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RFC 3662 - A Lower Effort Per-Domain Behavior (PDB) for Differen


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Network Working Group                                           R. Bless
Request for Comments: 3662                            Univ. of Karlsruhe
Category: Informational                                       K. Nichols
                                                              Consultant
                                                               K. Wehrle
                                                 Univ. of Tuebingen/ICSI
                                                           December 2003

  A Lower Effort Per-Domain Behavior (PDB) for Differentiated Services

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   This document proposes a differentiated services per-domain behavior
   (PDB) whose traffic may be "starved" (although starvation is not
   strictly required) in a properly functioning network.  This is in
   contrast to the Internet's "best-effort" or "normal Internet traffic"
   model, where prolonged starvation indicates network problems.  In
   this sense, the proposed PDB's traffic is forwarded with a "lower"
   priority than the normal "best-effort" Internet traffic, thus the PDB
   is called "Lower Effort" (LE).  Use of this PDB permits a network
   operator to strictly limit the effect of its traffic on "best-
   effort"/"normal" or all other Internet traffic.  This document gives
   some example uses, but does not propose constraining the PDB's use to
   any particular type of traffic.

1.  Description of the Lower Effort PDB

   This document proposes a differentiated services per-domain behavior
   [RFC3086] called "Lower Effort" (LE) which is intended for traffic of
   sufficiently low value (where "value" may be interpreted in any
   useful way by the network operator), in which all other traffic takes
   precedence over LE traffic in consumption of network link bandwidth.
   One possible interpretation of "low value" traffic is its low
   priority in time, which does not necessarily imply that it is
   generally of minor importance.  From this viewpoint, it can be

   considered as a network equivalent to a background priority for
   processes in an operating system.  There may or may not be memory
   (buffer) resources allocated for this type of traffic.

   Some networks carry traffic for which delivery is considered
   optional; that is, packets of this type of traffic ought to consume
   network resources only when no other traffic is present.
   Alternatively, the effect of this type of traffic on all other
   network traffic is strictly limited.  This is distinct from "best-
   effort" (BE) traffic since the network makes no commitment to deliver
   LE packets.  In contrast, BE traffic receives an implied "good faith"
   commitment of at least some available network resources.  This
   document proposes a Lower Effort Differentiated Services per-domain
   behavior (LE PDB) [RFC3086] for handling this "optional" traffic in a
   differentiated services domain.

   There is no intrinsic reason to limit the applicability of the LE PDB
   to any particular application or type of traffic.  It is intended as
   an additional tool for administrators in engineering networks.

   Note: where not otherwise defined, terminology used in this document
   is defined as in [RFC2474].

2.  Applicability

   A Lower Effort (LE) PDB is for sending extremely non-critical traffic
   across a DS domain or DS region.  There should be an expectation that
   packets of the LE PDB may be delayed or dropped when other traffic is
   present.  Use of the LE PDB 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 LE PDB when the
   goal is to protect all other packet traffic from competition with the
   LE aggregate, while not completely banning LE traffic from the
   network.  An LE PDB should not be used for a customer's "normal
   internet" traffic, nor should packets be "downgraded" to the LE PDB
   for use as a substitute for dropping packets that ought to simply be
   dropped as unauthorized.  The LE PDB is expected to be applicable to
   networks that have some unused capacity at some times of day.

   This is a PDB that allows networks to protect themselves from
   selected types of traffic rather than giving a selected traffic
   aggregate preferential treatment.  Moreover, it may also exploit all
   unused resources from other PDBs.

3.  Technical Specification

3.1.  Classification and Traffic Conditioning

   There are no required traffic profiles governing the rate and bursts
   of packets beyond the limits imposed by the ingress link.  It is not
   necessary to limit the LE aggregate using edge techniques since its
   PHB is configured such that packets of the aggregate will be dropped
   in the network if no forwarding resources are available.  The
   differentiated services architecture [RFC2475] allows packets to be
   marked upstream of the DS domain or at the DS domain's edge.  When
   packets arrive pre-marked with the DSCP used by the LE PDB, it should
   not be necessary for the DS domain boundary to police that marking;
   further (MF) classification for such packets would only be required
   if there was some reason for the packets to be marked with a
   different DSCP.

