Base Unit User Guide Issue 1
Tech-X Flex™
5-32
5: IP and Video Testing
Intro
Wi
-F
i
10/100
Sy
stem
IP/V
ideo
S
p
ecs
•
IP Address
- IP address of the multicast stream
•
IP Port
- UDP or TCP port of the stream, with respect to the
Encapsulation Method
•
Encapsulation Method
- Transport encapsulation used for the stream
•
Codec
- Video codec type
Results - Channel Change Time
The test reports the channel change time in msec, along with other parameters used in the calculation.
For more information, see
How channel change time is calculated
How channel change time is calculated
During a channel change test, the unit joins the first specified channel, leaves that channel, then joins the
second specified channel. During this process, four key events are used for the change time calculation,
as illustrated in the following figure:
Figure 5-10 Channel change calculation timeline
Referring to this figure, the basic formula for change time calculation is:
Time = (Last
A
- M
L
) + (First
B
- M
J
)
...where the individual terms are temporal instances, not quantitative amounts of time. In other words,
channel change time equals time it takes to leave the first stream, plus the time it takes to join the second
stream, measured from the respective IGMP requests.
M
L
Multicast join
request - Ch. A
First packet -
Ch. A
Multicast leave
request - Ch. A
Last packet -
Ch. A
Multicast join
request - Ch. B
First packet -
Ch. B
Last
A
M
J
First
B
Time
Channel A stream
Channel B stream
