Network Delivery Mechanisms - A Practical Guide to Video and Audio Compression - page 340

stream. The H.264 codec introduces a certain amount of error resilience and there may be
some smart things the decoder can do to help. Strangely enough, loss of data in the audio
is actually more disturbing to the viewer than the visual artifacts when data is lost from
the video channel.
If severe data loss occurs, you may notice jerky movement since the player is drop-
ping frames in order to make its best effort to play the video. The player may also drop
frames if the available bit rate falls so low that it cannot preserve the time base unless it
sacrifices a frame occasionally. The player will attempt to preserve the time base because
this ensures that the video remains synchronized with the sound track and any other
streams that may be playing.

19.7.6 Resource Allocation and Management

If you have a sophisticated gateway, you might be able to reserve a certain amount
of bandwidth for priority use, such as for the main view screen in the lounge, while
arranging that the downloading process consume less bandwidth since a human
being is not watching it. Large enterprise-sized servers provide resource allocation
that that can be measured and throttled under operating system control. This allo-
cates disk space, CPU time, and network bandwidth according to a scheme of priorities.

19.8 Firewall Issues

Getting your streamed content through a corporate firewall may present a significant chal-
lenge. There is no technical reason why this should be difficult but the security staff may
be justifiably paranoid about opening any chinks in the armor. Allowing outgoing con-
nections on certain ports for streaming protocols should be quite safe. The ports listed in
Table 19-2 are relevant for consideration although you should not just blindly open them
all without careful consideration.
Alternatives to opening firewall access include the deployment of proxy servers.
A proxy and a firewall are carefully configured to work cooperatively. If outgoing con-
nections are always proxied, then the firewall knows that traffic from other machines
should not be allowed through. This should provide adequate security for even the most
paranoid systems administrators.

19.9 Diagnostic Tools

If you have a computer equipped with some basic networking diagnostic tools, the
traceroute utility will display a series of connected devices between the two endpoints.
An example screen dump is shown in Figure 19-4. Another useful tool is the ping utility
that sends messages to a remote machine and tells you how long the round trip took when
it receives a reply.