draft-ietf-diffserv-efresolve-01.txt   rfc3248.txt 
Internet-Draft (Informational) Grenville Armitage Network Working Group G. Armitage
Alessio Casati Request for Comments: 3248 Swinburne University of Technology
Jon Crowcroft Category: Informational B. Carpenter
Joel Halpern IBM
Brijesh Kumar A. Casati
John Schnizlein Lucent Technologies
J. Crowcroft
April 20th, 2001 University of Cambridge
J. Halpern
Consultant
B. Kumar
Corona Networks Inc.
J. Schnizlein
Cisco Systems
March 2002
A Delay Bound alternative revision of RFC2598 A Delay Bound alternative revision of RFC 2598
<draft-ietf-diffserv-efresolve-01.txt>
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This memo provides information for the Internet community. It does
all provisions of Section 10 of RFC2026. not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Internet-Drafts are working documents of the Internet Engineering
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This document was submitted to the IETF Differentiated Services Copyright Notice
(DiffServ) WG. Publication of this document does not imply
acceptance by the DiffServ WG of any ideas expressed within.
Comments should be submitted to the diffserv@ietf.org mailing list.
Distribution of this memo is unlimited. Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract Abstract
At the Pittsburgh IETF meeting in August 2000, the Differentiated For historical interest, this document captures the EF Design Team's
Services working group faced serious questions regarding RFC2598 - proposed solution, preferred by the original authors of RFC 2598 but
the group's standards track definition of the Expedited Forwarding not adopted by the working group in December 2000. The original
(EF) Per Hop Behavior (PHB). An 'EF Design Team' volunteered to definition of EF was based on comparison of forwarding on an unloaded
develop a re-expression of RFC2598, bearing in mind the issues raised network. This experimental Delay Bound (DB) PHB requires a bound on
in the DiffServ group. At the San Diego IETF meeting in December the delay of packets due to other traffic in the network. At the
2000 the DiffServ working group decided to pursue an alternative re- Pittsburgh IETF meeting in August 2000, the Differentiated Services
expression of the EF PHB. For historical interest this document working group faced serious questions regarding RFC 2598 - the
captures the EF Design Team's proposed solution, preferred by the group's standards track definition of the Expedited Forwarding (EF)
original authors of RFC2598 but not adopted by the working group in Per Hop Behavior (PHB). An 'EF Design Team' volunteered to develop a
December 2000. The original definition of EF was based on comparison re-expression of RFC 2598, bearing in mind the issues raised in the
of forwarding on an unloaded network. This experimental Delay Bound DiffServ group. At the San Diego IETF meeting in December 2000 the
(DB) PHB requires a bound on the delay of packets due to other DiffServ working group decided to pursue an alternative re-expression
traffic in the network. of the EF PHB.
Specification of Requirements Specification of Requirements
This document is for Informational purposes only. If implementors This document is for Informational purposes only. If implementors
choose to experiment with the DB PHB, key words "MUST", "MUST NOT", choose to experiment with the DB PHB, key words "MUST", "MUST NOT",
"REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" are interpreted as described in "RECOMMENDED", "MAY", and "OPTIONAL" are interpreted as described in
RFC 2119 [3]. RFC 2119 [3].
1 Introduction 1 Introduction
RFC 2598 was the Differentiated Services (DiffServ) working group's RFC 2598 was the Differentiated Services (DiffServ) working group's
first standards track definition of the Expedited Forwarding (EF) Per first standards track definition of the Expedited Forwarding (EF) Per
Hop Behavior (PHB) [1]. As part of the DiffServ working group's Hop Behavior (PHB) [1]. As part of the DiffServ working group's
ongoing refinement of the EF PHB, various issues were raised with the ongoing refinement of the EF PHB, various issues were raised with the
text in RFC 2598 [2]. text in RFC 2598 [2].