   If there is not an agreement on a DSCP marking with the upstream
   domain for a DS domain using the LE PDB, the boundary must include a
   classifier that selects the appropriate LE target group of packets
   out of all arriving packets and steers them to a marker that sets the
   appropriate DSCP.  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 LE 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 LE aggregate inside a DS domain should be
   configured so that its packets are forwarded onto the node output
   link when the link would otherwise be idle; conceptually, this is the
   behavior of a weighted round-robin scheduler with a weight of zero.

   An operator might choose to configure a very small link share for the
   LE aggregate and still achieve the desired goals.  That is, if the
   output link scheduler permits, a small fixed rate might be assigned
   to the PHB, but the behavior beyond that configured rate should be
   that packets are forwarded only when the link would otherwise be
   idle.  This behavior could be obtained, for example, by using a CBQ
   [CBQ] scheduler with a small share and with borrowing permitted.  A
   PHB that allows packets of the LE aggregate to send more than the
   configured rate when packets of other traffic aggregates are waiting
   for the link is not recommended.

   If a CS PHB is used, note that this configuration will violate the
   "SHOULD" of section 4.2.2.2 of RFC 2474 [RFC2474] since CS1 will have
   a less timely forwarding than CS0.  An operator's goal of providing
   an LE PDB is 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

   The ingress and egress flow of the LE aggregate can be measured but
   there are no absolute or statistical attributes that arise from the
   PDB definition.  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 LE PDB egress from the domain.  When
   there is no other traffic present, the proportion of the LE aggregate
   that successfully crosses the domain should be limited only by the
   capacity of the network relative to the ingress LE traffic aggregate.

5.  Parameters

   None required.

6.  Assumptions

   A properly functioning network.

7.  Example uses

   o  Multimedia applications [this example edited from Yoram Bernet]:

      Many network managers want to protect their networks from certain
      applications, in particular, from multimedia applications that
      typically use such non-adaptive protocols as UDP.

      Most of the focus in quality-of-service is on achieving attributes
      that are better than Best Effort.  These approaches can provide
      network managers with the ability to control the amount of
      multimedia traffic that is given this improved performance with
      excess relegated to Best Effort.  This excess traffic can wreak
      havoc with network resources even when it is relegated to Best
      Effort because it is non-adaptive and because it can be
      significant in volume and duration.  These characteristics permit
      it to seize network resources, thereby compromising the
      performance of other, more important applications that are

      included in the Best Effort traffic aggregate but that use
      adaptive protocols (e.g., TCP).  As a result, network managers
      often simply refuse to allow multimedia applications to be
      deployed in resource constrained parts of their network.

      The LE PDB enables a network manager to allow the deployment of
      multimedia applications without losing control of network
      resources.  A limited amount of multimedia traffic may (or may
      not) be assigned to PDBs with attributes that are better than Best
      Effort.  Excess multimedia traffic can be prevented from wreaking
      havoc with network resources by forcing it to the LE PDB.

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

   o  For "downgraded" traffic from some other PDB when this does not
      violate the operational objectives of the other PDB or the overall
      network.  As noted in section 2, LE should not be used for the
      general case of downgraded traffic, but may be used by design,
      e.g., when multicast is used with a value-added DS-service and
      consequently the Neglected Reservation Subtree problem [NRS]
      arises.

   o  For content distribution, peer-to-peer file sharing traffic, and
      the like.

   o  For traffic caused by world-wide web search engines while they
      gather information from web servers.

8.  Experiences

   The authors solicit further experiences for this section.  Results
   from simulations are presented and discussed in Appendix A.

9.  Security Considerations for LE PDB

   There are no specific security exposures for this PDB.  See the
   general security considerations in [RFC2474] and [RFC2475].

