tecnologÍas de red avanzadas – master ic 2010-2011 – 1- protocolos de transporte con qos ...
TRANSCRIPT
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2010-2011 – http://www.grc.upv.es/docencia/tra/
1-Protocolos de transporte con QoS1-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 technologiesH. ShulzrinnePaul. E. Jones (from packetizer.com)
Computer Networking: A Top Down Approach
Featuring the Internet, 3rd edition.
Jim Kurose, Keith RossAddison-Wesley, July
2004.
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
What is multimedia?
Definition of multimediaHard to find a clear-cut definitionIn 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 multimediaDigital – key conceptIntegration of multiple media type, usually including
video or/and audioMay be interactive or non-interactive
2
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Various Media Types
Text, Graphics, image, video, animation, sound, etc.
Classifications of various media typesCaptured 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, Animation3
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Classification of Media Type
4
SoundSound VideoVideo
ImageImage
AnimationAnimation
TextText GraphicsGraphics
Captured From real world
Synthesized By computer
Discrete Discrete
Continuous Continuous
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Text
Plain textUnformattedCharacters coded in binary formASCII codeAll characters have the same style and font
Rich textFormattedContains format information besides codes for
charactersNo predominant standardsCharacters of various size, shape and style, e.g. bold,
colorful
5
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Plain Text vs. Rich Text
6
An example of Plain text
Example of Rich text
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Graphics
Revisable document that retains structural information
Consists of objects such as lines, curves, circles, etc
Usually generated by graphic editor of computer programs
7-4
-20
24
-4
-2
0
2
4-10
-5
0
5
10
Example of graphics (FIG file)
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Images
2D matrix consisting of pixelsPixel—smallest element of resolution of the imageOne pixel is represented by a number of bitsPixel depth– the number of bits available to code the
pixel
Have no structural informationTwo categories: scanned vs. synthesized still
image
8
Computer software
Computer software
Capture and A/D conversionCapture and
A/D conversion
Digital still imageDigital still image
Synthesizedimage
Scannedimage
Camera
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Images (cont.)
Examples of imagesBinary image – pixel depth 1Gray-scale – pixel depth 8Color image – pixel depth 24
9
Binary image
Gray-scale imagecolor image
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
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 picturesCaptured or SynthesizedConsists of a series of bitmap imagesEach image is called a frameFrame rate: the speed to playback the video (frame per
second)
Animation – moving graphicsGenerated by computer program (animation authoring
tools)Consists of a set of objectsThe movements of the objects are calculated and the
view is updated at playback10
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Sound
1-D time-based signal
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 Example: MIDI file1
1
0 100 200 300 400 500 600 700 800 900 1000-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Networked Multimedia
Local vs. networked multimediaLocal: 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.
12
InternetInternetVideo server
Image serverA scenario of multimedia networking
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Consideration of Networked Multimedia
Requirements of multimedia applications on the networkTypically 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
13
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Technologies of Multimedia Networking
Challenges of multimedia networking1. Conflict between media size and bandwidth limit of the
network2. Conflict between the user requirement of multimedia
application and the best-effort network3. How to meet different requirements of different users?
Media compression – reduce the data volumeAddress the 1st challenge Image compression Video compression Audio compression
Multimedia transmission technologyAddress the 2nd and 3rd challenges Protocols for real-time transmission Rate / congestion control Error control
14
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Multimedia Networking Systems
Live media transmission systemCapture, compress, and transmit the media on the fly
(example?)
Send stored media across the networkMedia is pre-compressed and stored at the server. This
system delivers the stored media to one or multiple receivers. (example?)
Differences between the two systemsFor live media delivery:
Real-time media capture, need hardware support Real-time compression– speed is important Compression procedure can be adjusted based on network
conditionsFor stored media delivery
Offline compression – better compression result is important Compression can not be adjusted during transmission
15
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Classes of multimedia applications
Streaming stored audio and videoStreaming live audio and videoReal-time interactive audio and video
16
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Streaming Stored Multimedia: What is it?
17
1. videorecorded
2. videosent
3. video received,played out at client
Cum
ula
tive
data
streaming: at this time, client playing out early part of video, while server still sending laterpart of video
networkdelay
time
t>0
100%
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Streaming vs. Download of Stored Multimedia Content
18
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” delaysReception Rate >= playback
rate. Why?