After the Pittsburgh IETF meeting in August 2000, a volunteer 'EF After the Pittsburgh IETF meeting in August 2000, a volunteer 'EF
design team' was formed (the authors of this document) to propose a design team' was formed (the authors of this document) to propose a
new expression of the EF PHB. The remainder of this Informational new expression of the EF PHB. The remainder of this Informational
document captures our feedback to the DiffServ working group at the document captures our feedback to the DiffServ working group at the
San Diego IETF in December 2000. Our solution focussed on a Delay San Diego IETF in December 2000. Our solution focussed on a Delay
Bound (DB) based re-expression of RFC 2598 which met the goals of Bound (DB) based re-expression of RFC 2598 which met the goals of RFC
RFC2598's original authors. The DiffServ working group ultimately 2598's original authors. The DiffServ working group ultimately chose
chose an alternative re-expression of the EF PHB text, developed by an alternative re-expression of the EF PHB text, developed by the
the authors of [2] and revised to additionally encompass our model authors of [2] and revised to additionally encompass our model
described here. described here.
Our proposed Delay Bound solution is archived for historical Our proposed Delay Bound solution is archived for historical
interest. Section 2 covers the minimum, necessary and sufficient interest. Section 2 covers the minimum, necessary and sufficient
description of what we believed qualifies as 'DB' behavior from a description of what we believed qualifies as 'DB' behavior from a
single node. Section 3 then discusses a number of issues and single node. Section 3 then discusses a number of issues and
assumptions made to support the definition in section 2. assumptions made to support the definition in section 2.
2. Definition of Delay Bound forwarding 2. Definition of Delay Bound forwarding
For a traffic stream not exceeding a particular configured rate the For a traffic stream not exceeding a particular configured rate, the
goal of the DB PHB is a strict bound on the delay variation of goal of the DB PHB is a strict bound on the delay variation of
packets through a hop. packets through a hop.
This section will begin with the goals and necessary boundary This section will begin with the goals and necessary boundary
conditions for DB behavior, then provide a descriptive definition of conditions for DB behavior, then provide a descriptive definition of
DB behavior itself, discuss what it means to conform to the DB DB behavior itself, discuss what it means to conform to the DB
definition, and assign the experimental DB PHB code point. definition, and assign the experimental DB PHB code point.
2.1 Goal and Scope of DB 2.1 Goal and Scope of DB
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MUST be defined in any per-domain behaviors (PDBs) composed from the MUST be defined in any per-domain behaviors (PDBs) composed from the
DB PHB. DB PHB.
A device (hop) delivers DB behavior to appropriately marked traffic A device (hop) delivers DB behavior to appropriately marked traffic
received on one or more interfaces (marking is specified in section 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 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 marked traffic meeting (i.e. less than or equal) a certain arrival
rate limit R. rate limit R.
If more DB traffic arrives than is acceptable, the device is NOT If more DB traffic arrives than is acceptable, the device is NOT
REQUIRED to deliver the DB behavior. However, although the original REQUIRED to deliver the DB behavior. However, although the original
source of DB traffic will be shaped, aggregation and upstream jitter source of DB traffic will be shaped, aggregation and upstream jitter
ensure that the traffic arriving at any given hop cannot be assumed ensure that the traffic arriving at any given hop cannot be assumed
to be so shaped. Thus an DB implementation SHOULD have some to be so shaped. Thus a DB implementation SHOULD have some tolerance
tolerance for burstiness - the ability to provide EF behavior even for burstiness - the ability to provide EF behavior even when the
when the arrival rate exceeds the rate limit R. arrival rate exceeds the rate limit R.
Different DB implementations are free to exhibit different tolerance Different DB implementations are free to exhibit different tolerance
to burstiness. (Burstiness MAY be characterized in terms of the to burstiness. (Burstiness MAY be characterized in terms of the
number of back-to-back wire-rate packets to which the hop can deliver number of back-to-back wire-rate packets to which the hop can deliver
DB behavior. However, since the goal of characterizing burstiness is DB behavior. However, since the goal of characterizing burstiness is
to allow useful comparison of DB implementations, vendors and users to allow useful comparison of DB implementations, vendors and users
of DB implementations MAY choose to utilize other burstiness of DB implementations MAY choose to utilize other burstiness
metrics.) metrics.)
The DB PHB definition does NOT mandate or recommend any particular The DB PHB definition does NOT mandate or recommend any particular
method for achieving DB behavior. Rather, the DB PHB definition method for achieving DB behavior. Rather, the DB PHB definition
identifies parameters that bound the operating range(s) over which an identifies parameters that bound the operating range(s) over which an
implementation can deliver DB behavior. Implementors characterize implementation can deliver DB behavior. Implementors characterize
their implementations using these parameters, while network designers their implementations using these parameters, while network designers
and testers use these parameters to assess the utility of different and testers use these parameters to assess the utility of different
DB implementations. DB implementations.
