Internet Engineering Task Force        		K. Nichols
Differentiated Services Working Group  		Packet Design
Internet Draft                         		B. Carpenter
Expires in December, 2000 April, 2001                 		IBM

Definition of Differentiated Services Per Domain Behaviors and Rules
for their Specification



Status of this Memo

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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This document is a product of the Diffserv working group. Com-
ments Comments
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Copyright Notice

Copyright (C) The Internet Society (2000). All Rights Reserved.


The differentiated services framework enables quality-of-service
provisioning within a network domain by applying rules at the edges to
create traffic aggregates and coupling each of these with a specific
forwarding path treatment in the domain through use of a codepoint in
the IP header [RFC2474]. The diffserv WG has defined the general
architecture for differen-
tiated differentiated services (RFC 2475) [RFC2475] and has been focused on
the definition
and standardization of the forwarding path behavior required in routers, known as "per-hop
forwarding behaviors" (or PHBs)
(RFCs 2474, 2597, and 2598). The differentiated services frame-
work creates services within a network by applying rules at the
network edges to create traffic aggregates [RFC2474, RFC2597, and coupling these with
a specific forwarding path treatment for the aggregate. RFC2598]. The WG
has also discussed the behavior functionality required at diffserv network (DS) domain edges
or boundaries for conditioning packet aggregates, such elements
as policers
to select (classifiers) and shapers [MODEL, MIB]. A major feature of the
diffserv architecture is that only the components applying condition (e.g., policing and shaping)
traffic according to the rules at the edge need to be changed in response to short-term [RFC2475, MODEL, MIB]. Short-term changes
in the QoS goals in for a DS domain are implemented by changing only the network,
configuration of these edge behaviors rather than reconfiguring the
behavior of interior behaviors. network nodes.

The next step for the WG is to formulate examples of how the for-

Nichols and Carpenter       Expires: December, 2000        [page  1 ]

warding forwarding path components
(PHBs, classifiers, and traffic condi-
tioners) conditioners) can be used within the architectural framework to compose
traffic aggregates whose packets experience specific forwarding
characteristics as they transit a differentiated services domain. The WG
has decided to use the term per-domain behav-
ior, behavior, or PDB, to describe the
behavior experienced by packets of a particular traffic aggregate set of packets as they cross a DS
domain. PDBs can
be used to characterize, A PDB is characterized by specific metrics, metrics that quantify the
treatment individ-
ual a set of packets with a particular DSCP (or set of DSCPs) will
receive as it crosses a DS domain. However, no microflow information
should be required as packets transit a differentiated services net-
work. A PDB is an expression of specifies a fowarding path treatment, but
treatment for a traffic aggregate and, due to the role that particular
choices of edge and PHB configura-
tion configuration play in its resulting attributes,
it is where the forwarding path and the control plane interact. The
measurable parameters of a PDB should be suitable for use in Service
Level Specifications at the network edge.

This document defines and discusses Per Domain Behaviors in detail
and lays out the format and required content for contribu-
tions contributions to
the Diffserv WG on PDBs and the rules that will be applied for
individual PDB specifications to advance as WG products. This format is
specified to expedite working group review of PDB submissions.

A pdf version of this document is available at: ftp://www.packet-

Table of Contents

1. Introduction ........................................  2

2. Definitions .........................................  3

3. The Value of Defining Edge-to-Edge Behavior .........  4

4. Understanding Diffserv PDBs .........................  5

5. Format

		Change log for Specification of Diffserv PDBs ...........  8

6. -01 version

-Noted that PDB Attributes .....................................  10

7. Reference Per-Domain Behaviors .....................  13

8. Procedure parameters may form part of SLS (1.0).

-Clarified that parameters are not absolute values (4.1, 5.3).

-Rewrote the PDB from PHB group section (4.3).

-Added traffic conditioning needs to PDB rules (5.2).

-Replaced reference to route pinning by general reference to traffic
engineering, added reference to assumption of standby capacity (5.5).

-Removed Example from Section 6 (6.3).

-Deleted Bulk Handling PDB (7.2).

-Add requirement for Submitting PDBs PDB deployment experience (section 8).

-General syntax cleanups etc. Shortened and tweaked the Abstract.
Tweaked the Introduction.

-Eliminated solo usage of "aggregate" since it seems to Diffserv WG .......  14

9. Acknowledgements ...................................  15

1.0 confuse people.
Using "aggregate" as an abbreviation for sometimes BA and sometimes
TA is definitely confusing. Removed the following from the definitions:
The terms "aggregate" and "behavior aggregate" are used interchangeably
in this document.

1 Introduction

Differentiated Services allows an approach to IP QoS Quality of Service
that is mod-
ular, high performance, modular, incrementally deployable, and scalable while
introducing minimal per-node complexity [RFC2475]. Although an ultimate From the end user's
point of view, QoS should be supported end-to-end between any pair of
hosts. However, this goal is not immediately attainable. It will require
interdomain quality of
service, there remain QoS support, and many untaken steps remain on the road
to achieving

Nichols and Carpenter       Expires: December, 2000        [page  2 ]

this goal. this. One essential step, the evolution of the business
models for interdomain QoS, will necessarily develop outside of the
IETF. A goal of the diffserv WG is to provide the firm technical
foundation that allows these business models to develop. The first
major step will be to support edge-to-edge or intradomain QoS between
the ingress and egress of a single network, i.e. a DS Domain in the
terminology of RFC 2474. The intention is that this edge-to-edge QoS
should be composable, in a purely technical sense, to a quantifiable
multi-domain QoS.

The Diffserv WG has finished the first phase of standardizing the
behaviors required in the forwarding path of all network nodes, the
per-hop forwarding behaviors or PHBs. The PHBs defined in RFCs 2474,
2597 and 2598 give a rich toolbox for differential packet handling. A handling by
individual boxes. The general architectural model for diffserv Conceptual Model has been
documented in RFC 2475. An informal router model [MODEL] describes a
model of traffic conditioning and other forwarding behaviors.

Although business models will have to evolve over time, there
also remain However,
technical issues remain in moving "beyond the box" to intradomain QoS
models that apply within a single network domain. Providing

The ultimate goal of creating scalable end to end QoS on a per-domain basis is useful in itself the Internet
requires that we can identify and will provide use-
ful deployment experience quantify behavior for further IETF work as well a group of
packets that is preserved when they are aggregated with other packets
as for they traverse the evolution of business models. Internet. The step of specifying forward-
ing forwarding path
attributes on a per-domain basis for a traffic aggregate set of packets distinguished
only by the mark in the DS field of individual pack-
ets packets is critical
in the evolution of Diffserv QoS and should provide the technical
input that will aid in the construction of business models. The ultimate goal of creating end to end QoS in the Inter-
net imposes the requirement that we can create and quantify a
behavior for a group of packets that is preserved when they are
aggregated with other packets. This
document defines and speci-
fies specifies the term "Per-Domain Behavior" or PDB
to describe QoS attributes across a DS domain.

