RFC 3714 (rfc3714) - Page 3 of 32

IAB Concerns Regarding Congestion Control for Voice Traffic in the Internet

RFC 3714       IAB Concerns Regarding Congestion Control      March 2004


   well as technical considerations, and technologies that can be
   deployed without changes to the infrastructure enjoy considerable
   advantages in the speed of deployment.  RFC 2990 outlines some of the
   technical challenges to the deployment of QoS architectures in the
   Internet [RFC 2990].  Often, interim measures that provide support for
   fast-growing applications are adopted, and are successful enough at
   meeting the need that the pressure for a ubiquitous deployment of the
   more disruptive technologies is reduced.  There are many examples of
   the slow deployment of infrastructure that are similar to the slow
   deployment of QoS mechanisms, including IPv6, IP multicast, or of a
   global PKI for IKE and IPsec support.

   Interim QoS measures that can be deployed most easily include
   single-hop or edge-only QoS mechanisms for VoIP traffic on individual
   congested links, such as edge-only QoS mechanisms for cable access
   networks.  Such local forms of QoS could be quite successful in
   protecting some fraction of best-effort VoIP traffic from congestion.
   However, these local forms of QoS are not directly visible to the
   end-to-end VoIP connection.  A best-effort VoIP connection could
   experience high end-to-end packet drop rates, and be competing with
   other best-effort traffic, even if some of the links along the path
   might have single-hop QoS mechanisms.

   The deployment of IP telephony is likely to include best-effort
   broadband connections to public-access networks, in addition to other
   deployment scenarios of dedicated IP networks, or as an alternative
   to band splitting on the last mile of ADSL deployments or QoS
   mechanisms on cable access networks.  There already exists a
   rapidly-expanding deployment of VoIP services intended to operate
   over residential broadband access links (e.g., [FWD, Vonage]).  At
   the moment, many public-access IP networks are uncongested in the
   core, with low or moderate levels of link utilization, but this is
   not necessarily the case on last hop links.  If an IP telephony call
   runs completely over the Internet, the connection could easily
   traverse congested links on both ends.  Because of economic factors,
   the growth rate of Internet telephony is likely to be greatest in
   developing countries, where core links are more likely to be
   congested, making congestion control an especially important topic
   for developing countries.

   Given the possible deployment of IP telephony over congested best-
   effort networks, some concerns arise about the possibilities of
   congestion collapse due to a rapid growth in real-time voice traffic
   that does not practice end-to-end congestion control.  This document
   raises some concerns about fairness, user quality, and the danger of
   congestion collapse that would arise from a rapid growth in best-
   effort telephony traffic on best-effort networks.  We consider best-
   effort telephony connections that have a minimum sending rate and



Floyd & Kempf                Informational