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Internet Engineering Task Force                 B. Carpenter
Differentiated Services Working Group           IBM
Internet Draft                                  K. Nichols
Expires in April, 2001                          Packet Design
draft-ietf-diffserv-pdb-bh-00                   October, 2000

A Bulk Handling Per-Domain Behavior for Differentiated Services


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
working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at
any time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

This document is a product of the Diffserv working group. Comments
on this draft should be directed to the Diffserv mailing list
<diffserv@ietf.org>.  The list of current Internet-Drafts can be
accessed at www.ietf.org/ietf/1id-abstracts.txt.  The list of
Internet-Draft Shadow Directories can be accessed at
www.ietf.org/shadow.html. Distribution of this memo is unlimited.

Copyright Notice

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


This document proposes a differentiated services per-domain behavior
in which it is possible, in a properly functioning network, for
traffic of this PDB to be "starved". This is in contrast to the
Internet's "best-effort" or "normal Internet traffic" model.

1 Description of the Bulk Handling PDB

This document proposes a differentiated services per-domain
behavior [PDBDEF] called bulk handling (BH) which makes it possible
to admit traffic of sufficiently low value (where "value"
may be interpreted in any useful way by the network operator) that
any other traffic should take precedence over this traffic in
consumption of network link bandwidth. There may or may not be memory
(buffer) resources allocated for this type of traffic.

In some networks, there are types of traffic which are considered
"optional"; that is, packets of these types ought to consume network
resources only when no other traffic is present. This traffic type
is considered to be distinct from "best-effort" traffic since the
network makes no committment to delivering the packets while in
the best-effort case, there is assumed to be an implied "good faith"
committment that there are at least some network resources available
for this traffic. This document proposes a bulk handling differentiated
services per-domain behavior to implement this "optional"
traffic service in a differentiated services domain.

2 Applicability

A Bulk Handling (BH) PDB is for sending extremely non-critical traffic
across a diffserv network. There should be the expectation that
these packets may be delayed or dropped when any other traffic
is present. Its use might assist a network operator in moving certain
kinds of traffic or users to off-peak times. Alternatively, or
in addition, packets can be designated for the BH PDB where the
goal is to protect all other packet traffic from competition with
the BH aggregate while not completely banning BH traffic from the
network. A BH PDB should not be used for a customer's "normal internet"
traffic nor for packets that ought to simply be dropped as unauthorized.
The BH PDB would not be usefully depolyed in a network which is
congested with non-BH traffic as this indicates no link resources
to spare.

3 Rules

3.1 Edge rules

There are no rules governing rate and bursts of packets beyond the
limits imposed by the ingress link. The network edge must include
a classifier that selects the appropriate BH target group of packets
out of all arriving packets and steers them to a marker which sets
the appropriate DSCP to select a PHB configured as described in
the next section. No other traffic conditioning is required.

3.2 PHB configuration

Either a Class Selector (CS) PHB [RFC2474], an Experimental/
Local Use (EXP/LU) PHB [RFC2474], or an Assured Forwarding (AF) PHB
[RFC2597] may be used as the PHB for the BH traffic aggregate. This
document does not specify the exact DSCP to use inside a domain, but
instead specifies the necessary properties of the PHB selected by the
DSCP. If a CS PHB is used, Class Selector 1 (DSCP=001000) is suggested.

The PHB used by the BH aggregate inside a DS domain must be configured
so that its behavior is that its packets are forwarded onto the
node output link when the link would otherwise be idle. If the
DS node uses a scheduler that is not capable of this strict starvation,
an operator might choose to configure a very small link share for
the BH aggregate and still acheive the desired goals. It is unlikely
that a "fair sharing" scheduler would be configurable to yield
the required PHB.

If a CS PHB is used, note that this configuration will violate the
"SHOULD" of section of RFC 2474 [RFC2474] since CS1 will
have a less timely forwarding than CS0. An operator's goal of providing
a BH PDB provides a sufficient cause for violating the SHOULD.
If an AF PHB is used, it must be configured and a DSCP assigned
such that it does not violate the "MUST" of paragraph three of
section 2 of RFC 2597 [RFC2597] which provides for a "minimum amount
of forwarding resources".

4 Attributes of the BH PDB

There are no quantifiable attributes of the PDB. The ingress and
egress flow of the BH aggregate can be measured but there are no
absolute or statistical metrics that arise from the PDB definition,
though a particular network operator may configure the DS domain
in such a way that a statistical metric can be associated with
that DS domain. When the DS domain is known to be heavily congested
with traffic of other PDBs, a network operator should expect to
see no (or very few) packets of the BH PDB egress from the domain.
When there is no other traffic present, the proportion of the BH
aggregate that successfully crosses the domain should be limited
only by the capacity of the network relative to the ingress BH
traffic aggregate.

5 Parameters

None required.

6 Assumptions

A properly functioning network.

7 Example uses

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

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

8 Experiences


[PDBDEF] "Definition of Differentiated Services Per-Domain Behaviors
and Rules for their Specification", K. Nichols, B. Carpenter,

[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, www.ietf.org/rfc/rfc2474.txt

[RFC2597] RFC 2597, "Assured Forwarding PHB Group", F. Baker, J.
Heinanen, W. Weiss, J. Wroclawski, www.ietf.org/rfc/rfc2597.txt

Authors' Addresses

Brian Carpenter                 Kathleen Nichols
IBM                             Packet Design, Inc.
c/o ICAIR                       66 Willow Place
Suite 150                       Menlo Park, CA 94025
1890 Maple Avenue               USA
Evanston, IL 60201
email: brian@icair.org          email: nichols@packetdesign.com

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