Transcript Protocolos de transporte QoS

Tema 4:
Protocolos de transporte con QoS
 Clases de aplicaciones multimedia
 Redes basadas en IP y QoS
 Gestión de los recursos: IntServ vs DiffServ

RSVP
 RTP/RTCP: Transporte de flujos multimedia
 RTSP: Control de sesión y localización de medios
 Multicasting
Computer Networking: A
Top Down Approach
Featuring the Internet,
3rd edition.
Jim Kurose, Keith Ross
Addison-Wesley, July 2004.
Thanks to :
RADCOM technologies
H. Shulzrinne
Paul. E. Jones (from packetizer.com)
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009 – http://www.grc.upv.es/docencia/tra/
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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What is multimedia?
 Definition of multimedia
 Hard to find a clear-cut definition
 In general, multimedia is an integration of text, graphics, still
and moving images, animation, sounds, and any other medium
where every type of information can be represented, stored,
transmitted and processed digitally
 Characteristics of multimedia
 Digital – key concept
 Integration of multiple media type, usually including video
or/and audio
 May be interactive or non-interactive
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Various Media Types
 Text, Graphics, image, video, animation, sound, etc.
 Classifications of various media types
 Captured vs. synthesized media
 Captured media (natural) : information captured from the real world
– Example: still image, video, audio
 Synthesized media (artificial) : information synthesize by the
computer
– Example: text, graphics, animation
 Discrete vs. continuous media
 Discrete media: space-based, media involve the space dimension
only
– Text, Image, Graphics
 Continuous media: time-based, media involves both the space and
the time dimension
– Video, Sound, Animation
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Classification of Media Type
Sound
Video
Continuous
Image
Discrete
Captured
From real world
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Animation
Continuous
Text
Graphics
Discrete
Synthesized
By computer
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Text
 Plain text




Unformatted
Characters coded in binary form
ASCII code
All characters have the same style and font
 Rich text




Formatted
Contains format information besides codes for characters
No predominant standards
Characters of various size, shape and style, e.g. bold, colorful
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Plain Text vs. Rich Text
An example of Plain text
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Example of Rich text
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Graphics
 Revisable document that retains structural information
 Consists of objects such as lines, curves, circles, etc
 Usually generated by graphic editor of computer
programs
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Example of
graphics (FIG file)
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-10
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Images
 2D matrix consisting of pixels
 Pixel—smallest element of resolution of the image
 One pixel is represented by a number of bits
 Pixel depth– the number of bits available to code the pixel
 Have no structural information
 Two categories: scanned vs. synthesized still image
Digital still image
Camera
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Computer
software
Synthesized
image
Capture and
A/D conversion
Scanned
image
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Images (cont.)
 Examples of images
 Binary image – pixel depth 1
 Gray-scale – pixel depth 8
 Color image – pixel depth 24
Binary image
Gray-scale
colorimage
image
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Video vs. Animation
 Both images and graphics can be displayed as a
succession of view which create an impression of
movement
 Video – moving images or moving pictures




Captured or Synthesized
Consists of a series of bitmap images
Each image is called a frame
Frame rate: the speed to playback the video (frame per second)
 Animation – moving graphics
 Generated by computer program (animation authoring tools)
 Consists of a set of objects
 The movements of the objects are calculated and the view is
updated at playback
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Sound
 1-D time-based signal
0. 2
0. 15
0. 1
0. 05
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-0. 05
-0. 1
-0. 15
-0. 2
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 Speech vs. non-speech sound
 Speech – supports spoken language and has a semantic content
 Non-speech – does not convey semantics in general
 Natural vs. structured sound
 Natural sound – Recorded/generated sound wave represented as
digital signal
 Example: Audio in CD, WAV files
 Structured sound – Synthesize sound in a symbolic way
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 Example: MIDI file
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Networked Multimedia
 Local vs. networked multimedia
 Local: storage and presentation of multimedia information in
standalone computers
 Sample applications: DVD
 Networked: involve transmission and distribution of
multimedia information on the network
 Sample applications: videoconferencing, web video
broadcasting, multimedia Email, etc.
A scenario of multimedia networking
Video server
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Internet
Image server
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Consideration of Networked Multimedia
 Requirements of multimedia applications on the network
 Typically delay sensitive
 end-to-end delay
 delay jitter:
– Jitter is the variability of packet delays within the same packet stream
 Quality requirement
 Satisfactory quality of media presentation
 Synchronization requirement
 Continuous requirement (no jerky video/audio)
 Can tolerant some degree of information loss
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Technologies of Multimedia Networking
 Challenges of multimedia networking
1. Conflict between media size and bandwidth limit of the network
2. Conflict between the user requirement of multimedia application
and the best-effort network
3. How to meet different requirements of different users?
 Media compression – reduce the data volume
Address the 1st challenge
 Image compression
 Video compression
 Audio compression
 Multimedia transmission technology
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Address the 2nd and 3rd challenges
 Protocols for real-time transmission
 Rate / congestion control
 Error control
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Multimedia Networking Systems
 Live media transmission system
 Capture, compress, and transmit the media on the fly
(example?)
 Send stored media across the network
 Media is pre-compressed and stored at the server. This system
delivers the stored media to one or multiple receivers.
(example?)
 Differences between the two systems
 For live media delivery:
 Real-time media capture, need hardware support
 Real-time compression– speed is important
 Compression procedure can be adjusted based on network
conditions
 For stored media delivery
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 Offline compression – better compression result is important
 Compression can not be adjusted during transmission
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Classes of multimedia applications
 Streaming stored audio and video
 Streaming live audio and video
 Real-time interactive audio and video
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Streaming Stored Multimedia:
What is it?
t>0
100%
1. video
recorded
2. video
sent
network
delay
3. video received,
played out at client
streaming: at this time, client
playing out early part of video,
while server still sending later
part of video
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time
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Streaming vs. Download of Stored Multimedia Content
 Download: Receive entire content
before playback begins
 High “start-up” delay as media file
can be large
 ~ 4GB for a 2 hour MPEG II movie
 Streaming: Play the media file while it is
being received
 Reasonable “start-up” delays
 Reception Rate >= playback rate.
Why?
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Streaming Stored Multimedia: Interactivity
VCR-like functionality: client can pause,
rewind, FF, push slider bar
• 10 sec initial delay OK
• 1-2 sec until command effect OK
• RTSP often used (more later)
timing constraint for still-to-be transmitted
data: in time for playout
constant bit
rate video
transmission
variable
network
delay
client video
reception
constant bit
rate video
playout at client
buffered
video
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Streaming Multimedia: Client Buffering
client playout
delay
 Client-side buffering, playout delay compensate for
network-added delay, delay jitter
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time
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Streaming Multimedia: Client Buffering
 Client-side buffering, playout delay compensate for
network-added delay, delay jitter
constant
drain
rate, d
variable fill
rate, x(t)
buffered
video
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Interactive, Real-Time Multimedia
applications: IP telephony, video conference, distributed
interactive worlds
 end-end delay requirements:
 audio: < 150 msec good, < 400 msec OK
 includes application-level (packetization) and network delays
 higher delays noticeable, impair interactivity
 session initialization
 how does callee advertise its IP address, port number, encoding
algorithms?
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Internet multimedia: simplest approach
 audio or video stored in file
 files transferred as HTTP object
 received in entirety at client
 then passed to player
audio, video not streamed:
 no, “pipelining,” long delays until playout!
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Progressive Download




