7. Basic Troubleshooting
In this section we review some common technical problems
in video conferencing, and suggest how these can be remedied.
We look in turn at problems with video (i.e. the image we
receive); problems with sound and connection problems (i.e.
network problems).
Problems with video
As discussed in lesson 6, we can’t expect broadcast quality
video in a video conference. We should nevertheless strive
to get the best picture quality possible. So let’s look at
some common problems with picture quality and how to improve it.
Problem |
Cause |
Solution |
The video image is blurry and jerky, with square blocks visible in the picture. |
You’re experiencing packet loss; i.e. video data is "lost" on the way from the far end party back to you.
This is a network–related problem – packet losses occur whenever there’s a bottleneck somewhere, which could be
because your network bandwidth is exceeded, or because one of the routers between you and the far end is
misconfigured (blocking packages etc). |
Reduce the call rate (e.g. from 512 kbit/s to 256 kbit/s).
If that doesn’t help, you’ll need to contact a network administrator to see if there’s a router somewhere along
the way "eating" your packets. |
The video quality is generally poor. |
If you’re using an outdated compression algorithm, video quality will not be optimized. The oldest
algorithm in use in video conferencing is called H.261, and gives poor video quality. A more sophisticated
algorithm is called H.263 which gives superior video quality to H.261. The newest compression algorithm
(as of June 2006) is called H.264, and this effectively doubles the video quality compared to H.263. |
If your equipment predates the H.264 compression algorithm, you should consider upgrading your hardware.
Unfortunately, H.264 compatibility cannot be achieved with a software upgrade; you’ll need to buy a new codec. |
I receive no video at all, but I’m getting sound from the far end. |
The far end party may inadvertently have selected a camera input with no signal, or there may be a poor
connection in some of the camera connectors. If you’re using a dual-monitor setup, the far end video connection could be faulty. |
As the far end party to check the video connectors (they may need the assistance of a technician to do this).
If you’re using a dual monitor setup, the problem could be at your end. You should check the video outputs of
your codec to see that the far end video signal is working. |
I receive neither video nor sound from the far end. |
Incompatibility issues between different brands of codecs can cause this. For instance: older Sony systems
(pre 2002-ish) are known to be incompatible with Tandberg codecs. |
There’s not a lot you can do with this. But if you’ve done your homework and tested beforehand, actions can
be taken in time to prevent a video lecture from becoming a total disaster (e.g. the far end may have to temporarily lease a codec that’s compatible with yours). |
The video picture is black and white. |
You’re using the S–video output of your codec to display the image on a TV screen, but your TV doesn't have an S–video input. |
Use the composite video output of your codec instead (or get a TV set with an S-video input) |
Problems with sound
Sound quality is in many respects more important than video,
in the sense that most people will put up with mediocre video
quality as long as the sound is good. Consequently, sound
problems should be taken seriously to ensure the best possible
sound quality.
Echo/feedback
The most common sound problem is related to the phenomenon
of echo or feedback. So what is an echo in this context? Sometimes,
when you speak into the microphone in a video conference,
you'll hear an echo of your own voice in your speakers a few
seconds later. This happens because the microphone at the
far end picks up the sound of your voice coming out of their
speakers (especially if the volume’s turned up high),
and sends it back through the codec to you.
You say the word “hello” into your microphone.
The sound of your voice is sent to the far end codec and played
through the far end’s speakers. But if the volume at
the far end is too loud, the far end microphone will pick
up your voice from the speakers, and send the signal back
to you as an echo.
In other words: if you hear an echo, the problem is (most
likely) at the other end! Echo problems crop up so often that
it deserves a special mention and a particular checklist to
eliminate echoes.
Cause |
Solution |
The sound volume is too high at the far end part. |
The other party must reduce the sound volume. |
The microphone at the other part is too close to the
loudspeakers. |
The other party moves the microphone away from the
loudspeakers (the distance should at least be 2 meters). |
The microphone at the other part is directional and
its orientation is wrong (towards speakers, not the
persons). |
The other party changes the orientation of the microphone. |
The other party has not activated the codec’s echo
control. |
The other part activates the codec's echo control
(this may require the assistance of a technician). |
The codec’s echo control might be set to a wrong size
of the video room (only a few codecs have got this functionality). |
The other part make changes in the codec’s echo control
(this may require the assistance of a technician). |
It should be noted that a slight echo at the start of a video
conference is normal. The echo cancellation mechanism in the
codecs needs some time to fine-tune itself.
Other sound-related problems
In addition to echoes, there are some other sound-related
problems worthy of a mention.
Problem |
Cause |
Solution |
The sound from the other party is muffled and weak. |
Their microphone is incorrectly orientated (if it’s
a directional microphone), or the distance from the
person who’s speaking to the microphone is too great. |
Instruct the other party to properly orientate the
microphone and reduce the distance to the microphone.
|
I’ve corrected the points above, but the sound is
still too low. |
The audio input level may be too low. |
A technician should increase the audio gain in the
codec menu. |
The sound is choppy and distorted |
If the network bandwidth is exceeded (because you’re
using too high a call rate), sound quality is affected
because audio packets are lost. |
Reduce the call rate. |
Connectivity/network problems
Network problems can make even the most thoroughly planned
video lectures a total disaster. That’s why testing
the connection beforehand is so critical.
The risk of a broken connection depends on your network configuration.
If you have a heavily crowded network and you’re holding
a multipoint conference (with three external participants,
say), there is a real danger of packet losses and broken connections.
Let’s review some common network problems, and how
these can be solved.
Problem |
Cause |
Solution |
I was in a video conference, and suddenly the connection
was broken. |
A network error can cause this. |
Try redialling. |
I've tried redialling, but to no avail. |
Once in a blue moon the codec may require restarting. |
Try restarting the codec (this can be done by pressing
the power button, or using the remote control. You may
need to contact a technician to do this) |
Restarting the codec didn't help either. |
This could indicate a more serious network error.
The network should be tested for any broken connections
and/or misconfigured routers. |
Run a traceroute program on a computer connected to
the internet. If you’re using Windows, you do this by
opening a command prompt window (by clicking Start ->
Accessories -> Command prompt) and enter the command
traceroute xxx.xxx.xxx.xxx, where the latter is the
IP address of the far end codec. The traceroute will
traverse all the routers on the way to the far end,
reporting any broken connections or faulty routers.
If the traceroute fails (i.e. if you can’t reach the
far end), a network administrator needs to be contacted. |
The traceroute works fine, but I still can’t make
contact with the far end. |
The worst case scenario is that there’s a compatibility
issue between your codec and the codec at the far end. |
There’s not a whole lot you can do about this, short
of urging the far end party to upgrade its codec. A
software upgrade may not be sufficient, though – some
older codecs just don’t work with newer codecs, and
have to be replaced. |
Because network problems can ruin your carefully planned
video lecture, it's a great asset having a codec with both
IP and ISDN capability. If either one fails, the other can
be used as a backup solution.
Note, however, that the if you’re going to make an
ISDN call to the other party, their codec also needs ISDN
capability. There’s an exception to this: if you have
access to an MCU (Multipoint Control Unit), you can "mix"
ISDN and IP connections as you please. For instance: you may
dial in to the MCU using ISDN, while the far end party is
connected by IP.
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copyright
2005-2007 MECCA Consortium