In diffserv, rules are imposed on certain packets arriving at the
boundary of a DS domain through use of classification and traffic condi-
conditioning which are set to reflect the policy and traffic goals for
that domain. Once packets have crossed the DS boundary, adherence to
diffserv principles makes it possible to group packets solely according
to the behavior they receive at each hop. This approach has well-known
scaling advantages, both in the forwarding path and in the control
plane. Less well recognized is that these scaling properties only
result if the per-hop behavior definition gives rise to a particular
type of invariance under aggregation. Since the per-hop behavior must be
equivalent for every node in the domain domain, while the set of packets marked
for that PHB may be different at every node, a PHB PHBs should be defined such
that its defining char-
acteristics don't their characteristics do not depend on the traffic volume of the
associated BA on a router's ingress link nor on a particular path
through the DS domain taken by the packets marked for it. packets. Specifically, different
streams of traffic that belong to the same traffic aggregate merge and
split as they traverse the network. If the properties of a PDB using a
particular PHB hold regardless of how the marked traffic aggregate
mutates as it traverses the domain, then that PDB scales. (Clearly this
assumes that numerical parameters such as bandwidth allocated to the
particular PDB may be different at different points in the network, and
may be adjusted dynamically as traffic volume varies.) If there are
limits to where the properties hold, that translates to a limit on the
size or topology of a DS domain that can use that PDB. Although useful
single-link DS domains might exist, PDBs that are invariant with network
size or that have sim-
ple simple relationships with network size and whose
properties can be

Nichols and Carpenter       Expires: December, 2000        [page  3 ] recovered by reapplying rules (that is, forming
another diffserv boundary or edge to re-enforce the rules for the
traffic aggregate) are needed for building scalable end-to-end quality
of service.

There is a clear distinction between the definition of a Per-
Domain Per-Domain
Behavior in a DS domain and a service that might be specified in a
Service Level Agreement. The PDB definition is a technical building
block that couples rules, specific PHBs, and configurations with a
resulting set of specific observable attributes which may be
characterized in a variety of ways. These definitions are intended to be
useful tools in configuring DS domains, but the PDB (or PDBs) used by a
provider are not expected to be visible to customers any more than the
specific PHBs employed in the provider's network would be. Network
providers are expected to select their own measures to make cus-
tomer-visible customer-
visible in contracts and these may be stated quite differ-
ently differently from the
technical attributes specified in a PDB definition. Similarly, specific
PDBs are intended as tools for ISPs to con-
struct construct differentiated services
offerings; each may choose different sets of tools, or even develop
their own, in order to achieve particular externally observable metrics.
Nevertheless, the measurable parameters of a PDB are expected to be
among the parameters cited directly or indirectly in the Service Level
Specification component of a corresponding SLA.

This document defines Differentiated Services Per-Domain Behaviors
and specifies the format that must be used for submis-
sions submissions of particular
PDBs to the Diffserv WG.


2 Definitions

The following definitions are stated in RFCs 2474 and 2475 and are
repeated here for easy reference:


" Behavior Aggregate: a collection of packets with the same codepoint
crossing a link in a particular direction. The terms "aggregate" and
"behavior aggregate" are used interchangeably in this document.


" Differentiated Services Domain: a contiguous portion of the Internet
over which a consistent set of differentiated services policies are
administered in a coordinated fashion. A differentiated services domain
can represent different administrative domains or autono-
mous autonomous systems,
different trust regions, different network technologies (e.g.,
cell/frame), hosts and routers, etc. Also DS domain.


" Differentiated Services Boundary: the edge of a DS domain, where
classifiers and traffic conditioners are likely to be deployed. A
differentiated services boundary can be further sub-divided into ingress
and egress nodes, where the ingress/egress nodes are the down-
downstream/upstream nodes of a boundary link in a given traffic
direction. A differentiated services boundary typically is found at the
ingress to the first-hop differentiated services-compliant router (or
network node) that a host's packets traverse, or at the egress of the
last-hop differentiated services-compliant router or network node that
packets traverse before arriving at a host. This is sometimes referred
to as the boundary at a leaf router. A differentiated services boundary

Nichols and Carpenter       Expires: December, 2000        [page  4 ] be co-located with a host, subject to local policy. Also DS

To these we add:


" Traffic Aggregate: a collection of packets with a codepoint that
maps to the same PHB, usually in a DS domain or some subset of a DS
domain. A traffic aggregate marked for a the foo PHB is referred to
as the "foo traffic aggregate" or the "foo aggregate" interchangeably.

This generalizes the concept of Behavior Aggregate from a link to
a network.

" Per-Domain Behavior: the expected treatment that an identifiable
or target group of packets will receive from "edge to edge" of a DS
domain. (Also PDB.) A particular PHB (or, if applicable, list of PHBs)
and traffic conditioning requirements are associated with each PDB.


" A Service Level Specfication (SLS) is a set of parameters and their
values which together define the service offered to a traffic stream
by a DS domain. It is expected to include specific values or bounds
for PDB parameters.

3 The Value of Defining Edge-to-Edge Behavior

Networks of DS domains can be connected to create end-to-end
services, but where DS domains are independently administered,
the evolution of

As defined in section 2, a PDB describes the necessary business agreements and future sig-
naling arrangements will take some time. Early deployments will
be within edge-to-edge behavior
across a single administrative domain. DS domain's "cloud." Specification of the transit expectations
of packets matching a target for a particular diffserv behavior across
a DS domain will both assists assist in the deploy-
ment deployment of single-domain QoS
and will help enable the composition of end-to-end, cross domain services
services.  Networks of DS domains can be connected to proceed. Putting aside the
business issues, create end-to-end
services by building on the same technical issues that arise in intercon-
necting DS domains with homogeneous administration will arise
in interconnecting PDB characteristics without regard to the autonomous systems (ASs)
particular PHBs used. This level of the Internet. abstraction makes it easier to
compose cross-domain services as well as making it possible to hide
details of a network's internals while exposing information sufficient
to enable QoS.

Today's Internet is composed of multiple independently adminis-
tered administered
domains or Autonomous Systems (ASs), represented by the
circles "clouds" in
figure 1. To deploy ubiquitous end-to-end quality of ser-
vice service in the
Internet, business models must evolve that include issues of charging
and reporting that are not in scope for the IETF. In the meantime,
there are many possible uses of quality of service within an AS and
the IETF can address the technical issues in creating an intradomain
QoS within a Differentiated Services framework. In fact, this approach
is quite amenable to incremental deployment strategies.

