gestion can occur because the stream is duplicated for
each user. Also, TCP checks to ensure error-free data
reception. When data slows from traffic or from error
checking, buffering occurs on the unicast stream. This
might be merely irritating when watching a movie or
video clip, but it can ruin a video conference call or
a live-streamed event.
Multicast transmission is one-to-many or many-tomany.
A single video stream sent from a device on the
network is delivered to multiple reception points via the
user datagram protocol (UDP). The video stream goes
from the sending device to each user who has tapped into
the stream at the network switch. Unlike unicast, all users
share the same stream, so they cannot play, pause or stop
the stream at will. Because UDP does not check to ensure
error-free data reception, it uses less overhead than TCP
and transmits data faster, making buffering less likely than
with unicast. This makes multicasting attractive for real-
time streaming applications, such as video conferencing
and live streaming. The downside of multicasting is that
UDP makes no guarantees that video stream data packets
will reach the destination error free. It is up to the
October/November/December 2019 I 15
container. During decoding, the compressed video
is de-encapsulated and decompressed using the
same H.264/AAC codec to recover the RGB video.
• Video Stream Transmission—When streaming
video over Ethernet, unicast and multicast are
two commonly used methods to transmit from
source to destination (see Figure 6).
Unicast transmission is point-to-point. The video stream
is sent from one device IP address to another via standard
TCP/IP network connection protocol based on where the
content is going. The video stream is transported from the
sending device directly to a user who has requested the
stream. Each requesting user gets a separate iteration of
the stream. Because unicast employs standard TCP/IP, it is
easy to use and seldom requires modifications to TCP/IP
network infrastructure. Unicasting works well for on-
demand video streamed at a user’s convenience. The user
can play, pause or stop the stream at will. The downside
of unicasting is that it does not scale well. If too many
users request the stream simultaneously, network con-
Unicast Delivery Multicast Delivery
Server
Network
Switch
Layer 3 Routing
Layer 2 Switching
192.168.0.1
Server
Network
Switch
Layer 3 Routing
Layer 2 Switching
IGMP Snooping and
Query Enabled
192.168.0.1
192.168.0.2
192.168.0.3
192.168.0.4
192.168.0.2
192.168.0.3
192.168.0.4
FIGURE 6: With unicast, the source sends a duplicate data stream to each requesting user; with multicast,
one data stream is shared by multiple users wishing to receive the stream.