TL;DR? Got VDSL speed issues?
Then read the 'Physical Connection' section at least, then, after you've grown a pair, read the rest of this post and you'll know pretty much all you need to know about getting the most out of your VDSL connection! If you've got questions or need additional help, feel free to post in this thread; it is frequented by a number of very knowledgeable, friendly people who would be happy to help you out!
While I have professional IT experience, I am just an end user when it comes to VDSL and I'm learning as I go, so I don't expect this info to be necessarily initially 100% complete / accurate. However I will be updating this post as new or updated / corrected information becomes available. If anyone has anything to contribute or questions to ask regarding the info here, please feel free to do so. Contributors will be acknowledged in the notes at the bottom of this post.
On your VDSL router there is likely to be a number of useful pages of information relating to your connection. I will be using the snap supplied Fritz!Box 7340 as an example here. The information you will likely be using the most is on the 'DSL Information' page, which can be accessed by going to the 'Internet' menu, then selecting the 'DSL Information' option, and then clicking on the 'DSL' tab. Another, quicker way to get to this information is to click on the 'DSL' link on the 'Overview' page.
Your current receive and send sync speeds
The latency between your router and the cabinet (Note these figures can vary by 1-2ms at times, but will be on or around 1, 8 or 16 depending on which DLM profile you are on - see further down).
Shows whether bitswap is active or not. Bitswap is a method by which frequencies which have excessive noise are swapped out with other frequencies with less interference.
Impulse Noise Protection (INP):
INP attempts to compensate for noise on your line by using a 4 different profiles. This is determined automatically by DLM.
Signal-to-Noise Ratio Margin (SNRM):
This is the SNR margin which is the amount of SNR reserved as a 'buffer' to allow for unexpected noise. It is the the difference between your current SNR and the SNR required to maintain a stable connection at your current connect speed. The lower the SNR margin is, the more SNR can be allocated to data transmission and therefore the higher your sync, and subsequently your throughput, will be. Of course, a lower SNR margin leaves less reserve for errors, so there is a tradeoff. If your SNR margin drops from say 12 to 11db, then you are one db closer to hitting the lowest acceptable SNR figure. *3 *8
This is the amount of signal lost between the cabinet and your router. As detailed below, you can also calculate a rough estimate of your line length using this figure.
I am unsure what this is, but it seems to be the same (A43) for all snap users at least.
This is the Bandplan profile that your connection is currently using. This will be either 8b (50mbit max) or 17a (70mbit max). At this point it appears that Chorus will not manually change your Bandplan profile and the only way to get to a 17a profile is if DLM determines that it is appropriate to do so. *4 According to Chorus VDSL documentation, line attenuation must be less than 2.75db (in other words; you are less than approximately 200m from the cabinet) for 17a to be activated, however attenuation figures as high as 4 have been observed prior to some lines being swapped to 17a. Note that this is different to your DLM Profile (see below).
ES means 'Errored Seconds' and is the number of seconds during the current sync session where one or more CRC errors have occurred.
Many Errors (SES):
SES means 'Severely Errored Seconds' and is the number of times where there has been 10 consecutive Errored Seconds.
Remedial Errors (FEC):
FEC stands for 'Forward Error Correction' which is a method of correcting errors introduced during data transmission without having to re-send any data. These errors have frequently been observed from as low as 30 to as high as 2000 per minute but do not indicate any issues to be concerned about. *6
Non-Remedial Errors (CRC):
CRC errors occur when FEC is not able to repair corruption in the data transmission. These are the errors that you need to be concerned about. The closer this figure is to 0 the better, but from our testing it appears that it is possible to have a 'CRC Per Minute' (CRCPM) rate of up to 10 and still maintain a stable line on the DLM-1 profile (see the 'Dynamic Line Management' section below).
The 'Per Minute' figure in this section can be used to calculate the Mean Time Between Errors (MTBE) which is used by DLM as one of the measures of line stability. In order to get the MTBE, divide 1 by the CRCPM figure and you will get the number of minutes between errors. Eg; if your CRCPM is 0.1; 1 / 0.1 = 10 minutes between errors.
