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Chap.4 IP Network
4.4.2 Transmission Protocols
This section introduces two types of protocols. UDP, TCP and HTTP are underlying protocols that carries the data.
RTSP/RTP/RTCP are real-time media transmission protocols.
● Data Transmission
UDP
A UDP (User Datagram Protocol) source port sends out packets continuously and does not require the destination
port to return a confirmation message, allowing for more real-time audio and video streams. However, the packets
may be lost due to network burst traffic and images may be broken. UDP connection is mainly used for time-
sensitive responses and when the video quality is less important.
TCP
A TCP (Transmission Control Protocol) source port sends out packets and waits for a confirmation message from
the destination port before sending out sequential packets. If no confirmation message is received, the source port
will send that packet again. TCP guarantees the complete delivery of streaming data and thus provides better video
quality. Nevertheless, its real-time effect is inferior to UDP.
HTTP
Designed for users to view information on a web page through a browser, HTTP (Hypertext Transfer Protocol)
allows the same quality as TCP protocol without needing to open specific ports for streaming under some network
environments. Users inside a firewall can utilize this protocol to allow streaming data to come through.
● Media Transmission
RTSP
RTSP (Real Time Streaming Protocol), which consists of RTP and RTCP, is a protocol used to facilitate multimedia
streaming over the Internet. As a protocol for 3GPP streaming, RTSP enables users to access video images via a
3G phone.
4.4.3 Video Transmission Methods
Unicast
With unicast, data is transmitted to the designated PC only and other PCs on the same network will not receive
the data. If more than one PC request for the same piece of data, the source PC has to send the data repeatedly
to different destinations. This is the most popular transmission method and is also known as One-to-One
transmission.
Broadcast
Broadcast is mainly used on the LAN. Compared with unicast, all network devices in broadcast on the same
network will receive data whether they need it or not. The source PC sends data to a router where data is replicated
and sent to multiple destination PCs requesting for the same data. It is also called One-to-All transmission.
Multicast
With multicast, data is transmitted to a multicast group consisting of PCs requesting for the same data on the
Internet. Once the data reaches the multicast group, it is duplicated and delivered separately to each PC in that
group.
Multicast significantly reduces bandwidth usage and is suitable for web video applications such as VoD, e-learning
and video conferencing. It is also called One-to-Many or Many-to-Many transmission.
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