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browser GETs metafile
browser launches player, passing metafile
player contacts server
server downloads audio/video to player
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Streaming from a streaming server
 This architecture allows for non-HTTP protocol between server and media player
 Can also use UDP instead of TCP.
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Multimedia Over Today’s Internet
 TCP/UDP/IP: “best-effort service”
 no guarantees on delay, loss
 But multimedia apps requires QoS and level of
performance to be effective!
 Today’s Internet multimedia applications use
application-level techniques to mitigate (as best
possible) effects of delay, loss
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Streaming Multimedia: UDP or TCP?
UDP
 server sends at rate appropriate for client (oblivious to
network congestion!)
 often send rate = encoding rate = constant rate
 then, fill rate = constant rate - packet loss
 short playout delay (2-5 seconds) to compensate for
network delay jitter
 error recover: time permitting
TCP
 send at maximum possible rate under TCP
 fill rate fluctuates due to TCP congestion control
 larger playout delay: smooth TCP delivery rate
 HTTP/TCP passes more easily through firewalls
Tema 4:
Protocolos de transporte con QoS.
 Clases de aplicaciones multimedia
 Redes basadas en IP y QoS
 Gestión de los recursos: IntServ vs
DiffServ

RSVP
 RTP/RTCP: Transporte de flujos
multimedia
 RTSP: Control de sesión y localización de
medios
 Multicasting
Thanks to :
RADCOM technologies
H. Shulzrinne
Paul. E. Jones (from packetizer.com)
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009 – http://www.grc.upv.es/docencia/tra/
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Requisitos de red.
 Se definen 3 parámetros críticos que la red debería
suministrar a las aplicaciones multimedia:
 Productividad (Throughput)
Número de bits que la red es capaz de entregar por unidad
de tiempo (tráfico soportado).
CBR (streams de audio y vídeo sin comprimir)
VBR (ídem comprimido)
– Ráfagas (Peak Bit Rate y Mean Bit Rate)
 Retardo de tránsito (Transit delay)
Mensaje listo
para envío
Envío del primer
bit del mensaje
Retardo
de acceso
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Primer bit del
mensaje recibido
Ultimo bit del
Mensaje listo
mensaje recibido para recepción
Retardo
Retardo de
de tránsito
transmisión
Retardo extremo-a-extremo
Retardo
de acceso
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Requisitos de red (II).
 Varianza del retardo (Jitter)
Define la variabilidad del retardo de una red.
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Emisor
3
t
1
D1
2
D2 = D1
3
D3 > D1
Receptor
t
 Jitter físico (redes de conmutación de circuito)
– Suele ser muy pequeño (ns)
LAN jitter (Ethernet, FDDI).
– Jitter físico + tiempo de acceso al medio.
Redes WAN de conmutación de paquete (IP, X.25, FR)
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– Jitter físico + tiempo de acceso + retardo de conmutación de paquete en
conmutadores de la red.
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Internet y las aplicaciones multimedia
 ¿Qué podemos añadir a IP para soportar los
requerimientos de las aplicaciones multimedia?
 Técnicas de ecualización de retardos (buffering)
 Protocolos de transporte que se ajusten mejor a las
necesidades de las aplicaciones multimedia:
RTP (Real-Time Transport Protocol) RFC 1889.
RTSP (Real-Time Streaming Protocol) RFC 2326.
 Técnicas de control de admisión y reserva de recursos
(QoS)
RSVP (Resource reSerVation Protocol) RFC 2205
 Arquitecturas y protocolos específicos:
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Protocolos SIP (RFC 2543), SDP (RFC 2327), SAP (RFC
2974), etc..
ITU H.323
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Internet Protocols
Slide thanks to Henning Schulzrinne
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Multimedia, Quality of Service: What is it?
Multimedia applications:
network audio and video
(“continuous media”)
QoS
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network provides
application with level of
performance needed for
application to function.
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Improving QOS in IP Networks
 Thus far: “making the best of best effort”
 Future: next generation Internet with QoS guarantees
 RSVP: signaling for resource reservations
 Differentiated Services: differential guarantees
 Integrated Services: firm guarantees
 simple model for sharing and congestion studies:
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Principles for QOS Guarantees
 Example: 1Mbps IPphone, FTP share 1.5 Mbps link.
 bursts of FTP can congest router, cause audio loss
 want to give priority to audio over FTP
Principle 1
packet marking needed for router to distinguish
between different classes; and new router policy
to treat packets accordingly
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Principles for QOS Guarantees (more)
 what if applications misbehave (audio sends higher than
declared rate)
 policing: force source adherence to bandwidth allocations
 marking and policing at network edge:
 similar to ATM UNI (User Network Interface)
Principle 2
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provide protection (isolation) for one class from
others
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Principles for QOS Guarantees (more)
 Allocating fixed (non-sharable) bandwidth to flow:
inefficient use of bandwidth if flows doesn’t use its
allocation
Principle 3
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While providing isolation, it is desirable to use
resources as efficiently as possible
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Principles for QOS Guarantees (more)
 Basic fact of life: can not support traffic demands
beyond link capacity
Principle 4
Call Admission: flow declares its needs, network
may block call (e.g., busy signal) if it cannot meet
needs
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Summary of QoS Principles
Tema 4:
Protocolos de transporte con QoS.
 Clases de aplicaciones multimedia
 Redes basadas en IP y QoS
 Gestión de los recursos: IntServ vs
DiffServ

