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1 Drop Precedence for Ethernet Frames November 9, 2003 Ali Sajassi

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1 1 Drop Precedence for Ethernet Frames November 9, 2003 Ali Sajassi

2 222 Need for Drop Precedence Drop Precedence if VBR type SLA is needed with CIR/PIR type thresholds DP would enable proper marking of frames that exceed CIR threshold During congestion, frames that are marked with higher DP, will be discarded before frames with lower DP for the same class Packet re-ordering should NOT happen within a class

3 333 Implicit v.s. Explicit DP Two ways of doing Drop Precedence a)Explicitly by using CFI bit b)Implicitly by using.1p code points

4 444 Advantages of Explicit Indication Can have all eight CoS No packet re-ordering if default configuration is used Can have drop precedence on all eight classes if needed

5 555 Disadvantage of Explicit Indication Requires H/W changes and thus new bridges Is not compatible with existing deployed bridges where marking is done implicitly Is not compatible with existing deployed router operation where L3 QoS marking is reflected in L2 CoS field Is not compatible when peering with MPLS/IP networks since MPLS/IP doesnt use explicit bit for Drop Precedence Frames can be discarded even without any congestion in the network (in some bridges). This issue can be very pronounced in enterprise networks where because of low cost of facilities (links) and over-provisioning, there can be no congestion.

6 666 Advantages for Implicit Indication Can be currently supported with deployed bridges w/ implicit marking Compatible with existing deployed router operation where L3 QoS marking is reflected in L2 CoS field Compatible when peering with MPLS/IP networks Frames dont get discarded when there is no congestion

7 777 Disadvantages for Implicit Indication Fewer than eight classes (e.g., seven or six classes). BUT even IEEE 802.1D doesnt define eight classes Possibility of frames re-ordering Possibility only exists if default mode is used and doesnt exist if bridges need to be configured which is very much the case for Service Provider networks (to deliver E2E QoS) Possibility can be minimize by proper assignment of DP to priority classes

8 888 Implicit Drop Precedence 7 classes – one of which w/ DP 6 classes – two of which w/ DP 5 classes – three of which w/ DP

9 D – Appendix G, Table G-2 user_priorityAcronymTraffic type 1BKBackground 2-Spare 0 (Default)BEBest Effort 3EEExcellent Effort 4CLControlled Load 5VIVideo, < 100 ms delay 6VOVoice, <10 ms delay 7NCNetwork Control

10 D – Appendix G, Table G-1 # of QsTraffic Types 1{BK, BE, EE, CL, VI, VO, NC} 2{BK, BE, EE} {CL, VI, VO, NC} 3{BK, BE, EE} {CL, VI} {VO, NC} 4{BK} {BE, EE} {CL, VI} {VO, NC} 5{BK} {BE, EE} {CL} {VI} {VO, NC} 6{BK} {BE} {EE} {CL} {VI} {VO, NC} 7{BK} {BE} {EE} {CL} {VI} {VO} {NC}

11 D – Appendix G, Table G-3 # of QsDefining Traffic Type 1BE 2 VO 3BECLVO 4BKBECLVO 5BKBECLVIVO 6BKBEEECLVIVO 7BKBEEECLVIVONC 8BK-BEEECLVIVONC

12 12 Frame Re-ordering To minimize frame re-ordering, we choose the following classes for DP If there are 7 classes - use P1 & P2 as one class - P1 indicates lower DP If there are 6 classes - use {P1, P2} and {P7, P8} as two classes - P1 and P7 would indicate lower DP

13 13 Frame Re-odering - Continue With this assignment: w/ 7 CoS, no re-ordering occurs for bridges with 1 to 7 queues w/ 6 CoS, no re-odering occurs for bridges with 1 to 6 queues

14 14 Encoding w/ 7 Class of Services one of which with DP Network Management Call Signaling Streaming Video (future) Voice Application CIR (Committed Information Rate) Typical L3 Classification IPP 2 CoS L2 2 Best Effort00 SP Routing & Control66 Mission-Critical Data33 PIR (Peak Information Rate) DSCP CS3 CS4 EF C PHB AF11 0 CS6 AF31 AF1211 Exp MPLS


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