Figure 1: Interconnection

Where DS domains are independently administered, the evolution of ASs the
necessary business agreements and future signaling arrangements will
take some time, thus, early deployments will be within a single
administrative domain. Putting aside the business issues, the same
technical issues that arise in interconnecting DS Domains domains with
homogeneous administration will arise in interconnecting the autonomous
systems (ASs) of the Internet.

A single AS (for example, (e.g., AS2 in figure 1) may be composed of subnetworks
and, as the definition allows, these can be separate DS domains. For a number of reasons, it An
AS might be useful to have multiple DS domains in an AS, for a number of reasons, most notable
being to follow topological and/or technological boundaries and to
separate the allocation of resources. If we confine ourselves to the
DS bound-
aries boundaries between these "interior" DS domains, we avoid the non-
technical problems of setting up a service and can address the issues
of creating characterizable PDBs.


              |                AS2                   |
              |                                      |
 -------      |     ------------     ------------    |
 | AS1 |------|-----X           |    |          |    |
 -------      |     |           |    Y          |    |        -------
              |     |           |   /|          X----|--------| AS3 |
              |     |           |  / |          |    |        -------
              |     |           | /  ------------    |
              |     |           Y      |             |
              |     |           | \  ------------    |
 -------      |     |           |  \ |          |    |
 | AS4 |------|-----X           |   \|          |    |
 -------      |     |           |    Y          X----|------
              |     |           |    |          |    |
              |     ------------     ------------    |
              |                                      |
              |                                      |

      Figure 1: Interconnection of ASs and Carpenter       Expires: December, 2000        [page  5 ] DS Domains

The incentive structure for differentiated services is based on upstream
domains ensuring their traffic conforms to agreed upon rules and
downstream domains enforcing that conformance, thus metrics associated
with PDBs can be sensibly computed. The
rectangular boxes "X's" in figure 1 represent the
DS boundary routers
and thus would contain the containing traffic conditioners that ensure and
enforce conformance (e.g., shapers and policers). Although we
expect that
policers and shapers will be required are expected at the DS bound-
aries boundaries of ASs (dark rectangles), ASs, they
might appear anywhere, or nowhere, inside the AS. Thus, Specifically, the boxes
X's at the DS boundaries internal to the AS (shaded rectangles) may or may not condition
traffic. Understanding a particular PDB's characteristics under
aggregation and multiple hops will result in Technical guidelines for the placement and configuration of DS boundaries.
boundaries should derive from the attributes of a particular PDB under
aggregation and multiple hops.

This approach definition of PDB continues the separation of forwarding path
and control plane decribed in RFC 2474. The forwarding path charac-
characteristics are addressed by considering what happens how the behavior at every
hop of a packet's path and what behaviors can be characterized under is affected by the merging and branching of
traffic aggregates through multiple hops. The Per-hop behaviors in nodes are
configured infrequently, representing a change in network
infrastructure. More frequent quality-of-service changes come from
employing control plane only needs to be employed functions in the configuration of the DS
boundaries. A PDB provides a link between the DS domain level at which
control is exercised to form traffic aggregates with qual-
ity-of-service quality-of-service
goals across the domain and the per-hop and per-
link per-link
treatments packets receive that results in meeting the quality-
quality-of-service goals.


4 Understanding PDBs

4.1 Defining PDBs

RFCs 2474 and 2475 define a Differentiated Services Behavior Aggregate
as "a collection of packets with the same DS codepoint crossing a
link in a particular direction" and further state that packets with
the same DSCP get the same per-hop forwarding treatment (or PHB)
everywhere inside a single DS domain. Note that even if multiple DSCPs
map to the same PHB, this must hold for each DSCP individually. In
section 2 of this document, we introduced a more general definition of a
traffic aggregate in the diffserv sense so that we might easily refer to
the packets which are mapped to the same PHB everywhere within a DS
domain. Section 2 also presented a short definition of PDBs which we
expand upon in this section:

Per-Domain Behavior: the expected treatment that an identifiable
  or target group of packets will receive from "edge to edge" of a
  DS domain. A particular PHB (or, if applicable, list of PHBs) and
  traffic conditioning requirements are associated with each PDB.


Each PDB has measurable, quantifiable, attributes are associated with each PDB
and these that can be used
to describe what will happen happens to its packets of
that PDB as they enter and cross the
DS domain. These derive from the

Nichols and Carpenter       Expires: December, 2000        [page  6 ] rules that are enforced during the
entry of packets into the DS domain and the forwarding treatment (PHB)
the packets get inside the domain. domain, but can also depend on the entering
traffic loads and the domain's topology. PDB attributes may be absolute
or statistical and they may be parameterized by network properties.
For exam-
ple, example, a loss attribute might be expressed as "no more than
0.1% of packets will be dropped when measured over any time period
larger than T", a delay attribute might be expressed as "50% of
delivered packets will see less than a delay of d milliseconds, 30% will
see a delay less than 2d ms, 20% will see a delay of less than 3d ms."
A wide range of metrics is possible.

Identification of the In general they will be expressed
as bounds or percentiles rather than as absolute values.

A PDB is applied to a target group of packets is carried out using
classification. arriving at the edge
of the DS domain. The Per-Domain Behavior applied to that target group is distinguished from all arriving
packets by use of packet is characterized in two parts: 1) classifiers [RFC2475] (where the relationship between
this target group classifier
may be "null"). The action of packets to the marked traffic aggregate which
results  from PDB on the application target group has two
parts. The first part is the enforcement of rules (through the use
of traffic conditioning) to the identified (classified) packets to create a traf-
fic aggregate traffic aggregate. Packets that
conform to the rules are marked with a DSCP for the associated PHB associated with
the PDB (see figure 2) and 2)
the attributes which result from 2). The second part is the treatment experienced
by packets from the same traffic aggregate transiting the interior
of a DS domain, between and inside of DS domain boundaries. The
following subsections further discuss these two effects on the target
group that arrives at the DS domain boundary.

