University of WürzburgDept. of Distributed SystemsProf. Dr. P. Tran-Gia
Performance of TCP/IP with MEDF Scheduling
4. Würzburger Workshop “IP Netzmanagement, IP Netzplanung und Optimierung”
Rüdiger Martin, Michael Menth, Vu Phan-GiaUniversity of Würzburg, Germany
[martin|menth|phan]@informatik.uni-wuerzburg.de
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
Motivation
> Best effort traffic only in today’s InternetNo prioritization
> Static Priority (SP) for high priority Transport Service Class (TSC)Starvation of low priority traffic
> Differentiated Services Architecture (DiffServ) implements appropriate per hop behavior to differentiate between TSCs
Common recommendations:– Weighted Round Robin (WRR)– Deficit Round Robin (DRR)– …
Fixed share of bandwidth for different TSCs
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
Motivation
Anticipated traffic mix:
TCP trafficsources TSChigh
TCP trafficsources TSClow
Destinations TSChigh
DestinationsTSClow
TSChigh
1
TSClow
3
:
Fixed bandwidth share TSChigh:TSClow = 2:3 (class based)
Bandwidth per flow TSChigh:TSClow 2:1
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
Motivation
Current traffic mix:
TSChigh
2
Fixed bandwidth share TSChigh:TSClow = 2:3 (class based)
Bandwidth per flow TSChigh:TSClow 1:1
TCP trafficsources TSChigh
Destinations TSChigh
: TCP trafficsources TSClow
DestinationsTSClowTSClow
3
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
Motivation
> Problem:Conventional scheduling algorithms:
– No priority– Starvation of low priority flows– Fixed bandwidth shares
Knowledge of traffic mix required to provision adequate Quality of Service
Is there a way to introduce traffic-mix-independentper-flow-prioritization?
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
Modified Earliest Deadline First (MEDF)
> MEDF descriptionOne queue per TSCPackets equipped with a time stamp
– Deadline=ArrivalTime+MTSC– Delay advantage: Mhigh=0, Mlow >0,
Scheduling decision– Take packet with the earliest deadline among all queues
> Difference to EDFSimple implementation, no searching / sorting required
Scheduling
TSChigh
TSClow
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
Modified Earliest Deadline First
4
1
6
2
Packet No.Arrival Time
Mhigh = 0, Mlow = 1
TSClowPackets
TSChighPackets
5
2
6
2
4
1
3
1
1
0
0
0
2
11
1 2
2
1
01
4
1
3
12
2
MEDF6
2
5
2
2
1
3
2
4
2
0
1
1
1
Packet No.Modified Deadline
0 1 2 3 4 5 6 Time Slot
ME
DF
Packet No.Arrival Time
20 1 Time Slot
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
MEDF: Service Differentiation in the UTRAN
> UMTS Terrestrial Access Network (UTRAN)
PSTN
Iur
Core Network
Internet
UE
RNC RNC
UMSC
NodeB
SGSN
NodeB NodeB NodeB NodeB NodeB
Iub
IubRNC
NodeB
Rural coverage: using leased lines causes extensive operating
costs.Optimization required!
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
Model of the Transport Network Layer (TNL)
Speech64 Kbit/s CSD
64 Kbit/s PSD
Stringent TSCS
cheduling
Tolerant TSC
Segm
entation
RNC NodeB
Iub
TNLP(W>t)
Waiting Time (W)Delay Budget (DB)
p
P(W>DB) ≤ p!
ptolerant = 10-2
pstringent = 10-4
QoS Requirements
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
Performance of MEDF Scheduling in the UTRAN
0,55
0,60
0,65
0,70
0,75
0,80
0,85
0,90
0,95
1,00
5:0 4:1 3:2 2:3 1:4 0:5
Traffic Mix Ratio CSD:PSD
Max
imum
Lin
k U
tiliz
atio
n
SP
FIFO
MEDF, Mtolerant =0.75 DB
0,55
0,60
0,65
0,70
0,75
0,80
0,85
0,90
0,95
1,00
5:0 4:1 3:2 2:3 1:4 0:5
Traffic Mix Ratio CSD:PSD
Max
imum
Lin
k U
tiliz
atio
n
SP
FIFO
MEDF, Mtolerant =0.125 DB
0,55
0,60
0,65
0,70
0,75
0,80
0,85
0,90
0,95
1,00
5:0 4:1 3:2 2:3 1:4 0:5
Traffic Mix Ratio CSD:PSD
Max
imum
Lin
k U
tiliz
atio
n
SP
FIFO
MEDF, Mtolerant =0.25 DB
0,55
0,60
0,65
0,70
0,75
0,80
0,85
0,90
0,95
1,00
5:0 4:1 3:2 2:3 1:4 0:5
Traffic Mix Ratio CSD:PSD
Max
imum
Lin
k U
tiliz
atio
n
SP
FIFO
MEDF, Mtolerant =0.25 DB
WRR(4:1)
Up to 10% more utilization
by MEDF
SP: Static PriorityFIFO: First-In First-OutWRR(n:m): Weighted Round Robin with Weights (n:m)
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
Motivation
> Features of MEDF (verified for the UTRAN application)
Best performanceDegree of prioritization of stringent TSC over tolerant TSC on the packet level
independent of the current traffic mix
Can MEDF be used to introduce traffic-mix-independent per-flow-prioritization?