RSVP
 RTP/RTCP: Transporte de flujos
multimedia
 RTSP: Control de sesión y localización de
medios
 Multicasting
Thanks to :
RADCOM technologies
H. Shulzrinne
Paul. E. Jones (from packetizer.com)
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009 – http://www.grc.upv.es/docencia/tra/
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Scheduling And Policing Mechanisms
 scheduling: choose next packet to send on link
 FIFO (first in first out) scheduling: send in order of arrival
to queue
 discard policy: if packet arrives to full queue: who to discard?
 Tail drop: drop arriving packet
 priority: drop/remove on priority basis
 random: drop/remove randomly
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Scheduling Policies: more
Priority scheduling: transmit highest priority queued
packet
 multiple classes, with different priorities
 class may depend on marking or other header info, e.g. IP
source/dest, port numbers, etc..
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Scheduling Policies: still more
round robin scheduling:
 multiple classes
 cyclically scan class queues, serving one from each
class (if available)
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Scheduling Policies: still more
Weighted Fair Queuing:
 generalized Round Robin
 each class gets weighted amount of service in each
cycle
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Policing Mechanisms
 Goal: limit traffic to not exceed declared parameters
 Three common-used criteria:
 (Long term) 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: e.g., 6000 pkts per min. (ppm) avg.; 1500 pps peak
rate
 (Max.) Burst Size: max. number of pkts sent consecutively (with
no intervening idle)
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Policing Mechanisms
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
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less than or equal to (r t + b).
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Policing Mechanisms (more)
 token bucket, WFQ combine to provide guaranteed
upper bound on delay, i.e., QoS guarantee!
arriving
traffic
token rate, r
bucket size, b
WFQ
per-flow
rate, R
D = b/R
max
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
IETF Integrated Services
 architecture for providing QOS guarantees in IP
networks for individual application sessions
 resource reservation: routers maintain state info of
allocated resources, QoS req’s
 admit/deny new call setup requests:
Question: can newly arriving flow be admitted
with performance guarantees while not violated
QoS guarantees made to already admitted flows?
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Intserv: QoS guarantee scenario
 Resource reservation
 call setup, signaling (RSVP)
 traffic, QoS declaration
 per-element admission control
request/
reply
 QoS-sensitive
scheduling (e.g.,
WFQ)
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Call Admission
Arriving session must :
 declare its QOS requirement
 R-spec: defines the QOS being requested
 characterize traffic it will send into network
 T-spec: defines traffic characteristics
 signaling protocol: needed to carry R-spec and T-spec to
routers (where reservation is required)
 RSVP
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Intserv QoS: Service models [RFC2211, RFC2212]
Guaranteed service:
 worst case traffic arrival: leaky-bucketpoliced source
 simple (mathematically provable) bound
on delay [Parekh 1992, Cruz 1988]
arriving
traffic
Controlled load service:
 "a quality of service closely
approximating the QoS that same flow
would receive from an unloaded
network element."
token rate, r
bucket size, b
WFQ
5
1
per-flow
rate, R
D = b/R
max
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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IETF Differentiated Services
Concerns with Intserv:
 Scalability: signaling, maintaining per-flow router
state difficult with large number of flows
 Flexible Service Models: Intserv has only two classes.
Also want “qualitative” service classes
 “behaves like a wire”
 relative service distinction: Platinum, Gold, Silver
Diffserv approach:
 simple functions in network core, relatively complex
functions at edge routers (or hosts)
 Don’t define service classes, provide functional
components to build service classes
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Diffserv Architecture
Edge router:
 per-flow traffic management
 marks packets as in-profile
and out-profile
Core router:
 per class traffic management
 buffering and scheduling based
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3
r
on marking at edge
 preference given to in-profile
packets
 Assured Forwarding
b
marking
scheduling
..
.
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Edge-router Packet Marking
 profile: pre-negotiated rate A, bucket size B
 packet marking at edge based on per-flow profile
Rate A
B
User packets
Possible usage of marking:
 class-based marking: packets of different classes marked differently
 intra-class marking: conforming portion of flow marked differently than nonconforming one
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Classification and Conditioning
 Packet is marked in the Type of Service (TOS) in IPv4,
and Traffic Class in IPv6
 6 bits used for Differentiated Service Code Point (DSCP)
and determine PHB that the packet will receive
 2 bits are currently unused
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Classification and Conditioning
may be desirable to limit traffic injection rate of some
class:
 user declares traffic profile (e.g., rate, burst size)
 traffic metered, shaped if non-conforming
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Forwarding (PHB)
 PHB result in a different observable (measurable)
forwarding performance behavior
 PHB does not specify what mechanisms to use to ensure
required PHB performance behavior
 Examples:
 Class A gets x% of outgoing link bandwidth over time intervals
of a specified length
 Class A packets leave first before packets from class B
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Forwarding (PHB)
PHBs being developed:
 Expedited Forwarding: pkt departure rate of a class
equals or exceeds specified rate
 logical link with a minimum guaranteed rate
 Assured Forwarding: 4 classes of traffic
 each guaranteed minimum amount of bandwidth
 each with three drop preference partitions
Tema 4:
Protocolos de transporte multimedia.
Clases de aplicaciones multimedia
Redes basadas en IP y QoS
Gestión de los recursos: IntServ vs
DiffServ
 RSVP
RTP/RTCP: Transporte de flujos
multimedia
RTSP: Control de sesión y
localización de medios
Multicasting
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009 – http://www.grc.upv.es/docencia/tra/
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Signaling in the Internet
connectionless
(stateless)
forwarding by IP
routers
+
best effort
service
=
no network
signaling protocols
in initial IP
design
 New requirement: reserve resources along end-to-end
path (end system, routers) for QoS for multimedia
applications
 RSVP: Resource Reservation Protocol [RFC 2205]
 “ … allow users to communicate requirements to network in
robust and efficient way.” i.e., signaling !
 earlier Internet Signaling protocol: ST-II [RFC 1819]
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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RSVP Design Goals
1. accommodate heterogeneous receivers (different
bandwidth along paths)
2. accommodate different applications with different
resource requirements
3. make multicast a first class service, with adaptation to
multicast group membership
4. leverage existing multicast/unicast routing, with
adaptation to changes in underlying unicast, multicast
routes
5. control protocol overhead to grow (at worst) linear in #
receivers
6. modular design for heterogeneous underlying
technologies
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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RSVP: does not…
 specify how resources are to be reserved
 rather: a mechanism for communicating needs
 determine routes packets will take
 that’s the job of routing protocols
 signaling decoupled from routing
 interact with forwarding of packets
 separation of control (signaling) and data (forwarding) planes
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RSVP: overview of operation
 senders, receiver join a multicast
group
 done outside of RSVP
 senders need not join group
 sender-to-network signaling
 path message: make sender
presence known to routers
 path teardown: delete sender’s
path state from routers
 receiver-to-network signaling
 reservation message: reserve
resources from sender(s) to
receiver
 reservation teardown: remove
receiver reservations
 network-to-end-system signaling
 path error
 reservation error
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Call Admission
 Session must first declare its QOS requirement and
characterize the traffic it will send through the network
 R-spec: defines the QOS being requested
 T-spec: defines the traffic characteristics
 A signaling protocol is needed to carry the R-spec and Tspec to the routers where reservation is required;
 RSVP is a leading candidate for such signaling protocol
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RSVP request (T-Spec)
 A token bucket specification
 bucket size, b
 token rate, r
 the packet is transmitted onward only if the number of tokens in
the bucket is at least as large as the packet
 peak rate, p
p>r
 maximum packet size, M
 minimum policed unit, m
 All packets less than m bytes are considered to be m bytes
 Reduces the overhead to process each packet
 Bound the bandwidth overhead of link-level headers
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Call Admission
 Call Admission: routers will admit calls based on their Rspec and T-spec and base on the current resource
allocated at the routers to other calls.
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Integrated Services: Classes
 Guaranteed QOS: this class is provided with firm
bounds on queuing delay at a router; envisioned for