           -----------   ------------   --------------------   foo
arriving _|classifiers|_|target group|_|traffic conditioning|_ traffic
packets   |           | |of packets  | |& marking (for foo) |  aggregate
           -----------   ------------   --------------------

      Figure 2: Relationship of the traffic aggregate associated with
     		 a PDB to arriving packets

The first part

4.1.1 Crossing the DS edge: the effects of rules on the target group

This effect is more straightforward than quantified by the second, but might relationship of the emerging traffic
aggregate to the entering target group. That relationship can depend
on the arriving traffic pattern as well as the configuration of the
traffic conditioners. For example, if the EF PHB [RFC2598] and a strict
policer of rate R are associated with the foo PDB, then the first
part of characterizing the foo PDB is to write the relationship between
the arriving target packets and the departing foo traffic aggregate. This would be formulated as the
In this case, "the rate of the emerging foo traffic aggregate being is less
than or equal to the smaller of R and the arrival rate of the target
group of pack-
ets packets" and additional temporal characteristics of the packets
(e.g., burst) would may be specified as desired. Thus, there is a "loss
that results to on the original arriving target group that results from sending too much
traffic or the traffic with the wrong temporal characteristics that characteristics. This
loss rate should be entirely preventable (or controllable) by the
upstream sender conforming to the traffic conditioning associated
with the PDB specification. A PDB might also apply traffic conditioning
at egress at a DS boundary.   This would be treated similarly to
the ingress characteristics (the authors may develop more text on

The issue of "who is in the future, but it does not materially affect the ideas pre-
sented in this document.) In section 4.3, we will revisit this dis-
cussion for PHB groups.

This aspect of "who is in control" of control" of the loss (or demotion) rate helps
to clearly delineate the first part of characterizing packet
performance this component of a PDB performance from that
associated with transiting the second part. Further, domain. The latter is completely under
control of the relation-
ship operator of the DS domain and the former is used to
ensure that the entering traffic aggregate is following the rules to
which the operator has provisioned the network. Further, the effects of
the enforcement of edge rules on the arriving target packet group can usually be
expressed more simply that than the traffic aggregate's tran-
sit transit attributes.

A PDB may also apply traffic conditioning at DS domain egress. The
effect of this conditioning on the overall PDB attributes and depends would be
treated similarly to the ingress characteristics (the authors may
develop more text on different elements. this in the future, but it does not materially
affect the ideas presented in this document.)

4.1.2 Crossing the DS domain: transit effects

The second part

Nichols and Carpenter       Expires: December, 2000        [page  7 ] component of PDB performance is illustrated in figure 3 as the quantifiable metrics that can be
used to characterize
the transit of any a packet of a particular the PDB's traffic aggregate between any
two edges of the DS domain boundary shown in figure 3, including those indicated with arrows. 3. Note that the
DS domain boundary runs through the DS boundary rout-
ers routers since the
traffic aggregate is generally formed in the boundary router before
the packets are queued and scheduled for output. (In most cases, this
distinction is expected to be important.)

                            |           |
                       -----X           |
                            |           |
                            |   DS      |
                            |   domain  X----
                            |           |
                       -----X           |
                            |           |

       Figure 3: Range of applicability of attributes of a traffic
      	 	aggregate associated with a PDB

The traffic aggregate associated with a PDB is formed by the
application of rules, through classification and traffic condition-
ing, to packets arriving at the DS boundary. Packets that conform
to (is between the rules are points
      	 	marked with a DSCP that maps to a particular
PHB within a domain. "X")

DSCPs should not mutate in the interior of a DS domain as there are
no rules "rules" being applied. applied to the traffic. If it is necessary to reapply
the kind of rules that could result in remarking, there should probably be
a DS domain boundary at that point; point, though such an inte-
rior one that "interior" boundary
can have "lighter weight" rules. Thus, if when measuring attributes between
locations as indicated in figure 3, the DSCP at the egress side can
be assumed to have held throughout the domain.

Though a DS domain may be as small as a single node, more complex
topologies are expected to be the norm, thus the PDB definition must
hold as its traffic aggregate is split and merged on the interior links
of a DS domain. Packet flow in a network is not part of the PDB
definition; the application of rules as packets enter the DS domain and
the consistent PHB through the DS domain must suffice. A PDB's
definition does not have to hold for arbitrary topologies of networks,
but the limits on the range of applicability for a specific PDB must be
clearly specified.

In general, though, a PDB operates between N ingress points and M egress points
at the DS domain boundary. Even in the degener-
ate degenerate case where N=M=1,
PDB attributes are more complex than the definition of PHB attributes
since the concatenation of the behavior of intermediate nodes affects
the former. A complex case with N and M both greater than one involves
splits and merges in the traffic path and is non-trivial to analyze.
Analytic, simulation, and experimental work will all be necessary
to under-
stand understand even the simplest PDBs.

4.2 Constructing PDBs

A DS domain is configured to meet the network operator's traffic
engineering goals for the domain independently of the perfor-
mance performance goals
for a particular flow of a traffic aggregate. Once the interior routers
are configured for the number of distinct traffic aggregates that
the network will handle, each PDB's allocation at the edge comes from
meeting the desired performance goals for

Nichols and Carpenter       Expires: December, 2000        [page  8 ] the PDB's traffic aggretae aggregate
subject to that configuration of link packet schedulers and bandwidth. bandwidth
capacity.  The rules at the edge may be altered by provisioning or
admission control but the decision about which PDB to use and how to
apply the rules comes from match-
ing matching performance to goals.

For example, consider the diffserv DS domain of figure 3. A PDB with an attribute of an explicit
bound on loss must have rules at the edge to ensure that on the average
no more packets are admit-
ted admitted than can emerge. Though, queueing internal
to the network may result in a difference between input and output
traffic over some timescales, the averaging timescale should not exceed
what might be expected for reasonably sized buffering inside the net-
network. Thus if bursts are allowed to arrive into the interior of the
network, there must be enough capacity to ensure that losses don't
exceed the bound. Note that explicit bounds on the loss level can be
particularly difficult as the exact way in which pack-
ets packets merge inside
the network affects the burstiness of the PDB's traffic aggregate and
hence, loss.

PHBs give explicit expressions of the treatment a traffic aggre-
gate aggregate
can expect at each hop. For a PDB, this behavior must apply to merging
and diverging traffic aggregates, thus characterizing a PDB requires exploring
understanding what happens to a PHB under aggrega-
tion. aggregation. Rules must
be recursively applied to result in a known behavior. As an example,
since maximum burst sizes grow with the number of microflows or traffic
aggregate flows streams merged, a PDB specification must address this. A
clear advantage of constructing behaviors that aggregate is the ease
of concatenating PDBs so that the associated traffi traffic aggregate has
known attributes that span inte-
rior interior DS domains and, eventually, farther.
For example, in figure 1 assume that we have configured the foo PDB
on the interior DS domains of AS2. Then traffic aggregates associated
with the foo PDB in each interior DS domain of AS2 can be merged at
the shaded interior boundary routers. Using the same (or fewer) rules
as were applied to create the traffic aggregates at the entrance to
AS2, there should be confidence that the attributes of the foo PDB
can continue to be used to quantify by the expected behav-
ior. behavior. Explicit
expressions of what happens to the behavior under aggregation, possibly
parameterized by node in-degrees or net-
work network diameters are necessary
to determine what to do at the inter-
nal internal aggregation points. One approach
might be to completely reapply the edge rules at these points. Another points; another
might employ some limited rate-based remarking only.

