cs 447 network & data communication qos (quality of service) & diffserv introduction...
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CS 447 Network & Data Communication
QoS (Quality of Service) & DiffServIntroduction
Department of Computer ScienceSouthern Illinois University Edwardsville
Fall, 2013
Dr. Hiroshi FujinokiE-mail: hfujino@siue.edu
QOS_PART1/001
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What are QoS & DiffServ?
QoS = Quality of Service
Techniques and standards developed for controlling ways networktraffic (= “packets”) is handled in a network.
DiffServ = Differentiated Service
A standard that implements QoS in the Internet
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Background
• Before the concept of QoS was introduced to the Internet, all what the Internet could provide was “best-effort service”.
What is “best-effort service”?
Sender Receiver
The Internet
No guarantee for transmitted packets to reach the destination
No guarantee for available transmission bandwidth
- They could be dropped at anytime anywhere
- Tx bandwidth dynamically changes
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No guarantee for successful transmissions nor Tx bandwidth
Time
Tx-
Rat
e (i
n b
ps)
Time
Tx-
Rat
e (i
n b
ps)
packetis lost
No guaranteed Tx rate (observed at the receiver)
No guarantee for successful Tx (observed at the receiver)
Sharp dropin Tx rate
UnpredictableTx-rate
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Background
• Before the concept of QoS was introduced to the Internet, all what the Internet could provide was “best-effort service”.
What is “best-effort service”?
Sender Receiver
The Internet
End-to-end delay dynamically fluctuates
- This is a result of in the previous slide
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Sender Receiver
Dynamically fluctuating E2E delay
R1 RN
Physical Distance
Sender transmitsa packet Router
Delay
E2EDelay• Router delay dynamically fluctuates
• The longer the physical distance, the longer E2E delay
• The larger the E2E hop-count, the longer E2E delay
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Background
• Before the concept of QoS was introduced to the Internet, all what the Internet could provide was “best-effort service”.
What is “best-effort service”?
Sender Receiver
The Internet
Unpredictable (no control for) delay jitter
- Delay jitter = variance in E2E delay for arriving packets
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Sender Receiver
R1 RN
Sender transmitsa packet Router
Delay
E2EDelay
Time Time
Tim
e
packet
Unpredictable (no control for) delay jitter
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Background
• Before the concept of QoS was introduced to the Internet, all what the Internet could provide was “best-effort service”.
What is “best-effort service”?
Sender Receiver
The Internet
Unpredictable (no control for) packet-loss rate
- Packet-loss rate = (number of lost packets)/(number of packets sent)
- Because router resources (memory buffers) are shared
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Sender Receiver
R1 RN
Unpredictable (no control for) packet-loss rate
• A large # of senders might be transmitting packets through a router(Router buffers’ are shared resource in the Internet)
• We can not predict which senders transmit how much and when(Senders do not reserve resources in advance in the Internet)
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QoS parameters and various network applications
• So far, we defined “best-effort service” as lack of controls for Tx-rate, E2E delay, delay jitter and packet-loss rate.
Question Which network applications need a good control for whichparameters?
Applications Control required for
HTTP (web)
FTP
E-mail(No MIME)
Telnet
VoIP
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QoS parameters and various network applications
• So far, we defined “best-effort service” as lack of controls for Tx-rate, E2E delay, delay jitter and packet-loss rate.
Question Which network applications need a good control for whichparameters?
Applications Control required for
Online chatting
On-line game (Real-Time)
Problem
The best-effort Internet service can not handle for network applicationswith various QoS requirements
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Existing QoS controlling components
Admission Control
Traffic Classifier
Traffic Policing and Shaper
Packet Scheduler
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Admission Control
Network
Router Router Router Router
Request forreserve resources
PositiveACKAdmitted
“signaling”
Reserveresources
Reserveresources
Reserveresources
Reserveresources
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Admission Control
Network
Router Router Router Router
Request forreserve resources
Reserveresources
I don’t haveenough resource
Rejected
Reserveresources
NegativeACK
On rejection, the requesting host:
Give up now and try again later
Reduce the requested resources and try again
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Admission Control
• Admission control is a mechanism that prevents overloading a network
• Each host must reserve network resources before it starts transmission(This is exactly what “virtual-circuit” networks do)
• Router resources are reserved by signaling messages
• On success, a positive ACK from the destination
• On fail, a negative ACK from a rejecting router
• The Internet does not perform admission control
(The Internet is a datagram packet-switching network)
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Traffic Classifier
Sender Receiver
R1 RN
ReceivingNIC
Routing Classifier Policing SchedulerTransmitting
NIC
Decide which transmittingNIC each packet is directed
Detect the type of packetso that a different policing
and scheduling can be applied for each different type
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Classifier
TrafficType-A
TrafficType-B
TrafficType-X
ShaperPolicing
ShaperPolicing
ShaperPolicing
Queues
Routing
Traffic Classifier
The classifier “classifies” incoming packets to groups, eachof which holds packets that have the same “requirements (demands)”
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-a Traffic Policing
• If some hosts (or a group of network applications) are transmitting more network traffic than they are supposed to, drop the traffic.
-b Traffic Shaping
• Reduce delay jitter
• Control on transmission rate (in bps)
• Reduce transmission burst
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-a Traffic Policing
Tra
ffic
Loa
d (
in b
ps)
Time
Upper Threshold
CS 447 Network & Data Communication
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-a Traffic Policing
Tra
ffic
Loa
d (
in b
ps)
Time
Upper Threshold
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-b Traffic Shaper
packet
Tra
ffic
Loa
d (
in b
ps)
TransmissionBurst
TransmissionBurst
TransmissionBurst
Time
(i) Jitter Reduction (micro-shaping)
(Zero jitter) (High jitter) (Low jitter)
(ii) Flattening transmission burst (macro-shaping)
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= an implementation of traffic policing/shaping
Token Bucket
Leaky Bucket
Bursty Traffic (Average Traffic Rate = R1 bps)
Drain (Output Rate = R2 bps)
Incoming Link
Bucket Capacity = B bits
Must be: R2 R1
(memory buffer in a router)
(network traffic with a high jitter)
(outgoing drain with a constant rate)
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Packet Scheduler
Classifier
TrafficType-A
TrafficType-B
TrafficType-X
ShaperPolicing
ShaperPolicing
ShaperPolicing
Queues
TransmittingNIC
Scheduler
• Decide from which queue packets will be forwarded to the transmitting NIC
Routing
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