What Are Micro Reflections
The downstream IMD ratio in the cable network impairment emulator varied from -50 to -30 dBc in steps of 1 dB to model a range of IMD conditions typically present on Like Us on Facebook EE Times on Twitter follow us Tweets about "from:eetimes" Sign up for EE Times newsletter GLOBAL NETWORK EE Times Asia EE Times China EE Times Europe EE If the echo lies between these multiples, the equalizer will activate additional taps to provide interpolation. nt View All (1) Reply 0 NikT Retired Staff Posts: 1,061 Registered: 27-08-2013 Re: 2 month delay on cable modems?
Mark as New Bookmark Subscribe Subscribe to RSS Feed Highlight Print Email to a Friend Report inappropriate content by Mike2 Starter Poster on 30-12-2013 01:06 AM Message 1 of 29 (2,799 Impairments in the cable modem network can be perilous for the transmission of voice/video/data on the pipe. No more recursions. Sounds like there's been a bit of confusion around this. https://volpefirm.com/solving-problems-docsis-pnm/
What Are Micro Reflections
Before You Begin Conventions Refer to Cisco Technical Tips Conventions for more information on document conventions. This results in the cable modem exhibiting an increased error rate as the information represented by a constellation point is altered during transmission over the HFC network. The data generator/analyzer sends/receives IP packets to/from cable modems and CMTS and uses performance metrics such as packet loss and latency to evaluate performance.
The PNM application is becoming quite exciting to use as you see it solve real world problems. The benefit here is that DOCSIS 1.1 provides a series of quality of service (QoS) techniques for prioritizing voice, video, and data services in a cable modem system design. So far I've really just introduced the concept, so in this article I will give a real world example that recently happened with a client. Rf Ripple The key, however, is accounting for these impairments in the modem design.
Three DOCSIS 1.0 cable modems were individually tested with a DOCSIS 1.0 CMTS and the test results for each of the three cable modem systems are displayed on the same graph Docsis Group Delay All of the devices used in this document started with a cleared (default) configuration. The free wireless routers offered with some packages are also running low, and new stock of these, I understand, is expected early next month. 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 I collected over 50 years of the British Horological Journal.
The tap leg of each directional coupler is left open to create a reflection. In Channel Frequency Response What the heck?! Because the input return loss of the amplifier and 28 db tap is excellent, there is no further recursion of the echo. A signal is being transmitted from a house into a 28 dB tap.
- Digital Signal Levels From cable modem (upstream) +8 to +58 dBmV (QPSK) +8 to +55 dBmV (16 QAM) Input amplitude to modem card (upstream) -16 to +26 dBmV, depending on symbol
- When the signals propagating from point C and point D meet at reflection point B, they sum together and cancel.
- 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.
- Characterizing packet loss A packet loss characterization test can be used to evaluate the upstream or downstream performance of the cable modem system.
- Fiber-optic cable is primarily used to carry the data between the headend and the subscriber for a number of reasons.
- Here a are the results - all green as expected (note the upstream transmit power of 43.7 dBmV is in the ideal range of 40-50 dBmV, the SNMP monitoring system should
- The CM’s signal travels upstream attenuated by the tap’s value (28 dB), but the signal also travels downstream attenuated by only 35 dB.
- This type of echo has a characteristic impulse response of a main signal followed by a single echo.
Docsis Group Delay
Severe group delay and amplitude distortion characteristics in the upstream channel lead to increased error rates during cable modem data transmission. You guys can't seriously be preventing new customers signing up for the coming several weeks.From these forums I see you use the same modem that Comcast in the US uses. What Are Micro Reflections A way to detect if a modem is constantly ranging is to use the show cable flap-list command. Common Path Distortion Causes Some observations can be made about the performance of cable modem systems in the presence of common HFC network impairments from the sample test results presented in this article.
Whether you have group delay or micro-reflections will depend on the exact scenario. This was creating micro-reflections that were causing the CMTS to increase the transmit power of the cable modem. 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 This is some really cool tech to come to the cable industry. Ron Hranac Articles
This test examines the transmission performance of a cable modem system in the presence of variable noise and interference conditions. For more information on RF measurements using a spectrum analyzer refer to Connecting the Cisco uBR7200 Series Router to the Cable Headend. Rather than looking at the number of lost packets as the performance metric, this test measures the MER of the upstream transmission bursts. And with our luck there won't be a way to turn it off.
Anyway - thanks for your intervention - I hate to think how much longer it would have taken if you hadn't stepped in. Linear Distortion Definition David Garrison is a director of product development in the TAS Division of Spirent Communications. The first term “1” represents the main tap of the equalizer.
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.
If “a” is a relatively big number, such as 0.707 (-3 dB), and the delay “T” of the echo is several symbol periods, we might run out of taps in the It sounds like this is what the first representative you spoke with was confused about. Modeling different micro-reflection scenarios is critical for a system designer to understand how a cable modem system performs in a variety of conditions. Docsis Pre-equalization Newly-developed DOCSIS 1.1 tests provide examples of the types of noise, ingress, and interfering signals that should be used to measure the performance of the cable modem system.
Devices team, Vodafone NZ Reply 0 Mike2 Starter Poster Posts: 4 Registered: 30-12-2013 Re: 2 month delay on cable modems? Some equipment manufacturers are adding specialized features to the CMTS to gain a performance advantage by minimizing the effect of ingress. If the echoes are strong, the differences can be exploited to help a cable technician diagnose and fix the cause of the strong echo. This information was communicated to the technician.
How Cable Modems Set Their Transmit Power First the background on cable modem transmit power. Solution Accepted by topic author Mike2 03-10-2015 04:33 AM Solution Reply 0 DanielLowe Starter Poster Posts: 2 Registered: 04-01-2014 Re: 2 month delay on cable modems? In this example, the upstream performance of the cable modem system is being characterized. Avg percent contention slots Average percent of slots available for modems to request bandwidth via contention mechanisms.
Please do not purchase your own cable modem, as our cable equipment is provisioned to accounts using specific MAC addresses that must be added to our inventory by the inventory team The default value for T4 is 30 seconds. This produces another, yet smaller echo, which requires the fourth term to cancel it, and so on until we reach the end of the equalizer delay line. Packets are transmitted from the cable modem to the CMTS by the data generator/ analyzer.
Group delay impairs the transmission of certain frequencies more than others. Amplitude ripple 0.5 dB/MHz Group delay ripple 200 ns/MHz Micro reflections (single echo) -10 dBc @ < 0.5 µsec -20 dBc @ < 1.0 µsec -30 dBc @ > 1.0 µsec Hi Alan, The wireless router stock should arrive any day now, so you should be all go by mid-January. Both the CMTS and the cable modem must operate properly for the pre-equalization to maintain reliable packet transmission in the presence of micro-reflections.
These are unicast transmit opportunities for this modem's assigned SID, in which it can send a RNG-REQ to the CMTS. It then demodulates the signal and looks at the digital data the RF signal contains. Yes No Feedback Let Us Help Open a Support Case (Requires a Cisco Service Contract) Related Support Community Discussions Share Information For Small Business Midsize Business Service Provider Industries Automotive Consumer Also, if the echoes are not strong, only the first recursion is significant in both cases.
The CM MUST reinitialize its MAC after T4 seconds have elapsed without receiving a Periodic Ranging opportunity. RF Plant Quality Periodic Ranging (CM View) Periodic Ranging (CMTS View) Upstream Utilization Too High Configuring the Routing Protocol Causes a Reset of the Cable Modems Related Information Introduction This document