Multiple PDBs might may use the same PHB. In the The specification of a
PDB, there might be PDB can
contain a list of PHBs and their required configura-
tion, configuration, all of which
would result in the same characteristics. PDB. In operation, though, it is expected that a
single domain will use a single PHB to implement a particular PDB. A PDB,
though different domains may select different PHBs. Recall that in
the diffserv definition [RFC2474], a single PHB might
beselected be selected
within a domain by a list of DSCPs. Multiple PDBs might use the same
PHB in which case the transit performance of traffic aggregates of
these PDBs will, of necessity, be the same.

Nichols and Carpenter       Expires: December, 2000        [page  9 ] Yet, the particular
characteristics that the PDB designer wishes to claim as attributes may
vary, so two PDBs that use the same PHB might not be specified with the
same list of attributes.

The specification of the transit expectations of behavior aggre-
gates PDBs across domains
both assists in the deployment of QoS within a DS domain and helps
enable the composition of end-to-
end, end-to-end, cross-domain services to proceed. proceed
by making it possible to hide details of a domain's internals while
exposing characteristics necessary for QoS.

4.3 PDBs using PHB Groups

When a set

The use of related PHB groups to construct PDBs are defined using can be done in several ways.
A single PHB member of a PHB group, they
should group might be defined in the same document. This would used to construct a single
PDB. For example, a PDB could be particu-
larly appropriate if the application defined using just one of the Class
Selector Compliant PHBs [RFC2474]. The edge rules for that create the
traffic aggregates associated with each PDB had some relation-
ships and interdependencies, as one would expect for the AF PHB
group [RFC2597]. Characterizing
the traffic conditioning effects
should then be described for these PDBs together. The transit
attributes will depend on required configuration of the particular PHB associated with the PDB and
will not would be defined
in such a way that there was no dependence or relationship with the same for all
manner in which other PHBs of the group are used or, indeed, whether
they are used in that DS domain. In this case, the group, thus each should
have a clearly separate treatment, though there may reasonable approach
would be some
parameterized interrelationship between to specify this PDB alone in a document which expressly called
out the attributes of each conditions and configuration of
these PDBs. the Class Selector PHB required.

A single PDB can be constructed using more than one PHB from the same
PHB group. For example, if the traffic conditioner described in RFC 2698 is
might be used to mark arriving packets a particular entering traffic aggregate for
one of the three AF1x PHBs [RFC2597] while the transit performance
of the resultant PDB is specified, statistically, across all the packets
marked with one of those PHBs.

A set of related PDBs might be defined using a PHB group. In this case,
the related PDBs should be defined in the same document. This is
appropriate when the application of the edge rules that create the
traffic aggregates associated with each PDB have some relationships and
interdependencies such that the traffic conditioning effects for these
PDBs should be described and characterized together. The transit
attributes will depend on the PHB associated with the PDB and will not
be the same for all PHBs in the group, though there may be some
parameterized interrelationship between the attributes of each of these
PDBs. In this case, each PDB should have a clearly separate description
of its transit attributes (delineated in a separate subsection) within
the document. For example, the traffic conditioner described in RFC
2698 might be used to mark arriving packets for three different AF1x
PHBs, then
the most reasonable approach each of which is to be treated as a separate traffic aggregate
in terms of transit properties. Then a single document could be used
to define and quantify the rela-
tionship relationship between the arriving packets
and the emerging traffic aggregates as they relate to one another.
The transit characteris-
tics characteristics of packets of each separate AF1x traffic
aggregate should be described separately.

A separately within the document.

Another way in which a PHB group might be used to create one PDB per
PHB might have decoupled edge rules, but some relationship between
the PHBs of the group. For example, a set of PDBs might be defined
using Class Selector Compliant PHBs [RFC2474] in such a way that the
edge rules that create the traffic aggregates are not related, but
the transit performance of each traffic aggregate has some parametric
relationship to the the other. If it makes sense to specify them in
the same document, then the author(s) should do so.

4.4 Forwarding path vs. control plane

A PDB's associated PHB and edge traffic conditioners are in the packet
forwarding path and operate at line rates while the config-
uration configuration
of the DS domain edge to enforce rules on who gets to use the PDB
and how the PDB should behave temporally is done by the control plane
on a very different time scale. For example, con-
figuration reconfiguration of PHBs
might only occur monthly monthly, quarterly, or quarterly. only when the network is upgraded.
The edge rules might be reconfigured at a few regular intervals during
the day or might happen in response to signalling decisions thou-
sands thousands
of times a day. Even at the shortest time scale, control plane actions
are not expected to happen per-packet. Much of the con-
trol control plane work
is still evolving and is outside the charter of the Diffserv WG. We
note that this is quite appropriate since the

Nichols and Carpenter       Expires: December, 2000        [page  10 ] manner in which the
configuration is done and the time scale at which it is done should
not affect the PDB attributes.


5 Format for Specification of Diffserv Per-Domain Behaviors

PDBs arise from a particular relationship between edge and inte-
rior interior
(which may be parameterized). The quantifiable characteris-
tics characteristics of
a PDB must be independent of whether the network edge is configured
statically or dynamically. The particular configuration of traffic
conditioners at the DS domain edge is critical to how a PDB performs,
but the act(s) of configuring the edge is a control plane action which
can be separated from the specification of the PDB.

The following sections must be present in any specification of a
Differentiated Services PDB. Of necessity, their length and con-
tent content will
vary greatly.

5.1 Applicability Statement

All PDB specs must have an applicability statement that outlines the
intended use of this PDB and the limits to its use.

5.2 Rules

This section describes the rules to be followed in the creation of
this PDB. Rules should be distinguished with "may", "must" and "should."
The rules specify the edge behavior and configuration configuration, including
whatever traffic conditioning is required, and the PHB (or PHBs) to be
used and any additional require-
ments requirements on their configuration beyond that
contained in RFCs.

5.3  Attributes

A PDB's attributes tell how Note that traffic conditioning may include
classification, admission control, marking, traffic shaping, and

5.3 Attributes

A PDB's attributes tell how it behaves under ideal conditions if
configured in a specified manner (where the specification may be
parameterized).  These might include drop rate, throughput, delay bounds
measured over some time period. They may be absolute
bounds or bounds, statistical bounds bounds,
or percentiles (e.g., "90% of all packets measured over intervals of at
least 5 minutes will cross the DS domain in less than 5 milliseconds").
A wide variety of characteristics may be used but they must be explicit,
quantifiable, and defensible. Where particular statistics are used, the
document must be precise about how they are to be measured and about how
the characteris-
tics characteristics were derived.