2.2 Description of DB behavior 2.2 Description of DB behavior
For simplicity the definition will be explained using an example For simplicity the definition will be explained using an example
where traffic arrives on only one interface and is destined for where traffic arrives on only one interface and is destined for
another (single) interface. another (single) interface.
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to some later time D(i). to some later time D(i).
Competing traffic includes all DB traffic arriving at the device on Competing traffic includes all DB traffic arriving at the device on
other ports, and all non-DB traffic arriving at the device on any other ports, and all non-DB traffic arriving at the device on any
port. port.
DB is defined as the behavior which ensures, for all i, that: DB is defined as the behavior which ensures, for all i, that:
D(i) - E(i) <= S * MTU/R. D(i) - E(i) <= S * MTU/R.
MTU is the maximum transmission unit (packet size) of the output. MTU is the maximum transmission unit (packet size) of the output. R
R is the arrival rate that the DB device is prepared to accept on is the arrival rate that the DB device is prepared to accept on this
this interface. interface.
Note that D(i) and E(i) simply refer to the times of what can be Note that D(i) and E(i) simply refer to the times of what can be
thought of as "the same packet" under the two treatments (with and thought of as "the same packet" under the two treatments (with and
without competing traffic). without competing traffic).
The score, S, is a characteristic of the device at the rate, R, in The score, S, is a characteristic of the device at the rate, R, in
order to meet this defined bound. This score, preferably a small order to meet this defined bound. This score, preferably a small
constant, depends on the scheduling mechanism and configuration of constant, depends on the scheduling mechanism and configuration of
the device. the device.
2.3 Conformance to DB behavior 2.3 Conformance to DB behavior
An implementation need not conform to the DB specification over an An implementation need not conform to the DB specification over an
arbitrary range of parameter values. Instead, implementations MUST arbitrary range of parameter values. Instead, implementations MUST
specify the rates, R, and scores S, for which they claim conformance specify the rates, R, and scores S, for which they claim conformance
with the DB definition in section 2.2, and the implementation- with the DB definition in section 2.2, and the implementation-
specific configuration parameters needed to deliver conformant specific configuration parameters needed to deliver conformant
behavior. An implementation SHOULD document the traffic burstiness it behavior. An implementation SHOULD document the traffic burstiness
can tolerate while still providing DB behavior. it can tolerate while still providing DB behavior.
The score, S, and configuration parameters depend on the The score, S, and configuration parameters depend on the
implementation error from an ideal scheduler. Discussion of the implementation error from an ideal scheduler. Discussion of the
ability of any particular scheduler to provide DB behavior, and the ability of any particular scheduler to provide DB behavior, and the
conditions under which it might do so, is outside the scope of this conditions under which it might do so, is outside the scope of this
document. document.
The implementor MAY define additional constraints on the range of The implementor MAY define additional constraints on the range of
configurations in which DB behavior is delivered. These constraints configurations in which DB behavior is delivered. These constraints
MAY include limits on the total DB traffic across the device, or MAY include limits on the total DB traffic across the device, or
total DB traffic targetted at a given interface from all inputs. total DB traffic targeted at a given interface from all inputs.
This document does not specify any requirements on an DB This document does not specify any requirements on DB
implementation's values for R, S, or tolerable burstiness. These implementation's values for R, S, or tolerable burstiness. These
parameters will be bounded by real-world considerations such as the parameters will be bounded by real-world considerations such as the
actual network being designed and the desired PDB. actual network being designed and the desired PDB.
2.4 Marking for DB behavior 2.4 Marking for DB behavior
One or more DiffServ codepoint (DSCP) values may be used to indicate One or more DiffServ codepoint (DSCP) value may be used to indicate a
a requirement for DB behavior [4]. requirement for DB behavior [4].
By default we suggest an 'experimental' DSCP of 101111 be used to By default we suggest an 'experimental' DSCP of 101111 be used to
indicate that DB PHB is required. indicate that DB PHB is required.
3. Discussion 3. Discussion
This section discusses some issues that might not be immediately This section discusses some issues that might not be immediately
obvious from the definition in section 2. obvious from the definition in section 2.