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Streaming Stored Multimedia: Interactivity
19
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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Streaming Multimedia: Client Buffering
20
Client-side buffering, playout delay compensate for network-added delay, delay jitter
constant bit rate videotransmission
Cum
ula
tive
data
time
variablenetwork
delay
client videoreception
constant bit rate video playout at client
client playoutdelay
bu
ffere
dvid
eo
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Streaming Multimedia: Client Buffering
Client-side buffering, playout delay compensate for network-added delay, delay jitter
21
bufferedvideo
variable fillrate, x(t)
constant drainrate, d
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
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 initializationhow does callee advertise its IP address, port number,
encoding algorithms?
22
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Internet multimedia: simplest approach
23
audio, video not streamed: no, “pipelining,” long delays until playout!
audio or video stored in filefiles transferred as HTTP object
received in entirety at clientthen passed to player
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Progressive Download
24
browser GETs metafile browser launches player, passing metafile player contacts server server downloads audio/video to player
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Streaming from a streaming server
This architecture allows for non-HTTP protocol between server and media player
Can also use UDP instead of TCP.
25
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
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
26
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Streaming Multimedia: UDP or TCP?
UDP server sends at rate appropriate for client
(oblivious to network congestion!)often send rate = encoding rate = constant ratethen, fill rate = constant rate - packet loss
short playout delay (2-5 seconds) to compensate for network delay jitter
error recover: time permittingTCP send at maximum possible rate under TCPfill rate fluctuates due to TCP congestion control larger playout delay: smooth TCP delivery rateHTTP/TCP passes more easily through firewalls2
7
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2010-2011 – http://www.grc.upv.es/docencia/tra/
1-Protocolos de transporte con QoS.
1-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 technologiesH. ShulzrinnePaul. E. Jones (from packetizer.com)
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
29
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)
Retardo extremo-a-extremo
Retardo de acceso
Retardo de tránsito
Retardo de transmisión
Mensaje listo para envío
Envío del primer bit del mensaje
Primer bit del mensaje recibido
Ultimo bit del mensaje recibido
Retardo de acceso
Mensaje listo para recepción
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
30
Varianza del retardo (Jitter)Define la variabilidad del retardo de una red.
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)– Jitter físico + tiempo de acceso + retardo de conmutación de
paquete en conmutadores de la red.
1 2 3
1 2 3D1 D2 = D1 D3 > D1
t
t
Emisor
Receptor
Requisitos de red (II).
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
31
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:Protocolos SIP (RFC 2543), SDP (RFC 2327), SAP (RFC
2974), etc.. ITU H.323
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
32
Internet Protocols
Slide thanks to Henning Schulzrinne
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Multimedia, Quality of Service: What is it?
33
Multimedia applications: network audio and video(“continuous media”)
network provides application with level of performance needed for application to function.
QoS
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Improving QOS in IP Networks
Thus far: “making the best of best effort”Future: next generation Internet with QoS
guaranteesRSVP: signaling for resource reservationsDifferentiated Services: differential guaranteesIntegrated Services: firm guarantees
simple model for sharing and congestion studies:
34
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Principles for QOS Guarantees
Example: 1Mbps IPphone, FTP share 1.5 Mbps link. bursts of FTP can congest router, cause audio losswant to give priority to audio over FTP
35
packet marking needed for router to distinguish between different classes; and new router policy to treat packets accordingly
Principle 1
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
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)
36
provide protection (isolation) for one class from others
Principle 2
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Principles for QOS Guarantees (more)
Allocating fixed (non-sharable) bandwidth to flow: inefficient use of bandwidth if flows doesn’t use its allocation
37
While providing isolation, it is desirable to use resources as efficiently as possible
Principle 3
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Principles for QOS Guarantees (more)
Basic fact of life: can not support traffic demands beyond link capacity
38
Call Admission: flow declares its needs, network may block call (e.g., busy signal) if it cannot meet needs
Principle 4
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
Summary of QoS Principles
39
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2010-2011 – http://www.grc.upv.es/docencia/tra/
1- Protocolos de transporte con QoS.
1- 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 technologiesH. ShulzrinnePaul. E. Jones (from packetizer.com)
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
41
Scheduling And Policing Mechanisms
scheduling: choose next packet to send on linkFIFO (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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
42
Scheduling Policies: more
Priority scheduling: transmit highest priority queued packet
multiple classes, with different prioritiesclass may depend on marking or other header info,
e.g. IP source/dest, port numbers, etc..
