/
More report summaries from Tolly Research:
Proprietary VoIP encoding falls short
RT24 voice encoding delivers inferior quality for business usage.
 
|
|||
 | |||
|
Testers at Tolly Research, which publishes ITclarity research reports, found that despite significant bandwidth savings, the RT24 voice encoding technique delivers inferior quality audio and should be used between remote sites only when no other voice communications are available. Tolly Research measured the voice quality of Lucent's ultra-low-bit-rate RT24 vocoder using Lucent's Voice over IP gateway products. RT24 is a Lucent-proprietary algorithm for ultra-low-bit-rate transmissions at 2.4K bit/sec. Voice quality was quantified objectively using the Perceptual Speech Quality Measure (PSQM), which provides, according to the ITU-T, the most accurate estimate of the subjective quality of coded speech (ITU-T Recommendation P.861). Voice-quality measurements were conducted for two different signaling methods, ISDN Primary Rate Interface (PRI) and T1 robbed-bit, to determine the impact on perceived voice quality. ISDN PRI uses a single out-of-band common channel for signaling separate information channels. In contrast, T1 robbed-bit signaling uses selective in-band bits to provide signaling, thereby reducing the 64K bit/sec bandwidth available for voice to 56K bit/sec. Each of these signaling methods was tested in combination with the proprietary vocoder we examined. The question we seek to answer in this Test Case is whether or not an ultra-low-bit-rate vocoder, which delivers a compression ratio greater than 25:1 compared to a standard G.711 vocoder for uncompressed voice, provides acceptable voice quality for business applications. The RT24 vocoder, as implemented in Lucent's MAX VoIP gateway products, does not come close to providing voice quality on par with other vocoders Tolly Research has tested. There was essentially no difference in voice quality when using Common Channel Signaling or T1 robbed-bit signaling in conjunction with the RT24 vocoder. And, unlike any of the PSQM results for the vocoders tested in previous tests, there basically is no difference between PSQM scores for male and female voices when using the RT24 vocoder. In general, the voice quality for RT24 is unacceptable for business use. The above information is derived from an ITclarity research track report. To purchase a subscription to Tolly Research's ITclarity service, click here.
About Tolly Research
Tolly Research, provider of ITclarity, is a technology research firm based in Brielle, N.J., that specializes in testing-based research. Tolly Research provides accurate test results, insightful analysis, and practical recommendations for leading-edge technologies required by network professionals. While many businesses have specific implementation issues, there is a broad base of technology research that is applicable to all organizations. Tolly Research offers a more cost-effective method of gathering data than committing internal resources to tackle each new technology. For more information on Tolly Research, point your browser to www.tollyresearch.com, send e-mail to itclarity@tollyresearch.com or call 732-292-9411.More report summaries from Tolly Research:
Low-bit-rate voice encoder gets VoIP nod
Link aggregation tests end in server crashTests yield impressive voice quality
Citrix ICA survives packet loss
Researchers find fault with Win2K TCP/IP gateway services
Tests show Microsoft's Terminal Server, RDP hog bandwidth