10.  History of the LE PDB

   The previous name of this PDB, "bulk handling", was loosely based on
   the United States' Postal Service term for very low priority mail,
   sent at a reduced rate: it denotes a lower-cost delivery where the
   items are not handled with the same care or delivered with the same
   timeliness as items with first-class postage.  Finally, the name was
   changed to "lower effort", because the authors and other DiffServ
   Working Group members believe that the name should be more generic in
   order to not imply constraints on the PDB's use to a particular type

   of traffic (namely that of bulk data).

   The notion of having something "lower than Best Effort" was raised in
   the Diffserv Working Group, most notably by Roland Bless and Klaus
   Wehrle in their Internet Drafts [LBE] and [LE] and by Yoram Bernet
   for enterprise multimedia applications.  One of its first
   applications was to re-mark packets within multicast groups [NRS].
   Therefore, previous discussions centered on the creation of a new
   PHB.  However, the original authors (Brian Carpenter and Kathleen
   Nichols) believe this is not required and this document was written
   to specifically explain how to get less than Best Effort without a
   new PHB.

11.  Acknowledgments

   Yoram Bernet contributed significant amounts of text for the
   "Examples" section of this document and provided other useful
   comments that helped in editing.  Other Diffserv WG members suggested
   that the LE PDB is needed for Napster traffic, particularly at
   universities.  Special thanks go to Milena Neumann for her extensive
   efforts in performing the simulations that are described in Appendix
   A.

Appendix A.  Experiences from a Simulation Model

   The intention of this appendix is to show that a Lower Effort PDB
   with a behavior as described in this document can be realized with
   different implementations and PHBs respectively.  Overall, each of
   these variants show the desired behavior but also show minor
   differences in certain traffic load situations.  This comparison
   could make the choice of a realization variant interesting for a
   network operator.

A.1.  Simulation Environment

   The small DiffServ domain shown in Figure 1 was used to simulate the
   LE PDB.  There are three main sources of traffic (S1-S3) depicted on
   the left side of the figure.  Source S1 sends five aggregated TCP
   flows (A1-A5) to the receivers R1-R5 respectively.  Each aggregated
   flow Ax consists of 20 TCP connections, where each aggregate
   experiences a different round trip time between 10ms and 250ms.
   There are two sources of bulk traffic.  B1 consists of 100 TCP
   connections sending as much data as possible to R6 and B2 is a single
   UDP flow also sending as much as possible to R7.

                      ...................
                    .                     .                R1
                  .                        .              /
                .                           .            /-R2
               .                             .          /
     S1==**=>[BR1]                          [BR4]==**==>---R3
             . \\                           // .        \
            .   \\                         //   .        \-R4
            .    **                       **     .        \
            .     \\                     //      .         R5
            .      \\                   //       .
   S2=++=>[BR2]-++-[IR1]==**==++==::==[IR2]      .
   (Bulk)   .      //                    \\      .
            .     //                      ::     .
            .    ::                        \\    .
             .  //                          ++  .
              .//                            \\.
    S3==::==>[BR3]                           [BR5]==++==>R6
    (UDP)       .                           . ||
                 .                         .  ||
                   .                      .   ::
                     ....................     ||
                                              VV
                                              R7

            Figure 1: A DiffServ domain with different flows

   In order to show the benefit of using the LE PDB instead of the
   normal Best Effort (BE) PDB [RFC3086], different scenarios are used:

   A) B1 and B2 are not present, i.e., the "normal" situation without
      bulk data present.  A1-A5 use the BE PDB.

   B) B1 and B2 use the BE PDB for their traffic, too.

