NCast Presentation Recorder Reference Manual
All units in one session use the same multicast address. The Video and Audio multicast addresses for a
session can be the same if the Port numbers are different. Units engaged in different sessions should
use different multicast addresses to minimize traffic loading on the network (the multicast routers
distribute all traffic to all points subscribed on a particular multicast address, independent of the port
number).
The default settings for a Presentation Recorder use Administratively-Scoped multicast addresses. This
implies that streams created using these addresses will not exit the organization’s network.
If the network is not multicast enabled, point-to-point communications between two Presentation
Recorders is possible by entering the numeric IP address of the remote unit into this field.
4.7.2. Set Video Stream Destination – Port Number
In addition to a multicast address, each media stream requires a unique port to be assigned. Ports must
be even-numbered (the succeeding odd number is used for control purposes and must be available).
Port numbers range from 1024 to 65,535 and this range is divided into two parts: the Registered Ports
are those from 1024 through 49151 and Dynamic and/or Private Ports are those from 49152 through
65535.
In practice, multicast applications assign port numbers in the range of 5002 and up. The port range 1024-
5000 is typically used by a Unix system to assign ports to applications desiring an automatically
generated port number.
Even if different multicast addresses are being used, it is recommended that different port numbers be
used for the different media streams (graphics, audio and collaboration). On some system
implementations, use of the same port number will cause errors.
For multicast traffic to get through a firewall, the even-odd pair defined in this entry must be opened by
the firewall administrator.
4.7.3. Set Video Stream Destination - MTU
The Maximum Transmission Unit (MTU) is the maximum length of a packet and is normally set to 1500.
For some special circuits (satellite links, others) the maximum size may need to be adjusted downward to
avoid packet fragmentation, which leads to inefficiencies and possible packet loss.
4.7.4. Set Audio Stream Destination - Address
An address entered for Audio (the Audio media stream) will be either a valid multicast address, or the
numeric host IP address of the remote unit if a point-to-point connection is being established.
For a discussion of multicast addresses, see the discussion above (Set Video Stream Destination -
Address).
All units in one session use the same multicast address. The Video and Audio multicast addresses for a
session can be the same if the Port numbers are different. Units engaged in different sessions should
use different multicast addresses to minimize traffic loading on the network (the multicast routers
distribute all traffic to all points subscribed on a particular multicast address, independent of the port
number).
If the network is not multicast enabled, point-to-point communications between two Presentation
Recorders is possible by entering the numeric IP address of the remote unit into this field.
4.7.5. Set Audio Stream Destination - Port
The port number assigned to the audio media stream.
See the discussion above (Set Video Stream Destination – Port Number) for more detailed information
on ports.
4.7.1. Set Audio Stream Destination – MTU
The Maximum Transmission Unit (MTU) is the maximum length of a packet and is normally set to 1500.
For some special circuits (satellite links, others) the maximum size may need to be adjusted downward to
avoid packet fragmentation, which leads to inefficiencies and possible packet loss.
4.7.2. Enable Video Bandwidth Smoothing
If enabled, the encoder smooths the stream transmission and sends packets at the prescribed target bit
rate (this is the default setting). This will increase network jitter and latency. If disabled, the encoder uses
burst transmission by sending all packets immediately after encoding. This will significantly decrease
NCast Corporation
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