hard real-time applications that are highly sensitive to
end-to-end delay expectation and variance
 Controlled Load: this class is provided a QOS closely
approximating that provided by an unloaded router;
envisioned for today’s IP network real-time applications
which perform well in an unloaded network
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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R-spec
 An indication of the QoS control service requested
 Controlled-load service and Guaranteed service
 For Controlled-load service
 Simply a Tspec
 For Guaranteed service
 A Rate (R) term, the bandwidth required
 R  r, extra bandwidth will reduce queuing delays
 A Slack (S) term
 The difference between the desired delay and the delay that would
be achieved if rate R were used
 With a zero slack term, each router along the path must reserve R
bandwidth
 A nonzero slack term offers the individual routers greater flexibility
in making their local reservation
 Number decreased by routers on the path.
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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QoS Routing: Multiple constraints
 A request specifies the desired QoS requirements
 e.g., BW, Delay, Jitter, packet loss, path reliability etc
 Two type of constraints:
 Additive: e.g., delay
 Maximum (or Minimum): e.g., Bandwidth
 Task
 Find a (min cost) path which satisfies the constraints
 if no feasible path found, reject the connection
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Path msgs: RSVP sender-to-network signaling
 path message contents:
 address: unicast destination, or multicast group
 flowspec: bandwidth requirements spec.
 filter flag: if yes, record identities of upstream senders (to allow
packets filtering by source)
 previous hop: upstream router/host ID
 refresh time: time until this info times out
 path message: communicates sender info, and reversepath-to-sender routing info
 later upstream forwarding of receiver reservations
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RSVP: simple audio conference
 H1, H2, H3, H4, H5 both senders and receivers
 multicast group m1
 no filtering: packets from any sender forwarded
 audio rate: b
 only one multicast routing tree possible
H3
H2
R1
R2
H1
H5
7
1
R3
H4
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RSVP: building up path state
 H1, …, H5 all send path messages on m1:
(address=m1, Tspec=b, filter-spec=no-filter,refresh=100)
 Suppose H1 sends first path message
m1:
m1:
in L1
out
L2 L6
in
L7
out L3 L4
L6
m1: in
out L5
L7
H3
H2
L3
L2
H1
7
2
L1
R1
L6
R2
L5
H5
L7
R3
L4
H4
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RSVP: building up path state
 next, H5 sends path message, creating more state in
routers
m1:
L6
L1
m1: in
out L1 L2 L6
in
L7
out L3 L4
L5 L6
m1: in
out L5 L6 L7
H3
H2
L3
L2
H1
7
3
L1
R1
L6
R2
L5
H5
L7
R3
L4
H4
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RSVP: building up path state
 H2, H3, H5 send path msgs, completing path state
tables
m1:
L1 L2 L6
m1: in
out L1 L2 L6
in L3 L4 L7
out L3 L4 L7
L5 L6 L7
m1: in
out L5 L6 L7
H3
H2
L3
L2
H1
7
4
L1
R1
L6
R2
L5
H5
L7
R3
L4
H4
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
reservation msgs: receiver-to-network signaling
 reservation message contents:
 desired bandwidth:
 filter type:
 no filter: any packets address to multicast group can use
reservation
 fixed filter: only packets from specific set of senders can use
reservation
 dynamic filter: senders who’s packets can be forwarded across link
will change (by receiver choice) over time.
 filter spec
 reservations flow upstream from receiver-to-senders,
reserving resources, creating additional, receiver-related
state at routers
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RSVP: receiver reservation example 1
H1 wants to receive audio from all other senders
 H1 reservation msg flows uptree to sources
 H1 only reserves enough bandwidth for 1 audio stream
 reservation is of type “no filter” – any sender can use
reserved bandwidth
H3
H2
L3
L2
H1
7
6
L1
R1
L6
R2
L5
H5
L7
R3
L4
H4
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RSVP: receiver reservation example 1
 H1 reservation msgs flows uptree to sources
 routers, hosts reserve bandwidth b needed on
downstream links towards H1
m1: in L1 L2
out L1(b) L2
m1:
L2
H1
b
b
L1
R1
b
L6
L4
L4
in L3
out L3
L7
L7(b)
L7
L6
L6(b) L7
m1: in L5
out L5
H2
7
7
L6
L6
b
R2
L5
H5
b
L7
b
R3
L3
b
L4
H3
H4
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RSVP: receiver reservation example 1 (more)
 next, H2 makes no-filter reservation for bandwidth b
 H2 forwards to R1, R1 forwards to H1 and R2 (?)
 R2 takes no action, since b already reserved on L6
L6
m1: in L1 L2
out L1(b) L2(b) L6
b
L2
H1
b
b
b L1
R1
b
L6
L4
L4
in L3
out L3
L7
L7(b)
L7
L6
L6(b) L7
m1: in L5
out L5
H2
7
8
m1:
b
R2
L5
H5
b
L7
b
R3
L3
b
L4
H3
H4
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RSVP: receiver reservation: issues
What if multiple senders (e.g., H3, H4, H5) over link (e.g., L6)?
 arbitrary interleaving of packets
 L6 flow policed by leaky bucket: if H3+H4+H5 sending rate exceeds b,
packet loss will occur
L6
m1: in L1 L2
out L1(b) L2(b) L6
b
L2
H1
b
b
b L1
R1
b
L6
L4
L4
in L3
out L3
L7
L7(b)
L7
L6
L6(b) L7
m1: in L5
out L5
H2
7
9
m1:
b
R2
L5
H5
b
L7
b
R3
L3
b
L4
H3
H4
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RSVP: example 2
 H1, H4 are only senders
 send path messages as before, indicating filtered reservation
 Routers store upstream senders for each upstream link
 H2 will want to receive from H4 (only)
H3
H2
L3
L2
H1
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0
L1
R1
L6
R2
L7
R3
L4
H4
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RSVP: example 2
 H1, H4 are only senders
 send path messages as before, indicating filtered reservation
in
L1, L6
L2(H1-via-H1
out L6(H1-via-H1
L1(H4-via-R2
in
; H4-via-R2
)
)
)
L3(H4-via-H4
out L4(H1-via-R2
L7(H4-via-H4
; H1-via-R3
)
)
)
H3
H2
R2
L2
H1
8
1
L4, L7
L1
R1
L7
L6
in
L3
R3
L6, L7
L6(H4-via-R3
out L7(H1-via-R1
)
)
L4
H4
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RSVP: example 2
 receiver H2 sends reservation message for source H4 at
bandwidth b
 propagated upstream towards H4, reserving b
in
L1, L6
L2(H1-via-H1
out L6(H1-via-H1
L1(H4-via-R2
H2
L2
H1
8
2
in
;H4-via-R2 (b))
)
)
L4, L7
L3(H4-via-H4 ; H1-via-R2
out L4(H1-via-R2 )
L7(H4-via-H4 (b))
)
H3
b
L1
R1
b
L6
in
R2
b
L7
L6, L7
L6(H4-via-R3 (b))
out L7(H1-via-R1 )
R3
L3
b
L4
H4
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RSVP: soft-state
 senders periodically resend path msgs to refresh (maintain) state
 receivers periodically resend resv msgs to refresh (maintain) state
 path and resv msgs have TTL field, specifying refresh interval
in
L1, L6
L2(H1-via-H1
out L6(H1-via-H1
L1(H4-via-R2
H2
L2
H1
8
3
in
;H4-via-R2 (b))
)
)
L4, L7
L3(H4-via-H4 ; H1-via-R3
out L4(H1-via-R2 )
L7(H4-via-H4 (b))
)
H3
b
L1
R1
b
L6
in
R2
b
L7
L6, L7
L6(H4-via-R3 (b))
out L7(H1-via-R1 )
R3
L3
b
L4
H4
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RSVP: soft-state
 suppose H4 (sender) leaves without performing teardown
 eventually state in routers will timeout and disappear!
in
L1, L6
L2(H1-via-H1
out L6(H1-via-H1
L1(H4-via-R2
H2
L2
H1
8
4
in
;H4-via-R2 (b))
)
)
L4, L7
L3(H4-via-H4 ; H1-via-R3
out L4(H1-via-R2 )
L7(H4-via-H4 (b))
)
H3
b
L1
R1
b
L6
in
R2
b
L7
L6, L7
L6(H4-via-R3 (b))
out L7(H1-via-R1 )
R3
L3
b
L4
gone
H4
fishing!
Tema 4:
Protocolos de transporte multimedia.
Clases de aplicaciones multimedia
Redes basadas en IP y QoS
Gestión de los recursos: IntServ vs
DiffServ
 RSVP
RTP/RTCP: Transporte de flujos
multimedia
RTSP: Control de sesión y
localización de medios
Multicasting
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009 – http://www.grc.upv.es/docencia/tra/
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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RTP (Real-time Transport Protocol)
 Se basa en el concepto de sesión: la asociación entre un
conjunto de aplicaciones que se comunican usando RTP
 Una sesión es identificada por:
 Una dirección IP multicast
 Dos puertos: Uno para los datos y otro para control
(RTCP)
 Un participante (participant) puede ser una máquina o
un usuario que participa en una sesión
 Cada media distinto es trasmitido usando una sesión
diferente.
 Por ejemplo, si se quisiera transmitir audio y vídeo
harían falta dos sesiones separadas  Esto permite
a un participante solamente ver o solamente oír
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RTP (Real-time Transport Protocol)
 Audio-conferencia con multicast y RTP
 Sesión de audio: Una dirección multicast y dos puertos
 Datos de audio y mensajes de control RTCP.
 Existirá (al menos) una fuente de audio que enviará un stream de
segmentos de audio pequeños (20 ms) utilizando UDP.
 A cada segmento se le asigna una cabecera RTP
 La cabecera RTP indica el tipo de codificación (PCM, ADPCM, LPC, etc.)
 Número de secuencia y fechado de los datos.
 Control de conferencia (RTCP):
 Número e identificación de participantes en un instante dado.
 Información acerca de cómo se recibe el audio.
 Audio y Vídeo conferencia con multicast y RTP
 Si se utilizan los dos medios, se debe crear una sesión RTP
independiente para cada uno de ellos.
 Una dirección multicast y 2 puertos por cada sesión.
 Existencia de participantes que reciban sólo uno de los medios.
 Temporización independiente de audio y vídeo.
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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RTP: Mezcladores y traductores
 Mezcladores (Mixers).
 Permiten que canales con un BW bajo puedan participar en una
conferencia. El mixer re-sincroniza los paquetes y hace todas las
conversiones necesarias para cada tipo de canal.
 Traductores (Translators).
 Permiten conectar sitios que no tienen acceso multicast (p.ej.
que están en una sub-red protegida por un firewall)
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RTP: Formato de mensaje (I)
32 bits
V PX
CC M
PT
Sequence number
Timestamp
Synchronization Source (SSRC) ID
Contributing Source (CSRC) ID