3.1 Mutability 3.1 Mutability
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only to other codepoints that satisfy the DB PHB. Packets marked for only to other codepoints that satisfy the DB PHB. Packets marked for
DB PHBs SHOULD NOT be demoted or promoted to another PHB by a DS DB PHBs SHOULD NOT be demoted or promoted to another PHB by a DS
domain. domain.
3.2 Tunneling 3.2 Tunneling
When DB packets are tunneled, the tunneling packets must be marked as When DB packets are tunneled, the tunneling packets must be marked as
DB. DB.
3.3 Interaction with other PHBs 3.3 Interaction with other PHBs
Other PHBs and PHB groups may be deployed in the same DS node or Other PHBs and PHB groups may be deployed in the same DS node or
domain with the DB PHB as long as the requirement of section 2 is domain with the DB PHB as long as the requirement of section 2 is
met. met.
3.4 Output Rate not specified 3.4 Output Rate not specified
The definition of DB behavior given in section 2 is quite explicitly The definition of DB behavior given in section 2 is quite explicitly
given in terms of input rate R and output delay variation D(i) - given in terms of input rate R and output delay variation D(i) -
E(i). A scheduler's output rate does not need to be specified, since E(i). A scheduler's output rate does not need to be specified, since
(by design) it will be whatever is needed to achieve the target delay (by design) it will be whatever is needed to achieve the target delay
variation bounds. variation bounds.
3.5 Jitter 3.5 Jitter
Jitter is not the bounded parameter in DB behavior. Jitter can be Jitter is not the bounded parameter in DB behavior. Jitter can be
understood in a number of ways, for example the variability in inter- understood in a number of ways, for example the variability in
packet times from one inter-packet interval to the next. However, DB inter-packet times from one inter-packet interval to the next.
behavior aims to bound a related but different parameter - the However, DB behavior aims to bound a related but different parameter
variation in delay between the time packets would depart in the - the variation in delay between the time packets would depart in the
absence of competing traffic, E(i), and when they would depart in the absence of competing traffic, E(i), and when they would depart in the
presence of competing traffic, D(i). presence of competing traffic, D(i).
3.6 Multiple Inputs and/or Multiple Outputs 3.6 Multiple Inputs and/or Multiple Outputs
The definition of 'competing traffic' in section 2.2 covers both the The definition of 'competing traffic' in section 2.2 covers both the
single input/single output case and the more general case where DB single input/single output case and the more general case where DB
traffic is converging on a single output port from multiple input traffic is converging on a single output port from multiple input
ports. When evaluating the ability of an DB device to offer DB ports. When evaluating the ability of an DB device to offer DB
behavior to traffic arriving on one port, DB traffic arriving on behavior to traffic arriving on one port, DB traffic arriving on
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When considering DB traffic from a single input that is leaving via When considering DB traffic from a single input that is leaving via
multiple ports, it is clear that the behavior is no worse than if all multiple ports, it is clear that the behavior is no worse than if all
of the traffic could be leaving through each one of those ports of the traffic could be leaving through each one of those ports
individually (subject to limits on how much is permitted). individually (subject to limits on how much is permitted).
3.7 Fragmentation and Rate 3.7 Fragmentation and Rate
Where an ingress link has an MTU higher than that of an egress link, Where an ingress link has an MTU higher than that of an egress link,
it is conceivable packets may be fragmented as they pass through a it is conceivable packets may be fragmented as they pass through a
Diffserv hop. However, the unpredictability of fragmentation is Diffserv hop. However, the unpredictability of fragmentation is
significantly counter to the goal of providing controllable QoS. significantly counter to the goal of providing controllable QoS.
Therefore we assume that fragmentation of DB packets is being avoided Therefore we assume that fragmentation of DB packets is being avoided
(either through some form of Path MTU discovery, or configuration), (either through some form of Path MTU discovery, or configuration),
and does not need to be specifically considered in the DB behavior and does not need to be specifically considered in the DB behavior
definition. definition.
3.8 Interference with other traffic 3.8 Interference with other traffic
If the DB PHB is implemented by a mechanism that allows unlimited If the DB PHB is implemented by a mechanism that allows unlimited
preemption of other traffic (e.g., a priority queue), the preemption of other traffic (e.g., a priority queue), the
implementation MUST include some means to limit the damage DB traffic implementation MUST include some means to limit the damage DB traffic
could inflict on other traffic. This will be reflected in the DB could inflict on other traffic. This will be reflected in the DB
device's burst tolerance described in section 2.1. device's burst tolerance described in section 2.1.