   C) B1 and B2 use LE PDB for their traffic with different PHB
      implementations:

         1) PHB with Priority Queueing (PQ)
         2) PHB with Weighted Fair Queueing (WFQ)
         3) PHB with Weighted RED (WRED)
         4) PHB with WFQ and RED

   C1) represents the case where there are no allocated resources for
   the LE PDB, i.e., LE traffic is only forwarded if there are unused
   resources.  In scenarios C2)-C4), a bandwidth share of 10% has been
   allocated for the LE PDB.  RED parameters were set to w_q=0.1 and
   max_p=0.2.  In scenario C2), two tail drop queues were used for BE
   and LE and WFQ scheduling was set up with a weight of 9:1 for the
   ratio of BE:LE.  In scenario C3), a total queue length of 200000
   bytes was used with the following thresholds: min_th_BE=19000,
   max_th_BE=63333, min_th_LE=2346, max_th=7037.  WRED allows to mark
   packets with BE or LE within the same microflow (e.g., letting
   applications pre-mark packets according to their importance) without
   causing a reordering of packets within the microflow.  In scenario
   C4), each queue had a length of 50000 bytes with the same thresholds
   of min_th=18000 and max_th=48000 bytes.  WFQ parameters were the same
   as in C2).

   The link bandwidth between IR1 and IR2 is limited to 1200 kbit/s,
   thus creating the bottleneck in the network for the following
   situations.  In all situations, the 20 TCP connections within each
   aggregated flow Ax (flowing from S1 to Rx) used the Best Effort PDB.
   Sender S2 transmitted bulk flow B1 (consisting of 100 TCP connections
   to R6) with an aggregated rate of 550 kbit/s, whereas the UDP sender
   S3 transmitted with a rate of 50 kbit/s.

   The following four different situations with varying traffic load for
   the Ax flows (at application level) were simulated.

      Situation                   |   I  |  II  |  III |  IV  |
      ----------------------------+------+------+------+------|
      Sender Rate S1 [kbit/s]     | 1200 | 1080 | 1800 |  800 |
      Sender Rate S2 [kbit/s]     |  550 |  550 |  550 |  550 |
      Sender Rate S3 [kbit/s]     |   50 |   50 |   50 |   50 |
      Bandwidth IR1 -> IR2        | 1200 | 1200 | 1200 | 1200 |
      Best Effort Load (S1)       | 100% |  90% | 150% |  67% |
      Total load for link IR1->IR2| 150% | 140% | 200% | 117% |

   In situation I, there are no unused resources left for the B1 and B2
   flows.  In situation II, there is a residual bandwidth of 10% of the
   bottleneck link between IR1 and IR2.  In situation III, the traffic
   load of A1-A5 is 50% higher than the bottleneck link capacity.  In
   situation IV, A1-A5 consume only 2/3 of the bottleneck link capacity.
   B1 and B2 require together 50% of the bottleneck link capacity.

   The simulations were performed with the freely available discrete
   event simulation tool OMNeT++ and a suitable set of QoS mechanisms
   [SimKIDS].  Results from the different simulation scenarios are
   discussed in the next section.

A.2.  Simulation Results

   QoS parameters listed in the following tables are averaged over the
   first 160s of the transmission.  Results of situation I are shown in
   Figure 2.  When the BE PDB is used for transmission of bulk flows B1
   and B2 in case B), one can see that flows A1-A5 throttle their
   sending rate to allow transmission of bulk flows B1 and B2.  In case
   C1), not a single packet is transmitted to the receiver because all
   packets get dropped within IR1, thereby protecting Ax flows from Bx
   flows.  In case C2), B1 and B2 consume all resources up to the
   configured limit of 10% of the link bandwidth, but not more.  C3)
   also limits the share of B1 and B2 flows, but not as precisely as
   with WFQ.  C4) shows slightly higher packet losses for Ax flows due
   to the active queue management.

