Excel is easy using the button at the bottom of the event log tab. Then you can filter it by error type. This filtering makes trends (such as PCR problems) from a faulty MUX show up easily. Based on the list of affected hubs, the headend that is common to all of the hubs can generally be determined as the culprit. If the problem is not attributable to an operator’s network equipment (a problem from the broadcast provider), then the issue, of course, shows up at all hubs. If a local modulator induces the problem, it only shows up at one hub.

If your DSAM meter display is inverted, a simple fix is available (you must have software version 3.4 or higher, and this fix does not apply to the DSAM XT).

First, press the Configure key on your DSAM meter. Next, select the General softkey, and find “Choose a utility,” and then select the Enter key. Use the arrow key (in the middle of the DSAM front panel) to select “Invert display.” From there, press the Select softkey, and then select the Enter key.

And just like that, your display is right-side up again! If you do not have DSAM software version 3.4 or higher, you can download the latest software version at http://catvsupport.com. For additional CATV test help, e-mail the TAC call center at catvsupport@jdsu.com.
 

A quick way to test if your Ethernet card is binding to your network settings is to set the Ethernet network settings accordingly on the DSAM meter.  Whether it is for a DHCP or a static IP network, it can be tested out simply by binding it to those specified settings.

To do this, go to configure/general/Ethernet networks on your DSAM and set the parameter “Obtain IP Address From” to either “DHCP” or “Let Me Specify Below.” Then go to configure/general/diagnostic/use virtual DSAM. The virtual DSAM mode will bind the Ethernet card to either a static IP if set to “Let Me Specify Below,” or it will be assigned an IP through the DHCP server on the network if set to “DHCP.”  These steps will tell you if the Ethernet card can be forced to bind and also confirm the card obtains an address via either setting on the “Obtain IP Address From” parameter.  

You can dig deeper and do more by trying virtual DSAM if you have TPP or a stand alone version of virtual DSAM. For additional CATV test help, e-mail the TAC call center at catvsupport@jdsu.com.
 

There are several QAM measurements that can be used for testing a QAM carrier in a CATV network. For instance, the MER is good for testing constant carrier to noise and CSO and CTB. However, MER lacks the ability to see intermittent or rapidly changing events. BER is good for testing for errors that occur in a CATV system, but it can only detect errors as they occur. The constellation of a QAM carrier is a good representation of the quality of the QAM downstream carrier, but it is hard to interpret and seeing all the points at the boundaries is almost impossible. The DSAM DQI or Digital Quality Index, does all the above and is very easy to interpret.

The DQI graph shown in Figure 1 has a 3 minute window and a scale from zero to ten. A 10 indicates the QAM RF is superior. A value of 9 indicates good. A value below 8.5 indicates some impairments are occurring, but the FEC is correcting them. A value below 7.0 likely indicates some uncorrectable errors.
 

For additional CATV help or to learn more about DQI on the DSAM, e-mail the TAC call center at catvsupport@jdsu.com. Also see our previous post on DQI.

In my last post, I briefly discussed MoCA basics. My next several posts will talk about how MoCA performs against different problems typically found in homes and MDUs. Specifically in this post, I will discuss how well MoCA works against loss in cable and how it affects services.

First, it is important to know that MoCA uses different frequency bans than the traditional CATV and DOCSIS® carriers. MoCA uses center frequency between 950 to 1500 MHz and occupies 50 MHz (versus the typical 6 or 8 MHz band). Because most operators want to maximize their 1 GHz plant, they typically use a frequency above 1 GHz, as shown in the graph below. The most common frequency used in the cable or telecommunications industry is around 1250 MHz.

Figure 1 - Using a frequency above 1 GHz (U.S. example)

MoCA signal paths are different than typical downstream or upstream carriers, because MoCA is used to talk between set top boxes. Figure 2 below shows two signal paths that are clearly different than TV or DOCSIS signal paths.
 

