NCast Presentation Recorder Reference Manual
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Global Addresses – The range of multicast addresses 224.0.1.0-238.255.255.255 are used for
global communications. These addresses are dynamically allocated and not statically reserved.
These addresses are unsuited for static assignment in the Channel Table.
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GLOP Addresses – A document, IETF RFC 3180, describes a mechanism for statically assigned
multicast addresses in the address space 233/8 based on a formula that incorporates the
Autonomous System (AS) number in the middle two octets. The AS number is owned by the ISP
providing service to the account and use of a GLOP address must be coordinated with that ISP.
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Administratively Scoped Addresses – The multicast address range of 239.0.0.0 to 239.255.255.255
has been defined to be a range of administratively scoped multicast addresses in IETF RFC 2365.
These addresses may be statically assigned by the administrator of an organization’s network, and
there will be no conflict with other organization’s use of these addresses because border routers on
the edge of an organization’s network enforce policies to stop multicast traffic flow for addresses
within this range. Further, these same border routers can enforce policies so that subsets of these
addresses are contained within administrative boundaries, such as a local LAN, a building, a
campus or a region. These are safe addresses to use in setting up an organization’s multicast
network and ideal entries for use in the Channel Table. Consult with the Network Administrator for
the particular address ranges in use on the network hosting the Presentation Recorder.
All units in one session use the same multicast address. The Video, Audio and Collaboration 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.
To disable multicasting of a session (e.g. in a record-only situation), set all multicast addresses to
“127.0.0.1”.
4.2.5. Video Port
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.
4.2.6. Video Bit-rate
The video bit-rate in kilobits-per-second defines the maximum bit-rate that the encoders may utilize in
creating the media stream. For static images the bit-rate may decrease from this peak level.
The following table lists the absolute minimum recommended bit-rates for high frame-rates:
NCast Corporation
Revision 1.1
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