Advice to a network operator would be to use these as guidelines in
creating a service specification rather than use them directly. For
example, a "loss-free" PDB would probably not be sold as such, but
rather as a service with a very small packet loss proba-
bility. probability.

5.4 Parameters

Nichols and Carpenter       Expires: December, 2000        [page  11 ]

The definition and characteristics of a PDB may be parameterized by
network-specific features; for example, maximum number of hops, minimum
bandwidth, total number of entry/exit points of the PDB to/from the
diffserv network, maximum transit delay of network elements, minimum
buffer size available for the PDB at a network node, etc.

5.5 Assumptions

In most cases, PDBs will be specified assuming lossless links, no link
failures, and relatively stable routing. This is reasonable since
otherwise it would be very difficult to quantify behavior. behavior and this
is the operating conditions for which most operators strive. However,
these assumptions must be clearly stated. Since PDBs with specific
bandwidth parameters require that bandwidth to be available, the
assumptions to be stated may include standby capacity. Some PDBs may be developed without
specifically targeted for cases where these assumptions, assumptions do not hold,
e.g., for high loss rate links, and these such targeting must also be made
explicit.  If additional restrictions, e.g., route pinning, especially specific traffic
engineering measures, are required, these must be stated.

Further, if any assumptions are made about the allocation of resources
within a diffserv network in the creation of the PDB, these must be
made explicit.

5.6 Example Uses

A PDB specification must give example uses to motivate the understanding
of ways in which a diffserv network could make use of the PDB although
these are not expected to be detailed. For example, "A bulk handling behavior aggregate
PDB may be used for all packets which should not take any resources
from the network unless they would otherwise go unused. This might
be useful for Netnews traffic or for traffic rejected from some other
PDB due to violation of that PDB's rules."

5.7 Environmental Concerns (media, topology, etc.)

Note that it is not necessary for a provider to expose which PDB (if
a commonly defined one) is being used nor is it necessary for a provider
to specify a service by the PDB's attributes. For exam-
ple, example, a service
provider might use a PDB with a "no queueing loss" characteristic
in order to specify a "very low loss" service.

This section is to inject realism into the characteristics described
above. Detail the assumptions made there and what constraints that
puts on topology or type of physical media or allocation.


6 On PDB Attributes

Attributes are

As discussed in section 4, measurable, quantifiable attributes
associated with each PDB: measurable, quantifi-
able, characteristics which PDB can be used to describe what will hap-
pen happen to
packets using that PDB as they cross the domain. These
expectations result directly from the application of edge rules
enforced during In itrole as a building
block for the creation construction of interdomain quality-of-service, a PDB
specification should provide the PDB's traffic aggregate and/or
its entry into answer to the domain and question: Under what
conditions can we join the forwarding treatment (PHB)
packets output of that traffic aggregate get inside this domain to another under the domain. There are

same rules and Carpenter       Expires: December, 2000        [page  12 ] expectations? Although there are many ways in which
traffic might be distributed, but creating a quantifiable, realizable service across PDBs
that can be concatenated into multi-domain services limits the DS domain will limit realistic
scenarios.  A PDB's attributes with a clear statement of the scenarios conditions
under which can occur. the attributes hold is critical to the composition of multi-
domain services.

There is a clear correlation between the strictness of the rules and the
quality of the charac-
terization of the PDB.

There PDB's attributes. As indicated earlier, numerical bounds
are two ways to characterize PDBs with respect likely to time.
First are its properties over "long" time periods, or average
behaviors. In a PDB spec, these would be the rates statistical or throughput
seen over some specified time period. In addition, there are prop-
erties of "short" time behavior, usually expressed as the allowable
burstiness in an aggregate. The short a percentile. Parameters
expressed as strict bounds will require very precise mathematical
analysis, whereas those expressed statistically can to some extent
rely on experiment. Section 7 gives the example of a PDB without strict
rules and concurrent work on a PDB with strict rules and attributes
is also in front of the WG [VW]. This section gives some general
considerations for characterizing PDB attributes.

There are two ways to characterize PDBs with respect to time. First
are properties over "long" time periods, or average behaviors. A PDB
specification should report these as the rates or throughput seen
over some specified time period. In addition, there are properties
of "short" time behavior, usually expressed as the allowable burstiness
in a traffic aggregate. The short time behavior is important is
understanding the in under-
standing buffering requirements (and associated loss characteristics)
and in quantifying how packets using the PDB aggregate, either
within a DS domain or for metering and conditioning considerations at the DS boundaries. For
short-time behavior, we are interested primarily in two things: 1) how
many back-to-
back back-to-back packets of the PDB's traffic aggregate will we see at
any point (this would be metered as a burst) and 2) how large a burst of
packets of this PDB's traffic aggregate can appear in a queue at once
(gives queue overflow and loss). If other PDBs are using the same PHB
within the domain, that must be taken into account.

Put simply, a PDB specification should provide the answer to the
question: Under what conditions can we join the output of this
domain to another under the same rules and expectations?

6.1 Considerations in specifying long-term or average PDB attributes

To make this more concrete, consider the DS domain of figure 4
for which we will define the foo PDB. To characterize the average or long-term behavior that must be specified for the foo PDB we
must explore a number of questions, for instance: Can the DS domain
handle the average foo traffic flow? Is that answer topology-dependent
or are there some specific assumptions on routing which must hold
for the foo PDB to preserve its "adequately provisioned" capability?
In other words, if the topology of D changes suddenly, will the foo
PDB's attributes change? Will its loss rate dramatically increase?

                 ____X________X_________X___________          /
                /                                   \    L   |
        A<---->X                                     X<----->|  E
               |                                     |       |
               |               D                     |        \
        Z<---->X                                     |
               |                                     |
                        X                 X

       Figure 4: ISP and DS domain D connected in a ring and connected
                 to DS domain E

Let domain D in figure 4 be an ISP ringing the U.S. with links of
bandwidth B and with N tails to various metropolitan areas. If Inside D, if
the link between the node connected to A and the node connected to Z
goes down, all the foo traffic aggregate between the two nodes must
transit the entire ring: Would the bounded behavior of the foo PDB
change?  If this outage results in some node of the ring now hav-
ing having a
larger arrival rate to one of its links than the capacity of the link
for foo's traffic aggregate, clearly the loss rate would change
dramatically.  In that this case, there were topological assumptions were made about the
path of the traffic from A to Z that affected the characteristics of the
foo PDB. Once If these topological assumptions no longer hold, any

Nichols and Carpenter       Expires: December, 2000        [page  13 ]

assumptions on the loss rate
of packets of the foo traffic aggregate transiting the domain would could
change; for example, a characteristic such as "loss rate no greater
than 1% over any interval larger than 10 minutes" would no longer hold. minutes." A PDB specification
should spell out the assumptions made on preserving the attributes.