Figure 2 - MoCA signal paths

It is important then to understand how much loss MoCA can handle; and when there are problems, how it creates issues for the end user. The following test was conducted to understand how well MoCA works against different types of loss. In a real-world situation, long cables, coax topology (splitters), and intermittent connections can cause loss. As shown below, there is a MoCA TCP/IP throughput of almost 90 Mbps until the attenuation passes 60 dB. These two MoCA boxes have 10/100BaseT, so it is getting close to the maximum throughput speed without experiencing problems. TCP/IP throughput speed is not the same as the physical layer rate, which can be accessed through the set top box diagnostics. Physical layer rate is pure throughput rate including overhead in packets, so a real TCP/IP rate could be around 50 percent. In other words, 90 Mbps of TCP/IP throughput rate is equivalent to 180 or above the physical layer rate.

Figure 3 – Sending TCP/IP packets to test throughput

In conclusion, MoCA can provide very consistent performance over a wide range of attenuation. However, one area to note is that by looking at throughput rate, technicians will be unaware of how much margin remains before services are affected due to low throughput speed.

Has everybody seen what's coming in the future for your PathTrak Forward and Return Path system if you have an RPM3000? No? Check this out: http://www.youtube.com/watch?v=iDy2QGnEhTM.

Now, to get all that cool stuff, you’ve got to have an RPM3000. That means if you have an HCU full of older RPMs, you're going to have to swap them out. As with most things, there is a right way and a wrong way to do this. Here is the right way.

First and foremost, RPM cards ARE NOT HOT-SWAPPABLE! Do not simply disconnect the RF, remove the old card, and jam the new one in there; or you will not like the results. Follow the procedure/steps below for a smooth, seamless transition from either the RPM1000 or the RPM2000 to the power of the RPM3000.

1. Disable the RPM(s) that you are replacing using the PathTrak client user interface. To do this, right click on the card, select properties, and de-select the "Enable Device" box.
2. Switch off the AC power to the HCU.
3. Be sure to ground yourself against ESD using either the ESD strap that came with the HCU, or use a disposable one that came with one of your new RPM3000s.
4. Remove the old RPM card(s).
5. BE SURE THE ROTARY SWITCH ON THE RPM3000 IS SET TO MATCH THE SLOT ON THE HCU YOU ARE PLUGGING IT INTO!
6. Slide the RPM3000 into the proper slot. (If you are replacing all of the cards in the whole HCU, it is best to tighten the screws after all the cards are in place)
7. Power up the HCU.
8. Enable the RPM(s) using the same process as in step 1.

Following this process will retain all of your existing port names, configurations, and monitoring plans; and should have you up and running with the RPM3000 in no time. Remember to call the TAC call center if you need more help.

Finally, contact your local sales representative to discuss our “Upgrade by Exchange” program for the RPM3000 and save some cash by trading in your old cards!

MSO’s business services and cell backhaul deployments are showing a renewed interest in deploying coarse wavelength division multiplexing (CWDM) based systems, because of its simplicity and lower price points. Component cost is one of the driving factors for the implementation of CWDM systems. Optical fiber inspection test tools and procedures must be part of these cost savings.

Installing and upgrading CWDM equipments in the field requires several steps to guarantee that systems are set up correctly and are working error free when brought into service. Field testing serves as an important component in the turn-up and upgrade process and must be conducted at several stages during the process. From early on, JDSU has understood these challenges and developed innovative point-test tools in order for field technicians to be equipped with the right solution for the right job.

For more information on this, I highly suggest reading my CWDM application note (link here). You may also get a copy of the “Understanding CWDM Networks poster” at http://www.jdsu.com/fiber.

