Streaming - A Practical Guide to Video and Audio Compression - page 348

20.4.3 Session Description Protocol

Session description protocol (SDP) describes multimedia sessions in a way similar to an
electronic program guide (EPG) for TV channels. SDP is also used to advertise new serv-
ices and invite clients to initiate a session.

20.4.4 Stream Control Transmission Protocol

A new standard is being worked on for streaming; it is called stream control transmission
protocol (SCTP). SCTP works extremely well in conjunction with the network-friendly
H.264. They are very flexible and adaptive, and well suited for delivery of uni-cast solu-
tions. This combination is apparently very robust and adaptive when faced with a trans-
mission route that is prone to packet loss. This topic is also being discussed by the Audio
Video Transport working group at the IETF.

20.4.5 Proxies and Firewalls

Certain port numbers are defined as well-known ports. Your security advisors will have
configured access through the firewall for some of these ports when you are working
within a corporate environment. Access through the firewall may involve a proxy server
that acts as your intermediary when connecting to the remote server. Your connection then
involves traversing the internal corporate network to reach the proxy server; thence
through the corporate firewall and across the Internet, possibly traversing further firewalls
as the connection enters the network belonging to the streaming company before hooking
up to the target server. A lot of things can go wrong if the preferences are set incorrectly.
The player must be configured correctly; otherwise it will be unable to connect to the
server with the streamed content.
The principal settings are the name and port number for the proxy server within
your corporate network. This is defined centrally as part of your network setup on the
desktop computer. There may be additional proxy settings in the various applications
you use and these obviously must be consistent. If you have an opportunity to use an
auto-proxy, that is likely to be the most correct set of configuration data. Not all applica-
tions honor the auto-proxy settings and will fall back to the static settings or to their own
preferences.
It is vital that you define these proxy configurations consistently. Otherwise,
when they come into play and are mutually exclusive, you may not even reach the right
proxy-server port, let alone penetrate your corporate firewall and reach the streaming
server.

20.5 Delivery Standards

With the increase in the amount of streamed and downloadable content over the last
decade, the number of available standards and alternative formats has become bewilder-