6.2 Considerations in specifying short-term or bursty PDB attributes

Next, consider the short-time behavior of the traffic aggregate
associated with a PDB, specifically whether permitting the maxi-
mum maximum
bursts to add in the same manner as the average rates will lead to
properties that aggregate or under what rules this will lead to
properties that aggregate. In our example, if domain D allows each of
the uplinks to burst p packets into the foo traffic aggre-
gate, aggregate, the
bursts could accumulate as they transit the ring. Packets headed for
link L can come from both directions of the ring and back-to-back
packets from foo's traffic aggregate can arrive at the same time. If the
bandwidth of link L is the same as the links of the ring, this probably
does not present a buffering problem. If there are two input links that
can send packets to queue for L, at worst, two packets can arrive
simultaneously for L. If the band-
width bandwidth of link L equals or exceeds
twice B, the packets won't accumulate. Further, if p is limited to
one, and the bandwidth of L exceeds the rate of arrival (over the
longer term) of foo packets (required for bounding the loss) then
the queue of foo packets for link L will empty before new packets
arrive. If the bandwidth of L is equal to B, one foo packet must queue
while the other is trans-
mitted. transmitted. This would result in N x p back-to-back back-to-
back packets of this traffic aggregate arriving over L during the
same time scale as the bursts of p were permitted on the uplinks.
Thus, configuring the PDB so that link L can handle the sum of the
rates that ingress to the foo PDB doesn't guarantee that L can handle
the sum of the N bursts into the foo PDB.

If the bandwidth of L is less than B, then the link must buffer
Nxpx(B-L)/B foo packets to avoid loss. If the PDB is getting less than
the full bandwidth L, this number is larger. For probabilistic bounds, a
smaller buffer might do if the probability of exceeding it can be

More generally, for router indegree of d, bursts of foo packets might
arrive on each input. Then, in the absence of any additional rules,
it is possible that dxpx(# of uplinks) back-to-back foo packets can
be sent across link L to domain E. Thus the DS domain E must permit
these much larger bursts into the foo PDB than domain D permits on
the N uplinks or else the foo traffic aggregate must be made to conform
to the rules for entering E (e.g., by shaping).

What conditions should be imposed on a PDB and on the associ-
ated associated PHB
in order to ensure PDBs can be concatenated, as across the interior
DS domains of figure 1? Edge rules for constructing a PDB that has
certain attributes across a DS domain should apply

Nichols and Carpenter       Expires: December, 2000        [page  14 ] independently of
the origin of the packets. With reference to the example we've been
exploring, the rules for the PDB's traffic aggregate entering link
L into domain E should not depend on the number of uplinks into domain D.

6.3  Example

In this example, we will make the above more concrete. We
assume that only the foo PDB is using its associated traffic aggre-
gate and we use "foo agggregate" interchangeably with "the traf-
fic aggregate associated with the PDB foo." We also use "foo
packets" interchangeably with "the packets marked for the PHB
associated with PDB foo."

Assume the topology of figure 4 and that all the uplinks have the
same bandwidth B and link L has bandwidth L which is less than
or equal to B. The foo traffic aggregates from the N uplinks each
have average rate R and are destined to cross L. If only a fraction
a of link L is allocated to foo, then R =axL/N fits the average rate
constraint. If each of the N flows can have a burst of p packets
and half the flows transit the ring in each direction, then 2xp
packets can arrive at the foo queue for link L in the time it took to
transmit p packets on the ring, p/B. Although the link scheduler
for link L might allow the burst of packets to be transmitted at the
line rate L, after the burst allotment has been exceeded, the queue
should be expected to clear at only rate axL. Then consider the
packets that can accumulate. It takes 2xp/(axL) to clear the queue
of the foo packets. In that time, bursts of p packets from the other
uplinks can arrive from the ring, so the packets do not even have
to be back-to-back.  Even if the packets do not arrive back-to-
back, but are spaced by less time than it takes to clear the queue
of foo packets, either the required buffer size can become large or
the burst size of foo packets entering E across L becomes large
and is a function of N, the number of uplinks of domain D.

Let L = 1.5 Mbps, B = 45 Mbps, a = 1/3, N=10, p = 3. Suppose
that the bursts from two streams of foo packets arrive at the queue
for link L very close together. Even if 3 of the packets are cleared
at the line rate of 1.5 Mbps, there will be 3 packets remaining to
be serviced at a 500 kbps rate. In the time allocated to send one of
these, 9 packets can arrive on each of the inputs from the ring. If
any non-zero number of these 18 packets are foo packets, the
queue size will not reduce. If two more bursts (6 of the 18 pack-
ets) arrive, the queue increases to 8 packets. Thus, it's possible to
build up quite a large queue, one likely to exceed the buffer allo-
cated for foo. The rate bound means that each of the uplinks will
be idle for the time to send three packets at 50 kbps, possibly by
policing at the ring egress, and thus the queue would eventually
decrease and clear, however, the queue at link L can still be very
large. PDBs where the intention is to permit loss should be con-
structed so as to provide a probabilistic bound for the queue size
to exceed a reasonable buffer size of one or two bandwidth-delay
products. Alternatively or additionally, rules can be used that

Nichols and Carpenter       Expires: December, 2000        [page  15 ]

bound the amount of foo packets that queue by limiting the burst
size at the ingress uplinks to one packet, resulting in a maximum
queue of N or 10 or to impose additional rules on the PDB. One
approach is to limit the domain over which the PDB applies so
that interior boundaries are placed at merge points (or between
every M merge points)  so that a shaping edge conditioner can be
reapplied.  Another approach is to use a PHB defined such that it
strictly limits the burstiness.


6.3 Remarks

This section has been provided to provide some motivational food for
thought for PDB specifiers. It is by no means an exhaustive catalog
of possible PDB attributes or what kind of analysis must be done.
We expect this to be an interesting and evolutionary part of the work
of understanding and deploying differentiated ser-
vices services in the Internet.
There is a potential for much interesting research work. However,
in submitting a PDB specification to the Diffserv WG, a PDB must also
meet the test of being useful and

7.0 relevant by a deployment experience,
described in section 8.

7 A Reference Per-Domain Behaviors Behavior

The intent of this section is to define one or as a few "reference"
PDBss; certainly reference a Best Effort
PDB, a PDB and perhaps others. This sec-
tion is very preliminary at this time and meant to be the starting
point for discussion rather than its end. These are PDBs that have has little in the way of rules or expectations.

