Outline brief review ‘you have read the draft’ concepts: dynamic bandwidth reservation & MAR

1. Max Allocation with Reservation (MAR)BW Constraint Model for MPLS/DiffServ TE & Performance Comparisons(draft-ash-mpls-dste-bcmodel-max-alloc-resv-01.txt) • Outline • brief review • ‘you have read the draft’ • concepts: dynamic bandwidth reservation & MAR • analysis of MAR • issues • conclusions Jerry Ash gash@att.com

2. MAR Bandwidth Constraint Model • allocates bandwidth to individual class types (CTs) • like the Maximum Allocation Model (MAM) • protects allocated bandwidth by bandwidth reservation methods, as needed, but otherwise fully share bandwidth • meets all requirements for BC models • works well with or without preemption • supports greater efficiency in bandwidth sharing • provides protection of allocated bandwidth under congestion • allows bandwidth sharing in absence of congestion • based on mechanisms in use for 10+ years for multiservice voice/data bandwidth allocation in large-scale networks

3. Dynamic Bandwidth Reservation • gives preference to certain traffic • for class types (CT) below their BWalloc • on preferred (shortest) path • preferred traffic allowed to seize any idle bandwidth on a link • non-preferred traffic (on CT above BWalloc or on alternate paths) can seize bandwidth only if there is a minimum level of idle bandwidth (called the “bandwidth-reservation threshold”) • on congested link preferred traffic sees low loss while non-preferred traffic sees much higher loss • this situation maintained across wide variation in percentage of preferred traffic • bandwidth reservation robust to traffic variations • as shown in mathematical models & in simulation studies • very widely used in practice

4. Illustrative Use of MARLink Load States & Allowed Load State • local link states kept of idle link bandwidth • reserved-bandwidth (RBW) • less than RBW + requested BW available • available-bandwidth (ABW) • more than RBW + requested BW available • bandwidth-not-available (BNA) • not enough bandwidth for flow/LSP • allowed load states for flow/LSP setup • when BW < BWalloc any idle link bandwidth can be seized if link not in BNA state • both RBW & ABW states allowed • when BW > BWalloc, links must be in ABW state • RBW state not allowed

5. Illustrative Use of MAR

6. Analysis of MAR • options compared • MAR -- flows/LSPs set up with bandwidth reservation • full sharing -- flows/LSPs set up without bandwidth reservation • full-scale 135-switch national network simulation model • 5 CTs -- normal priority voice, high priority voice, normal priority data, high priority data, & best-effort data

7. Performance Comparison forMAR & Full Sharing Bandwidth Constraint Models6X Focused Overload on Oakbrook(Total Network % Lost/Delayed Traffic)

8. Performance Comparison forMAR & Full Sharing Bandwidth Constraint Models50% General Overload(Total Network % Lost/Delayed Traffic)

9. Issues • all BC models MUST meet all requirements • e.g., MUST NOT require use of preemption to work well • many comments on list in support of this • more important now since all BC models are optional • SPs don’t want to get stuck with BC model not meeting requirements • comparisons of BC models • Russian Doll Model (RDM) • can work poorly when preemption not enabled • too much sharing under overload can degrade performance of some CTs • needs to be modified to have acceptable performance when preemption not enabled • MAM & MAR • provide protection of allocated bandwidth under congestion • MAR allows BW sharing in absence of congestion

10. Issues • protection from pathological traffic patterns & use • issue for all BC models • protect against any possible scenario, however unlikely or atypical? • examples given of bandwidth hogging • could add upper limits on allocated bandwidth to mitigate • but is this necessary? • DS-TE is a bandwidth allocation procedure, involving use of CAC • CAC & bandwidth allocations related to traffic demands • experience doesn’t match bandwidth hogging scenarios • need common assumptions of traffic characteristics & engineering use • assume DS-TE use based on common assumptions

11. Conclusions • MAR bandwidth constraint model • protects allocated bandwidth by bandwidth reservation methods, as needed, but otherwise fully share bandwidth • meets all requirements for BC models • works well with or without preemption • supports greater efficiency in bandwidth sharing • provides protection of allocated bandwidth under congestion • allows bandwidth sharing in absence of congestion • need common assumptions of traffic characteristics & engineering use • proposed next steps in specifying BC models • specify/progress MAM • specify/progress MAR • hold off on specifying/progressing RDM • needs modification to not perform poorly when preemption not enabled

12. Backup Slides

13. Dynamic Bandwidth Reservation Performanceunder 10% Overload

14. Network Instability Under Congestion • under congestion networks can exhibit “instability” with drastic loss of network throughput • by as much as 50% of traffic carrying capacity • shown mathematically in [NaM73, Kru82, Aki84] & in numerous simulation studies • simple example: fully-connected network with first-choice routing on the 1-link direct path or, if unavailable, on (one of many) 2-link alternate paths • under congestion 1-link direct path often not available & 2-link alternate path may be found and used • 2-link connections take twice the resources as 1-link connections, which leads to more congestion and more alternate routing on 2-link connections • can lead to two possible network states: • most or all connections on 1-link paths (desired condition) • most or all connections on 2-link paths (half the throughput) • solution: use dynamic bandwidth reservation to favor shortest paths vs. longer alternate paths