Home > Cable Modem > What Are Micro Reflections

What Are Micro Reflections


Rather than looking at the number of lost packets as the performance metric, this test measures the MER of the upstream transmission bursts. The first type is echoes – call them “multiple recursion” – that are created by two or more impedance discontinuities inside the cable. What the heck!?? It sounds like this is what the first representative you spoke with was confused about.

The CMTS MUST send out Periodic Ranging opportunities at an interval sufficiently shorter than T4 that a MAP could be missed without the CM timing out. For best performance it is recommended that 2000 homes passed per fiber node with ~10% penetration yielding 200 subscribing cable modems per upstream port is a highly effective framework by which This in turn causes all cable modems on that particular downstream to reinitialize, potentially interfering with data transmission on that downstream. The combined response of multiple filters produces increasing group delay and amplitude distortion near the edge of the filter passband. Get More Information

What Are Micro Reflections

Mark as New Bookmark Subscribe Subscribe to RSS Feed Highlight Print Email to a Friend Report inappropriate content by Mike2 Starter Poster on ‎02-01-2014 12:32 AM Message 4 of 29 (2,707 Cable modem systems must deal with a variety of impairments. Per the DOCSIS standard, when your upstream exceeds 200 nano-seconds / MHz you are no longer DOCSIS compliant.

You will need a free account with each service to share an item via that service. I much prefer silence from my appliances. The DOCSIS RF-PHY-22 upstream packet error rate test details a frame loss characterization test, which finds the carrier signal-to-impairment ratio that produces a target packet loss value. Rf Ripple David Garrison is a director of product development in the TAS Division of Spirent Communications.

However as she was on your faults team, she was unable/unwilling to talk to Downer and see if they could use any DOCSIS2.0 modems as an interim (as I presume the Docsis Group Delay The Class of Service for these modems specifies some non-zero value for the guaranteed upstream rate. The lack of a termination causes the signal to reflect back upstream, where it rejoins, after some time delay, the main signal. http://community.vodafone.co.nz/t5/Broadband-services/2-month-delay-on-cable-modems-What-the-heck/td-p/113496/jump-to/first-unread-message They installed the Modem last week?

There is still some in-channel ripple and indicates that there is another very small impairment over a thousand feet away, but nothing worth worrying about now since the modem is marked In Channel Frequency Response Periodic Ranging (CM View) The CMTS MUST provide each CM a Periodic Ranging opportunity at least once every T4 seconds. And with our luck there won't be a way to turn it off. Packets were again transmitted from CMTS to the cable modem for a period of 90 seconds for each step of the test and the packet loss was measured by the data

  • CableLabs has established a “DOCSIS Proactive” working group with the goal of utilizing the data in DOCSIS-based communications systems to improve plant operations.
  • Regardless of how well an HFC network is designed, some level of ingress and other interfering signals will be present and will have some effect on the performance of the cable
  • More on the maximum number of users can be found in What is the Maximum Number of Users per CMTS?.
  • Micro-reflections Impedance mismatches between items in the coaxial cable plant, such as amplifiers, couplers, and the coax cable, produce another impairment called micro-reflections.
  • Bandlimited noise and modulated interferers best model transient ingress conditions that can be present at severe levels for a given set of frequencies.
  • Various types of noise and interference, including wideband noise, bandlimited noise, or modulated interference, can be used to model the different conditions that are present on the HFC network.
  • Handling micro-reflections The upstream performance of a cable modem system can be characterized using a modulation error rate (MER) versus micro-reflections test.
  • Using the PNM application we are able to locate the type of impairment and the location of the impairment with a very high degree of certainty.
  • A pair of directional couplers is chosen, with tap values selected to adjust the strength of the echo.
  • New stock arrived early December, and I should not imagine it has been depleted this rapidly!

Docsis Group Delay

Configuring the Routing Protocol Causes a Reset of the Cable Modems Be aware that when configuring a routing protocol on a Cisco uBR7200 series cable interface on older versions of IOS https://www.cedmagazine.com/article/2010/04/docsis-upstream-cable-echoes-come-two-flavors When the signal reaches the end of the line, it encounters a two-way splitter that is not terminated. What Are Micro Reflections The system returned: (22) Invalid argument The remote host or network may be down. Common Path Distortion Causes THE MATHA single recursion echo can be modeled by: 1 + a, where 1.0 is the main signal amplitude and “a” is the echo’s amplitude in linear terms.