+-------------------------+--------+-----------------------------------+
|                         |        |   Bulk Transfer with PDB:         |
| QoS Parameter           |   A)   |  B)  |  C)  Lower Effort          |
|                         |No bulk | Best |  1)     2)     3)      4)  |
|                  Flows  |transfer|Effort|  PQ  | WFQ  | WRED |RED&WFQ|
+----------------+--------+--------+------+------+------+------+-------+
|                |   A1   |    240 |   71 |  240 |  214 |  225 |   219 |
|                |   A2   |    240 |  137 |  240 |  216 |  223 |   218 |
|                |   A3   |    240 |  209 |  240 |  224 |  220 |   217 |
| Throughput     |   A4   |    239 |  182 |  239 |  222 |  215 |   215 |
| [kbit/s]       |   A5   |    238 |   70 |  238 |  202 |  201 |   208 |
|                |   B1   |      - |  491 |    0 |   82 |   85 |    84 |
|                |   B2   |      - |   40 |    0 |   39 |   31 |    38 |
+----------------+--------+--------+------+------+------+------+-------+
|Total Throughput| normal |   1197 |  669 | 1197 | 1078 | 1084 |  1078 |
| [kbit/s]       | bulk   |      - |  531 |    0 |  122 |  116 |   122 |
+----------------+--------+--------+------+------+------+------+-------+
|                |   A1   |      0 | 19.3 |    0 |  6.3 |  5.7 |   8.6 |
|                |   A2   |      0 | 17.5 |    0 |  6.0 |  5.9 |   8.9 |
|                |   A3   |      0 | 10.2 |    0 |  3.2 |  6.2 |   9.1 |
| Paket Loss     |   A4   |      0 | 12.5 |    0 |  4.5 |  6.6 |   9.3 |
| [%]            |   A5   |      0 | 22.0 |    0 |  6.0 |  5.9 |   9.0 |
|                |   B1   |      - | 10.5 |  100 | 33.6 | 38.4 |  33.0 |
|                |   B2   |      - | 19.6 |  100 | 19.9 | 37.7 |  22.2 |
+----------------+--------+--------+------+------+------+------+-------+
| Total Packet   | normal |      0 | 14.9 |    0 |  5.2 |  6.1 |   9.0 |
| Loss Rate [%]  | bulk   |      0 | 11.4 |  100 | 29.5 | 38.2 |  29.7 |
+----------------+--------+--------+------+------+------+------+-------+
| Transmitted    |        |        |      |      |      |      |       |
| Data [MByte]   | normal |   21.9 | 12.6 | 21.9 | 19.6 | 20.3 |  20.3 |
+----------------+--------+--------+------+------+------+------+-------+

      Figure 2: Situation I - Best Effort traffic uses 100% of the
                          available bandwidth

   Results of situation II are shown in Figure 3.  In case C1), LE
   traffic gets exactly the 10% residual bandwidth that is not used by
   the Ax flows.  Cases C2) and C4) show similar results compared to
   C1), whereas case C3) also drops packets from flows A1-A5 due to
   active queue management.

+-------------------------+--------+-----------------------------------+
|                         |        |   Bulk Transfer with PDB:         |
| QoS Parameter           |   A)   |  B)  |  C)  Lower Effort          |
|                         |No bulk | Best |  1)     2)     3)      4)  |
|                  Flows  |transfer|Effort|  PQ  | WFQ  | WRED |RED&WFQ|
+----------------+--------+--------+------+------+------+------+-------+
|                |   A1   |    216 |  193 |  216 |  216 |  211 |   216 |
|                |   A2   |    216 |  171 |  216 |  216 |  211 |   216 |
|                |   A3   |    216 |   86 |  216 |  216 |  210 |   216 |
| Throughput     |   A4   |    215 |  121 |  215 |  215 |  211 |   215 |
| [kbit/s]       |   A5   |    215 |  101 |  215 |  215 |  210 |   215 |
|                |   B1   |      - |  488 |   83 |   83 |  114 |    84 |
|                |   B2   |      - |   39 |   39 |   39 |   33 |    38 |
+----------------+--------+--------+------+------+------+------+-------+
|Total Throughput| normal |   1078 |  672 | 1077 | 1077 | 1053 |  1077 |
| [kbit/s]       | bulk   |      - |  528 |  122 |  122 |  147 |   122 |
+----------------+--------+--------+------+------+------+----+-+-------+
|                |   A1   |      0 |  9.4 |    0 |    0 |  1.8 |     0 |
|                |   A2   |      0 | 14.6 |    0 |    0 |  2.0 |     0 |
|                |   A3   |      0 | 22.4 |    0 |    0 |  2.1 |     0 |
| Paket Loss     |   A4   |      0 | 15.5 |    0 |    0 |  1.8 |     0 |
| [%]            |   A5   |      0 | 17.4 |    0 |    0 |  1.9 |     0 |
|                |   B1   |      - | 11.0 | 32.4 | 32.9 | 35.7 |  33.1 |
|                |   B2   |      - | 21.1 | 20.3 | 20.7 | 34.0 |  22.2 |
+----------------+--------+--------+------+------+------+------+-------+
| Total Packet   | normal |      0 | 14.9 |    0 |    0 |  1.9 |     0 |
| Loss Rate [%]  | bulk   |      - | 12.0 | 28.7 | 29.1 | 35.3 |  29.8 |
+----------------+--------+--------+------+------+------+------+-------+
| Transmitted    |        |        |      |      |      |      |       |
| Data [MByte]   | normal |   19.8 | 12.8 | 19.8 | 19.8 | 19.5 |  19.8 |
+----------------+--------+--------+------+------+------+------+-------+

