Filter
Top Products
IP Telephony and QSIG Over IP
Pre-installation Guidelines
Strata CTX I&M 06/04 9-5
IP Telephony and QSIG
Over IP
Review Voice Quality Considerations
For best speech quality we recommend not using the older CTX analog line cards for CTX IP
telephone connections. If these cards are used, IP telephones will experience fair or bad voice
quality. (See “Dos and Don’ts for Setting Up the System” on page 9-2.)
The amount of bandwidth required for communications over a particular IP network segment
depends on the number of voice channels supported, the anticipated call setup traffic, and how
much other data network traffic is present.
The quality of service (Excellent, Good, Fair, and Bad) provided by CTX IP Telephones and CTX
IP QSIG channels depends heavily on the LAN parameters as shown in Table 9-1.
Table 9-1 Quality of Service
IP Network Quality Parameters
Speech
Excellent Good Fair Poor
No one perceives
delay.
1
1. Ratings of Excellent, Good, Fair, Poor were based on the tester in a quiet room and the tester could not see the other call
party. IPT is usable even with a "Poor" rating if delay is acceptable.
Very few people
perceive delay.
1
Some people may
perceive delay.
1
Many people may
perceive delay.
1
Latency (Round trip delay)
2
2. When selecting router equipment, the Latency, Jitter, Packet loss and Packet error conditions above should be considered as
well as the bandwidth. Bandwidth can be calculated with the CODEC and packet size. For better results, more bandwidth may
be required, depending on the amount of overall data traffic. For more details on QoS refer to “A Handbook for Successful
VoIP Deployment: Network Testing, QoS, and More” by John Q. Walker, NetIQ Corporation on www.netiq.com.
20ms or less 50ms or less 100ms or less 200ms or less
Jitter
2
20ms or less 50ms or less 50ms or less 50ms or less
(-10 ms ~ +10ms) (-25ms ~ +25ms) (-25ms ~ +25ms) (-25ms ~ +25ms)
Packet loss
2
1×10
-3
or less 1×10
-3
or less 1×10
-3
or less 1×10
-3
or less
Packet error
2
1×10
-4
or less 1×10
-4
or less 1×10
-4
or less 1×10
-4
or less
CODEC &
Packet Interval
(Prgs. 250-07,
152-01)
Bandwidth per
channel (Single
direction, control
channel included)
Speech quality per the combination of the network environment described
above and the CODEC parameters.
G.711 at 20ms
115kbps
3
(Speech 88kbps)
3. Use this number to estimate the bandwidth needed for the CODEC and interval timing required to achieve an expected
Quality of Service (Excellent, Good, etc). This bandwidth includes header and control information and a 25% margin for
network traffic variances.
Excellent Good Fair Poor
G.711 at 40ms
99kbps
3
(Speech 76kbps)
Excellent Good Fair Poor
G.729A at 40ms
29kbps
3
(Speech 20kbps)
Good Good Fair Poor
G.729A at 80ms
22kbps
3
(Speech 14kbps)
Good Fair Poor Poor