1 / 11

PCN WG (Pre-Congestion Notification) – a brief status update

PCN WG (Pre-Congestion Notification) – a brief status update. Philip Eardley, BT TSVAREA, IETF-73 Minneapolis 18 Nov 08 http://tools.ietf.org/wg/pcn/. Main message. The key docs are at critical stage… Architecture (Info): about to do IETF Last Call

kyla-price
Download Presentation

PCN WG (Pre-Congestion Notification) – a brief status update

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. PCN WG (Pre-Congestion Notification)– a brief status update Philip Eardley, BT TSVAREA, IETF-73 Minneapolis 18 Nov 08 http://tools.ietf.org/wg/pcn/

  2. Main message • The key docs are at critical stage… • Architecture (Info): about to do IETF Last Call • Baseline encoding (Std): WG Last Call very soon • Marking behaviour (Std): WG Last Call very soon • Feedback welcome asap • … so you may want to think about how to implement and/or use it, or how it might impact on what you’re doing

  3. What is Pre-Congestion Notification? • Objective: • Protect the quality of service of established inelastic flows within a single DiffServ domain, • by using flow admission and termination based on pre-congestion information • Flow Admission (for “normal” situations) • Flow Termination (for “unusual” situations, eg failures) • Motivation: • Admission control: there are a range of existing CAC approaches with a range of scalability-accuracy tradeoffs • classic trade-off between flow admission ctrl (smarts) vs. generous sizing (capacity) • PCN offers a scalable light-weight solution with strong QoS assurances • Flow termination: typical current approach is just to wait for users to hang up • PCN rapidly removes some flows in order to preserve QoS of the rest

  4. MSC MSC V V V BTS BTS PCN: Example scenario • PCN-boundary-node = VoIP Trunk GW • VoIP Trunk GW handles high number of calls • All per-flow state restricted to VoIP GWs PCN-interior-node PCN-boundary-node PCN PCN-boundary-node

  5. MSC MSC V V V BTS BTS PCN: Example scenario • DiffServ forwarding • typically EF PHB • measure current load of PCN-traffic • selectively mark packets if congestion appears imminent (hence pre-congestion) PCN-interior-node PCN-boundary-node PCN PCN-boundary-node • monitor PCN-marks (for a pair of boundary nodes) • and hence make decisions about whether to admit new flows (or terminate existing flows)

  6. PCN Concept • 2 levels of pre-congestion notification encoded into pkt headers • or 1 level if short of PCN codepoints

  7. Encoding • (STD) Baseline encoding • Uses 1 DSCP • Allows re-use of other DSCPs • Switches on PCN behaviour using ECN field • Compatible with existing tunnels (RFC 3168 & 4301) • Gives 1 level of PCN-marking • (EXPTL) Extension encodings • Extra encoding states so can distinguish different sorts of PCN-marking

  8. Next steps • Complete current WG docs to RFC • Architecture; baseline encoding; marking behaviour • Progress one or more boundary node behaviours (EXPTL) • ie methods to do flow admission & termination based on the PCN-marked pkts • Several on the table • Progress one or more Encoding extensions (EXPTL) • Several on the table • Signalling reqts for PCN info (eg ingress informed about measurements made by egress)

  9. Spare slides

  10. generoussizing PCN motivation • flow admission ctrl (smarts) vs. generous sizing (capacity) • classic trade-off with diseconomy of scale either way • the more hops away from admission control smarts • the more generous sizing is needed for the voice/video class edge & interiorflow admission controlover Diffserv € € €€ €€ €€ € € edge flowadmission controlover Diffserv € € €€ €€ €€€ PCN with Diffserv Customer Access Provider Backbone provider Access Provider Customer CustomerN/wk CustomerN/wk Core Access Backhaul Backhaul Access Customerrouter MSAN MetroNode MetroNode MSAN Customerrouter

  11. Is it a PCN-pkt? If rate of PCN-pkts > PCN-threshold-rate then mark all pkts (optional) PCN-interior-node If rate of PCN-pkts > PCN-excess-rate then mark pkts above this rate Write encoding in pkt Marking behaviour

More Related