The CM has already transmitted an inverse first recursion, shown at point D. This field also shows how many of these modems are active. So yet another recursion is needed to take out the echo in the signal you used for cancellation, and so forth, repeating endlessly. The HFC network Multiple service operators, (MSOs) have completed extensive upgrades to their cable network transmission facilities to support high-speed, two-way data, voice, and video communications. Ron Hranac Articles

The key, however, is accounting for these impairments in the modem design. Mark as New Bookmark Subscribe Subscribe to RSS Feed Highlight Print Email to a Friend Report inappropriate content by NikT Retired Staff on ‎03-01-2014 11:06 AM Message 5 of 29 (2,674 Related Information Determining RF or Configuration Issues on the CMTS Troubleshooting [uBR7200] Troubleshooting uBR Cable Modems Not Coming Online Connecting the Cisco uBR7200 Series Router to the Cable Headend Flap List With micro-reflections the cable modem signal goes to the CMTS, but at the same time a small reflected signal (a micro-reflected signal if you will) is following the main cable modem

No phone call to explain why not. Linear Distortion Definition Seriously? One fundamental point that will ensure success is keeping customer return domains within reason.

Note: For a full set of the specifications for the European Standard, please read RF Specifications.

Apologies for the miscommunication on this one, the DOCSIS 3.0 modems are definitely in stock, and I've passed feedback along. Note: Best to keep this around 200 maximum. Avg percent contention slots Average percent of slots available for modems to request bandwidth via contention mechanisms. Docsis Pre-equalization What the heck?!

Note that the recursions in the above equation have alternating signs. However, the equations are easier to present if we simply use “a.”  The equalizer solution for a single recursion echo is  So the result is what was expected: infinitely recursive. The modem is considered offline by the CMTS if there is no reply after these retries. If a UBR9xx modem goes offline because of a T4 timeout, you will see following error messages in the debug cable mac log: router#debug cable mac log verbose .... 11:05:07: 39907.082

This type of echo has a characteristic impulse response of a main signal followed by several echoes, with each succeeding echo having smaller amplitude. (An impulse response is nothing more than However, in doing so, it causes another, smaller echo in the response. An example set from a packet loss versus CNR test is shown Figure 3. Generated Thu, 02 Feb 2017 06:59:09 GMT by s_nt6 (squid/3.5.23) ERROR The requested URL could not be retrieved The following error was encountered while trying to retrieve the URL: Connection

The PNM application is becoming quite exciting to use as you see it solve real world problems. The resulting impulse response is shown at the bottom of Figure 3. This is some really cool tech to come to the cable industry. What the heck?! [Edited] Mark as New Bookmark Subscribe Subscribe to RSS Feed Highlight Print Email to a Friend Report inappropriate content by johnr Ninja Master ‎04-01-2014 03:55 PM - edited

Check the received upstream SNR level. Periodic Ranging (CMTS View) The CMTS will retry polling the CM until it either receives a reply or until the number of retries (default is sixteen) are exhausted. A better method would be to let the cable modem do the work for you. What the heck?! [Edited] Mark as New Bookmark Subscribe Subscribe to RSS Feed Highlight Print Email to a Friend Report inappropriate content by NikT Retired Staff ‎30-12-2013 10:13 AM - edited

A signal is being transmitted from a house into a 28 dB tap. I do hope this issue will be sorted out soon as we were both advised that we would be installed with new modem and wireless router by mid january 2014. If you found this interesting or useful, please use the links to the services below to share it with other readers. He replaced the connector just in case there was existing corrosion on it.

Group delay and micro-reflection impairments have been covered in many other articles, but it is always good to have a cursory reminder. I collected over 50 years of the British Horological Journal. Hi Daniel, Really sorry to hear you've had a run-around. See solution cable Home Broadband Modem Shortage Router Shortage View All (4) Solved!

by MikeHales 1 Kudo Modem by gilmo 0 Kudos Our company Corporate responsibility Our Executives Media centre Careers Legal Why Vodafone Network Environment Sponsorship Buying online Delivery Returns & exchange Trade