3.9 Micro flow awareness 3.9 Micro flow awareness
Some DB implementations may choose to provide queuing and scheduling Some DB implementations may choose to provide queuing and scheduling
at a finer granularity (for example, per micro flow) than is at a finer granularity, (for example, per micro flow), than is
indicated solely by the packet's DSCP. Such behavior is NOT precluded indicated solely by the packet's DSCP. Such behavior is NOT
by the DB PHB definition. However, such behavior is also NOT part of precluded by the DB PHB definition. However, such behavior is also
the DB PHB definition. Implementors are free to characterize and NOT part of the DB PHB definition. Implementors are free to
publicize the additional per micro flow capabilities of their DB characterize and publicize the additional per micro flow capabilities
implementations as they see fit. of their DB implementations as they see fit.
3.10 Arrival rate 'R' 3.10 Arrival rate 'R'
In the absence of additional information, R is assumed to be limited In the absence of additional information, R is assumed to be limited
by the slowest interface on the device. by the slowest interface on the device.
In addition, an DB device may be characterized by different values of In addition, an DB device may be characterized by different values of
R for different traffic flow scenarios (for example, for traffic R for different traffic flow scenarios (for example, for traffic
aimed at different ports, total incoming R, and possibly total per aimed at different ports, total incoming R, and possibly total per
output port incoming R across all incoming interfaces). output port incoming R across all incoming interfaces).
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4. IANA Considerations 4. IANA Considerations
This document suggests one experimental codepoint, 101111. Because This document suggests one experimental codepoint, 101111. Because
the DSCP is taken from the experimental code space, it may be re-used the DSCP is taken from the experimental code space, it may be re-used
by other experimental or informational DiffServ proposals. by other experimental or informational DiffServ proposals.
5. Conclusion. 5. Conclusion.
This document defines DB behavior in terms of a bound on delay This document defines DB behavior in terms of a bound on delay
variation for traffic streams that are rate shaped on ingress to a DS variation for traffic streams that are rate shaped on ingress to a DS
domain. Two parameters - capped arrival rate (R) and a 'score' (S) domain. Two parameters - capped arrival rate (R) and a 'score' (S),
are defined and related to the target delay variation bound. All are defined and related to the target delay variation bound. All
claims of DB 'conformance' for specific implementations of DB claims of DB 'conformance' for specific implementations of DB
behavior are made with respect to particular values for R, S, and the behavior are made with respect to particular values for R, S, and the
implementation's ability to tolerate small amounts of burstiness in implementation's ability to tolerate small amounts of burstiness in
the arriving DB traffic stream. the arriving DB traffic stream.
Security Considerations Security Considerations
To protect itself against denial of service attacks, the edge of a DS To protect itself against denial of service attacks, the edge of a DS
domain MUST strictly police all DB marked packets to a rate domain MUST strictly police all DB marked packets to a rate
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possible denial of service attacks or serious network possible denial of service attacks or serious network
misconfiguration. misconfiguration.
Acknowledgments Acknowledgments
This document is the product of the volunteer 'EF Resolve' design This document is the product of the volunteer 'EF Resolve' design
team, building on the work of V. Jacobson, K. Nichols, K. Poduri [1] team, building on the work of V. Jacobson, K. Nichols, K. Poduri [1]
and clarified through discussions with members of the DiffServ and clarified through discussions with members of the DiffServ
working group (particularly the authors of [2]). Non-contentious working group (particularly the authors of [2]). Non-contentious
text (such as the use of DB with tunnels, the security text (such as the use of DB with tunnels, the security
considerations, etc) were drawn directly from equivalent text in RFC considerations, etc.) were drawn directly from equivalent text in RFC
2598. 2598.
Intellectual Properties Considerations
To establish whether any considerations apply to the idea expressed
in this document, readers are encouraged to review notices filed with
the IETF and stored at:
http://www.ietf.org/ipr.html
References
[1] Jacobson, V., Nichols, K. and K. Poduri, "An Expedited Forwarding
PHB", RFC 2598, June 1999.
