We performed measurements to determine whether ECN is usable with
UDP-based transport protocols in the public Internet. These validate
the utility of
our previous work on ECN for RTP over UDP/IP, and feed
into
current IETF activities on congestion control for RTP-based interactive
multimedia running over UDP/IP, and on the
use of UDP as a
substrate for deployment of new transport protocols. Using
measurements from two residential sites in the UK, the University of
Glasgow, and servers in each of the nine EC2 regions worldwide, we test
reachability of 2500 servers from the public NTP server pool, using
ECT(0) and not-ECT marked UDP packets. We show that an average of
98.97% of the servers that are reachable using not-ECT marked packets
are also reachable using ECT(0) marked UDP packets, and that ~98% of
network hops pass ECT(0) marked packets without clearing the ECT bits.
We compare reachability of the same hosts using ECN with TCP, finding
that 82.0% of those reachable with TCP can successfully negotiate and
use ECN. Our findings suggest that ECN is broadly usable with UDP
traffic, and that support for use of ECN with TCP has increased.
RFC
6679 has been published, describing a standard for use of ECN with
RTP over UDP/IP. It describes how ECN marks can be used with RTP data
packets, and defines a new RTCP Extended Report (XR) block for periodic
ECN reporting, a new RTCP transport feedback message of timely reports
of congestion events, and STUN/ICE extensions to probe usability of ECN
on a path. SDP extensions to negotiate ECN support are also specified.
The standard works with both unicast and multicast RTP sessions, and in
point-to-point and group communication scenarios.
RFC 6336
has been published, defining the IANA Registry for ICE Options. This fixes an
oversight in RFC 5245,
which states that the registry for ICE options exists, but did not create
it with IANA or specify the syntax of
legal options. Defining this registry is a necessary precursor to the ECN
for RTP work, which needs to use an ICE option.