The spectrum tab shows performance & noise statistics relating to your line. Various groups of frequencies are used for different services and directions of data flow (as indicated *3). Frequencies are also grouped into smaller units called 'Carriers'. A carrier corresponds to a frequency band of 4312.5 Hz. Each xDSL band is subdivided into a number of carriers, of which some may be used for upstream and the remainder for downstream transmission:
ADSL1 256 Carriers (up to 1.1MHz)
ADSL2+ 512 Carriers (up to 2.2MHz)
VDSL2 8b 2048 Carriers (up to 8.8MHz)
VDSL2 17a 4096 Carriers (up to 17.6Mhz) *3
You can see which band is being used by looking at the Spectrum graph. The spectrum graph below is that of a very good line with the 17a bandplan profile enabled on it.
The upper diagram shows the signal-to-noise ratio at each individual downstream carrier.
The lower diagram is a graph of the modulation depth or 'bit loading'. The higher the modulation depth, the more bits per time unit are transmitted by the carrier. If you add the bits together you will get your sync rate.
The red marking indicates the pilot tone which is used to synchronize the DSL-Controller with the exchange.
Also, for reference, here is a near perfect line with the 8b profile on it:
Line distance to Cabinet
You can calculate the approximate distance between you and your cabinet by taking your receive attenuation figure and divide it by 13.81 - this will give you the distance in kilometers. Note that this is quite an inaccurate measure and can change as your attenuation is subject to change due to a number of factors as well.
Expected Speeds Here is a calculator for expected VDSL speeds vs distance *1. Note that is based on what VDSL is technically capable of and the setup here in NZ may give slightly different results. Signal loss is much greater at the higher frequency's that VDSL uses and is also affected by increased power on longer lines.
Unlike ADSL/ADSL2 which was quite tolerant of internal wiring issues, VDSL is not. While it is technically possible to run VDSL without a splitter or a direct connection from the cabinet to the DSL jack point, you are highly likely to experience lower performance and / or higher errors than would otherwise be achievable if you do. *2
For best results, or if you are having issues with stability or errors on your connection, there are a few things you can do to improve the line conditions:
1) If you have a POTS (analogue) phone on your VDSL line, install a VDSL capable splitter. At present, Chorus are charging ~$400 for the installation of a splitter, however, it is possible to do this yourself by purchasing a splitter from the likes of Trademe (~$30) and installing it (apparently this is very easy to do and requires only minimal technical skill).
2) If you are running a Naked connection (no POTS), a splitter is not required and is not necessarily the best option. A cheaper, and possibly better performing, approach is to connect the phone jack which your VDSL router is using directly to the incoming line, and disconnect all other phone jacks. This avoids 'signal reflections' which interfere with the VDSL signal. The absolute best method here is to run a new twisted pair (eg; Cat5 or Cat6 network cable) from the line demarcation point outside your house, directly to the back of the VDSL router (the shorter the better), but obviously this is not always possible.
Be aware that internal phone extension cables may also contribute to signal loss and the introduction of noise. If you have to use an extension cable you would be best to make one up out of twisted pair (such as Cat5/6 network cabling).
To demonstrate how much internal wiring can effect your line quality, here are some images from one user's connection, both before and after he made adjustments to his internal wiring: *12
It has been proven that faulty power multiboxes can contribute significantly to line stability issues. If you have your Fritz plugged into a multibox and are having issues, try plugging the Fritz directly into the power socket on the wall and see if there is any difference. *10
DYNAMIC LINE MANAGEMENT (DLM)
What is DLM?
DLM is an automated system for tuning the connection between your router and the cabinet in order to improve your line speeds and reduce errors. A more detailed explanation can be found here, and some additional information here. Note that this info is from the perspective of a BT service, but I think most of it is relevant to us.
DLM is an ongoing process, with an initial 10 day 'Validation' phase; which is a period where minimum connect speed baselines are determined, the line is monitored once a minute, and DLM profile changes can occur daily. After the validation phase, DLM falls back to it's normal 'Operations' mode. In this mode, the line is monitored only once a day and profiles change only weekly.
