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rfc:rfc3662

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

Bless, et al. Informational [Page 1] RFC 3662 Lower Effort PDB December 2003

 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.

Bless, et al. Informational [Page 2] RFC 3662 Lower Effort PDB December 2003

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.

Bless, et al. Informational [Page 3] RFC 3662 Lower Effort PDB December 2003

 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

Bless, et al. Informational [Page 4] RFC 3662 Lower Effort PDB December 2003

    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

Bless, et al. Informational [Page 5] RFC 3662 Lower Effort PDB December 2003

 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.

Bless, et al. Informational [Page 6] RFC 3662 Lower Effort PDB December 2003

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

Bless, et al. Informational [Page 7] RFC 3662 Lower Effort PDB December 2003

 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.

Bless, et al. Informational [Page 8] RFC 3662 Lower Effort PDB December 2003

 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.

Bless, et al. Informational [Page 9] RFC 3662 Lower Effort PDB December 2003

+————————-+——–+———————————–+

Bulk Transfer with PDB:
QoS Parameter A) B) C) Lower Effort
No bulk Best 1) 2) 3) 4)
Flows transferEffort 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

Bless, et al. Informational [Page 10] RFC 3662 Lower Effort PDB December 2003

 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 transferEffort 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

Bless, et al. Informational [Page 11] RFC 3662 Lower Effort PDB December 2003

 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 transferEffort 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%

Bless, et al. Informational [Page 12] RFC 3662 Lower Effort PDB December 2003

 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 transferEffort 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.

Bless, et al. Informational [Page 13] RFC 3662 Lower Effort PDB December 2003

 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.

Bless, et al. Informational [Page 14] RFC 3662 Lower Effort PDB December 2003

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.

Bless, et al. Informational [Page 15] RFC 3662 Lower Effort PDB December 2003

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/

Bless, et al. Informational [Page 16] RFC 3662 Lower Effort PDB December 2003

Full Copyright Statement

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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
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Bless, et al. Informational [Page 17]

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