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
43
Scheduling Policies: still more
round robin scheduling: multiple classes cyclically scan class queues, serving one from each class (if available)
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
44
Scheduling Policies: still more
Weighted Fair Queuing: generalized Round Robineach class gets weighted amount of service in
each cycle
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
45
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)
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
46
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
less than or equal to (r t + b).
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
47
Policing Mechanisms (more)
token bucket, WFQ combine to provide guaranteed upper bound on delay, i.e., QoS guarantee!
WFQ
token rate, r
bucket size, b
per-flowrate, R
D = b/Rmax
arrivingtraffic
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
48
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?
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
49
Intserv: QoS guarantee scenario
Resource reservationcall setup, signaling (RSVP) traffic, QoS declarationper-element admission control
QoS-sensitive scheduling (e.g.,
WFQ)
request/reply
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
50
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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
51
Intserv QoS: Service models [RFC2211, RFC2212]
Guaranteed service: worst case traffic arrival: leaky-
bucket-policed source simple (mathematically provable)
bound on delay [Parekh 1992, Cruz 1988]
Controlled load service: "a quality of service closely
approximating the QoS that same flow would receive from an unloaded network element."
WFQ
token rate, r
bucket size, b
per-flowrate, R
D = b/Rmax
arrivingtraffic
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
52
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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
53
Edge router: per-flow traffic
management
marks packets as in-profile and out-profile
Core router: per class traffic management buffering and scheduling
based on marking at edge preference given to in-profile
packets Assured Forwarding
Diffserv Architecture
scheduling
...
r
b
marking
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
54
Edge-router Packet Marking
class-based marking: packets of different classes marked differently
intra-class marking: conforming portion of flow marked differently than non-conforming one
profile: pre-negotiated rate A, bucket size B packet marking at edge based on per-flow profile
Possible usage of marking:
User packets
Rate A
B
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
55
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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
56
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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
57
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 lengthClass A packets leave first before packets from class B
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
58
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 trafficeach guaranteed minimum amount of bandwidtheach with three drop preference partitions
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2010-2011 – http://www.grc.upv.es/docencia/tra/
1-Protocolos de transporte multimedia.
1-Protocolos de transporte multimedia.
Clases de aplicaciones multimedia
Redes basadas en IP y QoSGestión de los recursos: IntServ
vs DiffServ RSVP
RTP/RTCP: Transporte de flujos multimedia
RTSP: Control de sesión y localización de medios
Multicasting
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
60
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]
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
61
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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
62
RSVP: does not…
specify how resources are to be reservedrather: a mechanism for communicating needs
determine routes packets will takethat’s the job of routing protocolssignaling decoupled from routing
interact with forwarding of packetsseparation of control (signaling) and data (forwarding)
planes
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
63
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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
64
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 requestedT-spec: defines the traffic characteristicsA signaling protocol is needed to carry the R-spec
and T-spec to the routers where reservation is required;
RSVP is a leading candidate for such signaling protocol
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
65
RSVP request (T-Spec)
A token bucket specificationbucket size, btoken rate, rthe packet is transmitted onward only if the number of
tokens in the bucket is at least as large as the packet
peak rate, pp > r
maximum packet size, Mminimum policed unit, m
All packets less than m bytes are considered to be m bytes
Reduces the overhead to process each packetBound the bandwidth overhead of link-level headers
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
66
Call Admission
Call Admission: routers will admit calls based on their R-spec and T-spec and base on the current resource allocated at the routers to other calls.
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
67
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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
68
R-spec
An indication of the QoS control service requestedControlled-load service and Guaranteed service
For Controlled-load serviceSimply a Tspec
For Guaranteed serviceA Rate (R) term, the bandwidth required
R r, extra bandwidth will reduce queuing delaysA 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.