      Figure 3: Situation II - Best Effort traffic uses 90% of the
                          available bandwidth

   Results of simulations for situation III are depicted in Figure 4.
   Due to overload caused by flows A1-A5, packets get dropped in all
   cases.  Bulk flows B1 and B2 nearly get their maximum throughput in
   case B).  As one would expect, in case C1) all packets from B1 and B2
   are dropped, in cases C2) and C4) resource consumption of bulk data
   is limited to the configured share of 10%.  Again the WRED
   implementation in C3) is not as accurate as the WFQ variants and lets
   more BE traffic pass through IR1.

+-------------------------+--------+-----------------------------------+
|                         |        |   Bulk Transfer with PDB:         |
| QoS Parameter           |   A)   |  B)  |  C)  Lower Effort          |
|                         |No bulk | Best |  1)     2)     3)      4)  |
|                  Flows  |transfer|Effort|  PQ  | WFQ  | WRED |RED&WFQ|
+----------------+--------+--------+------+------+------+------+-------+
|                |   A1   |    303 |  136 |  241 |  298 |  244 |   276 |
|                |   A2   |    316 |  234 |  286 |  299 |  240 |   219 |
|                |   A3   |    251 |  140 |  287 |  259 |  236 |   225 |
| Throughput     |   A4   |    168 |   84 |  252 |  123 |  209 |   219 |
| [kbit/s]       |   A5   |    159 |   82 |  132 |  101 |  166 |   141 |
|                |   B1   |      - |  483 |    0 |   83 |   73 |    83 |
|                |   B2   |      - |   41 |    0 |   38 |   31 |    38 |
+----------------+--------+--------+------+------+------+------+-------+
|Total Throughput| normal |   1199 |  676 | 1199 | 1079 | 1096 |  1079 |
| [kbit/s]       | bulk   |      - |  524 |    0 |  121 |  104 |   121 |
+----------------+--------+--------+------+------+------+------+-------+
|                |   A1   |    9.6 | 17.6 | 12.1 |  9.3 |  8.6 |  12.8 |
|                |   A2   |    8.5 | 13.6 |  8.4 |  9.8 |  8.1 |  14.5 |
|                |   A3   |    8.8 | 18.7 |  7.7 | 11.6 |  7.8 |  13.6 |
| Paket Loss     |   A4   |   14.9 | 22.3 | 11.2 | 18.9 |  8.2 |  12.4 |
| [%]            |   A5   |   12.8 | 19.0 | 15.6 | 19.7 |  8.3 |  14.3 |
|                |   B1   |      - | 11.9 |  100 | 32.1 | 39.5 |  33.0 |
|                |   B2   |      - | 17.3 |  100 | 22.5 | 37.7 |  22.8 |
+----------------+--------+--------+------+------+------+------+-------+
| Total Packet   | normal |   10.4 | 17.3 | 10.3 | 12.2 |  8.2 |  13.4 |
| Loss Rate [%]  | bulk   |      - | 12.4 |  100 | 29.1 | 39.0 |  29.9 |
+----------------+--------+--------+------+------+------+------+-------+
| Transmitted    |        |        |      |      |      |      |       |
| Data [MByte]   | normal |   22.0 | 12.6 | 22.0 | 20.2 | 20.6 |  20.3 |
+----------------+--------+--------+------+------+------+------+-------+