V: versión; actualmente es la 2
P: si está a 1 el paquete tiene bytes de relleno (padding)
X: presencia de una extensión de la cabecera
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RTP: Formato de mensaje (II)
32 bits
V PX
CC M
PT
Sequence number
Timestamp
Synchronization Source (SSRC) ID
Contributing Source (CSRC) ID
CC: Identifica el número de CSRC que contribuyen a los datos
M: Marca (definida según el perfil)
PT: Tipo de datos (según perfil)
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RTP: Formato de mensaje (III)
32 bits
V PX
CC M
PT
Sequence number
Timestamp
Synchronization Source (SSRC) ID
Contributing Source (CSRC) ID
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Sequence number: Establece el orden de los paquetes
Timestamp: Instante de captura del primer octeto del campo de datos
SSRC: Identifica la fuente de sincronización
CSRC: Fuentes que contribuyen
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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RTP header definition
/*
* RTP data header
*/
typedef struct {
unsigned int version:2;
unsigned int p:1;
unsigned int x:1;
unsigned int cc:4;
unsigned int m:1;
unsigned int pt:7;
u_int16 seq;
u_int32 ts;
u_int32 ssrc;
u_int32 csrc[1];
} rtp_hdr_t;
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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RTP y las aplicaciones
 La especificación de
RTP para una
aplicación particular va
acompañada de:
 Un perfil (profile) que
defina un conjunto de
códigos para los tipos
de datos transportados
(payload)
 El formato de
transporte de cada uno
de los tipos de datos
previstos
Ej.: RFC 1890 para audio y vídeo
PT
encoding audio/video clock rate channels
name
(A/V)
(Hz)
(audio)
______________________________________________
0
PCMU
A
8000
1
1
1016
A
8000
1
2
G721
A
8000
1
3
GSM
A
8000
1
...
34-71 unassigned
?
72-76 reserved
N/A
N/A
N/A
77-95 unassigned
?
96-127 dynamic
?
PCMU
Corresponde a la recomendación CCITT/ITU-T
G.711. El audio se codifica con 8 bits por
muestra, después de una cuantificación
logarítmica. PCMU es la codificación que se
utiliza en Internet para un media de tipo
audio/basic.
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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RTCP (RTP Control Protocol)
 RTCP se basa en envíos periódicos de paquetes de
control a los participantes de una sesión RTP
 Permite realizar una realimentación de la calidad de
recepción de los datos (estadísticas).
 Los paquetes de control siempre llevan la
identificación de la fuente RTP: CNAME
Asociar más de una sesión a un mismo fuente
(sincronización).
 El envío de estos paquetes debe ser controlado por
cada participante (sistema ampliable).
 Control de sesión (opcional)
Información adicional de cada participante.
Entrada y salida de participantes en las sesión.
Negociación de parámetros y formatos.
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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RTCP (RTP Control Protocol)
 RTCP permite controlar el trafico que no se auto-limita
(p.ej cuando el número de fuentes aumenta)
 Para ello se define el ancho de banda de la sesión. RTCP
se reserva el 5% (bwRTCP)
 A cada fuente se le asigna 1/4 de bwRTCP
 El intervalo entre cada paquete RTCP es > 5 sec
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RTCP (RTP Control Protocol)
 Formato de un paquete RTCP:
 Existen distintos tipos de paquetes RTCP:
SR (Sender Report): Informes estadísticos de transmisión y
recepción de los elementos activos en la sesión.
RR (Receiver Report): Informes estadísticos de recepción
en los receptores.
SDES (Source Description): Información del participante
(CNAME, e-mail, etc).
BYE: Salida de la sesión.
APP: Mensajes específicos de la aplicación.
 Cada paquete RTCP tiene su propio formato.
Su tamaño debe ser múltiplo de 32 bits (padding).
Se pueden concatenar varios paquetes RTCP en uno
(compound RTCP packet).
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RTCP: Mensajes SR
32 bits
Sender
info
Report
block 1
9
7
RC
PT=SR=200
Longitud
SSRC del sender
NTP timestamp msw
NTP timestamp lsw
RTP timestamp
Contador de los paquetes del sender
cabecera V P
Contador de los bytes del sender
SSRC_1
Frac perd
Total paquetes perdidos
Num sec más alto recibido
Jitter de inter-llegada
Ultimo SR (LSR)
Retraso del último SR (LSR)
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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RTCP: Cálculo del Jitter
 Es una estimación de la variancia del tiempo de interllegada de los paquetes RTP
D(i, j)  ( R j  Ri )  (S j  Si )  ( R j  S j )  ( Ri  Si )
 Si  RTP timestamp del paquete i
 Ri  Instante de llegada del paquete i
J i  J i 1   Di 1, i   J i 1 / 16
Tema 4:
Protocolos de transporte multimedia.
Clases de aplicaciones multimedia
Redes basadas en IP y QoS
Gestión de los recursos: IntServ vs
DiffServ
 RSVP
RTP/RTCP: Transporte de flujos
multimedia
RTSP: Control de sesión y
localización de medios
Multicasting
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009 – http://www.grc.upv.es/docencia/tra/
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
1
0
0
Real-Time Streaming Protocol
RFC 2326
 Tiene la función de un “mando a distancia por la red”
para servidores multimedia
 Permite establecer y controlar uno o más flujos de datos
sincronizados
 NO existe el concepto de conexión RTSP sino de sesión
RTSP
 Además, una sesión RTSP no tiene relación con ninguna
conexión especifica de nivel transporte (p.ej. TCP o
UDP)
 Los flujos de datos no tienen por que utilizar RTP
 Está basado en HTTP/1.1
 Diferencias importantes:
No es stateless
Los clientes y servidores pueden generar peticiones
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Terminología RTSP
 Conferencia
 Media stream
 Una instancia única
de un medio
continuo:
Un stream audio,
Un stream vídeo
Una “whiteboard”
Voz del
conferenciante
Imagen de las
transparencias
Imagen del
conferenciante
 Presentación:
 Es el conjunto de
uno o más streams,
que son vistos por el
usuario como un
conjunto integrado
1
0
Imagen del
público
Voz del
público
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RTSP: Ejemplo de una sesión
HTTP GET
Cliente
SETUP
PLAY
RTP audio
RTP vídeo
RTCP
PAUSE
TEARDOWN
1
0
2
Web
server
descripción de la sesión
Media
server
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RTSP: Comandos de petición
Request =
Request-Line ;
*( general-header | request-header | entity-header )
CRLF
[ message-body ]
Request-Line = Method SP Request-URI SP RTSP-Version CRLF
Method
=
"DESCRIBE“ | "ANNOUNCE" | "GET_PARAMETER" |
"OPTIONS“
| "PAUSE" | "PLAY" | "RECORD" |
"REDIRECT" | "SETUP" | "SET_PARAMETER" |
"TEARDOWN" | extension-method
extension-method = token
Request-URI = "*" | absolute_URI
RTSP-Version = "RTSP" "/" 1*DIGIT "." 1*DIGIT
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0
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RTSP: Mensajes de respuesta
Response =
*(
|
|
Status-Line ;
general-header
response-header
entity-header )
CRLF
[ message-body ]
Status-Line = RTSP-version SP Status-Code SP Reason-Phrase CRLF
Status-Code =
1xx: Información (Comando recibido, procesando,..) |
2xx: Exito (Comando recibido y ejecutado con éxito) |
3xx: Re-dirección (Comando recibido pero aún no completado) |
4xx: Error del cliente (El comando tiene errores de sintaxis) |
5xx: Error del servidor (Error interno del servidor)
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RTSP: Una sesión completa (I)
1
2
media server A
4
web server W
cliente C
3
media server V
C->W: GET /twister.sdp HTTP/1.1
Host: www.example.com
Accept: application/sdp
W->C: HTTP/1.0 200 OK
Content-Type: application/sdp
1
0
5
v=0
o=- 2890844526 2890842807 IN IP4 192.16.24.202
s=RTSP Session
m=audio 0 RTP/AVP 0
a=control:rtsp://audio.example.com/twister/audio.en
m=video 0 RTP/AVP 31
a=control:rtsp://video.example.com/twister/video
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RTSP: Una sesión completa (II)
C->A: SETUP rtsp://audio.example.com/twister/audio.en RTSP/1.0
CSeq: 1
Transport: RTP/AVP/UDP;unicast;client_port=3056-3057
A->C: RTSP/1.0 200 OK
CSeq: 1
Session: 12345678
Transport: RTP/AVP/UDP;unicast;client_port=3056-3057;
server_port=5000-5001
C->V: SETUP rtsp://video.example.com/twister/video RTSP/1.0
CSeq: 1
Transport: RTP/AVP/UDP;unicast;client_port=3058-3059
V->C: RTSP/1.0 200 OK
CSeq: 1
Session: 23456789
Transport: RTP/AVP/UDP;unicast;client_port=3058-3059;
server_port=5002-5003
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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RTSP: Una sesión completa (III)
C->V: PLAY rtsp://video.example.com/twister/video RTSP/1.0
CSeq: 2
Session: 23456789
Range: smpte=0:10:00V->C: RTSP/1.0 200 OK
CSeq: 2
Session: 23456789
Range: smpte=0:10:00-0:20:00
RTP-Info: url=rtsp://video.example.com/twister/video;
seq=12312232;rtptime=78712811
C->A: PLAY rtsp://audio.example.com/twister/audio.en RTSP/1.0
CSeq: 2
Session: 12345678
Range: smpte=0:10:00A->C: RTSP/1.0 200 OK
CSeq: 2
Session: 12345678
Range: smpte=0:10:00-0:20:00
RTP-Info: url=rtsp://audio.example.com/twister/audio.en;
seq=876655;rtptime=1032181
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
RTSP: Una sesión completa (IV)
C->A: TEARDOWN rtsp://audio.example.com/twister/audio.en RTSP/1.0
CSeq: 3
Session: 12345678
A->C: RTSP/1.0 200 OK
CSeq: 3
C->V: TEARDOWN rtsp://video.example.com/twister/video RTSP/1.0
CSeq: 3
Session: 23456789
V->C: RTSP/1.0 200 OK
CSeq: 3
1
0
8
Tema 4:
Protocolos de transporte multimedia.
Clases de aplicaciones multimedia
Redes basadas en IP y QoS
Gestión de los recursos: IntServ vs
DiffServ
 RSVP
RTP/RTCP: Transporte de flujos
multimedia
RTSP: Control de sesión y
localización de medios
Multicasting
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009 – http://www.grc.upv.es/docencia/tra/
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Multicast = Efficient Data Distribution
Src
Src
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
1
1
1
Why Multicast ?
 Need for efficient one-to-many delivery of same data
 Applications:










