Transcript Slides - Terena

Building Differentiated
Services Using the Assured
Forwarding PHB Group
Juha Heinänen
Telia Finland Inc.
[email protected]
AF PHB Group (RFC 2597)

Provides forwarding of IP packets in four
independent service classes
 at each hop, each class has its own,
configurable forwarding resources

within each class, an IP packet is assigned
one of three levels of drop precedence
lower drop precedence means higher
probability of forwarding
© Juha Heinanen
2
AF PHB Group Implementation

forwarding resources (buffer space and
bandwidth) can be allocated using
 FBA, CBQ, WFQ, priorities, etc.

dropping of packets is based on the
Random Early Drop (RED) algorithm
each level of drop precedence (green,
yellow, red) has its own RED threshold
© Juha Heinanen
3
Example of Output Behavior
R
RED threshold
for “Red” packets
R
R
R
R
R
Each AF class has
its own queue and
forwarding resources
© Juha Heinanen
RED threshold
for “Yellow” packets
4
RED with Multiple Thresholds
Discard
Probability
“Red”
Packets
“Yellow”
Packets
“Green”
Packets
1
Average
Queue Length
0
0
“Red”
Threshold
© Juha Heinanen
“Yellow”
Threshold
“Green”
Threshold
Full
5
AF Based Services

service characteristics of an AF class
depend on
traffic conditioning actions at the edge
relative traffic load and scheduling policy of
the class in the core

different combinations result in relative
or quantitative bandwidth and/or delay
assurances
© Juha Heinanen
6
Metering, Marking and Policing
May classify
packets to
service classes
Host
May meter host
behavior and
shape packets
May police host
behavior and
classify packets on
behalf of host
© Juha Heinanen
May select outgoing packets
and drop excess
R
Enterprise
Network
R
May meter aggregate
behavior, classify,
(re)mark, drop, and
shape packets
R
ISP
Polices aggregate
behavior and remarks
or drops excess
7
Examples of Markers

Two Rate Three Color Marker (trTCM)
marks packets green, yellow, or red based on
Peak and Committed Information Rates
useful when peak rate needs to be enforced

Single Rate Three Color Marker (srTCM)
marks packets green, yellow, or red based on a
rate and two burst sizes
useful when only burst size matters
© Juha Heinanen
8
A Two Rate Marker
New token
PIR times/sec
New token
CIR times/sec
CBS
Not enough
yellow tokens
PBS
Enough yellow tokens,
but not enough green tokens
Enough yellow and
green tokens
?
© Juha Heinanen
9
A Single Rate Marker
New token
CIR times/sec
CBS
Overflow tokens
from C
EBS
Te
Not enough green nor
yellow tokens
Enough yellow tokens, but
not enough green tokens
Tc
Enough green
tokens
?
© Juha Heinanen
10
Selection of Outgoing Traffic
Guaranteed Minimum
Allowed Maximum
Weight
...
Service
Classes
Outgoing
“streams”
Link
© Juha Heinanen
11
Assured Bandwidth (AB) Service
traffic is policed at the ingress using one
of the two three color markers
 green packets are delivered with high
probability, yellows as best effort, and
reds are discarded
 resources are allocated so that the AF
class is only moderately loaded with
greens

© Juha Heinanen
12
Assured Delay (AD) Service
traffic is policed so that only green
packets are allowed into the network
 green packets are delivered with high
probability and low delay variation
 resources are allocated so that the AF
class is very lightly loaded with greens

© Juha Heinanen
13
VoIP/Web Example
20 Mb AB
128 Kb AD
ISP
10 Mb AB
Web
Server
512 Kb AD
Enterprise
Network
VoIP GW
No Profiles
PRI ISDN
128 Kb AD
IP PBX
© Juha Heinanen
PSTN
14
Service Implementation
Policer keeps links only
lightly loaded with green
packets
R
R
R
Best Effort service can
implemented as an
AB Service with CIR = 0
© Juha Heinanen
Assured Delay WFQ
Weight: 80 %
Assured Bandwidth
WFQ Weight: 20 %
15
Mapping AF PHBs to ATM
each service class is allocated a set of
forwarding resources on every link
 signaling of UBR VCs is extended by a
service class indicator
 hierarchical scheduling first per service
class and then per VC within the class
 AF drop precedence is mapped to the
CLP bit

© Juha Heinanen
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Example of Diff-Serv Mapping
R
Drop
Prec
ATM
CLP
0
1
ATM Backbone
R
R
UBR VC for Assured Delay Service
UBR VC for Assured Bandwidth Service
© Juha Heinanen
17
Summary
AF PHB group provides a flexible means to
implement services for both delay sensitive
and delay insensitive applications
 AF support is already available at least in a
limited form in popular routers
 AF based services will become available
from ISPs during 1999

© Juha Heinanen
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