Transcript PPT Version

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
Two proposals
• DSCP for each class of
“emergency” traffic
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–
–
–
How many classes?
PHB?
For what classes?
How many DSCPs was
that?
• Policy controls
allocation of bandwidth
from a capacityadmitted 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:
Bandwidth for
elastic traffic
– Enhance probability of completion
• 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.
Additional
allocation for
emergency
real time traffic
Routine Real Time
Bandwidth
• New routine call: admit up to X
• New priority call: admit up to X+Y
Total real time Bandwidth
– Total reserved bandwidth in a real-time
class may not exceed <threshold>
– Provide two thresholds:
Total Interface Bandwidth
• Simple policy:
Bandwidth for
real time traffic
Dealing with legacy equipment
– Bandwidth-admitted traffic
class available (works with
the network)
– Legacy admission available
DSCP: EF’
• Effects of policy
DSCP: EF
• e.g., no CAC, or callaccounting CAC like H.323
Gatekeeper exercised in
enterprise
Elastic Bandwidth
Classes:
•Data
•Routing
•Whatever
Total real time Bandwidth
– Some bandwidth set aside
for telephones with no
bandwidth admission
Total Interface Bandwidth
• Simple policy:
Priority Admitted
real time Bandwidth
Routine Admitted
real time Bandwidth
Routine no-CAC
real time Bandwidth
So the proposal is
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•
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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