Internet DRAFT - draft-heinanen-diffserv-af

draft-heinanen-diffserv-af



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Internet Engineering Task Force                            Juha Heinanen
INTERNET DRAFT                                       Telia Finland, Inc.
Expires February 1999                                       August, 1998


                      Assured Forwarding PHB Group
                  <draft-heinanen-diffserv-af-00.txt>



Status of this Memo

   This document is an Internet-Draft.  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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   ftp.isi.edu (US West Coast).

Abstract

   This document proposes a general use Differentiated Services (DS)
   [Black] Per-Hop-Behavior (PHB) Group called Assured Forwarding (AF).
   AF PHB group consists of two code points AF1 and AF2.  A DS node
   delivers packets marked as AF1 with a very small propability of loss,
   whereas packets marked as AF2 are delivered as best effort.  The DS
   node will not reorder AF packets of the same microflow no matter if
   some of the packets are marked as AF1 and some as AF2.  There is no
   timing requirements associated with the delivery of AF packets.

1. Overview and Purpose

   There is a demand for assured delivery of packets over IP networks,
   for example, when a company uses the Internet to interconnect its
   geographically distributes sites or wants to provide high quality
   access to its Web pages.  It is desirable that the delivery assurance
   holds for a certain information rate, which can be exceeded on best
   effort basis.  It is also important that the IP network does not
   reorder packets that belong to the same microflow no matter if the



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INTERNET DRAFT                                              August, 1998


   assurance holds only to some of the packets of the microflow.

   Assured Forwarding (AF) PHB group is a means for a provider DS domain
   to assure delivery of some portion of IP packets received from a
   customer DS domain and offer best effort delivery for some other
   portion of the packets without reordering packets that belong to the
   same microflow.  Those packets that belong to the assured portion of
   the traffic are marked with AF code point AF1 and those packets that
   belong to the best effort portion are marked as with AF code point
   AF2.  Together these two code points form the AF PHB group.

   In order to avoid discarding AF1 packets in case of congestion (and
   thus violating the SLA that the provider DS domain has given to the
   customer DS domain), the assumption is that the volume of AF1 packets
   that enter the provider DS domain is limited by traffic conditioning
   actions at the ingress to the domain.  Such an assumption is not
   needed for AF2 packets, since the provider DS domain needs to deliver
   them only as best effort on the basis of available resources.

   The AF PHB group is proposed for general use.  It can be used to
   implement either end-to-end or domain edge-to-domain edge services.

2. Queueing and Discard Behavior

   It is possible that some packets of the same microflow get marked
   with code point AF1 and some with code point AF2.  In order to avoid
   reordering of packets within a microflow, a DS node must place all
   packets of the same microflow to the same queue in the same order in
   which they were received no matter if they are marked as AF1 or AF2.

   In order to protect AF1 packets from being discarded due to
   congestion, a DS node must start discarding AF2 packets well before
   the queue space allocated for the particular AF1 packets starts to
   fill up.  The discard mechanism may be based, for example, on the RED
   algorithm.

3. Packet Promotion/Demotion

   AF packets may be promoted or demoted within the AF PHB group by
   traffic conditioning actions at the edge of a DS domain.  Promoting
   means remarking an AF2 packet as an AF1 packet and demoting means
   remarking an AF1 packet as an AF2 packet.  No re-marking of AF
   packets should occur inside the DS domain.

   In addition to promoting and demoting AF packets, the traffic
   conditioning actions at the edge of a DS domain may also include re-
   marking packets marked with the default (best effort) PHB code point
   with AF1 or AF2 code point.  In order to avoid packet reordering,



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INTERNET DRAFT                                              August, 1998


   such re-marking must be applied to all or none of the packets of the
   same microflow.

4. Tunneling

   AF packets may be tunneled provided that the PHB of the tunneling
   packet does not reduce the level of delivery assurance of the
   tunneled AF packet and does not cause reordering of AF packets
   belonging to the same microflow.

5. Interactions with Other PHB Groups

   Other PHB groups may co-exist with the AF group within the same DS
   domain provided that AF1 packets need not be discarded in a DS node
   due to lack of resources caused by packets belonging to these other
   PHB groups.

6. Security Implications

   In order to protect itself against denial of service attacks, a DS
   domain must limit at the edge the volume of incoming AF1 packets.
   Also, in order to protect a link to a customer DS domain from denial
   of service attacks, the provider DS domain should allow the customer
   DS domain to specify how the link to the customer DS domain is
   allocated to AF packets.  Because source IP address may be one of the
   allocation criterias, the provider DS domain should verify the source
   addresses of all received AF packets.

References

   [Black] Black, David, et al., An Architecture for Differentiated
   Services. Internet draft draft-ietf-diffserv-arch-00.txt, May 1998.

Author Information

   Juha Heinanen
   Telia Finland, Inc.
   Myyrmaentie 2
   01600 VANTAA
   Finland

   Phone +358 303 944 808
   Email jh@telia.fi








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