Subject: [tsvwg] Text from RFC 3246 regarding excess traffic

From: "Fred Baker (fred)" <[email-masked]>
Date: Tue, 22 Jul 2014 14:18:21 +0000

The EF PHB is intended to be a building block for low loss services.
   However, under sufficiently high load of EF traffic (including
   unexpectedly large bursts from many inputs at once), any device with
   finite buffers may need to discard packets.  Thus, it must be
   possible to establish whether a device conforms to the EF definition
   even when some packets are lost.  This is done by performing an
   "off-line" test of conformance to equations 1 through 4.  After
   observing a sequence of packets entering and leaving the node, the
   packets which did not leave are assumed lost and are notionally
   removed from the input stream.  The remaining packets now constitute
   the arrival stream (the a_j's) and the packets which left the node
   constitute the departure stream (the d_j's).  Conformance to the
   equations can thus be verified by considering only those packets that
   successfully passed through the node.

   If the EF PHB is implemented by a mechanism that allows unlimited
   preemption of other traffic (e.g., a priority queue), the
   implementation MUST include some means to limit the damage EF traffic
   could inflict on other traffic (e.g., a token bucket rate limiter).
   Traffic that exceeds this limit MUST be discarded.  This maximum EF
   rate, and burst size if appropriate, MUST be settable by a network
   administrator (using whatever mechanism the node supports for non-
   volatile configuration).