RFC 3248 (rfc3248) - Page 3 of 11

A Delay Bound alternative revision of RFC 2598

RFC 3248      Delay Bound alternative revision of RFC 2598    March 2002


2.1 Goal and Scope of DB

   For a traffic stream not exceeding a configured rate the goal of the
   DB PHB is a strict bound on the delay variation of packets through a
   hop.

   Traffic MUST be policed and/or shaped at the source edge (for
   example, on ingress to the DS-domain as discussed in RFC 2475 [5]) in
   order to get such a bound.  However, specific policing and/or shaping
   rules are outside the scope of the DB PHB definition.  Such rules
   MUST be defined in any per-domain behaviors (PDBs) composed from the
   DB PHB.

   A device (hop) delivers DB behavior to appropriately marked traffic
   received on one or more interfaces (marking is specified in section
   2.4).  A device SHALL deliver the DB behavior on an interface to DB
   marked traffic meeting (i.e. less than or equal) a certain arrival
   rate limit R.

   If more DB traffic arrives than is acceptable, the device is NOT
   REQUIRED to deliver the DB behavior.  However, although the original
   source of DB traffic will be shaped, aggregation and upstream jitter
   ensure that the traffic arriving at any given hop cannot be assumed
   to be so shaped.  Thus a DB implementation SHOULD have some tolerance
   for burstiness - the ability to provide EF behavior even when the
   arrival rate exceeds the rate limit R.

   Different DB implementations are free to exhibit different tolerance
   to burstiness.  (Burstiness MAY be characterized in terms of the
   number of back-to-back wire-rate packets to which the hop can deliver
   DB behavior.  However, since the goal of characterizing burstiness is
   to allow useful comparison of DB implementations, vendors and users
   of DB implementations MAY choose to utilize other burstiness
   metrics.)

   The DB PHB definition does NOT mandate or recommend any particular
   method for achieving DB behavior.  Rather, the DB PHB definition
   identifies parameters that bound the operating range(s) over which an
   implementation can deliver DB behavior.  Implementors characterize
   their implementations using these parameters, while network designers
   and testers use these parameters to assess the utility of different
   DB implementations.

2.2 Description of DB behavior

   For simplicity the definition will be explained using an example
   where traffic arrives on only one interface and is destined for
   another (single) interface.



Armitage, et al.             Informational