       Figure 4: Situation III - Best Effort traffic load is 150%

   In situation IV, 33% or 400 kbit/s are not used by Ax flows and the
   results are listed in Figure 5.  In case B) where bulk data flows B1
   and B2 use the BE PDB, packets of Ax flows are dropped, whereas in
   cases C1)-C4) flows Ax are protected from bulk flows B1 and B2.
   Therefore, by using the LE PDB for Bx flows, the latter get only the
   residual bandwidth of 400 kbit/s but not more.  Packets of Ax flows
   are not affected by Bx traffic in these cases.

+-------------------------+--------+-----------------------------------+
|                         |        |   Bulk Transfer with PDB:         |
| QoS Parameter           |   A)   |  B)  |  C)  Lower Effort          |
|                         |No bulk | Best |  1)     2)     3)      4)  |
|                  Flows  |transfer|Effort|  PQ  | WFQ  | WRED |RED&WFQ|
+----------------+--------+--------+------+------+------+------+-------+
|                |   A1   |    160 |  140 |  160 |  160 |  160 |   160 |
|                |   A2   |    160 |  124 |  160 |  160 |  160 |   160 |
|                |   A3   |    160 |  112 |  160 |  160 |  160 |   160 |
| Throughput     |   A4   |    160 |  137 |  160 |  160 |  159 |   160 |
| [kbit/s]       |   A5   |    159 |  135 |  159 |  159 |  159 |   159 |
|                |   B1   |      - |  509 |  361 |  362 |  364 |   362 |
|                |   B2   |      - |   43 |   40 |   39 |   38 |    40 |
+----------------+--------+--------+------+------+------+------+-------+
|Total Throughput| normal |    798 |  648 |  798 |  798 |  797 |   798 |
| [kbit/s]       | bulk   |      - |  551 |  401 |  401 |  402 |   401 |
+----------------+--------+--------+------+------+------+------+-------+
|                |   A1   |      0 |  9.2 |    0 |    0 |    0 |     0 |
|                |   A2   |      0 | 12.2 |    0 |    0 |    0 |     0 |
|                |   A3   |      0 | 14.0 |    0 |    0 |    0 |     0 |
| Paket Loss     |   A4   |      0 |  9.3 |    0 |    0 |    0 |     0 |
| [%]            |   A5   |      0 |  6.6 |    0 |    0 |    0 |     0 |
|                |   B1   |      - |  7.3 | 21.2 | 21.8 | 25.0 |  21.3 |
|                |   B2   |      - | 14.3 | 19.4 | 20.7 | 24.5 |  20.7 |
+----------------+--------+--------+------+------+------+------+-------+
| Total Packet   | normal |      0 | 10.2 |    0 |    0 |    0 |     0 |
| Loss Rate [%]  | bulk   |      - |  8.0 | 21.0 | 21.7 | 25.0 |  21.2 |
+----------------+--------+--------+------+------+------+------+-------+
| Transmitted    |        |        |      |      |      |      |       |
| Data [MByte]   | normal |   14.8 | 12.1 | 14.8 | 14.8 | 14.7 |  14.7 |
+----------------+--------+--------+------+------+------+------+-------+

        Figure 5: Situation IV - Best Effort traffic load is 67%

   In summary, all the different scenarios show that the "normal" BE
   traffic can be protected from traffic in the LE PDB effectively.
   Either no packets get through if no residual bandwidth is left (LE
   traffic is starved), or traffic of the LE PDB can only consume
   resources up to a configurable limit.