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
69
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., delayMaximum (or Minimum): e.g., Bandwidth
TaskFind a (min cost) path which satisfies the constraintsif no feasible path found, reject the connection
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
70
Path msgs: RSVP sender-to-network signaling
path message contents:address: unicast destination, or multicast groupflowspec: bandwidth requirements spec.filter flag: if yes, record identities of upstream senders
(to allow packets filtering by source)previous hop: upstream router/host IDrefresh time: time until this info times out
path message: communicates sender info, and reverse-path-to-sender routing infolater upstream forwarding of receiver reservations
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
71
RSVP: simple audio conference
H1, H2, H3, H4, H5 both senders and receiversmulticast group m1no filtering: packets from any sender forwardedaudio rate: bonly one multicast routing tree possible
H2
H5
H3
H4H1
R1 R2 R3
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
72
inout
inout
inout
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
H2
H5
H3
H4H1
R1 R2 R3L1
L2 L3
L4L5
L6 L7
L5 L7L6
L1L2 L6 L3
L7L4m1:
m1:
m1:
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
73
inout
inout
inout
RSVP: building up path state
next, H5 sends path message, creating more state in routers
H2
H5
H3
H4H1
R1 R2 R3L1
L2 L3
L4L5
L6 L7
L5 L7L6
L1L2 L6 L3
L7L4
L5
L6L1
L6
m1:
m1:
m1:
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
74
inout
inout
inout
RSVP: building up path state
H2, H3, H5 send path msgs, completing path state tables
H2
H5
H3
H4H1
R1 R2 R3L1
L2 L3
L4L5
L6 L7
L5 L7L6
L1L2 L6 L3
L7L4
L5
L6L1
L6L7
L4L3L7
L2m1:
m1:
m1:
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
75
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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
76
RSVP: receiver reservation example 1
H1 wants to receive audio from all other sendersH1 reservation msg flows uptree to sourcesH1 only reserves enough bandwidth for 1 audio
stream reservation is of type “no filter” – any sender can
use reserved bandwidth
H2
H5
H3
H4H1
R1 R2 R3L1
L2 L3
L4L5
L6 L7
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
77
inout
RSVP: receiver reservation example 1
H1 reservation msgs flows uptree to sources routers, hosts reserve bandwidth b needed on
downstream links towards H1
H2
H5
H3
H4H1
R1 R2 R3L1
L2 L3
L4L5
L6 L7
L1L2 L6
L6L1(b)
inout
L5L6 L7
L7L5 (b)
L6
inout
L3L4 L7
L7L3 (b)
L4L2
b
bb
b
bb
b
m1:
m1:
m1:
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
78
inout
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
H2
H5
H3
H4H1
R1 R2 R3L1
L2 L3
L4L5
L6 L7
L1L2 L6
L6L1(b)
inout
L5L6 L7
L7L5 (b)
L6
inout
L3L4 L7
L7L3 (b)
L4L2
b
bb
b
bb
b
b
b
(b)m1:
m1:
m1:
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
79
inout
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
H2
H5
H3
H4H1
R1 R2 R3L1
L2 L3
L4L5
L6 L7
L1L2 L6
L6L1(b)
inout
L5L6 L7
L7L5 (b)
L6
inout
L3L4 L7
L7L3 (b)
L4L2
b
bb
b
bb
b
b
b
(b)m1:
m1:
m1:
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
80
RSVP: example 2
H1, H4 are only senderssend path messages as before, indicating filtered
reservationRouters store upstream senders for each upstream link
H2 will want to receive from H4 (only)
H2 H3
H4H1
R1 R2 R3L1
L2 L3
L4L6 L7
H2 H3
L2 L3
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
81
RSVP: example 2
H1, H4 are only senderssend path messages as before, indicating filtered
reservation
H2 H3
H4H1
R1 R3L1
L2 L3
L4L6 L7
H2 H3
L2 L3
L2(H1-via-H1 ; H4-via-R2 )L6(H1-via-H1 )L1(H4-via-R2 )
in
out
L6(H4-via-R3 )L7(H1-via-R1 )
in
out
L1, L6
L6, L7
L3(H4-via-H4 ; H1-via-R3 )L4(H1-via-R2 )L7(H4-via-H4 )
in
out
L4, L7
R2
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
82
RSVP: example 2
receiver H2 sends reservation message for source H4 at bandwidth bpropagated upstream towards H4, reserving b
H2 H3
H4H1
R1 R3L1
L2 L3
L4L6 L7
H2 H3
L2 L3
L2(H1-via-H1 ;H4-via-R2 )L6(H1-via-H1 )L1(H4-via-R2 )
in
out
L6(H4-via-R3 )L7(H1-via-R1 )
in
out
L1, L6
L6, L7
L3(H4-via-H4 ; H1-via-R2 )L4(H1-via-R2 )L7(H4-via-H4 )
in
out
L4, L7
R2
(b)
(b)
(b)
L1
bb b
b
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
83
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
H2 H3
H4H1
R1 R3L1
L2 L3
L4L6 L7
H2 H3
L2 L3
L2(H1-via-H1 ;H4-via-R2 )L6(H1-via-H1 )L1(H4-via-R2 )
in
out
L6(H4-via-R3 )L7(H1-via-R1 )
in
out
L1, L6
L6, L7
L3(H4-via-H4 ; H1-via-R3 )L4(H1-via-R2 )L7(H4-via-H4 )
in
out
L4, L7
R2
(b)
(b)
(b)
L1
bb b
b
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
84
RSVP: soft-state
suppose H4 (sender) leaves without performing teardown
H2 H3
H4H1
R1 R3L1
L2 L3
L4L6 L7
H2 H3
L2 L3
L2(H1-via-H1 ;H4-via-R2 )L6(H1-via-H1 )L1(H4-via-R2 )
in
out
L6(H4-via-R3 )L7(H1-via-R1 )
in
out
L1, L6
L6, L7
L3(H4-via-H4 ; H1-via-R3 )L4(H1-via-R2 )L7(H4-via-H4 )
in
out
L4, L7
R2
(b)
(b)
(b)
L1
bb b
b
eventually state in routers will timeout and disappear!
