QBSS Deployment Recommendation
Internet2 QoS working group document
Working Group Consensus Reached: February 15, 2002
Editor: Stanislav Shalunov <shalunov@internet2.edu>


The Internet2 Quality of Service working group has designed and
published a service definition for the QBone Scavenger Service (QBSS)
(http://qbone.internet2.edu/qbss/qbss-definition.txt).  QBSS allows
users and leaf networks to identify and mark a scavenger class of
traffic that may receive degraded treatment at downstream bottleneck
links.  By allocating forwarding resources at those links more
intelligently, QBSS can be used to extend or restore an uncongested
service to default best-effort traffic.

Scavenger service is currently implemented by the Internet2 Abilene
backbone and several Internet2 members are actively using it.

To facilitate experimentation with QBSS by all interested parties, it
is recommended that all Internet2 networks minimally pass and ignore
the QBSS diff-serv codepoint (DSCP).  In terms of the service
definition, this means that:

* Any packet leaving the domain must be marked with the QBSS codepoint
  (DSCP 001000) if that packet entered the domain (either from a
  peering domain or from an end host) marked with the QBSS codepoint;

* Routers in a participating domain should treat scavenger traffic in
  the same manner as best-effort.

Notice that a vast majority of Internet2 networks is already
QBSS-compliant in this sense.

Additionally, where congestion is an issue, Internet2 networks are
encouraged to experiment with scavenger service by configuring their
routers to place scavenger-marked traffic into a separate queue on
congested links.

Notice that DSCP 001000 is to be interpreted throughout Internet2 as a
request for scavenger treatment; for the purposes of compatibility
with older equipment, no traffic for which treatment other than
scavenger is expected should be marked with IP precedence 1.

Primarily, marking should be voluntary on the part of users (to
discourage cat-and-mouse games with port numbers and traffic becoming
hard to characterize).  However, leaf networks may choose to mark all
traffic coming from a specific set of router ports or may choose to
coerce users into marking.  For example, high-volume users could be
asked to mark their traffic for QBSS or to identify traffic that could
be marked on their behalf by the network operator.

While QBSS is an Internet2 initiative, potential for rapid technology
transfer is high.  Therefore, members are encouraged to mark relevant
traffic destined for commodity Internet with the QBSS codepoint.  An
immediate benefit of doing so is the ability to control congestion on
an outgoing commodity circuit.

More information about QBSS (including configuration examples and
other documents) can be found at http://qbone.internet2.edu/qbss/