   Furthermore, the results substantiate that mass data transfer can
   adversely affect "normal" BE traffic (e.g., 14.9% packet loss in
   situations I and II, even 10.2% in situation IV) in situations
   without using the LE PDB.

   Thus, while all presented variants of realizing the LE PDB meet the
   desired behavior of protecting BE traffic, they also show small
   differences in detail.  A network operator has the opportunity to
   choose a realization method to fit the desired behavior (showing this
   is - after the proof of LE's efficacy - the second designation of
   this appendix).  For instance, if operators want to starve LE traffic
   completely in times of congestion, they could choose PQ.  This causes
   LE traffic to be completely starved and not a single packet would get
   through in case of full load or overload.

   On the other hand, for network operators who want to permit some
   small amount of throughput in the LE PDB, one of the other variants
   would be a better choice.

   Referring to this, the WFQ implementation showed a slightly more
   robust behavior with PQ, but had problems with synchronized TCP
   flows.  WRED behavior is highly dependent on the actual traffic
   characteristics and packet loss rates are often higher compared to
   other implementations, while the fairness between TCP connections is
   better.  The combined solution of WFQ with RED showed the overall
   best behavior, when an operator's intent is to keep a small but
   noticeable throughput in the LE PDB.

Normative References

   [RFC3086]  Nichols, K. and B. Carpenter, "Definition of
              Differentiated Services Per Domain Behaviors and Rules for
              their Specification", RFC 3086, April 2001.

   [RFC2474]  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.

   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.
              and W. Weiss, "An Architecture for Differentiated
              Services", RFC 2475, December 1998.

Informative References

   [RFC2597]  Heinanen, J., Baker, F., Weiss, W. and J. Wroclawski,
              "Assured Forwarding PHB Group", RFC 2597, June 1999.

   [CBQ]      Floyd, S. and V. Jacobson, "Link-sharing and Resource
              Management Models for Packet Networks", IEEE/ACM
              Transactions on Networking, Vol. 3, No. 4, pp. 365-386,
              August 1995.

   [LBE]      Bless, R. and K. Wehrle, "A Lower Than Best-Effort Per-Hop
              Behavior", Work in Progress, September 1999.

   [LE]       Bless, R. and K. Wehrle, "A Limited Effort Per-Hop
              Behavior", Work in Progress, February 2001.

   [SimKIDS]  Wehrle, K., Reber, J. and V. Kahmann, "A simulation suite
              for Internet nodes with the ability to integrate arbitrary
              Quality of Service behavior", in Proceedings of
              Communication Networks And Distributed Systems Modeling
              And Simulation Conference (CNDS 2001),  Phoenix (AZ), USA,
              pp. 115-122, January 2001.

   [NRS]      Bless, R. and K. Wehrle, "Group Communication in
              Differentiated Services Networks", in Proceedings of IEEE
              International Workshop  on "Internet QoS", Brisbane,
              Australia, IEEE Press, pp. 618-625, May 2001.

Authors' Addresses

   Roland Bless
   Institute of Telematics, Universitaet Karlsruhe (TH)
   Zirkel 2
   76128 Karlsruhe
   Germany

   EMail: bless@tm.uka.de
   URI:   http://www.tm.uka.de/~bless/

   Kathleen Nichols
   325M Sharon Park Drive #214
   Menlo Park, CA 94025

   EMail: knichols@ieee.org

   Klaus Wehrle
   University of Tuebingen, Computer Networks and Internet
   Morgenstelle 10c, 72076 Tuebingen, Germany &
   International Computer Science Institute (ICSI)
   1947 Center Street, Berkeley, CA, 94704, USA

   EMail: Klaus.Wehrle@uni-tuebingen.de
   URI: http://net.informatik.uni-tuebingen.de/~wehrle/

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