gonefishing!
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2010-2011 – http://www.grc.upv.es/docencia/tra/
1-Protocolos de transporte multimedia.
1-Protocolos de transporte multimedia.
Clases de aplicaciones multimedia
Redes basadas en IP y QoSGestión de los recursos: IntServ
vs DiffServ RSVP
RTP/RTCP: Transporte de flujos multimedia
RTSP: Control de sesión y localización de medios
Multicasting
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
86
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 multicastDos 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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
87
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.
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
88
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)
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
89
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
RTP: Formato de mensaje (I)
V P CCX M PT Sequence number
Timestamp
Synchronization Source (SSRC) ID
Contributing Source (CSRC) ID
32 bits
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
90
CC: Identifica el número de CSRC que contribuyen a los datosM: Marca (definida según el perfil)PT: Tipo de datos (según perfil)
RTP: Formato de mensaje (II)
V P CCX M PT Sequence number
Timestamp
Synchronization Source (SSRC) ID
Contributing Source (CSRC) ID
32 bits
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
91
Sequence number: Establece el orden de los paquetesTimestamp: Instante de captura del primer octeto del campo de datosSSRC: Identifica la fuente de sincronizaciónCSRC: Fuentes que contribuyen
RTP: Formato de mensaje (III)
V P CCX M PT Sequence number
Timestamp
Synchronization Source (SSRC) ID
Contributing Source (CSRC) ID
32 bits
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
92
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;
/* * 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;
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
93
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 ?
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 ?
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
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.
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.
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
94
RTCP (RTP Control Protocol)
RTCP se basa en envíos periódicos de paquetes de control a los participantes de una sesión RTPPermite realizar una realimentación de la
calidad de recepción de los datos (estadísticas).Los paquetes de control siempre llevan la
identificación de la fuente RTP: CNAMEAsociar 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.
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
95
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 bwRTCPEl intervalo entre cada paquete RTCP es > 5
sec
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
96
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).
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
97
RTCP: Mensajes SR
V P RC PT=SR=200 Longitud
SSRC del sender
32 bits
NTP timestamp mswNTP timestamp lsw
RTP timestamp
Contador de los paquetes del sender
Contador de los bytes del senderSSRC_1
Frac perd Total paquetes perdidos
Num sec más alto recibidoJitter de inter-llegada
Retraso del último SR (LSR)Ultimo SR (LSR)
Report block 1
Sender info
cabecera
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
98
RTCP: Cálculo del Jitter
Es una estimación de la variancia del tiempo de inter-llegada de los paquetes RTP
Si RTP timestamp del paquete i
Ri Instante de llegada del paquete i
)()()()(),( iijjijij SRSRSSRRjiD
16/,1 11 iii JiiDJJ
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2010-2011 – http://www.grc.upv.es/docencia/tra/
1-Protocolos de transporte multimedia.
1-Protocolos de transporte multimedia.
