DSCP for Admitted Voice

Fred Baker, Cisco

Martin Dolly, AT&T

draft-baker-tsvwg-admitted-voice-dscp

Existing recommendation

• RFC 4594 “Configuration Guidelines for DiffServ Service Classes”– “Telephony” service class for voice– Other service classes for other real time traffic– Recommends but does not require capacity

admission at bottleneck interfaces

• draft-ietf-tsvwg-diffserv-class-aggr– Common service class for all real time traffic for

core-facing interfaces

The problem

• Existing Voice on IP generally operates in a manner in which there is no topology-aware capacity admission – Depends largely on traffic engineering and large

margins of error

• Folks who want to apply preferential policy to traffic need a way to enforce preferential policy at bottlenecks they worry about – military+civilian, preemptive+non preemptive,

US+non-US

Y e sNOCo u ld I p le a s e h a v e a DS CP fo r a ll e me rg e n c y tra ffic th a t c a n n o t b e o v e rrid d e n a n d g iv e s me p rio rity o v e r a ll o th e r tra ffic ?B u t I wa n t it!

Y e sNOCo u ld I p le a s e h a v e a DS CP fo r a ll e me rg e n c y tra ffic th a t c a n n o t b e o v e rrid d e n a n d g iv e s me p rio rity o v e r a ll o th e r tra ffic ?B u t I wa n t it!

Y e sN OC o u ld I p le a s e h a v e a D S C P fo r a ll e me rg e n c y tra ffic re g a rd le s s o f s e rv ic e th a t c a n n o t b e o v e rrid d e n a n d g iv e s me p rio rity o v e r a ll o th e r tra ffic ?B u t I w a n t it!

Two proposals

• DSCP for each class of “emergency” traffic– How many classes?– PHB?– For what classes?– How many DSCPs was

that?

• Policy controls allocation of bandwidth from a capacity-admitted pool– If this were circuits, it

would be preferential allocation of circuits to certain classes of calls

– In an IP network, preferential allocation of chunks of bandwidth at a set of bottlenecks

So now I have two sets of traffic in one class

• Today’s VoIP does minimal very coarse CAC or none at all

• I’m suggesting that preferential traffic classes can be deployed with capacity admission– E-911, NS/EP, and others

• If admitted and non-admitted traffic are in the same traffic class, then the non-admitted traffic can destroy my preferred and carefully managed traffic

• oops

NS/EP case: accepting only emergency calls under stress

• Requirement:– Enhance probability of completion

• Simple policy:– Total reserved bandwidth in a real-time

class may not exceed <threshold>– Provide two thresholds:

• New routine call: admit up to X• New priority call: admit up to X+Y

• Effects of policy– When busy with routine calls, still have

room to add a priority call, “borrowing” bandwidth from elastic

– When any call completes, room for new priority call becomes available

– When more calls complete, room for new routine calls becomes available.

Bandwidth for elastic traffic

Bandwidth for real time traffic

Additional allocation for emergency real time traffic

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Routine Admittedreal time Bandwidth

Routine no-CACreal time Bandwidth

Priority Admittedreal time Bandwidth

Elastic BandwidthClasses:

•Data•Routing•Whatever

Dealing with legacy equipment

• Simple policy:– Some bandwidth set aside

for telephones with no bandwidth admission

• e.g., no CAC, or call-accounting CAC like H.323 Gatekeeper exercised in enterprise

• Effects of policy– Bandwidth-admitted traffic

class available (works with the network)

– Legacy admission availableD

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EF

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: E

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So the proposal is

• A new DSCP value related to EF’s

• PHB is EF, but with a different code point

• Requires capacity admission

• Used by all policies including routine, but specifically allowing for e-911, NS/EP, etc.

DSCP for Admitted Voice

Fred Baker

draft-baker-tsvwg-admitted-voice-dscp