2000-A2-GB20-10
- 130 -
February 2004
Setting Jit-
ter Delay
Inter-arrival jitter is the difference in relative transit time for two packets. It
is the difference between the packet’s RTP time-stamp and the receiver’s
clock at the time of arrival of the packet.
As shown in the equation below, this is equivalent to the difference in the
relative transit time for two packets: the relative transit time is the
difference between a packet’s RTP time-stamp and the receivers clock at
the time of arrival, measured in the same units.
If Si is the RTP time-stamp from packet i and Ri is the time of arrival in
RTP time-stamp units for packet i, then for two packets i and j, D may be
expressed as:
D(ij) = (Rj -Ri) -(Sj -Si) = (Rj -Sj) -(Ri -Si)
The interval jitter is calculated continuously as each data packet i is
received from source SSRC-n, using this difference D for that packet and
of the previous packet i-1 in order of arrival (not necessarily in sequence),
according to the formula:
J = J + ({D (i-l, i)} -J)/16
The Jitter Delay should only be set by a Network Administrator. To set jitter
delay (0 to 50 ms—default 0 ms), follow these steps:
1. Type
J
on the Voice Configuration menu to select Set Jitter Delay.
2. The IAD displays this prompt:
Enter number of ms to delay [10]:
Type the delay value and press Enter.
3. The IAD saves the jitter delay and displays the Voice Configuration
menu so you can continue with other voice path configuration.
4. Reset the IAD (page
14
) when you finish voice path configuration.
Displaying
Jitter Delay
To display the current jitter delay value, type
D
on the Voice Configuration
menu. The IAD displays the current value:
Jitter Delay: 12 ms
Press any key to display the Voice Configuration menu and continue.
Setting
Start Mode
To set start mode (for POTS only), type
S
on the Voice Configuration menu
to display the Start Mode Selection menu:
Figure 7–4. Start Mode Selection Menu
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Start Mode Selection
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1. Set All Ports to Loop Start
2. Set All Ports to Ground Start
3. Display Start Mode
4. Configure Individual Port
