Summary
The proliferation of broadband and high-speed Internet core networks has
moved the placement of QoS for voice from the network to the endpoints.
Endpoint design for high-quality interactive voice includes state-of-the-art
Internet codecs, far end and near end echo control, automatic level control,
and other voice application design items.
There is a good assortment of network layer QoS and link layer QoS mech-
anisms available, but they can be applied mostly in intradomain communica-
tions, and this is not too interesting.
The simplest and most scalable approach for intradomain QoS are differen-
tiated Services, followed by RSVP, and the least favored by us is MPLS.
By contrast, interdomain QoS is not deployed on the Internet because of an
assortment of showstoppers, ranging from differences between domains in
ownership, policies and commercial competition. Last but not least, interdo-
main QoS has to be protected against theft of service and DOS attacks.
The best effort QoS on the Internet is, therefore, well grounded in reality and
works well as long as network congestion is avoided by adequate provision-
ing of bandwidth. Voice uses a negligible fraction of Internet traffic.
Monitoring the voice quality is best done in the SIP endpoints, closest to the
end-user experience.
References
[1] “Mr. QoS vs. Mr. Bandwidth” by S. Borthick. The Business Communication
Review, September 2005, pp 16–17.
[2] “Voice Quality Measurement” Technical Note, Telchemy, Inc., January
- http://telchemy.com/appnotes/TelchemyVoiceQuality
Measurement.pdf.
[3] “RTP Control Protocol Extended Reports (RTCP XR)” by T. Friedman et al.
RFC 3611, IETF, November 2003.
[4] “Network and Acoustic Echo Issues in Voice-Over-Packet Telephony Sys-
tems” by P. Sorquist. Global IP Sound AB, white paper, 2002. http://www.global
ipsound.com.
[5] The home page for the iLBC freeware is http://www.ilbcfreeware.org.
[6] “Internet Low Bit Rate Codec (iLBC) “ by S. Andersen et al. RFC 3951, IETF,
December 2004.
[7] “Real-time Transport Protocol (RTP) Payload Format for Internet Low Bit
Rate Codec (iLBC) Speech” by A. Duric et al. RFC 3952. IETF, December
Quality of Service for Real-Time Internet Communications 315