Lines are considered stable if there are no spontaneous resyncs for 48hrs, after which a dlm profile change will be initiated if there is a profile upgrade available and the expected noise margin & bit rates are sufficient.
Note that DLM will periodically re-sync your router in order to effect 'profile' changes (see below). It will do this in intervals ranging from 75 minutes (in the case of significant transmission errors) to 7 days. During the validation period, profile switches can take place at any time. During the Operations phase profile switches take place between 04:10 and 06:30. Due to the way DLM works and the time-frames involved, the best method of dealing with it is to simply wait for it to do it's thing. Significant improvements in line statistics and speeds can take weeks to come into effect. If you are not where you want to be after 2 months, then you could start looking at router tweaks to move things in the right direction.
With DLM, it is important not to reset your router too frequently (more than 2-3 times per day), especially during the first 10 day period, as this may be interpreted as instability and may adversely affect your attainable speeds or DLM profile.
There are 9 different DLM profiles which may be used on your line. *3 In the list below, the first item is the name of the profile, the second item is the latency introduced by Interleaving on the profile, and the third item is the INP (Impulse Noise Protection) figure.
DLM-1 1ms 0INP
DLM-2 8ms 0INP
DLM-4 8ms 1INP *9
DLM-6 8ms 2INP
DLM-3 16ms 0INP
DLM-5 16ms 1INP
DLM-7 16ms 2INP
DLM-8 16ms 4INP
There are also 2 Target Noise Margin (TNM) settings per profile: 9 & 12, but apparently the 9db TNM is only active when on the 17a profile.
Profiles are only changed one level at a time, you won't for instance, go from DLM-1 to DLM-4 in one step. So either TNM will be changed or INP and/or Interleaving latency will be changed as a result of a profile change.
Note that the DLM profile is different from the Bandplan Profile which determines the maximum attainable sync speed for your line (see above). Sync rates are not directly managed by DLM.
ADVANCED ROUTER TUNING
SNRM Tweaking *3
Using a couple of different methods, it is possible to adjust the SNR margin to be either above or below the standard setting to achieve one of two objectives:
1) Increased stability / lower error rates
2) Increased sync speeds
- All SNRM tweaking affects only downstream sync speeds and errors. There is currently no way to tweak upstream SNRMs.
- When evaluating the effectiveness of an SNRM tweak, you will need to run your router on it for at least 24 hours as error rates can increase to 3-4 times their initial levels after a few hours of operation.
Optimal Tweaking Procedures *11
Due to various oddities in the Fritz firmware and the DLM system, the best method to employ when tweaking your line is as follows:
1) Physically disconnect the line from the Fritz
2) Apply tweaks & allow the Fritz to reboot
3) Power off the Fritz for 5 minutes
4) Plug the line back into the Fritz and power it on
Using this method will ensure that you employ the least number of line resyncs and receive the lowest error rate possible.
If you are having issues with line instability or higher error rates than you would like, (assuming you have already sorted out your internal cabling) you can increase the SNRM on the line to increase the line stability. Obviously the side effect of this is decreased sync rates, but often, even a small (1-2mbit) speed drop can have a huge impact on error rates. Also, you may wish to sacrifice a small amount of speed to get onto (or stay on) a lower latency DLM profile.
Increasing SNRM is simple on the Fritz; on the 'Internet\DSL Information' page and the 'Line Settings' tab, simply move the 'Intended signal-to-noise ratio' left, toward 'Maximum stability'. Each move left will increase your SNRM by 1db, up to a maximum of +4db. Since an 8b VDSL profile in NZ has a standard SNRM of 12, this means that by using this method, you can increase the SNRM up to 16db. For each db of additional SNRM you will probably lose around 1-2Mbits of sync speed. Moving the SNRM setting all the way right to 'Maximum performance', will restore the standard 12db SNRM.
While +4db is the maximum possible SNRM tweak available via the GUI, it is possible to increase this using the next SNRM tweaking method.
