Video
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User defined text message
This message can be defined and enabled by the user, using the Siqura Programming Interface
API, for example. There is no maximum limit on the amount of characters. Considering that this
data is part of a video stream, the maximum should be reasonable.
12.3.7
Notes
Note on Differentiated Services:
Differentiated Services (DiffServ, or DS) is a method for adding
QoS (Quality of Service) to IP networks. In routed networks, critical network traffic such as video
and audio streams, which require a relatively uninterrupted flow of data, can get blocked due to
other traffic. DiffServ can be used to classify network traffic and give precedence - i.e.
low-latency, guaranteed service - to high-priority traffic, while offering best-effort service to
non-critical traffic such as file transfers or web traffic.
Each stream has a DSCP (Differentiated Services Code Point) field in the IP header. Routers will
identify the network service type in the DSCP field and provide the appropriate level of service.
Low-latency service can be realized, for example, through priority queuing, bandwidth
allocation, or by assigning dedicated routes.
Note on RTP and RTCP:
The Real-time Transport Protocol (RTP) is designed for end-to-end
real-time, audio or video data flow transport. It is regarded as the primary standard for
video/audio transport over multicast or unicast network services. RTP does not provide
guaranteed delivery, but sequencing of the data makes it possible to detect missing packets. It
allows the recipient to compensate for breaks in sequence that may occur during the transfer on
an IP network. Error concealment can make the loss of packets unnoticeable.
RTP is usually used in conjunction with the Real-time Transport Control Protocol (RTCP). RTP
carries the media streams. RTCP provides reception quality feedback, participant identification
and synchronization between media streams.
Note on the Session Announcement Protocol (SAP):
SAP, defined in
RFC 2974
(see RFC 2974 -
http://www.ietf.org/rfc/rfc2974.txt
), is a protocol for advertising multicast session information.
A SAP announcer periodically broadcasts announcement packets which include the session
description information of multicast sessions presented by the announcer. SAP uses the Session
Description Protocol (SDP) as the format of the session descriptions. The announcement is
multicast with the same scope as the session it is announcing, ensuring that the recipients of the
announcement are within the scope of the session the announcement describes. SAP listening
applications can listen to the announcements and use the information to construct a guide of all
advertised sessions. This guide can be used to select and start a particular session. The SAP
announcer is not aware of the presence or absence of SAP listeners.