News/sports/stock/weather updates
Distance learning
Configuration, routing updates, service location
Pointcast-type “push” apps
Teleconferencing (audio, video, shared whiteboard, text editor)
Distributed interactive gaming or simulations
Email distribution lists
Content distribution; Software distribution
Web-cache updates
Database replication
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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1
2
Why Not Broadcast or Unicast?
 Broadcast:
Send a copy to every machine on the net
Simple, but inefficient
All nodes must process packet even if they don’t care
Wastes more CPU cycles of slower machines (“broadcast
radiation”)
 Network loops lead to “broadcast storms”




 Replicated Unicast:




Sender sends a copy to each receiver in turn
Receivers need to register or sender must be pre-configured
Sender is focal point of all control traffic
Reliability => per-receiver state, separate sessions/processes at
sender
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Multicast Apps Characteristics
 Number of (simultaneous) senders to the group
 The size of the groups
 Number of members (receivers)
 Geographic extent or scope
 Diameter of the group measured in router hops
 The longevity of the group
 Number of aggregate packets/second
 The peak/average used by source
 Level of human interactivity
 Lecture mode vs interactive
 Data-only (eg database replication) vs multimedia
1
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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1
4
Reliable Multicast vs. Unreliable Multicast
 When a multicast message is sent by a process, the
runtime support of the multicast mechanism is
responsible for delivering the message to each process
currently in the multicast group.
 As each participating process may be on a separate
host, due to factors such as failures of network links
and/or network hosts, routing delays, and differences in
software and hardware, the time between when a
message is sent and when it is received may vary
among the recipient processes.
 Moreover, a message may not be received by one or
more of the processes at all.
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Classification of multicasting mechanisms in terms of message
delivery
 Unreliable multicast:
 The arrival of the correct message at each process is not
guaranteed.
 Reliable multicast:
 Guarantees that each message is eventually delivered in a noncorrupted form to each process in the group.
 The definition of reliable multicast requires that each
participating process receives exactly one copy of each
message sent. It does not put any restriction of the
order the messages delivered.
 Reliable multicast can be further classified based on the
order of the delivery of the messages: unordered, FIFO,
causal order, atomic order.
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Classification of reliable multicast -- unordered
 An unordered reliable multicast system guarantees the
safe delivery of each message, but it provides no
guarantee on the delivery order of the messages.
 Example: Processes P1, P2, and P3 have formed a
multicast group. Three messages, m1, m2, m3 have
been sent to the group. An unordered reliable multicast
system may deliver the messages to each of the three
processes in any of these:
m1-m2-m3,
m1-m3-m2,
m2-m1-m3,
m2-m3-m1,
m3-m1-m2,
m3-m2-m1
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Classification of reliable multicast - FIFO
 If process P sent messages mi and mj, in that order,
then each process in the multicast group will be
delivered the messages mi and mj, in that order.
 Note that FIFO multicast places no restriction on the
delivery order among messages sent by different
processes. For example, P1 sends messages m11 then
m12, and P2 sends messages m21 then m22. It is
possible for different processes to receive any of the
following orders: m11-m12-m21-m22,
m11-m21-m12-m22,
m11-m21-m22-m12,
m21-m11-m12-m22
m21-m11-m22-m12
m21-m22-m11-m12.
1
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Classification of reliable multicast – Causal order
 If message mi causes (results in) the occurrence of
message mj, then mi will be delivered to each process
prior to mj. Messages mi and mj are said to have a
causal or happen-before relationship.
 For example, P1 sends a message m1, to which P2
replies with a multicast message m2. Since m2 is
triggered by m1, the two messages share a causal
relationship of m1-> m2. A causal-order multicast
message system ensures that these two messages will
be delivered to each of the processes in the order of
m1- m2.
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Classification of reliable multicast –
Atomic order
 In an atomic-order multicast system, all messages are
guaranteed to be delivered to each participant in the
exact same order. Note that the delivery order does not
have to be FIFO or causal, but must be identical for
each process.
 Example:
 P1 sends m1, P2 sends m2, and P3 sends m3.
 An atomic system will guarantee that the messages will
be delivered to each process in only one of the six
orders:
m1-m2- m3, m1- m3- m2, m2- m1-m3,
m2-m3-m1, m3-m1- m2, m3-m2-m1.
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
IP Multicast Architecture
Service model
Host-to-router protocol
(IGMP)
Routers
Multicast routing protocols
(various)
1
2
0
Hosts
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
IP Multicast model: RFC 1112
 Message sent to multicast “group” (of receivers)
 Senders need not be group members
 A group identified by a single “group address”
 Use “group address” instead of destination address in IP packet sent to
group