Typically the signal level into a forward laser is 15 dBmV for analog video, 10 dBmV for 256 QAM and 5 dBmV for 64 QAM (contact your optoelectronics manufacturer to find out the recommended level for your forward laser). All RF carriers should be within 1 dB and stable. The audio level should be 13.5 dB below the video. Ensuring these levels at all times will ensure the fiber node is getting the best possible level for balancing. If the pilot carrier is unstable, the amplifier’s AGC will change, causing the levels to fluctuate. If the video tilt carrier is off by 2 dB, the tilt for the amplifier will be either 2 dB too high or too low. Remember, there may be 5 amps in cascade and the level may vary as much as 2 dB. Add a 2 dB variation in level at the headend and you now have a 4 dB variation, which could cause the technician to fail to pass the proper level at the TV input! This will lead the technician to unnecessarily replace splitters and the drop cable.

Remember, the headend has the most stable environment in a Hybrid Fiber Coax system. With proper HFC monitoring it should be the easiest to maintain. For additional CATV help or to learn more about PathTrak™ Forward and Return Path monitoring systems, just follow the links.

Video quality is a big deal. I should know — I watch TV like the rest of the world and get irked when it looks bad! But I saw something at a customer site recently that caught my eye. Not the usual tiling or macro blocking issues that have gotten much attention recently. While those issues are common, their causes are normally pretty simple to figure out. If the content provider is giving a clean signal, it usually turns out to be an issue transporting over the core network or through the HFC (Hybrid Fiber Coax) network. If you have packet loss or BER problems, you see tiling. This was a more interesting issue.

Have you ever been watching the telly and the color sort of takes on a greenish look? Or the audio drops, you change channels, then it’s okay? Turns out these problems can be caused by PCR issues. PCR is the program clock reference in a MPEG stream that allows time synchronization between the set top box and video source so the packetized stream can be reassembled. Just to add to the fun of troubleshooting these issues, set top boxes deal with PCR impairments differently. So, not every subscriber sees the problem the same way. If you see issues described by your customers as color fade, loss of color, or audio drop—take a look at your PCR measurements.

For more digital video testing and MPEG monitoring tips, check out the JDSU MPEG pocket guide here.

To more efficiently upgrade your DSAM cable test field meter, be sure to synchronize the meter and archive any pertinent files to ensure all work is accounted for before purging the file from the meter manually. To gain access, press the round access key and select the file tab. Under the work folders category, highlight a work folder to select. Then highlight a folder at the bottom of the screen and select purge. Repeat this process for multiple work folders.

Once you have completed these steps, ensure that your DSAM is connected via Ethernet and the battery charger is plugged in with the lightning bolt icon displayed next to the battery icon. The meter is now ready to synchronize to your server for upgrading to the new version.

Be sure to contact the TAC call center if you need help.

Do you need to change the IP addresses of your RSAM devices and your PVM (PathTrak Video Monitoring) server but are not sure how to go about it? Here is an overview on how to accomplish it.

• Close the PVM client interface (if it is open) and stop the PathTrakVM service.
• Go to the properties of your network adapter (NIC Card) and change its static IP address to the new network address. (IP address, subnet mask, and gateway).
• Restart the PathTrakVM service and log onto PVM. Click on the JDSU icon in the upper-right corner to verify that it has obtained the new IP address.
• Connect to the RSAM and set the new IP address, subnet mask, and gateway. Refer to the manual on how to accomplish this. In firmware version 3.2 or higher, you only need to type the word setup at the prompt to change the IP address. From there just follow the displayed instructions.
• Enter the new PVM server IP into the RSAM. Reboot the RSAM.
• Next, go to the “configure this RSAM” section of PVM software and enter the new RSAM IP address into the PVM software for that RSAM and then select the “Test this Connection” button. If working, the reply should say:

• The RSAM will usually synchronize. If not, synchronize the RSAM.

That’s it. All of your IP addresses are changed and the system is still collecting vital information for you. Changing the IP addresses in this manner will allow you to preserve your history and naming nomenclature.

This is a high-level overview, if you need CATV help or more detailed instructions on how to change IP addresses on the RSAM equipment, the PVM server, or you have any other MPEG analysis questions, e-mail the TAC call center at catvsupport@jdsu.com. Please make reference to this blog in your e-mail.