[2] Davie, B., Charny, A., Baker, F., Bennett, J.C.R., Benson, K., Le
Boudec, J.Y., Chiu, A., Courtney, W., Davari, S., Firoiu, V.,
Kalmanek, C., Ramakrishnan, K. and D. Stiliadis, "An Expedited
Forwarding PHB (Per-Hop Behavior)", RFC 3246, March 2002.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[4] Nichols, K., Blake, S., Baker, F. and D. Black, "Definition of
the Differentiated Services Field (DS Field) in the IPv4 and IPv6
Headers", RFC 2474, December 1998.
[5] Black, D., Blake, S., Carlson, M., Davies, E., Wang, Z. and W.
Weiss, "An Architecture for Differentiated Services", RFC 2475,
December 1998.
Authors (volunteer EF Design Team members) Authors (volunteer EF Design Team members)
Grenville Armitage Grenville Armitage
email: gja@ureach.com Center for Advanced Internet Architectures
Swinburne University of Technology,
Melbourne, Australia
EMail: garmitage@swin.edu.au
Brian E. Carpenter (team observer, WG co-chair) Brian E. Carpenter (team observer, WG co-chair)
IBM IBM Zurich Research Laboratory
iCAIR, Suite 150 Saeumerstrasse 4
1890 Maple Avenue 8803 Rueschlikon
Evanston IL 60201, USA Switzerland
email: brian@icair.org EMail: brian@hursley.ibm.com
Alessio Casati Alessio Casati
Lucent Technologies Lucent Technologies
Swindon, WI SN5 7DJ United Kingdom Swindon, WI SN5 7DJ United Kingdom
email: acasati@lucent.com EMail: acasati@lucent.com
Jon Crowcroft Jon Crowcroft
Department of Computer Science Marconi Professor of Communications Systems
University College London University of Cambridge
Gower Street, Computer Laboratory
London WC1E 6BT, UK William Gates Building
email: J.Crowcroft@cs.ucl.ac.uk J J Thomson Avenue
Cambridge
CB3 0FD
Phone: +44 (0)1223 763633
EMail: Jon.Crowcroft@cl.cam.ac.uk
Joel M. Halpern Joel M. Halpern
Longitude Systems, Inc. P. O. Box 6049
15000 Conference Center Drive Leesburg, VA 20178
Chantilly, VA 20151 Phone: 1-703-371-3043
email: joel@longsys.com EMail: jmh@joelhalpern.com
Brijesh Kumar Brijesh Kumar
Corona Networks Inc., Corona Networks Inc.,
630 Alder DRive, 630 Alder Drive,
Milpitas, CA 95035 Milpitas, CA 95035
email: brijesh@coronanetworks.com EMail: brijesh@coronanetworks.com
John Schnizlein John Schnizlein
Cisco Systems Cisco Systems
9123 Loughran Road 9123 Loughran Road
Fort Washington, MD 20744 Fort Washington, MD 20744
email: john.schnizlein@cisco.com EMail: john.schnizlein@cisco.com
Intellectual Properties Considerations
To establish whether any considerations apply to the idea expressed
in this document, readers are encouraged to review notices filed with
the IETF and stored at:
http://www.ietf.org/ipr.html Full Copyright Statement
References Copyright (C) The Internet Society (2001). All Rights Reserved.
[1] V. Jacobson, K. Nichols, K. Poduri, "An Expedited Forwarding This document and translations of it may be copied and furnished to
PHB", RFC 2598, June 1999 others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
[2] A Charny, ed. "EF PHB Redefined", INTERNET DRAFT <draft-charny- The limited permissions granted above are perpetual and will not be
ef-definition-00.txt> (work in progress), July 2000 revoked by the Internet Society or its successors or assigns.
[3] S. Bradner, "Key words for use in RFCs to Indicate Requirement This document and the information contained herein is provided on an
Levels", RFC 2119, BCP 14, March 1997 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
[4] K. Nichols, S. Blake, F. Baker, D. Black, "Definition of the Acknowledgement
Differentiated Services Field (DS Field) in the IPv4 and IPv6
Headers", RFC 2474, December 1998.
[5] D. Black, S. Blake, M. Carlson, E. Davies, Z. Wang, W. Weiss, "An Funding for the RFC Editor function is currently provided by the
Architecture for Differentiated Services", RFC 2475, December 1998. Internet Society.
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