Toshiba CTX28 manual Review Voice Quality Considerations, Prgs, Above and the Codec parameters

IP Telephony and QSIG Over IP

Pre-installation Guidelines

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
				Speech
IP Network Quality Parameters			Excellent	Good	Fair	Poor
			No one perceives	Very few people	Some people may	Many people may
			delay.1	perceive delay.1	perceive delay.1	perceive delay.1
Latency (Round trip delay)2			20ms or less	50ms or less	100ms or less	200ms or less
Jitter2			20ms or less	50ms or less	50ms or less	50ms or less
			(-10 ms ~ +10ms)	(-25ms ~ +25ms)	(-25ms ~ +25ms)	(-25ms ~ +25ms)
Packet loss2			1×10-3or less	1×10-3or less	1×10-3or less	1×10-3or less
Packet error2			1×10-4or less	1×10-4or less	1×10-4or less	1×10-4or less
CODEC &		Bandwidth per
Packet Interval		channel (Single	Speech quality per the combination of the network environment described
(Prgs. 250-07,		direction, control	above and the CODEC parameters.
152-01)		channel included)
G.711 at 20ms		115kbps3	Excellent	Good	Fair	Poor
		(Speech 88kbps)
G.711 at 40ms		99kbps3	Excellent	Good	Fair	Poor
		(Speech 76kbps)
G.729A at 40ms		29kbps3	Good	Good	Fair	Poor
		(Speech 20kbps)
G.729A at 80ms		22kbps3	Good	Fair	Poor	Poor
		(Speech 14kbps)

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.

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.

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.

IP Telephony and QSIG Over IP

Strata CTX I&M 06/04 9-5