7.1 Best Effort Behavior PDB

7.1.1 Applicability

A Best Effort (BE) PDB is for sending "normal internet traffic" across
a diffserv network. That is, the definition and use of this PDB is
to preserve, to a reasonable extent, the pre-diffserv deliv-
ery delivery
expectation for packets in a diffserv network that do not require any
special differentiation.

7.1.2 Rules

There are no rules governing rate and bursts of packets beyond the
limits imposed by the ingress link. The network edge ensures that
packets using the PDB are marked for the Default PHB (as defined in [RFC2474]).
[RFC2474]), but no other traffic conditioning is required. Interior
network nodes use the Default PHB on these packets.

7.1.3 Attributes of this PDB

"As much as possible as soon as possible".

Packets of this PDB will not be completely starved and when resources
are available (i.e., not required by packets from any

Nichols and Carpenter       Expires: December, 2000        [page  16 ] other traffic
aggregate), network elements should be configured to permit packets
of this PDB to consume them.

Although some network operators may bound the delay and loss rate for
this aggregate PDB given knowledge about their network, these attributes are
not part of the definition.

7.1.4 Parameters


7.1.5 Assumptions


A properly functioning network, i.e. packets may be delivered from
any ingress to any egress.

7.1.6 Example uses

	1. For the normal Internet traffic connection of an organization.

	2. For the "non-critical" Internet traffic of an organization.

	3. For standard domestic consumer connections

7.2  Bulk Handling Behavior PDB

7.2.1  Applicability

A Bulk Handling (BH) PDB is for sending extremely non-critical
traffic across a diffserv network. There should be an expectation
that these packets may be delayed or dropped when other traffic is

7.2.2  Rules

There are no rules governing rate and bursts of packets beyond
the limits imposed by the ingress link. The network edge ensures
that packets using this PDB are marked for either a CS or an AF
PHB. Interior network nodes must have this PHB configured so
that its packets may be starved when other traffic is present. For
example, using the PHB for Class Selector 1 (DSCP=001000), all
routers in the domain could be configured to queue such traffic
behind all other traffic, subject to tail drop.

7.2.3  Attributes of the BH PHB

Packets are forwarded when there are idle resources.

7.2.4  Parameters


7.2.5  Assumptions

Nichols and Carpenter       Expires: December, 2000        [page  17 ]

A properly functioning network.

7.2.6  Example uses

1. For Netnews and other "bulk mail" of the Internet.

2. For "downgraded" traffic from some other PDB.


8 Procedure for submitting PDB specifications to Diffserv WG

1. Following the guidelines of this document, write a draft and submit
it as an Internet Draft and bring it to the attention of the WG mailing
list. Either as an appendix to the draft, or in a separate document,
provide details of deployment experience with measured results on
a network of non-trivial size carrying realistic traffic.

2. Initial discussion on the WG should focus primarily on the merits
of the a PDB, though comments and questions on the claimed attributes
are reasonable. This is in line with our desire to put relevance before
academic interest in spending WG time on PDBs. Academically interesting
PDBs are encouraged, but not for submission to the diffserv WG.

3. Once consensus has been reached on a version of a draft that it
is a useful PDB and that the characteristics "appear" to be correct
(i.e., not egregiously wrong) that version of the draft goes to a
review panel the WG Co-chairs set up to audit and report on the
characteristics. The review panel will be given a deadline for the
review. The exact timing of the deadline will be set on a case-by-
case case-by-case
basis by the co-chairs to reflect the complexity of the task and other
constraints (IETF meetings, major holidays) but is expected to be in the
4-8 week range. During that time, the panel may correspond with the
authors directly (cc'ing the WG co-
chairs) co-chairs) to get clarifications. This
process should result in a revised draft and/or a report to the WG from
the panel that either endorses or disputes the claimed characteristics.

4. If/when endorsed by the panel, that draft goes to WG last call.
If not endorsed, the author(s) can give a itemized response to the
panel's report and ask for a WG Last Call.

5. If/when passes Last Call, goes to ADs for publication as a WG
Informational RFC in our "PDB series".


9 Acknowledgements

The ideas in this document have been heavily influenced by the Diffserv
WG and, in particular, by discussions with Van Jacob-
son, Jacobson, Dave Clark,
Lixia Zhang, Geoff Huston, Scott Bradner, Randy Bush, Frank Kastenholz,
Aaron Falk, and a host of other people who should be acknowledged
for their useful input but not be held accountable for our mangling
of it. Grenville Armitage coined "per domain behavior (PDB)" though
some have sug-

Nichols and Carpenter       Expires: December, 2000        [page  18 ]

gested suggested similar terms prior to that.


[RFC2474] RFC 2474, "Definition of the Differentiated Services Field
(DS Field) in the IPv4 and IPv6 Headers", K.Nichols, S. Blake, F.
Baker, D. Black,

[RFC2475] RFC 2475, "An Architecture for Differentiated Ser-
vices", Services",
S. Blake, D. Black, M.Carl-
rfc2475.txt M.Carlson,E.Davies,Z.Wang,W.Weiss,

[RFC2597] RFC 2597, "Assured Forwarding PHB Group", F. Baker, J.
Heinanen, W. Weiss, J. Wroclawski,

[RFC2598] RFC 2598, "An Expedited Forwarding PHB", V.Jacobson,
K.Nichols, K.Poduri,
rfc2598.txt rfc/rfc2598.txt

[RFC2698] RFC 2698, "A Two Rate Three Color Marker", J. Heinanen, R.
Guerin. rfc2698.txt

[MODEL]	"A Conceptual "An Informal Management Model for Diffserv Routers", draft-ietf-
diffserv-model-02.txt, Bernet et. al.
draft-ietf-diffserv-model-04.txt, Y. Bernet, S. Blake, D. Grossman,
A. Smith

[MIB] "Management Information Base for the Differentiated Services
Architecture", draft-ietf-diffserv-mib-01.txt,
Baker et. al. draft-ietf-diffserv- mib-01.txt, F. Baker, K. Chan,
A. Smith

[VW] "The 'Virtual Wire' Behavior Aggregate", draft-ietf-diff-
serv-ba-vw-00.txt, Per-Domain Behavior",
draft-ietf-diffserv-pdb-vw-00.txt, V. Jacobson, K. Nichols, and
Poduri (being modified to reflect new terminology). Poduri.

Authors' Addresses

 Kathleen Nichols                 Brian E. Carpenter
 Packet Design, Inc.              IBM
 66 Willow Place                  c/o iCAIR
 Menlo Park, CA 94025             Suite 150
 USA                              1890 Maple Avenue
                                  Evanston, IL 60201
 email:  email: