Transcript Slide 1

Chapter 6
Multimedia Networking
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Thanks and enjoy! JFK / KWR
All material copyright 1996-2002
J.F Kurose and K.W. Ross, All Rights Reserved
Computer Networking: A Top Down
Approach Featuring the Internet,
2nd edition.
Jim Kurose, Keith Ross
Addison-Wesley, July 2002.
Chapter 6 outline
 6.1 Multimedia Networking
 6.5 Beyond Best Effort
Applications
 6.2 Streaming stored audio and
video
 RTSP
 6.3 Real-time, Interactivie
Multimedia: Internet Phone
Case Study
 6.4 Protocols for Real-Time
Interactive Applications
 RTP,RTCP
 SIP
 6.6 Scheduling and Policing
Mechanisms
 6.7 Integrated Services
 6.8 RSVP
 6.9 Differentiated Services
Quality of Service on IP Networks Review
Quality of Service:
The ability to provide consistent, predictable data service delivery to
satisfy customer application requirements. [Sysmaster.com]
 “Best-effort” does not guarantee Quality of Service
 End-to-end packet delay and loss
 All packets are treated equally at routers
Beyond “Best Effort”
Future: next generation Internet with QoS guarantees

Differentiated Services

RSVP

Integrated Services
 Four principles of QoS Guarantees
 Packet classification
 Isolation: scheduling and policing
 High resource utilization
 Call Admission
Why do we NEED QoS guarantees?
The Chronicle of Higher Education. Napster Was Nothing Compared With This Year’s
Bandwidth Problems, 28 Sept. 2001. http://chronicle.com/free/v48/i05/05a04401.htm
Download File Size Comparison
Compressed movies
• Crouching Tiger Hidden Dragon
800 Mb
Video Games
• Tomb Raider 3
203 Mb
TV shows
• The Simpsons
25 Mb
MP3s
• Metallica song
5.7 Mb
Photos
• 8 x 10 Color image
81 Kb
Text documents
• Microsoft Word Document
19 Kb
Inbound/Outbound Traffic
Simple Network Scenario w/2 applications
Principles for QOS Guarantees
 Example: 1Mbps IP phone, FTP share 1.5 Mbps link.
 bursts of FTP can congest router, cause audio loss
Principle 1
packet marking needed for router to distinguish
between different classes; and new router policy to
treat packets accordingly
IP datagram format
32 bits
ver
head. type of
len service
16-bit identifier
upper
time to
layer
live
length
flgs
fragment
offset
Internet
checksum
32 bit source IP address
32 bit destination IP address
Options (if any)
data
(variable length,
typically a TCP
or UDP segment)
Application Priority?
 Should multimedia applications get priority over
non-delay sensitive applications?
Bandwidth Shaping
1. Monitor
a. Traffic types
b. Traffic issues
c. Problem location
2. Classify
a. WAN links or Departments
b. Applications and Protocols
3. Enforce (Traffic Control)
a. Policy writing and application
4. Report
5. Conclude
Bandwidth Shaping: Traffic Types
 What Internet applications are we running?
 Which applications are important to academics?
 Which applications are not important?
 Which applications are sensitive to delay?
Bandwidth Shaping: Traffic Issues
 What do you think are some of the traffic issues on this
campus?
 Where is the problem?
Bandwidth Shaping: Classify
 Pipes

WAN links

Departments
 Virtual Channels

SMTP

VoIP

FTP

HTTP
• MP3 downloads (*.mp3)
Bandwidth Usage Analysis by Pipes
Department B andwidth Usage
120
100
80
G raphics
Sales
60
Administrative
40
20
0
1
2
3
4
5
6
7
8
9
10
11
12
13
Bandwidth Usage Analysis by Virtual Channel
Administra tiv e Dept Bandwidth Usage
HTTP
VoIP
Email
FTP
ICMP
MP3 Downloads
Other media
S ales Dept Bandwidth Us age
H T TP
VoIP
Email
F TP
IC MP
MP3 D ow n lo ad s
Othe r me dia
Pipe Bandwidth Usage Analysis by Time of Day
Sales Dept Serv er Access at 1pm
1000
900
800
700
Hotmail
600
Napster
500
Main
CNN
400
iTunes
300
200
100
0
Hotmail
Napster
Main
CNN
iTunes
Pipe Bandwidth Usage Analysis by Time of Day
Sales Dept Serv er Access at 7pm
80
70
60
50
G oogle
Smith.edu
40
CNN.com
NY Times.com
30
iTunes
20
10
0
G oogle
Smith.edu
CNN.com
NY
Times.com
iTunes
Bandwidth Shaping: Enforcing Policy
 Policy Writing and Application

Minimum

Maximum

Maximum number of connections

Priority
NetEnforcer Training Demo
Principles for QOS Guarantees (more)
 Scenario 1: 1Mbps Audio app and FTP transfer
 Scenario 2: 1Mbps Audio app and High-Priority FTP
 Scenario 3: Misbehaving Audio App and FTP transfer
Principles for QOS Guarantees (more)
 what do you think it means when an audio app misbehaves?



usually audio app needs and uses 1Mbps
sometimes either maliciously or due to application error, it sends out
packets at 1.5Mbps or higher
this is usually termed application misbehaving
 what do you think happens when an audio app misbehaves?


ftp starvation (FTP packets starve and get no bandwidth)
they will receive no service on the R1 – R2 link
Principles for QOS Guarantees (more)
 policing mechanisms at the network edge


marks all packets so it can tell
if application misbehaves the policing mechanism will enforce by:
• drop or delaying packets
• audio cannot exceed peak rate of 1Mbps
Principle 2
provide protection (isolation) for one class from others
Principles for QOS Guarantees (more)
 second enforcement scenario


Can allocate a fixed amount of bandwidth (audio: 1 Mbps, ftp: 0.5Mbps)
Any forseeable problems?
• when audio is not in use, ftp will be stuck with 0.5 Mbps
Principle 3
While providing isolation, it is desirable to use
resources as efficiently as possible
Principles for QOS Guarantees (more)
 Scenario 1: 1Mbps Audio app and FTP transfer
 Scenario 2: 1Mbps Audio app and High-Priority FTP
 Scenario 3: Misbehaving Audio App and FTP transfer
 Scenario 4: Two 1Mbps Audio apps overloaded 1.5Mbps
link
Principles for QOS Guarantees (more)
 Final scenario two 1Mbps audio applications
 even with the first three principles, this is a lose-lose
situation
 If they share, each will get 0.75Mbps, which is no good for
audio transfers
• 25% loss on both lines
Principles for QOS Guarantees (more)
 So what to do?
 when minimum quality of service is needed
• network will block flow or allow flow

telephone network is an example that performs call blocking
Principle 4
Call Admission: flow declares its needs, network may
block call (e.g., busy signal) if it cannot meet needs
Summary of QoS Principles
Let’s next look at mechanisms for achieving this ….
Chapter 6 outline
 6.1 Multimedia
 6.5 Beyond Best Effort
Networking Applications
 6.2 Streaming stored
audio and video
 6.6 Scheduling and
Policing Mechanisms
 6.7 Integrated Services
 RTSP
 6.8 RSVP
 6.3 Real-time, Interactivie
 6.9 Differentiated
Multimedia: Internet
Services
Phone Case Study
 6.4 Protocols for RealTime Interactive
Applications


RTP,RTCP
SIP
What is Scheduling?
Scheduling:
the mechanism
which chooses
the next packet
to send out on a link
Four Scheduling Mechanisms
What are some possible scheduling mechanisms?
(hint: similar policies are used for the dispatcher in OS )
 First-In-First-Out (FIFO)
 Priority Queuing
 Round Robin
 Weighted Fair Queuing (WFQ)
First In First Out
 FIFO scheduling: send in order of arrival to queue
 Non-Preemptive: Transmission of a packet is not
interrupted once it has begun.

real-world example: Airline check in.

discard policy: if packet arrives to full queue
• Tail drop: drop arriving packet
• priority: drop/remove on priority basis
• random: drop/remove randomly
Priority Queuing
Priority scheduling: transmit highest priority queued
packet first.
 multiple classes, with different priorities


class may depend on marking or other header info, e.g. IP
source/dest, port numbers, etc..
Real world example: Airplanes
Potential Problem with
Priority Queuing
 Starvation Prone.
 Motivation for our next two scheduling mechanisms
Round Robin
 multiple classes

cyclically scan across queues, serving one
from each class (if available)
 real world example: traffic jam
Weighted Fair Queuing (WFQ)
 Generalized Round Robin
 Each class gets weighted amount of service in each
cycle
 Guaranteed a percentage of the bandwidth
Policing Mechanisms
Goal: limit traffic to not exceed declared parameters
Three common-used criteria:
Average Rate: How many pkts can be sent per unit time
(in the long run)?

crucial question: what is the interval length: 100 packets
per sec or 6000 packets per min have same average!
Peak Rate: 6000 pkts per min. (ppm) avg. rate
1500 pkts per sec. (pps) peak rate
 Burst Size: max. number of pkts sent consecutively
(with no intervening idle)
The Leaky Bucket
Token Bucket: limit input to specified Burst Size and
Average Rate.
 bucket can hold b tokens
 tokens generated at rate r token/sec unless bucket full
 over interval of length t: number of packets admitted
less than or equal to (r t + b).
The Leaky Bucket
 token bucket, WFQ combine to provide guaranteed
upper bound on delay, i.e., QoS guarantee!
arriving
traffic
token rate, r
bucket size, b
per-flow
rate, R
WFQ
D = b/R
max
Other Sources
The Chronicle of Higher Education. Napster Was
Nothing Compared With This Year’s Bandwidth
Problems, 28 Sept. 2001.
http://chronicle.com/free/v48/i05/05a04401.htm
Allot Communications. NetEnforcer Online Tutorial.
http://www.bandwidth-qos.co.uk/bandwidth-shapingproduct/