Clases de aplicaciones multimedia
Redes basadas en IP y QoSGestión de los recursos: IntServ
vs DiffServ RSVP
RTP/RTCP: Transporte de flujos multimedia
RTSP: Control de sesión y localización de medios
Multicasting
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
100
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 RTPEstá basado en HTTP/1.1
Diferencias importantes:No es statelessLos clientes y servidores pueden generar peticiones
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
101
Terminología RTSP
ConferenciaMedia stream
Una instancia única de un medio continuo:Un stream audio,Un stream vídeoUna “whiteboard”
Presentación:Es el conjunto de
uno o más streams, que son vistos por el usuario como un conjunto integrado
Voz del público
Imagen del conferenciante
Imagen del público
Imagen de las transparencias
Voz del conferenciante
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
102
RTSP: Ejemplo de una sesión
Web server
SETUP
PLAY
PAUSE
TEARDOWN
HTTP GET
descripción de la sesión
RTP audio
RTP vídeo
RTCP
Cliente
Media server
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
103
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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
104
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)
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
105
RTSP: Una sesión completa (I)
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
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
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
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
web server W
cliente C
media server A
media server V
1
3
2
4
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
106
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
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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
107
RTSP: Una sesión completa (III)
C->V: PLAY rtsp://video.example.com/twister/video RTSP/1.0 CSeq: 2 Session: 23456789 Range: smpte=0:10:00-
V->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=0:10:00-
A->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
C->V: PLAY rtsp://video.example.com/twister/video RTSP/1.0 CSeq: 2 Session: 23456789 Range: smpte=0:10:00-
V->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=0:10:00-
A->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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
108
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
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
TECNOLOGÍAS DE RED AVANZADAS – Master IC 2010-2011 – http://www.grc.upv.es/docencia/tra/
1-Protocolos de transporte multimedia.
1-Protocolos de transporte multimedia.
Clases de aplicaciones multimedia
Redes basadas en IP y QoSGestión de los recursos: IntServ
vs DiffServ RSVP
RTP/RTCP: Transporte de flujos multimedia
RTSP: Control de sesión y localización de medios
Multicasting
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
110
Multicast = Efficient Data Distribution
Src Src
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
111
Why Multicast ?
Need for efficient one-to-many delivery of same data
Applications:News/sports/stock/weather updatesDistance learningConfiguration, routing updates, service locationPointcast-type “push” appsTeleconferencing (audio, video, shared whiteboard, text
editor)Distributed interactive gaming or simulationsEmail distribution listsContent distribution; Software distributionWeb-cache updates Database replication
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
112
Why Not Broadcast or Unicast?
Broadcast: Send a copy to every machine on the netSimple, but inefficientAll nodes must process packet even if they don’t careWastes more CPU cycles of slower machines (“broadcast
radiation”)Network loops lead to “broadcast storms”
Replicated Unicast:Sender sends a copy to each receiver in turnReceivers need to register or sender must be pre-
configuredSender is focal point of all control trafficReliability => per-receiver state, separate
sessions/processes at sender
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
113
Multicast Apps Characteristics
Number of (simultaneous) senders to the groupThe size of the groups
Number of members (receivers)Geographic extent or scopeDiameter of the group measured in router hops
The longevity of the groupNumber of aggregate packets/secondThe peak/average used by sourceLevel of human interactivity
Lecture mode vs interactiveData-only (eg database replication) vs multimedia
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
114
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.
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
115
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 non-corrupted 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.
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
116
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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
117
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.
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
118
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.
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
119
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.
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
120
IP Multicast Architecture
Hosts
Routers
Service modelService model
Host-to-router protocol(IGMP)
Multicast routing protocols(various)
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
121
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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
122
IP Multicast Addresses
Class D IP addresses224.0.0.0 – 239.255.255.255
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
1 1 1 0 Group ID
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
123
IP Multicast Service
SendingUses normal IP-Send operation, with an IP multicast
address specified as the destinationMust 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
ReceivingTwo new operations
Join-IP-Multicast-Group(group-address, interface) Leave-IP-Multicast-Group(group-address, interface)
Receive multicast packets for joined groups via normal IP-Receive operation
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
124
Link-Layer Transmission/Reception
TransmissionIP multicast packet is transmitted as a link-layer
multicast, on those links that support multicastLink-layer destination address is determined by an
algorithm specific to the type of link
ReceptionNecessary 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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
125
Using Link-Layer Multicast Addresses
Ethernet and other LANs using 802 addresses: Direct mapping! Simpler than unicast! No ARP etc.