You can now also follow JDSU on Twitter. Go to www.twitter.com/jdsu for current company news, recent industry developments, upcoming events and related information.

Great News! TPP 4.2 (TechComplete Test Productivity Pack) now works through NAT (Network Address Translation).

Click here for more information.

There are several Ethernet over Coax (EoC) technologies. One of which is MoCA, which stands for Multimedia over Coax Alliance. Verizon is using this technology for FiOS service and most MSOs in North America use it to support whole home DVR applications. MoCA will also be used to stream any IP multimedia content from the main gateway (the main set top box will be a DOCSIS® set top gateway in the future).

MoCA technology will enable streaming content from one set top to another. This signal path is unique, because it has to go through the splitter’s port-to-port isolation path or bounce off the point-of-entry filter (some operators install point-of-entry filters at the ground block to block the MoCA signal from bleeding into other houses). MoCA is built to handle 50 dB of attenuation between two set top boxes and uses orthogonal frequency division multiplexing, or OFDM, as the physical layer modulation technology. OFDM is more robust to multi-path (reflection, etc.) than single QAM and MoCA adapts the modulation type in OFDM to handle noise and loss.

Because MoCA technology is very robust, the most important aspect of successful MoCA deployment is having consistent, standardized home wiring and networking topologies to help technicians know which will work the best. Technicians need to know what splitters and in-home amps are present in the home so that they can make appropriate adjustments such as replacing the splitter with a quality splitter, removing in-home amp, swapping out two-way splitters for four-way ones to create even loss across all outlets).

For more information about MoCA visit the MoCA Alliance website at http://www.mocalliance.org.

The JDSU DSAM Remote Access Tool is a software application that is available as part of the JDSU Test Productivity Pack (TPP) product. It is also available as a stand-alone application, and both are available for download at http://catvsupport.com. The DSAM Remote Access Tool will allow you to access and control the DSAM from your computer using the remote access software application. This tool has proven to be useful in training sessions, remotely troubleshooting DSAM issues, and in some cases assisting a tech in the field. Questions arise on how to set up and use the remote DSAM feature. I will describe and illustrate just how easy it is to do. I will use TPP to illustrate the process, but the stand-alone tool works the exact same way.

After TPP is installed on your computer, find the Test Productivity icon on your desktop, open the application and login to TPP. The default login name is Administrator and the password is fdm250. Your login information may be different. In the sever box, put the IP address of the TPP server or local host if your computer has TPP Server software installed. Next, press OK. We are just doing your normal everyday logon event here. After you are logged in, select the DSAM remote access application and a software representation of the DSAM is now displayed as shown below.

Now we just need to get the DSAM to communicate with the software interface. At this point, your computer is already connected to your network or a router or cable modem. Connect the DSAM to that same network or router and turn on the DSAM. Unless are connecting the DSAM directly to your computer, use a straight Ethernet cable. If you want to connect directly to the computer, respond to my Blog and I will tell you how it is done; but the preferred way is through a network, router, or cable modem so that the DSAM can get a Dynamic Host Configuration Protocol (DHCP) IP address.

Now that the DSAM is on, select the round “Configure” key, next select the “General” soft key. Use the up or down arrow keys (in the middle of the DSAM keypad layout) and arrow over to the word “diagnostic” and select the “Enter” key. Under the header of “choose a diagnostic,” select “use virtual dsam” and then press the select soft key.

The DSAM is now requesting an IP address via DHCP. Shortly the results will be displayed on the DSAM as the bind result. This is the IP address that we will use to connect to the virtual DSAM. To enter the DSAM IP into the virtual DSAM, select “connection” on the menu bar of the virtual DSAM and then select connect to meter. In the “connect to meter” box, type the IP address of the DSAM and select OK.

It is that easy. You are now connected to your DSAM via remote access. You can now control the meter functions via your computer or use a projector for training. The DSAM remote application has proven to be a useful tool, and with these steps you can easily set it up and start using it today.