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
MEDF: Single Link Simulation Environment
> TCP adapts its rate to Packet loss ploss ( space priority)Round Trip Time RTT ( time priority MEDF)
> Network Simulator 2
> Classical dumbell topology to isolate MEDF characteristics
TCP trafficsources TSChigh
Destinations TSChigh
TCP trafficsources TSClow
DestinationsTSClow
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
MEDF Analysis: Traffic Mix
1
1,5
2
2,5
3
3,5
4
4,5
0 64 128 192 256
Nor
mal
ized
Ban
dwid
th R
atio
(TS
Chi
gh:n
high
)(TS
Clo
w:n
low)
Number of Users
nhigh:nlow = 1:3
nhigh:nlow = 1:1
nhigh:nlow = 3:1
Mlow = 0.5s
)erFlow(TSCBandwidthP)erFlow(TSCBandwidthP
RatioBandwidth Normalized
low
high=
=
Number of users
=Level of network congestion
^
Slight differences due to influence of buffer space:
full buffer sharing
MEDF offers traffic-mix-independent per-flow-prioritization
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
MEDF Analysis: Mlow parameter
0
2
4
6
8
10
12
14
128 640 1152 1664 2176
Ban
dwid
th R
atio
TS
Chi
gh: T
SC
low
Bandwidth [Kbit/s]
Mlow = 0 = FIFO^Mlow = 0.1s
Mlow = 0.5s
Mlow = 1.0s
Mlow = 1.5s
Sufficient capacity available
Increase due to -Less competition for resources-Decreasing RTT Mlow relatively larger
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
MEDF: Multi-Link Simulation Environment
Cross Traffic
Router A Router B
Router C
Router D
BW BW’ = 2*BW
BW
TCP trafficsources TSChigh
TCP trafficsources TSClow
Destinations TSChigh
DestinationsTSClow
TCP cross trafficsources TSChigh
TCP cross trafficsources TSClow
Destinations crosstraffic TSChigh
Destinations crosstraffic TSClow
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
MEDF Analysis: Multiple Links
05
101520253035404550
0 64 128 192 256
Ban
dwid
th R
atio
TS
Chi
gh: T
SC
low
Number of Users
Mlow = 1.0s
3 links
2 links
1 link
Relative delay advantage increases with the number of links
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
TCP trafficsources TSChigh
TCP trafficsources TSClow
Destinations TSChigh
DestinationsTSClow
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
MEDF Analysis: Buffer Space Priority
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
0 64 128 192 256
FIFO full sharing
FIFO space priority
Mlow = 0.5s space priority
Mlow = 0.5s full sharing
Ban
dwid
th R
atio
TS
Chi
gh: T
SC
low
Number of Users
Space priority slightly prefers TSChigh
Space priority prohibits the typical decrease of
the bandwidth ratio
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
Summary
> Problem
Conventional scheduling disciplines:– No prioritization or starvation or fixed bandwidth shares per
TSC or– traffic mix required for adequate QoS provisioning (not
available)
> Solution
MEDF – traffic-mix-independent per-flow-prioritization in TCP/IP
networks– Single parameter: delay advantage Mlow
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
Conclusion
> Results
Effective prioritization of TCP trafficImpact of delay advantage Mlow
Comparison with buffer management strategies
> MEDF
Simple and parameterizable prioritization in TCP/IP networks without starvationApplication in Differentiated Services network
University of WürzburgDistributed Systems
Rüdiger Martin
Performance of TCP/IP with MEDF Scheduling
Q&A