Groups can have any size;
Group members can be located anywhere on the Internet
Group membership is not explicitly known
Receivers can join/leave at will
 Packets are not duplicated or delivered to destinations outside the
group
 Distribution tree constructed for delivery of packets
 No more than one copy of packet appears on any subnet
 Packets delivered only to “interested” receivers => multicast delivery
tree changes dynamically
 Network has to actively discover paths between senders and receivers
1
2
1
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
1
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IP Multicast Addresses
 Class D IP addresses
 224.0.0.0 – 239.255.255.255
1 110
Group ID
 Address allocation:
 Well-known (reserved) multicast addresses, assigned by IANA:
224.0.0.x and 224.0.1.x Transient multicast addresses, assigned
and reclaimed dynamically, e.g., by “sdr” program
 Each multicast address represents a group of arbitrary
size, called a “host group”
 There is no structure within class D address space like
subnetting => flat address space
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
IP Multicast Service
 Sending
 Uses normal IP-Send operation, with an IP multicast address
specified as the destination
 Must provide sending application a way to:
 Specify outgoing network interface, if >1 available
 Specify IP time-to-live (TTL) on outgoing packet
 Enable/disable loop-back if the sending host is/isn't a member of
the destination group on the outgoing interface
 Receiving
 Two new operations
 Join-IP-Multicast-Group(group-address, interface)
 Leave-IP-Multicast-Group(group-address, interface)
 Receive multicast packets for joined groups via normal IPReceive operation
1
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Link-Layer Transmission/Reception
 Transmission
 IP multicast packet is transmitted as a link-layer multicast, on
those links that support multicast
 Link-layer destination address is determined by an algorithm
specific to the type of link
 Reception
 Necessary steps are taken to receive desired multicasts on a
particular link, such as modifying address reception filters on
LAN interfaces
 Multicast routers must be able to receive all IP multicasts on a
link, without knowing in advance which groups will be used
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Using Link-Layer Multicast Addresses
 Ethernet and other LANs using 802 addresses:
 Direct mapping! Simpler than unicast! No ARP etc.
IP multicast address
1110
28 bits
Group bit
0000000100000000010111100
23 bits
LAN multicast address
 32 class D addresses may map to one MAC address
1
2
5
 Special OUI for IETF: 0x01-00-5E.
 No mapping needed for point-to-point links
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Multicast over LANs & Scoping
 Multicasts are flooded across MAC-layer bridges along a spanning
tree
 But flooding may steal sending opportunity for non-member stations
which want to transmit
 Almost like broadcast!
 Scope: How far do transmissions propagate?
 Implicit scoping: Reserved Mcast addresses => don’t leave subnet.
 Also called “link-local” addresses
 TTL-based scoping:
 Multicast routers have a configured TTL threshold
 Multicast datagram dropped if TTL <= TTL threshold
 Useful as a blanket parameter.
 Administrative scoping:
1
2
6
 Use a portion of class D address space (239.0.0.0 thru 239.255.255.255)
 Truly local to admin domain; address reuse possible.
 In IPv6, scoping is an internal attribute of an IPv6 multicast address
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Multicast Scope Control – Small TTLs
 TTL expanding-ring search to reach or find a nearby
subset of a group
 Rings can be nested, but not overlapping
s
1
2
3
1
2
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
IP Multicast Architecture
Service model
Host-to-router protocol
(IGMP)
Routers
Multicast routing protocols
(various)
1
2
8
Hosts
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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2
9
Internet Group Management Protocol
 IGMP: “signaling” protocol to establish, maintain,
remove groups on a subnet.
 Objective: keep router up-to-date with group
membership of entire LAN
 Routers need not know who all the members are, only that
members exist
 Each host keeps track of which mcast groups are
subscribed to
 Socket API informs IGMP process of all joins
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
How IGMP Works
 On each link, one router is elected the “querier”
 Querier periodically sends a Membership Query message
to the all-systems group (224.0.0.1), with TTL = 1
 On receipt, hosts start random timers (between 0 and
10 seconds) for each multicast group to which they
belong
Routers:
Hosts:
1
3
0
Q
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
How IGMP Works (cont.)
 When a host’s timer for group G expires, it sends a
Membership Report to group G, with TTL = 1
 Other members of G hear the report and stop (suppress)
their timers
 Routers hear all reports, and time out non-responding
groups
Routers:
1
3
1
Hosts:
Q
G
G
G
G
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
How IGMP Works (cont.)
 Normal case: only one report message per group
present is sent in response to a query
 Query interval is typically 60-90 seconds
 When a host first joins a group, it sends immediate
reports, instead of waiting for a query
 IGMPv2: Hosts may send a “Leave group” message to
“all routers” (224.0.0.2) address
 Querier responds with a Group-specific Query message: see if
any group members are present
 Lower leave latency
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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The Java Basic Multicast API
 At the transport layer, the basic multicast supported by
Java is an extension of UDP (the User Datagram
Protocol)
 For the basic multicast, Java provides a set of classes
which are closely related to the datagram socket API
classes
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Datagram - recap
sender process
receiver process
a byte array
a byte array
receiver's
address
a DatagramPacket object
a DatagramPacket object
send
receive
a DatagramSocket
object
a DatagramSocket
object
object reference
1
3
4
data flow
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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The Java Basic Multicast API - 2
 There are four major classes in the API, the first three of which we
have already seen in the context of datagram sockets.
 InetAddress: In the datagram socket API, this class represents the
IP address of the sender or receiver. In multicasting, this class
can be used to identify a multicast group.
 DatagramPacket: As with datagram sockets, an object of this class
represents an actual datagram; in multicast, a DatagramPacket
object represents a packet of data sent to all participants or
received by each participant in a multicast group.
 DatagramSocket: In the datagram socket API, this class represents
a socket through which a process may send or receive data.
 MulticastSocket : A MulticastSocket is a DatagramSocket, with
additional capabilities for joining and leaving a multicast group. An
object of the multicast datagram socket class can be used for
sending and receiving multicast packets. In the Java API, a
MulticastSocket object is bound to a port address, e.g. 3456, and
methods of the object allows for the joining and leaving of a
multicast address, e.g. 239.1.2.3
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Joining a multicast group
To join a multicast group at IP address m and UDP port p, a
MulticastSocket object must be instantiated with p, then the object’s
joinGroup method can be invoked specifying the address m:
// join a Multicast group at IP address
// 239.1.2.3 and port 3456
InetAddress group =
InetAddress.getByName("239.1.2.3"); MulticastSocket s =
new MulticastSocket(3456); s.joinGroup(group);
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Sending to a multicast group
A multicast message can be sent using syntax similar with the datagram
socket API.
String msg = "a multicast message.";
InetAddress group =
InetAddress.getByName("239.1.2.3");
MulticastSocket s =
new MulticastSocket(3456);
s.joinGroup(group);
// optional
DatagramPacket hi =
new DatagramPacket(msg.getBytes( ),
msg.length( ),group, 3456);
s.send(hi);
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Receiving messages sent to a multicast group
A process that has joined a multicast group may receive messages sent to the group
using syntax similar to receiving data using a datagram socket API.
byte[] buf = new byte[1000];
InetAddress group =
InetAddress.getByName("239.1.2.3");
MulticastSocket s =
new MulticastSocket(3456);
s.joinGroup(group);
DatagramPacket recv =
new DatagramPacket(buf,buf.length);
s.receive(recv);
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Leaving a multicast group
 A process may leave a multicast group by invoking the
leaveGroup method of a MulticastSocket object,
specifying the multicast address of the group.
 s.leaveGroup(group);
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Setting the “time-to-live”
 The runtime support needs to propagate a multicast message from
a host to a neighboring host in an algorithm which, when executed
properly, will eventually deliver the message to all the participants.
 Under some anomalous circumstances, however, it is possible that
the algorithm which controls the propagation does not terminate
properly, resulting in a packet circulating in the network indefinitely.
 Indefinite message propagation causes unnecessary overhead on
the systems and the network.
 To avoid this occurrence, it is recommended that a “time to live”
parameter be set with each multicast datagram.
 The time-to-live (ttl) parameter, when set, limits the count of
network links or hops that the packet will be forwarded on the
network.
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Setting the “time-to-live”
The recommended ttl settings are:
0 if the multicast is restricted to processes on the same host
1 if the multicast is restricted to processes on the same subnet
32 if the multicast is restricted to processes on the same site
64 if the multicast is restricted to is processes on the same region
128 is if the multicast is restricted to processes on the same
continent
 255 is the multicast is unrestricted






TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Setting the “time-to-live”
String msg = "Hello everyone!";
InetAddress group =
InetAddress.getByName("239.1.2.3");
MulticastSocket s = new MulticastSocket(3456);
s.setTimeToLive(1);
// set time-to-live to 1 hop
DatagramPacket hi =
new DatagramPacket(msg.getBytes( ),
msg.length( ),group, 3456);
s.send(hi);
The value specified for the ttl must be in the range 0 <= ttl <= 255; an
IllegalArgumentException will be thrown otherwise.
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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The C version: Joining Multicast Groups
 To join a group, you use the setsockopt() kernel service call with a
new parameter. The new parameter is the ip_mreq structure:
/************************************************************/
/*** The ip_mreq structure for selecting a multicast addr ***/
/************************************************************/
struct ip_mreq
{
struct in_addr imr_multiaddr;
/* known multicast group */
struct in_addr imr_interface;
/* network interface */
} ;
 The imr_multiaddr field specifies the multicast group you want to
join. It is the same format as the sin_addr field in the sockaddr_in
structure. The imr_interface field lets you choose a particular host
interface. This is similar to a bind(), which lets you specify the host
interface (or leave the host option wide open with an INADDR_ANY
value).
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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The C version: Joining Multicast Groups
 The following code snippet shows you how to join a group using the
ip_mreq structure. It sets the imr_interface field to INADDR_ANY
merely for demonstration. Do not use it unless you have only one
interface on your host; the results can be unpredictable .
/************************************************************/
/*** Join a multicast group
***/
/************************************************************/
const char *GroupID = "224.0.0.10";
struct ip_mreq mreq;
if ( inet_aton(GroupID, &mreq.imr_multiaddr) == 0 )
panic("address (%s) bad", GroupID);
mreq.imr_interface.s_addr = INADDR_ANY;
if ( setsockopt(sd, SOL_IP, IP_ADD_MEMBERSHIP,&mreq,sizeof(mreq))!= 0)
panic("Join multicast failed");
/************************************************************/
/*** Drop a multicast group
***/
/************************************************************/
if ( setsockopt(sd, SOL_IP, IP_DROP_MEMBERSHIP, &mreq, sizeof(mreq)) != 0 )
panic("Drop multicast failed");
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
IP Multicast Architecture
Service model
Host-to-router protocol
(IGMP)
Routers
Multicast routing
protocols
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Hosts
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Multicast Routing
 Basic objective – build distribution tree for multicast
packets
 The “leaves” of the distribution tree are the subnets containing
at least one group member (detected by IGMP)
 Multicast service model makes it hard
 Anonymity
 Dynamic join/leave
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Simple Multicast Routing Techniques
 Flood and prune




Begin by flooding traffic to entire network
Prune branches with no receivers
Examples: DVMRP, PIM-DM
Unwanted state where there are no receivers
 Link-state multicast protocols
 Routers advertise groups for which they have receivers to entire
network
 Compute trees on demand
 Example: MOSPF
 Unwanted state where there are no senders
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
How to Flood Efficiently ?
 A router forwards a packet from source (S) iff it arrives
via the shortest path from the router back to S
 Reverse path check!
 Packet is replicated out all but the incoming interface
 Reverse shortest paths easy to compute  just use info
in DV routing tables
 DV gives shortest reverse paths
 Efficient if costs are symmetric
S
y
x
z
Forward packets that arrive
on shortest path from “t” to “S”
(assume symmetric routes)
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t
a
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Problem
 Flooding can cause a given packet to be sent multiple times over the same
link: can filter better than this!
S
x
y
a
duplicate packet
z
b
 Solution: Reverse Path Broadcasting
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Reverse Path Broadcasting (RPB)
 Basic idea: forward a packet from S only on child links for S
 Child link of router x for source S: link that has x as parent on the
shortest path from the link to S
S
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x
forward only
to child link
child link of x
for S
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y
a
z
b
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0
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
How to Find Child Links?
 Routing updates !
 If z tells x that it can reach S through y,
 and if the cost of this path is >= the cost of the path from z to S
through x,
 then x knows that the link to z is a child link
 In case of tie, lower address wins
S
5
x
forward only
to child link
child link of x
for S
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y
a
z
1
5
1
b
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Truncated RPB
 This is still a broadcast algorithm – the traffic goes
everywhere – lousy filtering!
 First order solution: Truncated RPB
 Don't forward traffic onto networks with no receivers
 Identify leaves
 Leaf links are the child links that no other router uses to reach
source S
 Use periodic updates of form:
– “this is my next-link to source S”
 If child is not the “next-link” for anyone, it is a leaf
 Detect group membership in leaf (IGMP)
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Reverse Path Multicast (RPM)
 Prune back transmission so that only absolutely
necessary links carry traffic
 Use on-demand pruning so that router group state
scales with number of active groups
S
data message
prune message
v
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3
a
b
x
y
t
a
b
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Basic RPM Idea
 Prune (Source,Group) at leaf if no members
 Send Non-Membership Report (NMR) up the tree
 If all children of router R prune (S,G)
 Propagate prune for (S,G) to parent R
 On timeout:




Prune dropped
Flow is reinstated
Down stream routers re-prune
Note: this is a soft-state approach
 Grafting: Explicitly reinstate sub-tree when
 IGMP detects new members at leaf, or when a child asks for a
graft.
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Putting it together: Topology
G
G
S
G
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Flood with Truncated Broadcast
G
G
S
G
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Pruning
G
S
G
Prune (s,g)
Prune (s,g)
G
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Grafting
G
S
G
G
Report (g)
Graft (s,g)
Graft (s,g)
G
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TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
After Grafting Complete
G
G
G
S
G
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Reliable Multicast: The Goal
 Implement reliability on top of IP multicast
 Why is this hard ?
 Sender cannot keep state for unknown number of dynamic
receivers
 Remember open & dynamic group semantic?
 Algorithms like TCP that estimate path properties such as RTT
and congestion window don’t generalize to trees.
 Remember: TCP is only for a unicast session!
 Has to address (N)ACK implosions
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Implosion
Packet 1 is lost
All 4 receivers request a resend
Resend request
S
1 2
R1
R1
R2
1
6
1
S
R3
R2
R4
R3
R4
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
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Retransmission
 Re-transmitter
 Options: sender, other receivers
 How to retransmit
 Unicast, multicast, scoped multicast, retransmission group, …
 Problem: retransmissions (aka repairs) may reach destinations that
don’t require a retransmission
 A.k.a “exposure” problem
 Solution: subcast the re-transmission only to receivers that need it.
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Why Subcast? Exposure problem…
Packet 1 does not reach R1;
Receiver 1 requests a resend
Resend request
Packet 1 resent to all 4 receivers
S
Resent packet
1
1 2
R1
1
R1
R2
R2
1
6
3
R3
S
R4
R3
R4
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Ideal Recovery Model
Packet 1 reaches R1 but is lost
before reaching other Receivers
Only one receiver sends NACK to
the nearest S or R with packet
Resend request
S
Resent packet
1 2
1
R1
Repair sent
only to
those that
need packet
R1
1
R2
1
6
4
S
R3
R2
R4
R3
R4
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2008-2009
Reliable Multicast Transport: Issues
 Retransmission can make reliable multicast as inefficient
as replicated unicast
 (N)ACK-implosion if all destinations ack at once
 “Crying baby”: a bad link affects entire group
 Heterogeneity: receivers, links, group sizes
 Anonymous/Open/Dynamic Group Model:
 Source does not know # of destinations, and destinations may
vanish
 Multicast applications do not need strong reliability of
the type provided by TCP.
 Can tolerate some reordering, delay, etc
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