32 class D addresses may map to one MAC address Special OUI for IETF: 0x01-00-5E. No mapping needed for point-to-point links
LAN multicast address
0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 1 0 1 1 1 1 0 0
1 1 1 0 28 bits
23 bits
IP multicast address
Group bit
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
126
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: 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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
127
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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
128
IP Multicast Architecture
Hosts
Routers
Service model
Host-to-router protocolHost-to-router protocol(IGMP)(IGMP)
Multicast routing protocols(various)
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
129
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 LANRouters need not know who all the members are, only
that members exist
Each host keeps track of which mcast groups are subscribed toSocket API informs IGMP process of all joins
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
130
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
QRouters:
Hosts:
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
131
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
Q
G G G G
Routers:
Hosts:
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
132
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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
133
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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
134
Datagram - recap
a by te a rra y
a D a ta g ra m Pa ck e t o bje ct
r e c e i ve r 'sa d d r e s s
a D a ta g ra m S o ck e t o bje ct
s e nde r pro c e s s
a by te a rra y
a D a ta g ra m Pa ck e t o bje ct
a D a ta g ra m S o ck e t o bje ct
re c e ive r pro c e s s
s e n d
re ce iv e
o bje ct re f e re n ce
da ta f lo w
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
135
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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
136
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);
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
137
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);
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
138
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);
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
139
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);
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
140
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.
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
141
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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
142
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.
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
143
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 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).
/************************************************************//*** 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 */} ;
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
144
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");
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
145
IP Multicast Architecture
Hosts
Routers
Service model
Host-to-router protocol(IGMP)
Multicast routing protocols
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
146
Multicast Routing
Basic objective – build distribution tree for multicast packetsThe “leaves” of the distribution tree are the subnets
containing at least one group member (detected by IGMP)
Multicast service model makes it hardAnonymityDynamic join/leave
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
147
Simple Multicast Routing Techniques
Flood and pruneBegin by flooding traffic to entire networkPrune branches with no receiversExamples: DVMRP, PIM-DMUnwanted state where there are no receivers
Link-state multicast protocolsRouters advertise groups for which they have receivers
to entire networkCompute trees on demandExample: MOSPFUnwanted state where there are no senders
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
148
How to Flood Efficiently ?
A router forwards a packet from source (S) iff it arrives via the shortest path from the router back to SReverse path check!
Packet is replicated out all but the incoming interface
Reverse shortest paths easy to compute just use info in DV routing tablesDV gives shortest reverse pathsEfficient if costs are symmetric
xxyy
tt
SS
a
zz
Forward packets that arriveon shortest path from “t” to “S” (assume symmetric routes)
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
149
Problem
Flooding can cause a given packet to be sent multiple times over the same link: can filter better than this!
Solution: Reverse Path Broadcasting
xx yy
zz
SS
a
b
duplicate packet
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
150
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
xx yy
zz
SS
a
b
5 6
child link of xfor S
forward onlyto child link
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
151
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
xx yy
zz
SS
a
b
5 6
child link of xfor S
forward onlyto child link
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
152
Truncated RPB
This is still a broadcast algorithm – the traffic goes everywhere – lousy filtering!
First order solution: Truncated RPBDon't forward traffic onto networks with no receiversIdentify 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)
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
153
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
xx yy
tt
SS
vv bbaa
aa bb
data messageprune message
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
154
Basic RPM Idea
Prune (Source,Group) at leaf if no membersSend 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 droppedFlow is reinstatedDown stream routers re-pruneNote: 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.
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
155
Putting it together: Topology
G G
S
G
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
156
Flood with Truncated Broadcast
G G
S
G
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
157
Pruning
G G
S
Prune (s,g)
Prune (s,g)
G
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
158
Graft (s,g)
Graft (s,g)
Grafting
G G
S
G
G
Report (g)
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
159
After Grafting Complete
G G
S
G
G
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
160
Reliable Multicast: The Goal
Implement reliability on top of IP multicastWhy 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
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
161
R1
Implosion
S
R3 R4
R2
21
R1
S
R3 R4
R2
Packet 1 is lost All 4 receivers request a resend
Resend request
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
162
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.
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
163
R1
Why Subcast? Exposure problem…
S
R3 R4
R2
21
R1
S
R3 R4
R2
Packet 1 does not reach R1;Receiver 1 requests a resend
Packet 1 resent to all 4 receivers
1
1
Resend request Resent packet
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
164
Ideal Recovery Model
S
R3 R4
R2
2
1
S
R3 R4
R2
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
1 1Resent packet
Repair sent only to those that need packet
R1 R1
TEC
NO
LOG
ÍAS D
E R
ED
AV
AN
ZA
DA
S –
Mast
er
IC 2
01
0-2
01
1
165
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 sizesAnonymous/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