Increasing Sync Speeds
This is the one you've all been waiting for isn't it?? :D Let's face it, it's all about the speed! If you want more speed, and you've got your internal wiring up to scratch, there's only one way to do it; configuration hacking. Be aware that this method is outside the normal operating parameters of the router, and while it is highly unlikely to cause any damage, AVM will not support the router until it's configuration has been returned to normal. In fact, after you perform this kind of hack, you will notice a 'changes not supported by manufacturer' label near the top right of the Overview page on the Fritz, and a link for 'Additional information', which explains it.
In order to perform this configuration hack, you will need to do the following:
1) Export the current router configuration to a file on your PC ('System\Save Settings' page, 'Save' tab). Note that you don't need to use a password in this case.
2) Open the saved configuration file using Notepad++ (important; using Windows Notepad will not work)
3) Add the line 'NoChecks=yes' at the top of the config file, between 'Country' and 'Language':
Note: The 'NoChecks=yes' line is case sensitive. Pay attention to the lower case 'y' at the beginning of 'yes'; if you get this wrong it won't work and you will get the following error:
4) Search for the line 'DownstreamMarginOffset = 0;'
5) Modify the 'DownstreamMarginOffset' setting as follows:
You can change the value in increments of 1 from 1 to up to 100 (1 = 0.1db, 10 = 1db)
In order to increase the SNRM, increase the value
In order to decrease the SNRM, decrease the value
6) Save the modified configuration file
7) Re-import the modified configuration file to the Fritz ('System\Save Settings' page, 'Restore' tab).
8) All going well, the Fritz should automatically restart and your hacked config should be active! If not, you've stuffed something up! :)
OTHER USEFUL INFORMATION
FritzBox Firmware Updates
The latest firmware available for the FRITZ!Box 7340 is 99.05.22, which was released in April 2012.
Restarting your Fritz
If you are getting odd behavior or higher than normal errors from your Fritz and you want to restart it, it is better to switch it off completely for 5 minutes and then back on again. I don't know why this happens (as it shouldn't), but I have tested this a number of times and confirmed that it makes a difference!
Gateway / Broadband POP Info
On a Fritz!Box, you can determine which of your ISP's Gateways or Broadband POPs you are connected to by going to the 'System' Menu, then clicking on the 'Event Log' page and then the 'Internet Connection' tab. On this tab there should be an entry from the last successful PPP connection which shows the gateway and Broadband POP you are connected to. eg;
09.07.12 22:11:17 Internet connection established successfully. IP address: xxx.xxx.xxx.xxx, DNS server: 22.214.171.124 and 126.96.36.199, Gateway: 188.8.131.52, Broadband PoP: SNAPDSL-AKL
This can be useful to check if you suspect that you are being connected to a non-local gateway. *5
Issues with Slow Upload Speeds
If your real world (eg; speedtest) upload speed is significantly lower than what your 'Current Throughput' send speed is indicating it should be, there may be an issue with unintentional rate limiting if you have a Fritz!Box. To resolve this do the following: *7
- Go to the 'Internet' menu
- Click on the 'Account Information' option
- Select the 'Internet Connection' tab
- Make a note of all of the current connection settings on this tab
- Under the 'Connection' section, select 'External Modem or Router'
- Under the 'Connection Settings' section, change both the 'Upstream' and 'Downstream' rates to 100000
- Untick the 'Check the Internet connection after "Apply" has been clicked' option
- Click 'Apply'
- After the settings have been applied, click 'OK' to go back to the previous screen
- Reapply your previously recorded connection settings
- Click 'Apply'
*1 Thanks to Instinct for this link.
*2 Thanks to sbiddle and Napster for information regarding this and much other information regarding VDSL and Internet connectivity in general.
*3 Thanks to Napster for his assistance with this info.
*4 This is still to be officially confirmed.
*5 Thanks to maxzzz for this tip.
*6 This has been observed over time by McGee.
*7 Thanks to RalphFromSnap and stevehodge for this tip.
*8 Thanks to stevehodge for clearing this up for me.
*9 Note that on the Fritz, this may show as INP: 0 rather than 1. This appears to be a bug in the firmware
*10 Thanks to Jekkyl and the snap! support team for this tip!
*11 Thanks to sidefx for his help with developing this method.
*12 Thanks to gavinbennett for these examples.
Last Updated: 13 May 2013