Introduction:
Video
surveillance systems currently are undergoing a transition where more and more
traditional analog solutions are being replaced by digital solutions. Compared
with an analog video surveillance system, a digital video surveillance offers
much better flexibility in video content processing or data transmission. At
the same time, it, also, have ability to implement advanced features such as
motion detection, facial recognition and object tracking. Applying digital
systems, makes the security system capable of transmitting video through the
Internet, so we need to study the different methods of video streaming over the
network. Streaming is the process of playing a file while it is still
downloading. Streaming video is a sequence of "moving images" that
are sent in compressed form in a way that it can start being proceed before it
is completely received like video clips on a Web page.
Here, some
of the network protocols used in video
streaming are described. The focus is on the features of most important protocols
in video surveillance including TCP, UDP and RTSP.
Protocols in streaming technology:
Protocols
are the rules implemented for a particular technology, which in streaming
technology are used to carry message packets, and communication takes place only
through them. Some of the protocols used in streaming technology are described
as follows:
SDP:
SDP,
standing for Session Description Protocol, used to describe multimedia sessions
in a format understood by the participants over a network. The purpose of SDP
is to convey information about media streams in multimedia sessions to help
participants join or gather information of a particular session. In fact, SDP
conveys information such as session name and purpose, times the session is
active, codec format, media in the session, Information to receive those media
(addresses, ports, formats and so on). A participant checks these information
and takes the decision about joining a session.
SDP is aimed
primarily for using in large WANs (Wide-Area Network) including the internet.
However, SDP can also be utilized in proprietary LANs (Local Area Networks) and
MANs (Metropolitan Area Networks).
DHCP:
Dynamic Host
Configuration Protocol (DHCP) is a network protocol that enables a server to
automatically assign a dynamic IP address to each device that connected to the
network. By this assigning, a new device can be added to a network without the
bother of manually assigning it a unique IP address. The introduction of DHCP
eased the problems associated with manually assigning TCP/IP client addresses,
resulting in flexibility and ease-of-use to network administrators.
DHCP is not
a secure protocol, since no mechanism is built to allow clients and servers to
authenticate each other. Both are vulnerable to deception, as one computer can
pretend to be another.
RTP:
Real-Time
Transport Protocol (RTP) is an internet protocol standard to manage the
real-time transmission of multimedia data over unicast or multicast network
services. In other words, RTP defines a standard packet format to deliver
real-time audio and video over IP networks. RTP does not guarantee real-time
delivery of data, but it provides mechanisms for the sending and receiving
applications to support streaming data. It is utilized in conjunction with
Real-Time Transport Control Protocol (RTCP) to ensure that monitor data
delivery for large multicast networks is provided and Quality of Service (QOS)
can be maintained. Monitoring is used to detect any packet loss and to
compensate any delay jitter.
RTP is used
extensively in communication and applications which involve streaming media
such as telephony or video teleconference applications. The recent application
of RTP is the introduction of VoIP (Voice over Internet Protocol) systems which
are becoming very popular as alternatives to regular telephony circuits.
RTCP:
Real-Time
Control Protocol (RTCP) is the control protocol that works in conjunction with
RTP to monitor data delivery on large multicast network. Providing feedback on
the quality of service being provided by RTP, is the RTCP's primary function.
RTCP control
packets are periodically transmitted by each participant in an RTP session to
all other participants. It is important to point out that RTCP carries
statistical and control data, while RTP delivers the data. RTCP statistics
contain sender or receiver reports such as the number of bytes sent, packets
sent, lost packets and round trip delay between endpoints. RTCP provides a way
to correlate and synchronize different media streams that have come from the
same sender.
RTSP:
The main
protocol in streaming is Real Time Streaming Protocol (RTSP), which used to
transmit stored or live media data over the IP network. It provides client
controls for random access to the stream content. This application layer
protocol is used to establish and control either a single or several
time-synchronized streams of continuous media such as video and audio. RTSP
servers use the Transport RTP in conjunction with RTCP, so that RTP acts as the
transport protocol and RTCP will be applied for QOS (Quality of Service)
analysis and also synchronization between video and audio streams.
Consequently, RTSP can both control and deliver real-time content. The RTP and
RTCP are independent of the underlying transport and network layers. In fact,
RTSP is considered more than a protocol and provides a simple set of basic
commands to control the video stream.
