An edge-to-edge Deployment Model for Pre-Congestion Notification: Admission Control over a DiffServ Region

Document Type Expired Internet-Draft (individual in tsv area)
Author Bob Briscoe 
Last updated 2015-10-14 (latest revision 2006-10-25)
Stream Internet Engineering Task Force (IETF)
Expired & archived
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Responsible AD Lars Eggert
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This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


This document describes a deployment model for pre-congestion notification (PCN) operating in a large DiffServ-based region of the Internet. PCN-based admission control protects the quality of service of existing flows in normal circumstances, whilst if necessary (eg after a large failure) pre-emption of some flows preserves the quality of service of the remaining flows. Each link has a configured- admission-rate and a configured-pre-emption-rate, and a router marks packets that exceed these rates. Hence routers give an early warning of their own potential congestion, before packets need to be dropped. Gateways around the edges of the PCN-region convert measurements of packet rates and their markings into decisions about whether to admit new flows, and (if necessary) into the rate of excess traffic that should be pre-empted. Per-flow admission states are kept at the gateways only, while the PCN markers that are required for all routers operate on the aggregate traffic - hence there is no scalability impact on interior routers.


Bob Briscoe (

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